9th INTERNATIONAL CONGRESS ON DETERIORATION AND CONSERVATION OF STONE
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Proceedings of the 9th INTERNATIONAL CONGRESS ON DETERIORATION AND CONSERVATION OF STONE
Venice June 19-24, 2000 Edited by
Vasco Fassina
Organised by
Istituto Veneto pet t Beni Culturali
ELSEVIER Amsterdam
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Organised by Istituto Veneto per i Beni Culturali
In association with ICCROM-International Centre for the Study of the Preservation and Restoration of Cultural Property SMITHSONIAN INSTITUTION-Smithsonian Center for Materials Research and Education UVO-Unesco Venice Office CNR-Consiglio Nazionale delle Ricerche. Progetto finalizzato Beni Culturali ICR- Istituto Centrale per il Restauro UniversitS. degli Studi Ca' Foscari, Corso di Laurea in Conservazione dei Beni Culturali IUAV-Istituto Universitario di Architettura di Venezia
International Scientific Committee Vsevolode Romanowsky (President), La Rochelle, France Andreas Arnold, Zurich, Switzerland Susan Bradley, London, United Kingdom A. Elena Charola, New York, USA Jos6 Delgado Rodrigues, Lisbon, Portugal Wieslaw Domaslowski, Torun, Poland Rosa Esbert, Oviedo, Spain Vasco Fassina, Venice, Italy Marisa Laurenzi Tabasso, Rome, Italy Lorenzo Lazzarini, Venice, Italy Isabelle Pallot Frossard, Paris, France Josef Riederer, Berlin, Germany Raffaella Rossi Manaresi, Bologna, Italy Ornella Salvadori, Venice, Italy Theodore Skoulikidis, Athens, Greece V6ronique Verges Belmin, Paris, France George Wheeler, New York, USA
vi
Honorary Committee Marino Folin Stefano Gasparri PierFrancesco Ghetti Angelo Guarino Vladimir Kouzminov Marc Laenen Pierre Lasserre Paolo Morachiello
Lionello Puppi Maurizio Rispoli Mario Serio Gabriele Zanetto Francesco Zofrea
Rettore Istituto Universitario di Architettura di Venezia Preside della Facolt/~ di Lettere e Filosofia dell'Universit/t degli Studi di Venezia Preside della Facolt/t di Scienze Matematiche, Fisiche e Naturali dell'Universit/t degli Studi di Venezia Presidente Comitato di Progetto Finalizzato Beni Culturali, CNR, Roma Deputy director of Unesco Venice Office General Director International Centre for the Study of the Preservation and Restoration of Cultural Property, Rome Director of Unesco Venice Office Presidente del Corso di Laurea in Storia e Conservazione per i Beni Architettonici e Ambientali dell'Istituto Universitario di Architettura di Venezia Presidente del Corso di Laurea in Conservazione dei Beni Culturali dell'Universit~ degli Studi di Venezia Rettore Universit~t degli Studi Ca' Foscari di Venezia Direttore Generale Ministero per i Beni e le Attivit/t Culturali Presidente del Corso di Laurea in Scienze Ambientali dell'Universitfi degli Studi di Venezia Presidente Eni Tecnologie, Milano
Organising Committee Vasco Fassina, Corso di Laurea in Conservazione dei Beni Culturali, Chairman Guido Biscontin, Universit/t agli Studi Ca' Foscari di Venezia Monica Favaro, Istituto Veneto per i Beni Culturali Giovanni Perego, Eni Tecnologie, Milano Lionello Puppi, Universit/t degli studi Ca' Foscari di Venezia Renzo Ravagnan, Istituto Veneto per i Beni Culturali Akatsuki Takahashi, Unesco Venice Office Alessandro Vigato, Consiglio Nazionale delle Ricerche, Progetto Finalizzato Beni Culturali
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Under the Patronage Ministero per i Beni e le Attivit~ Culturali Consiglio Nazionale delle Ricerche ICCROM-International Centre for the Study of the Preservation and Restoration of Cultural Property Regione Veneto Provincia di Venezia Universitfi degli Studi Ca' Foscari di Venezia IUAV-Istituto Universitario di Architettura di Venezia
Sponsors CNR, Progetto Finalizzato Beni Culturali Regione Veneto Scuola Grande San Giovanni Evangelista Eni Tecnologie, Milano Mazzali Systems S.p.A., Milano Philips Electron Optics-FEI, Milano Torggler S.p.a., Merano Dionex s.r.l., Roma
Organising Secretariat Monica Favaro, Chairperson Francesca Crivellari Gianfranco Favaro Damiana Magris Andrea Naccari Marta Pigo Raffaella Portieri Mariangela Rossi
Editing Francesca Crivellari Gianfranco Favaro
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Message de bienvenue de M. Vsevolode Romanovsky Monsieur le Pr6sident, Mesdames, Messieurs, En organisant, il y a 28 ans, le premier 'Congr6s International sur la D6t6rioration et la Pr6servation des Pierres en ouvre' je ne pr6voyais pas un 96me Congr6s en l'an 2000. Cette ann6e nous paraissait si lointaine et moi-m6me, je n'6sp6rais pas pouvoir y parvenir. Pourtant nous y sommes en 2000 et dans le merveilleux site de Venise que j'ai si bien connu dans les ann6es 60 et 70. A la suite de ce l er Congrbs a la Rochelle, que j'avais organis6 malgr6 de nombreuses oppositions nationales, nous avons pris l'initiative de cr6er le 'Comit6 International Permanent pour l'Organisation des Congr6s sur la D6t6rioration et la Pr6servation de la Pierre', charg6 de fixer les lieux et les dates des Congrbs successifs ainsi que d'aider les responsables nationaux dans l'organisation de ces manifestations. Le Comit6 fonctionna d'une mani6re satisfaisante et aboutit au pr6sent Congr6s. Apr6s La Rochelle, notre ami Theodore Skoulikidis d6cida, sans h6sitations, de nous inviter au suivant, fi Ath6nes en 1976. Ce fut lui qui lanca r6ellement la s6rie. Pour cela nous lui devons une grande reconnaissance. En 1979 Lino Marchesini organisa le 36me Congr6s ~ Venise. En 1982 le 46me traversa l'Atlantique car il eut lieu ~ Louisville (Kentucky) aux Etats Unis. Par suite de la conjoncture 6conomique de l'6poque, la participation europ6enne fut assez r6duite. En 1985, mon vieil ami Vinicio Furlan nous offrit un magnifique Congr6s 5, Lausanne. Ce fut le 56me de la s6rie. En 1988, le Congr6s organis6 par Wieslaw Domaslowsky fut exceptionnel car il se d6roula fi Torun (Pologne) encore sous influence sovi6tique. Malgr6 cette servitude, Wieslaw Domaslowsky parvint /~ cr6er une ambiance de libert6, de joie et de gaiet6 aussi tousles participants revinrent enchant6s de ce s6jour dans une ville trbs belle. En 1992, Josh Delgado-Rodriguez nous offrit fi Lisbonne, un Congr~s d'une efficacit~ et d'une magnificence dignes de ce beau pays et ses sympathiques habitants. En 1996, Josef Riederer organisa le Congr6s fi Berlin. Maintenant, pour la seconde fois, nous sommes ~t Venise, l'une des plus belles villes du monde, malheureusement tr6s atteinte par la 'maladie de la pierre' due fi tous les exc6s de notre civilisation. Une fois de plus, je suis Pr6sident du Comit6 Scientifique, mais probablement la derni6re fois. Je dois/t mon ami Vasco Fassina, et fi tous ses collaborateurs, mes vives et sinc6res excuses de n'avoir pas pu, compte tenu de mon fige et de mes occupations d'6crivain scientifique, les aider et les assister dans l'organisation de ce Congr~s. Je leur dois de chaleureux remerciements d'avoir bien voulu me confier, probablement la dernibre fois, la Pr6sidence du Comit6 Scientifique. Je suis persuad6 que ce Congr6s sera un grand succ6s et que l'on avancera dans la r6solution des problbmes que posent les 'maladies de la pierre'. Avant de terminer ce court expos6, off j'ai voulu rappeler l'historique des Congr6s, je souhaite fi tous les
participants un merveilleux s6jour fl Venise, off tout est fi voir et fl visiter. Je fais 6galement des voeux pour un excellent d6roulement des travaux du Congr6s.
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Foreword An important part of our culture is chiselled in stone, and we are in danger of losing it. The heritage we have of past and present glories of human creativity is slipping away, slowly, silently, but inexorably and at an increasing rate. Stone decay is not a new phenomenon. It starts as soon as an artefact or structure has been completed, and continues progressively for as long as the object is in contact with any kind of environment. The conservation and preservation of works in stone gradually acquired increasing numbers of practitioners in the early part of the twentieth century. However, the problems of deterioration of exposed stone proved to be intractable to the science and technology of the nineteenth century. It was not until about the second and third decades of the twentieth century that it was justified to speak of a Science of Stone Conservation beginning to take form. Traditionally, preservation restoration and maintenance, considered technically, have been closely related to crafts and prevalent contemporary building practice. This meant that earlier, problems were solved mostly within existing traditional know-how among craftsmen and architects. Successively, during the period of industrialisation, conservation was characterized by a scientific approach strongly influenced by the dominant role played by natural sciences and technology. The conservation of historic monuments, sites and structures constitutes an interprofessional discipline co-ordinating a range of aesthetic historic, scientific and technical methods. Conservation is a rapidly developing field, which, by its true nature, is a multidisciplinary activity with experts respecting one another's contributions and combining to form an effective team. Conservation is an artistic activity aided by scientific and historical knowledge. The problem of conserving architecture and the fine and decorative arts is not simple. Even in a scientific age that has developed the technology of space travel and atomic power, the solution to local environmental problems and the prevention of decay still present a major challenge. Only through understanding the mechanisms of decay and deterioration can we increase conservation skills for prolonging the life of cultural property for future generations, but we must admit that decay is the Law of Nature and we can only slow the process down. The first meetings on stone conservation took place in 60's, while only in 1972, in La Rochelle, prof. Romanovsky organised the first International Congress on Deterioration and Conservation of Stone. The first series of events started then, and were systematically repeated every 4 years. At that time the panorama was completely different, very few people were working in this field. This series of Congresses has strongly contributed to the increase in the quality of research and the number of people working in this field. A significant degree of understanding of the nature and mechanism of action of the various decay processes has been developed, and detailed understanding can be expected to be followed by successful techniques of intervention.
xii
The present is, therefore, a propitious time to survey the state of our knowledge, to review the treatment methods that have been proposed and tried out, and to consider what needs to be further explored, and what experience should not be repeated. 21 years after the third edition of the International Congress on Deterioration and Conservation of Stone, organised by prof. Lino Marchesini, Venice is hosting the ninth edition of this prestigious Congress. In these two decades the number of scientific meetings held each year around the world has increased a lot and is a definite proof of the great interest of the Scientific Community to give appropriate answers to stone conservation problems. The IX Congress is a good opportunity for presenting the most recent developments of research on stone decay and to discuss the ways of having them transformed in methods and procedures of practical use in stone conservation. The main purpose of this Congress is to point out: 9 the most appropriate methodology for the assessment of the degree of the weathering of stone, 9 the development of new methods and instruments for the diagnosis of the state of conservation, for the study of alteration mechanisms and for conservation treatments, 9 the definition of Technical European Standard Methods for the evaluation of conservation treatments of artistic and historic stone objects and monuments. The Scientific Committee is deeply interested in having valuable research results and demonstrations of their actual or potential applications to real life degraded stone monuments. The Congress is addressed to: 9 Restorers of works of art who want to improve their knowledge in conservation problems 9 Architects who seek full information on restoration problems 9 Conservators who want to exchange their knowledge and experience 9 Scientific people (geologists, chemists, physicists, biologists, mineralogists, etc.) involved in the conservation field 9 Public authorities and governmental institutions with responsibility for conservation of the Cultural Heritage 9 Art historians dealing with conservation problems It is highly gratifying to acknowledge the interest and enthusiasm that this Congress has raised worldwide. About 400 people coming from 45 countries have expressed their will to participate in the Congress and more than 270 abstracts were received, from which 176 papers have been selected. The members of the Permanent Scientific Committee were asked to review the papers and to approve their publication by dividing them into the following seven themes: 1. Weathering of natural stone: causes, mechanism and measurement of stone damage 2. External factors of decay: environmental influence on stone decay 3. Biological damage on stone
xiii
4. Laboratory methods and techniques 5. In situ evaluation of damage 6. The conservation of stone: treatment methods and products 7. Case studies of conservation of Cultural Heritage The diversity of subjects dealt with in the submitted papers and their scientific level are a demonstration of the opportunity of this event and will certainly make these proceedings a very important reference book for people involved in the field of stone conservation. The view expressed by the individual authors of these papers are not necessarily those of the editor nor of the Scientific Committee. Since no modifications were asked for, the content of the paper remains, the full responsibility of the authors. Achievement of the Congress' aims is due, in great measure, to sponsoring organisations, Institutes and the staff of the Organising Committee and the Secretary of the Istituto Veneto per i Beni Culturali which made a precious work of editing a cameraready copy of the papers for the International publisher. Sincere thanks are expressed to the members of the Permanent Scientific Committee for their assistance in the selection process of these proceedings. The editor wishes to thank all the participants attending from all over the world for their interest towards this Congress and hope that people have a fruitful discussion and exchange of opinions in order to improve their knowledge thus allowing a better preservation of our heritage of the past and present glories of human creativity. It should be desiderable that this Congress could represent a milestone in the slow change of the classical approach to the study of conservation of cultural property based on the knowledge of the causes of decay of specific objects. In fact a new focus on historic buildings, structures and materials is recently developing. Major attention was paid to management of conservation worksites, regular inspection of historic structures and maintenance strategies. Regular inspections of cultural property are the basis of sound management and can be used to develop a preventive maintenance strategy, which can greatly reduce the cost of caring for our cultural heritage. Developing a preventive maintenance strategy is the most important step in preparedness for a natural disaster. Half of the damage caused by an earthquake to historic buildings can generally be attributed to lack of maintenance. It is a great pleasure for the Scientific Venetian Community to host this Congress on the threshold of the third millennium in a scientific age that has developed a sophisticated technology but has not completely solved the problems of safeguard of our Cultural Heritage. Vasco Fassina
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TABLE OF CONTENTS VOLUME 1
Theme 1 - Weathering of natural stone" causes, mechanism and measurement of stone damage
Restoration of the historical brick masonry Bajare D., Svinka V. Comparative study of different methods for gap filling applications and use of adhesives on the biocalcarenite surfaces of the 'Tempio della Concordia' in Agrigento Bennardo C., Meli P., Biscontin G., Berlucchi N., Ginanni Corradini R., Mattolin F. Gr6dener sandstone, a historical building material in south Tyrol/Italy- The problem of large variability of stone properties for monument conservation Franzen C., Mirwald P. Evaluation of materials used in the replacement of sculptures in historical monuments Boutin F,. Bromblet P. White granites used in lombard architecture Bugini R., Pavese A., Borroni S., Folli L. A research into intrinsic parameters material to the durability of highly porous building stones Calia A., Mecchi A. M., Quarta G. Preliminary contribution on durability of some macroporous monumental stones used in historical towns of Campania Region, Southern Italy Langella A., Calcaterra D., Cappelletti P., Colella A., de' Gennaro M., de Gennaro R. Durability of tuffeau stone in buildings: influence of mineralogical composition and microstructural properties Dessandier D., Bromblet P., Mertz J-D. Water-rock interaction and monuments stone decay" the case of Basilica da Estrela, Portugal Figueiredo A. M. C., Marques J.M., Mauricio A.M., Aires-Barros L. Analyses of the physical parameters correlated to bending phenomena in marble slabs Garzonio C. A., Fratini F.F., Manganelli del F~ C., Giovannini P., Cavallucci F. Geoegyptology of A1-Muzawaka tombs, Dakhla oases, Egypt Helmi F. M. Thermal stress and weathering of Carrara, Pentelic and Ekeberg marble Lindborg U., Dunakin R. C., Rowcliffe D. J.
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25
31 41
49
59
69
79
89 99 109
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Weathering of runestones in a millenian perspective Lbfvendahl R., Gustavson H., Lundberg B. A. Petrophysical analysis of the sculptures decay at the Cathedral of Burgos, Spain Fort Gonzdles R., L6pez de Azcona M. C., Mingarro Martin F. Durability of sandstones in Serbian ancient monasteries and modern buildings Matovic V.B., Milovanovic D. J., Joksimovic S. M. Sandstone architectural deterioration in Petra, Jordan Paradise T. R. Preliminary studies for the consolidation of Guadalupe tuff from the Philippines Paterno M. C., Charola A. E. Secondary phosphate phases in altered trachyte from S. Miguel Island (Azores, Portugal) - A possible contribution to the stone degradation Pruddncio M. I., Nasraoui M., Trindade M. J., Sequeira Braga M. A., Figueiredo M. O. Comparison between traditional and chamber accelerated ageing tests on granitic rocks Rivas T., Prieto B., Silva B., Birginie J. M. Physical properties and durability of fresh and impregnated limestone and sandstone from central Sweden used for thin stone flooring and cladding Sahlin T., Malaga-Starzeg K., Stigh J., Schouenborg B. Stress from crystallization of salt in pores Scherer G. W. Stone materials used in the masonry of Ortigia (Siracusa, Sicily) Calia A., Mecchi A. M., Scudeler Baccelle L. Control of marble weathering by thermal expansion and rock fabrics Siegesmund S., Weiss T., Tschegg E. K. The relationship between deterioration, fabric, velocity and porosity constraint Weiss T., Siegesmund S., Rasolofosaon P. N. J. Saline pollution in trachyte monuments of the Azores Islands (Portugal) Alves C. A. S., Sequeira Braga M. A., Trancoso A. Trachyte stones in monuments of the Silo Miguel and Terceira Islands, Azores (Portugal) Sequeira Braga M. A., Figueiredo M. 0., Prud~ncio M. I, Delgado Rodrigues J., Alves C. A. S., Costa D., Silva T., Trindade M. J., Waerenborgh J. C., Nasraoui M., Gouveia M. A. Determination of structural anisotropy of Carrara marble with ultrasonic measurements Sheremeti-Kabashi F., Snethlage R.
119
125
135 145
155
165
171 181 187 195 205 215 225
235
247
xvii The stone of Piraeus at the monuments of the Acropolis of Athens Theoulakis P., Bardanis M. Petrophysical properties modifications of Strasbourg's Cathedral sandstone by black crusts Thomachot C., Jeanette D. Freeze-thaw resistance of the Yazilikaya tufts Topal T., SSzmen B. An evaluation of geology and weathering in the preservation of marl objects Ventikou M., Halls C., Lindsay W., Batchelder M., Hubbard C.
265
Theme 2 - External factors of decay: environmental influence on stone decay
293
Topoclimatic mapping, a tool for cultural heritage conservation: the case of Roman Theater of Lisbon, Portugal Aires-Barros L., Dionisio A. Characterization of surface morphology of carbonate stone and its effect on surface uptake of SO2 Bede E. A. Sea water absorption, permeability evolution and deterioration assessment of building stones subjected to marine exposure Birginie J. -M. Colour changes and reactivity to SO2 of some cladding stones at the 'Gran Theater del Liceu' (Barcelona-Spain) Grossi C. M., Esbert R. M., Alonso F. J., Valdeon L., Ordaz J., Diaz-Pache F. Early mechanisms of development of sulphated black crusts on carbonate stone Ausset P., Lefbvre R. A., Del Monte M. Past air pollution recordings on stone monuments: the heads of the r~Nigs'oc Juda statues from Notre-Dame cathedral (Paris) Ausset P., Lefbvre R. A., Del Monte M., Thidbault S. Laboratory investigations of weathering behaviour of fresh and impregnated limestone and sandstone from Central Sweden Malaga-Starzeg K., Sahlin T., Lindqvist O. The influence of building orientation on climate weathering cycles in Staffordshire, U. K. Mitchell D. J., Halsey D. P., Macnaughton K., Searle D. E. Corrosion of limestone in humid air containing sulphur and nitrogen dioxides: a model study Moroni B., Poli G. The Doria Pamphilj exhibition Gallery: the study of environmental conditions Artioli D., Giovagnoli A., Nugari M. P., Ivone A., Lonati G.
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275 283
295
303
313
323
329
339
349
357
367
375
xviii Analytic methodologies for carbon compound identification: Leaning Tower and Baptistery of Pisa Sabbioni C., Ghedini N., Gobbi G., Riontino C., Zappia G. The effects of coal and diesel particulates on the weathering loss of two major building stones in the United Kingdom- A comparative microcatchment study Searle D. E., Mitchell D. J., Halsey D. P., Dews S. J., Smith J. P. Evaluation of the environmental influence on sulphate salt formation at monuments in Dresden (Germany) by sulphur isotope measurements Siedel H., Klemm W. Granitic building stone decay in an urban enviroment: a case of authigenic kaolinite formation by heterogeneous sulphur dioxide attack Schiavon N. Theme 3 - Biological damage on stone
Polysaccharides as a key step in stone bio-erosion Albertano P., Bruno L., Bellezza S., Paradossi G. The temples of the archaeological area of Paestum (Italy): a case study on biodeterioration Altieri A., Pietrini A. M., Ricci S., Roccardi A., Piervittori R. Biological patinas on the limestones of the Loches Romanic Tower (Touraine, France) Zagari M., Antonelli F, Urzi C. Chemiolithotrophic bacteria on stone monuments: cultural methods set-up Bartolini M., Monte M. New methods to study the detrimental effects of poikilotroph microcolonial micromycetes (PMM) on building materials Dornieden T., Gorbushina A. A. Diversity of heterotrophic bacteria isolated from three European mural paintings Heyrman J., Mergaert J., Swings J. A study of biologically decayed sandstone with respect to Ca and its distribution Jones M. S., Wakefield R. D., Forsyth G. Microbial environmental monitoring of stone cultural heritage Pitzurra L., Giraldi M., Sbaraglia G., Bistoni F., Bellezza T., Spera G. The Silo Sebastiio Church of Terceira Island (Azores, Portugal)Characterisation of the stones and their biological colonisation Romeo P., PrudYncio M. I., Trindade M. J., Nasraoui M., Gouveia M. A., Figueiredo M. 0., Silva T.
383
391
401
411 423
425
433
445 453
461
469
473 483
493
xix Rapid diagnosis of microbial growth and biocide treatments on stone materials by bioluminescent low-light imaging technique Ranalli G., Pasini P., Roda A. The action of Caloplaca Citrina on concrete surfaces: a preliminar study Rosato V. G., Traversa L., Cabello M. N. Endolithic lichens and conservation: an underestimate question Pinna D., Salvadori O. Biological colonization features on a granite monument from Braga (NW, Portugal) Leite Magalh6es S., Sequeira Braga M. A. Efficiency of biocide in 'in situ' and 'in vitro' treatment. Study case of the 'Templete de Mudejar', Guadalupe, Spain Urzi C., De Leo F., Galletta M., Salamone P., Balzarotti R. Theme 4 - Laboratory methods and techniques
Instrumental chemical analysis of the more common marbles historically used for decorative purposes or to create works of art Campanella L., Gregori E., Grossi R., Tomassetti M. Bandini G. Presence of D, L amino acids in oxalate patinas on a stone monument Casoli A., Negri S., Palla G. Unite Technologique portable et autonome de diagnostic- Analyse Investigation, de choix d'intervention avec video assistance a distance et banque de donnees Catalafini J. Large scale experimental facilities at ENEA for seismic tests on structural elements of the historical/monumental cultural heritage De Canio G. Evaluation of stone pore size distribution by means of N M R Alesiani M., Capuani S., Curzi F., Mancini L., Maraviglia B. New results in the application of innovative experimental techniques for investigation of stone decay's processes Giorgi R., Baglioni P., Alesiani M., Capuani S., Mancini L., Maraviglia B. Fractal geometry description of the permeability of a natural fissured rock Miguel A. F., Rosa R., Silva A. M. Microstructural changes in granitic rocks due to consolidation treatments: their effects on moisture transport Mosquera M. J., Rivas T., Prieto B., Silva B. The use of sound velocity determination for the non-destructive estimation of physical and microbial weathering of limestones and dolomites Papida S., Murphy W., May E.
499 507 513
521
531 541
543 553
557
565 579
587 595
601
609
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Analytical techniques for characterizing polychromated coatings on quartzite samples from a prehistorical cave Carmelo Prieto A., Jimdnez J., Pdrez B., Leal L. Stone drying: an approach of the effective evaporating surface area Tournier B., Jeanette D., Destrigneville C. Fractal modelling of particulate deposition in the development of black crusts on stone Watt J., Massey S., Kendall M. Characterization and physico-chemical action of condensed water on limestone surfaces Zendri E., Biscontin G., Kosmidis P., Bakolas A. Author index
TABLE
OF CONTENTS
VOLUME
619 629
637
647 657
2
Theme 5 - In situ evaluation of damage
The effects of the strong use of cements in restoration: the case of Barga Duomo (Northern Tuscany) Baccaro M. L. P., Balzi S., Del Chiaro L., Vannucci S. A simple technique for rapid field assessment of stone decay on buildings Ball J., Young M. E. 'La Fenice' T h e a t r e - Foyer and Apollinee r o o m s - Consolidation of firedamaged stucco and marmorino decorations by means of combined applications of ion-exchange resins and barium hydroxide Berlucchi N., Ginanni Corradini R., Bonomi R., Bemporad E., Tisato M. A petrographic atlas as a decision-tool in replacement and substitution of ornamental stone in historical buildings and monuments Dingelstadt C., Dreesen R., Thorez J., Lorenzi G., Bossiroy D., Antenucci D., Banier J. Study on the deterioration and conservation of the stone monument in 'Dell'Aquila' Square, Ravenna (Italy) Macchiarola M., Fiori C., Belacchi S. Deterioration of rock monuments in Petra/Jordan Heinrichs K., Fitzner B. The risk map and the blackening index: a new recording apparatus Giovagnoli A., Marabelli M., Canegallo P., Ivone A. A four-year survey of the water contents and movements within a masonry core after a restoration campaign: a case study in Notre-Dame la Grande (Poitiers, France) Godin J., Pithon M., Vergks Belmin V. Conservation of stone flooring, ancient and modern Hunt B. J., Grossi C. M.
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23
33
43 53 63
73 83
xxi The restoration of the Ursino Castle (century XIII) in Catania Barone G., Ioppolo S., Majolino D., Migliardo P., Muscarh A., Neri N. F. Decay mapping of polishable limestone Martin B., Mason D., Bryan P. Conservation of the pigmented plaster in "Red Temple" at Monte D'Accoddi (North Sardinia) Massidda L., Meloni P., Piras M. G., Sanna U. Innovative strategies for the preservation of historic cities by ND monitoring techniques and GIS management of data regarding environmental impact on historic materials and structures Moropoulou A., Koui M., A vdelidis N. P. Deterioration features in the apse of Orvieto Cathedral (Terni, Italy): a mechanical model Moroni B., Poli G. Ultrasonic measurements on weathering alpine marble. A study on field exposed samples and on the medieval marble. Portals of Schloss Tirol/South Tyrol-Italy Recheis A., Bidner T., Mirwald P. Deterioration characteristics of columns from the Marmorpalais Potsdam (Germany), by ultrasonic-tomography Siegesmund S., Pretzschner C., Ruedrich J., Lindner H., Weiss T., Richter I., Richter D., Woyde M. Damages in monuments produced by the corrosion of metallic junctions. The Acropolis case Skoulikidis T., Vassiliou P. Durability of consolidants on a French altered limestone after eighteen years of natural ageing Vallet J.M., Simon S., Mertz J. D., Martinet G. Deterioration and conservation of monuments of Latvia Lgtsis R., Vit~ia I., Igaune S. Quantification of the long-term effects of stone-cleaning on decay of building sandstones Young M. E., Ball J., Laing R. A. The Coltea Church in Bucharest Zbirnea I.M., Bonafede L. Color and weight evolution of limestones protected by water repellents after three-year ageing period in urban conditions Boutin F., Leroux L.
91 101
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129
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179 187
197
xxii Theme 6 - The conservation of stone" treatment methods and products
An integrated approach to design fluoro substituted 'smart' polymers for protection of monumental buildings Aglietto M., Castelvetro V., Ciardelli F., Matteoli U., Botteghi C., Chiantore 0., Lazzari M., Alessandrini G., Peruzzi R., Toniolo L., Fassina V. Effect of fluorinated groups on the photooxidative stability of polymeric protectives applied on calcareous stone Chiantore 0., Poli T., Aglietto M., Castelvetro V., Peruzzi R., Colombo C., Toniolo L. Effects of combined application of biocides and protectives on marble Malagodi M., Nugari M. P., Altieri A., Lonati G. A comparative study of the efficiency of siloxanes, methacrylates and microwaxes-based treatments applied to the stone materials of the Royal Palace of Madrid, Spain Fort Gonzgtles R., Ldpez de Azcona M. C., Mingarro Martin F., Alvarez de Buergo Ballester M., Rodriguez Blanco J. Study of porosity and specific area evolutions on porous material depending on hydrophobic treatments Naizot S, Barbary P., Mark S. Performance testing of transparent protective coatings on Globigerina Limestone Cassar J., Tonna G., Torpiano A., Zammit G. Evaluations of the effectiveness of innovative perfluoropolyurethanes polymers as consolidants for porous materials Croveri P., Chiavarini M. Assessment of durability of water repellents by means of exposure tests Ferreira Pinto A. P., Delgado Rodrigues J. D6consolidation par absorption d'eau de gr~s trait6s avec le silicate d'6thyle. Mesures non destructives de E, G e t v. Fdlix C., Ferrari P., Queisser A. Injectable slurries for the in situ conservation of pavement mosaics Flatt R. J., Girardet F. J. Silica bound mortars for the repairing of outdoors granite sculptures Rolland 0., Floc'h P., Martinet G., Vergks Belmin V. Ultrasonic testing method for the characterization of Pietra d'Istria structural elements Almesberger D., Geometrante R., Rizzo A., Suran P. Ionexchange resins for historic marble desulfatation and restoration Guidetti V., Uminski M. Development of lime mortars with improved resistance to sodium chloride crystallization Henriques F. M. A., Charola A. E.
207
209
215 225
235
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263 273
287 297 307
317 327
335
xxiii Slaked lime mortar: comparison between two samples supposed to be alike Jornet A., Romer A. A comparative study of mortars containing barium hydroxide (Ba(OH)2). Application on monument's conservation Lambropoulos V. N., Ghiossi S., Karatasios I. Measuring the penetration depth of consolidating products: comparison of six methods Leroux L., Vergbs Belmin V., Costa D., Delgado Rodrigues J., Tiano P., Snethlage R., Singer B., Massey S., De Witte E. Preliminary study on the set up of mortars displaying biocidal activity Ferone C., Pansini M., Mascolo M. C., Vitale A. Durability of tufaceous stones treated with protection and consolidation products Dell'Agli G., Ferone C., Mascolo G., Marino 0., Vitale A. Mineral inorganic treatments for the conservation of calcareous artefacts Lanterna G., Mairani A., Matteini M., Rizzi M., Scuto S., Vincenzi F., Zannini P. Change in properties of the stone treated with historical or modern conservation agents Maxov~ I. Criteria and methodology for restoration mortars compatible to the historic materials and structures Moropoulou A., Bakolas A., Moundoulas P. The role of consolidants in the conservation of Sydney sandstone buildings O'Connor J. Chemistry for conservation of cultural heritage: application of in situ polymerisation for the consolidation and protection Vicini S., Parodi V., Simonetta M., Moggi G., Pedemonte E. Study of the colourings of the St. Peter Fagade (Vatican) Previde Massara E., Perego G. A new white cement resistant to sea-water. Development of a white repairing mortar Puertas F., Blanco-Varela M. T., Palomo A., Vhzquez T. Hydrophobic materials - how effective are they? Puterman M. Physical properties of fine grained marble before and after conservation Rohatsch A., Nimmrichter J., Chalupar I. Compatible consolidants from particle-modified gels Escalante M. R., Valenza J., Scherer G. W. Performance evaluation of preservative coatings on stone surface of heritage buildings having hygric state Sharma R. K., Saxena V. K., Saxena K., Tewari S. K.
343
351
361 371
379
387
395
403 413
419 425
435 443 453 459
467
xxiv Dispersed hydrated lime for the preservation and conservation of stone monuments Strotmann R., Maryniak-Piaszczynski E. Ceramic additions in the restoration of stone sculpture and ceramics Tcheremkhine V. I. Effectiveness of surface treatments for sedimentary limestone in Greece Theoulakis P., Tzamalis A. Assessment of the performance of silane treatments applied to Egyptian limestone sculptures displayed in a museum environment Thickett D., Lee N. J., Bradley S. M. Scientific investigation and large scale sandstone treatments: the Washington State Legislative Building Twilley J., Leavengood D. The conservation of the sculpture work of the National Monument in Amsterdam Van Hees R. P. J., Larbi J. A. Development and assessment of a conversion treatment for calcareous stone Weiss N. R., Slavid I., Wheeler G. Evaluation of alkoxysilane coupling agents in the consolidation of limestone Wheeler G., Mdndez-Vivar J., Goins E. S., Fleming S. A., Brinker C. J. Regularities of conservation of porous material-ancient terracotta of Prichernomorye by acrylic polymer solutions Levko L. V., Yemelyanov D. N. Impregnation and strengthening of porous stone by acrylic polymer solutions Yemelyanov D. N., Volkova N. V., Pavlovskaya M. V. New proposals for the conservation-consolidation of stones and plasters: analytical characterization and trial applications of Ba aluminates Messori M., Zannini P., Mairani A., Matteini M. Integration of laser with conventional techniques in marble restoration Siano S., Pini R., Salimbeni R., Giamello M., Scala A., Fabiani F., Bianchini P. In field tests and operative applications of improved laser techniques for stone cleaning Pini R., Siano S., Salimbeni R. Results of Laser cleaning on encrusted oolithic limestone of angel sculptures from the Cologne Cathedral Siedel H., Hubrich K., Kusch H. G., Wiedemann G., Neumeister K., Sobott R.
477 485 493
503
513
523 533 541
547 553
561
569
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583
Theme 7 - Case studies of conservation of Cultural Heritage
591
Study of stone deterioration in the Palficio do Freixo in Oporto Begonha A., Teles M.
593
XXV
Polychromy traces and stone decay in the church of S. Maria dei Miracoli in Venice Fassina V. Survey on the polychromy and stone materials of funeral monuments dedicated to Jacopo and Ubertino da Carrara in Eremitani Church in Padua Favaro M., Portieri R., Crivellari F., Naccari A., Spiazzi A., Fassina V. New findings on past treatment's effects on the Lunette of San Giovanni Evangelista in Venice Favaro M., Naccari A., Crivellari F., Magris D., Pigo M., Burtet B., Fumo G., Fassina V. La pierre du portail peint de la Cath6drale de Lausanne" nature, 6tat de conservation, et consolidation Furlan V., Fdlix C., Queisser A. The Roman aqueduct of Carthage: a minerochemical study on water conduit mortars and deposited crusts Figueiredo M. 0., Veiga J. P., Pereira Da Silva T., Alvarez A., Torrens F., Khosrof S., Ferchiou N. CastelManiace, Syracuse (Sicily): the deterioration of the marble of the monumental portal and window Alberti S. A., Antonelli F., Cancelliere S., Lazzarini L., Mannuccia F., Santalucia F. The South Portal of Sint Martinusbasiliek in Halle, Brabant: technical study and conservation de Henau P., Leirens I. Documentary and analytical analogies in the study of patinas of the 'Quattro santi coronati' by Nanni di Banco Giusti A. M., Lalli C., Lanterna G., Matteini M., Rizzi M. The case of the 'Portale of S.Maria a Mare' in Giulianova: results of physicochemical inquires Amorosi E., Di Marco F., Rosignoli R., Quaresima R., Scoccia G., Volpe R. Study of stone deterioration in the cloister of the Mosteiro de Grij6, Portugal Begonha A., Sequeira Braga M. A. Study of weathering factors and evaluation of treatments for the stones of 'Santa Maria de la Encarnaci6n' Church, Constantina (Sevilla, Spain) Villegas Sanchez R., Espinosa-Gaitan J., Alcalde Moreno M. The Aragonese Portals in eastern Sicily: relationship between form, materials, decay and the environment Salemi A., Sanfilippo G. The Columbus monument at Huelva (sw Spain): preliminary survey on stone decay Galgm E., Carretero M.I., Bernabe J.M., Fernandez-Caliani J.C., Requena A.
603
613
623
633
641
649
661
671
679 689
697
707
715
xxvi Conservation problems of the statue of Saint Michael by Raffaello da Montelupo, Castel Sant'Angelo, Rome Fiori C., Lorusso S., Casalicchio G., Pentrella R., Prestileo F. Painted sandstone as protection and as an architectural and historical concept Andersson T., Von Haslingen B. Detaching methodology for fresco paintings. The case study of a renaissance cycle Casadio F., Colombo C., Toniolo L. Weathering of painted marly limestones in the Temple ruin of Merenptah, Qurna/Luxor, (Egypt) Zehnder K., Arnold A., Kung A. Ossuccio (CO): a case study to assess the causes of degradation in some terracotta statues Valentini M. Old Khmer styled sandstone monuments in Thailand. Aspects of weathering and development of conservation concept Wendler E., Prasartset C. Ethical issues in the restoration of stone sculpture in the State Tretiakov Gallery. Moscow: evolution of methods and elaboration of new polymer materials Vassilieva O. A. The deterioration of Nubian sandstone blocks in the Ptolemaic temples in upper Egypt Abd El-Hady M. M. Conservation and safeguard of stone rural buildings: an example in a mountain area Agostini S., Calvi G. A historiography of recent past interventions at the ancient theatre of Ephesos Aktiire Z. The implication of stone cleaning for planned building maintenance Laing R. A., Ball J., Scott J., Young M. E. Campo dei Greci in Venice: the case of conservation of San Giorgio of the Greeks Ioannidou N. Masonry of Abruzzo historical buildings D'Anselmo M. The rupestral monument of Basarabi-Murfatlar. Conservation of the decoration incised in the chalk walls Niculescu G., Vlad A. M. Investigations on technology of joint mortars in brick walls Domastowski W.
721
731
739
749
759
765
775
783
793
801 813
819 829
837 843
xxvii The knowledge of the plasters typical of the buildings of Ortigia (Siracuse, Italy). Part 1 - Finishing layers Alessandrini G., Negrotti R., Bocci A. M., Amadori M. L., Ercolani G., Fabbri B., Campisi T. The knowledge of the plasters typical of the buildings of Ortigia (Siracuse, Italy). Part 2 - The mortar and mortar/finishing layer combination Alessandrini G., Negrotti R., Bocci A. M., Amadori M. L., Ercolani G., Fabbri B., Campisi T. Preliminary studies about the ancient mortars of the church of Santa Maria de Irache Monastery (Navarra, Spain) Alvarez J.I., Montoya C., Navarro I., Martin A. Study of the lime renderings decay from Plaza de la Corredera, Cordoba, Spain Gonzdles Limdn T., Alvarez De Buergo Ballester M. Problems and solutions in practical restoration of freshwater limestone-tufa Sidraba I., Krage L., Graudums I. Technical aspects of stone conservation in Jerusalem Lobovikov-Katz A. Sacrificial layers for conservation of calcareous stone in Austria-theory, practice and evaluation Nimmrichter J., Koller M., Paschinger H., Richard H. An example of a practical 'cleaning' of the architectural facades of Jubilee Rome Pecoraro I. Investigation of damage in old stone structures caused by the latest strong earthquake in Northern Greece Stavrakakis E. J., Karaveziroglou-Weber M. K., Mavrikakis S. P. Author index
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881 889 897
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Theme 1 Weathering of natural stone" causes, mechanisms and measurement of stone damage
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RESTORATION OF THE HISTORICAL BRICK MASONRY Diana Bajare*, Institute of Silicate Materials, Riga Technical University, Riga, Latvia Visvaldis Svinka, Institute of Silicate Materials, Riga Technical University, Riga, Latvia
Abstract
The architectural heritage of Latvia mainly consists of manufactured materials. The Building of Riga City Council, Fortification Wall of Riga, Turaida's Palace, Ventspils Castle, etc. are some examples of historical buildings of Latvia from 12th-17th centuries. These buildings were made from brickwork. The major causes of damages in the structure of historical bricks are: migration of the water-soluble salts, and frost influence in wintertime - mechanic damage of structure by crystallisation and growing of salts or ice crystals. There is an increased corrosion of single brick or brick masonry fragments in the architectural monuments of the Middle Age observed. There is a necessity to replace these bricks with the new ones of the same size, color and physical properties. Nowadays, bricks produced in Latvia do not meet all these requirements, Therefore there is a need to develop new materials suitable for restoration works of brick masonry. The aim of the research is to analyze the old bricks, to get knowledge about the manufacturing process used, and to develop similar materials from local clays for replacement of damaged original bricks in the historical buildings. This paper is mainly aimed to analyze the historical bricks. Key words: brick, mineralogy, texture, pore size distribution, porosity, absorption, density, salts, durability of soluble salts and frost. 1. Introduction
Ventspils Castle is one of the symbols of the military fortifications of Livonian Order, which was built in 13t~ century. During centuries Castle had several rebuilding periods concerning with the growing needs of the city. The poor state of conservation of certain areas needing to be restored, together with the limited information available on the exact chronology of the erection of particular zones, have led to an extensive research project aimed to characterise the materials used in the monument. Investigation of historical bricks taken from different areas could help to estimate the age of materials in zones of uncertain date in ease there are noticeable differences between periods. It could give information about the economical situation in different periods, skills and development of civil engineering. In 1995, the reconstruction and restoration of Ventspils Castle started. The gallery of Ventspils Castle inner yards is the first and most powerful impression of the castle's actual age that the visitor gets passing through the gate vault./1/The interior of the castle in the beginning was designed as a castle- museum, without claiming restoration of any style. One should exhibit things that help to understand essential coherence of the building's development. One should preserve and not exhibit as much as possible out of the rest of the things that exist in the castle and are less essential. At present, when making some changes * Author to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservation of Stone, Venice 19-24June 2000
in the building, the restorers have to keep the inherited feeling of the Castle Awareness. By "exhibiting" one must understand priorities of accentuation of certain elements. These priorities have definite aesthetic and cultural historical aims, and they operate with various methods like volume, surface, texture, lights and shades, patina, etc, at the same time preserving the original in as much unchanged condition as possible. Exhibition priority is part and fragments of the brick wall created under impression of the order's construction traditions, namely, large size bricks in jointed brickwork. All other parts of the wall do not fall under priority. This work is the first major event in conservation of large-scale brick wall and plaster in Latvia. Different lime mortars were used. The historical brick walls are conserved with maximum preservation of medial parts. Bricks are widely stuff with lime mortar providing a possibility to preserve partly destroyed parts of the wall in situ in opposite to replacing them with new materials. In many cases dents and grooves of unknown purpose, traces of earlier made repair works, pegs, metal anchors, fragments of painting and plaster are lett open. In places where it is allowed by composition aesthetics, wall erosion traces are preserved, thus indirectly pointing at the condition of wall during a certain period of its history. Even very hopeless brick walls can be saved and made attractive. The conservation of brick walls definitely is a creative process and must be carried out together by architect and brick wall master. 2. Experimental Methods This paper mainly tries to characterise the Middle Age bricks taken from Ventspils Castle (built 13th - 17th). To this aim, the following techniques were applied: visual inspection, Xray diffraction, mercury porosimetry, physical laboratory tests (water absorption, density, open porosity, saturation coefficient) and chemical analysis. 3. Damage of historical brick masonry Brick masonry is composed of brick that are silica based and relatively acidic while the mortar in the most of old buildings is made of lime that is more alkaline. The influence of water on the degradation process is complex. Water affects not only the possibility of the reactants solution but also the presence of salts in the materials. The major cause of damage in the structure of historical bricks is a migration of salts originating from the materials in the masonry, and also from reactants from outdoor pollution or microbiological conversions in the porous system of the brick and the mortar. The frost causes damage only in a wet structure of bricks. Due to frost the bricks usually are damaged - smaller or lager flakes split from the brick surface. A structural fault can make the brick frost susceptible even though the brick frost material was strong. Pieces can also split from the bricks or they can flake off the surface./2/ The low concentration of soluble salts in the masonry do not influence durability of bricks, if the intensive water migration is not observed. Salts can not be incorporated into the hydrogen bonds of ice crystals./3/The dissociated ions in the water can bind so strongly with the water molecules that water can not freeze - depression of freezing point. Salts solution of low concentration attacks a porous material more strongly in the freeze/thawing cycles than solution of high concentration. Highly concentrated salts solution freezes in the form of ice slurry of limited volumetric expansion and relatively low compressive strength. The historical bricks were fired at low temperatures comparatively to the ceramic materials produced at the end of 20th century. The corrosion resistance and porosity of historical bricks are usually higher, but other general properties are similar with the bricks
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
5
produced nowadays. From the deterioration point of view ceramics are characterised by the following aspects: 1. Physical corrosion: erosion of particles in air or water; absorption of water in pores leading to expansion and cracking; freezing of water in pores leading to expansion, cracking and spilling. 2. Chemical corrosion: - acid- base and solubility reactions with surrounding moist air or water. 3. Physico-chemical corrosion: - recrystallization of salts to high- water and high- volume substances; - slow crack growth due to stress corrosion; - efflorescence from soluble salts is usually not harmful to ceramics, but could give unaesthetic appearance to the surface and may indicate future recrystalization damage. In the development and implementation of new materials and structural solutions, the reliable knowledge of frost and soluble salts resistance is always needed. The main purpose is to make bricks with good resistance to soluble salts, with similar physical properties as original ones.
4.
Visual
inspection
The oldest historical bricks (13-14 th centuries) have dimensions up to 30x15x10 cm. They compose the biggest part of the large bricks used in Ventspils Castle. Historical bricks, which are dated of 14-15th centuries, have dimensions up to 30x15x10 cm. That type of historical bricks is more yellowish in comparison with others. They are quite similar with the oldest bricks, but with different color and different additives used for producing. The newest bricks (15-17th centuries) are more reddish and have smaller dimensions: 28x15x6.5 cm.
The historical bricks were hand-made using wooden moulds (sander or water slopmoulded bricks) to perform the shaping. The moulds were smoothed with a appropriate moulding board and, depending on the nature of the body, immediately released from the mould or with the help of soft - mud bodies left for a short time to dry in the mould. The pieces of broken bricks (shamote) or pieces of soft clays and organic like grass or straw were used like additives. The organic components burned out during the firing, though creating more porous materials. Firing conditions and maximum firing temperature of historical bricks were unknown. There were not recognised any visible damages after visual inspection. The historical bricks still are in a good condition.
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9th International Congresson Deteriorationand Conservationof Stone, Venice 19-24June 2000
5. Chemical analyses Table 1 Chemical analysis of historical bricks N O. Sample sio 2 Ai203 1. Historical brick 59.44 14.99 (13-14~ century) . 2. Historical brick 68.99 14'.58 (14-15~ century) 3. Historical brick 64.96 19.87 (15-17m een.tury)
Fe20i 3.71
CaO., M~O 4.22 2.26
Na20 2.93
K 20 2.93
1.37'
4167
3.41
1.46
1.53
4.97
2.56' 0.83
1.41
3.14
,,
According to the results of chemical analysis, all types of historical bricks were made in the different places and centuries. There were used different types of clays for the production of these bricks. The newest bricks were made of limless days, but oldest bricks were produced from more calcareous days. (Table 1) Bigger amount of iron makes newest bricks more reddish. There was found small amount of soluble salts in the historical bricks. This concentration of soluble salts is not dangerous for ceramic materials. The presence of soluble salts in historical bricks came from the pollution of air and earth. An important role plays geographic location of Ventspils Castle- very close to the Baltic see.
6. Physical properties of historical bricks Table 2: Physical properties of historical bricks 13-14th centuries 1. Waterabs0rption,% ' 17.83 2. Density, g/era3 1.70 3. Open porosity, % 26.39 4. Saturation coefficient .... 0.75
13-14na centuries 19.4~8 1.68 30.84 0.86
13-i4thcenturies ' 18.21 ' 1.81 27.81 0.86
All types of bricks, not depending on chemical composition, have quite similar physical properties. The porosity of these bricks is from 26 to 30 %. The bulk density is between 1.7 and 1.8 g/era3. The water absorption is between 18-19%. (Table 2) The saturation coefficient gives information about possible frost resistance of bricks. The results indicate that bricks are frost resistant if saturation coefficient is smaller than 0,78. The saturation coefficient of oldest bricks is 0,75 (this is one of the characteristic measurements of good frost resistance), but for other types it is higher- 0,86. All types of historical bricks have higher porosity and water absorption to compare with commercial bricks produced nowadays in Latvia.
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
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7. X-ray diffraction None types of historical bricks have illite connection with X-ray diffraction analysis. It means that sintering temperature of historical bricks was higher than 900~
Figure 1 X ray diffraction of historical bricks: A - historical brick from 13-1~.th centuries, B - historical brick from 14-15th centuries; B-light - historical brick from 14-15th centuries, light pieces; C - historical brick from 15-17th centuries: Q-quarts, A-anothite, C-calcite, Dgelenite, H-hematite There was found calcite in the historical bricks. Normally calcite disappears at the temperature below 800 oC. (Figure 1) It means that calcite found in the bricks is secondary calcite. The secondary calcite got into the structure of bricks from lime mortars by influence of water migration
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
8. Pore size distribution There have been made many suggestions in the literature what pore size, as well as the quantity can influence durability of bricks. /4, 5/Bricks with low durability have pores between 0.04 and 1 ~tm, but with good durability - majority larger than 2 ~tm. The majority of pores 0.04-1om charaeterise deficient frost damage. Water in smaller pores requires temperatures below - 40oC to freeze. Pores >1 ~tm do not saturate with water. The pore size depends on the composition of raw materials and methods of bricks' formation: 9 grog and shale particles larger than 200 mesh favored the formation of larger pores; 9 pure clays produced pores smaller 0.1 ~tm 9 soft moulding produces larger pores to compare with the extrusion; 9 higher firing temperature and increasing soaking time reduce the quantity of pores but not the predominant pore size in a span of normal temperatures. The pore size distribution was determined by mercury porazimeter. The weight of samples used was approximately 0.5 g.
Figure 2: Pores size distribution of historical bricks: A - historical brick from 13-14m centuries; B - historical brick from 14-15th centuries; B-light - historical brick from 14-15th centuries, light pieces; C - historical brick from 15-17th centuries
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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The dimensions of pores are mainly in interval from l to 2 ~tm for all historical bricks. (Figure 2) The oldest bricks from 13-14th centuries have bigger pores than other bricks. It means, that these historical bricks have better resistance to frost and soluble salts. The newest bricks (15-17 th centuries) have different pore size distribution and shape. The dimensions of pores are around 1lam. It indicates that bricks have lower resistance to frost and soluble salts. Historical bricks B have light pieces of additive. The dimensions of pores of additive is concentrated in interval 0.8-0.9 pm. The pieces of additive are more porous with smaller pore dimensions. The durability of these pieces to soluble salts and frost is lower. The pieces of additive could be shamote or soft pieces of clay - with smaller proportion of water. In reality, all historical bricks are in rather good condition atter 5-7 centuries. The pores can be divided into small, middle and big ones. The possibility of ice formation and crystallisation of salts crystals is most obvious in middle size pores (0,0041pm) of bricks. Relatively bigger amount of middle size pores is observed in historical bricks B - 56%, because they have light peace of additive with big amount of middle size p o r e s - 84%. (Figure 3) Historical bricks A have only 25%, but C - 48% middle size pores.
Figure 3: Cummulative pore volume: A - historical brick from 13-14th centuries; B historical brick from 14-15 th centuries; B-light - historical brick from 14-15th centuries, light pieces; C - historical brick from 15-17th centuries.
The historical bricks A have 55% big size pores, C - 47%, but B - 7%. Due to that historical bricks A have better durability to soluble salts and frost.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Magge suggested an equation that allows one to calculate a Durability Factor for a brick based on its pore structure. /6/ A sufficiently large value of the Durability Factor is associated with a durable brick. The equation is: DF=(3,2/PV)+2,4xP3
(1)
DF - durability factor of brick; 3,2/PV- maximum intruded pore volume of brick, cm3/g; 2,4xP3 - percentage of the pore volume lying in pores with diameter greeted 3 lam. The first term of Maage's equation, 3,2/PV, expresses the obvious trend that a greater pore volume may lead to less durable brick. This portion of Magge's criterion is in parallel with the ASTM criterion that sets limits on water absorption for several climates. The second term, 2,4 x P3, recognises the fact that large pores, while contributing to the total volume, are unlikely to full of water. They drain easily. Thus a brick's durability rating can be increased be the proportion large pores that are present. Or, put another way, a brick should not be penalised for having a large pore volume if those pores are large and drain easily. The results indicate that bricks are frost resistant if DF>70 but not frost resistant if DF<55 and less predictable in between./7/ In compliance with the theory of Maage and table 3, all historical bricks have deficient durability to frost and soluble salts, because none of these bricks have a lot of pores larger than 3 lam. The dimensions of pores of all historical bricks are concentrated in interval from 1 to 2 lam. Table 3. Maage's Durability Factor for historical bricks. No. Sample 1. 2. .
Historical brick (13-14 th century) Historical brick (! 4-15 th eentu~) Historical brick (15-17 th century)
9. Durability Factor 33.17 30.07 40.96
Conclusions
- By visual inspection all types of historical bricks are in relatively good condition. - There are three types of historical bricks made from different clays using various production methods. - All historical bricks are porous - open porosity is 26-30%. - The secondary calcite got into the structure of bricks from lime mortars by influence of water migration. - The sintering temperature of all bricks was higher than 900~ - Pore size of all bricks is concentrated in interval 1-2 ~tm.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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- Historical bricks have additive, which makes bricks less durable to soluble salts and frost. -Magges's index for all historical bricks is less than 0.55 and it means that they are not durable to soluble salts and frost. Literature
Blums P., 1999. Old is beautiful:See Yourself, Latvijas Arhitelaura, No.24, p.86-88. Ylii-Mattila R., 1991. Frost Damage and Frost Resistance of Masonry, Frost Resistance of Building Materials, Proceedings of Nordic seminar in Bor~, 29-30 October, p. 50. Ptihringer J., 1991. Freezing in Porous Materials, Frost Resistance of Building Materials, Proceedings of Nordic seminar in Bor~s, 29-30 October, p. 14 Robinson G. C., 1984. The Relationship between Pore Structure and Durability of Bricks, AM Ceram. Soc. Bull., Vol.63 (Nr. 2), p 295-300 Ricciakddli F. G., Minichelli D., 1995.Problems in the Determination of Frost Resistance of Bricks, Fourth Euro-Ceramics, Bricks and Rolling Tiles, Vol. 12, Edited by F. Braga- S. Cavallini, G. t'. Di Cesare, Winslow D., 1991. Predicting the Durability of Paving Bricks, Jumal of Testing and Evaluation, JTEVA, Vol. 19, No. 1, Jan., pp. 29-33 Magge M. 1990. Frost Resistance and Pore Size Distribution of Bricks, ZI, No. 9, p. 472480
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COMPARATIVE STUDY OF DWFERENT METHODS FOR GAP FILLING APPLICATIONS AND USE OF ADHESIVES ON THE BIOCALCARENITE SURFACES OF THE "TEMPIO DELLA CONCORDIA" IN AGRIGENTO C. Bennardo, P. Meli Superintendence for the Cultural and Environmental Heritage in Agrigento, Agrigento, Italy G. Biscontin Department of Environmental Sciences- University of Venice- Venice, Italy N. Berlucchi*, R. Ginanni Corradini, F. Mattolin I1 Cenacolo s.r.l., Rome, Italy
Abstract
A large-scale survey has been carried out to detect and quantify the deterioration on the biocalcarenite surfaces of the "Tempio della Concordia" in Agrigento together with the other remains in the Valley of the Temples. As part of this survey, a series of laboratory tests were carried out with the aim of choosing an adequate material to be used for the repair of missing sections and for the fixing with adhesive of fallen parts or parts that are flaking away. As this was an experiment that had not been attempted previously and for which no standard procedures existed, a large number of different tests were carried out, ranging from small trials to larger operations, in order to draw up comparative analyses. The results have been compared in terms of compatibility with the supporting surface, and also in terms of durability and hardness. The outcome has led to important conclusions from the point of view of on-site operations and of knowledge of the behaviour of materials which, though well-known and widely used, have not always shown good compatibility with the biocalcarenite of the Agrigento temples. Key words: comparison between gap filling works and adhesive application, artificial ageing of mortar, and comparative analyses. 1. Introduction
The Superintendence for the Cultural and Environmental Heritage in Agrigento have set up a diagnostic project (still underway at present) aimed at surveying the existing situation (materials and deterioration) and determining the correct methodology for the restoration and conservation of the "Tempio della Concordia", the main temple on the archaeological site of the "Valley of the Temples". Numerous tests as well as chemical and physical analyses have been carried out including: photogrammetric surveys, mapping the various types of deterioration, integration tests, static and dynamic structural tests, environmental and structural monitoring, tests of consolidation and gap filling and adhesive application, as well as cleaning in the laboratory and on-site. Within the framework of these tests, a study and comparison phase has just been concluded regarding the commonest types of gap filling and adhesive application, in order to choose the most adequate material which has to be the least harmful for the biocalcarenite which the temples are made of. We feel that, independently of the type of materials involved, such comparisons may be of interest to other people working in the restoration field from the point of view of evaluating * Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
the analytical methodology, and of acquiring information and guidelines which apply to stone and marble restoration in general. 2. Methods and results
The following sections describe the operative methodologies and the different analytical phases used in carrying out this study. 2.1 Sampling
To carry out the laboratory analyses for 214 normal tests, six irregular tests and 36 samples, research was conducted to find a quarry that could provide the type of material as similar as possible to that most frequently found in the construction of the temples. For this purpose, a previous study relating to materials and deterioration was used. The "Tempio della Concordia" is made of a type of biocalearenite that has been classified by Dunham (1962) as Packstone. This is a soft sedimentary elastic rock with inter-granular material composed of a low micritie matrix and predominantly of spatie cement (about 1015%) eharacterised by a high proportion of bioelasts (65-75%), with granular features ranging from very fine to medium fine, with the frequent presence of micro-conglomerate sandstone pieces. The quartz component (10-15%) and the limestone component (5%) show granular features respectively of coarse silt and coarse sandstone ranging from fine to medium to very coarse. The overall porosity is about 20-30% which is high for a sandstone. The search for the quarry took place near the temple (geological sheet no. 271 - Agrigento) and concentrated on two Pleistocene formations (Q1 s e Qla); the type of stone most similar to that most frequently used in the "Tempio della Concordia" came from the Villaseta quarry. 2.2 Preparation of the tests
On the basis of the tests to be carried out on blocks of stone (bioealcarenite) taken from the ViUaseta quarry (w and for the preparation of the mortar for gap filling work (w and the adhesive mortar for fixing pieces (w five types of test samples were prepared: 1) test samples measuring 3x3x3 em and 4•215 cm: for the regular homogeneous samples of gap filling mortar and for the regular "sandwich" samples made up of stone/mortar/stone (the shape and dimensions were established by checking the water absorption by capillary action- Rec. Normal 11/85); 2) test samples measuring 5x5xl.2 cm: for regular homogeneous samples of gap filling mortar (the shape and dimensions were established by checking water vapour permeability - Rec. Normal 21/85); 3) test samples 9x8x3 cm: for regular "sandwich" samples of stone/mortar/stone and stone/mortar-adhesive/stone (the shape and dimensions were established by direct traction tests); 4) cylindrical test samples with 6=2.6 cm and h= 6.7 em: for regular mortar samples (the shape and dimensions were established by single axis compression tests); 5) irregular test samples (dimensions of about 30x20x10 em): for tests in which three sections were taken from each sample and subsequently re-attached with mortar-adhesive (the shape and dimensions were established by macroscopic observation during and after artificial ageing with salt crystallisation, on a sufficiently representative selection of samples).
9th I n t e r n a t i o n a l C o n g r e s s o n D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f Stone, Venice 19-24 J u n e 2000
15
2.3 Investigation methodologies During the diagnosis, several basic parameters were checked by submitting the laboratory samples to a large number of analyses before and after three different types of artificial ageing, relating to salt crystallisation by forced capillary action and exposure to UV radiation. The parameters taken into consideration are shown in table 1: tab. 1 - analytical methodologies used for the evaluation of procedures for gap filling work, adhesive and fixin~ work AIM
ANALYTICAL METHODOLOGY
a) to establish the degree of water repellence of mortar for single gap fdling work on the stone surface and for adhesive systems
The homogeneous samples of gap filling mortar and "sandwiches" of the type stone/mortar/stone and stone/ac~esive~mortar/stone were tested, under total immersion, for water absorption by capillary action before ageing by salt crystallisation;
b) to establish the degree of water vapour permeability of the single The homogeneous samples of mortar were submitted to m e a s u r ~ gap filling under total itmnersiot~ of water vapour permeability before ageing with salt crystallisation; c) to establish the open integral porosity of the single gap filling mortar d) to measure physical changes after hardening of the single gap filling mortar
The samples taken l~om those in b) above were submitted to mercury porosity measurement; The homogeneous m e a ~
e) to establish resistance to simple ~ i o n
of the single gap
filling~
test samples of mortar were submitted to
of weight and ~n'inkage variation before and after hardening;
The homogeneous mortar test samples were submitted to single axis compression tests after natural carbonate formation (the best of three tests for each mortar sample);
f) to establish variations in colour for the single gap filling mortar
The homogeneous mortar test samples were submitted to measurement of eolour and reflectivity before and after exposure to UV radiation;
g) to evaluate microscopically the interface of the gap filling system and the adhesive procedure
Transverse samples of stone/mortar/stone and stone/adhesivemortar/stone were submitted to microscopic observation of thin sections, after salt crystallisation by total immersion;
h) maQrosoopic evaluation
of the induced effect of salt
The "sandwich" test samples, stone/mortar/stone and stone/adhesivecrystallisation caused by forced capillary action, on the gap mortar/stone, were submitted to constant macroscopic observation during
filling system and on the adhesive system (also when studs or artificial ageing by salt crystallisation with forced capillary action pins are used) (des~bed below); i) to evaluate the ac~esion of the gap filling system and the reThe "sandwich" test samples, gone/mortar/stone and stone/ac~esive~ adhesive system (also when studs or pins are used) 1) macroscopic
evaluation
of the induced
effect of salt
mogtar/stone, were submitted to direct traction tests; The irregular test samples, stone/ac~esive-mortar/stone, were submitted
c~ystallisation by total immersion on the adhesive system for to constant macroscopic observation during mtilicial ageing by salt large,pieces .
.
.
.
.
.
.
.
crystal!i ,sation under tota,,1 immersion .
.
.
.
.
The artificial ageing procedures mentioned above were carried out as follows: - exposure to UV radiation was carried out, for a total of 100 hours, using a "Wood" lamp placed at a distance of about 55 cm. from the samples; - ageing with salt crystallisation by total immersion involved twenty cycles both for the mortar for gap filling work and the adhesive systems for large pieces; each cycle consisted of four hours of immersion in a saturated sodium sulphate solution, followed by 20 hours in a heat-stabilised oven at 60~ - salt crystallisation by forced capillary action was carried out by placing the sample in a container in which there was a standard filter paper to permit capillary ascent of water saturated with sodium sulphate; the ascent was forced in as much as transpiration took place over the height of the sample by means of the application of parafilms on the outer edge; in
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9th International
Congress
on Deterioration
and Conservation
of Stone, Venice 19-24 June 2000
practice, the upper surface of the sample was where transpiration took place; the ageing process lasted for a total of sixty days. 2.4 Formulation and experimentation of mortars and systems for gap filling work To evaluate the suitability of mortars for gap filling work, eight types of mortar were prepared in the laboratory, as shown below (tab. 2): work
tab. 2 - composition of mortars for B[lllder FOR GAP FILLING WORK
(lr)
Aggregate
Water(ml)
P ~
(gr)
Cement
Ochre
Primal
(gr)
(gr)
(gr)
(gr)
m o r t a r M1.
710
2150
600
.
m o r t a r M2
800 O)
1600 0)
300
-
m o r t a r M3
66O
2000
350
.
.
.
.
24 (1)
B/A (by weight) 1/3
s.q.
-
0)
1/2 J
330 rich [ 330 Lafarge
2000
600
.
.
.
.
.
.
1/3
.
1/3
,,
m o r t a r M5
9 9
m o r t a r M7 9
,
170
500
.
.
.
I000
1500
600
1500
~0
2000
580
.
~0
2000
350
-
.
.
ca 1/3
.
.
1/3
.
1/3
,
mortar M8
-
-
15
1/3
Lafarge lime and crushed biocalcarenite; MORTAR M2: mortar for restoration from the early 20th century, reconstructed in laboratory; MORTAR M3: rich lime and crushed biocalcarenite; M O R T A R M4: rich lime, Lafarge lime and crushed biocalcarenite; MORTAR M5: Akeogard CO and crushed biocalcarenite; MORTAR M6: rich lime, pozzolana and crushed biocalcarenite; MORTAR M7: hydraulic conglomerate C30 and crushed biocalcarenite; MORTAR M8: rich lime, primal and crushed biocalcarenite (1) The quantities are by volume (ml) and not by weight (gr) since the composition has been deduced by processing an image of a thin section thereby obtaining the ratio of B/A (Binder/A~,__~g~regate)by volume
N.B. M O R T A R
M1
The evaluation of the characteristics of the above mortars was carried out on 160 regular test samples and 24 samples which had undergone tests as shown in 2.3.1. The gap filling mortars (table 2, a-b-c) can be grouped by the following typologies: adequate mortars (mortars M1, M3, M4 and M8), slightly adequate mortars (mortar M6), slightly inadequate mortars (mortar M2), inadequate mortars (mortars M5 and MT). None of the mortars showed significant variation in colour after artificial ageing by exposure to UV radiation; any variation there might have been was not visible to the naked eye. It should be noted that the adequate and slightly adequate mortars are based on a binder with rich lime (M3, M4, M6 and M8) and/or mortars based on Lafarge lime (Mland M4). Generally speaking, all these mortars show a rather low resistance to salt crystallisation by total immersion, accompanied by detachment from the rock (between the second and fourth cycles) which, however, remains in good condition even after the detachment of the mortar. The resistance to direct traction ranges from low to fair, with detachment of the mortar leaving little trace on the rock surface. In general, the permeability to water vapour, and absorption of water by forced capillary action, are fairly similar to untreated rock; for permeability to water vapour, at most one can find a reduction ranging from low to fair (15-30%). In particular, mortar M6 displays the lowest characteristics because, during salt crystallisation by total immersion, large amounts of the material break away, and because not much mortar is left on the rock after the direct traction test.
9 t h I n t e r n a t i o n a l C o n g r e s s on D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f Stone, Venice 19-24 J u n e 2000
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The slightly inadequate and inadequate mortars have a binder which is either too rigid (mortar M2, with cement-based binder, and mortar M7 with conglomerate C30 binder) or too elastic (mortar M5). Mortar M2 shows a fairly low resistance to salt crystallisation by total immersion, with detachment (between the second and third cycles) and partial removal from the rock accompanied by the breakdown of the mortar itself. The resistance to direct traction, though mediocre, involves detachment from the rock, with a low to fair quantity of mortar left attached to the rock. The absorption of water by capillary action is similar to that of untreated rock, and the permeability to water vapour is slightly reduced (by about 15%). Mortar M5 shows a high resistance to salt erystaUisation by total immersion since the mortar remains unaffected with breakage of the rock. The resistance to direct traction, though fair, involves detachment with a significant quantity of mortar left attached to the rock. The absorption of water by capillary action is different from that of the untreated rock, and leads to the formation of "steps" on the corresponding curve; the permeability to water vapour is slightly reduced (by about 15%). Mortar M7 displays a significant resistance to salt crystallisation by total immersion since the mortar detaches itself between the fifth and sixth cycles, with a fair amount of mortar left attached to the rock. This also happened during the direct traction test where there was high resistance leading to breakage of the rock and pieces coming away. The absorption of water by capillary action and the permeability to water vapour are much lower than that of the untreated rock; in the case of water absorption, there was also a "step" on the corresponding curve. N.B. 2.5 Formulation and experimentation of products and systems for re-adhesion and f'Lxing
To evaluate the effectiveness of products and systems for re-adhesion and fixing, six adhesive-mortars (more precisely, five adhesives and one mortar) were prepared in the laboratory. The adhesive-mortars prepared in the laboratory are shown in table 3 below: tab. 3 -compositio n characteristics of adhesive-mortars for re-adhesion and fixin8 RE-ADHESION PRODUCTS SC1
SC2
COMIN~SITION Eurostac 2101:56 glr, Eurostac 2102 (hardener): 14 gr crushed biocalcarenite: 150 gr, Aerosil: 8 gr Eurostac 2501:96 gr, Eurostac 2502 (hardener): 24 gr crushed biocalcarenite: 100 fit', aerosil: 12.5 gr
SC3
Araldite BY158: 48 gr, H Y 2 9 9 6 (hardener): 12 gr, aerosil: 3 gr
SC4
UHU-PLUS (two components 1/1)
SC$
Lafarge lime: 90 gr, water: 110 ml crushed biocalcarenite: 360 gr, Primal: 3 ml (1 teaspoon)
Ledan TB: 100 fir, water: 100 ml SC6 crushed biocalcarenite: 200 gr . . . . . . . . . . . . . . . . . . . . . N.B. SCI" epoxy resin Eurostae 2101mixed with crushed local stone and with aerosil; SC2" epoxy resin Eurostac
2501 mixed with crushed local stone and with aerosil; SC3" epoxy resin Araldite BY158 with aerosil; SC4: epoxy glue Uhu-plus with two components, not mixed with anything; SCS" Lafarge hydraulic lime and Primal mixed with crushed local stone; SC6" Ledan TB mixed with crushed local stone
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Overall, sixty test samples were used (54 regular samples and six irregular ones) and twelve samples; the results made it possible to choose the adhesive-mortar(s) which are most adequate for re-adhesion and fixing. The characteristics of the systems for re-adhesion and fixing (table 3, a-b) show that those with Eurostac 2501, crushed local stone and aerosil (SC2), Araldyte BY158 and aerosil (SC3) and Uhu-plus not mixed with anything (SC4) are not adequate since, during the resistance tests for salt erystallisation by total immersion and forced capillary action, the adhesive was unaffected while the rock surface deteriorated significantly. These data were confirmed by the high resistance to direct traction (about 2.1-2.6 kg/cm2) causing breakage to occur always in the rock. Moreover, water absorption by capillary action shows a curve with a "step" indicating probable halting of the ascent. Therefore, the most adequate systems are those using Eurostae 2101, crushed local stone and aerosil (SC1), Lafarge lime, primal and crushed local stone (SC5) and Ledan TB with crushed local stone (SC6). During the resistance tests for salt erystallisation by total immersion, all these systems showed the detachment of the rock area corresponding to the adhesive. However, system SC1 shows a higher resistance since, on regular samples, the breakage generally occurs (two or three eases) between the ninth and tenth cycles and after the fiReenth cycle, while when using two other systems (SC5 and SC6) breakage occurs on average between the fifth and sixth cycles. The same test carried out on irregular samples of large dimensions showed a higher resistance than systems SC1 and SC5 - there was no detachment during the whole process (twenty cycles), while the system SC6 (between the fifteenth and twentieth cycle) caused detachment of three pieces with breakdown within the adhesive. The visual appearance of SC1 is fair (similar to that of the rock) while that of systems SC5 and SC6 is poor to insufficient (the adhesive is lighter in eolour than the rock however, it can be coloured during the process). This behaviour is confirmed by the direct traction resistance which ranges overall from low (about 0.15-0.20 kg/cm2) to mediocre (about 0.6 kg/cm2), with breakage either at the point where the adhesive is (SC1), or at the point of contact with the rock with a fairly small amount of material left attached to the rock. Furthermore, water absorption by capillary action shows a curve that is generally similar to that of untreated rock (without a "step" in the graph). R.G.C. 3. Conclusions
For reasons of brevity, since so many test were carried out, it is not possible to print here all the comparative graphs enabling immediate analysis to be made of the different performances of the various systems of gap filling work and adhesive fixing However, we have attempted from the outset of this paper to provide an evaluation of the systems by subdividing them into adequate and inadequate for restoration work on the biocalcarenite of the 'q'empio della Concordia" The temple itself is characterised by a marked degree of "friability" as shown by large quantities of detached flaky and powdered material caused mainly by the presence of soluble mineral salts, by a high level of open porosity, and by low structural strength It is felt, therefore, that any type of material used for gap filling work or adhesive fixing should have characteristics that are similar, both me~hanicxdly and chemically, to the original, and which will ensure a gradual deterioration of the mortar or the adhesive over time, but not at the expense of the stone This view of the situation implies that one should give up the idea of applying an artificial stone material which would be guarantee~ to last for many years, as was done in the recent cement restoration work on the temple, with serious damage to the stone Rather, one should
9 t h I n t e r n a t i o n a l C o n g r e s s o n D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f S t o n e , V e n i c e 19-24 J u n e 2 0 0 0
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choose softer and more compatible materials- a choice which would inevitably lead to a change in policy: no longer, the one-off major restoration project, but an initial generalised approach followed by continuous and constant maintenance. tab. 2a - systems ,of mortar for gap filling work: summary of experimentation tests M1 " (Lafarge lime and crushed local stone)
RESISTANCE TO SALT CRYSTALL BY TOT, IMM. stone/mortar/stone
Single mortar
~
2nd cycle: mortar breakage, with detadunent from rock in good state,
3rd-4th cycles: mortar breakage, with detachment of
M2 (restoration mortar early 20th century)
-
2rid cycle: mortar breakage, with detadmaeat from rock and partial damage to rock
3rd cycle: mortar broke down completely,
coarse flakes, RESISTANCE TO SALT CRYSTALL. BY FORCED CAPILL. ACTION stone/mortar/stone
Interface: no change External surface: slight breaking up.
M3 (rich lime and crushed local stone) .....
2nd cycle: mortar unaffected, with detadmaeat from rock in good state.
3rd-4th cycle: mortar breakage, with detachment of small or coarse flakes.
Interface: no change External surface: slight breaking up.
Interface: no change External surface: slight breaking up.
INTERFACE MORTAR/STONE (AFTER AGEING)
Mortar: formation of microMortar: increased and Mortar: increased and (xacks; adhesion: from good to widened cracking; adhesion: widened craddng; adhesion: low low low
RESISTANCE TO DIRELW TRACTION
FAIR (about 0.7.-0.8 kg/cm2), MEDIOCRE (about 0.5 LOW TO MEDIOCRE (ca 0.3 breakage at the stone/mortar face kg/cm2), breakage at the - 0.4 kg/cm2), breakage at the with hardly any mortar attached to stone/mortar face with little or som~ stone/mortar face with hardly any the rock mortar left attached to the rock mortar left attached to the rock
RESISTANCE T O SIMPLE COMPIL ABSORPTION OF WATER BY CAPILLARY ACTION
FROM FAIR TO GOOD (about 33.3 kg/cm 2)
Only mortar: similar to tmtreat~ rock stone~mortar~stone: similar to untreated rock
COLOURING APPEARANCE PERMEABILITY TO WATER VALOUR ,
POROSITY
FROM LOW TO FAIR (about 21.7 kg/cm2)
Only mortar: similar to ~ rock stone~mortar~stone: similar to maremed rock
LOW (about 11.3 kg/cm2)
Only mortar: similar to untreated rock stone~mortar~stone: similar to untreated rock
In general, Class I
FAIR REDUCTION (ca 30%) with respect to untreated rock
LOW REDUCTION (ca. 15%) with respect to untreated rock
TYPE Ia Open porosity = 27.3-28.4% single symmetrical mode with principal mode at 0.2-0.3 tan and average at 0.25 van
TYPE Ia Open porosity -- 31.8-32% single symmetrical mode with principal mode at 0.2-0.3 lain and average at 0.26-0.27 van
meso= 17.6% maero=81.2%, mega= 1.5%
meso= 12.4% macro=g4- 5%, mega=3.4%
LOSS OF WEIGHT AFTER HARDENING
FAIR (ca. 9.3-9.7%)
SIGNIFICANT (ca. 14.218.9%)
SHRINKAGE % AFTER HARDENING
VERY LOW (ca. 0.11%)
HIGH (ca. 4.6%)
LOW REDUCTION (ca. 15%) with respect to untreated rock TYPE H Open porosity = 31.2% dual mode with principal mode at 2-5 van (av~age 4.6 tan) and secondary mode at 0.2-0.3 van (average 0.21-0.26 pro) meso=7.7% macro=88.9%, mega=3.4%
SIGNIFICANT (ca. 14.218.9%)
SIGNIFICANT (ca. 2.3-3.1%)
(1) refetmce characteristics for untreated rock: pemmability towater vapour (average value of 209.~/g/m 2'. 24h), water absorption'by capillary action (CA=I.2 910.2 g/m2 9s u2, M *= 0.71 g/cm).
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
tab. 2b - systems o f mortar for s a p filling work: summary o f experimentation tests . . . . . . RESISTANCE TO SALT CRYSTALL. BY TOT. IMM. stone/mortar/~mte single mortar
RESISTANCE TO SALT CRYSTALL BY FORCED CAPILLARY ACTION rock/mortar/reek
INTERFACE MORTAR/ROCK (AFTER AGEING)
M4 (rich lime, Lafarge _ lime, crushed local stone) .
M5 ( A k e o g a r d C O and crushed local stone)
2nd cycle: mortar fracture 5th-6th cycle: d e t a ~ through mortar fiactur~, fair ac~esion to rock
1l th cycle: mortar unaffected but rock breakdown
3rd-4th cycle: mortar fracture with detachment of coarse flakes
.
Test not carried out dueto breakage of sample after hardening
Interface: no change External surface: slight breaking up
Interface: mortar detached from rock and broke up, with fair ac~esion to lower rock surface External surface: (2/3 samples.) slight breaking up. (1/3 samples.) slight flaking,
Mortar: formation ofmkax~cracking Adhesion: good
Mortar: internal fraaa~e without m i ~ c t t a a l changes; Adhesion: locally reduced
MEDIOCRE (ca. 0.5 kg/cm2) FAIR (ca. 0.7-0.8 kg/cm2) RESISTANCE TO fracture at rock/mortar face with DIRECT TRACTION , fracture at rodt/mortar face with hardly any mortar left attached to quite a lot of mortar left attached tc the rock the rock RESISTANCE TO SIMPLE COMPIL
FAIR (ca 27.8 kUcm2) increase of 1.5 times (150%) with respect to that of M3 (without Lafarge lime)
ABSORPTION OF WATER BY CAPILLARY ACTION
Only mortar: slight reduction in speed of absorption (37 times less) Rock/mortar~rock: similar to untremed rock
VERY LOW (ca 7 kg/cm2)
Only mortar: test not carried out, sample deteriorated during hardening Rock~mortar~rock: formation of "step" showing halting of ascent
COLOUR APPEARANCE PERMEABILITY TO WATER VAPOUR POROSITY
SHRINKAGE % ii AFTER HARDENING
4th-5th cycle: mortar unaffected, with detachment from rock (2/3) 8th cycle: mortar fracture (1/3 samples) 3rd-4th cycle: same as M1 with heavy loss of material
Interface: molar detached l~om b~h rocks External surface: slight breaking up.
Mortar: increase and widening ofamddng Adhesion: poor FROM LOW TO MEDIOCR~ (ca. 0.3-0.4 kg/cm2) fracture at rock/mortar face with little mortar left attached to rock LOW (ca 17.3-18.8 kg/cm2)
Only mortar: similar to tmtreated rock Rock~mortar~rock: similar to untreated rock
in general Class I
LOW REDUCTION (ca. 15%) with respect to untreated r o ~
FAIR REDUCTION (ca. 30%) with respect to tmtreated rock
TYPE IH Open porosity = 27.8-30.8% single asynmmUical left-hand mode with average at 17-30 pan
TYPE Ib Open porosity = 31.5-31.9% single ~ c a l mode with principal mode at 0.1-0.2 ~ n and average at 0.17-0.20 tun
meso= 10.2% macro=33.3%, mega=56.4%
meso=l 5.5% macro=83.4%, mega=l.l%
WEIGHT LOSS AFTER HARDENING
M6 (rich lime, pozzoisna, crushed local stone)
FAIR (ca. 9.3-9.7%)
LOW(ca. 1.2%)
SIGNIFICANT (ca. 14.2-18.9%) t
VERY HIGH (not measured because internal)
SIMILAR to tameated rock
TYPE H Open porosity = 34.8-36.6% dual mode with principal mode at 1-2 ttm and 2-5 van (average 4.85.5 tan) and secondary mode at 0.05-0.1 van and 0.1-0.2 pan (average 0.27-0.3 l~tn) meso=16.2% macro=73.3V~ mega=2.6% SIGNIFICANT (ca. 14.2-18.9%) SIGNIFICANT (ca. 2.3-3.1%)
9 t h I n t e r n a t i o n a l C o n g r e s s o n D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f S t o n e , V e n i c e 19-24 J u n e 2 0 0 0
tab. 2c
-
21
systems of mortar for gap fillin8 work: summary of experimentation tests ,
RESISTANCE TO SALT CRYSTALL BY TOT. IMM. rock/mortar/rock Single mortar
RESISTANCE TO SALT CRYSTALL. B Y FORCED C A P I L L ACTION rock/mortar/rock
M7 (hydraulic conglomerate C30 and crushed local stone)
5th cycle: mortar fracture and, in 1/3 samples,
detaclnnent from rock
(2/3)
9th-10th cycle: low deterioration with slight breaking up which increasedgradually
Interface: no change External surface: heavy deterioration with d~dmmnt
RESISTANCE TO DIRECT TRACTION
HIGH (ca. 2-2.1 kg/cm2) with 2/3 samples, rock fracture, 1/3 samples, fracture at rock/mortar face with local detachment of rock
POROSITY
up
Interface: no change External surface: slight breaking up (like mortar M1)
Mortar: in.ease and widening oforaeks Adhesion: low
VERY HIGH (ca. 180 kg/oIl 2)
FROM LOW TO MEDIOCRE (ca. 0.3-0.4 kg/cm2) fracture at rock/mortar face with hardly any mortar ldL attached to rock LOW (ca. 17.3-18.8 kg/cm2) increase of 60% with respect to that of M3 (without Lafarge lime)
Only mortar: Quantity absorbed: 70% 1 ~ than untreated roc~ Speed of absorption: 340 lowerthan untreated rock Rock~mortar~rock: heavy reduction in speed of ascent with reduction of overall quantity of water absorbed
COLOURING APPEARANCE PERMEABILITY TO WATER VAPOUR
3rd-4th cycle: deop fra~ure with marked breaking
of coarse flakes
Mortar: formation of micro-cracks Adhesion: good Rock: local daadnnent of coarse granules
ABSORPTION OF WATER B Y CAPILLARY ACTION
3rd-4th cycle: mortar unaffected (2/3 samples) with
detadunent from rock
6th cycle: mortar fracture with fair adhesion to rock
INTERFACE MORTAR/ROCK (AIRIER AGEING)
RESISTANCE TO SIMPLE COMPIL
MS (rich lime, primal tug crushed local stone)
,
Only mortar." similar to tm-treat~ rock Rock~mortar~rock: similar to tmtrem~ rock
in general Class I
HIGH REDUCTION (ca. 60%) with respect to untreated rock TYPE IV Open porosity = 23.6-24.8% single symmdxical mode with principal mode at 0.05-0.1 Jam and average at 0.070.09/mi
SIMILAR to untreated rock
TYPE II Open porosity = 32.2-32.4% dual mode with principal mode at 2-5 tun (average 3.9-4.2 pro) and secondary mode at 0.1-0.2 pm (average 0.21 pro)
meso=35.9% macro=62%, mega=2.4%
meso=8.5% maoro=87.1%, mega=4.6%
WEIGHT LOSS AFTER HARDENING
MINIMAL (ca. 5.3%)
FAIR (ca. 9.3-9.7%)
SHRINKAGE % AFTER HARDENING
NONE
SIGNIFICANT (ca 2.3-3.1%)
(1) Reference charact~stics for maxeated rock: permeability to water vapour (average value of 209.7 g/mz 924h), water absorption by capillary action (CA=I.2 910.2 g/m2 9s v2, M *= 0.71 g/cm).
22
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
tab. 3 a - systems o f adhesive-mortar for re-adhesion and fixing: sununmy o f experimentation tests SCI
SC2
SC3 (Araldtte BY158,
(Eurostac 2101, crushed local stone, aerosil)
(Eurostac 2501, crushed local stone, aerosll)
9th-10th cycle: (2/3 samples) detadunmt due to adhesive fracture 15th cycle: (1/3 samples.) detachmmt dueto adhesive fracture
20th cycle: adhesive unaffected but rock severely deteriorated
20th cycle: adhesive unaffected but rock severely deteriorated
Adhesive: resisted up to 20th cycle with differing degrees of deterioration with respect to the rock; visual ,appearance fair (similar to rock) Rock: heavy loss due to surface crumbling
Adhesive: resisted up to 20th cycle with diffiamg degrees of deterioration with respect to the rock; visual accearance insufficient (darker and mote resinous with respect to rock) Rock: heavy loss due to surface crumbling
Adhesive: resisted up to 20th cycle with differing degrees of deterkraion with respect to the rock; uneven formation at 2-3 mm within the adhesive, visual a~earance poor (noticeably resinous) Rock: heavy loss due to surface crumbling
Interface: adhesive unaffes~xi External surface: slight brealdng up
Interface: adhesive unaffected External surface: very deteriorated with liRing and coarse flaking
Interface: adhesive unaffected External surface: very deteriorated with li~ing and coarse flaking
Mortar: formation of more frequent transwrsal shrinkage cracks and long cavities in oontact with the rock Adhesion: low with increased daachmmt Rock: in good concfition
Mortar: no change after crystallisation Adhesion: good on both parts of the rock Rock: in good condition
Mortar: no change after crystallisation (like C2) (some dosed pores 0.2-0.7 nun) Adhesion: good on both parts of the rock Rock: formation of occasional long fractures and frequent miarofractures
RESISTANCE TO DIREC~ TRACTION
LOW (ca. 0.154).20 kg/cm2) fracture in adhesive area
HIGH (ca. 2.1-2.6 kg/cm2) always with rock fracture
HIGH (ca. 2.1-2.6 kg/cm2) always with rock fracture
ABSORPTION OF WATER BY CAPILLARY ACTION
Rock/adhesive/rock: similar to untreated rock
RF~ISTANCE TO SALT
e-mortar/rock)
~maOes rock/adhesive-mortar/reck)
RESISTANCE TO SALT CRYSTALL BY FORCED CAPILLARY ACTION (SANDWICH SAMPLES)
INTERFACE MORTAR/ROCK (AFTER AGEING)
Rock/adhesive/rock: formation of "step" with probable halting of ascent
aerosH)
(likeC2)
Rock/adhesive/rock: formation of "step" with probable halting of ascent
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
23
tab. 3b - systems of adhesive-mortar for re-adhesion and fixing:summary of experimentation tests SC4
(Uhu-Plus not mixed with a n y t h i n g , else) .... RESISTANCE TO SALT CRYSTALL BY TOT. IMM.
(re~,~tr~m~la~
rock/adl~slve-morlarlrock)
0rr~t~t~r samples
rock/adl~eslve-mortar/rock)
6th cycle: detadmaent due to adhesive fracture
2nd cycle: (1/3 samples) detachment due to adhesive fracture 5th cycle: (2/3 samples) detadmaent due to adhesive fracture
Adhesive: resisted up to 20th cycle with differing degrees of deterioration with respect to the rock; uneven formation at 2-3 ram. within the adhesive; v'k~al appearance; poor to insufficient (resinous, but transparent) Rock: heavy loss due to surface crumbling
Adhesive: resisted up to 20th cycle with differing degrees of deterioration with respect to the rock; uneven formation at 2-3 mm within the adhesive; visual am~arance: poor to insufficient (lighter eolour than the rock), but can be coloured Rock: heavy loss due to surface crumbling
Adhesive: bawem the 15th and 20th cycles three pieces of rock became detached with internal fracturing of the adhesive; visual appearance: poor to insufficient (lighter oolour than the rock), but can be ooloured Rock: heavy loss due to surface crumbling
Interface: no change External surface: (1/3 samples) slight breaking up (2/3 samples) heavy deterioration as with adhesive C2
INTERFACE MORTAR/ROCK (AFTER AGEING)
Adhesive: no change alter erystallisation (like C2) (some dosed pores max 3-4 ram) Adhesion: good on [xxh parts of the rock. Rock: formation of extended cracks
RESISTANCE TO DIRECW TRACTION
ABSORPTION OF WATER BY CAPILLARY ACTION
SC6 ( L e d a n TB, c r u s h e d l o c a l stone)
20th cycle: adhesive unaffected and rock severely deteriorated
RESISTANCE TO SALT CRYSTALL. BY FORCED CAPILLARY ACTION
(SAm)WI~ SAMPLES)
SC5 (Lafarge lime, primal, c r u s h e d local, stone)
HIGH (ca. 2.1-2.6 kg/cm2) always with rock fra~are
Rock~adhesive~rock: formation of"step" with probable halting of ascent
Interface: no change External surface: slight breaking up
Adhesive: no change after crystallisation (like C2) (freq. closed pores of 50-700 ~m) Adhesion: good on both parts of the rock. Rock: formation of localised micro~aeks
Interface: (2/3 samples) de~chment External surface: slight breaking up Adhesive: formation of mkro-o'aeks in the binder and in contact with the aggregate Adhesion: from poor to good Rock: in good condition
LOW (ca. 0.15-0.20 kg/cm2) FROM MEDIOCRE TO FAIR (ca. 0.6 kg/cm2) fracture (in 2/3 cases) mainly at ac~esiveJrock face with little fracture at mortar/rock face with adhesive left attached to the very little ~ left attached to thq detached rock (1/3: fracture within rock the adhesive)
Rock~adhesive/rock: similar to untreated rock
Rock~adhesive~rock: similar to untreated rock
3. Notes The study was carried out under the supervision of Prof. R. Alaimo and Prof. G. Biseontin. 4. References - Carbonara G., "I1 Cemento nel Restauro dei Monumenti in Restauro and Cemento in Architectura 2" (Cement in restoring monuments and cement in architecture) Rome, 1984 - I1 Cenacolo s.r.l., Diagnostic project to define the methodologies and products for restoration work on the "Tempio della Concordia" and other monuments in the Valley of the Temples- investigation of the materials and their deterioration, 1988, Rome
24
9th International Congresson Deterioration and Conservation of Stone, Venice 19-24June 2000
Lazzarini L., Lautenzi Tabasso M., "I1 Restauro della pietra" (stone restoration), published by CEDAM, Padua 1981 Normal Recommendations (CNR-ICR, Rome) 1/88, 4/80, 6/81, 7/81, 10/82, 11/85, 12/83, 14/83, 21/85, 26/87, 33/89, 43/89 - Pace B., report by the Commission for the conservation works carried out on the Agrigento temples, published in '~ollettino d'Arte", no. XXVII, third series, dated 10/04/1934 - Patricolo G., "Tempio della Concordia". Report to the Royal Commissioner on Museums and Excavations in Sicily regarding the work carried out on the ancient ruins in Girgenti in the years 1884 and 1885. February 1886: contained in studies and documents relating to Agrigento archaeological sites, Palermo 1887 - Rossi Doria P., Note on conservation treatments for stone artifacts, published in "Sulla conservazione della pietra, Quaderni 2" Rossi Manaresi R., Tutti A., Pore structure and salt crystallization: "salt decay" of Agrigento biolealcarenite and "ease hardening" in sandstone, published in '%a Conservazione dei monumenti nel bacino mediterraneo" (conservation of monuments in the Mediterranean basin), Proceedings of 1st International Symposium, Bail, 1989. - Trinizio G., "Tempio della Coneordia", studies relating to restoration, published by Ed. Flacovio, Palermo 1984. ~-
-
-
25
oo
G R O D E N E R SANDSTONE, A HISTORICAL BUILDING MATERIAL IN SOUTH TYROL/ITALY- THE PROBLEM OF LARGE VARIABILITY OF STONE P R O P E R T I E S FOR MONUMENT CONSERVATION
Christoph Franzen*, Peter Mirwald Institute for Mineralogy and Petrography, University Ibk, Innrain 52, A-6020 Innsbruck
Abstract Gr6den Sandstone is a historical stone materials of regional significance in South Tyrol /Italy. Due to its geological position this permian sandstone is characterised by considerable variation in its properties which creates a variety of damages as well as conservatory problems. In the frame of an Italian-Austrian EU-Interreg program a petrographical-mineralogical study has been started, which concentrated first on determination of basic petrographical, chemical and physical parameters, such as sedimentary fabrics, mineralogy, salt content, pore and hygric properties.
Keywords: Gr6den Sandstone, South Tyrol/Italy, weathering damages, stone properties
1. Introduction South Tyrol is located in a geology characterised by an enormous variety of rock materials. Despite that only a few gained significance as stone materials. The marbles from Laas and Sterzing are the most prominent and widely exported materials of that area. In addition, the "Bozener Quartzporhyr" and the "Brixen Granite" have gained a high reputation as pavement and building materials. Less known but historically of greater importance is the Gr6dener Sandstone used as building stone as well as material for building decoration purposes and stone cutting. It is most common in the Etsch-valley area between Bozen and Meran. It has been mainly used in medieval to baroque times, where transport facilities and economical capacities were mostly very limited. Due to that, Gr6dner Sandstone has been used predominantly for construction of locally important objects such as churches, monasteries, castles, nobleman houses. The Cathedral of Bozen is the most renowned monument built from that sandstone in the 14th century. The conservation of these monuments creates considerable problems. To elucidate possible conservatory concepts a petrographical- mineralogicalstudy on that material has been started within the frame of an EU-Interreg-program between South Tyrol/Italy and North Tyrol/Austria.
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
2. Geological Setting Geologically the GrSdener Sandstone is a permian sediment (= 255 Ma) situated on the top of the mass of Bozener Quarzporhyr complex (fig. 1). The thickness of Gr6dener Sediments reaches about 100 m in the west and grow up to 500 m in the very east. While the lower sequence is mainly dominated by the porphyr detritus, the upper parts reflects also influence of metamorphic sources. The sandstones were sedimented in a semiarid climate and show several fluviatile structures. The layers change between sandstone to siltstone. Beside this vertical diversification there is a considerable facies differentiation in horizontal direction due to a diverse paleogeography. This implies with respect to its possible use as working material considerable local variation between argillaceous, arcoseous and pure quartztic facies are given. This impairs its employment to a certain extent. Even in case of good material quality insufficient layer thickness appears as an additional restricting factor for quarrying. Our search for the historical quarries revealed so far only a limited number of localities, mainly located in the plateau forming the northern rim of the Etsch-valley between Bozen and Meran.
Fig. 1. Distribution of the stone material in South Tyrol/Italy (modified after Brandner 1980).
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
27
3. Petrography, chemical and petrophysical data The sandstone used in historical objects may be described as arcosic arenites or lithic arenites (Pettijohn et al. 1973), characterised by a brownish to yellowish red colour in general which may often be related to its stone properties, e. g. the low quality greyish sandstone in the area of Kaltem or the red brownish high quality used in the area around Meran. Detailed sedimentological description of the sandstone complex are given by (Buggisch 1978, Wopfner 1984). Depending on the amount of clay and arcosic components the grain binding of the sandstones ranges from argilliceousto quartzitic. Its advantage compared to most other stone materials of the region is, however, that the Gr6dener Sandstone is little affected by tectonic cleavage/joints. This and good homogenity made it well apt for stone curing. Chemically, soluble components are essential since they represent the inherent salt content of the material which plays - in conjunction with its hygric properties - an important role under weathering conditions. As shown in table 1 the content of soluble salt components eluted by bidestilled water and analysed by ionchromatography is comparatively low. The most important pore and hygric property data are given in figure 2 and table 2. The data were determined from stone of slightly varying petrography. The range of the data lies within in the range of data of other medium to fine grained sandstones.
Fig.2. The capillary uptake water of Gr6den Sandstone. Data for the well known Baumberger Sandstone, Laaser Marble and Bozener Porphyry are given for reference.
28
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Table 1. Example of soluble ions content (gg/g rock) of Gr6den Sandstone (locality: Naifjoch, Meran). F
,
Cl 4gg/g
K+ 61 gg/g
13gg/g Mg 2+ 28gg/g
NO319gg/g
S042-
917 gg/g
Na + 922gg/g
pH I)
C a 2+
291 gg/g
8.4
1) pH of the elute. Table 2. Gr6den Sandstones show a range its physical and hygrical properties.
inner surface1) m2g "1I inner surface 2) w-Value 3) m2g -1 kgm-2h-0 5 0.9-2.5
1.3 - 3.5
0.9-1.7
Porosity bulk density pure density g/cm 3 Vol.% g/cm: 6-11 2.30-2.57! 2.60-2.76
N2. H20 sorption at 6% r. h. at roomtemperature.
1) BET measurement with 2) Calculated from
3) Capillary water uptake coefficient; w = AW * At~ [kgmZh~
4. Weathering and damage feature Due to the south alpine climate conditions the impact by rain and/or humidity plays a less important role for the material than frost and thaw effects. For pure sandstone surface corrosion processes by grain loosening is often indicated by vanishing of stone cutting features. In particular, sanding off and small dimensional scaling is a frequent damage problem for ornamental and plastic stone. Large sized scaling is restricted to the more argillaceous facies types. Repair works and restoration on Gr6dener Sandstone objects where cement-based mortars have been applicated instead of lime lead - under normal weathering exposure - to salt damage effects in their next vicinity. As indicated by the salt analysis (tab. 1) salt load of the material itself is low and salt damage phenomena thus have to be related to external salt bearing sources. Damage phenomena, due to capillary rise of salt components bearing ground humidity, such as a honeycomb related features, are common. Statically induced cracking of the sandstone is seldom. Features clearly related to biological impact are relatively seldom. To a small extend black coatings can be observed.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
29
5. Conservation aspects.
So far little practical experiences are available. A systematic study with preservatives is planned. The major problem to be envisaged is that the pronounced local variability of stone facies may not allow the development of a general scheme of preservation measures but may require intense case and laboratory studies before treatment. Possibly, a frame concept can be derived from those experiences later. However, direct consequence of this problem is that good quality material is needed for repair work. This can be achieved by geological mapping of all still open quarries.
6. References
Brandner, R. (1980), Tirol-Atlas, Geologische Obersichtskarte von Tirol. Institut fOr Landeskunde, Universit~it Innsbruck, Innsbruck. Buggisch, W. (1978), Die Gr6dener Schichten (Perm, Stidalpen). Sedimentologischeund geochemische Untersuchungen zur Unterscheidung mariner und kontinentaler Sedimente. Geologische Rundschau, 67/1. Pettijohn, F.J., Potter, P.E., and Siever, R. (1973), Sand and Sandstones. Springer, Heidelberg. Wopfner, H. (1984), Permian deposits of the Southern Alps as product of initial alpidic taphrogenesis. Geologische Rundschau, 73/1,259-277.
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31
EVALUATION OF MATERIALS USED IN THE REPLACEMENT OF SCULPTURES IN HISTORICAL MONUMENTS Francois BOUTIN* Cercle des Partenaires du Patrimoine, Champs-sur-Marne, FR Philippe BROMBLET Laboratoire de Recherche des Monuments Historiques, Champs-sur-Marne, FR
Abstract
The objective of the present study is to appreciate the aptitude of various materials to imitate stone for the realisation of a moulding which is to replace the original piece in situ. After having referenced the main defects which appear on the copies, the moulding of a statue representative of the main difficulties encountered on the statuary of monuments was made with each of the materials. A set of tests were carried out in order to examine and characterise the four mortar formulations (pre-formulated or hand made) as well as two resin-based products (polyester resin and resin mortar) in order to establish the connection between defects and implementation. Results indicate that the quality of a moulding greatly depends on product use, particularly in the ease of hydraulic mortars. Moreover, the choice of a product must be determined in relationship with the environment in which the copy is to be installed, and more specifically taking into account the properties of the stone, the severity of the climate and the level of pollution. Key words: Copy, Compatibility, Durability, Mortars, Moulding, Resin
1. Introduction
As part of the restoration of the western facade of the cathedrals of Reims and Rouen, numerous high-quality sculptures or elements of sculpture were removed, cleaned, treated and then replaced by copies moulded using micro-concrete. However, the examination of copies which had previously been installed on these buildings and a number of other copies located in such places as the Tuileries Gardens in Paris or a motorway rest area in the South of France (Lozay- a Romane itinerary in Saintonge thematic area) shows the main problems encountered when c a n i n g out moulding tests (Boutin and Bromblet, 1999) : difference in the aspect of the stone and its natural patina - the heterogeneity in the aspect of the copy (colour, texture) the apparent blowing - superficial cracking (micro-cracking) - the difficulty to obtain a satisfactory aspect at the seams and when touching-up - the negative reaction to ageing (modification of the hue, cracking, erosion, powdering...). These defects were observed with various materials, both in the case of hydraulic bonding-agent industrial mortars in the form of ready-mix and in the case of resin-based materials and of hand -made mortars mixed on site by the moulders.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
It is with the intention of understanding the origin of these defects and to evaluate the various products used that a comparative study was undertaken in collaboration with moulding workshops and laboratories specialised in the characterisation of mortar and concrete. Product implementation, as well as the mechanical and petrophysical properties, and the durability of each material was therefore tested
2. Description of the tested products
Four out of the six tested products are mortars using a hydraulic bonding agent as a base. Ready-mix mortars are materials that are industrially designed, packaged in bags and ready to be mixed. Hand-made mortars designate the materials that are formulated on site. Last of all, pre-formulated mortars are materials that are specifically designed on request in a laboratory and hence with a distinct formulation. The other two products are a polyester resin including 50% marble powder and a 'mortar-resin' (an acrylic resin and a semihydrate-alpha plaster) also including a mineral load. The main characteristics of the mentioned products are shown in the following table. Table 1" Description Of the 6 tested products Products Ready-mix Ready-nlix' 'Hand-trmde i:~e-' mortar mortar with mortar formulated fibre mortar MPE
MPEF
MA
Polyester Resin mortar resin
MP
RP
MR
silica nature of the aggregates limestone and limestone limestone limestone marble and silica and silica powder silica and silica CPA-CEM I CPA-CEMI CPJ-CEM II CPA-CEM I Synolite acrylicresin cement and filler polyester and plaster resin Silica gel, retarder additives supersupersupersilica in plasticiser and plasticiser, plasticiser, suspension colour additives defoamer defoamer colour and fibres additives / / 0.5 0.5 0.9 0.6 water-cement ratio density (g/cm3) 2.1 2.1 1.8 2.0 1.3 1.8 compressive hardness 45.0 45.0 23.4 46.5 / 25-30 (MPa) . . . . i
i
i
i
i
Ill
I
I
II
I
Comparatively to these six products used for the realisation of a moulding, two stones were tested. (tab.2) 9 Vernon chalk and Courville limestone, which are construction and restoration stones used in Reims and Rouen cathedrals. Table 2 Description of the two referenced stones Stone " Vernon chaik PV
description density(g/cm3) compressive hardness (MPa)
fine chalk, whitish colour.
i
Ill
2.0 47.0 Ill
I
I
I
Ill
PC grey micritique limestone containing some fossil and shell fragments 2.2 51.1 I
I
.I
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
33
3. Description of the experimental protocol Three sets of tests were undertaken :for all 6 products : - a test to determine the aptitude of the product for the realisation of the moulding. - a series of tests to characterise the mechanical and petrophysical properties of the materials and to ascertain an adequate compatibility between the mortar used for the copy and the stone of the monument where it is to be installed; - a frost cycle resistance test and a climatic ageing-room test to assess the durability of the replacement materials.
3.1. Implementation test The products' aptitude for the realisation of a moulding was determined by the implementation of a moulded copy of a statue presenting complex shapes. The statue "L'enfant /l la coquille (Child with shell)" (fig. 2) was chosen as the 'test' sculpture. Sculpted into Estaillades stone (dose-grained homogeneous limestone) and 80 em high, this statue is representative of the main difficulties which can be encountered during the realisation of the moulding of a sculpture from the statuary of a monument. It shows difficulties such as the presence of feather-edge, of back feather and the tortuous shapes which require a very careful implementation of the product. The taking of the print on the original is carried out using a thixotropic mix of two silicones. The moulding of the test piece is carried out according to traditional moulding techniques, following the principles for the execution of piece moulding, i.e. a reusable plaster mould made with a number of parts (Baudry and Bozo, 1978). The cover is in plaster. Small plaster covers provide the means to maintain the silicone inside the cover and make the removal operation from the mould easier. Vents, set in the areas where air is the most likely to be trapped, make its evacuation from the mould easier when it is being filled and they also provide the means to control the access of the product in the whole volume of the mould. This mould is to realise the six copies with each of the products. 9 Hydraulic mortars are poured in the mould. The mould is filled with the product using gravity for its positioning. It is possible to use a dip tube to limit the height from which the mortar will flow. The material is always vibrated (manually or with a vibrating needle) in order to facilitate the access of the product in the mould and to provoke the suppression of its air included. 9 Resin-based products are stratified. The stratification technique consists in the application of a "gel-coat" on the different parts of the mould and therefore require to work on an open mould. The applications are carried out in various successive coats (until a 5 to 6 mm thickness is reached), the last applications being rigidified through the use of fibre. Once the "gel-coat" has been applied, the mould is shut and "blocked" (Fibre bands impregnated with resin are applied at the seams in order to join the different parts of the mould together), then filled. The vents must therefore be blocked for the realisation of two resin-based mouldings, realised using the stratification technique. Alter the realisation of the six mouldings of the test statue, the implementation defects were noted (tab. 3).
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.2. Moulding products and stone compatibility Only the four hydraulic material formulations have been characterised. The main parameters controlled to verify compatibility with the stone are the hydric properties (water accessible porosity, capillary), the dilation coefficients (thermal and water-related) and the mechanical properties (compressive strength, dynamic modulus of elasticity). 3.3. Durability test of the molding products A set of two tests and trials the purpose of which was to assess the durability was carried out for each of the products. r Frost resistance, measured only on hydraulic products, according to the P 18-425 norm. r Ageing test in climatic room This test is carried out over a period of 600 hours that represent 18 double cycles as represented in fig. 1. Minimal temperature reached was -25~ and maximum temperature +60~ The temperature increase is obtained through heating and a onehour raining period is included in the temperature-decrease phase of every other cycle.
6h / 60~
6h / 60~
211
~_~h
611 / -25~
/ 5~
2h
611 / -25~ 2 e y d e s = 35 h
Figure
1 " ageing cycles of the cfimatic room
4. Results 4.1. Implementation defects
Table 3 "implementation an d main defects observed, on the c o p i e s 0fthe statue Polyester Resin Products Ready-mix Ready-mix HandPr162 resin mortar mortar mortar made formulated with fibre mortar mortar RIP MR MPE MPEF MA MP cleaning, 'cleaning cleaning cleaning~ cleaning " cleaningsilicone preparation and and brushing and and and brushing brushing brushing humidification brushing brushing and wax o = ap~p_~cation ' ~ n g .................................................... cemeni-~xer..... -t~yhand.........~ment .......... ~men( paddle paddle mixer mixer mixer mixer ............................................................................................................................................................................................................ ~ filling up poured, with poured in poured in poured in stratifistratifi. - .................................................................................. d~p_..~
vibration blowings" average ~ repartition bleeding colour variation at the vent and at the seams presence of cracks lack of product i
Key
9~
........ ~ _ m o ~ d _ . _ ~ e m o ~ d _
manually by oscillation 1 nun + d ++ + +
a b s e n c e 9- p u n c t u a l
....~ _ m o ~ d
..........~_tio.n . . . . .
~on._
vibrating needle 2'ram ++
vibrating needle 'lmm ++
vibrating needle l'io 2 m m ' ++ ~ +++
/
/
~' ~
i to2 mm -
+ +
++ +
+
n.a. ~
n.a. -
~ ~
~ +
~ ~
+ +
i 9+ a f e w z o n e s
i
9+ + w i d e z o n e s
i
9+ + + l a r g e r z o n e s
9n.a. n o n a p p l i c a b l e
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
35
9 All the tested products were combined with integral colour in order to obtain the colour of the original stone statue. The four hydraulic mortars and the resin mortar show a very similar aspect to the stone's. However, the polyester resin is to smooth and too shiny and not granular enough. All the products were also used for specific touch-ups and the repairs undertaken with resin-based products noticeably turned out to be almost invisible, whereas repairs carried out after removal from the mould in the case of hydraulic mortars all showed an aspect which was very different from that of the same material previously poured into the mould. 9 Among all the tested products, mortars are the most likely to have a surface presenting blowings. Figures 4 and 5 display zones in the test statue where the blowing of the copies is very important. The blowing is mainly present in the zones where the air remains trapped in the mould, i.e. at the folds or in the feather edges. Although many vents were located in those places, and despite all the care taken during the realisation of the moulding, numerous bubbles clung to the surface of the silicone. A high control of the product poured, with the use of a dip tube for example, allows to limit the blowing surface (results on the MPE moulding, in comparison with MPEF moulding). A large number of blowings on the surface will entail the realisation of touch-up operations which result in problems due to different eolours and durability. 9 The presence of bleeding zones is to be attributed either to a lack of fines in the product or to excess water (hand-made mortar) (Geoffray, 1991). 9 Colour variations are located at the vents and the seams of the mould. They are provoked by the water movements. Actually, needle vibration of the product in the mould provokes a water migration to the vents and the seams of the mould. In those places, the mortar is hydrated differently (variation in the Water/Cement ratio), which has an incidence on the eolour of the material (fig. 3 and 4). These variations are almost identical for all the mortars. 9 Fine cracks were observed on one of the mouldings realised using stratification. They were created during the manipulation of the two shells of the mould, during assembly, before the pour. Stratification moulding realisation requires a great deal of attention during the fitting of the mould, because the smallest flexion of the mould can provoke ruptures in the stratified coat (which is only 5 to 6 mm thick). 9 Lack of material, observed in two cases, correspond to a part of the mould which is difficult to access (a finger of one of the hands). The absence of that element is due to a problem in the implementation of the material in the case of the gel-coat and a viscosity problem in the case of the MPE mortar.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figure 2" test copy in MPEF
Figure 3: test piece 1 =blowings 92=darker zone (venO
Figure 4: test piece 1= important blowing around vent" 2=colour variation at seam
4.2. Stone compatibility Betides the problems of difference of aspect and colour, the installation of a moulded copy on a building can provoke a degradation of either of the materials should there be considerable differences between the properties of the artificial stone and of the stone of the building. One of the essential parameters to control is the respect of the hydric properties. Figure 5 is a representation of hydric properties of the material, it brings to light the similar behaviours of each material. Thus, MPE and MPEF mortars have hydric properties which are very near to those of PC Courville limestone, but in the case of MP and especially MA mortars, we can note that the capillary coefficient is from twice to 4 times as important as that of the two test stones. This can later provoke a preferential circulation of water inside the moulded element once it is installed on the building, and thus accelerate the deterioration processes (dissolution of the hydrates, 1.00 formation of neoformated MA 0.75 compounds...). For PV Vernon stone, MP 0.50 it is observed that both MP and MA MPEF products have a porosity which is very PC. 9 * MPE 9 PV similar to that of the stone, but a much ~ ' - " 0.00 higher level of capillarity whereas the a 15 20 25 30 other two products (MPEF & MPE) p o r o s i t y (%) show comparable capillarity, but a Figure 5 9hydric properties o f tested products much lower degree of porosity.
•
9 in the same way, the mechanical properties of the mortars are essential factors towards an adequate durability. The hand-made MA mortar, with weak mechanical resistance due to a high mix rate (E/C=0.9) but which also shows greater elasticity, is certainly the material most sensible to mechanical stresses. The calculation of the relative flexibility (compressive strength / elasticity modulus) shows that in spite of different mechanical properties the materials are relatively equivalent in
9th International Congresson Deterioration and Conservation of Stone, Venice 19-24June 2000
37
flexibility (fig. 6). Only the MP mortar is susceptible to bear more important stresses for an equivalent deformation. On the other hand, Courville limestone reacts differently, being more flexible (weaker elasticity modulus) but with a higher compressive strength.
Figure 6 : calculated relative flexibility
Figure 7 : thermal and water-related flexibifity (RILEM VI.3 et 11.7 recommendations)
9 Thermal a n d water-related flexibifity (fig. 7) are important in comparison to the Courville limestone flexibility values, especially in the case of pre-formulated mortar. This will be more sensitive to variations in the climate and can lead to a progressive damaging of the cement paste due to stresses provoked by thermal and water-related flexibility.
4.3. Durability of products 4.3.1. Frost cycle resistance test The good performance of the mortars in terms of durability during the frost/thaw test shows the existence of two categories of materials. The MPEF and MP mortars possess a very good resistance to the fi,ost/thaw cycles (dimensional variations below 200~tm and absence of decrease in the elasticity modulus even after 300 cycles) and can be used in harsh climatic environments. On the other hand, the MPE mortar (heavily damaged after the 11 lth cycle) and the MA mortar (also damaged after the 53rd cycle) show a very limited resistance to the frost/thaw cycle, and their use in rigorous wintry zones is therefore to be avoided. The factors which provide an improved resistance to the frost/thaw cycle seem to be the presence of fibres in the matrix, as well as a more compact matrix with a weaker porosity (Pigeon and Regourd, 1986). The nature of the hydrates is also a determining factor to obtain an adequate durability (Vernet, 1992). The MP mortar which is rich in C-S-H, is more stable when submitted to frost/thaw cycles than MPE mortar, the matrix of which is rich in portlandite content (a hydrate more sensible to dissolving phenomena) as is revealed by observations made with an electronic microscope. 4.3.2. A g e i n g simulation in climatic ageing r o o m The parameters measured to assess the impact of the climatic ageing cycles on the materials are colorimetric measurements and crack measurements. The climatic cycles do not cause ultraviolet ageing, and, as no development of micro-organisms were observed on the test-samples, few colour variations were measured, be it on the moulded products or on the stone test-samples. The global variations of colour AE are included between 0.4 and 1.5 for all the products except the MR mortar resin for which AE = 4.0 (the colour variation limit for the human eye is AE=3). This important change in colour, corresponding to lighter sample surface, is caused by the formation of efflorescence on the surface.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
On the other hand, the measures of cracking (fig. 8) show the existence of two categories of product: those having a weak cracking rate, attributable either to the presence of fibres in the matrix (MPEF) or to a greater flexibility of the material (MA and MR). The other products have a cracking rate 5 40 2.0 to 6 times as important, but the cracks 1.5 are thin (from 0.02 to 0.04 mm/mL) except in the case of some RP ; ~2o 1.0 polyester resin samples on which _~ 0.5 large cracks appeared during the resin ~ 10 polymerisation phase. A more precise [] 0 0.0 [] MPE MPEF MA MP RP MR control of exothermie would have probably avoided the initial outbreak Figure 8 9cracks observed on samples of these cracks. alter the climatic ageing
5. Conclusions The present article gives the results we reached towards a characterisation and an analysis of the durability of various materials used for the realisation of copies of sculptures achieved through moulding, and sums up the most frequently observed defects on moulded copies realised with each product.
The quality of a moulded copy rests on a large number of parameters such as the nature and the properties of the material, but also closely related with the implementation techniques which are used. It is undeniable that hydraulic mortars provide the most faitl~l restoration in terms of stone-like texture and colour, and that, without having to patina the copy. But quality in the implementation of hydraulic mortars is essential. The risk of blowing can be reduced through careful mixing and the limitation of product pour height (for example, through the use of a dip tube which is progressively drawn upwards during the pour), also reducing the risk of segregation. The mould should not be over-wetted because this can also favour the occurrence of pattern cracking. However, we can observe that through a relatively precise formulation of the mortars, it is possible to minimise the risks of defects. In relation with the traditional mortar, the readymix or pre-formulated mortars, whose adjuvantation was the object of a deepened survey, permit to limit defects as opposed to hand-made mortars. The ready-to-mix mortars are also very efficient because their composition is adapted to their implementation while minimising the risk for defects. The hand-made mortar which was formulated for this study is an excellent counter-example : empirically formulated, it was obviously mixed using too much water, thus provoking important visible defects (bleeding) and providing it with properties which are very different to that of industrial mortars. The stratification technique, applied to resin-based products can minimise the risks for defects, particularly the presence of bubbles on the surface of the statue and bleeding. Touch-ups, which bring about colour variation problems and the question of durability, are also less numerous and almost invisible. The choice and the composition of a replacement material must also be made according to the material it is to replace and also to the climatic environment. In order to respect the
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
39
imperatives of compatibility with the type of dense and "dosed" stone which is generally used for the statuary, it is necessary to formulate the product adequately in order to take into account some of the major properties of the initial stone while also guaranteeing adequate durability. The durability trials and tests carried out with the different materials enabled us to bring to light several factors which provide them with adequate features when ageing. A good compactness and the presence of fibre in the material seem to procure an adequate behaviour when faced by climatic aggression (frost, variations of temperature and humidity...) (Regourd, 1982). The first results of the durability tests show that some products (MPEF, MP, RP and MR) react well to ageing. Natural ageing tests have been in progress on two cathedrals (Notre-Dame of Reims and Notre-Dame of Rouen) for more than a year now, and the results will complete those of the other durability tests as soon as they become available. 6. References
Baudry M.T., Bozo D., 1978. La sculpture : methode et vocabulaire. Boutin F. and Bromblet P., 1999. Characterisation of materials used in the replacement of sculptures in historical monuments, in 8th International Conference on Durability of Building Materials and Components, May 30-June 3, 1999, Vancouver (Canada). Geoffray J.M., 1991. D6fauts d'aspect des parements b6ton. Guide technique Laboratoire Central des Ponts et Chauss6es, Paris Regourd M., 1982. La r6sistance du b6ton aux alt6rations physiques et chimiques, in Le b6ton hydraulique- connaissanee et pratique, Presses de I'ENPC, 29, 513-530 Pigeon M. and Regourd M., 1986. The effects of the freeze-thaw cycles on the microstructure of hydratation products, in Durability of Buildings Materials, 4, 1-19 Vemet, G., 1992. Stabilit6 chimique des hydrates - M6canismes de d6fense du b6ton face aux agressions chimiques, in Durabilit6 des b6tons, Presses de rENPC, 5, 129-169 NF P 18-425 Essai de gel sur b6ton durei - Gel dans l'air-d6gd dans reau, Octobre 1994 7. Thanks This study was financed by the Cercle des Partenaires du Patrimoine association thanks to the sponsorship of Lafarge group. This association of sponsor companies ("Caisse des D6p6ts et Consignation", "Calcia-Ciment Fran~;ais", "Delphi", "Lafarge", "Usinor") permits to gather private funds for research on the conservation of the Heritage materials in link with the Laboratoire de Recherche des Monuments Historiques. We thank the moulding (and restoration) workshops J.L. Bouvier, Legrand and M6rindol, the Etudes et Pr6fabrication Industrielle, Jesmonite Limited and the Soci6t6 de D6coration et de Moulage companies as well as the LERM and Lafarge Mortiers laboratories which carried out part of the analyses presented here for their active participation.
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41
WHITE GRANITES USED IN LOMBARD ARCHITECTURE
Roberto Bugini* - Centro CNR "Gino Bozza", p. Leonardo da Vinci 32, Milano, Italy Alessandro Pavese- Dip. Scienze Terra, Milano, Italy Stefano Borroni - Geologist, Castellanza (VA), Italy Luisa Folli - Geologist, Lodi, Italy
Abstract
The so-called "Graniti dei Laghi" are among the stone materials most employed in buildings of Lombardy and Piedmont (North-Western Italy). The outcrops are located in the lower Val d'Ossola near the Lago Maggiore and they belong to different late-ercinians granitic plutons: Mottarone-Baveno, Montorfano, Alzo-Roccapietra. Different lithotypes used for building come from different quarries: pink and white granite from MottaroneBaveno, white granite from Montorfano and white granite from Alzo-Roccapietra. The mineralogical composition is always the same (potash feldspar, quartz, oligoclase, biotite) with very few differences. The use for building begins in 16th century, particularly for column shafts, pilasters, socles, portals, etc. and the stone is still in use. A macroscopic observation allows easily to distinguish the pink granite, but the whites one are always mistaken. The aim of the present study is the distinction among the white granites using simple analytical methods (XRD, XRF, colour measurements). Many samples were collected in the quarries in order to point out the characters of each lithotype: mineralogical composition, chemical composition, surface colour. In particularly is noticeable: an higher content of biotite in Montorfano and Alzo; an higher value of iron oxide in Montorfano and Alzo (> 1,5%); a yellow shade in Baveno. Moreover dark marie xenoliths are diffused only in Montorfano and rust spots coming from oxidation are diffused in Mortorfano and Alzo. The results were tested on different buildings from Milan and Turin where the use of different granite was witnessed by book references. Keywords: building material, stone, granite, quarry. 1. Introduction
Granites were employed as building stones in Northern Italy starting from 16th century. Different kinds of artifacts as ashlars, slabs, column shafts, pilasters, portals, balustrades, stairs, paving stones, etc. were made by granites. The use was facilitated by the good characteristics of the rock and by the transport facilities (i.e. the water way called Naviglio) from the quarry area to the main cities (mainly Milano and Pavia, Lombardy). The quarry area is located northwest from Milano near the lake Maggiore and Val d'Ossola (see map). The most employed is the pink granite from Baveno, but also the white granite is important as building stone; white granite comes from Baveno, Montorfano and Alzo. The three granites are almost equal and distinctive markers useful for macroscopic observation were not found in literature. The aim of the present study is to define distinctive markers among the varieties in order to facilitate the distinction; the markers must be easy to find at macroscopic observation without long and expensive analyses and they must be recognizable also on buildings with minimum sampling.
* Author to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
2. Geology The so-called "Graniti dei Laghi" belong to a granitic batholith intruded in the "StronaCeneri zone" (metamorphic rocks, marie rocks and kinzigites) and composed by different plutons (fig. 1). Three different plutons are noticeable: Mottarone-Baveno, Montorfano, Alzo-Roccapietra; details on datation (about 275 m.y.) and on the mechanism of emplacement are reported in references (Boriani et al. 1992). The Mottarone-Baveno pluton (lake Orta - lake Maggiore) is composend mainly by medium grained, white, granite with quartz, K-feldspar, plagioclase and biotite as main components (GalliteUi 1937). A pink variety (pink is the K-feldspar) occours in the NorthWestern part of the pluton, the main components are the same as white variety. The Montorfano pluton (lower Val d'Ossola) is composed mainly by medium grained, white granite with plagioclase, quartz, K-feldpsar, biotite as main components. The northern part of the pluton is occupied by a green variety composed by albite, chlorite, quartz, sericite (Gallitelli 1938). The Alzo-Roccapietra (lower Val Sesia - lake Orta) pluton is a medium grained, white granite composed by quartz, K-feldspar, plagioclase, biotite (Ccallitelli 1941).
Figure 1 - Geological sketch map of"Graniti dei Laghi" area (Boriani 1974)
3. History Another aim of the study is to determine the exact date of the beginning of the quarry exploitation. The start of the exploitation of Baveno and Montorfano granites is not clearly
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
43
reported, but it is about the first years of 16th century and still continues; Alzo quarry was opened in 1847 (Peverelli 1922) and closed in 1956 (Gazzetta del Popolo 1956, june 21). Granites of Baveno and Montorfano are not known by Giorgio Vasari (Vasari 1568). P. Morigia (Morigia 1603) uses the local name "meiarolo" and Vineenzo Seamozzi (Seamozzi 1615) describes a granite with small black and red spots and white background, called "migliarolo", and a black and white granite without red spots. Authors in 18th and 19th centuries also witness the use of granite mainly in Lombardy (Vagliano 1710, Pini 1779, Amati 1829, Rondelet 1832). An accurate report is made by G. Casalis (Casalis 1839-40) where Alzo granite is not reported. Carlo Amoretti (Amoretti 1814) indicates the increase of the use of "migliarolo" when the cardinal Carlo Borromeo (born 1538) was archibishop of Milan (1565-1584). G. Barzan6 reports a catalogue of the Milan's monuments made by granite and this report is very important because of many buildings were aiterwards destroyed (Barzano 1853). Alzo white granite was first reported by Giovanni Jervis (Jervis 1889); Jervis also remarks the presence of dark xenoliths in Montorfano white granite. The diffusion of pink and white granites as building stones is reported by Authors at the end of 19th century (Salmojraghi 1892, Blangino 1895): Salmojraghi remarks the presence of iron sulphides in Montorfano white granite as a defect. In the XX century the features of granites are reported in handbooks and papers (Anon. 1939, Fagnani 1956, Pied 1964).
4. Sampling and methods of study Different quarries were sampled in order to detect chemical and physical characters of the rocks: Fedolo (Mottarone-Baveno pluton) 2 samples; Donna (Montorfano pluton) 1 sample; Cirla (Montorfano) 2 samples; Alzo (Alzo pluton) 2 samples. Data from the same quarry are very similar and also the samples from Donna and Cirla (Montorfano) are quite similar. Samples were taken from Milan and Turin buildings in order to compare the analytical data with quarry samples; sampling points are reported in chapter 8. Samples were studied by optical microscopy on thin section, X-ray diffraction on powder, X-ray fluores~nee, scanning electron microscopy, eolour measurements, mercury posimetry. 5. Characteristics of white granites 5.1 Colour Baveno granit is easy distinguished from Montorfano and Alzo granites: the first one is yellowish, the others are white. An exact measurement of the eolour according to the CIELab system was impossible in this ease because of the area investigated by the eolorimeter is wider than the feldspar crystals that bear the eolour in the granite. Furthermore this method is not suitable on the stone used in buildings because of the eolour changes caused by the stone decay. 5.2 Mineralogical composition White granites are medium grained plutonie rocks with high biotite content. Quartz, K-feldspar, plagioclase and biotite are the most important minerals determined by optical microscopy in the "Graniti dei Laghi". Quartz: xenomorphie grains (size 4-8 turn), undulose extinction, rare inclusions. K-feldspar: xenomorphie grains (size 4-9 turn), often perthitie, Carlsbad twinning.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
Plagioclase (about 25% anorthite): automorphic grains (size 2-6 mm), regular zoning (more calcic in the core), polysynthetic twinning. Biotite: automorphie lamellae (size 2,5-3,5 mm), pleoehroism from light yellow to redbrown, zircone and apatite as inclusions, sometime transfomed in chlorite. Accessory minerals are: zircone, apatite, epidote, fluorite, titanite, etc. The composition shows small differences among the quarries, but it is impossible to find distinctive markers among these using the optical microscopy; because of a comparison must be based on a great number of thin sections and this is incompatible with the care of the buildings. The presence of iron sulphides mainly in the Montorfano granite and in a lesser extent in Alzo granite, together with the absence of these minerals in Baveno granite, leads to an easily recognizable difference. Rust spots are very diffused on Montorfano granite surface and they are dearly visible also in ancient buildings. This is one marker to distinguish the Montorfano granite: only the freshly cleaned surfaces don't show the spots. Dark, microgranular xenoliths are diffused in the Montorfano granite only. They have some marie composition (biotite, plagioclase) and look as black spots with size ranginng from some millimetres to some decimetres, more compact and resistant to the decay than the surrounding rock. Xenolith is a good marker to distinguish Montorfano granite from Baveno and Alzo granites. X-ray fluorescence detects a higher silica content and a lower iron content in Baveno granite than those of Montorfano and Alzo granites (tab. 1). The values are: Baveno - Silica >75%, Iron <1,5%; Montorfano and Alzo - Silica <75%, Iron > 1,5%. The possible local changes make these data untruthful as markers. X-ray diffraction data show a biotite peak at d-spacing 10.1 A (tab.2-3). The measurement of the mean value of the parameter H,FWHM (height * full width at half maximum) shows a lower value in Baveno granite (assumed as value 1) than in Alzo granite (value 3.4) and Montorfano granite (value 10.2). These data indicate a lower biotite content in Baveno according to the iron value of X-ray fluorescence and are useful as marker to distinguish the granites. Table 1 XRF analyses M0 Donna Mo Cirla .... SiO2...... 73.66 72.23 ' A1203. . . . . 14.23 14.71 Tio2 o.21 0.24 Fe203 2.22 2.31 Mno 0'04 .... 0.04 01'28 'MIjO 0.22 CaO 1.40 1.38 Na20 3'.37 3.42 K20 4179 5. 11 "P205 ~ 0.07 0.07 [ ....Tot~ i ' 100.21 99.79 ~ ,
,,
Alzo 2 Alzo 1 Baveno 1 Baven0 2 73.86 . . . . 73.52 75.05 77.49 14.08 14.5....... 14.09 13.'02 ' 0.17 0'20 0'.09 0.08 1.97 2.35 i.42 1.17 0.04 0.05 .... 0.03 ....0.02 0113 L0.20 0.10 0.08 1.34 1.36 0.76 0.66 3.53 3.60 ~1.02 3.72 4.24 4.31 4.85 4.90 0 . 0 6 ' [ 0 .06 [ 0.06 . l 0.04 99.43 [ 100.15 | 100.'47 i' ~ i 0 1 . 3 6
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Table 2: XRD analyses Montorf. Donna Montoff. d-sPat. ' A .......i..count s ...... d-spac. A 10.1 7500 10.1 6139 2000 613'9
4.26
9000
4.26
Ciria counts 7500 2000
[ Alzo 1 ] [ dlspae. A 10.1 '6.39
10500
26000 ' 3.'34 3.34 ' 31ooo J 3.22 ' 15500 3.22 17500 19000 3.20 23000 3.20 Note: biotite i0.1; albite 6.39- 3.20; quartz 4.26- 3.34; .
.
.
.
.
.
.
.
4.26
!
45
counts 2400 ~ibo0
4200
3.34 15000 .... 6400 3.22 3.20 9500 orthoclase 3.22. ....
Table 3: XRD analyses Alzo 2 ] Baveno 1 [ Baveno 2 d'spac-A counts i d'spac:A . counts ~ d-spac.A counts 10.1 6500 10.1 1000 10.1 600 6.39 1500 6.139 i200 6.39 1300 4.26 11000 " 4.26 4800 4.26"' 3700 3.34 8600 ' 3.34 32000 ..... 3.'34 '13500 6900 3.22 11600 3.22 3.22 11500 13000 8500 3.20 16000 3.20 .... 3.20" Note: biotite 10.1; albite 6.39- 3.20; quartz 4.26- 3.34; orthoclase 3.22. ,
,
,
,
,
5.3 Porosity Measured values are very scattered and this method is not suitable for the detection of a distinction marker. Furthermore the total porosity increases together with the stone decay and any comparison within building stones is untruthful. 5.4 Morphology Samples investigated are very similar and any distinction is impossible. Observation show the great extention of craks in the K-feldspar crystals and quartz crystals. The presence of iron in the rust spots is clearly detected. 6. Distinctive markers The most representative markers for a macroscopic distinction of the white granites are: rust spots (mainly Montorfano); dark xenoliths (Montorfano); yellowish eolour (Baveno). The use of these markers is important to verify the correctness of the book references regarding some Milan and Turin buildings. 7. White granites as building material The catalogue of the white granites use was pointed out on whole Milan buildings with macroscopic examination and microscopic study when the sampling collection was possible. A less complete examination was made on Turin buildings. The direct examination involved also the monuments reported by ancient Authors. It is very difficult to establish an exact datation of the buildings because of the restoration carried out during 19th century and after the World War 2; restorations often involved the reconstruction of whole parts of the
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
buildings; this is a source of mistakes when we try to understand the development of the use of the stone during the centuries. The catalogue of buildings is presented according to the date of construction and contains the indication of the granite used. The most important use of the granite is for column shafts according to the great resistence of this stone. We have no evidence of the granite use in roman and medioeval buildings: shafts, lintels and other structural elements were made by the so-called Serizzo (a gneiss coming from outcrops in Val d'Ossola) or by the so-called Ghiandone (a granodiorite coming from Valtellina and present in quaternary glacial deposits in Brianza, North of Milan). The most important use reported for Alzo white granite is S.Gaudenzio church in Novara (48 shafts of the dome, architect Alessandro Antonelli, 1858-64), but the approached examination of the monument was impossible. 7.1
Milan
buildings
Lazzaretto (1488-1513, destroyed 1880): some column shat~ from the portico remain in place (2 pink granite, 2 white granite), some shafts of white granite were transferred in Bagatti-Valsecchi house (1882), they show rust spots and dark xenoliths. - San Pietro in Gessate monastery (1509, partially destroyed 1943, rebuilt 1956): 38 column shafts in the cloister (3 pink granite, 35 white granite); only the shafts of North and West sides seem to be original and show rust spots and dark xenoliths. - Trivulzio chapel (1512-1500): four parastades, two pieces each, always with rust spots and dark xenoliths. - S.Sebastiano church (1577-1617): the curvilinear base of the walls is made by white granite ashlars with rust spots and dark xenoliths. - S. Angelo church (circa 1605): four column shafts for the facade, after 1989 restoration no rust spots are visible, but only a great numebr of dark xenoliths. - Ospedale Maggiore great court (1621-1635, partially destroyed 1943, rebuilt 19461951): 78 column shafts in the portico and 78 in the loggia, pink granite for the shafts and white granite for the bases; after restoration (1990-1993) only dark xenoliths are visible in the white granite. - S.Giuseppe church (1607-1630): the portal is made by white granite, rust spots and dark xenoliths are clearly visible. - S.Vittore monastery (1553-1587, partially destroyed 1943, rebuilt 1953): two cloisters with loggia with 36 column shafts each, mainly white granite always with rust spots and dark xenoliths (until 20 cm in diametre). - S.Maurizio monastery (1687): squared cloister - 12 column shafts made by pink and white granite, the last one presents rust spots and dark xenoliths. - S.Ambrogio monastery (Ionic cloister 1497-1513, Doric cloister 1620-1630, reconstruction first half XX century): 44 column shafts in each cloister, mainly white granite with rust spots and dark xenoliths. - Scuole Arcimbolde court (1664-1684): twin column sha~s for the portico and the loggia, all made by white granite always with rust spots and dark xenoliths. - Ospedale Maggiore Cemetery (called Foppone) (1725): lobed court with a portico, 80 column shat~s made by pink granite, base made by white granite. Rust spots and dark xenoliths are visible on white granite. - Caserma dei Veliti (1807-1843): 8 column shafts on the fagade made by white granite with dark xenoliths. -
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
47
- Porta Garibaldi (1826): 4 column shafts and 8 pilasters made by white granite with dark xenoliths. The white granite is used in other buildings, but his use is very restricted. Historic notes from Bascap6 and Mezzanotte (Bascape 1948). 7.2 Turin buildings
- S.Francesco di Sales church (1846-50, faCade 1870): 6 column shafts and bases made by white granite. Rust spots and dark xenoliths are visible on the bases. - Palazzo Carignano, East faCade (1864-1871): many architectural elements and decorative dements were made by white granite (Jervis 1889). Some have rust spots and dark xenoliths, some are perfectly white. - Mole Antonelliana (1863-1897): pronao with column base made by white granite, no evidence of rust spots or dark xenoliths. - Israelitic temple (1880-1884): 12 twisted columns of different size made by white granite; no spots or xenoliths are visible, the colour is yellowish. G. Jervis (Jervis 1889) indicates Baveno as the extraction quarry, the macroscopic markers confirm this provenance. 7.3 R o m e building
- S.Paolo fuori le Mura church (1825-1840): 80 column shafts of the naves (Jervis 1889, Salmojraghi 1892), white granite with dark xenoliths. 8. Use of markers to distinguish different granites on buildings.
Sample coming from buildings in the catalogue were studied by X-ray diffraction method in order to verify the precision of the markers used for macroscopic distinction among the white granites. Milan buildings sampled are: S.Ambrogio monastery cloister (column shaft), Caserma dei Veliti (column shaft), Porta Garibaldi (column shaft). Turin building sampled is: Palazzo Carignano (column shaft with rust spots from the East facade). The X-ray diffraction pattern shows always a peak of biotite (d-spacing 10.1 A); the measurement of the mean value of the parameter H,FWHM (assuming value 1 for Baveno) is:
S.Ambrogio - 11.2 ; Veliti- 9.2 ; Garibaldi- 8.3 ; Carignano - 10.8 The parameter H,FWHM measured in quarry samples from Montoffano pluton is about 10.2. The peculiarity of the macroscopic markers (rust spots and balck xenoliths) is confirmed by X-ray diffraction patterns. 9. References Amati C., 1829. Delrarchitettura di Marco Vitruvio Pollione libri dieci. Milano Amoretti C., 1814. Viaggio ai Tre laghi, Maggiore, di Lugano e di Como, e ne' monti che li circondano. Milano. Anonymous, 1939. I marmi italiani. Roma Barzano G., 1853. I1 granito di Baveno. Milano. Bascap6 G.C., Mezzanotte P., 1948. Milano nell'arte e nella storia. Milano Blangino S., 1895. Principali cave di pietre da lavoro dell'alta Italia. Torino.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Boriani A., Sacchi R., 1974. The Insubric and other tectonic lines in the Southern Alps. Memorie Soc. Geol. It., 13/1,327-337. Boriani A., Caironi V., Giobbi E., Vannucci R., 1992. The Permian intrusive rocks of Serie dei Laghi. Acta vulcanologica, 2, 73-86. Casalis G., 1839-40. Dizionario Geografico Storico Statistico Commerciale degli stati di S.M il Re di Sardegna. Torino. Fagnani G., 1956. Giacimenti di rocce e minerali utili tra il Lago Maggiore e il Lago di Garda. Natura, 48, 3-55. Gallitelli P., 1937. Ricerche petrografiche sul granito di Baveno. Memorie Soc. Tosc. So. Nat., 46, 150-226. Gallitelli P., 1938. Ricerche petrografiche sul Montorfano (lago Maggiore). Memorie R. Ace. So. Lett. Arti Modena, 3, 1-92. Gallitelli P., 1941. Ricerche geopetrochimiche sul massiccio eruttivo compreso fra la bassa Val Sesia ed il lago d'Orta. Memorie R. Ace. So. Lett. Arti Modena, 5, 5, 220-316. Jervis G., 1889. I tesori sotterranei dell'Italia. Torino. Morigia P., 1603. Historia del Lago Maggiore. Milano. Peverelli G., 1922. Alzo e le sue cave di granito. Torino. Pieri M., 1964. I marmi d'Italia: graniti e pietre omamentali. Milano. Pini E., 1779. M6moire sur des nouvelles cristallizations de Feldspath et autres singularit6s dans les granites des environs de Baveno. Milano. Rondelet J., 1832. Trattato teorico e pratico dell'arte di edificare. Mantova (trad. it.). Salmoiraghi F., 1892. Materiali naturali da costruzione. Milano. Scamozzi V., 1615. L'idea della architettura universale. Venezia. Vagliano G.G., 1710. Le rive del Verbano. Milano. Vasari G., 1568. Levite de' pifi eccelenti pittori, scultori e arehitettori. Firenze.
49
A RESEARCH INTO INTRINSIC PARAMETERS MATERIAL DURABILITY OF HIGHLY POROUS BUILDING STONES
TO
THE
tCalia A., Mecehi A.M., Quarta G. C.N.R.-Is.C.O.M. (Istituto Conservazione Opere Monumentali), Lecce - Italy.
Abstract
The present work represents the first stage of a study of the main characteristics that influence the changes in highly porous stone materials and of the parameters that most clearly quantify this degradation. For this purpose we have compared two types of similar calcarenite material, used in the Apulian region and called "carpari", which in practice present different states of conservation. The laboratory study was carried out by means of examination of their characteristics before and after artificial ageing. Observations by thin section, XRD analyses, porosimetric measurements, permeability and evaporation tests, absorption by capillarity and immersion tests, measures of ultrasonic wave velocity were carried out on samples from quarries providing each type. The same samples were then exposed to artificial ageing with sodium sulphate, which effectively produced deterioration comparable with that "in situ", and then they underwent the same measurements that were carried out before ageing. On examination of the results obtained, it would seem that the porosimetrie analysis and the petrographic analysis on thin section are those which best provide useful dements in understanding the diverse reaction of materials to this type of weathering. The most significant parameter for the measurement of the deterioration produced was weight loss, while the other properties and characteristics measured have not displayed marked variation, probably because of the superficial location of the degradation.
Keywords: highly porous stones, artificial ageing, parameters of deterioration, durability
1. Introduction
"Carparo" is a highly porous calcarenite cropping up mainly in Salento (Apulia) with characteristics similar to other materials used largely in the historic buildings in the south of Italy. It covers a range of types of different conservation states: two of these, known in the trade as Casalabate carparo (C.c.) and Gallipoli carparo (G.e.), come under consideration here. Previous studies on such materials pointed out the differences from the mineralogicalpetrographical and physical point of view (Cal6 G. et al., 1985; Calia A. et al., 1995; Mecehi A. et al., 1998). In the present work, we have centered the attention around their durability, measuring some parameters which could explain the diverse resistance to the processes of artificial ageing and lead to a measure of the deterioration. This study is a first step towards individuation of the parameters for the evaluation of the durability of highly 1Authorto whomcorrespondenceshouldbe addressed
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
porous materials. The further development of the work intends to submit these materials to other different processes of artificial ageing whose effects could be various and measurable with different parameters from those we have individuated.
2. Experimental
Two blocks of quarry carparo, from "Casa di mosto", near Casalabate (Lecce) and that of"Mater Gratiae" near Gallipoli, were used. The two varieties of materials were defined by means of." - thin section observation by optical microscopy; - powder XRD analyses (Philips PW 1710, 40 kV, 20 mA); - porosimetric analyses by mercury porosimetry (Carlo Erba Porosimeter 4000); - measurements of weight density (~/~) by helium pycnometer (Ruska Instrument), measurements of apparent specific gravity (~/b) by mercury pycnometer (Chandler Engineering) and calculus of total porosity as Pt = (]tw-~b)/]t w; - measurements of ultrasonic waves velocity carried out in transparency along the three orthogonal axes (Doe. Normal 22/86, 1987). Samples of different dimensions were taken from each block. The number of samples, their dimension and tests carried out on them are listed as follows: a) 10 samples of 5x5xl cm for water vapour permeability test; b) 10 samples of 5x5x2 cm for water absorption by capillarity test; c) 10 samples of 5x5x5 cm for immersion and evaporation tests; d) 10 samples of 5x5x5 cm for measurements of ultrasonic waves velocity. After the above tests, the samples underwent to the artificial ageing, with aim of reproducing the mechanical stress occurring in the presence of sodium sulphate. This ageing consisted of 6 cycles composed as follows: 1 hour of immersion in Na2SO4 saturated liquid; 15 minutes of draining in a laboratory environment; 22 hours 45 min. of drying at T = 20~ and R.H.= 70%. The aged samples were washed in running tap water and then in deionized water, until the water conductivity reached the same value as that obtained by washing the samples before the ageing cycles (25-35 ITS). After washing, the samples were dried to a constant weight and the weight loss after ageing was calculated. The a), b), c) and d) tests were then repeated on them. The porosity characteristics were also measured again on the 5x5xl cm samples.
3. Results and discussion 3.1. Petrographical and chemical-mineralogical characteristics
On the basis of the petrographical information evidenced by means of observation on thin sections, both the materials are classifiable as grainstones (Dunham R.J., 1962). They are made up of calcareous fossil shells, free of micrite and cemented by microcrystalline calcite of chemical precipitation. Lithoclastic components, made up of calcareous rock fragments and of calcarenites rich in quartz can sometimes be seen in the G.c. The secondary components are detrital fragments of silicate minerals mainly made up of quartz, feldspars, chert and, lastly, ferrous oxides and shapeless aggregates of a ferrous nature. Impregnating ferrous substances are probably responsible for the reddish colour of the
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51
bioclastic granules, from which the materials take their yellowish eolour which is more or less observable macroscopieally. The two materials differ in their percentage of secondary components, granulometry of grains, dimensions of the pores and characteristics of cement. The G.e. evidences a scarce presence of secondary components, whereas C.c. contains about 20% of these. Moreover, the G.c. has no good sorting; the dimensions of the elasts range from about 200 ix to 2-3 mm., while those of the secondary components (essentially quartz) are not more than 10 It. The C.c. is, however, remarkably uniform in its granulometry as far as regards the bioelastic and silicate components, with average dimensions of the granules ranging from about 200-400 microns. The degree of compaction of the constituent grains is very low in both materials, with contacts between the granules generally punctiform. The cement is made up of chemical precipitation calcite and is present only in small quantities, especially in the C.c., where it is found essentially on the border of the granules, with a mierosparitic texture (crystals of <10 It). A cement with crystals of more developed texture is sometimes to be seen in certain points, as well as inside the cavities of the microfossils. In the G.e. the cement is also present on the sides of the granules, and mostly shows a sparitic texture (> 10 It). The porosity is great in both materials, and is represented by holes which are intra- and intergranular, of an irregular shape and rather large, generally around 500-600 It in the G.c., 200-400 It in the C.c.. The percentage of carbonates in the two materials was determined by means of calcimetry (Doe. Normal 32/89, 1991). The C.c. contains 78% calcium carbonate, with an insoluble fraction of 22%, while that of G.c. is made up of 98% calcium carbonate and an insoluble residue of 2%. The mineralogical composition was determined by powder XRD. The diffractometric analyses give calcite as the main mineral component. Those Table 1. Components of the insoluble residue on the insoluble fraction, obtained qz(%) I kf+ pl (%)i C.m. + gh. (%) after acid attack on the carbonate C.c. III 5 .... 6 G.c. I I component, showed the presence of qz = quartz; kf= kfeldspars; pl = plagiociases; secondary minerals like quartz, c..m.= clay minerals; gh = goethite feldspars and goethite in both the stones, as previously seen by thin section. It was also found that there are clay minerals. These were studied by following treatment procedures as laid down by Doe. Normal 34/91, 1994. The percentage of the component minerals of the insoluble residue is shown in the table 1. As can be seen from this, the G.c. contains a very low clay amount as kaolinite, illite and vermiculite. The C.c. contains greater quantities of clay minerals. They are not clearly distinguishable because they have very not defined peaks, denoting a low degree of crystallinity, kaolinite, illite and mixed strata of chlorite-vermiculite type have been recognized. Of the minerals individuated, vermiculite and chlorite-vermiculite have an expandable lattice and are therefore subject to swelling in the presence of water. .
.
.
.
3.2. Weight variations In the table 2 we can see the average weight losses after ageing, measured on samples of different dimensions. The 5x5x5, 5x5x2 and 5x5xl samples of the G.c. appear to have stood up well, with weight losses respectively of 0,73%, 1,6% and 4%. The initial
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
morphology of the 5xSxl samples remained unaltered for some of them, without evident loss of material, while others show rounded edges following the detachment of granules. All the C.c. samples showed notable damage to the surfaces and to the jutting edges, due to Table.2 Weight loss in samples. disgregation and exfoliation of the material, with C.c. G.c. a reduction in thickness of between 1 and 2 mm. Samples av. val st.dev, av. vai st. dev. Those measuring 5x5xl cm in particular 5x5xl 8,60 4.i2 1,36 2.23 underwent the most dramatic changes due to 5x5x2 7',77 3 1 7 1,20 0,58 ageing and 3 of them were lost after 5 cycles 5x5x5 14,4'1 2.4 1,34 0,47 because of transversal fractures. During the washing stages following ageing there was a further loss of the constituent granules because of a superficial decohesion. The weight losses measured on the samples of 5x5x5, 5x5x2 and 5xSxl em were, respectively, of 6,7%, 9,3% and 20,2%. .
.
.
.
.
3.3. Density and porosity The values of the weight density are, for all the samples, around that of calcite (2,72 g/cm3). Table 3 shows the values of the bulk density (Tb), open integral porosity (P), total porosity (Pt) for C.e. and G.e. samples, before and after ageing. Table 3.
b.a. samples y~ Pt% 1,57 4 2 ,
2 3 4 5 av. Val.
~
characteristics of G.c. and C.c. before and after a
1,56 1,55 1,54 1,57 1,56
43 42 43 43 43
,i
,i
G.c. i
i
C.c. ,i
i a.
P~ i5
7b 1,56 1,6
16 i4 1,53 18 1,55 14 ,1,58 15 1,56
i
'b.
a.
,,,i
a.a.
i
a.
Pt~
43
41 44 43 42 43
P/o
rb
14 16 16 13 14
1,75 1,74 1,73 1,7 . 1,72
15
1,73
et%
P,~
36 ' 25 36 27 36 23 38 25 37. 26
37
rb
P'% P~
1,75
],74 1,73 1,74 1,74
25 i,74~
,
'36 36 37' 36 36
21' 30 26 32 29
36
28
,
As can be seen, the P values are lower than the Pt ones. This registered gap can be attributed mainly to the presence of macro-pores (>7513) which are observable both macroseopically and on thin sections, but not measurable by means of mercury porosimetry; this discrepancy is more marked in the G.e. From the difference between P and Pt values the percentage of pores with a radius greater than 7513 Fig.1. Pore size distribution: C.c. vs. G.e has been deduced. Each
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53
class of pores obtained by means of mercury porosimetry has been calculated again, related to the Pt value. In this way we can compare the two materials and each of them before and after ageing, considering also the contribution of the macro-pores. As will be seen in the Fig.2. Pore size distribution in G.c. before and after ageing next paragraph 3.6, this consideration is more valid for the G.c than for the C.c.. For this latter if we consider the water absorption on a long time, we can probably suppose the presence of pores under the minimum size measurable by mercury porosimetry. However this approximation is still acceptable in the light of the microscopic observations which reveal a prevailing presence of bigger than micro-pores. In fig. 1 we see the average porosimetric distributions relative to the two nonaged materials, while in fig.2 and 3 those of the same materials before and after ageing. They are expressed as percentages of the total volume of the samples. From the observation of fig. 1 we can see that for the G.c. more than 60% of the Pt is represented by pores with a radius greater than 75 IX and by 20-25% of pores with a radius between 0.01 and 0.5 IX, while lower percentages make up the other classes. The C.c. shows a very different distribution: the pores with a radius over 75 IX are about 30%, like those falling in the range between 10 and 40 IX, while the other classes of pores are all represented in small percentages. The diverse distribution existing between the two materials, with a clear predominance of large pores in the G.c., could be an important factor influencing Fig. 3. Pore size distribution in C.c. before and after ageing their behaviour regarding the deterioration caused by soluble salts. After ageing the porosimetric distribution in the G.c. roughly resembles that of the non-aged material both in the trend and in the percentages fractions. Before and after ageing the C.c. shows variations, though not marked ones: a reduction in the pores with a radius between 0.1 and 5 Ix and an increase in those between 5 and 40 Ix.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.4 Ultrasonic wave velocity The average values of the ultrasonic wave velocities, before and aider ageing, are respectively of 3457 rn/s (st. dev. = 175) and 3319 m/s (st. dev. = 132) in the G.e., while in the C.c. they are 3649 m/s (st. dev. = 117) and 3369 m/s (st. dev. = 74). The velocity value for each sample has been obtained as average of three measures performed on the three orthogonal directions. More marked differences before and after ageing are in the C.e. than in G.e., reflecting the stronger damage induced on it by the ageing. The velocity values for the two non-aged materials are different from those already obtained in a previous study (Calia A. et al., 1999). That eould be attributed to the different dimensions of the samples.
3.5. Water absorption by capillarity The test was carried out on 10 samples measuring 5x5x2 cm for each lithotype (Doe. Normal 11/85, 1986). The absorption in very short periods was also calculated (30 seconds and 5 minutes) since these, although with a notable margin of error, can help us to calculate the first inflection point of the absorption curves. If we compare the curves shown in rigA, we can observe that both materials before ageing absorb large quantities of water. The G.e. absorbs about 20% more water than that of C.c., because of its greater porosity, for both materials the inflection point in the initial part of the absorption curve is reached between 30 seconds and 5 minutes. The asymptote value of absorption (Moo), evaluated in compliance with Doc. Normal 11/85, is reached after 6 days for both the materials and is equal to 619 mg/cm 2 for the G.c. and 475 mg,/cm2 for the C.c.. The G.c. absorbs 35% of water at 30 seconds .... increasing to 92% in the time (sec-1/2) first 5 minutes. The standard deviation is of Fig.4 Water absorption by capillarity 30% on the first measurements but it declines to 3% in the second measurements and remains roughly unvaried until the end of the triM. The average coefficient of capillary absorption (C.A.) is equal to 41 mg/cm 2 s '~ The C.c. already absorbs 82% of water at 30 seconds increasing to about 90% in the first 5 minutes. The standard deviation is of 13% on the first measurement; it declines to 3% on the second measurement and remains more or less unvaried until the end of the triM. The average coefficient of capillary absorption (C.A.) is equal to 78 mg/em2 s "~. After ageing the samples of both materials absorb a slightly smaller amount of water: Moo for G.c. is 581 mg/cm2 while that of C.e. is 430 mg/em2. This reduction seems mainly correlatable with the weight losses occurring in the samples due to weathering and therefore with the consequent loss of absorbing volume. The maximum quantities of water absorbed,
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
55
related to the weight of samples, are equal to 21 and 20,3% for the aged and non-aged G.c., 14,4% and 14,5% for the C.c.. To carry out a more thorough investigation into the behaviour around water, on the nonaged samples the test was held over a period of time which was notably longer than that required by the Normal document. The asymptote value was considered to have been achieved when the difference between two successive value of the quantity of water absorbed was 0,06%. This occurs in 36 days with a quantity of water absorbed equal to 510 mg/cm2 for the C.c., in 33 days with 636 mg/cm2 for the G.c..
3.6. Water absorption by total immersion The trial was carried out on 10 samples of 5x5x5 cm for each lithotype (Doe. Normal 7/81, 1981). The fig. 5 illustrates the absorption curves before and aider ageing. The maximum value of water absorbed, as advised by the above-mentioned Doe. Normal, is achieved on the 6th day by G.c. and on the 7th by C.c., with an imbibing capacity (I.C.) equal, respectively, to 20,9 and 13,2 %. The st. dev. are rather low, around 3% for all the measurements. The near-totality of water absorbed is reached in both materials in very early stages of the trial. The saturation index S.I. = time (see''~) I.Cv/Pt (I.Cv = I.C. x Yb) is equal to 75% for the Fie. 5. Water absorotion bv total immersion G.c. and 62% for the C.c.. The lower S.I. value in the C.c. is explained by its porosimetric characteristics, and, in particular, by the greater presence of small sized pores. The same samples, alter artificial ageing, show water absorption values coinciding in the C.c. as slightly superior in the G.c.. The measurements on the non-aged samples were prolonged well over the times recommended in the Doe. Normal in this ease too, for the same reasons as in the previous paragraph. Water absorption continues in the C.c. up to 234 days of immersion with a corresponding S.I. of 83% and I.C. 18%. For the G.c. the water absorption continues for up to 35 days with S.I values of 74% and I.C. of 22%. This prolonged absorption leads us to suppose the presence of very small pores which slowly saturate. Therefore the difference between total and integral open porosity is not attributable only to the class over 751a, but probably also to that under 37A.
3.7. Evaporation of water and Drying Index The trial was carried out in compliance with Doe. Normal 29/88, 1991 on 10 samples for each lithotype. In fig.6 we can see the average drying curve relative to the two materials. If we consider this curve and the values of the Drying Index calculated after 48 hours with
56
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Simpson's integral and equal to 0.374 for the G.c. and 0.417 for the C.c., we can see how the G.c., while having a greater water content, dries more quickly than C.c.. In fact, in the G.c. aider 48 hours the water residue inside the samples is equal to 1% of the initial quantity, time (hours) while the same percentage is found in Fig.6 Water evaporation the C.c. a~er 4 days. The standard deviations in both materials are variable over the trial, starting from values around 2-3% in the first measurements, rising gradually to 10% in the measurements at 4 days. 3.8. Water vapour permeability This was measured by following the procedures indicated in the Normal 21/85, 1986. The values obtained are 378 g/m2 (st. dev. = 34), 322 g/m2 (st. dev. = 21) for the G.c. and 308 g/m2 (o=21), 277 g/m 2 (st. dev. =19)for the C.c., respectively before and after ageing. For both materials, therefore, after ageing a modest reduction can be seen. 4. Conclusions On artificial ageing the C.c. deteriorates more radically than the G.c.. These two diverse reactions resemble what is observable when the materials are employed. The change can be seen in considerable loss of material in the C.c. and in an increase of superficial roughness; the G.c. loses more a contained amount of weight and great variation on the surface layer are not observable. None of the other properties measured have shown clear distinctions between the materials before and after ageing. By comparing the two materials before the ageing, we observe that they have different values for almost all the measured parameters. However, only some of them make the difference in the behaviour during the ageing. The total porosity, which is higher in the G.c., though it does mean greater absorption of water (trough capillarity and immersion), is not reflected in a weaker resistance to ageing. So the mere behaviour in water can not be an index of the durability of the material. The pore size distribution and some textural characteristics are more material to the response of the deterioration. In fact, the G.c. has about 60% of its total porosity composed of pores with a radius greater than 751~, while the same for the C.c. is distributed in the classes inferior to 751~, with a concentration of the pores between 10 and 401~. Moreover the prolonged water absorption of the C.c., probably due to pores that very slowly saturate, let us suppose the presence inside it of very small pores, under the minimum size measurable by mercury porosimetry. After the ageing G.c. shows no changes at all in pore size distribution, while slight variations are observable in the C.c. (see paragr. 3.3). The cement,
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
57
although it is in poor quantity in both materials, probably influences their resistance: its microsparitic texture in the C.c. could make this material more v-alnerable to the stress induced by the artificial ageing. On the contrary, the presence of expandable lattice clay minerals, among the secondary components, does not seem to have any influence in virtue of the low percentage involved. The absence of marked variation in the properties measured before and after ageing in contrast to the considerable loss of material, suggest that the deterioration does not involve the entire volume of the sample, but only superficial strata. In fact, the variations observed are only those relative to the trial which react to the influence of superficial conditions, also because of the greater surface/volume ratio of samples such as the capillarity and permeability. Its intensity however, is different and, considering the previous observations, probably connected to the mierostructural characteristics of the two materials. Pore size distribution and textural characteristics of cement are not quantifiable to the deterioration measurement, because of its superficial location. On the contrary the most significant parameter for the evaluation of durability would seem to be the weight variation due to the loss material. References Cal6 G., Di Pierro M., Federico A., Mongelli G, 1985. Caratteri geologici, petrografici, mineralogiei e meceanici dei "earpari" della provincia di Lecee, Quarry and Construction. Calia A., Mecehi A., Luprano V.A.M., Rubino G., Rota P.,1999. 6th International Conference on 'r Destructive Testing and Mieroanalysis for the Diagnostics and Conservation Of Cultural and Environmental Heritage-ART 99, Roma. 147-162. Calia A., Mecehi A.M., Quarta G., Rota Rossi-Doria P., 1999. Le pietre naturali da costruzione in Puglia. I1 "earparo": impiego e conservazione. Science and Technology for the Safeguard of Cultural Heritage in the Mediterranean Basin, Proceed.1 th Int. Congr. Catania, 1995.885-891. Mecchi A., Calia A., Quarta G., 1998. Caratterizzazione di un materiale da costmzione della Puglia: il Carparo. Recuperate l'Edilizia, I, 3. Alberto Greco Editore, Milano. 33-37. Doe. Normal 4/80, 1980. Distribuzione del volume dei pori in funzione del loro diametro, C.N.R.-I.C.R., Roma. Doe. Normal 7/81, 1981. Assorbimento d'acqua per immersione totale - Capacit/t di imbibizione, C.N.R.-I.C.R., Roma. Doe. Normal 11t85, 1986. Assorbimento d'aequa per capillarit/l- Coefliciente di assorbimento capillare, C.N.R.-I.C.R., Roma. Doe. Normal 22/86, 1987. Misura della velocit/t di propagazione del suono, C.N.R.I.C.R., Roma. Doe. Normal 29/88, 1991. Misura dell'indice di aseiugarnento (dryng index), C.N.R.I.C.R., Roma. Doe. Normal 32/89, 1991. Determinazione gas volumetrica della CO2, C.N.R.-I.C.R., Roma. Doe. Normal 34/91, 1994. Analisi di materiali "argillosi" mediante XRD, C.N.R.-I.C.R., Roma. Doe. Normal 21/85, 1986. Permeabilith al vapor d'acqua, C.N.R.-I.C.R., Roma. Dunham R.J., 1962. Classification of carbonate rocks according to depositional texture. Classification of carbonate rocks. Mem. American Association Petrology and Geology, 1, W.E. Ham Ed. 108-121.
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59
PRELIMINARY CONTRIBUTION ON DURABILITY OF SOME MACROPOROUS MONUMENTAL STONES USED IN HISTORICAL TOWNS OF CAMPANIA REGION, SOUTHERN ITALY
Alessio Langella* Faculty of Science, Sannio University, Benevento, Italy Domenico Calcaterra Dept. of Geotechnical Engineering, Federico II University of Napoli, Italy Piergiulio Cappelletti, Abner Colella, Maurizio de' Gennaro, Roberto de Gennaro Dept. of Earth Sciences, Federico II University of Napoli, Italy
Abstract
A preliminary study of the decay phenomena of three maeroporous volcanic rocks (Neapolitan Yellow Tuff, Campanian Ignimbrite, Piperno) from Campania, Italy is here presented, carried out by means of ageing tests. The latter were chosen taking into account the basic environmental and climatological characteristics of the Campania region. According to standard procedures the wet-dry and salt crystallization tests were carried out. In order to assess the evolution of physico-mechanical and mineralogical features the following parameters were measured at regular intervals: open porosity; water absorption by total immersion; ultrasonic velocities, uniaxial compressive strength. SEM observations allowed to follow changes of intergranular relationships. Aiming at a better comprehension of durability, IRD (Index of Rock Durability) was determined, based on rock swelling tests. The overall results so far obtained pointed out a poorer durability of Neapolitan Yellow Tuff, if compared to the other stones, especially as wet-dry tests are regarded. Key words: macroporous rocks, Piperno, Neapolitan Yellow Tuff, Campanian Ignimbrite, ageing tests, durability, Italy. 1. Introduction
In many Italian towns the use of local stones for architectural purposes has been a very wide practice throughout all the historical ages of the country. In Campania region (Southern Italy) the large availability of volcanic products, characterized by ease of workability, good physico-mechanical properties and an agreeable aspect as well, determined the utilization of these materials both for structural and for ornamental purposes. Among the most widespread volcaniclastic products widely used in the historical architecture of the main towns of Campania region, an outstanding role was played by the Neapolitan Yellow Tuff (NYT) and the Piperno (PI) in Napoli, and by the Campanian Ignimbrite (CI) in its different facies used over the whole Campanian territory (Calcaterra et al., 1999a). Literature on these volcanic products is, in some instances, almost updated. In fact, as far as NYT and CI are concerned, a wide volcanologieal, mineralogical, and petrographical bibliography is available. The behavior of these materials, when used as dimension stones ('Tacciavista"), has been widely investigated, as well. In contrast, this kind of information is lacking for PI even though some researches in progress are trying to fill this gap. Some hypotheses have also been drawn on the decay phenomena in different
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
microenvironmental contexts, whereas very little has been carried out in order to experimentally verify the actual causes of the stone weathering (Rossi Manaresi, 1976; de' Gennaro et al., 1993, 1995). The present study aims at improving the knowledge of the mineralogical and petrographical features of these materials in order to discriminate similar lithotypes and to understand the decay phenomena by means of laboratory simulations which reproduce the ageing processes of the stone. 2. Materials
The investigated materials represent the products of different eruptive episodes of Campi Flegrei volcanic area (Napoli) (Di Girolamo and Morra, 1987; Cole and Scarpati 1993). Their widespread diffusion favored an intensive exploitation (Calcaterra et al., 1999a) mainly concentrated in Napoli and Caserta provinces (fig. 1). Hereat~er, a short description of these volcanic rocks is reported.
Figure 1: Sketch map of Napoli and Caserta provinces, along with quarry locations. Legend: cross = Piperno quarry; full circle = NYT active quarry; full lozenge = NYT inactive quarry; open circle = CI active quarry; open lozenge = CI inactive quarry. Neapolitan Yellow Tuff (NYT): trachytic volcaniclastic rock made up of pumice, obsidian fragments, crystals and lithies set in an abundant zeolite-bearing ashy matrix. Age 12,000 years b.p. Widely used as dimension stone since the former Greek settlings, it has been employed with structural and architectural function, so far. It represents about the 20% of the "facciavista" walls of the ancient centre of Napoli and almost all the plastered ones. The macroporous texture along with the presence of zeolites make this rock particularly prone to the action of weathering agents. Investigation of these processes were carried out on specimens collected in a quarry, located in Quarto (Napoli).
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
61
Campanian Ignimbrite (CI): trachytic volcaniclastic rock made up of pumice and scoria~ in a cineritic matrix. Two distinct facies, both lithified, are present: a gray facies, with epigenetic feldspars, and a yellow facies, characterized by the presence of zeolites. Age: 37,000 years b.p. Widespread over the entire Campanian territory, both facies have been utilized for the production of dimension stones. The gray one, displaying better physicomechanical features, has been used for particular architectural parts. The Medieval town of Casertavecchia represents the highest expression of the massive utilization of this rock. The material used for the present research comes from one of the quarries (Pozzovetere) nearest to the urban settlement. Piperno (PI): traehytic volcanic rock characterized by eutaxitic texture with black flattened fiamme, with sanidine phenocrysts set in a light-gray ashy matrix. Age: ~ 37,000 years b.p. It is the most used ornamental stone in Napoli, either as facing slabs or particular architectural dements, and covers about 50% of the exposed surfaces in its ancient centre. It is sometimes also found in other provinces of the region. Physico-mechanical parameters are sensibly better than those of NYT even though they scatter in a quite wide range. Notwithstanding these good features, the stone is affected by diffuse weathering phenomena. The material used for tests was sampled in one of the rare outcrops still accessible located in Pianura, western periphery ofNapoli (Calcaterra et al., 1999b). 3. Methods
Mineralogical characterization was carried out both by SEM observations and by means of X-ray powder diffraction analysis (XRPD - Philips PW1730/3710) using a CuKF1 radiation, incident- and diffracted-beam SoBer slits, curved graphite crystal monochromator, 2[] range from 3 to 100 ~ step size 0.02 ~ 2B and 10s counting time per step. Quantitative mineralogical analyses were also performed by XRPD using an internal standard, D-A1203 (1 lxm, Buehler Mieropolish) added to each sample in amount of 20 wt %. Powder data set were analysed both by RIR (Chipera and Bish, 1995) and Rietveld methods (Bish and Post, 1993), the latter using GSAS package (Larson and von Dreele, 1995). Open porosity was calculated by means of apparent and real volumes with a Hepycnometer (Micromeritics Multivolume Pycnometer 1305) on at least 10 specimens for each material. Water absorption by total immersion: the total absorbed water after immersion in deionized water at room temperature and pressure was evaluated according to NORMAL 7/81. Ultrasonic tests were carried out according to Italian suggested standards (NORMAL, 22/86), taking into account international recommendations (I.S.R.M., 1978), as well. PUNDIT (CNS Instruments Ltd.) ultrasonic non-destructive digital tester was used with a pair of 24 kHz transducers, in direct arrangement (i.e. transmitter and receiver positioned on opposite sides). Uniaxial Compressive Strength (UCS): tests were made on the specimens previously used for the ultrasonic measures. I.S.R.M. (1979) suggestions have been followed, even though the tests were conducted on cubic samples. Before each test, rock density was determined. Ageing tests: wet-dry and salt crystallization tests were performed according to standard procedures (Rossi Manaresi, 1976; RILEM, 1980; Topal and Doyuran, 1998). The tests were chosen taking into account the basic environmental and climatic characteristics of the Campania region. The total number of cycles for each test was determined on the basis of
62
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
macroscopical changes of the samples, i.e. presence of cracks on the specimens, disgregation, etc. In order to assess the evolution of physieo-mechanical and mineralogical features the following parameters were measured at regular intervals: weight, open porosity, water absorption by total immersion, ultrasonic velocity and UCS. Careful SEM observations allowed to follow changes of intergranular relationships. Swelling strain: determined on cubic samples following the procedures suggested by Nascimento et al. (1968). Depending on the tested material, the swelling strain was measured on variable time spans (usually 24 or 48 hrs.), with a precision of l laxn. 4. Results
Table 1 reports the quantitative mineralogical composition of representative samples of the studied rocks. The NYT shows its typical mineral assemblage with prevailing epigenetic phases (phillipsite, chabazite and analcime), feldspar, and minor amount of mica, hydrated iron oxides and volcanic glass. As regards the other two rocks, they have a very similar mineralogical composition characterized by predominant feldspar, both pyrogenic and epigenetic, and in very subordinate amounts unaltered volcanic glass. The presence of sodalite is characteristic of the PI, and may represent an useful marker which can enable to discriminate PI s.s. from a very similar facies of Campanian Ignimbrite, as far as these rocks are used as dimension stone (fig. 2). Table 1: Quantitative mineralogical evaluation ofvoleanielastic units. Sampte
feta
bio
sod
magn
pyrox
amph
phi
cha
aria
cm
am*
NYT 24.0 tr. tr. tr. 42.5 6.2 7.0 3.4 16.5 PI 85.5 0.4 3.5 '0.3 ' tr. tr. 10.3" CI 88.9 1.0 0.3 tr. 9.8 Note: feld= K- and Na-feldspars, bio= biotite; sod= socialite; magn= magnetite; amph= amphibole; phi= phillipsite; cha= chabazite; ana= analcime; cm= clay minerals and am= glass (including hydratediron oxides); *= calculated by difference , ,
Figure 2 XRPD spectra of Pipemo and Campanian Ignimbrite samples. The variation of the physico-meehanical properties are reported in figure 3 and in table 2. As far as weight is regarded, a slight loss (0.7-2.8%) was measured in the wet-dry tests for all the materials, while the salt-crystallization tests caused a greater reduction (4.4-11.8%).
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
63
On the other hand, open porosity is the parameter less influenced by the ageing tests, with increases ranging between 0.3 and 4.4%. The NYT seems more sensitive to water absorption (increase by 13.7% in wet-dry and 6.6% in salt crystallization tests) if compared to CI and PI (0.7-3.0% and 2.1-4.7%, respectively). The P-wave velocities as a rule, decrease for all the materials, regardless the kind of test; however NYT shows again the worst behavior (2.3% - wet-dry test in CI; 39.8% - wet-dry test in NYT). Considering the uniaxial compressive tests, NYT turned to be affected by a significant reduction in strength, showing severe decrease of this parameter both for wet-dry (43.6%) and salt crystallization (76.6%) tests: the latter result was achieved after only six cycles. On the contrary, UCS values for Piperno did not seem to be influenced by the tests carried out, thus testifying a substantial unaltered mechanical behavior. CI holds an intermediate position as far as wetdry tests are considered, whereas is more sensitive to salt crystallization cycles (-31.3%). A different approach to the evaluation of durability considers the swelling tests performed on unaltered samples which, along with UCS and porosity, enables to calculate the IRD (Index of Rock Durability- Delgado Rodrigues and Telmo Jeremias, 1990). The tests gave IRD mean values of 0.04 for the NYT samples, 0.066 for IC and 0.439 for Piperno.
Table 2: Variation of the physico-mechanical properties after ageing tests (mean values). Neapolitan Yellow Tuff Bwd F,,d B,, F,, Porosity,(%) 53.9 55.2 54.8 57.2 1-120absorption,(wt %) 43.0 48.9 49.1 52.4 Vp,(m/s) 1789 1076 1891 1380 UCS, (MPa) 4.64 2.62 4.07 0.95
Campanian Ignimbrite B~
55.6 39.3 1812 4.18
Fwd B,,
56.6 39.6 1770 3.50
55.0 39.3 1726 4.11
F,,
56.9 40.5 1652 2.82
B., 45.1 21.6 2597 6.43
Piperno V., B.~ 45.2 44.8 22.1 25.1 2394 2274 6.60 6.32
v~ 45.1 26.2 2008 5.25
Bwa= Blank values for wet-dry tests; Fwd= Final values after wet-dry tests B~= Blank values for salt crystallization tests; F~= Final values after salt crystallization tests 5. Discussion and conclusions
The obtained results give a further contribution to the interpretation of the behavior of these three important Campanian rocks towards the decay agents. From the mineralogical point of view, a substantial difference was found out between the NYT on one side, and CI and PI on the other. The matrix of the former is mainly constituted by zeolites (phillipsite and subordinate chabazite) which also act as cement of the rock and, subordinately, by amorphous phases and volcanic glass; on the contrary, the latter (CI and PI) have a matrix almost totally constituted by feldspars and minor amount of glass. The response of these materials to ageing tests (figs. 4 and 5) is that the NYT is the most affected, followed by CI, whereas PI undergoes only slight variations of its physical and mechanical features (tab. 2). Notwithstanding any particular alteration of the crystalline phases of the matrix (fig. 4d), as far as salt crystallization test is regarded, NYT exhibits weathering evidences since after few cycles which determine a weight loss and a sensible reduction of the original volume (fig. 5). Wet-dry tests, conversely, preserve the original shape of the specimens but in the final cycles (30) a net of cracks appears on their surface. This phenomenon is also recorded on SEM observation (figs. 4b and c).
iii
Wet-d~
Salt crystallization
Wet-dry
Piperno
Campanian Ignimbrite
Neapolitan Yellow Tuff
Salt crystallization
i
Salt crystallization
Wet-d~
105
~oo ~9
~o
=-,
80
110 , 105 "~
0
P_ 95
0 O'Q
,
90
1 2 0 ~ ~
~
115
r~ 0
110 105
s
ca 90 110 lOO
m .~ ~,
~
0 ~t 0
80
7o
~o
5O 0
120 ..-.,
100
~ 8o ~ 0 ~
--,._.______
6o
0
40
20 0
0
0
10 20 Number of cycles
30 0
,
Number of cycles
e
o
,o
20
Number of cycles
3o o
;
4
Number of cycles
6 o
20
4o
Number of cycles
~o
o
~
4
6
Number of cycles
0 (1)
Figure 3: Variation of physical and mechanical properties for the considered materials after ageing tests.
< t~ i
4~
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
65
Figure 4. SEM micrographs of NYT. a) untreated specimen; b) and c) after 30 wet-dry cycles; d) aider 6 salt crystallization cycles.
Figure 5: macroscopical features evolving during the wet-dry (let~ column) and saltcrystallization tests (fight column). First row =NYT, second r o w - CI, third row = PI
66
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
However, both tests bring about an overall abatement of the measured properties. As reported in Colantuono et al. (1991) zeolite-rich tufts display an initial shrinkage induced by heating, much higher than any other materials. Consecutive wet and dry environments and the consequent contractions and swellings seem to be responsible for loss of cohesion and disgregation of the stone. CI macroscopically showing modificatiom similar to those of NYT in the salt crystallization tests, denotes only slight decrease of the checked parameters. On the contrary, PI does not reveal appreciable variations either of its macroscopieal character or of its physieo-mechanical features. A further confirmation of the different behavior is given by the swelling tests and by the IRD data. The lowest value of I R parameter pertains to NYT (0.04) which, along with CI (0.06), is characterized by values even lower than those found out in other macroporous rocks, such as the Cappadocian tufts, which are in the 0.10 + 0.13 range (Topoi and Doyuran, 1998). The same parameter turned to be quite variable for PI giving values between 0.123 and 0.439. This wide range can be explained by the presence, within the same formation, of very different facies already evidenced in previous papers (Caleaterra et al., 1999b). It likely seems that the most discriminating parameter is represented by the compressive strength, much higher in PI if compared with NYT and CI. Based on the classification proposed by Delgado Rodrigues and Jeremias (1990), all the studied materials are considered as low durability rocks since their IRD is lower than 2. The reported data enables to deepen the knowledge on the studied materials, providing distinctive features between Piperno s . s . and piperno belonging to CI, otherwise hardly macroseopieally distinguishable, once both used in the same monument. Furthermore, they can help to better understand some weathering phenomena of the studied materials. However, further investigations are still required in order to explain, for example, the marked response of NYT to swelling test. A first hypothesis accounts for the textural relationship of the different mineralogical composition of the studied rocks. The above considerations suggest, as a consequence, that only an interdisciplinary approach which consider all the fundamental aspects of the stone will allow to get the results necessary for a correct evaluation of the restoration of these materials when used as dimension stone.
Acknowledgements Work carried out with the financial support of Italian National Council of Research (C.N.R.) Progetto Finalizzato "Beni Culturali", contr, n. 97.00630.PF36 granted to Prof. Maurizio de' Gennaro and MURST - Progetto di Rieerea di Interesse Nazionale, Cofinanziamento 99. Thanks are due to Mr. Antonio CanzaneUa (Federico II University, Napoli) for his help in SEM observations. 6. References Bish D.L., Post J.E., 1993. Quantitative mineralogical analysis using the Rietveld fullpattern fitting method, Am. Mineral., 78, 932-940. Calcaterra D., Cappelletti P., Carta L., de' C~nnaro M., Langella A., Morra V., 1999a. Use of local building stones in the architecture of historical towns: some ease histories from southern Italy. Proe. 2nd Inter. Congr. on "Science and technology for the safeguard of cultural heritage in the Mediterranean basin", Pads, 5-9 July 1999. In press.
9th International Congresson Deterioration and Conservationof Stone,Venice 19-24June 2000
67
Calcaterra D., Cappelletti P., Langella A., Morra V., de Gennaro R., ColeUa A., 1999b. The building stones of the ancient centre of Naples (Italy): the Piperno from Phlegrean Fields. Contributions to the knowledge of a long-time used stone. Journal of Cultural Heritage. In press. Chipera S.J., Bish D.L., 1995. Multireflection RIR and intensity normalizations for quantitative analyses: applications to feldspar and zeolites, Powder Diffraction, 10 (1), 47-55. Colantuono A., Dal Vecchio S., Marino O., Maseolo G., 1991. On the mechanism of water movement inside zeolitized tuff stones. Atti 1~ Convegno Nazionale di Scienza e Tecnologia delle Zeoliti, De Frede, Napoli, 115-121. Cole P.D., Searpati C., 1993. A facies interpretation of the eruption and emplacement mechanisms of the upper part of the Neapolitan Yellow Tuff, Campi Flegrei, Southern Italy. Bull. Volcanol. 55, 311-326. de' Gennaro M., Colella C., Fusealdo M., 1993. Weathering typologies of monumental tuff-stone masonries in the Naples downtown area. Science and Technology for Cultural Heritage, 2, 53-62. de' Gennaro M., Colella C., Langella A., Cappelletti P., 1995. Alteration and decay of campanian ignimbrite dimension stones in some monuments sited in Caserta area. Science and Technology for Cultural Heritage, 75-86. Delgado Rodrigues J., Telmo Jeremias F., 1990. Assessment of rock durability through index properties. Proc. 6th Int. IAEG Congress, Balkema, Rotterdam, 3055-3060. Di Girolamo P., Morra V., 1987. "The Campanian Ignimbrite", Petrographical, petrochemical and volcanological characters. In: Di Girolamo P., (ed.) The voleaniclastic rocks of Campania (Southern Italy): Rend. Ace. So. Fis. Mat., Special Issue, 177-199. International Society for Rock Mechanics, 1978. Suggested methods for determining sound velocity. Int. J. Rock Mech. Min. Sci. Geomech. Abstr., 15, 53-58. International Society for Rock Mechanics, 1979. Suggested methods for determining the uniaxial compressive strength and deformability of rock materials. Int. J. Rock Mech. ~ . Sci. & Geomech. Abstr., 16, 135-140. Larson A.C., von Dreele R.B., 1995. GSAS. General Structure Analysis System. Report LAUR 86-748, Los Alamos National Laboratory, NM, USA. Nascimento U., Oliveira R., Gra~a R., 1968. Rock swelling test. Proc. Int. Symp. on Determination of the properties of rock masses in foundations and observation of their behaviour, Editorial Blume, Madrid-Barcelona, 363-365. NORMAL 7/81, 1981. Assorbimento d'acqua per immersione totale e capacit~ d'imbibizione. Ed. CNR-IC1L Rome. NORMAL 22/86, 1986. Misura della velocit/t di propagazione del suono. Ed. CNR-ICR, Rome. RILEM, 1980. Recommended tests to measure the deterioration of stone and to assess the effectiveness of treatment methods. Materiaux et Constructions, 13, 175-253. Rossi Manaresi R., 1976. Causes of decay and conservation treatments of the tuff of Castel dell'Ovo in Naples. Proc. 2na Int. Symp. on the Deterioration of Building Stones. Athens, September 27- October 1, 1976, 233-248. Topal T., Doyuran V., 1998. Analyses of deterioration of the Cappadocian tuff, Turkey. Environmental Geology, 34, 5-20.
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DURABILITY OF TUFFEAU STONE IN BUILDINGS : INFLUENCE OF MINERALOGICAL COMPOSITION AND MICROSTRUCTURAL PROPERTIES David Dessandier* Bureau de Recherches G6ologiques et Mini6res, Od6ans, France Philippe Bromblet, Jean-Didier Mertz Laboratoire de Recherche des Monuments Historiques, Champs-sur-Marne, France
Abstract
Five types of tuffeau of poor to good durability were selected for a comparative study. After a mineralogical and petrophysical characterization in the laboratory, the samples were subjected to an accelerated ageing test by salt crystalli~tion and hydration, from which an experimental comparative durability index was determined. At the same time, a general investigation of the physicochemical mechanisms of weathering led to the determination of a theoretical durability index calculated from some of the petrophysical properties of each sample. The influence of mineralogical composition and of certain mierostructural properties on the overall durability of the tuffeau was also studied. Key words: tuffeau, durability, mineralogy, mierostructure. 1. Introduction
The principal dimension stone used in the architectural heritage of the Loire Valley, is a chalky limestone facies and more precisely, a variety of Upper Cretaceous (Middle Turonian) chalk of the Paris Basin. It is tuffeau that, due to its intrinsic properties, is liable to severe weathering, entailing the continual restoration of the monuments. A comparison of the state of preservation of tuffeau historical monuments, however, reveals extremely variable situations, attesting to the diversity of the types of stone gathered together under the general name "tuffeau'" and the broad range of corresponding durabilities. Five types of tuffeau of poor to good durability were thus selected for a comparative study. 2. Materiel and methods 2.1 Samples analysed
The term "tuffeau" includes a wide variety of microfacies, reflecting the space-time variability of the sedimentary depositional conditions: the expression "tuffeau series" is employed. This variety of stone types used in monuments is reflected by a wide variety of states of preservation and hence of durability of the material. Within the framework of this study, five stone types belonging of the "tuffeau series" were selected (Table 1) from an existing database [1] according to the "durability" criterion estimated from in situ observations of the state of preservation.
* Author to whom correspondence should be addressed.
70
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000 Sample CHAM
~ Sampling location
Durability observed in situ Poor
' Chateau de Chambord ' Restoration 19th contrary .... FoNT Abbey of Fontevraud Good Built in the 12th century LOUD Saint Hilaire Church in Loudun Average Built in the 15th century LUZE Abbey of Bois-Aubry in Luz6 .... Good' Built in the 12th century VILL Villentrois Quarry Not observable Table 1 Sampling location and in situ durability of the five tuffeau facies studied.
2.2 Test procedures The mineral components of each tuffeau were identified by X-ray diffraction on a Siemens D5000 diffractometer. The major minerals (calcite, opal-CT and quartz) were quantified: i) by X-ray diffraction and optical microscopy in polarized light for quartz, ii) by infrared spectrometry, using the calibration curves of calcite- quartz - opal-CT mixtures [2] on a Perkin Elmer 16PC FT-IR spectrometer for opal-CT; and iii) according to standard NF ISO 10693 for calcite. The total content of accessory minerals (clays [smectite, muscovite, glauconite] and clinoptilolite) was calculated from the difference with the major mineral contents obtained by infrared spectrometry. To evaluate the influence of clays in the behaviour of the ~mples in the presence of water, tests were also carried out with methylene blue according ' " to standard NF P 94-068. Each tuffeau was subjected to basic petrophysical characterization, including the determination of." i) the total porosity Nt, according to standard NF B 10-503; ii) the water absorption coefficient S4s, according to standard NF B 10-504; iii) the capillary coefficient C, according to standard NF B 10-502; iv) the compressive strength Re, according to standard NF B 10-509; and v) the specific surface area SSEXby the BET method, according to standard NF X 11-1021. Certain hydrodynamic characteristics, representative of the fluid transfer properties, were also determined for the five tuffeau facies: i) The kinetics of water capillary suction of each sample was measured by a procedure derived from standard NF B 10-502. This test helped to determine two parameters denoted A and B [4, 5], according to the Washburn flow law (1921) [3], reflecting the "water weight gain rate" and the "linear migration rate of the capillary fringe" as a function of the square root of time; ii) Linear deformation during imbibition by capillary suction (unidirectional water expansion) of each sample was determined using a contactless optical feeler by laser triangulation. The use of an automated 1-micron resolution prototype [6] served to quantify the maximum deformation and allowed tracking of the deformation rate as a function of the water saturation of the free pore network of the stones; iii) Each sample was evaporated by drying following the Rilem No. 11-5 experimental procedure for regulated evaporation conditions (T=20~ and H.R.=33%) maintained by a salt solution saturated with MgCI2. In these conditions, the shape of the curves reveals two parameters that are representative of drying: the evaporation flux is constant and can be used to calculate a drying rate denoted ct. This evaporation regime only affects a fraction of the water present in the porous medium: beyond a certain degree of residual water saturation, corresponding to the critical water content Se of the stone, the
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
71
regime changes and drying mainly takes place by diffusion according to Fick's law [7]. Evaporation tests were performed for an initial total water saturation obtained by imbibition under vacuum, and for a partial saturation according to the procedure of standard NFB 10504. 3. Results 3.1 Mineralogical composition and parameters associated with clay minerals Mineralogical composition As a first approximation, the tuffeau consists of an assembly of microcrystals of calcite and opal-CT giving the rock a micritic texture. Other phases are disseminated in this microcrystalline matrix: elastic phases, chiefly grains of quartz of various size and accessory minerals including clays (illites, smeetites, glauconites) and zeolites (clinoptilolite). In detail, most of the illites are present in grains of glauconite about 50 lam in diameter. Similarly, part of the calcite is present in bioclasts, but in amounts that can be considered negligible. Quantitatively, the mineralogical compositions differ in the five facies analysed (Table 2). As to the cementation of the rock, it varies between a ealeitic pole (FONT) and a siliceous pole of opal-CT (LUZE). The elastic quartz accounts for 2 to 6% of the total composition, and clinoptilolite was identified in three samples with contents not exceeding 3%. The difference from 100 can be attributed to other minerals: clays and micas, the latter present in small amounts. The measured quartz contents and the calculated contents of clays, micas and other accessory minerals, are clearly correlated, justifying ex post facto the classing of the clays, micas and other accessory minerals in the elastic fraction of the rock, at least as a first approximation.
Cementation ' Calcite (%) OP'aI-CT
z Z Clastic minerals '(%)' 'Quartz (%) Clays, nficas ' Clmoptilolite and other (%),* (%), ' CHAM 57'.5 25 83.5 5 12.5 ,. 'FONT ' 67' 27 94 2 . . . . . 4. . traces LOUD 41 31 72 6 15to20 lto5 LUZE 53.5 39 92.5 2 5.5 <1 VILL 57 25 82 5 13 Table 2: MinerMogical composition of the five tuffeau facies analysed (,calculated by difference).
Sample
9
.
.
.
.
,
.
Sample. VILL CHAM
I
IUite/micas ++ +
.
.
LUZE
+
+ ...... +
. .
.
LOUD
FOtCr
,
Smeetite + + -~ + .
.
.
.
.
.
Other Chlor~ in traces
.
+++ .
.
.
t
++
-
+ traces
'"
Palygorski~ retraces
.
Table 3 Evaluations of proportions of Clay minerals from the measurement of peak areas on diffractograms of the -2 pm fraction. ++++ very abundant, + + + abundant, + + occasional, + rare
72
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
A more detailed identification of the clay phases reveals the presence of illite and swelling smectites in all five samples, while chlorites and palygorskite were each only identified in one sample (Table 3). These results also show that the proportions of these phases vary from sample to sample. On the whole, the LUZE and FONT facies contain the least amount in swelling smectites in their clay fraction, and are also the least rich in accessory minerals (clays, micas). Parameters associated with clay minerals Certain measurements or characterization of the tuffeau may indirectly reflect the behaviour of the clay minerals, qualitatively or quantitatively. Table 4 gives the results of specific surface area measurements (BET) and the methylene blue test.
SB~T(m2/g) Methylene blue test (mg/g) , CHAM 14.4 '15:4 FoNT ' 12.'5 ' 19.3 LOUD .... 21.7 28.5 " 'LUZE 12.9 . . . . . . 8.7 VILL 19.3 20.4 Table 4: Results of the methylene blue test and specific surface area measurements (BET) of the five tuffeau specimens analysed. Sample
.
.
.
.
The high specific surface areas and high values in the methylene blue test are conventionally associated with high proportions of clays, particularly swelling clays like smectites. These correlations are not so evident for the five facies analysed. The specific surface area of the LUZE facies, one of the least rich in smectites, is much smaller than that of the other four facies. On the contrary, that of the FONT facies, which is the least clayey of all the samples, is much higher, as much as the facies in which the proportion of smectite can be considered high (VILL and CHAM). LOUD, which is not the most clayey, also has the highest specific surface area of all the samples investigated. These observations indicate that another parameter is needed (clinoptilolite) instead of the clay content to explain the large specific surface area developed by FONT and by LOUD. The values of the methylene blue test are better correlated with the proportions of clay. FONT and LUZE, which are the poorest in smectites, yield the lowest values in this test. While the methylene blue test is relatively well correlated with the specific surface area for LOUD, CHAM and VILL, and even for LUZE, this does not apply for FONT, which, with a methylene blue test value approximately identical to that of LUZE, exhibits more than twice the specific surface area. 3.2 Petrophysicai and hydrodynamic characteristics Basic petrophysical parameters The five tuffeau facies are characterized by a particularly high total porosity hit, up to nearly 50%, largely explaining their low compressive strength IL. Their water absorption coefficient is also high, with values between 0.8 and 0.86.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
, Sample CHAM
Fotcr
LouD ' LUZE VILL Table 5- Basic petrophysical
73
Ro (MPa,),,. s. Nt (%) 7.6 0.s6 45 " 38 ..... 0.85' 20.7 ' 48 0.84 9.1 .... '39 0180 i6.0 46' 0.87 ~ 7.4 properties of the five tuffeau facies.
Capillary and dilatometric properties The tuffeau facies display high and very discriminating kinetic coefficients A and B (Table 6). They range respectively from 0.16 to 0.42 g/cm2/~/min, and 0.56 to 1.18 cmN min. With all the tuffeau types, the imbibition of all the porosity freely accessible to water by capillarity occurs simultaneously with the arrival of the capillary fringe at the top of the specimen. As it travels through the network, therefore, the water flows uniformly not only by superficial wetting of the pore walls of the network [8] but also by total and continuous filling of the free macropores encountered as it advances. This characteristic does not appear to be confirmed for LUZE and FONT, in which the filling appears to accelerate before reaching the level of freely accessible porosity by capillarity (Fig. 1). naL A (g~/cmV~/min)' 0.73 0.26 0.40 ' 0.47 0.42 1.18 CHAM 0.65 0.81 LOUD . . . . 0.28 0.41 FONT 0.16 0.56 0.42 0.56 .... LUZE 0.16 Table 6: Parameters of capillary suction and water expansion.
Sample VILL
9
i
.
.
.
.
.
.
.
d(AL)mxl(%o) ,,
0.109 0.066 0.197 0.074 0.087
" '
Figure 1 Curves of mass absorption of water versus time for the five tuffeau facies. The dilatometric response of the tuffeau samples was immediate upon contact of their circular base with a level of free water. The maximum final elongations due to the hydraulic softening [9] of their structure are fairly low (Table 7) and cannot be simply correlated with the capillarity coefficients. The increase in hydric expansion measured with rising water contents (Fig. 2) suggests contrasting variations: the LOUD tuffeau, which is the most porous, displays a linear elongation 1.5 times higher than that of the other facies, and maximum deformation at a water content of about 35%. By contrast, the dilatometric behaviour of the other facies reveals the existence of an earlier maximum expansion threshold, reached at a water saturation below 20%, before tending towards an asymptotic
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9th International Congresson Deterioration and Conservation of Stone, Venice 19-24June 2000
expansion close to 0.03• At higher saturations (>40%), the expansion of the VILL and CHAM tuffeau samples was slightly greater than that of the LUZE and FONT samples. This deformation, produced by the effect of the pressures applied by the water meniscus at the grain boundaries, is fairly well correlated with the weaker mechanical properties and the extent of the suite of accessory minerals (table) in these tuffeau facies. Conversely, the tuffeau facies displaying the lowest capillary properties (FONT and LUZE) display less contrasted and less intense expansion. These different water related behaviours emphasise structural differences in the pore networks, which were not identifiable from the analysis of the macroscopic imbibition tests alone.
Figure 2: Water expansion as a function of water content in the five tuffeau samples.
Characteristics of water transfer by evaporation The shape of the evaporation curves (Table 7, Fig. 3) conforms to the conventionally described kinetics [7, 10, 11]. Regardless of the initial saturation, evaporation is broken down into two distinct periods: rapid evaporation at constant flux r which occurs until the stone has reached a critical residual saturation Se followed by a slower drying phase. " Sample
Initial saturation Under vacuum Rate cq-cq,(. 103) Criticalwater (g/cmZ./h) comem,so, (0,6) VILL 1.68-1.97" 38 CHAM i.79-1.88 ~ ' 4i LOUD 2.12 35 FONT . . . . 2.03. . . . 66 LLIZE 1.84 .... 68 Table 7: Petrophysicaiproperties of drying dynamics. .
.
.
.
.
Initial partial saturation (N48) Rate at2 (. 103) Criticalwater
(g/omVh)
, cont., sc~ (%),
2.01
54 54 60 70
1.93 2.27 1.98 1.83
.
.
.
.
.
79
During the first phase, evaporation occurs primarily along the free water surface, and since gravitational effects are ignored, the water movements resulting from capillary effects predominate. Below the water content Sc, the capillary forces causing transfers of water present in the samples are no longer sufficient. This lack of liquid movements attests to a reduction of the driving forces, which increases as the residual water content of the samples decreases. During desaturation, the capillary pressures applied at the water meniscii are very high. These pressures, which only affect the volumes of water in the smallest pores or in the dihedral angles at the grain boundaries, progressively decrease and no longer exert a sufficient force to drain the water towards the evaporating surface. This transition phase,
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
75
which conditions the remaining water coment Sc in the stone, is generally associated with the fact that the liquid network becomes discontinuous [7, 12], only partially connected by water films that are so thin as to be no longer mobilizable. The break in the hydraulic continuity of the network then results in a significant decrease in the evaporation rate. This marks the onset of the new, slower drying phase, at decreasing flux rate, primarily governed by water diffusion mechanisms in a pore network, in which the saturation vapour pressures are no longer present.
Figure 3: Characteristic evaporation curves (LUZE and VILL). The drying tests suggest contrasting behaviours between the different tuffeau facies, depending on the initial saturation mode. In the case of drying atter total imbibition of the sample pores, the duration of the capillary water remobilization phase corresponds to a fairly long interval during which the flux oq can be considered constant as a first approximation. The corresponding residual content Sc~ is relatively low in comparison with the duration and rate of this phase (Table 7). The values of Sol between the different samples are sufficiently different to class the facies into two categories: tuffeau with a low residual water content (Sc<45%; LOUD, CHAM and VILL) and tuffeau with a high residual water content (Sc>65%; FONT and LUZE). These two families are thus distinguished by the nature (by mass) of the predominant evaporation regime governing their drying. A detailed analysis of the morphology of the curves (Fig. 3) reveals that the rate OCl is not exactly a constant. A break in slope occurs above a certain desaturation value of the tuffeau, corresponding to an acceleration of the drying phase before reaching the value SOl. This feature, which is only observable in tuffeau with low water content Sc (LOUD, but above all CHAM and VILL), suggests that capillary transfer occurs with two successive kinetics, with slopes OCl then cq' with Ctl
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.3 Durability
Experimental durability The experimental comparative durability of the five tuffeau facies was assessed via an accelerated ageing test by salt crystallization and hydration [13], performed in a climatic enclosure controlling the ambient temperature and relative humidity during a 24-hour cycle (Fig. 4), reproduced 26 times. This accelerated ageing test by salt crystallization and hydration (thenardite - mirabilite system) is used to calculate an experimental durability index ID~k for each tuffeau, defined as the number of ageing cycles corresponding to a 50% weight loss of the test sample (Table 8). MIRAlllLITE
II
THENARDITE
~
MIRABILITE
1|
oo
1
,
f_
|
i 0
]
,
i
I
t .
.
.
.
.
*
.
.
.
.
24
Figure 4: Temperature and relative humidity profiles of the ageing test.
Theoretical durability The theoretical comparative durability of the five tuffeau facies was determined from the general analysis of the stone weathering mechanisms [14, 15], which reveals four types of characteristic affecting their development: i) mineralogical composition, which acts through the behaviour of certain minerals in the presence of water (swelling of clays assessed by the methylene blue test); ii) the mobilizable pore volume (role of porous expansion vessel evaluated by the total porosity Nt and water absorption coefficient S4s) in case of a volume change of an element (crystallization of salts, gelifraction, etc.) in the porous medium; iii) water saturation rate by imbibition (evaluated by the capillarity coefficient A); and iv) quality of the grain boundaries (appreciated by the compressive strength R~) which acts in the response to mechanical loads (generated by the crystallization of salts and gelifraction). A theoretical durability index lD~di~l can accordingly be expressed by the formula: IDth,o,.,a,& a . N t + b.S4s + c.A + d . R + e.Blue
The coefficients a, b, c, d and e are determined by multivariable linear adjustment of the theoretical durability index H~~ti=l to the experimental durability index ID~a~ of the five samples. This gives an equation which serves to calculate the theoretical durability index of the five facies (Table 8) from a number of parameters previously detemained in the laboratory: IDt~o,.,n~ = 4.83N t - 242.7S4~ - 25.4C + 3.82R~ - 1.55Blue
4. Discussion and interpretation 4.1. Durability indexes developed From the comparative standpoint (Table 8), a first validation indicator of the theoretical durability index l D ~ r ~ l is the very low difference in value (correlation factor 1) from the
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
77
experimental durability index ID~k of the five tuffeau facies. A second validation indicator of the theoretical durability ]Dtheoretieal is its good correlation with the in situ observation of the state of preservation of the tuffeau: the monument blocks displaying the best durability indexes are samples from the 12th century (FONT and LUZE) which have perfectly resisted weathering. Conversely, a sample installed in the 19th century for restoration (CHAM) has a low durability index, and has itself since been replaced. Observed in situ ID~,,t .durability 4.7 Poor 4.7 CnAM FONT Good 32.9 32.9 Average ..... 22.0 LOUD 22.0 Good 31.3 LUZE 31.3 " VILL Not observable 2.8 2.8 Table 8: Observed in situ durability and theoretical and experimental durability indexes of the five tuffeau facies. Sample
IDthomotioa,
,
.
.
.
.
.
.
.
,,
1,,
,
.
.
.
.
.
,
4.2 Influence of mineralogical composition on total durability
Mineralogical composition has a clear influence on durability considering the proportions of the calcite and opal-CT phases that constitute the cement of the material. It clearly appears that the most durable facies are those that are richest in calcite and/or opal-CT. The influence of these phases is easily explained if we consider the role they play, as a cement, on the texture of the material and hence on its porosity and mechanical strength. Conversely, the high contents of elastic minerals (quartz, clays and micas) are obviously unfavourable to the durability of the tuffeau. The richer the rock in elastic elements, the poorer its cementation. Among the accessory minerals, however, the tuffeau samples contain a variable proportion of days, and particularly swelling clays like smectite. It is difficult to quantify these clays, but the evaluations that were made are relatively well correlated with the total durability of the five facies examined. Hence the involvement of clays in the weathering mechanism is highly probable. 4.3 Relationship between critical water content and vulnerability of tuffeau to weathering
It is universally acknowledged that beyond the critical saturation level, capillary water transfers become insufficient, and since evaporation then takes place by diffusion, the salts present in the solutions precipitate in the network, in the places where evaporation occurs [7, 16]. Hence for facies exhibiting a low residual water content Sc, most of the evaporation takes place by capillary transfer towards the surficial evaporation zones of the stones, draining most of the solutions, and probably limiting the risks of further degradation by the crystallization of salts. This mechanism is probably variable because at the same time, these small quantities of residual water (not mobilizable by capillarity) determine environments containing less and less water vapour, setting the stage for possible precipitation by relative depletion of the water. On the contrary, with higher a Se content (LUZE, FONT), the volumes of water remaining to be evaporated are high, and hence imply a higher relative humidity in the network, forcing the salts to remain dissolved for a longer period. The assessment and the influence of these two processes could be clarified by further tests of water content profiles as a function of depth and at different times during drying.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
5. References
[1] Dessandier D. (1995) - Etude du milieu poreux et des propd6t6s de transfert des fluides du tuffeau blanc de Touraine. Application /l la durabilit6 des pierres en oeuvre. Doctoral Thesis, University of Tours. [2] Fr6hlich F. (1993) - Pdncipes de la d6termination des min6raux en m61anges naturels par spectroscopie infrarouge. Applications min6ralogiques et g6ologiques. Colloque 15/XH, Centre ORSTOM, 3-7. [3] Washburn E.W.,1921- The dynamic of capillary flow. Phys. Rev., 17, 3,273-283. [4] Bousqui6 P., 1979- Texture et porosit6 des roches caleaires. Doctoral Thesis, Mines de Paris. [5] Mertz J-D., 1989- R61e des structures de porosit6 dans des propd6t6s de transport: application aux gr6s du Buntsandstein et du Brent. Doctoral Thesis, Strasbourg. [6] CRITT, 1996- Rapport E1862 (unpublished). [7] Hammecker C., 1993- Importance des transferts d'eau dans la d6gradation des pierres en oeuvre. Doctoral Thesis, Strasbourg. [8] De Gennes P-Y.,1985- Wetting: statics and dynamics. Review of Modern Physics, 53, 3, 827-863 [9] F61ix C., 1981- Caract6res p6trographiques et comportement par rapport/~ l'eau de gr6s molassiques du Plateau suisse, comparaison avec d'autres gr6s. In: The Conservation of Stone II, Part A. International Symposium, Bologne, 219-232. [10] Jeannette D. (1994) - Transferts capiUaires dans les roches. La pierre des monuments dans son environnement physique et culturel. European Doctoral Course. Ravello / Florence. [ 11] Kahn J.A., Beasley E., Atalas B., 1991- Evaporation from a packed bed of porous particles into a superheated vapor. Int. J. Heat Mass Tran., 34, 267-280. [12] Coussot P., Gauthier C., Nadji D., Borgotti J-C,, Vi6 P., Bertrand F., 1999Mouvements capillaires durant le s6chage dune p~te granulaire. C.R.A.S Pads, s6rie IIb, 327, 1101-1106. [13] Sperling C.H.B., Cooke U. (1985) - Laboratory simulation of rock weathering by salt crystallization and hydration processes in hot, arid environments. Earth Surface Processes and Transforms, 10, 541-555. [14] Winkler E.M. (1994) - Stone in Architecture, Properties, Durability. SpringerVerlag. [15] Philippon J., Lef+vre R.A., Jeannette D. (1991) - La conservation de la pierre en France. Presses du CNRS. [ 16] Jeannette D., Hammecker C., 1992- Facteurs et m~eanismes des alt6rations. In: La conserv, de la Pierre Monum. en France. Presse du CNRS, 73-81.
79
W A T E R - R O C K INTERACTION AND MONUMENTS CASE OF BASILICA DA ESTRELA, PORTUGAL
STONE DECAY:
THE
Carlos A.M. Figueiredo, Jos6 M. Marques, Ant6nio M. Mauricio & Luis Aires-Barros* Laboratory of Mineralogy and Petrology, IST, LAMPIST, Lisboa, Portugal
Abstract Chemical analyses of rain and seepage waters were carried out in order to establish the main source of soluble salts detected inside of Basilica da Estrela, the most relevant 18th century monument in Lisbon built with calcareous stones. Chemical weathering forms present are associated to calcite re-precipitation and soluble salt (trona and thenardite) local precipitation. Rain and seepage waters were collected at the terrace and inside of Basilica da Estrela. Statistical and graphical methods were used to data analysis. HIDSPEC computational hydrogeochemical model was also used to calculate saturation indexes (S.I.) of some minerals commonly involved in the weathering process of carbonate monument stones. Rain and seepage waters are chemically very different. All rainwater samples are under-saturated, showing decreasing S.I. values for the following minerals (gypsum > calcite > aragonite > halite > dolomite). Concerning seepage waters, the S.I. values increase for most of the minerals, but saturation is reached only with respect to calcite and aragonite. Since trona and thenardite could only be precipitated through seepage evaporation and since the environmental conditions are the same all over the interior of Basilica da Estrela, their punctual occurrences point to a local source and/or enrichment of salt solution (cleaning activity and repair works). Keywords: Rainwater, seepage water, stone-decay, monument, limestone, soluble salts. 1. Introduction Periodic chemical analyses were carried out on both rain and seepage waters in order to establish the main source of the soluble salts detected inside of Basilica da Estrela. Basilica da Estrela, the most relevant 18th century monument in Lisbon, was started in 1779 and finished eleven years later (fig. 1). It is located in a moderately polluted area about 15 Km far from the sea. It was built with Jurassic and Cretaceous calcareous limestones exploited at Lisbon region. The interior is all covered with beige, greyish-blue, rose and ochre limestones. These are essentially pure and calcitic limestones with more than 95% of calcium carbonate and less than 3% of silica. The yellowish variety is slightly dolomitic and clayey. With effective porosity less than 1% and permeability ranging from 1.34 x 101 (mD) to 4.96 x 101 (mD), the limestones under study have very little porosity and are practically impermeable materials. Physical weathering forms (granular disintegration, flakes, scales and spalling) prevail inside of Basilica da Estrela. Chemical weathering forms (salt efflorescences and calcitic concretion), however, are also present due largely to calcite re-precipitation (large white zones) on the lining stones and soluble salts (trona and thenardite) precipitation in a very small and located area displayed in fig. 2. As the environmental conditions are the same all *Author to whom correspondenceshouldbe addressed.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
over the interior of Basilica da Estrela (Figueiredo, 1999), this punctual occurrence of soluble salts precipitation points to a local source and to the evaporation of seepage waters leading to the enrichment and to the precipitation from the solution.
Figure 1: Basilica da Estrela, principal facade
Figure 2: Local of trona and thenardite salts precipitation inside of Basilica da Estrela. Close up of Nave elevation (N-S cross section)
2. Methodology and results To deal with this situation, chemical analyses of rain and seepage waters were performed on waters collected outside (at the terrace) and inside (at the high choir) of Basilica da Estrela. Rain and seepage waters were sampled simultaneously over three years from February 1993 to February 1996. The main anions and cations determined were respectively CI', NO3", SO42, HCO3", CO32 and Na +, K*, Ca 2+, Mg 2+, NH4+. Silica, given as
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
81
SiO2 was also determined. Physical and chemical properties of waters, such as pH, electrical conductivity and temperature were also measured. All chemical analyses of water samples were made at LAMPIST. The data gathered over the sampling period was worked and analysed by statistical and graphical methods. Some scatter diagrams of possible hydrogeochemical significance have been attempted. A methodology based on the calculation of saturation indexes (S.I.) of some minerals commonly involved in the weathering process of carbonate stone monuments has also been adopted. The HIDSPEC computational program used is an hydrogeochemical model that using physical and chemical analyses of waters, estimates the activity of 68 aqueous species and the saturation indexes (S.I.) of 55 minerals (Carvalho & Almeida, 1989). The interpretation of water analyses allowed the chemical characterisation of rain and seepage waters that were involved in the stone decay processes ongoing at Basilica da Estrela. Rain and seepage waters typology as well as the origin of the chemical species analysed was established. Relationships between seepage waters dissolved-solids concentration and rock material percolated by rainwater have been investigated. Possible soluble salts precipitating from rain and seepage waters evaporation on free surfaces of the stone can be pointed out and justify the local occurrence of the soluble salts (trona and thenardite) identified by X-ray diffraction and FTIR.
3. Water-data analysis, interpretation and discussion 3.1 Chemistry of the waters Rain and seepage waters are chemically very different. Rain waters belong to S O 4 - CI Ca and C1 - SO4 - Na type (fig. 3), showing a strong sea-water influence (Begonha et al., 1995). pH values range from 5 to 7, conductivity values are around 90 ~tS/cm and total mineralisation lies between 40 and 100 mg/l.
Figure 3: Piper (trilinear) diagram of rain and seepage waters
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Seawater could be practically pointed out as the only source for chloride and sodium ions present in many of the rainwater samples (fig. 4). However, to other rainwater samples seawater mean contribution for sodium concentration is about 83%.
Figure 4: CI and Na § scatter diagram
Figure 5:SO4
2- and
Ca 2§ scatter diagram
According to Begonha (1997), the mean contribution from the sea to the r a i n w a t e r SO42, was estimated and is about 18%. The presence of sulphates suggests then the existence of other factors controlling rainwater chemical composition. The origin of sulphates could be attributed to air pollution (atmospheric gaseous SO2 and particulate matter) (Arnold et al., 1989; Aires-Barros, 1991; Begonha et al., 1995). The SO42 concentration in rainwater samples is strongly correlated to the Ca 2§ concentration, with a correlation coefficient equal to 0,92 (fig. 5). The equation of the regression straight line fitted to the data points of the scatter diagram SO42 concentration versus Ca2+ concentration is relatively closer to that corresponding to gypsum 5 0 4 2 " / C a 2+ ratio than to that of sea water SO42"/Ca2+ ratio. So, gypsum could be faced as an important (or even the major) source for the sulphate ions, not excluding the contribution from others sources. This high non-marine origin of the SO42 present in rainwater samples is also observed to calcium concentration. On average, more than 92% of the calcium present in rainwater samples is likely to be also of non-marine origin. Rainwater percolating monument stone structures bring about changes in composition of the water and stone material owing to evaporation, dissolution and precipitation of some components. The chemical composition of the water varies widely in response to these and to other related influences. Seepage waters belong to H C O 3 - Na type (fig. 3), showing pH values between 7 and 12. Compared to rain waters, seepage waters are much more mineralised as shown by conductivity (about 700 ~tS/cm) and total mineralisation (between 200 and 3000 mg/1) values. This comparatively high dissolved solids concentration is due to the interaction with the rock and the mortar located in the joints of the block stones of monument structures. When plotted on the Piper diagram the solute concentrations of seepage waters show a rather narrow range of variation in composition during the monitoring time of the monument and considerable clustering of points occurs. The rather hydrochemical uniformity revealed by the seepage waters suggests very similar conditions and mechanisms of water-rock interaction corresponding to the same type of percolating system through the building stone for all of the analysed waters. This hypothesis seems to be corroborated when the data available is plotted against CI concentrations and remarkable
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
83
regularities emerge for most water points, as is indicated by the relatively good linear correlations observed between HCO3-CI, Na-Cl, K-CI, and NO3-CI (figs. 6 to 9). Contrary to the other chemical species analysed, Ca2§ and SO42" are less concentrated in many seepage water samples than they are in rain water samples, mainly due to CaCO3 precipitation observed in-situ as stalactites occurring when seepage waters are exposed to the air (figs. 10, 11). Seepage waters
Seepage waters
350,00 300,00
25,00
15,00 O'~ 10,00
200,00
0 e/ 9 /
E
150,00
;X"
Z
100,00
5,00
50,00 0,00 0,00
NO~'= o,3967cr - 4,451 / A R2 = 0,6142
20,00
250,00
E
/"
K* = 4,6487C1 + 15,662 /
20,00
40,00
60,00
0,00 0,00
80,00
20,00
CI" (rag/I)
Seepage waters
,..-,
,,_..
*~ z
350,00
Na§ = 1,6294cr + 10,689 j l , R2 = 0,7311 /
300,00
60,00
250,00 E "-" 200,00 0 O 150,00
40,00
100,00
20,00
50,00
ee~
80,00
0,00 0,00
20,00
40,00
80,00
Seepage waters
400,00
140,00
100,00
60,00
Figure 7" CI and NO3 scatter diagram
Figure 6: CI" and K § scatter diagram
120,00
40,00 CI (mg/I)
60,00
0,00 0,00
80,00
W
,
-
20,00
,
40,00
i
60,00
80,00
CI (mg/I)
CI" (mg/I)
Figure 8" CI and Na § scatter diagram
HCO3= 7,1515C1 - 1 3 y e R2 = 0,8177
Figure 9: CI" and HCO3scatter diagram ._. 50,00
~ 30,00
9
~- 20,00
~ 40,00 ~. 30,00
=o
0=
~ 20,00 10,00
o,oo
0,00
~ 10,00
10,00
20,00
30,00
SO42(mg/I) (Rain waters)
Figure 10 SO4 2- rain and seepage waters diagram
~
o,oo
0,00
10,00 20,00 30,00 40,00 50,00 Ca2§(mg/I) (Rain waters)
Figure 11 Ca 2+ rain and seepage waters diagram
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.2 Saturation indexes
The saturation index (S.I.), for a given mineral, is defined, at any temperature, as the ratio between the activity product of the species involved in the chemical reaction and the equilibrium constant. At a given temperature, the solution is in equilibrium with the mineral if S.I. =1 or log S.I. = 0. Estimated saturation indexes (S.I.) indicate that all rainwater samples are under-saturated with respect to many minerals. Concerning the most important minerals of interest for our study, the analysed rainwaters show decreasing S.I. values for the following minerals: gypsum > calcite > aragonite > halite > dolomite (tab. 1). This trend seems to indicate that salt crystallisation is only possible from rainwater evaporation. Table l" Log S.I. (Saturation Indexes). Rain waters Mineral
sample Calcite :Aragonite Dolomite Gypsum Halite -3,32 = -3,47 -7,77 -2,43 -8,52 RI R2 -3,31 ! -5,45 -10,79 -4,14 -8,77 -4,83! -4,98 R3 -9,95 -3,97 -8,57 R4 -4,27 -4,42 -8,94 -3,52 -8,14 -3,66 -3,80 R5 -7,96 -3,21 -8,20 R6 -5,00 -5,15 -10,68 -3,55 -8,87 R7 -3,15 -3,29 -7,13 -3,16 -8,61 R8 -5,93 -6,08 -12,37 -4,22 -9,22 -4,10 -4,25 -9,29 -2,82 -7,68 R9 RI0 -3,74 -3,89 -8,61 -2,92 -9,07 RII -4,25 -4,40 -9,30 -3,38 -8,58 RI2 -4,61 -4,76 -9,70 -4,14 -8,65 RI3 -4,93 -5,08 -10,87 -3,01 -9,14 RI4 -3,54 -3,69 -7,67 -3,58 -8,54 RI5 -2,94 -3,09 -6,64 -2,94 -8,36 RI6 -4,02 -4,17 -8,50 -3,50 -8,58 RI7 -3,02 -3,17 -6,91 -3,41 -9,17 -3,09 -6,64 -2,43 -7,68 MAX -2,94 MIN -5,93: -6,08 -12,37 -4,22 -9,22 |
-
Seepage waters
Seepage waters 350,00 r 300,00
~Thenardite
=,,=- ~ T r o n a H C O 3 = 3,5942Na § - 131,8 . 0 R2 = 0,7501 9
300,00
/
250,00
250,00
g
_~ 200,00
200,00
0" oT 150,00 100;00
HCO3" = 0,8847 qa*
" 9 /' "
E
150,00
")
100,00
/
30,00
60,00
90,00
120,00
Na § (mg/I)
Figure 12: HCOa and Na + linear fit
150,00
0,00 0,00
/
/
SO42" = 0,1986Na § - 4,3 R 2 = 0,3999
50,00
50,00 0,00 --0,00
SO42 = 2,0891 N~#'
50,00
100,00
150,00
Na § (mg/I)
Figure 13" SO4 2- and Na + linear fit
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
-'--
85
-"Gypsum
120,00 100,00 ._.
80,00
E ,~
60,00
co
40,00
6
/
/ SO42" = 2,3966Ca2>
9
/
/
/
/
20,00 ~/ / 0,00 v 0,00
10,00
1
i
i
20,00
30,00
40,00
50,00
Ca2. (mg/I)
Figure 14:S04 2- and Ca2§ scatter diagram Concerning seepage waters, S.I. values increase for most of the minerals, but saturation is only reached with respect to calcite and aragonite (tab. 2). However, only a small number of these waters are over-saturated with respect to the above mentioned minerals. Table 2" Log S.I. (Saturation Indexes). Seepage waters Mineral Sample
S1 $2 $3 $4 $5 $6 $7 $8 $9 SI0 SI1 S12 S13 S14 S15 S16 S17 MAX MIN
Calcite Aragonite Dolomite Gypsum Halite 1,01 0,86 0,43 -3,77 !' -6,68 2,07 1,92 0,67 -2,80 -7,47 0,22 0,07 -0,64 -4,67 -7,47 0,79 0,64 0,43 -4,49 -7,31 0,87 0,72 0,52 -4,23 -6,97 0,47 0,32 0,02 j -4,59 . -7,08 0,72 0,57 0,11 . -4,08 . -6,85 0,46 0,32 -7,46 -0,87 -1,01 -2,46 "i -4,18 . -7,10 0,58 0,43 0,61 -4,59 -7,18 0,59 0,44 -0,24 -4,30 -7,24 0,60 0,45 -0,05 -4,50 -7,33 0,60 0,45 -0,07 -4,42 -7,25 0,01 -5,33 -7,2, r 0,57 0,42 0,53 0,38 -0,26 -4,82 -7,38 0,42 0,27 -0,34 -5,03 -7,58 0,66 0,52 -0,02 -4,65 -7,45 2,07 1,92 0,67 -2,80 -6,68 -0,87 -1,01 -2,46 -5,33 -7,58 .
.
.
.
Trona Thenardite -10,96 -7,78 -14,08 -8,81 -13,59 -8,99 -13,75 -9,22 -11,62 -8,57 -12,08 -8,85 -11,68 -8,25 -13,51 -14,00 -8,80 -12,41 -8,72 -12,45 -8,62 -12,63 -8,99 -12,67 -9,07 -12,99 -9,65 -12,68 -9,24 -13,20 -9,50 -13,22 -9,27 -10,96 -7,78 -14,08 -9,65
Another relevant aspect is that seepage waters are under-saturated with respect to trona and thenardite (locally found soluble salts). This implies that these salts could only be precipitated due to seepage water evaporation. Regarding the scatter diagrams that have been prepared from seepage samples some remarks should be made:
86
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000 9 The pattern of points plotted in the scatter diagram SO4 2" concentration versus Ca 2+ concentration (fig. 12), shows a rather narrow range of variation and considerable clustering of points so that a regression line cannot be drawn through them. However, they are plotted either over or very near to the theoretical SO42/ Ca 2+ gypsum ratio. So gypsum could be pointed out as a probable sulphate salt that can be precipitated from seepage water evaporation. 9 The regression straight line (with a slope of 0,1986) fitted to the data points of the scatter diagram SO42" concentration versus Na + concentration (fig. 13), is very far from the theoretical SO42/Na § thenardite ratio. This shows that sources of these ions other than thenardite should be considered. Seepage waters show high concentration of Na § The thenardite hardly will be the most important sulphate salt precipitating from seepage waters evaporation. 9 Trona will not be the most important nor the only carbonate salt precipitating from seepage waters evaporation, according to a similar interpretation of its respective scatter diagram. In spite of HCO3" concentration in seepage waters is strongly correlated to the Na § with a correlation coefficient equal to 0,87 (fig. 14), the regression line fitted to the points plotted in the scatter diagram is relatively far from that oftrona dissolution. This is, the molar ratio of bicarbonate to sodium in seepage waters is relatively far from the theoretical value of 0,8847 suggested by CO32/Na § ratio of trona.
4. Conclusions Since seepage waters are under-saturated with respect to trona and thenardite, these salts could only be precipitated through seepage water evaporation in this monument. As environmental conditions for this soluble salt precipitation are the same all over the inside Basilica da Estrela, one has to think on a local source and/or enrichment of salt solution that could intensify the precipitation of these salts. This fact could be attributed to cleaning activity and repair (maintenance/restoration) works performed in the last few years. Besides, the evolution of seepage water composition under the environmental conditions found inside Basilica da Estrela, shows that the stone decay induced by salt deposition cannot be attributed to trona and thenardite, given the punctual spatial distribution and quantity expected to occur. However, this is not expected for calcite as is confirmed for example by the existence of secondary calcite deposition as crusts, stalactites and stalagmites observed inside the church. Although there is strong evidence of the contribution of sea water to rain water composition, there is no evidence, inside the church, of the influence of chlorides dissolved in the seepage waters as likely causes of the monument stone decay in the sampled areas.
5. Acknowledgements This study was partly financed by Praxis project 2/2.1/CTA/437/94. 6. References Aires-Barros L., 1991. Altera~:ao e Alterabilidade de Rochas. INIC, Lisboa. Arnold A., Zehnder K., 1989. Salt Weathering on Monuments. The conservation of monuments in the Mediterranean Basin, Proc. of the First International Symposium, Bari, Grafo Edizioni. 31-58.
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Begonha A., Sequeira Braga M.A., Gomes da Silva F., 1995. A Ac~.o da /kgua da Chuva na Meteoriza~ao de Monumentos Graniticos. Mem6ria n~ 4, Universidade do PortoMuseu e Laborat6rio Mineral6gico e Geol6gico. 177-181. Begonha A., 1997. Meteorizaqao do Granito e Deteriora~ao da Pedra em Monumentos e Edificios da Cidade do Porto, PhD. Thesis, Universidade do Minho, Braga. Carvalho M.R., Almeida C., 1989. HIDSPEC, um programa de especia~ao e chlculo de equilibrios ~iguaJrocha. GeociSncias, Revista da Universidade de Aveiro, 4 (2), 1-22. Figueiredo C., 1999. Altera~ao, Alterabilidade e Patrim6nio Cultural Construido: O caso da Basilica da Estrela. PhD. Thesis, Universidade T6cnica de Lisboa, IST.
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ANALYSES OF THE PHYSICAL PARAMETERS CORRELATED TO BENDING PHENOMENA IN MARBLE SLABS. Carlo A. Garzonio* Dip. Urbanistica e Pianificazione del Territorio, Firenze, Italia Fabio Fratini F & Carlo Manganelli del F/t CNR,Opere d'Arte, Firenze, Italia. Prisca Giovannini & Fabio Cavallucci Dip. Storia dell'Architettura e Restauro, Firenze, Italia
Abstract
The paper analyses mechanical decay processes in stone materials, which are represented mainly by Carrara marble used in architecture, historical buildings and monuments. These processes are often related to the bending of marble-slabs and architectural elements which are affected by creep processes. Mechanical and physical parameter analyses were carried out on some of the more representative slabs, and significant variations were found in the mechanical resistance, density and above all porosity values. Other slabs and bars were prepared from quarry material and they were subsequently bent with long term flexure load tests. The analyses of thin sections and of SEM images allowed us to identify the various structures of the blasts, the microfractures caused by pressure or disconnections, etc. In particular the results of systematic analysis carried out on over 80 slabs from some cemetries in Florence- are discussed and using these data preliminary models of creep phenomena are being drawn up. Key words: creep phenomena, physical and mechanical decay, Carrara marble slabs.
1. Introduction Research has been underway for a few years now on mechanical decay processes of stone materials - represented mainly by Carrara marble, in particular white marble- used in architecture, historical buildings and monuments. These time-dependent deformation phenomena are often triggered off by effects of stress release, due, in turn, to residual stress (Voight, 1966; Kieslinger, 1967). The processes are connected to the tectonic and geomorphological history, to the effects of new environmental conditions and to the new geometry of the stone elements. It is very important to identify and study these phenomena as it has already been proven that they play an important role in controlling and increasing the effects of environmental and meteoric degradation and atmospheric pollution, and of physical-chemical surface weathering. At the same time, in many cases, creep processes are the vehicle for the more rapid, and sometimes obvious, effects of bowing type deformation, caused by thermal cycles or by the incorrect fixing of stone materials. There have been some well known cases in recent architectural works which present bending phenomena in the covering material, e.g. the Amoco Tower (Chicago), the Arc de la D6fense (Paris), the Finlandia House (Helsinki). Other cases are related to ancient monuments, e.g. the many facades and external walls of Romanesque and gothic churches, in Tuscany in particular. In many cases we have a modest deformation effect, however micro-deformations, and
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
sometimes micro-cracks, are present in the intergranular and transgranular structure of the marble and they are a vehicle of degradation processes. As regards the state of art of the research in this field we should mention in particular the papers by Winkler (1972;1996), Logan et alii (1993), Sorace (1996). A more detailed analysis of the literature on creep phenomena linked to the problem examined is contained in previous papers by the research group (Garzonio et alii, 1995, Cavallucci et alii,1997). Some of these international contributions refer to creep phenomena which involve rock masses, where we can nevertheless deduce behaviour laws which are useful for defining the bending processes of slabs and of architectural elements (Cristecu,1985; Fakhimi & Fairhurst, 1994; Fossum, 1977; Hudson et alii, 1993; Ottosen, 1986 ).
2. Experimental Methodology Having said this, it is clear that it is necessary, not only to continue the studies and the tests for characterizing and modelling creep phenomena, with the identification of the constitutive laws, etc., but also to examine and apply analysis and forecasting methods to small scale processes. Deformation tests were therefore carried out on various bent, white Carrara marble slabs in order to evaluate physical and mineralogic parameters. Mechanical and physical parameter analyses were carried out on some of the more representative ones, and significant variations were found in the mechanical resistance, density, and above all, porosity values. Other slabs and bars were prepared from quarry material and they were subsequently bent with long term flexure load tests. The parameters refer to different patterns of the values in relation to the strains and the position of the samples with respect to the concave and convex surfaces. The study then focused on the microscopic analysis of thin sections and on the analysis of SEM images of various points of the slabs. These analyses allowed us to identify the various structures of the blasts, the evolution of the deformations and discontinuities, the presence of cracks, the microfractures caused by pressure or disconnections, etc. In particular the results of systematic analysis carried out on over 80 slabs from some cemetries in Florence are discussed. The data resulting from this analysis is contradictory at times if we correlate some geometric and physical parameters with the deformation pattern. The slabs refer to the period between 1833 and 1986. Five of them were examined in detail, applying all the above mentioned tests, the aim being to perfect and improve study methods in order to normalize all the various analyses and test phases. This operation becomes even more necessary in the very frequent case of interacting processes in order to understand the role played by creep phenomena linked exclusively to the weight of the slab itself, to stress release, to thermal or environmental variations and to fixing techniques.
3. Previous results In the initial phase of the research programme, tests were carried out, (and they are still being carried out) on slabs of Carrara marble from the fagade of the Collegiata di Sant'Andrea in Empoli (near Florence), and from some cemeteries in the Florence area. It is a well-known fact that the Carrara marble in the Apuan Alps in the North of Tuscany derives from limestone, as a result of a tectonic-metamorphic deformation, which occurred from around 27 to 12 x 10 6 years B.P. The latter greatly deformed the pre-existing stratigraphic structure and created new ones. White Carrara Marble and Ordinary White Carrara Marble are homogeneous white fine grained marbles. Grain size is bimodal,
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
clustered around 0.1 and 0.3-0.4 mm; (Blasi et al. 1990). Table 1 contains data regarding some physical parameters and mechanical properties. . . . .
Table 1" Mechanical parameters and physical properties of the White Carrara marbles unit
A
B
Uniaxial compressive strength MPa 133.2 MPa 128.2 Compressive strength after gelivity MPa 18.5 Bending rupture load 10-6 C 5.93 Linear thermal expansion coeff. % 0.131 Imbibition coefficient KN/m 3 26.92 Unit weight cm 57.80 Impact collapse weight MPa 71370 Young's modulus mm 5.27 Wear thickness loss A" White Marble (Bianco P); B' Ordinary White; C: Quarry E:Slab (cemetery)
C
E
D
136.6 128.1 36.7 53.7 129.8 122.0 16.5 18.8 2.0 7.12 7.4 0.129 0.090 0.16 0.19 26.97 26.85 27 27.2 58.2 65.0 71620 64800 27800 53800 5.31 5.55 (Ordinary); D:Slab (Collegiata);
In particular, the geomechanical features, the extent of the viscous deformations of the marbles and the results of the laboratories tests are described, the objective being to obtain a preliminary definition of the creep phenomenology. It is within this context that the slab from the facade of the Collegiata of Empoli was analyzed from the point of view of the variations in some physical and mineralogic-petrographic properties linked to the deformations (Garzonio et al. 1995). This analysis highlighted the different geometric distribution of the points of physical-mechanical decay. On the basis of the results of the physical analysis, we find an interesting correlation (see example in Fig.l) between the deformations the material has undergone and, above all, the porosity values (mean porosity value is 5.2 % for the concave side of the slab, and 6.1% for the convex one, with an elevated coefficient of variation CV=35%, max value 10.5%, min 3.9% ). This property determines and highlights the degradation processes. 3O
10
% o
20
4
%
~2
"~ 10 5 0
0 0
5
10
15
bending strength(MPa)
Figure 1.
Correlation
between
20
25
0
5
10
15
20
25
bending strength(MPa)
bending strength, porosity and strains
As a confirmation of these results, two white Carrara marble from two different quarries, located in zones with slabs of different tectono-metamorphic histories were analysed (Barsottelli et alii, 1998). The experimental results highlighted two different granoblastic microstructures, characterized by regular, straight grain boundaries or, on the contrary, by
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
irregular and suturated grain boundaries. These different structures are correlated to different physical properties as table 2 shows. Table 2: Physical parameters and microstructural features Marble type ~'s P P(Hg) ICv SI A 2.65 2.4 0.7 0.79 34 B 2.69 1.3 0.2 0.16 12 Per S/L Sg D 0.4152 0.173 0.118 0.0198 A(Mean) 0.66 0.146 B(Mean) 0.0159 0.7908 0.156 0.108 0.68 0.132 7s =bulk density (t/m3); P= total open porosity(%); P(Hg) = mercury porosity (%); ICv = volume imbibition coefficient (%); SI = saturation index; Sg = grain surface; Per = grain perimeter; L = long axes; S = short axes; S/L = axial ratio; D = mean grain diameter.
Figure 2. Thin sections of type A and type B marble. Cross polarized light.
4. Sampling and analysis A systematic analysis was carried out on eighty slabs of white marble characterized by clear signs of deformation, from six different cemeteries in Florence. These slabs which are directly exposed to the elements and face different directions, form the covers of ground tombs (horizontal slabs) and wall tombs (vertical slabs) respectively. As far as the marble is concerned, it was identified macroscopically on the basis of the main colour and the absence of veining of a different shade. As regards dating, the year which figures in the inscription on the slabs was taken as the year the slabs were laid. In this way the time interval was set at about 160 years (1830-1990). The deformations were measured with respect to many sections; the maximum linear strain (s) with respect to the plane on which the slab is laid (both horizontal and vertical), or the tangent at the base of free standing vertical slabs. A total of 45 horizontal slabs and 16 vertical slabs were examined. The slabs were of varying lengths, ranging from 51 to 237 cm. Taking into consideration this parameter, it was possible to identify three groups of horizontal slabs ( I, II, III,) and two groups of vertical slabs (IV, V). The mean value of these intervals is equal to about 93 cm Group IV; 98 cm Group I; 174 cm Group II; 208 and 210 cm Groups III and V respectively. Four horizontal slabs and three vertical slabs were not included in these intervals, two horizontal ones have a length of 237 cm, one 125, and the last one 140 cm, with widths varying from 78 to 90 cm. The three vertical slabs have lengths of 51, 77 and 103 cm. The other dimensions and the strain are comparable with the ones shown in Table 3. The bending B, both longitudinal and transversal, was measured with B-1/r (where r is the bending radium).
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Table 3" Dimensions, strain and age of the slabs Group length width thickness total cm cm cm number I II III IV V
strain B1 B2 Age mm cm ~ cm l 11.6+3.6 0.00132 0.00139 1880 97.8_+8.8 75.5_+4.3 3.5+0.8 12 1961 13.5+5.7 0.00056 0.00135 1867 174.1+11.5 77.3+9.8 4.9+2.5 22 1986 14.2+3.1 0.00028 0.00102 1891 208.3+4.4 78.9+9.1 4.7+2.1 11 1956 17.5+9.1 0.00135 1833 92.5+0.7 60+12.7 2.0+0.2 4 1851 16.5+8 0.00044 1908 210+0.6 64.2+0.4 2.2+0.4 12 1924 B 1= longitudinal bending ; B2 =transversal bending (mean values)
As we can observe in Table 3, given that the width (average value 77.26 cm) and thickness (average value 4.38 cm) of the horizontal slabs are similar for all groups, the length does not influence the maximum linear strain at all. The vertical slabs show greater strain values up to about 40 mm (and B1 = 0.00073), due to the positioning, the free edges and the greater stress. Regarding this point, vertical slabs measured showed outward bulging even though inverse phenomena were observed on other slabs not considered in this study (Garzonio et al. 1995). The deformations of the horizontal slabs laid at the edges and rarely fixed, present downward bending in the centre and upward bending at the edges, with the exception of two cases which still have to be clarified. On the contrary, the vertical ones present more irregular deformations. Nevertheless situations are often found where the distribution of the deformations is irregular and they do not correspond with the configuration of the stresses due to their own weight. However as far as dimensions are concerned, it is possible to make some observations on the different extent of the deformations. Greater "normalized" deformation values are found as a function of the 1/s (length-strain) e w/s (width-strain) ratios, and these are confirmed by B values. With thickness of less than 2.5 cm the relative strain (~%) increases, almost independently of the dimensions. Creep tests have been carried out and are still underway, based on the results of the previous tests, and in particular of the bending tests, which identified a reduction of up to 34% as to the instantaneous breaking load. They consist of bending tests (Ito & Sasajima, 1987), compression tests and tension tests with 0.35 ~. In addition some triaxial tests were carried out, the main aim being to try to identify the anomaly of the main stresses. The material analysed regards white marble slabs from quarries which are well known from a geo-structural point of view. The diagrams of bending tests are given in Figures 2 and 3.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
bending test
bending test
Figure 3. Time to rupture points
Figure 2. Bending Tests (0.35 of instantaneous ~)
Table 4 shows the limit parameters of the three creep phases obtained by the tests. These experimental data are in agreement with the measurements and data relating to the tests on the ancient deformed slabs, even though they are almost equal to breaking values at times less than 25% of the unaltered instantaneous ones. Long term tests are still underway on 5 slabs chosen to represent the ones used for the census. However the instantaneous tests have already given even lower breaking values and, above all, very low moduli of elasticity. Table 4. Creep parameters from bending test g0 tI ~;i t" (xl 04) 8.52
(days) 75
(xl 05) 10.84
(days) 635
tm
III
(days) 710
(xl0 -5) 23.16
~EII
(xl0 -5) 18.15
5. Preliminary analytic model The second phase of the research concerns an initial classification of the viscous deformation processes which are only indicative of some of the cases observed (Garzonio 1995). This leads us to place them within the general creep law (Hudson et al. 1993 ): = r l & / d t + ~E (1), which can be attributed to simple linear visco-elastic behaviour (Kelvin-Voight) where:
~(t) = A tn (0
(2),
with n=l because the bending creep tests are less than 2/3 of the instantaneous failure stress (Garzonio et al. 1995). The following relations were taken into consideration for the analytical representation of the experimental tests, depending on subsequent useful estimates
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of the mechanical effects of the creep processes obtained with the damage analysis (Cristescu & Hunsche,1998; Sorace,1996; Kachanov, 1958). The equations are formulated in terms of total strain, since ~~ contain elastic, as well as, plastic deformation components: e(O= eo + oct~ primary creep (O<_t<_tI)
(3)
where: a and n are characteristic coefficients (see below ) ~(t) = eI + BcyV(t_tI) steady-state creep tI
(4)
where: B = rate modulus; v = viscosity exponent ( ~ = ~I for t = tI). The equations 3 and 4 were applied to the tertiary creep stage (t"
(5)
where: d is a scalar damage index, within the hypothesis of isotropic damage.
d--(~
k
(6)
where A and k are two characteristic damage coefficients for the material (Kachanov, 1958). Integrating between 0 and d: d = 1-(1 - t/tI") 1/k+l
(7)
where: t III = 1/k+l. (cy/A)"k. Introducing the coefficient r in place of (k+l) and after integration between t" and t we have: 8(t):
8II -t- bey~tlII/(1-v/r) .[(1-tII/tIII)(1-v/r) - (1-t/tIII) (1-v/r)]
(8)
This equation represents the coupling between creep damage and viscous-plasticity. Analytical curves well fit the experimental results. The creep model coefficients identified from the bending tests are the followings: (x (unit:[1/days]) and then oc (x10-5) = 0.305; n = 0.49, and r = 7.78. The v exponent is 3.28. We can observe that the general trends in the mechanical decay of strength are in total agreement with the results of the experimental tests (considering 0.35~) carried out on Carrara marble from the quarry. The strength decay values, in particular in the instantaneous tests relating to ancient deformed slabs are comparable to the values, but we have higher strain values and anomalous modulus of elasticity values (less than one hundred times). In other words, if the long term predictions are generally satisfactory and the deformation times are also confirmed by the census of the slabs which present deformations precisely in the first few years after they have been laid, the deformation and mechanical behaviour values in terms of long term strength present other anomalous components which are probably linked to the effects of thermal fatigue, humidity etc. and, as we have already said in previous paragraphs, stress history. In the cases studied the position seems to have hardly any influence at all.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
6. Conclusions The mechanical analysis of creep phenomena and the related numerical simulations show a very complex behaviour. Long term tests carried out on slabs taken from quarries show noticeable reductions in the creep fracture stress values after quite short testing periods (with a strength decay in the range of 65-70% with respect to the instantaneous one in 13-14 months). In reality, in the bending of ancient slabs or even in the more recent ones, the strength decay, both with respect to compression and bending, can be as great as 80%, but loads of this size would mean extremely long laboratory tests. However some tests are currently underway on a few samples. In addition, the deformations observed are even twice as great as the ones obtained in the laboratory and the loads are obviously those of their own weight. For this reason it is necessary to analyse the effects of environmental alterations, above all thermal ones, in relation to the results of the census and to study the anomalous viscous-plastic behaviour could be connected to residual stresses. Only in some cases the effects of the residual stress show clear anomalous deformations. However the experimental tests have highlighted a viscous-plastic behaviour which finds a good correspondence in the analytical simulation adopted for the phenomenological reproduction of creep response. This is also well suited to the time-delayed response of the ancient slabs, at least as a phenomenon trend. Finally the damage analysis developed with reference to the degradation tertiary phase showed clear non-linear accumulation effects. The strength decay creep model defined in this way can easily be applied to more general analyses of the long-term behaviour of marble slabs. Future research will therefore be based on long term triaxial tests and monitored tests carried out directly on full size slabs (i.e. the slab as it is used), with low loads.
This research has been carried out with the financial support of CNR, "National Commitee for the Science and Technology of Cultural Heritages", resp. C.A. Garzonio.
7. References Barsottelli M., Fratini F., Giorgetti G., Manganelli Del Fa C. & Molli G., 1998. Microfabric and alteration in Carrara marble: a preliminary study. Science and Technology for Cultural Heritage, 7 (2),115-126 Blasi C., Sorace S., Coli M., 1990. Decay of Mechanical properties of marble due to a long term small stress configuration. DIC 9/90, sezione Strutture, 1-17. Cavallucci F., Garzonio C.A., Giovannini P., Fratini F., Manganelli Del Fa C., 1997. Mechanical decay processes in lapideous materials (Carrara marbles): preliminary study of creep phenomena. Proc. 4th Int. Symp. on the Conservation of Monuments in the Mediterranean. Rhodes, 1, 91-100 Cristecu N., 1985. Visco-plastic Creep of Rocks around horizontal Tunnels. Int. J.Rock Mech. Min. Sci. & Geomech. Abstr. 6, 435-459. Cristecu N, Hunsche U., 1998. Time effects in rock mechanics. Wiley & Sons, 342 pp Cruden D.M., 1971. The form of the creep law for rock under uniaxial compression. Int. J.Rock Mech. Min. Sci. & Geomech. Abstr.8,105-126. Fakhimi A.A., Fairhurst C., 1994. A model for the time-dependent behaviour of rock. Int. J.Rock Mech. Min. Sci. & Geomech. Abstr.31, 117-126. Fossum A.F., 1977. Visco-plastic behaviour during the escavation phase of a salt cavity. Int. J. Num. Anal. Methods in Geom. 1, 45-55.
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Fratini F., Ceccherini S., Pecchioni E., Manganelli del F/t C., Scala A., Galletti G., 1991. Alterazioni del marmo e della serpentinite costituenti il rivestimento della facciata della Collegiata di Sant'Andrea in Empoli ( Firenze ). In " Atti del convegno di Studi Scienza e Beni Culturali. Le Pietre nell'Architettura: Struttura e Superfici". Bressanone, Giugno 2528,1991. 323-334. Garzonio C.A., 1995. Effects of Creep Phenomena in Stone Materials used in Historical Monuments. I n " Proceedings of 8 th Int. Congr. ISRM.", Tokyo, September 25-30,1995, 1, 291-294. Garzonio C.A., Fratini F.,Manganelli del F/t C., Giovannini P., Blasi C., 1995. Analysis of geomechanical decay phenomena of marbles employed in historical monuments in Tuscany. In " Proceeding of MJFR,2th International Conference". Vienna, April 10-14 1995,259-263. Garzonio C.A., 1998. Correlation between bending phenomena and the physical and mechanical decay and degradation of marble slabs. Proc. 8th Intern. IAEG Congress, 28892896. Hudson et. alii., 1993. Comprehensive Rock Engineering: Principles, Practice and Project. In " Comprehensive Rock Engineering". J.A. Hudson et al. Editors. Pergamon Press, Oxford. 1,228-241 Ito H., Sasajima S., 1987. A ten year creep experiment on small rock specimens. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. 24, 113-121. Kieslinger A., 1967. Residual Stress: Summary. Proc. 1 st. Congr. Int. Soc. Rock Mech.3,354-357. Logan J.M., Hastedt M., Lehnert D., Denton M., 1993. A case study of the properties of marble as building Veeneer. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. 30, 15311537. Ottosen N.S., 1986. Viscoelastic-viscoplastic formulas for analysis of cavities in rock salt. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. 23, 201-212 Sorace S., 1996. Long-term tensile and bending strength of natural building stones.Materials and Structures, 29,426-435. Winkler E.M., Singer P.C., 1972. Crystallization Pressure of Salts in Stone and Concrete. Geol. Soc. Am. Bull., 83,3509-3514. Winkler E. M., 1975. Natural Deformation of Rock and stone. In "Stone: Properties, Durability in Man's Environment" Springer Verlag, Wien-New York. 51-67. Winkler E.M., 1996. Properties of marble as building veneer. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr.33,2, 215-218. Voight B., 1966. Residual stresses in Rocks. Proc. 1 st Congr. Int. Soc. Rock Mech.,l, 45-50.
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99
GEOEGYPTOLOGY OF AI~MUZAWAKA TOMBS, DAKHLA OASES, EGYPT
Fatma M. Helmi* Conservation Department, Faculty of Archaeology, Cairo University, Giza, Cairo, Egypt.
Abstract
A1-Muzawaka cut-rock tombs are situated at Dakhla oases, Western desert in Egypt. They are belong to the Roman Period, 1a century. They represent a unique deterioration phenomenon declaring the effect of geological area and how the type of rocks play an important role in the destruction of tombs. There is a serious depression at the ceiling of the tombs, in addition to a fall of some mural paintings covering their walls and roofs. X-ray diffraction XRD, Infrared IR, thermal analyses DTA & TGA were carried out for rocks of the plateau and the mural paintings of Al-Muzawaka tombs. Also polarizing microscope PLM, and scanning electron microscope SEM attached with EDX examinations were determined. The data showed that rocks constituting the plateau of AI-Muzawaka tombs are shale interbeded with laminae of gypsum and anhydrite. XRD, DTA, and TGA analyses confirmed that the shale consists mainly of montmorillonite, in addition to a trace amount of kaolinite, which declare the great problem of swelling and shrinkage of shale due to absorption and loss of water. The problem is more sophisticated by the presence of gypsum and anhydrite as laminae between shale beds as a result of a large increase of anhydrite unit cell volume during transformation into gypsum. The data indicated that the blue pigment of the mural paintings of the tombs consists essentially of Egyptian blue, whereas the green one is Egyptian green, and the red pigment is red ochre. Stabilization of shale beds was carried out by applying some consolidating and inorganic materials to minimize the swelling phenomenon of A1-Muzawaka cut-rock tombs. It is found that styrene monomer and lime wash are the best ones to realize this purpose. Keywords: Geoarchaeology, El-Muzawaka tombs, Clay minerals swelling, Geology of Dakhla oases, Evaporites.
1. Introduction
AI-Muzawaka tombs are situated 35 km from the town Mut, capital of Dakhla oases, (200 km N.W. of Kharga oases), Western desert in Egypt. Dakhla oases occupy a shalefloored low land with dimensions 40 km WNW-ESE by 5-15 km N.S., centered on the town of Mut. The tombs are belong to the Roman Period 1st Century. The most important two tombs are: Pa-dy-Osir, means the gift of Osiris god who was the reign of this area, and Pady-Bastet, means gift of Bastet Goddess, his assistant. The tombs were known by ElMuzawaka due to their beautifiJl colored wall painting scenes, inspite of their small size. The scenes combined classical ancient Egyptian art and the graeco-Roman style. On the ceiling are the signs of the zodiac in a circle made by a dragon. These tombs were cured in rocks constituting the plateau which exposed directly to weathering agents. They have a serious deterioration phenomenon represented by a depression of their ceiling and a fall of some
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
mural paintings. The aim of the present work is to study the geoarchaeology of these Egyptian tombs i.e. GeoEgyptology", to investigate this unique deterioration phenomenon, to find out a solution for conservation and preservation of these tombs.
Fig. 1
Deterioration of Al-Muzawaka cut-rock tombs a) Depression at the ceiling b) Fall of mural paintings
2. Materials and methods Rock samples from the Plateau whereas E1-Muzawaka tombs were carved and their mural paintings were analyzed by XRD method. A Philips X-ray diffractometer unit PW/1710 was used. conditions of operation : Cukcx radiation ~, = 1.5418 A~ with Ni filter, 40 Kv, 35 mA, scanning speed 0.02~ Three oriented slides were prepared for the silt and clay fractions of the rock samples. The analyses were carried out as follows : one bulk sample without treatment, the 1st is dried in air, the 2nd is after exposure to glycerol vapour in a vacuum dessicator at 60~ for 2 hours, and the 3rd is after heating up to 550~ for 2 hours. The obtained X R patterns were compared with JCPDS files, and by using Pierce and Siegel method for semiquantitative analysis of minerals. The thermal analysis (DTA & TGA) was carried out for clay samples by means of s h i m a ~ DTA-50 H, and TGA-50 H. The powdered samples were heated by 10~ up to 1000~ with r as a reference material. The temperature, weight, change in wt., and the thermal behaviour of each mineral are recorded on the chart. Infrared analysis was carried out for cut-rock using Unicarn unit and Potassium bromide method. The clay samples were examined also by PLM and SEM using Leits PLM and Philips XL 30 SEM attached with EDX. The physical properties of the clay rock and its swelling ratio were determined. Stabilization of clay was made using styrene monomer with benzophenon as a catalyst, wacker H, Polymethyl methacrylate and Ca(OH)2 Sol.
3. Results 3.1. X-Ray diffraction XRD XRD data showed that the clay fraction of the plateau rock is composed of 93% montmorillonite Cao.2 (Al, Mg)2 ShO~0 (OH)2.n H20, card No. (13-135), Nao.3 (Al, Mg)2 Si4010 (OH)2.n H20, card No. (13-255), and 6% kaolinite A12Si2Os(On)4 card No. (14-164). This is in addition to the existence of gypsum CaSO4.2HzO (4-0046) and (21-0816), Anhydrite CaSO4 (6-0226), quartz ~-SiO2 (5-0490), and traces of halite NaC1 (5-0628), as
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shown in Fig. 2. An intense peak appears at 16.367A ~ which change to 15.265 A ~ after exposure to glycerol vapour. This peak disappears after heating to 550~ and is transformed into a broad peak at 15.171 A~ It was assigned to the (001) reflection peak of montmorillonite. The blue pigment consists of Egyptian blue Ca CuSi4Ol0 (12-129), green pigment constitutes of Egyptian green cupro-wollastonite CaSiO3 (27-088), brown one is the red ochre hematite ct-Fe203 (13.0534), the ground layer consists essentially of gypsum.
Fig. 2
X-ray diffraction p~ttems of cut-rocks of A1-Muzawaka tombs. a) bulk sample b) dried in air c) after exposure to glecyrol vapour, d) after heating at 550~
3.2. Thermal analysis DTA & TGA The data declare that the rock consists of montmorillonite, quartz, and gypsum as major minerals: kaolinite and boehmite a-AIO(OH) as minor ones. The total loss in wt. due to heating is 12.89%. Montmorillonite exhibits three peaks on DTA curve in the studied sample, the first is a large endothermic peak at low temperature 90~ related to a loss of adsorbed moisture. The second is a main endothermic peak at temperature 530 ~ due to a loss of hydroxyl group (OH), and the third is a very small exothermic reaction at temperature 853 ~ due to structural change, and crystallization of spinel (Mg A1204). Kaolinite yields two peaks on DTA curve, the 1st is a medium endothermic peak which is overlapped with the main peak of montmorillonite at temperature 530 ~ due to a loss of hydroxyl group, and the 2nd is a very small exothermic reaction at temperature 905 ~ due
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to structural change and crystallization of corandum ~-A1203. Gypsum gives a double endothermic peak, the 1st at 107 ~ due to a loss of one and half molecules of water to give plaster, and the 2nd at temperature 165 ~ related to a loss of half molecule of water to give anhydrite. Quartz exhibits a small kick at temperature 575 ~ due to transformation of txquartz to 13- quartz - Boehmite exhibits a small endothermic peak at temperature 415 ~ related to a loss of hydroxyl group as shown in Fig. 3
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3.3. Infrared analysis
The infrared spectra of the clay portion of the rock have absorption bands at the following wave numbers c,m"] ranges: 3600-3500, 3400, 1610, 1050-1010, 905,790, 520, 460. The absorption bands at 3600-3500, 3400, 1610 indicate the presence of OH group and H20. The bands at 1050-1010, 905, 790, 520, 460 declare the presence of silicate group. The infrared spectra of the white interlaminaes between clay have absorption bands at the following wave numbers cm "l" 3400, 2220, 2210, 1600, 1200-1100, 670,580, 500. The absorption bands at 3400 and 1600 indicate the existence of H20. The presence of bands at 1200, 1100, 670, 380 and 500 assure the existence of sulphate group.
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Fig. 4. Infrared spectra of cut-rocks of A1-Muz. tombs a) Clay b) Gypsum & Anhydrite
3.4. Polarizing microscope PLM Cut-rock of AI-Muzawaka tombs were examined under the polarized light and crossed nicols (CN). The slides showed the intrusions of gypsum and anhydrite with clay minerals and the presence of quartz and iron oxides as opaque minerals. Anhydrite is characterized by its strong interference ,colours under the (CN), whereas gypsum was identified through its V shape. See Fig. 5.
a
Fig. 5
b
Thin section of cut-rocks of A1-Muz. tombs showing a) gypsum & anhydrite interlaminae with clay minerals C.N. 40X b) showing anhydrite & gypsum 25 X C.N.
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3.5. Scanning electron microscope SEM SEM micrographs of the cut-rock tombs show clay and gypsum crystals as shown in Fig. 6. The dissolution of salts is very clearly seen as droplets on the surface of clay crystals. EDS analysis of the clay fraction declared the existence of Si, AI, Mg, K, and traces of Ca, Ti, Na, CI, which informed the presence of montmorillonite and traces of illite, halite, and iron oxides. (see Fig. 7 a, b). EDS analysis of the gypsum portion showed the existence of Ca, S as a major elements and traces of Si, A1, P, CI, Ti, Fe, which assured the existence of gypsum as a major and traces of halite, iron oxides & phosphates, (Fig.7 c&d).
Fig. 6
SEM of cut-rocks of AI-Muzawaka tombs showing; a) disintegration of clay minerals, b) dissolution of salts as droplets on the surface of clay, c) gypsum crystals.
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Fig. 7
105
EDX analysis of SEM examination showing; a) & b) constituting elements of the clay minerals, c & d) constituting elements of the gypsum.
3.6. Swelling and stabilization The free crystalline and osmotic swelling of the cut-rock of AI-Muzawaka tombs were determined. It is found that the free swelling is 95% whereas the osmotic swelling is 29% as shown in Fig. 8. After treatment with styrene monomer, wacker H, poymethyl methacrylate, and Ca(OH)E, it is found that styrene monomer and Ca(OH)E are the best ones for minimizing the swelling of this rock. The swelling is reduced by 30%. STRESS (Kg/Cm2) 35.00 30.oo 25.00 20.00
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Showing the osmotic swelling of the cut-rock of A1-Muzawaka tombs.
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4. Discussion X-ray diffraction, thermal analysis, infrared, petrographic study, and scanning electron microscope examination confirmed the existence of montmorillonite as a major component 93% and kaolinite 6% and traces of illite in the clay fraction of the cut-rock AI-Muzawaka tombs. This beside the presence of anhydrite and gypsum as interlaminae between the clay and shale strata and quartz, boehmite, halite as trace minerals. The data showed that the free crystalline swelling of the cut-rock tombs is 95%, whereas its osmotic swelling is 29%. The rock is weak, friable and very easily damaged either by handling or by absorption of water. This rock is belong to Dakhla formation of early Maastrichtian to early Paleocene age. This is a thick (230 m) sequence of finely stratified dark gypsiferous shale and siltstone as mentioned by (Brookes, 1987). It lies on Duwi formation of late companion age 90 m of sandy shales and silisified limestone. It is not capped by Tarwan formation (chalk limestone). So, the cut-rock of the tombs is exposed directly to weathering agents without any protection. Dakhla oases are one of the semi circular chain of structurally controlled depressions Kharga, Dakhla, Farafra and Bahariya around the southern and western borders of the Libyan plateau. Dakhla oases are underlain by sedimentary rocks of late-Cretaceous (cenomanian) to Eocene age which dip east of north at less than 5 degrees. There are NE trending anticlines, synclines and several normal faults throw up to 80 m which exerts important hydrogeological control (Brookes, 1987). Montmorillonite is a clay mineral belong to phyllosilicate subclass, whereas the basic structural feature is the presence of SiO4 tetrahedra linked by sharing three of the four oxygens, and thereby forming sheets with a Pseudohexagonal network. These sheets are variously referred to as the "silica layer" or the "silica sheet" or "the tetrahedral layer". This tetrahedral layer is combined with another sheet-like grouping of cations A1, Mg or iron. So the crystal structure of montmorillonite consists of 2 silica : 1 Alumina layers "Unit" and the spacing between layers exceeds than 8 A ~ Usually there is a substitution of A1 and Si by Mg & A1 respectively, which led to a net negative charge on the layers which is compensated by cations such as Ca2§ Na l§ K§ and H20 adsorbed between the layers. This is the reason for swelling phenomenon of clay minerals. There are two types of clay swelling processes: 1st : crystalline swelling "short range particle which is due to hydration of the exchangeable cations of the clay (Rodriguez-Navarro et al., 1997, Van Olphen, 1977). 2nd 9 Osmotic swelling "long-range particle interaction", which is due to "electrostatic forces", the large difference in the ion concentration close to the clay surface and the pore water. The latter swelling type largely depends on ionic concentration, type of the ion exchange, pH of water in the pores, and the type of the clay (Van Olphen, 1977). Crystalline swelling of clay is well known in expandable clay minerals such as montmorillonite, smectite and vermiculite. Therefore the presence of montmorillonite in the cut-rock tombs as essential component causes both crystalline and osmotic swelling phenomenon. The Problem is more complicated by the existence of anhydrite and gypsum minerals as interlaminae between clay in the rock. Transformation of anhydrite to gypsum and vice versa causes a great change in the volume of the crystal structure units which exceeds more than 60%. This will be an additive factor to the swelling character of montmorillonite leading to flaking, disintegration, depression of the ceiling of cut-rock tombs. The presence of Na in halite and K in illite-montmorillonite as proved by EDX, also play an important role by time in the swelling phenomenon, i.e., increase the osmotic swelling of the cut-rocks of the tombs. The high osmotic swelling of the studied
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rocks is not only due to the presence of montmorillonite-illite but also due to the existence of anhydrite and halite. To stabilize and reduce' the swelling capacity of clay, K and Na could be replaced with Ca which is less hydrated through cation exchange methods, Grim, 1962 used lime-wash to stabilize clay-rich soils. So, Ca from the Ca(OH)2 could replace K and Na or adsorbed on the clay surface. This will reduce both crystalline and osmotic swelling capacity of clays. Surfactants would be used also for reducing the swelling capacity as reported by Permien et al. (1995). They form hydrophobic coating on the clay surface. Wendler et al. (1996) succeeded to reduce the swelling capacity of clay-rich-tuff by using surfactants. In the present study, styrene and Ca(OH)2 minimize sufficiently the swelling of the cut-rock of tombs. Further work will be done for controlling the swelling capacity of the cut-rock of AIMuzawaka tombs which is the author's current research work.
5. Conclusions
The serious deterioration phenomenon of cut-rocks AI-Muzawaka tombs is due to the swelling of montmorillonite mineral which, is existed as a major in the clay layers and the transformation of anhydrite to gypsum and vise versa which are existed as interlaminaes between Clay. The rock is not capped with another formation, so it is exposed directly to the atmosphere, i.e., to humidity variation in temperature, led to swelling of clay and changes in the volume of crystal structure units of anhydrite and gypsum. Also, the presence of Na in halite and K in illite enhance the swelling capacity of the clay. Stabilization of the ceiling of the tombs could be carried out by using styrene and lime wash. This phenomenon declares the exciting field of geoarchaeology, i.e., the geological and geochemical interpretation of deterioration phenomena in the archaeological fields. In this study, the mineralogical composition of the rock is the factor of distortion of A1-Muzawaka tombs in Dakhla oases: a depression of the ceiling and a fall of mural paintings.
6. References
Brookes I.A., 1987. Quatemary Geology and Geomorphology of the Dakhla Oases Region SouthCentral Egypt, Report, 28-40. Grim R.E., 1962. Applied clay mineralogy. New York, McGraw-Hill. Madsen F.T. and Muller-Vonmoos M., 1989. The swelling behavior of clays - applied Clay Science, 4, 143-56. McEwan D.M.C. and Wilson J.J,, 1980. Interlayer and intercalation complexes of clay minerals. Crystal structures of clay minerals and their X-ray identification. Brindley & Brown London : Mineralogical Society, 197-248. Rodriguez-Navarro C., Hansen E., Sebastian E., and Ginell W.S., 1997. The role of clays in the decay of ancient Egyptian limestone sculptures. JAIC, 36, 151-63. Permien T., and Lagaly G., 1995. The rheological and colloidal properties of bentonite dispersions in the presence of organic compounds. Part 5. Bentonite and sodium montmorillonite and surfactants. Clays and clay minerals, 43,229-36. Van Olphen H., 1977. An introduction to the clay colloid chemistry. 2nd ed. N.Y: J. Wiley & Sons. Wendler E., Charola A., E., and Fitzner B., 1996. Easter island tuff: Laboratory studies for its consolidation, Proc. of the 8th International Congress, Berlin, J. Riederer, 1159-70.
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THERMAL STRESS AND WEATHERING OF CARRARA, PENTELIC AND EKEBERG MARBLE
UlfLindborg* and Robert C. Dunakin National Heritage Board, Box 5405, 114 84 Stockholm Sweden David J. Rowcliffe Department of Materials Science and Engineering, KTH, 100 44 Stockholm Sweden
Abstract This paper describes laboratory studies of the formation and growth of micro-cracks in marble. Swedish Ekeberg, Italian Carrara, and Greek Pentelic marbles have been studied using four point bending in both air and water environments at different loading rates. It has been shown that a water environment surrounding the tested marble bars led to decreases in apparent fracture toughness. Also, the apparent fracture toughness decreases with decreasing loading rate. The existence of a large process zone full of micro-cracks and crack branching, starting from a precut notch, is thought to reduce the fracture toughness value. The laboratory results give evidence of environmentally assisted slow crack growth along the grain boundaries. Thermal gradients and temperature fluctuations cause high stress, particularly in calcitic marbles like Carrara marble. A consequence for the preservation of sensitive objects is that large thermal fluctuations should be avoided, if possible. Keywords: Crack, Stone, Long term, Life, Marble, Deterioration, Fracture toughness 1. Introduction The weathering of marble appears to be rather different from the weathering of other stone materials. The sudden destruction of sculptures like the one at the Sanssouci Palace is an evidence that damage of marble to a large extent occurs in the interior of an object rather than mainly at the surface. Also the strange bending of calcitic marble panels, for instance on the facade of the Finlandia building in Helsinki and the Amoco house in Chicago, points at special weathering mechanisms. Weathering of marble is accompanied by the formation of microcracks in the interior, primarily in the boundaries between the mineral grains. This is evident from microscopic studies of cross sections taken from weathered sculptures. Microcracks form as a result of mechanical stresses. The question arises whether long-term mechanical stress in the stone material could be an important cause for deterioration besides, or in combination with, chemical dissolution and, possibly, microbiological activity. Conservation measures may very well have to be different if mechanical stress is the main problem rather than air pollution or damage from water. Mechanical stress may originate from mechanical loads and from variations in temperature and humidity. This article presents the latest findings of the Swedish group involved in the EU funded HERMES project which investigates the deterioration of marble due to many natural causes. In particular, the Swedish group considers the mechanical aspects of crack growth focusing especially on the stress intensity surrounding the crack tip. The research has been concentrated on creating crack growth in the laboratory to determine if this relates to the real situation with weathering. Figure 1 shows Carrara marble after about 140 years of weathering exposure to the elements. The picture shows intercrystalline fracture, which is a common
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effect of marble due to weathering. The sample is from a toe that broke off 1 of 17 statues mounted on the facade of the National Museum in Stockholm. The facade underwent extensive restoring during 1995-96/Bylund 1996/. One of the statues, the architect Tessin, was in such bad condition that a 1:1 replacement was commissioned to be carved and was just recently finished and mounted on the facade.
Figure 1. A SEM photomicrograph of grain boundary cracks in aged Carrara marble (80x).
2. Marble Properties The major difference among these three marbles is that both Pentelic and Carrara are calcitic while Ekeberg is a dolomitic marble. The Swedish marble contains magnesium that affects the mechanical and chemical properties of the marble. A simple comparison of the three was shown when the marbles were etched. Using a 2% Nital solution, Pentelic and Carrara etched quickly in about 10 seconds. Ekeberg required about 5 hours to obtain the same visible etching effect. After etching, another difference was that the calcitic marbles appear to show a higher twinning density. In addition, Pentelic has a visible second phase, quartz, randomly distributed throughout the calcitic grains. Figure 2 shows the Vickers microhardness of the three marbles. Again, Ekeberg is substantially different than the calcitic marbles. The Ekeberg hardness, measured at 100g, was 2.85 GPa compared to Carrara and Pentelic at 1.19 GPa and 1.05 GPa respectively. Figure 3 shows the average grain size of 30 samples. The average grain sizes range from 100 to 200~tm, Pentelic having the smallest and Ekeberg the largest.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figure 2. The Vickers microhardness of the three marbles. confidence level.
Figure 3. The average grain size of the three marbles. confidence level.
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The variances show the 95%
The variances show the 95%
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3. Slow Crack Growth Slow crack growth is a phenomenon that occurs in most materials, having different names such as crazing in polymers or stress corrosion cracking in metals, but the basic mechanism is similar. The combination of a stress and an aggressive environment leads to deterioration of the material at lower stresses than its fracture stress. The effect is an environmentally assisted failure of the material. In brittle materials, such as glass, ceramics, and minerals, the bonds at the tip of a crack are highly stressed. The distortion in these bonds is thought to cause them to be more chemically active and these bonds break preferentially. Environmentally assisted slow crack growth occurs so slowly that the crack tip can choose its path through the weak points of the material. The aggressive environment can be acid residue from rainfall, a product from a gypsum reaction, or even water. The stresses can either be externally applied or residual. Thermal stresses are caused by the varying orientations of the grains of the polycrystalline material and daily fluctuating temperatures. Ice crystals stuck in the crack can exert a tensile stress on the crack tip opening. 4. Sample Preparation and Testing Procedure Four-point bending was chosen to study the marble crack growth because of the advantage that only compressive loads are applied which simplifies sample preparation and the testing apparatus. However, despite an applied compression, both compression and tension arise in the sample due to the bending moment between the testing application points on opposite sides of the beam. Since cracks propagate from tensile stresses, it is simple to predict where the crack will grow in a given specimen. In addition, a notch (see below) was cut into the specimen to concentrate the stress to initiate the crack growth through the bar. The Single Edge Notched Beams (SENB), as shown in Figure 4, were prepared as follows. The as-delivered 50x50xYmm marble pieces were mounted with beeswax onto a steel plate. Y was 6, 8, or 10ram respectively for Ekeberg, Carrara, or Pentelic. The pieces were cut into approximately 50xl0xYmm beams with a diamond edged saw blade and then removed by melting the wax and remounted individually onto a base for the wire saw. Notches were then cut into each piece using a wire saw (with a 0.127ram wire) and a 3 parts silicon carbide:5 parts glycerine:l part water slurry. The approximate 2ram deep notches were cut halfway along and perpendicular to the length of the piece. After cutting the notches, the samples were removed from the base using a warm plate that melted the wax. Beeswax melts between 62-65~ and the warm plate was never heated higher than 100~ A paper towel wiped off the excess wax before the sample was thoroughly rinsed under running water to remove any remaining cutting slurry. In necessary cases, thread was also used to help remove the dried slurry from the notch. Afterwards, the samples were placed in alcohol to dissolve any extra wax and again wiped with a paper towel.
Figure 4. A schematic drawing of the SENB. The four-point bend testing was performed using an 8561 Instron Materials Testing machine with 8500 plus software and a simple LabView program recorded the load and position at a given time. The data points sent out from the Instron machine vary in voltage
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between 0-10V which are convertible to load and displacement values with scale factors. The data points were collected with a compilation time to about every 500ms/Dunakin 1999/. Ten samples of each marble were tested at the loading rates 10~-103mm/min in air and at 10-2-10-3mm/min in water. Each sample was measured after the test so that the distances ascertained were always around the crack path. The notch crack lengths were measured using an Olympus PMG3 optical microscope. These distances were used in calculating the corresponding stress intensity for slow crack propagation, the "apparent fracture toughness" of the marble, with the following equation derived from elastic analysis/Simpson 1974/.
L (bw )
w
w
w
w
Where P is the fracture load, [N] d is the distance between loading points, [m] b is the beam thickness, [m] a is the depth of starting notch, Ira], usually 2-3 mm w is the beam height, [m], usually about 10 mm The equation expresses the stress concentration at the tip of a crack, starting from a notch of length a. The polynomial in square brackets varies in fact only very slowly for moderate a/w values and may be set constant = 2.0 within a 5% error. The local stress at the crack tip increases in proportion to the square root of the crack length. 5. Results and Discussion Figures 5-6 show the apparent fracture toughness for the various loading rates and the two environments. It is evident that the apparent fracture toughness decreases with decreasing loading rate. The influence of water also decreases this KIC value for the marbles. Each point represents the average of 10 samples and the error bars show the 95% confidence level. There are two points that do not follow decreasing trend of apparent fracture toughness for decreasing stressing rate. Both of the points are Ekeberg marble: the 10 -2 mm/min point in air and the 10 .3 mm/min point in water. These two points also have the two largest confidence level spreads of all of the data Fracture toughness is normally considered as a material constant and gives a measure of how easily a material can initiate and propagate crack growth. It is normally measured in fast fracture, not in slow crack growth situations. The reduction in apparent fracture toughness in slow loading conditions is most likely due to the fact that subcritical crack growth occurred during loading. In all cases, the initial notch was considered as the critical notch length, which is standard practice for fracture toughness testing. It is very difficult to measure the actual crack length in these cases because of three reasons. The first is that it is unknown when the sample will break and what the actual crack length is at that point. This is due to the natural defects in the marble and that the maximum load is difficult to predict. The second is that the crack that propagates from the notch is not straight but meanders through the material making accurate measurement difficult. Thirdly, the crack that propagates is not actually one crack, but one main crack with branching subsidiary cracks as shown in Figure 7. These cracks fill a large area in front of the pre-cut notch, which is called the process zone. The actual size of the process zone is difficult to measure, but the shape is rounded with the widest part about halfway through the bar. Sometimes the size and shape is easily visible after the water tests because the part of the beam with the micro-cracks takes longer to dry after the sample has been removed from water.
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Figure 5. The apparent fracture toughness of the marble in air versus the decreasing loading rates.
Figure 6. The apparent fracture toughness of the marble in water versus the decreasing loading rates. It is also important to mention that Figure 7 shows mostly intercrystalline crack growth even though this Carrara sample was tested at 10lmm/min in air. At first glance, this picture looks similar to Figure 1 with the intercrystalline crack growth. The total test time, however, was about 20 seconds, which is dramatically shorter than 140 years! This result gives evidence for an environmental effect of marble crack growth in that the natural damage situation can be simulated in the laboratory. A major difference of the two examples is the stress level that caused them. The stress in the natural weathering case is much lower than in the laboratory. Due to this fact, the two damaging mechanisms could be entirely different, but if not, the main difference is in the amount of time needed to produce intercrystalline fracture.
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If this is the case, this four-point bending laboratory experiment may be an excellent method to investigate environmentally assisted slow crack growth in marble.
Figure 7. Intercrystalline crack growth and crack branching from the notch tip (on the right). The arrows demark the crack branching into subsidiary cracks.
Figure 8. Comparison load vs. time curves for soda-lime glass and Carrara marble. Both tests were performed at a stressing rate of 10 .3 mm/min in water. Figure 8 shows comparison load vs. time curves between soda-lime glass and Carrara marble. The glass curve shows the typical result of a brittle material: an increase in load until a catastrophic failure at a maximum load. The marble curve deviates from the constant increase in load and levels off to a sustained maximum load before decreasing. The decrease in load is controlled failure taking about 100 seconds instead of the instantaneous reduction as in glass. The growth of the microcracks within the process zone decreases the load. This is also a measure of a decrease of material stiffness. This curve for Carrara is fairly typical of all three types of marble in that the maximum of the curve is sustained for some time before the load reduction occurs. Research is currently investigating the timing of the origin of the growth of the microcracks. It is known, however, that the decrease in load corresponds to crack growth.
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Another observation worthy of note is that the maximum load decreases for decreasing stressing rates and with the addition of water as an environment. This corresponding reduction in strength and loading rate is typical of brittle material susceptible to environmentally assisted slow crack growth. Mechanical tests performed in the laboratory during prolonged periods suggest that natural stones deform in a manner similar to creep deformation in metals / Sorace 1996/. It is difficult to imagine a "true ", microscopic dislocation creep process in stone materials at room temperature, however, since the temperature for decomposition or melting is high. Is the macroscopic deformation caused by micro-cracks? The extreme anisotropy of the calcite crystals, as concerns thermal expansion as well as other physical properties, contribute to particularly high thermal stresses in calcitic marbles /Zezza 1985/. Increasing temperature in calcite crystals leads to expansion in the crystallographic c-direction but, abnormally, to contraction in perpendicular directions. Dolomite shows a more normal behaviour in that the thermal expansion is positive in all crystallographic directions. Thermal fluctuations lead to local mechanical stresses between grains, particularly in calcitic marble, even if all grains have the same temperature. The porosity is low in marbles at the onset of weathering which will make the accommodation of thermal expansion difficult. The presence of non-random preferred crystallographic orientation of the grains affects the build-up of thermal stress/Widhalm 1996/and also the shape of the grains has been suggested as a factor influencing marble deterioration / Weiss 1998/. Freezing may, of course, be an additional hazard in creating stress. 6. Implications for conservation Mechanical stress in marble objects arises chiefly from temperature changes. If thermal stresses are definitely proven to be the main reason for marble destruction, it is important to limit the thermal gradients between one side of the object and another. These temperature differences may create stresses on a macroscopic scale. Also, heating induces local microstresses even if the whole object is at the same temperature. If temperature fluctuations are reduced, there will in practise be a reduction also of thermal gradients and thus a reduction of macroscopic stress as well as local micro-stress. If possible, avoid exposure to direct sunshine in south directions and increase thermal conduction around the object to decrease the maximum temperatures. The tradition of sheltering sculptures in the winter with wooden constructions is beneficial in reducing the number of freeze-thaw cycles that the object encounters and thus in reducing weathering damage. 7. Conclusions The findings of the current research are that marble displays behaviour suggesting that it is susceptible to environmentally assisted slow crack growth. The cracks form and grow mainly in the grain boundaries. The stress intensity for crack growth, the apparent fracture toughness, decreases with decreasing loading rate and with the addition of water as the surrounding environment. The maximum applicable load of the marble also decreases due to these factors. A large process zone, originating at the pre-cut notch, contains micro-cracks that branch out from the primary crack and reduce the internal stresses of the marble. It is possible to simulate the appearance of naturally weathered marble with a short four-point bending test in the laboratory. Conservation practises should be directed towards reducing temperature fluctuations in a marble object. Calcitic marbles are believed to be more sensitive than dolomitic marbles to the creation of thermal stress and to cracking and shape changes caused by thermal stress.
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8. References Bylund, Ch., Osterlund, E. L6fvendahl, R., Marchner.......S., Petersen, M 1996. The state of deterioration of the Carrara marble sculptures in the facade of the National Museum of Fine Arts in Stockholm. Proc 8th Int Congress on Deterioration and Conservation of Stone. pp. 977-991.Berlin Dunakin, R., 1999 May. Mechanical Aspects of Weathering in Marble Crack Growth. A Master of Science Thesis, KTH, Stockholm Simpson, L.A., 1974. Use of the Notched-Beam Test for Evaluation of Fracture Energies of Ceramics. Journal of the American Ceramic Society, vol. 57, no. 4 Sorace,S., Long term tensile and bending strength of natural building stones. Materials and Structures, Vol 29, pp 426-435 Weiss,T., Siegesmund, S., Leiss,B., Oppermann,H. 1998. Microfabric of fresh and weathered marbles. Proc 9 th workshop EUROCARE EUROMARBLE,pp 15-30, Munich, Landesamt ftir Denkmalpflege Zezza, U., Massara, E.P., Massa,V., Venchiarutti,D 1985. Effect of temperature on intergranular decohesion of the marbles. 5 th Int. Congress on Deterioration and Conservation of Stone, pp. 131-140, Lausanne 9. Acknowledgement The authors would like to thank the support of the EU grant ENV4-CT98-0704 that funds HERMES.
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W E A T H E R I N G OF RUNESTONES IN A MILLENNIAN PERSPECTIVE
Rtmo L6fvendahl*, Helmer Gustavson & Bengt A. Lundberg National Heritage Board, Box ~5405 S E - 114 84 Stockholm
Abstract
There are few types of cultural objects, for which the natural weathering and deterioration can be followed during longer periods of time. The Scandinavian rune monuments make an exception, as some of them were documented already 400 years ago. The majority of these monuments was chiselled and erected during Viking age in the 1 lth century. Principally, when left alone, the monuments are altered by weathering of chemical, biological and physical nature. Through the centuries the chemical and biological weathering alter the surface by increasing the porosity after the dissolution of more easily weathered minerals such as calcite, biotite and anorthitic plagioclase (calcium-rich feldspar). This will facilitate material loss by physical processes such as freeze/thaw cycles and salt crystallization/dissolution. The weathering will thus increase strongly with time. Different bedrock types show different weathering rates. Isotropic siliceous rocks such as granite will be more resistant, while anisotropic rocks such as limestone and sandstone will degrade more rapidly. This pattern is illustrated in the present examination of 22 different runic monuments in Sweden. Many factors tend to disguise this general pattern, the most important being human interference. Key words: Sweden, runestone, Viking age, rock type, long-time weathering rate
1. Introduction
Runic monuments are a Scandinavian speciality (cf. Jansson 1987). They can be divided into three groups, namely: 9 Ancient runestones with the old futhark of 24 characters from AD 400-800. 9 Viking age runestones with the common futhark of 16 characters, mainly from the 11th century. 9 Medieval runic monuments, with characters corresponding to the latin alphabet, from the 12 th century and later. The older, pre-Viking age runestones are few and mostly found in the southem and western parts of Scandinavia. The Viking age runestones are numerous, concentrated in the eastern part of Sweden, in the Lake M~ilaren district. The Medieval runic monuments such as grave slabs, are distributed in southern and central Scandinavia. Our interest here is focused on the Viking age monuments, because they are most numerous and often consist of erected, standing stones. The runic inscriptions were chiselled out as a coil in the form of one or more serpents filled with runes. The message of the inscription is *Author, to whom correspondence should be addressed.
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usually memorizing deceased persons. The climax of runic inscriptions was the middle of the 11th century, roughly contemporaneous with the christianization of Scandinavia. Hence, Christian crosses were often chiselled centrally on the surface of the stone inside the coil. After the erection of these Viking age monuments, they were soon forgotten. Many were fragmentized and used in churches or other buildings during the Middle ages. A reasonable number survived in situ. Late in the 16th century, there was a revived interest in history and language in Scandinavia. The first pioneer retracing the runes and collecting information on them was Johannes Bureus (1568-1652), scholar and antiquarian. He and his assistants documented and described 663 runic inscriptions and copied Figure 1: Drawing of runestone U 287, Vik them with drawings (F-collection, Hammarby circa 1690 by J. Peringski61d now in the Royal Library, Stockholm). (from GOransson 1750). Note material loss These drawings not only pictured the down to the left and up to the right. runes and serpent coils, but also the stone surface and its damages (fig. 1). Documentation with drawings and descriptions was later repeated several times to the present day, not least in connection with publication of the runic monuments in Sweden and the other Nordic countries. Thus, it is possible to follow the progression of damage of rune-stones from the 17th century onwards. The stone material in the runic monuments varies with the region. They usually consist of Precambrian siliceous rocks, mostly granites and gneisses. Locally, other types dominate; on the islands of 01and and Gotland they consist of limestone (cf. Brate & S6derberg 1900-06) and in the province of G/~strikland and bordering areas of Jotnian metasandstone (Jansson 1981).
2. The present study The precarious situation for the runic inscriptions called for a study of damages. The major considerations directing the choice of monuments for the examination were: 9 The monuments show damages. 9 The monuments represent different types- erected stones, boulders and outcrops. 9 Different types of bedrock are represented. 9 The monuments are dispersed geographically and climatologically.
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The inventory consisted of photodocumentation of each object 2-3 times, accompanied by a damage documentation in the field. After the study had started, it became evident that quantification of the damage at different documentation times would be possible, i.e. it was obvious that the timing and number of earlier documentations were important. Thus, a thorough documentation in site of state and damage was made. The damages were defined, following a classification developed for building stone (L6fvendahl et al. 1994). This examination includes 22 runic monuments (fig. 2), consisting of 17 erected stones, 2 boulder carvings, 2 outcrop carvings and 1 carving on a building. Of the 17 erected stones, only 5 have remained in situ, while 7 were broken and 7 were or had been built into buildings or other constructions. Of the 22 monuments, 7 consist of gneiss and 5 each of granite, metasandstone/quartzite and limestone respectively (tab. 1). Earlier documentation back to the 17th century with description of the runes, their status and Figure 2: Areal distribution of the 22 studied accompanying drawings, or dorunic monuments. Numbering according to cumentation in the form of late tab. 1. 19th century or later photographs, was evaluated. The damages at each occasion were marked by hand on a recent black and white photo. Different colours were used to quantify the damage progression between the different times of documentation. Further, the status of the runes was estimated, divided into four categories- intact runes, damaged and readable, damaged and unreadable and lost runes. The number of punctuation marks between words was also noted. Thus, we could quantify the damage of the runes and their substrate.
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Table 1: Data on the 22 examined runic monuments. Num- Runest. Locality Rock Year of Number Intact * ber number type manufac, ofrunes runes,% 2 DR 264 Vismarl6v Gneiss 1025 37 27 6 Sm 101 N~ivelsj0 Gneiss 1050 89 81 7 Vg 190 M~nstadskulle Gneiss 1050 36 83 12 SO 56 Fyrby Gneiss 1050 94 91 19 U 513 Rimbo ch. Gneiss 1050 84 86 21 Hs 10 H~ilsingtuna ch. Gneiss 1075 300 38 22 Hs 21 J~ittendal ch. Gneiss 1050 87 41 9 Og136 R0kch. Granite 875 757 91 Granite 13 U 58 Riksby 1075 54 65 Granite 14 U 11 Hovg~den 1075 106 74 Granite 16 U 287 Vik 1075 76 83 Granite 18 U 455 N~isby 1050 78 100 1 DR 345 Simris ch. Quartzite 1050 73 74 Jotnian sst. 1050 105 84 11 SO 14 Ggtsingech. Str~ingn~is ch. Jotnian sst. 1050 15 SO 278 29 55 Jotnian sst. 1050 17 U 296 SkS.nelach. 50 76 Jotnian sst. 1040 112 89 20 U 1149 Fler~ing Limestone 1050 3 O1 18 Segerstad 58 59 Limestone 1050 125 43 4 O1 37 Lerkaka Limestone 1300 27 100 5 G104:C Lye ch. Limestone 1500 8 G $5 St. Hoburga 5 60 Limestone 1050 10 Vg 55 K/~llbyhs 77 84 * Percentage of intact runes at the latest documentation in 1995 or 1996
3. Results
We have grouped the runic monuments according to material type, i.e. gneiss, granite, metasandstone and limestone. The results are summarized in tab. 1. In fig. 3 the percenage - mean value for respective rock type - of intact runes at the latest documentation time (1995 or 1996) is given. The regression lines show similar patterns for the different rock types. The time between the making of the monument in the 1 lth century (later for two of the limestones) and the first reliable documentation time, the progression of damage of runes and material is much slower than between the first and the latest documentation time, although the later period is always shorter. This means that the alteration is initially relatively slow. When the continuous, slow chemical weathering has operated for some centuries, it reaches a critical moment when the deterioration increases strongly (figs. 3 and 4). There are certainly many interfering factors; the major one being human interference i.e. breaking the stones to fit into buildings, mainly churches. It is interesting to compare the different rock types. Fig. 3 indicates that granite, metasandstone and limestone deteriorate slower than gneiss. This is certainly at variance with our expectations; siliceous Precambrian gneiss is generally more resistent to weathering than most nonsiliceous rock types such as limestone. However, most of the examined gneiss monuments have been broken by humans, and are thus far from representative for
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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natural weathering. This also indicates that the studied material is not ideal for the intended purpose. It will, however, not alter the general picture of accelerating weathering. We have also observed that the increase in weathering of granite with time is smaller than that of the other rock types. The reason why the sedimentary rocks are more vulnerable is their anisotropy. They often tend to flake along their bedding; the stones can be split into several thin slabs. This fact makes many of the sedimentary stones to weather strongly in the long run. The damage development of individual stones with time is also of interest. The granites are the least influenced by human interference. Hence, these have been plotted in fig. 4. All reliable documentations are included in this diagram. On one of these stones (U 455) all runes are preserved undamaged. On the most weathered one (U 58), 1/3 of all runes are damaged. We can also note that during some shorter periods (decades) the damage is negligible, during others the deterioration is rapid (large slope). This is a consequence of the episodic nature of physical weathering. The overall pattern during a millennium is initially more or less continuous chemical (and biological) weathering weakening the surface. This slow continuous process is in course of time interrupted by episodic and extensive physical weathering resulting in discrete material loss (erosion).
4. Conclusions The present study shows that chronological century-long studies of stone weathering are feasible and necessary to define the total deterioration. Especially the physical processes can only be estimated after long periods of time. More or less continuous chemical dissolution and biological influence are in time interrupted by episodes of physical material loss, giving a steep decay curve. All types of rock show this pattern, although the rates differ strongly. In order to prolong the survival of a stone object, it is important to establish when the physical weathering becomes the major decay factor. When, or still better before, this process starts, the environment of the object must be improved or the object will have to be moved to more harmless surroundings.
5. Acknowledgement We thank Stig Englund, Visby for the construction of fig. 2.
6. References Brate, E. & S~derberg, S., 1900-06. The runic inscriptions of r (In Swedish). Books 1-2. Stockholm. Jansson, S.B.F., 1981. The runic inscriptions of G~strikland (In Swedish). Book 1. Stockholm. Jansson, S.B.F., 1987. Runes in Sweden. Stockholm. GOransson, J., 1750. Bautil. Stockholm (In Swedish; in the Royal Library, Stockholm). L6fvendahl, R., Andersson, T., Aberg, G. & Lundberg, B.A., 1994. Swedish building stones and damage atlas (In Swedish with English summary). Central Board of National Antiquities (now National Heritage Board), Stockholm.
125
PETROPHYSICAL ANALYSIS OF CATHEDRAL OF BURGOS, SPAIN
THE
SCULPTURES
DECAY AT
THE
Rafael Fort Gonz~dez* Institute of Economic Geology (CSIC-UCM), Madrid, Spain 1VPConcepci6n Lopez de Azcona Institute of Economic Geology (CSIC-UCM), Madrid, Spain Francisco Mingarro Martin Department of Petrology, Institute of Economic Geology (CSIC- UCM), Madrid, Spain
Abstract The statues located on the facade known as Fachada de Santa Maria in the Cathedral of Burgos are sculpted on a variety of limestone (biosparite) extracted from the Hontoria quarries. The petrophysical characteristics of the statues portraying the Infantes, added to the monument in the mid-14th century, are slightly different than those of the Kings, dating from the 19th century. The limestone used for the Infantes is finer-grained (has smaller pores) than that used for the Kings. The limestone used to sculpt the Infantes is more homogeneous, uniform and dense than that used for the Kings, which is more fragile and breakable. On account of their petrophysical characteristics and of the durability assays carried out in a climatic chamber, we can conclude that the Kings statues are more sensitive to decay processes derived from freeze-thaw cycles whereas the Infantes owe their decay mainly to wetting-drying variations. The state of preservation the Kings statues was assessed using ultrasound prospecting techniques and the following results were obtained: 14 % of the damage was found to correspond to cracking, 30 % to fissures and 30 % decay due to a loss of cohesiveness. In the Infantes, 10% of the decay corresponded to fissures and 55 % to degradation owing to dissolution. Keywords: Decay, limestone, Hontoria, durability, hydric behavior, ultrasounds, heritage
1. Historical and architectural issues On July, 20, 1221, King Fernando III and Bishop Mauricio lay the first stone of the Cathedral of Burgos. Sculptures were placed in the monument around 1350. 8 sculptures portraying unidentified members of the Royal Family (known as the Infantes) were placed on the third section of the Santa Maria facade (fig. 1). A great number of sculptures was also placed on the archivolts of the first section. On the four buttresses that divide the three entrance doors to the cathedral there are 16 additional sculptures. Between 1753 and 1768, after remodeling of the atrium carried out in 1663, many of these statues were removed in order to prevent their collapsing, and in 1788 they were declared "in decay due to the passage of time", broken and unrecognizable (Orcajo, 1856). All imagery was removed from
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Figure 1" The eight statues of the Infantes on the third section of the Santa Maria facade the first section in 1790, the fagades were refurbished and all sculptures disappeared from the archivolts and jambs. The four statues currently seen in the Cathedral were placed there in 1805 in place of the former 16 ones that, according to some scholars, were sculpted expressly for the Cathedral. The two statues located on the buttress on the let~-hand side portray King Femando III and Bishop Mauricio, whereas the other two, on the right-hand side buttress, represent King Alonso VI and Bishop Asterio. We refer to these four statues as the Kings. 2- Atmospheric characteristics There is any weather station in the Cathedral itself. In consequence, the only existing data for the last 30 years was obtained from the air base of Villafranca, 7-km northeast from the monument. The main weather conditions in the area are summarized in Table 1. Thermal winter in Burgos is long, as temperatures remain below 10~ for six months; summer is mild, with temperatures above 17~ during July and August. The minimum temperature is -22~ with strong thermal oscillations. Absolute values for these oscillations have reached 39.0 ~ in January, but there are yearly thermal oscillations of up to 60~
Tablel Climatic data in Burgos (Station of Villafranca) 9,9 ~ Annual average rainfall Annual average temperature Rainfall (maximum) 15,5 ~ Average temperature (max.) Rainfall (minimum) 4,3 ~ Average temperature (min.) Annual rainfall 38,0 ~ (Ag.) Absolute temperature .(max) Absolute temperature (min.) -22 ~ (Jan.) Maximum rainfall (24 h) Minimum rainfall (24 h) 39.0 ~ Thermal Oscillation (maxi.) 31,4~ (April) Diary relative humidity Thermal Oscillation (min.) Directions winds Wind velocity SW; W ,,
9
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Average rainfall in a year is of 47.7 mm, spread out over the year between May, with 65.0 mm, and August, with 24.8 mm. This abundant rainfall, added on to the effect of river Arlanz6n, which flows nearby, makes relative humidity in the area very high with an average of 88 % at 7 a.m. As a result of these conditions the climate in Burgos can be defined as COLD and HUMID, with some oceanic influence. According to Kreppen's categories, the climate in Burgos could be classified as humid mesothermic oceanic weather. The statues in the Santa Mafia facade, that faces west and is subject to strong westernly and southwesternly winds that coincide with the most abundant rainfall, suffer greatly from these extreme atmospheric conditions There is little information available regarding atmospheric pollution, but its effects are noticeable on the stone, that suffers sulfation, dissolution and soiling revealing the existence of sulfuric oxides, acid rain and suspension particles.
3. Method In order to classify the materials and monitor changes, ten 53-mm diameter and 200-mm long samples were collected. These samples were then subdivided into various test specimens of different morphology according to the type of assays to be done. Assays were carried out following the RILEM (1980) and the CNR-ICR NORMAL (1981-86) guidelines. The following assays were carried out: petrographical analysis under polarized light microscopy, X-ray diffraction, chemical analysis, hydric behavior (water sorption and desorption, capillarity, water steam permeability, contact angle, density, chromatic parameters, mercury porosimetry, ultrasound propagation velocity). Durability tests (carried out in a climatic chamber) included 24 freeze-thaw cycles and 20 wetting-drying cycles.
4. Petrological characteristics 4.1 Petrography The statues are cast in white limestone with some yellow hues. Fossil traces can be found in the stone as well as wide pores filled partly by microcrystalline calcite. The oldest statues, Infantes, made of medium-grain stone, are more homogeneous, while the Kings are made of coarse grained heterogranular stone with abundant fossil traces. These materials were extracted from the Hontoria quarries located on calcareous formations from the Cretaceous (Turonian), located south of Burgos. Under the microscope, the limestone shows abundant bivalves skeletons with lesser amount of echinodermata, bryozoans, foraminifers, corals and micritic peloids. The Kings are also made with fossiliferous limestones. Fossil remains in these limestones are smaller in the Infantes are richer in peloids. The skeletons are cemented with sintaxial sparite, butther whereas poikilotopic sparite is pervasive in peloidal-rich parts of the rocks. The stone of the sculptures can be classified, according to its composition, as biosparite and, according to its texture, as grainstone. This indicates the absence of micrite matrix.
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4.2 C h e m i c a l analysis
The average results obtained from the Hontoria limestone samples are shown in table 2. These results indicate that we are dealing with a very pure and homogeneous stone, made up of calcite, with only 1.5 % of impurities. Dolomite, orthose and albite constitute these impurities. Table2: Chemical anab,sis of the SiO2 A 1 2 0 3 Fe203 0,33 0,17 0,09 +0,15 +0,17 +0,06
stones from Hontoria CaO MgO Na20 55,27 0,14 0,02 +0,50 +0,02 +0,01
K20 0,04 +0,02
SO4-0,02 +0,01
LOI 43,57 +0,37
4.3 P e t r o p h y s i c a l characteristics
The chromatic characteristics of the surface and internal areas of the statues are shown in table 3. A high degree of lightness is characteristic for both types of sculpture, although lightness is slightly more pronounced in the Infantes. As is reflected in their chromatic indexes, the Kings statues tend to show yellower hues, while the Infantes are whiter. Chromatic differences between internal and external areas of the statues indicate that a protective treatment was applied to the stone in the past. Table3: Chromatic parameters of the stone L
KINGS
Surface Internal
~
83.65 86.76
a*
b*
C*
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2.72 1.99
14.31 10.19
14.57 10.38
4.43 23.86
23.28 16.51
,
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Infantes and the Kings is high, with average values of 23.3
Figure 2: Pore size distribution
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between both types of stone. The main differences are found for pores bigger than 5 ~tm (macroporosity), where a modal gap between 10-20 ~tm was found for the Infantes, and 3040 ~tm for the Kings. Table4: Physical properties of the sculpture Saturation (%) PorOsity accessible to water (%) Real density (Kg-m3) Bulk density (Kg-m-3) Compacity Ultrasonic velocity (m-s1) Classification (A.S.T.M.) Coefficient Of Capilarity (Kg~m2.s-1) Coefficient of water sorption (%) Water vapor permeability (g.m2.hl) ' Porosity by Intrusion Hg (%) (200-0.006 :m) Microporosity (%) Macroporosity (%) Mean size of the pores (~tm) Specific surface area (200-0.006 ~tm) m2.g
....
,
....
INFANTES KINGS 7.42 9.50 16.9 20.44 2,703 2,708 2.252 2,159 0.83 0.79 2,648 2,408 Medium-low Low 0.0533 0.1215 4.59 6.21 9.34 12.39 20.20 23.30 10.50 9.80 9.70 13.5 1.4 1.3 0.24 0.30
4.3.1 Mechanical properties Both types of statues have a similar density. The Infantes have slightly higher values as the stone is finer grained. In general, density is higher for the inside of the stone than for the outside as a result of the changes the stone has undergone. Bulk values are higher for the Kings than for the Infantes by 93 Kg-m3. This difference indicates that the Infantes have undergone more acute dissolution processes and that the Kings have a higher recrystallization rate. The bulk-real density ratio reveals that the stone with which the Kings statues are made is more compact. The ultrasonic waves propagation velocity values reveal low mechanical quality, lower for the Infantes than for the Kings. In determining the dynamic modulus, the values obtained are also quite low, which highlights the structural differences between both types of stone. According to the ASTM C-568 guidelines, and taking the dynamic modulus and the stone density into account, the mechanical quality of the materials can be described as medium to low for the Kings and low for the Infantes 4.3.2- Hydric behaviour On account of the atmospheric conditions to which the sculptures are subject, their resistance to decay processes is very directly linked to their hydric behaviour. The main results obtained are shown on table 4. It should be noted that the amount of water the limestone used for the Infantes absorbs is higher than the amount of water the Kings absorbs. Another important characteristic of the Kings statues is that they absorb more
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water (% saturation) into their internal zones, which might indicate that a protective treatment was applied in the past reducing open porosity on the surface of the stone. Although sorption kinematics is similar for both types of material, some differences are observed owing to the textural variations (fig. 3). Hence, sorption takes place at a faster rate for the Infantes. Aiter the first 30 minutes, the Infantes have already taken in an 57 % of the water necessary to reach saturation levels, while the Kings have only taken in 54.31%. Aiter this, sorption becomes very slow and after, 7 days, the Infantes have taken in up to 70.2 % and the Kings 66,12 %.
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up to the first 1.77 hours. Absorption gradually slows down reaching the end of the assay 6.25 hours later. After this period of time, the Infantes have taken in 7.57 Kg-m-2, while the Kings have only taken in 5.21 Kg-m2. The Infantes have smaller pores, so they can absorb more water faster than the Kings can.
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5. Durability of materials Durability assays, carried out in a climatic chamber, indicate that the Infantes sculptures are more sensitive to wetting-drying cycles, with 0.3 % weightloss after 20 cycles. On the other hand, these statues are more resistant to freeze-thaw processes, where petrophysical parameters hardly suffer any variations. The Kings statues suffer an average weight loss of 0.1% as a result of freezing with a significant increase in open porosity (2.66 %), and, most notably, a decrease in ultrasound wave propagation velocity (410 m.sl). This alteration indicates that a decay process has already started in these materials.
6. Statue decay In view of the compositional and petrophysical characteristics of the sculpting materials, as well as the location of the statues in an aggressive environment, it can be deduced that the stone has decayed dramatically. Already the carving of the statues results in the opening of innumerable chiseling microfissures conducive to water intake. Water absorbed increases its volume with temperature variations and acts as a wedge. This is especially so when it is transformed into
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ice. As this happens within a closed system, volume increases by 9.5 % and at -30 ~ C it generates a pressure of up to 2,100 Kg.cm -2 The statue portraying Bishop Asterio had a severed head, and the one representing King Fernando was also split at the waist. Both statues were restored and held together using natural resin (quite possibly pine). They were then reassembled using a 3 cm-wide wooden pole. Later, the wood expanded with humidity and caused severe fissures. All the statues were attached from the shoulders to the walls with iron clamps, and secured with pressed lead. The Infantes were similarly secured onto their base. As iron oxidizes and becomes hydroxide (Goethita), it increases its volume by 291%. As a result cracking and fissuring occur. Acid water loaded with carbonic, sulfuric and nitric acid, etc. penetrates cracks and fissures and drips down the surface of the sculpture. Limestone undergoes dissolution processes when the pH level of water dripping on its surface or its porous system is below 7.8. These dissolution processes are more noticeable for small-grain minerals (micrites) than for larger-grained stones (sparites). This effects a differential dissolution that causes the sculpted ornamentation to lose definition. Soot and smoke, responsible for the soiling of statues, also carry metal oxides (iron, vanadium...) that catalyze sulfur oxides, giving way to sulfuric acid which, in turn, produces sulphations in areas protected from rainwater. This transformation of calcite into gypsum (sulfation) induces an increase in volume of 83.24 % that adulterates the superficial morphology and leads to the appearance of blisters. After these detach from the surface of the stone, the whole process is ready to start again. This leads, on the one hand, to the stone pulverizing and, on the other, to the formation of blemishes that wears off the ornamental surface of the sculptures. In the case of the lnfantes, this is mainly due to processes of dissolution, and in the case of the kings to sulphation mechanisms (CaSO4. 21-120), dissolution and blisters detaching.
7. Ultrasound propagation prospecting Ultrasound propagation prospecting allowed us to determine the advanced state of decay the stone (fig. 6). The Kings statues have an average velocity of 2642~1087 m.s1. The average velocity for the Infantes is of 2408a:384 m.s"~. Standard deviation for the Kings is high, which indicates greater heterogeneity of material as a result of fissures and cracks. The statistical Figure 6: Decay of the sculpture Bishop Asterio. Lines continuous: cracking, Lines discontinuous: fissuring. Points: loss of material.
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analysis of measurements reflects three types of differential groups that coincide with areas with cracks, fissures and decay. 14 % of readings correspond to cracks, with values bdow 1,500 m.s-1. Ultrasound propagation velocity in zones with fissures ranges between 1,500 m.s~ and 2,400m.s'l,which correspond to 30 % of readings. Decayed zones where there has been a loss of material or of material consistency represent another 30 % with ultrasound propagation velocity values ranging between 2,400 m . s "1 and 3,000 m.s"1. Of all the Kings statues the decay process is more advance~ in those portraying Fernando HI and Bishop Asterio (fig. 6). They register the lowest ultrasound propagation velocity values (528 msl). On the other hand, the sculpture portraying King Alonso reaches higher velocity, in places above 6,000 m . s "i. The Infantes have a lower average ultrasound velocity than the Kings do. Standard deviation is of 384m.s ~, which reflects a more homogeneous state of preservation. Statistical analysis does not reveal any internal cracking, although some fissures can be observed. Fissure percentage corresponds to nearly 10 ~ of readings, but 55 ~ of the readings reveal a significant decay, with ultrasound propagation velocity values below 2,300 m.s ~. Maximum velocity recorded is of 3.700 m.s ~, below values recorded for the Kings. All Infantes statues are in a similar state of preservation.
8.Conclusions All sculptures were carved on the same type of stone (Hontoria limestone). Differences between the two types of statues, Kings and Infantes can be found in the textural contrast that their petrophysical properties reveal. These differences are owed to the different quarry sections the stones were extracted from and to the different carving periods. The Kings are more water permeable than the Infantes. They are, therefore, more fragile. According to the ASTM standards, the limestone used for sculpting the Kings is of medium to low quality, whereas the limestone used for the Infantes is of low quality. The Kings are more sensitive to freeze-thaw cycles, while the Infantes are more sensitive to wetting-drying variations. The Kings have suffered more decay as a result of cracking and sulphation mechanisms, while the Infantes owe their decay mainly to processes of dissolution. Ultrasound velocity prospection indicates that the Kings statues have severe cracks and fissures, while the lnfantes have suffered more homogeneous decay as dissolution affects the whole of the sculptures. Acknowledgements We are grateful to the National Heritage Conservation Department of Junta de Castilla y Le6n for their assistance in carrying out this study. References CNR-ICR 1981, 1985,1994. Raccomandazioni NORMAL. 7/81, 21/85, 43/93. RILEM, 1980. Recommended test to measure the deterioration of stone and to assess the effectiveness of treatment methods. Comisission 25 PEM. Mat6riaux et Constructions, 13,75: 175-253. Orcajo P., 1856. Historia de la Catedral de Burgos. Facsimil 1997 Fundacion para el apoyo de la Cultura. Amigos de la Catedral.
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DURABILITY OF SANDSTONES IN SERBIAN ANCIENT MONASTERIES AND MODERN BUILDINGS Vesna B. Matovic* Faculty of Mining and Geology, Belgrade, YU Dragan J. Milovanovic Faculty of Mining and Geology, Belgrade, YU Slobodan M. Joksimovic The Highway Institute, Belgrade, YU
Abstract The arkose sandstones of the Lower Miocene age, from the village Bele Vode and the Red Permian sandstones from the river Grza were used extensively as building stones since medieval time. These rocks were built in the Lazarica Church, in the Monastery Manasija as well as in some new buildings in Belgrade, for example in the St. Marco Church and for the riverbank pillars of Branko's bridge. The sandstone blocks display different stages and shapes of decay. The most important damage types on the Lazarica church and the Manasija monastery are honeycomb weathering and granular disintegration, while on new buildings dominated shapes are exfoliation, spalling, blistering, peeling and granular disaggregation. In this paper causes of decay of the mentioned sandstones based on the results of their petrography and physical properties, exposed to different environment conditions are determined and presented. Keywords: sandstones, decay, cause, honeycomb weathering, exfoliation.
1. Introduction Sandstones are traditional building material in Serbia. Various objects were built of it due to its colour, easy exploatation and superficial working. Sandstones marked our medieval parochial architecture of Raska and Morava shool, but also were built in facades of some important objects in Belgrade between two World War, or later. Ancient monasteries were built with different styles and a plenty of architectural elements and sculptural decorations. In the sense of their historical and artistic value, they are orginal and eternal cultural treassures of Serbian architectural heritage. Their architecture reveal the sensitivity and creative imagination of people of that period. Sandstones used for the most of churches orginated from two localities: Bele Vode (20 km NW of Krusevac) and Red Permian sandstones from the river Grza (20 km east of Paracin). Majority of ancient monasteries from 14th and 15th century were built from the former or by bricks and sandstones together. In the aim to protect the view of ancient churches, facades of some new ortodox buildings were also built from the same sandstones. Within contemporary objects sandstone were mainly used as stone panel in facades of big and important buildings.
Faculty of Mining and Geology, Djusina 7, 11000Belgrade, Yugoslavia
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For this investigation were chosen two ancient objects (the Church Lazarica and the Monastery Manasija) situated in rural area and two new buildings (the St. Marco church and the riverbank pillars of Branko's bridge) situated in urban area (fig. 1). Shapes of decay are the most intensive and obvious on mentioned objects, that enabled correlation between the influence of environmental pollution on velocity and types of degradation.
2. History and architecture of objects 2.1. The church Lazarica The church Lazarica was built as court church from 1374. to 1377. in Krusevac (fig.l). The architectural conception of this church derived from the Morava architecture school. Its ground plan is in the form of reduced trefoil while the dome from the central part is supported by the pilasters projecting from the walls. It was built as alternate courses of sandstone ashalrs (from Bele Vode quarries) while brick are connected with courses of mortar. Their facades are divided by cordon cornices and colonnetes into zones and richly ornamented with sculptured stonework with plastic ceramic details and chequered panels (fig. 2A). Bas-releifs decoration in a form of cable moulding and palmete, are located around single and biforium windows, on archivoltes, on rosettes, arcade friezes and on the arches above the windows of the dome and on tower above the nartex (Janicijevic,1998). 2.2. The monastery Manasija It was built as well as its surrounding buildings between 1407. and 1418. about 20 km north from Paracin (fig. 1). The whole complex was encircled by massive wall with towers. The entrance is in a form of barrel arch, and the ground plan of the church is in a form of developed trefoil with central cube and four small cupolas (fig. 2B). Its facades are covered with sandstones ashlars, and have relatively little plastic decoration: only cordon cornice by arcade friezes supported by the console and small capitals of colonnetes above apses. The massive wall of monastery fortification was built of limestone blocks held by courses of mortar. Vaults and intrados of the main entrance and windows on the other buildings are of travertine while flanks and edges of towers are of sandstone achlars. The facade of the church was re-built during 70 th years of this century, when some parts of massive wall and towers were redesigned partly. 2.3. The St. Marco church The St. Marco church in Belgrade was built from 1931. to 1939., and represent the first building of Byzantine style made of ferro-concrete in our country. Roofs are also of ferroconcrete and covered with copper, while walls are of cement-mortar.
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The church facades were made of the sandstone from Bele Vode and of Red Permian sandstones. Plinth with outflows, out of walls are facing with granitic rocks. Ground plan of the church is in the form of trefoil with belfry on the parvis (fig. 2C). Central doma is like eight limb tambour, while small cupolas are located outside of its central part. The porch of the church as well as the other part of facade are without representative sculpture's decor that is typical for parochial architecture. Triforiums on sidewise facades, are also without plastic decoration. Four castels with small cupolas, are connected by arcades.
2.4. Riverbank pillars of the Branko' s bridge The Branko's bridge is an important utilitarian object connecting the old part of the Belgrade on the right bank of the river Sava with the new part of the city, situated on its left bank (fig. 1). Riverbank pillars of the former suspension bridge (destroyed during Second World War) anchor the terminal parts of the bridge construction.The old, decorated pillars represent an extraordinary union of modem engineering and old architecture. Some of them are still used for communication, as stairways (fig. 2D). Pillars built from 1931. to 1933. are made of ferro-concrete while stone paneling were made of Bele Vode sandstones. In the aim of estetic appearance, the most of the surface blocks (upper part of facades) were made by bushhamer and in a form of rock-faced quoin (lower part of facades). They were constructed in Romano-Byzantine style adorned by numerous architectural elements and sculpture's decorations. Friezes with small blind arcades are located above three limb arcades with New-Byzantine capitals. Upper parts of facades are ornamented by cornices, rosettes and consoles (Kadijevic, 1996).
3. Analytical techniques 30 samples of fresh sandstones from the four quaries of Bele Vode and 22 samples of Red Permian sandstones from abandoned quaries of Grza were used for petrographic study. Sampling were done according to their similarity with sandstones built in objects. Number of analyzed samples depended on the type of sandstone, its position on the objects, type and degree of decay. Nine samples were taken from Lazarica from the most damaged elements all over facades;, two samples from arch of windows, two samples from lower part of southem facade and two samples were taken from the main entrance the monastery Manasija; two samples were taken from rossetes of the riverbank pillars of Branko" bridge; two samples from lowest part of western facade were taken from the St. Marco church.
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From the sandstone surfaces with well developed efflorescence were taken samples for identification salts using the method of X-ray diffraction.
4. Petrography and physical properties of sandstones Sandstones of Bele Vode" The Lower Miocene sandstones are exposed in Krusevac area (vilagge Kukljina and Bele Vode) and represent shallow lacustrine sediments. They cover an area of aproximately 5 km 2. They are transgressive to crystalline schists and their boundaries with neighbouring geological units are tectonic. Some blocks slide downward within the sandstone mass along dm-m faults (Petkovic et al., 1973). The lower part of sandstone is massive while the upper is layered and banked. The thickness of productive horizon is from 3.5 m to 7 m. Sandstones are gray to yellow-brown, sometimes pink or red coloured. They are massive to well bedded, often with cavities (aproximately 0.5 mm in diametar) and coarse- to finegrained (grain size vary from 0.2 to 1 ram). Sandstones are composed of partly rounded to angular slightly sorted clasts of quartz (50-60 vol. %), K-feldspar (orthoclase and microcline, to 15 % vol.), plagioclase (to 5 vol. %) muscovite (up to 10 vol. %) and fragments of rocks, mainly metamorphic (to 10 vol. %). Contact-pore filling of yellow and red varieties of sandstones is ferrous-calcitic cement, while in gray varieties (subordinated) is siliceous-clay. The cement content is about 10 vol. %. Correlation among physical and mineralogic-petrographical characteristics is the base for determination the decay causes. The obtained data for bulk density (1880-2420 kg/m 3) and density (1940-2720 kg/m3), absolute porosity (7.4-27.9 %) and water absorption (2.43-9.16 %) considered sandstones of Bele Vode as medium heavy, high porous rocks with moderate to high water absorption. Red Permian sandstones are generated in lacustrine basins and river vallies by fast erosion with simultaneously transgression. They built horizon of 50-700 m thick (well bedded to banked with rare lamination and cross-bedings) over thrusted Cretaceous limestones. Permian sandstones are of characteristic red colour with occasional occurences of colorless and gray-colored parts. Within the sandstones interbeds of conglomerates, coarse-grained arkoses, siltstone,clay, rarely dolomite and limestone occur (Veselinovic et al., 1964). Red Permian sandstones are mainly arkoses, rarely quartz sandstones. They are composed of subrounded to angular, slightly sorted clasts of quartz (50-70 vol. %), feldspar (orthoclase and plagioclase, up to 25 vol. %). Micas (biotite and muscovite) made about 2 % of rock. Fragments of rocks are determined as: volcanic rocks, cherts, quartzites and schists (5 vol. %). Cement in red sandstones occur (ferruginous and carbonaceous or siliceous matter) as thiny coating on detritial grains or as pore filling. Physical properties suggest on uniform quality of Red Permian sandstones. They are heavy (2630-2692 kg/m3), extremely to moderate porous (4.9-11.2 %) rocks with slightly to moderate water absorption (1.53-3.06 %). 5. Enviromental conditions The velocity of sandstone decay is influenced by climate and atmospheric pollution. Ancient buildings in the area of Krusevac are exposed to more sevear climate than those in Belgrade (tab. 1).
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Table 1. Summary of climatic data from 1961 to 1990.
Climatic data Yearly average temperature average maximume (monthly) average minimum (monthly) Frost days per year (min T< 0~ Ice days per year (max T< 0~ Month with more frost days Number of sunny days
Yearly average precipitation The rainiest month The driest month
Relative humidity -yearly average Average of maximume (monthly) Average of minimume (monthly)
Belgrade
Krusevac
11.9~ July (21.7~ January (0.4~ 61.5 17.6 January (7.9) 2047.6 h 684.5 mm June (90.4 mm) October (40.3 mm) 69.0% December (79.8%) April (61.5 %)
10.8~ July (20.6~ January (-0.3~ 92.3 17.6 January (8.2) 1790.4 h 650.4 m June (86.0 mm) October (38.9) 76.8 % December (86.0%) April (70.7 %)
The climatic data of the Meteorology National Institute
Generally, all buildings are exposed to the medium continental climate with wet and hot summers, and a long cold, winters, often with fogs and snow. Average yearly precipitation, number of the frost-icy days and the value of high relative humidity during winter, undoubtely accelerate the degradation of sandstones. The Manasija monastery and the Lazarica church are located in rural area while riverbank pillars of the Branko's bridge and the St. Marco church are located in urbane area with intensive traffic, especially trucks (tab. 2). Table 2.Pollutant concentrations data for the period 1991 to 1999. Concentrations (~g/m 3) SO2 Yearly average 25.6 Max. yearly average 174 Number of days over limit 3 Sanitary limit for: 802- 150 (~tg/m3); smoke- 50 (~g/m 3)
Smoke 39.2 280.7 74
Yearly average poluttant concentrations are relatively low but maximum yearly average for individual years (1991, 1992) were appreciably over limit in Belgrade,. The main part of SO2 in the air changes pH of rain. These acidic rains attack on building facades. During last ten years, contents of SO2 and smoke show descending trend even their lower content are also pernicious for stone. 6. Types of decay Observing of the sandstone elements enabled identification of the different destruction contours: granular disintegration, contour scalling, honeycomb weathering, exfoliation, spaling, efflorescences and black crust. The most important damage types on the Lazarica church and some part of the Manasija monastery are honeycomb weathering, granular disaggregation along with contour scalling,
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while on the St. Marco church and on the Riverbank pillars dominated shapes followed by granular disintegration are :exfoliation, spaling, flaking, and blistering. 6.1. The Lazarica church Honeycomb weathering appears on elements of the eastward side of facade within the zone of ground water capillary rise and on the elements directly exsposed to rain, blowing wind and sun, in a shape of irregular cellular depressions or as alveoles to 20cm in size (fig. 3A). Granular disaggregation occurs on the most of sandstone blocks. The scale and depth of decay are influenced by water, sun and moisture. On southern and eastern facades it occupied shallow zone (0.5-2cm in depth) of elements that are overlaping on plinth with projecting part and on external part of cordon cornices also, while contour scalling were noted on sandstone block of church portal on it's western fasade. After destroying of an outer layer (about 2-5cm thick) independently from the bedding , newopened surface consisting of sand, spalls and flakes are more sensitive for further decay. On the western and northern facades, granular disaggregation along with contour scaling produced the crumbling zones (to 10cm in depth) leading to important losses of volume,and to a rounding of comers and edges (fig. 3B). These blocks have scars and sanding surface with pieces that have a tendency to fall easy due to weak cohesion between grains. Becouse of that some part of cordon cornices already have lost its architectural shape (fig. 3C). Generally, granular disaggregation and contour scalling take place in the areas where rain and snow can be collected during winter time. 6.2. The Manasija monastery Honeycomb weathering and granular disintegration developed on the main entrance of the Manasija monastery. Honeycomb weathering, associated with granular disintegration, occurs on sandstone blocks in flanks of arc, and also in intrados of portal, on sheltered blocks exposed to moisture (from the wall above) and fast drying by current air. Differential weathering with forming alveoles (size of 5cm) is controlled by bedding of sandstones (fig. 3D,E). Granular disintegration with rounding, occurs on sandstone blocks directly exposed to rain and sun. This type of damage develope along mortar joints where water can easy move towards outer edges and towards the inner parts of block. Deep granular disintegration is evident on the sandstone block in towers of monastery wall. These elements are directly exposed to rain, sun, wind erosion and their surface are eroded up to 15 cm in depth. The church facade in monastery complex was re-built during 70 th years thus the sandstones block are relatively sound. On its northern facade, efflorescence occurs along mortar joints (fig. 3F). Unfavourable effect of efflorescences is aesthetic and for now it hasn't destroying influence on sandstons blocks. The X-ray difraction data of salt samples from surface sandstones, show the presence of gipsum, thenardite and calcite. 6.3. The St. Marco church The sandstone elements from the church facade were observed and established on deep destruction in some sandstone elements especially on its southern and on the eastward side. According to height of built elements deep destruction appears on those located in the lower part of facade.
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Figure 3. Decay types: Lazadca church- A- honeycomb weathering; B,C- contour scaling. erosion and granular disaggregation; Monastery Manasija - D, E- honeycomb weathering; F- efflorescences; St. Marco church - G-granular disintegration; H-chipping and spalling; I- exfoliation; Riverbank pillars of Bmnko's bridge - j_ erosion and granular disintegration K- exfoliation, L- contour scaling and granular disintegration.
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The first bed from red sandstones is over laping on plinth with projecting part (thickness about 15cm), where during winter time and rain months rain and snow are collecting causing the deep granular disintegration (up to 10cm in depth, fig. 3G). Peeling develop on shaltered surface sandstones of the first bed (in arcades), as superficial loosening of 0.5-3mm thick sheets which tend to blister and fall off. New opened surface underwent chipping and granular desintegration besides clear prominence of more durable cement-mortar ofjoints (fig. 3H). Dominant shape of decay on the southern and on the eastward side of facade is exfoliation. The primary surface of the most elements was completely destroyed and sheets are separating from the stone element perpendicular to layering. Hard surface crusts are forming in the upper parts of facades, especially in the southern side beside triforiums, and after breaking of hardened surface the sheets (up to 3 mm thick) separate and exfoliation and granular disintegration continue (fig. 3 I). Efflorescence occurs on the sandstone blocks in arcade's portch and it is composed of mirabilite and thenardite. ,
6.4. The riverbank pillars of the Branko's bridge The riverbank pillars are heterogeneous structure. The sandstone blocks, depending from type of sandstones, kind of superficial working, location, and distance from the river, microclimate factors (temperature, wind, sun, rain), atmospheric pollution, show different type of degradation: exfoliation, case hardening, granular disintegration, contour scaling, spalling and peeling. Besides efflorescence, black crust occurs too (Matovic, 1999). Deep erosion and granular disintegration occupied all sandstone blocks in lower part of the facades. Blowing wind, influence of rain, ground water etc. caused physical and chemical decomposition, why some elements lost superficial shapes, rock-faced quion, with rarely preserved primary parts (fig. 3J). Deep granular diisintegration, contour scaling, peeling caused that the most of architectural elements lost their own shape (rossete, capitals and base of colonnas). Black crust occur on sheltered sandstone blocks, untouchable for rain. Practicles of dust, smoke and other atmospheric pollution are easy deposited on blocks with rock-faced quion surface. During dry months, in arcade's porches efflorescence of thenardite and thermonatrite occur in the upper zone of ground moisture rising. It acceleratied peeling, chipping and later exfoliation of sandstone blocks.
7. Conclusion The Bele Vode sandstones were used for the most of ancient churches while in the last 80 th years it was combined with Red Permian sandstones as stone panel for facades in Belgrade. Sandstones are strongly disintegrated on all examined objects. Type and velocity of sandstone decay depend of: mineral composition, texture, physical properties, atmospheric influence (including water and temperature changes as the most important), atmospheric pollution, their position in objects (exposed to sun and wind, or not), type of mortar joints, as well as of way of superficial working. Used sandstones are medium to coarse-grained arkoses with contact and pore filling cement (carbonaceous, ferruginous or clay-siliceous). According to porosity and water absorption, i.e. the most important properties for durability, they are high porous, able to absorb and keep water.
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Even almost all of surfaces of the original sandstone elements are completely destroyed the difference between intensity and morphology of sandstone decay in urbane or rural places is evident. On the ancient objects dominant types of decay present almost 600 years are honeycomb weathering and contour scalling followed by granular disintagration. The shape and intensity of decay imply on chemical-physical influence of water and frost as the main causes. Sandstone porosity enable penetration of rain, as well as of ground water. Majority of secondary calcite in sandstone surfaces resulted from the atmospheric influence or from lime-mortar, as well as from cement material within sandstone. Dissolved material were unequally deposited parallelly to evaporate surfaces or parts with faster evaporation, during sunny or windy period (Winkler, 1994) The sandstone structure prevailing lamination and more intensive diferential dissolution, enable accelerated honeycomb weathering. Granular disintegration and contour scalling are evident in the lower part of facades, i.e. on elements permanently exposed to moisture (ground water), as well as on elements where rain and snow could be longer kept (cordon cornices, rossetes, window frame). Chemical dissolution as well as mechanical disintegration of sandstones are accelerated and more intensive in rural than in urbane areas, due to climate, especially due to the number of frosty and icy days ( cyclic freezing-thawing) and to the amount of precipitation. On new objects sandstones have been deeply destroyed after 60 years by exfoliation, case hardening, spaling followed by granular disintegration. The main cause of these decay types is physical activity of water and frost, that enables further chemical dissolution As sandstones are high porous rocks, water absorbed to a certain depth enable freezing and thawing of the outer oarts of block. Repeated cycles, even daily formed weak surface zones. At the beginning it is hardened crust that soon loose contact with the sound parts of rock, thus its blistering and breaking, perpendicular to layering caused exfoliation and spaling. The influence of water activity and of position in objects on decay degree is especially notable on riverbank pillars on the Branko's bridge, whose base parts are next to river, and thus permanently water saturated. Due to weak current air all elements within the zone of capillary rise present in arcades sufered scalling and grain disintegration. Same or similar situation included elements of the upper fagade, that are built just under steel bridge construction. They are ptotected from the rain influence, but due to bad sluice system from the bridge floor, water and mud continualy flow over their surfaces, producing intensive erosion of the sandstone surfaces. The influence of the building type and superficial working on type and velocity od decay is visible on the same object. Perpendicular to layering, exfoliation and scalling occur on all surfaces, whereas fractures could be seen on blocks cut normal to layering. Bushhammering enable degradation of sandstone elements and produce an mechanical, degraded layer with high porosity and sensitivity on water and frost, as well as microfractures that enable intensive penetration of water in surface parts of sandstone, causing weakly cohesion and stronger influence of frost. Sandstone blocks with rock face of the riverbank pillars, sheltered from the rain influence, are covered with black crust due to deposition of smoke and dust from traffic, common in an urbane area. There are no traces of granular disintegration or other types of alteration beneath these black surfaces. Efflorescence, the common occurrence on objects in urbane area, developed during dry periods on surfaces that are sheltered from the rain, i.e. inside or over the zone of capillary rise, where following salt could be deposited: halite, thenardite/mirabilite (Na2SO4 with, or without of water). Majority of sodium originated from soil, but some parts could be from
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streets salted during winter, whereas sulfate ($04) come from atmosphere. Over the zone of capillary rise, the main salt is gypsum and calcium for it is from mortar or sandstone. Efflorescence usually follows and accelerates exfoliation. Mentioned processes of sandstone decay can't be interrupted or stopped, but it is necessary to slow down them by properly sanation. That will enable many valuable monuments of our cultural heritage to be saved and last for further generation. References
Article reference: Kadijevic A., 1996. istorija i arhitektura zamunskog mosta Kralja Aleksandra I Karadjordjevica, Pinus, Zapisi 4, 4-10. Matovic V., 1999. Decomposition of stone in the riverbank pillars of Branko's bridge. Heritage, Insitute for the protection of cultural monuments of Belgrade, II,107-114. Petkovic K., Vukasinovic M., Smiljanic R., 1973. Krusevacki zemljotres 1. oktobra 1972. i geolosko seizmotehnicke karakteristike terena krusevackog tercijarnog basena i njegovog oboda. Geol. an. Balk. polu., knj. XXXVIII, Beograd, 371-467. Veselinovic M., Antonijevic I., Milosakovic R., Micic I., Krstic B., Ciculic M., Divljan M., Maslarevic Lj.,1970. Tumac za list Boljevac 1:100000, Savezni geoloski zavod, Beograd 1-73. Book references: Janicijevic J., 1998. Kulturna riznica Srbije, IDEA, Beograd, 321-323. Winkler E. M., 1994: Stone i arcitecture, Properties, Durability. Springer-Verlag, New York.
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SANDSTONE ARCHITECTURAL DETERIORATION IN PETRA, JORDAN Thomas R. Paradise, Ph.D. Associate Professor of Geography & Environmental Studies University of Hawaii, Hilo, Hawaii USA 96720 email: [email protected]
Abstract Petra, Jordan was an extensively occupied city during the Nabataean and Roman eras (300 BCE to 500 CE). Incorporating Hellenistic, Assyrian, Egyptian and Roman architectural motifs and techniques, the Nabataeans created an architecture style that was both derivative and unique. However stable and 'eternal' is this spectacular setting, its architecture is deteriorating from natural and induced influences. Comprehensive networks of surface baseline measurements were made in Al-Khazneh; Petra's most celebrated structure, the Roman Theater, and the Anjur Quarry. Since this architecture was hewn, it is an ideal environmental laboratory for the study of weathering features, causes and rates they have not been moved, altered or obscured since their construction 2,000 years ago, and their lithologic composition is relatively consistent and well-documented. This study investigated intrinsic (lithology) and extrinsic (climate, sunlight, human impact) influences on sandstone deterioration. It was found that iron and silica constituents in the sandstone matrix decreased overall weatherability, while calcium constituents increased deterioration in areas that exceed 5500 megajoules/meter/year (a typical southern aspect in arid regions). In fact, when iron matrix concentrations exceeded 4% (by weight), original stonemason dressing marks were still clearly evident, indicating a nearly unweathered state in 2,000 years. Insolation (sunlight) was found to have its greatest deteriorating effect on southwestern and southeastern aspects, indicating that sunlight is most effective in stone weathering when in tandem with increased wetting/drying and/or heating/cooling cycles. Visitors to Petra have increased from 100,000 (1990) to 350,000 (1998), and anthrogenic deterioration is accelerating. Tourist groups entering the chamber of Al-Khazneh caused interior relative humidity to increase from 20~ to 50%. While, surface recession from visitor touching, leaning and rubbing has receded as much as 40mm in less than 10 years. A 4 by 3 meter wall area has lost sandstone volume of approximately one half meter of sandstone in 100 years from 0.5 to 2m above the floor indicating surface recession from human contact. Keywords: sandstone deterioration, Petra, Nabataean Architecture, weathering 1. Introduction The ruined city of Petra lies hidden in a deep valley surrounded by steep, impassable sandstone walls and winding, earthquake-defined gorges in the arid expanse of Jordan's great southern desert. However, it is the spectacular architecture rather than its beautiful setting that has drawn international attention and wonder. Although its structures and archaeological evidence indicate occupation in the Petra area since 7,000 BCE, it was its Nabataean occupants and Roman neighbors that gave Petra notoriety then and now. These * Author to whom correspondence should be addressed.
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residents worked the valley walls into simple and elaborately carved tombs and structures, sculpted directly into the reddish-brown and yellowish sandstone cliffs, many exceeding fiity meters in height. Since then, however unique and precise their construction, natural and unnatural influences have been effective in deteriorating this architecture. Prior weathering studies have separated weathering influences into two distinctive categories: those affected by the characteristics of the stone itself or intrinsic effects (i.e. lithologic constituents, fractures), and those affected by external influences or extrinsic effects (i.e. climate, human contact). The decay of Petra's sandstone architecture can be similarly identified as those surface features related to variability in rock composition and/or caused by running water, human touch, etc. Previous research has emphasized the importance of intrinsic agents like rock composition and integrity, but recent research indicates that extrinsic influences like climate and human contact (tourism) are also important. This report addresses recent studies in Petra, Jordan that are attempting to answer these questions of sandstone weathering causes, effects and rates and possible solutions they might yield. Weathering studies for sandstone architecture in arid environments are relatively rare. Early observations on stone and architectural deterioration in the Near East and their oiten unusual features were made by Herodotus (c.450BCE), Strabo (c.CE10), Pliny (c.CE50), J.L. Stephens (c. 1830) and R.F. Burton (c. 1850), however it isn't until the 20th Century that we begin to see the conceptual development of weathering studies (Paradise 1995). Bryan (1922, 1928) and Blackwelder (1929) discussed many of the processes responsible for weathering. These were some of the first Western works that addressed sandstone weathering processes and not just the descriptions of weathering features (i.e tafoni). Later research in arid regions established important relationships between weathering and various influences including lichen overgrowth (i.e. Jackson & Keller 1970, Jones et al. 1980, Paradise 1997), case hardening (i.e. Conca & Rossman 1982), permeability (i.e Pfluger 1995), tafoni development (i.e. Mustoe 1983), salt (i.e. Smith & McGreevy 1988, Young 1987), insolation and moisture availability (i.e. Robinson & Williams 1992, Paradise 1995, 1998). These studies indicate that sandstone weathers two ways. Since sandstone is made of sandy clasts in a binding matrix, either the clast fractures or dissolves to fall out, or the matrix fractures or dissolves to release the clast. These weathering types represent the processes of disaggregation that produce loose sand as the by-product of deterioration - - the source of many of the sand dunes throughout the Near East.
2. Methodology Historical architecture and monuments represent under-utilized resources for the investigation into weathering rates and influences. Limestone and marble tombstones have been used for weathering analysis since Geikie's work (1880) in Scottish cemeteries. Marble and limestone weathering research using structures and objects has been studied by Rahn (1971), Hoke (1978), Meierding (1981), Klein (1984), Dragovich (1986), Neil (1989), and Trudgill (1989). Granite weathering and architecture was studied by Winkler (1965), Amoroso and Fassina (1983), and Smith and Magee (1990). While other rock types used in construction such as slate, arkose (Matthias 1967) and calcarenite (Spencer 1981) have also been studied and discussed. These studies used similar techniques whereby the known relative or absolute date of the
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structure (or objects) enabled the researcher to determine the change due to weathering since its creation or construction. Basically, it is this difference between the original and contemporary surfaces that explain the causes and relationships of the influences affecting stone surfaces. The difference between the current weathered surface and the original Roman surface represents how much sandstone has receded from weathering and erosion over 2,000 years. Since many of these previous works were conducted in Europe, Australia, and the U.S. friable sandstones are not as frequently used as the more resistant and accessible stone building materials such as granite, limestone or marble. This is why sandstone is an often under-studied building material, potentially valuable for weathering studies in arid regions where its use is common because its intrinsic weatherability is decreased due to reduced precipitation which decreases overall weathering rates (Paradise 1995). 3. The Roman Theater: weathering and lithology An extensive study was conducted on the Roman Theater of Petra (Paradise 1999, 1995a, b), a huge arena that may have seated up to 10,000 persons. The sandstone Theater was carved during the first century CE according to the recommendations of the great Roman engineer, Marcus Pollio Vitruvius m the highest Roman engineering and construction standards of the period. These early requirements for theater and building construction were so standardized that the level of the original surfaces can be estimated from contemporary weathered surfaces. Five hundred locations were examined in the Theater for intrinsic influences like variations in rock composition and particle size; and extrinsic effects like sunlight angle, lichen coverage, slope, and surface temperature. Important relationships were found. First, it was discovered that sandstone deterioration is accelerated by sunlight (where temperatures exceed 50~ and the sandstone contains high amounts of calcium carbonate: CaCO3), and when the sandstone sand grains are spaced far apart (high matrix-to-clast ratio). These are often observable influences since calcium-rich and/or high-matrix sandstones are often softer and more friable than the darker-colored, iron-rich ones. Second, other relationships were found where natural effects decreased weathering. It was discovered that iron oxides (Fe203, FeO2) and silica (SiO2) in the sandstone matrix (the binding agent that holds the sand grains together in the rock) dramatically decreased weathering. These findings were so sound that original Roman stonemason tool marks were obvious atop iron-rich sandstone while large weathered cavities had developed on the rock areas that were iron-poor. In fact, statistical analysis (r~) found that the iron and silica constituency of the sandstone matrix explained for 50% of all deterioration in the Roman Theater.
Statistical Correlations (<0.01) between Lithologic Constituents and Surface Recession(r) Surface Surface Surface Surface Surface
recession to density (g/cm3) recession to iron (%) recession to silica (%) recession to matrix (%) recession to calcium (%)
-0.845 (n=14), -0.645 (n=202), -0.635 (n=202) -0.845 (n=14),-0.531 (n=202), -0.170 (n=264) -0.845 (n=14), 0.862 (n=14), 0.805 (n=202) 0.712 (n=202), 0.660 (n=202), 0.614 (n=264) 0.658 (n=202), 0.611 (n=202), 0.504 (n=264)
The Roman Theater study not only recognized important weathering influences, it also established weathering rates for Petra sandstone; ranging from 15-70 millimeters per
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millennia on horizontal surfaces and 10-20 mm/millennia on vertical surfaces. In addition, this study established a previously unknown hierarchy of weathering processes responsible for sandstone decay. Principle component statistical analysis (PCA) was used to explain the relative importance of the various agents deteriorating sandstone in an arid environment like Petra. It was found that general rock composition was the most important single influence (25%), followed by the effects of iron concentrations (17%), and climatic influences like sunlight and moisture (12%) in affecting rock-architecture decay. These findings emphasize the importance of lithology in understanding and predicting stone decay rates, specifically in Petra and generally in arid regions. Moreover, such a hierarchy is vital in grasping the comparative controls on sandstone deterioration and the possible conservation priorities. Finally, a sad comment on the condition of the Roman Theater must be made. When the Theater was first examined for this study in 1990, at least 15-20% of the Theater displayed original stonemason dressing marks. However, recently (1999) these marks are disappearing at a faster rate, especially on horizontal surfaces affected by visitor contact (foottread). Currently only 5-10% of the Theater still exhibits stone dressing - - an indication that sandstone weathering of the Theater is accelerating. Since this change in the rate of decay cannot be attributed to intrinsic changes, nor a change in climate (climatic
change during this period has been minimal), it must be attributed to changes in
tourism, such as increased foot-tread in tandem with new footwear. Also, this accelerated surface recession is especially evident in the areas near the orchestra, praecincterae and itinerae; parts of the Theater most commonly visited by tourists to Petra. As more visitors tromp throughout Petra, however sensitive they may be in their interaction with monuments and landscape, new soft, gripping shoe soles increase the relative friction between the visitors' feet and the sandstone, increasing the gripping and tipping action from walking. Therefore, visitor-accelerated weathering in Petra will only decrease when tourism decreases, shoe soles become less durable, and/or visitor access is restricted. Theater access could be limited to the orchestra and praecincterae (concentric walkways), with minimal access given to the main theater since the common practice of jumping between seatbacks drastically increases surface deterioration and wear.
4. The Quarry of Anjur: weathering and aspect Many studies since Blackwelder (1933) have indicated that sunlight, if not a direct cause of weathering, may be a significant influence on stone weathering. Roth (1965) confirmed Griggs (1936) work, but emphasized the importance of sunlight as an overall weathering agent. Later, Smith (1977) established that rock (limestone) temperatures vary greatly with time of year and aspect; a direct influence of insolation. Research followed that explained a number of interesting relationships between insolation and accelerated weathering due to albedo and conductivity (Kerr et al. 1984), salt and relative humidity (Sperling & Cooke 1985), and increased heating-cooling cycles (Jenkins & Smith 1990).
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More specifically, studies have examined topography, aspect and moisture availability as surrogates for insolation-induced weathering. Sancho & Benito (1990) discussed weathering features in Spain; Robinson & Williams (1989, 1992) explained surface morphology (polygons, skins, gnammas) in France and Morocco; and Paradise and Yin (1993) addressed gnamma or solutions pit development, size and shape in Georgia, USA. These studies have explained the importance of aspect, heating-cooling cycles, and moisture availability in the acceleration of surface recession, and/or weathering feature development, reinforcing the notion that the Sun is important in the acceleration of weathering. Since the effect of sunlight as a major weathering agent had been somewhat abandoned in research since the 1930s, another study was conducted to attain a better understanding of the effect of sunlight on weathering - - an obvious effect on Petra's architecture. The sandstone surfaces of the quarry at Anjur were studied since many of its quarried surfaces face different directions, therefore making them ideal for observing the effects of sunlight on stone deterioration. The Nabataeans prepared these quarry surfaces by chiseling them into distinctive herringbone patterns (Shaer 1997), a style not used by Romans stonemasons. These dressed faces were chosen because their surfaces were carved at the same time (50BCE to 100CE), are vertical surfaces with easy access, and have not been modified or obscured since their exposure. Using the original Nabataean-dressed surfaces for baseline studies, weathering features like pits, channels, and cavities were located and measured. Preliminary examination indicated that sunlight was having some effect, but in-depth analysis confirmed these observations. Northern-facing surfaces (340-20~ showed the least weathering with 90% of the original stone-dressing visible with no recesses exceeding 2cm in any dimension. The relatively minor decay on northern faces can be attributed to decreased weathering from lichen overgrowth (Paradise 1997), since they are rarely found on other surfaces, and that less sunlight produces fewer wetting and drying cycles. Southern faces (185~ displayed 40% of the original dressing with few cavities larger than 15em in any dimension. The increased weathering on southern faces may be due to increased sunlight increasing daily heating and cooling cycles. Western to southwestern faces (230-250~ and eastern to southeastern faces (70-110~ however, displayed the greatest amount of deterioration and recession, with hardly any original Nabataean stone-dressing remaining (<10%) with many cavities exceeding 20cm across. This may be due to the ideal daily and yearly balance that occurs on these faces, where temperatures are hot enough to expand the rock, but also wet enough to keep it hot and cool, wet and dry ~ important cycles known to accelerate stone deterioration. These discoveries reinforce the conventional notion that the deterioration of sandstone is greatly accelerated from increased heating and cooling, or wetting and drying. However, it is now believed to be faster and more destructive than previously understood. In Petra, this implies little influence from increased tourism, but adds to our basic understanding of the delicate balance of weathering between climate, people and rock-cut architecture.
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5. 5. A l - l ~ a z n e h Tomb Chamber: weathering and tourism Current research in Petra is investigating changes in anthrogenic (human-caused) humidity and its effects on weathering rates. Previous research and the recent study at Anjur indicates that moisture and temperature in tandem accelerate stone deterioration. However, few studies can be found on the direct effects of humans and small-space humidity changes in chambers like Petra's AI-Khazneh. This large temple/tomb is elaborately faced with classical elements (pediment, columns, entablature, ere)and consists of a primary chamber with three antechambers (interior volume of approximately 2,000m3). This hewn structure was made famous in Spielberg's 1987 film 'Indiana Jones and the Last Crusade'. Since 1998, environmental monitoring in the interior of AIKhazneh indicate that there is a strong relationship between large numbers of visitors in the tomb and a subsequent rise in relative humidity (and unrelated to outside climatic fluctuations). Preliminary measurements indicate that the greatest increases in humidity occur when visitor groups exceeding 25-30 persons remain within the tomb for more than five minutes. This is an important finding since many tour groups visiting A1-Khazneh in Petra consist of at least 20 persons and remain more than 5 minutes in the inner chamber. Prior studies have shown that increased moisture in restricted spaces can increase the production of surface salts (efflorescence), increase in-rock permeability, moisture wicking, and a general accelerated deterioration of sandstone from particle disaggregation (Paradise 1999). Extensive research in arid regions (i.e. Egypt, Arizona) suggests that drier structures exhibit slower deterioration rates than wetter ones (i.e. Emery 1960). Precisely how this increased moisture regime contributes to accelerated deterioration in Petra, however, needs further study. So, as tourist numbers increase in Petra's chambers or tombs, interior humidity increases will accelerate deterioration. Because Petra's visitors have increased from roughly 100,000 in 1990 to 350,000 in 1998 (with single day attendance otten nearing 4,000 persons in 1999), it is essential that we monitor all environmental variables (external and internal) in order to evaluate carrying capacities and accessibility in this UNESCO World Heritage Site. Finally, since the tomb chambers in Petra were hewn directly from the local cliffs, many of these surfaces still display the original stonemason dressing grooves. In fact in most of the tombs, some remnants of these marks remain. In AI-Khazneh, for example, the four interior walls all exhibited explicit stone dressing as recently as 1990. However, it is now obvious that dressing is rapidly
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deteriorated from 0.5 to 2.5m above the floor, in the past decade. This surface recession was recently mapped (Summer 1999) using laser leveling devices and leveling cord to establish a baseline study. Using computer modeling, it was found that over the 4 by 3 meter surface, over one half meter (526,000cm 3) of sandstone has eroded from the inner chamber wall, mostly in the past decade from increased visitors in Petra. The area of recession suggests that it is caused by direct tourist contact like touching and leaning. In fact, on the
more than 100 occasions that AI-Khazneh was visited, numerous individuals and tour groups were seen leaning, touching, rubbing and propping their feet against the chamber walls. It then comes as no surprise that the area of increased recession seems to be a function of recent visitor contact (during this Century and moreover during this decade). Possible solutions may involve modification of interior micro-climates (such as adding fans or dehumidifiers) or the restriction of in-tomb visitor numbers at any one time, with time spans between visitors long enough to permit the tomb chambers to re-stabilize to a naturally lower humidity.
6. Summary Holistic weathering research that includes both intrinsic (i.e. lithology) and extrinsic (i.e. climate, human effects) influences are increasingly vital in stone weathering studies. Not only do they assist in establishing rates of deterioration that help forecast surface condition, features and recession, but they can help us better understand methods that can be used to
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decrease natural and induced rates of decay. Through these three research sites, we are able to better understand the complex dynamics of sandstone weathering in Petra. , / T h e Roman Theater study helps us better understand the importance of rock chemistry and composition in interpreting deterioration mechanisms. ,/Research at the quarry of Anjur brought a much-needed re-examination of the role of sunlight in the acceleration of weathering and architectural decay. r Measurements of the inner chamber walls and the human-induced humidity in AIKhazneh is bringing new attention to the effect of tourism on accelerating stone deterioration. As time passes and visitors increase, the unique architecture of Petra deteriorates at rates often faster than conservation efforts are able to halt or decrease this decay. Crumbling and broken pediments, archways and decorations are visible on most of the tomb facades. With regional tourism swelling from Israel's newly open border and the millennium celebrations, direct contact between visitors and these beautiful structures also increases. Tourism accelerates rock decay through touching, climbing, treading and elevated moisture levels. So, theoretical and applied studies that examine both intrinsic and extrinsic conditions to better understand weathering influences are vital to the preservation and conservation of the unique architecture and history of Petra. From previous and ongoing research we are slowly beginning to understand the complex and delicate nature of sandstone architectural deterioration in Petra and possible solutions that can help keep it a truly magical place. *This research has beenfunded in part by the US National Science Foundation (NSF), US Information Agency (USIA), and the Jordanian-American Commission on Educational Exchange (Fulbright Commission).
7. References
Amoroso, G. G., Fassina, V. 1983. Stone Decay and Conservation. Amsterdam: Elsevier Publishing Blackwelder, E. 1933. The insolation hypothesis of rock weathering. American Journal of Science 26:97-113 Blackwelder, E. 1929. Cavernous rock surfaces of the desert. American Journal of Science 217:3 93-3 99 Bryan, K. 1928. Niches and other cavities in sandstone at Chaco Canyon, New Mexico. Zeitschriit fur Geomorphologie 3:125-140 Bryan, K. 1922. Erosion and sedimentation in Papago country, Arizona. U.S. Geological Survey Bulletin 730-B: 19-90 Burton, R. F. 1879. The Land of Midian. London: C. Kegan Paul and Company. Conca, J. L., Rossman, G. R. 1982. Case hardening of sandstone. Geology 10:520-523 Emery, K. O. 1960. Weathering of the Great Pyramid. Journal of Sedimentary Petrology 30:140-143 Geikie, A. 1880. Rock weathering as illustrated in Edinburgh church yards. Proceedings of the Royal Society of Edinburgh 10:518-532 Griggs, D. T. 1936. The factor of fatigue in rock exfoliation. Journal of Geology 44:781796 Herodotus 450 BCE. The Histories. New York: Dutton and Company (reprinted 1862).
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Hoke, E. 1978. Investigation of weathering crusts on Salzburg stone monuments. Studies in Conservation 23:118-126 Jackson, T. A., Keller, W. D. 1970. A comparative study of the role of lichens and inorganic processes in the chemical weathering of recent Hawaiian lava flows. American Journal of Science 269:446-466 Jenkins, K. A., Smith, B. J. 1990. Daytime rock surface temperature variability and its implications for mechanical rock weathering, Tenerife, Canary Islands. Catena 17:449-459 Jones, D., Wilson, M. J., Tait, J. M. 1980. The weathering of basalt by Petrusaria corallina. Liehenologist 12:277-289 Klein, M. 1984. Weathering rates of limestone tombstones measured at Haifa, Israel. Zeitschritt fur Geomorphologie 28:105-111 Matthias, G. F. 1967. Weathering rates of Portland arkose tombstones. Journal of Geological Education 15:140-144 Meierding, T. C. 1981. Marble tombstone weathering rates: a transect of the United States. Physical Geography 2:1-18 Mustoe, G. E. 1983. Cavernous weathering in the Capitol Reef Desert, Utah. Earth Surface Processes and Landforms 8:517-526 Neil, D. 1989. Weathering rates of subaerially exposed marble in eastern Australia. Zeitschriit fur Geomorphologie 33: 464-473 Paradise, T. R. 1999. Environmental Setting and Stone Weathering. In Petra's Southern Temple, ed. M. Joukowsky:63-87. Providence: Brown University Paradise, T.R. 1999. "Deterioration of Classical Sandstone Architecture in Petra, Jordan" in Annual of the Department of Antiquities of Jordan (ADAJ) (editor Ghazi Bisheh), Jordan National Press, Amman. Paradise, T. R. 1998. Limestone Weathering and rate variability, Great Temple of Amman, Jordan. Physical Geography 19 (2): 133-146 Paradise, T. R. 1997. Disparate Weathering from Lichen Overgrowth, Red Mountain, Arizona. Geografiska Annaler Paradise, T. R. 1995. Sandstone Weathering Thresholds in Petra, Jordan. Physical Geography 16:205-222 Paradise, T. R., Yin, Z. Y. 1993. Weathering Pit Characteristics to Topography, Stone Mountain, Georgia. Physical Geography 14:68-80 Pfluger, F. 1995. Archaeo-Geology in Petra, Jordan. Annual of the Department of Antiquities of Jordan 39:281-295 Rahn, P. H. 1971. Weathering of tombstone and its relationship to the elevation topography of New England. Journal of Geological Education 19:112-118 Robinson, D. A., Williams, R. B. 1992. Sandstone weathering in the High Atlas, Morocco. Zeitschrifi fur Geomorphologie 36:413-429 Robinson, D. A., Williams, R. B. G. 1989. Polygonal cracking of sandstone at Fontainebleau, France. Zeitschrift fur Geomorphologie 33:59-72 Roth, E. S. 1965. Temperature and water content as factors in desert weathering. Journal of Geology 73 (3):454-468 Sancho, C., Benito, G. 1990. Factors controlling tafoni weathering in the Ebro basin, Spain. Zeitschritt fur Geomorphologie 34:165-177 Shaer, M. 1997. The Nabataean Mortars in the Petra Area: investigations of types and applications. M.A. Thesis. Yarmouk University Institute of Archaeology and Anthropology (Irbid, Jordan)
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Smith, B. J. 1977. Rock temperature measurements from the northeast Sahara and their implications for rock weathering. Catena 4"41-63 Smith, B. J., Magee, R. W. 1990. Granite weathering in an urban environment: an example from Rio de Janiero. Singapore Journal of Tropical Geography 11(2): 143-153 Smith, B. J., McGreevy, J. P. 1988. Contour scaling of a sandstone by salt weathering under simulated hot desert conditions. Earth Surface Processes and Landforms 13:697-705 Spencer, T. 1981. Microtopographic change on calcarenites, Grand Cayman Island, West Indies. Earth Surface Processes and Landforms 6:85-94 Sperling, C. H., Cooke, R. U. 1985. Laboratory simulation of rock weathering by salt crystallization and hydration processes in hot, arid environments. Earth Surface Processes and Landforms 10:541-555 Stephens, J. L. 1837. Incidents of Travel in Egypt, Arabia Petraea and the Holy Land. Strabo 22AD. Geography. London: H.G. Bohn Publishers (reprinted 1857). Winkler, E. M. 1965. Weathering rates as exemplified by Cleopatra's Needle, New York City. Journal of Geological Education 13:50-52 Young, A. g. 1987. Salt as an agent in the development of cavernous weathering. Geology 15:962-966
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PRELIMINARY STUDIES FOR THE CONSOLIDATION OF GUADALUPE TUFF F R O M THE PHILIPPINES Maria Cristina Paterno and A. Elena Charola* Graduate Program in Historic Preservation, University of Pennsylvania Philadelphia, PA 19104-6311, U.S.A.
Abstract The study focuses on the consolidation tests carried out on samples from the Mount Mayamot quarry near Manila. The samples were consolidated using Conservare OH Stone Strengthener (trade name for Wacker OH in the USA). Samples of the tuff, both treated and untreated were artificially aged by wet-dry cycles alternating with exposure to 100% RH. The results, based on microscopy, IR analysis, water absorption data and mechanical tests, showed that even this relatively short artificial weathering produced significant deterioration for both treated and untreated specimens. Apart from an increase in porosity, the main effect observed in the untreated specimens was the partial leaching of iron ions decreasing the colour of the stone to a depth of 2-mm. In some cases, a surface deposition of amorphous silica was observed. For the case of the treated samples, similar but less severe erosion around pumice and basalt clasts was observed. However, under SEM examination it was seen that the polymerization cracks in the silicate ester were increased by microcracking originating from a single point and attributed to stress-cracking. Some flaking of the consolidant was observed and all samples showed the presence of a faint white efflorescence of amorphous silica. Keywords: weathering
volcanic tuff, silicate ester, consolidation, artificial weathering, tropical
1. Introduction The tradition of building with stone is a Spanish introduction to Philippine culture. Prior to the Spanish colonization in 1565, indigenous Filipino architecture used wood and thatch. The Spanish adopted the local architecture to build their settlements since this technology was quicker, cheaper and better suited to the local climate and terrain. However, the fire of 1583 that set the whole town of Manila ablaze resulted in a decree, issued four years later, to build mainly with stone. The new stone architecture, called Spanish Colonial, frequently used wooden poles as the main structural members sheathing them with stone curtain walls. The stone was commonly stuccoed, which served both an aesthetic purpose by imitating more costly building materials or unifying an otherwise heterogeneous facade, and a practical one by serving as the protective layer for porous materials such as tuff and coral stone. Restorations carried out in the mid-1970's promoted the removal of this exterior render from many buildings, resulting in a faster deterioration of the tuff as compared to that protected by a stuccoed facade.
* Author to whom correspondence should be addressed.
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The weathering of tufts may be due to many factors but the most important one, particularly in a climate such as found in The Philippines, is the action of water, both as moisture (water vapour) and as rain (Charola and Lazzarini 1987/88, Beloyannis 1993, Helmi 1994, Caner-Saltik et al. 1995). Water-repellents can be used as a protective treatment, but if the tuff has already weathered, a previous consolidation may be needed. For this purpose, a silicate ester based product appears to be one of the most appropriate treatments (Roth 1990; De Witte et al. 1988). However, the treatment itself may influence significantly the weathering characteristics of the stone (Wendler, Charola and Fitzner 1996). Hence, this study focuses on the evaluation of the treatment, applied to sound unweathered stones, after artificial weathering.
2. Description of the Guadalupe tuff The volcanic tuff used in Manila and surrounding areas was extracted from local quarries. The Mount Mayamot quarry is currently active and the tuff quarried from it, Guadalupe tuff, is being used extensively as cladding material in modern construction. It is similar in nature to some of the volcanic tuff used in historic construction and to that of an important petroglyph site in nearby Angono (Charola 1998, Charola and Paterno n.d.). The tuff resulted from pyroclastic flows which vary from scoria to scoria-to-pumice dominated flows and has been identified as belonging to the Pleistocene Laguna Formation of the Quaternary volcanics (Scholl 1989). The tuff is composed of a glassy matrix (60%) with clasts (30%) of pumice (dark brown/black approximately 65 mm, light brown ranging from 6-25 mm and white around 1.5 mm) and some basalt (ranging between 1.5-20 mm). The dominant minerals are feldspars (10%) ranging in size from 0.05-1 mm. Clay content is negligible.
3. Experimental 3.1 Sample consolidation Three sample sizes were used in the study: 5x5x5cm cubes for water absorption, drying rate tests and for microscopy; and, l x l x l c m cubes and 0.5xlx4cm parallelepipeds for mechanical tests. Half of each sample suite was treated with Conservare OH Strengthener following the manufacturer's specifications. The product was applied to saturation using a foam brush and curing was carried out a room temperature (22~ and 70%RH). Three cycles of three applications were made, separated by a waiting time of 10 minutes between applications and of 30 minutes between cycles, to allow for adequate penetration. The stones were left to cure for two weeks 1. After this period, given the high porosity of the Guadalupe tuff, the treatment was re-applied and the samples left to cure for another two weeks.
3.2 Artificial weathering The weathering cycle selected aimed to increase both the temperature and the humidity of the typical conditions existing in the Manila area, where temperature averages range from 22~ to 29~ and seasonal humidity fluctuates between 65.5% and 85%RH.
ProSoCo Inc., the manufacturerof Conservare OH Stone Strengthenerhad included a 1996 data sheet which indicated the minimumcuring time as two weeks. ProSoColater changed this period to three weeks.
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Both treated and untreated specimens were subjected to a total of 21 weathering cycles, each 24-hour cycle consisting of two subcycles of 1-hour immersion in 60~ distilled water followed by a 1.5-hour hot-air drying at about 40~ with a 19-hour exposure to 100%RH. During immersion the water was left to cool from its original 60~ Upon removal from the water, the samples were wiped dry with a paper towel and exposed to hot-air blowers while drying on a rack. A thermometer placed about 1-cm from the surface of the samples was used to insure that the temperature of the hot air was not above 40~ The drying time was selected based on the loss of about 50% of the absorbed water for the 5x5x5cm cubes.
4. Results Both treated and untreated, weathered and unweathered samples were studied by optical microscopy, aided in some cases by SEM. The samples were also evaluated by the changes in water absorption and drying rate as well as by in their mechanical resistance as evidenced by compressive strength and three-point bending tests. 4.1 Microscopical Examination Alteration due to artificial weathering is visually apparent when comparing weathered (surface) areas with sound stone. Apart from surface erosion, a lightening in colour of the darker areas, a fading of the crystalline boundaries around pores and a widening of the cleavage planes in feldspars was observed. As expected, these changes are most distinct closer to the surface and diminish with increasing depth (fig. 1). The leaching of the iron from the glassy matrix and from rock fragments such as pumice and scoria is clearly visible in the 2-mm surface layer.
Figure 1. Chromatic alteration in the artificially weathered tuff showing the loss of iron close to the surface shown at right of the photograph. Depth of alteration (marked) is approximately 2-mm (PPL, 25X)
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Fig. 2a. Untreated, unweathered
Fig. 2b. Treated, unweathered
Fig. 2c. Treated, weathered Figure 2. The silicate ester consolidant appears to concentrate in the crystalline edges of the pores enhancing them (2b) as compared with the untreated speciment (2a). After weathering, a noticeably increase of porosity is evident (2c) (XPL, 25X).
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Comparison of treated and untreated samples, both unweathered, show that the consolidant appears to concentrate around the crystalline edges of the pores (figs. 2a and 2b). However, after weathering this "concentration" visible on the treated specimens seems to diminish somewhat while porosity increases (fig. 2c). The porosity increase is relatively more pronounced for the glassy phases suggesting that the more crystalline material may be protected from weathering by the consolidant bonding to it. SEM examination of the consolidated samples shows an even coming of the pores with few and unrelated shrinking cracks, confirming the optical microscopy results (fig. 3a). Upon weathering, a larger amount of cracks are visible, which in some cases appear to radiate from a single point, while the consolidant appears to detach from the stone surface (fig. 3b).
4.2 Water Absorption and Evaporation Capillary water absorption and total immersion were measured following the NORMAL 11/85 and 7/81 procedures. The results are summarized in Table I. Table 1.
Results from capillary water absorption and total immersion tests.
Capillary absorption coefficient (g/cm 2. secs. 1/2) Maximum Capillary water absorption (g) Total Immersion water absorption (g) % Porosity
UNTREATED Unweathered Weathered 0.019 0.029
TREATED Unweathered Weathered 0.004 0.002
57.0
58.8
35.4
44.2
58.0
61.3
37.7
45.7
32.3%
34.2%
18.0%
23.4%
As mentioned, an increase in porosity is observed for both treated and untreated specimens upon weathering. However, for treated specimens, the increase is nearly twice as much, although the weathered specimens still have a porosity below that of the untreated and unweathered stone. The same effect was also noticed for the other parameters measured, such as the capillary water absorption or the maximum amount of water absorbed. The drying curve of the samples showed that the initial slope increased upon weathering for both treated and untreated specimens. However, treated weathered specimens reached the same asymptotic value as the untreated samples while the treated and unweathered specimens reached a lower value (fig. 4).
4.3 Mechanical Tests The results obtained from the mechanical tests, compressive strength and three point bending are summarized in table 2. As can be seen there is no significant change of compressive strength for the untreated sample upon weathering. The consolidation increases the compressive strength significantly, but loses it in part upon weathering, although the resulting value is still higher than that for the untreated specimens. On the other hand, the bending strength of the untreated specimens decreases more upon weathering than for the treated specimens.
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Fig. 3a. SEM micrograph, x 1,000
Fig. 3b. SEM micrograph, x 851) Figure 3. SEM of the silicate ester treated tuff samples. The amorphous silica deposit is visible covering the crystalline material, presumably zeolites, lining the pores (3a). After artificial ageing, increased cracks can be seen in the coating of the consolidant which also appears to detach from the surface of the stone (3b).
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Figure4. Drying curves for treated and untreated, weathered and unweathered specimens. Note that the treated unweathered specimen starts at a lower moisture content than the other samples. Table 2: Results from compressive strength and three-point bending tests UNTREATED
XRrAXrD
Unweathered Weathered Unweathered Weathered Compressive Strength (MPa) 8.50 8.84 12.06 10.91 Bending Strength (MPa)
3.68
2.90
5.12
4.85
For the unweathered specimens, results of the three-point bending test suggest that the treatment embrittled the material as the treated set required higher loads than the untreated one to reach its plastic limit in the same time (Patemo 1999). Upon weathering, both untreated and treated samples increased in elasticity, the latter showing some irregular dips in the slopes reflecting mechanical weakening of localized areas. This is consistent with the SEM observations of areas with microcrack formation and consolidant detachment.
4.4 Other measurements The weight of the samples was measured before and after weathering for both treated and untreated specimens. For untreated specimens the weight loss was approximately 0.3%, while for treated specimens it ascended to nearly 4%. The high loss in weight of the treated samples suggests that part of the treatment was leached out, although considering that the weight increase aider treatment was slightly above 15%, this loss may not be significant, as reflected by the results of the mechanical tests. After weathering it was observed that both untreated and treated specimens developed a faint whitish surface deposit concentrated mainly in surface recessions. The deposits were more evident on the larger 5x5x5 cm cubes and their appearance differed slightly depending
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on whether it formed on a treated or an untreated sample. FTIR analysis of these efflorescences proved them to be amorphous silica with traces of some silicate. These could be interpreted as originating from the sample itself, for untreated specimens, or from residues of the consolidant on the sample surface, for the case of the treated specimens. Also to be noted is that the conductance and pH of the de-ionized water (>0.1 ~tS and 4.65, respectively) used for immersion of the untreated samples during the artificial weathering increased after the 21 cycles (190 l.tS and 6.90 respectively). For the case of the treated specimens, a slightly lower increase in both measurements was observed (170 ~tS and 6.70, respectively) suggesting that also consolidant material was lost and confirming the observed weight loss of these samples. The colour of the stone, yellow brown, darkened upon treatment, but after weathering both treated and untreated specimens acquired a blueish-gray tint due to iron depletion. 5. Conclusions The artificial weathering by water immersion of the Guadalupe tuff from The Philippines was similar to that observed for other tufts under comparable tests (Beloyannis 1993, Helmi 1994). Consolidation with a silicate ester proved to be effective in increasing the mechanical strength and decreasing the porosity of the tuff. It appears to impart an increased resistance to deterioration, at least after the relatively short artificial weathering, although part of the consolidating material was lost during this process. Although it can be argued that insufficient curing time (2 weeks after the second application) was allowed, this reflects likely in-situ conditions for application to be encountered in this country. The study has shown that the amorphous silica layer left by the silicate ester treatment may be susceptible to dissolution through exposure to moisture and water and may also enhance the solubilization of the vitreous material present in the stone as had been suggested in a previous study (Wendler et al. 1996). To elucidate this dissolution mechanism further studies are required, since the solubilized silica that redeposits on the surface of the object may lead to its eventual flaking by the formation of a less porous, indurated layer as observed on the Angono petroglyph site. The susceptibility of this tuff to solubilization by water is reflected in the increased deterioration rate observed when facades of this stone are not protected by a surface treatment. Although the studied treatment may serve to strengthen the material and slow down its deterioration, traditional treatments such as rendering can provide a more efficient and economic solution to the deterioration of this stone. 6. Acknowledgements The authors are indebted to Dr. Elizabeth Price, Philadelphia Museum of Art, and Dr. Silvia Centeno, Metropolitan Museum of Art, for their collaboration and help with FTIR analysis. Thanks are also due to Dr.s Gomaa Omar and Alex Radine, University of Pennsylvania, for their valuable input. 7. References Beloyannis, N., 1993. Deterioration of Volcanic Lavas by the Action of Water and Salts. Conservation of Architectural Surfaces: Stones and Wall Covering. Venice, I1 Cardo. 161167.
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Caner-Saltik, E.N., Demirci, S., Ttirkmenoglu, A., Ozgnoglu, A., G6kttirk, H., Oser, A., B6ke, H. and Inalulat, E., 1994. Examination of Surface Deterioration of G6reme Tufts for the Purpose of Conservation. The Safeguard of the Rock-hewn Churches of the G6reme Valley. Rome, ICCROM. 85-94 Charola, A.E., 1998. The Angono Petroglyphs. Stone Deterioration and Conservation Measures. Unpublished Report, National Museum, Manila, Philippines Charola, A.E. and Lazzarini, L., 1987/88. The Statues of Easter Island: Deterioration and Conservation Problems. Wiener Berichte tiber Naturwissenschafl in der Kunst, 4/5, 392401. Charola, A.E. and Patemo, M.C., n.d., The Angono Petroglyphs: Deterioration Mechanisms and Conservation Issues. Submitted to the Pacific 2000: Fifth International Conference on Easter Island and the Pacific. Waimea, Hawai'i, U.S.A. August 7-12, 2000 De Witte, E., Tervfe, A., Koestler, R.J. and Charola, A.E., 1988. Conservation of the G6reme Rock: Preliminary Investigations. Proceedings of the 6th Intemational Congress on Deterioration and Conservation of Stone. Torun, Nicholas Copemicus University. 346-355. Helmi, F.M., 1994. Study of the Deterioration of Volcanic Rocks from Egypt. Lavas and Volcanic Tufts, Rome, ICCROM. 53-61. Patemo, M.C., 1999. A Study of the Weathering of Volcanic Tufts in a Tropical Environment, Including the Evaluation of a Consolidant. Master of Science Thesis in Historic Preservation. University of Pennsylvania. Scholl, W.U., 1989 Geological Map of Cardona Quadrangle. NIGS/Philippine German Geology Project, Sheet 3263 III NE. Wendler, E., Charola, A.E., and Fitzner, B., 1996. Easter Island Tuff: Laboratory Studies for its Consolidation. Proceedings of the 8th International Congress on Deterioration and Conservation of Stone. Berlin, Moeller Druck & Verlag. 1159-1170 8. Materials
Conservare OH Strengthener. ProSoCo, Inc. PO Box 171677, Kansas City, KS, 66117-9971. Phone : (800)255-4255, (913)281-2700 Fax: (800) 877-2700
www.prosoco.com
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SECONDARY PHOSPHATE PHASES IN ALTERED TRACHYTE FROM S. MIGUEL ISLAND (AZORES, P O R T U G A L ) - A POSSIBLE CONTRIBUTION TO THE STONE DEGRADATION M.I. Prud~ncio*, M. Nasraoui, M.J. Trindade Instituto Tecnol6gico e Nuclear, EN 10, 2686-953 Sacav6m, Portugal. M.A. Sequeira Braga CCA/CT, Universidade do Minho, 4700-320 Braga, Portugal. M.O. Figueiredo Instituto de Investigagao Cientitica Tropical, A1. Af. Henriques, 41, 4~ Portugal.
1000 Lisboa,
Abstract
Geochemical and mineralogical research were undertaken to determine the origin of degradation observed in stone monuments of the Miseric6rdia church which facade was constructed using volcanic rocks of trachyte composition. This work has enabled a more precise distinction of the nature of main forms of degradation of this type of stone. The occurrence of secondary phases including REE-minerals could be a plausible way to the stone degradation. The mineralogy of the REE is mainly controlled by phosphate phases. The primary apatite partly altered allows the generation of LREE-phosphate of rhabdophane type. These phosphate phases, specially connected to feldspar grains, show negative Ce anomaly of variable intensity, some are totally Ce-free. The intensity of the Ce-anomaly, and in some cases the Ce absence, are interpreted as the result of the oxidation of Ce3+ to Ce4+ and the deposition of Ce-phase, probably as cerianite, whereas the other LREE3+ are hosted by the phosphate phases. The oxidation of Ce seems to be driven by the microporosity in altered feldspar, which plays a leading part in the nature of REE-phases composition. Key words: Azores, S. Miguel, Monument, Degradation, Rare Earth Elements. 1. Introduction
The magnitude of the degradation and the rapidity of its development in Azores monuments, even on recently restored parts, needed a broad study to be carried out to investigate the causes of degradation and, if possible, to suggest plausible ways for its limitation. Despite the fact that the formation of secondary minerals on buildings depends on the materials and the atmospheric contributions, it is mainly gouverned by the transfer and concentration of the solution. It is still poorly understood the dual influence of the chemical composition of solutions flowing through the stones and their physical contribution in forming superficial coating and secondary minerals. Many monuments in Azores Islands were built using trachyte. A general feature macroscopieally observed in trachyte outcrops and in monument stones is a brownish coating of the feldspar phenocrysts. Petrographic observations showed different degrees of brownish coating in the alkaline feldspars. It was in this context that the studies were carried out on the church of Miseric6rdia (Ribeira Grande, S. Miguel Island) which was constructed using traehyte rocks. The work * Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
undertaken on this church has enabled a more precise distinction of the nature of the mineralogical transformations occurring in the altered stones. The degradation process seems to be correlated to the precipitation of secondary phases as saline minerals and REEphases; the latter could be used as 'fingerprinter' of the alteration conditions, including Eh variation. Indeed, the Rare Earth Elements (REE) have very similar chemical proprieties, which tend to vary gradually along the group (Henderson, 1986). During supergene alteration processes, the behavior of REE depends on several factors for example Eh, pH, the presence of organic and inorganic ligands, the mineralogical distribution of REE in the parent material. Among the REE, cerium is specially interesting to study because it can occur in nature as Ce3+ like the majority of lanthanides, or as Ce 4+ in oxidizing conditions. The mineralogical transformations (dissolution/precipitation), including the nature of secondary minerals incorporating the REE, and specially Ce, could drive the degradation of the stones in monuments. Loss of material can result from the dissolution reactions of primary minerals inducing an increase in the porosity, whereas the precipitation of secondary phases can cause physical constraint increasing the fragility of the stones. In the present investigation, the REE-bearing minerals in altered trachyte from S. Miguel island, are described and discussed combining SEM observations made in both monument stones and quarry samples. These observations allow us to follow the evolution of phosphate REE-bearing minerals during the alteration. 2. Results 2-1- Primary minerals Among the major minerals, alkaline feldspars are relatively stable. Some zones in the observed crystals present dissolution aspects, and porous are spread by secondary REE minerals (Fig. 1). Secondary REE-phosphate can also occur as coatings or in micro-cracks following twin and cleavage plans. Pyroxene is relatively preserved in the monument stones as well as magnetite crystals which are abundant and can contain small dark inclusions Ti-rich and Mn-poor as indicated by X-ray dement images. Apatite occurs as elongated grains (4-15 lam), as inclusions in magnetite, or as large individual grains (up to 80 lam).
Figure 1: A- Crystal of alkaline feldspar showing spread surface by REE-enriched grains (SEM-backscattered electrons). B- Energy dispersive pattern of the alkaline feldspar.
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2-2- Secondary REE phases Based in SEM observations, the types of secondary REE phases were classified in terms of morphology and qualitative composition, particularly considering the presence or lack of Ce. REE-phosphate phase occurring on altered feldspar surface as small rounded crystals (5 to 10 ~tm) more or less aggregated (Fig. 2A) showing an energy dispersive X-ray emission spectrum (EDS) LREE-enriched with variable amount of Ce (Fig. 2B), has been distinguished from small donut-like shape (up to 5 lain) phosphate LREE-enriched but Cefree (Fig. 3). On the other hand, widespread aggregates of Ce-fich nodules have been observed (Fig. 4A). With EDS indicating the presence of Ce as unique REE (Fig. 4B) could correspond to the cefianite chemical pattern.
Figure 2: A- Aggregate ot small rounded grains of LREE-phosphate (SEM-backscattered electrons). B- Energy dispersive pattern of the LREE-phosphate showing the presence of Ce.
Figure 3: A- Nodular grams of LREE-phosphate Ce-free (SEM-backscattered electrons). BEnergy dispersive pattern of the LREE-phosphate showing the absence of Ce.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
Figure 4: A- Aggregate of small rounded grains of Ce-phase (SEM-backscattered electrons). B- Energy dispersive pattern of the Ce-phase. 3. Discussion
The primary LREE-bearing mineral in trachyte is mainly apatite, but the alteration process lead to different LREE-mineral precipitation and Ce accumulation. The simple way of the formation of secondary LREE-phosphate could be connected to the apatite alteration. The LREE 3+ and (PO4) 3" released participate in the formation of secondary phosphate of rhabdophane type according to the following reactions (1) and (2): ( C a2+5-2~,LREE3+~,Na+e)[PO4]3F(s) + 3H+(aq)r (5-2e)Ca2+<~q) + eLREE3+~,o + eNa+~,o + 3I-IPO42"~:aq)+F'faq)(1) Ca2+(aq) + LREE3+(~q)+ I-IeO42"(aq)"4"-nH20 <:=>(Ca 2+, LREE3+)(PO4) nH20(s) (2) Remark: In the reaction (1) the incorporation of REE in apatite is supposed via a substitution involving monovalent cation: 2Ca 2+= REE 3+ + Na +. It is also possible to write the same equation taking into account the incorporation of REE in the apatite via the coupled substitution Ca 2++ pS+ = REE3+ + Si4+ (Burt, 1989; Braun, 1991; Nasraoui, 1996). It is important to point out that most of the observed LREE-phosphates are spatially connected to feldspar grains and have a negative Ce-anomaly of variable intensity, suggesting a competitive precipitation process with a Ce-rich phase. Therefore, when LREE are incorporated into secondary phosphate, Ce has not the same behavior as the other REE, which could operate during a change in redox conditions. The presence of Ce as unique REE in the Ce-phase, probably as cerianite 'CeO2', indicates that Ce occurs in its tetravalent state. The oxidation and the precipitation of the Ce-phase could be interpreted as the result of a differential fluid circulation in the macro (inter-granular, micro-crack...) and the micro-porosity (intra-granular) of altered stones, in response to the alternative imbibition and drying cycles. It is well known that primary mineral like feldspar can develop an intra-granular porosity during the alteration process. Under natural exposure conditions, rocks are affected by alteration leading to a loss of cohesion and matter. In monuments, the stones are placed in different conditions of exposure, and they may be affected by different degradation morphologies. The exposure
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conditions corresponding to distinct imbibition-drying cycle's influence the capillary transfer process and the nature as well as the location of the precipitation of secondary phases. Indeed, the different types of porosity control the dynamics of the incoming flow of water in the stones. When the water content in the stones falls after the imbibition period, the run-off of water in the macroporosity is probably much faster than in the intra-feldspar porosity where the water remains a longer time. During the drying cycle, when the water has almost disappeared from the macroporosity, water could be retained only in smallest intragranular pores. The largest pores can contain air atmosphere and especially CO2 and 02, and consequently Ce can behave differently from the other LREE 3§ in these micro-domains. During the aerated conditions of the drying cycle, diffusion of 02 into the solution located at the interface of the micro-porosity can occur. A Eh increase will result, which will induce the oxidation of Ce and the precipitation of Ce4+ probably as cerianite. The remaining solution will be Ce-depleted and if mobilized during the next imbibition cycle could allow the precipitation of REE-phosphate phase with negative Ce-anomaly. 4. Conclusion Based in the nature and the spatial distribution of secondary mineral precipitation, the present petro-mineralogical approach specifies the importance of the mechanisms involved in the development of stone degradation. This analysis showed that an analogy could be drawn between the degradation of the stones and the occurrence of secondary REE-phases. The importance of the internal parameters governing the fluid transfer and the precipitation and the nature of secondary phases should be taken into account for a better understanding of stones degradation. The 'in situ' evaluation of these internal parameters combined with their quantification and the determination of their role in solution transfer, will be of a great importance. The gEE geochemistry and mineralogy can allow a precise record of the alteration/degradation conditions of the monument stones, including Eh variation if element with different valence state as Ce are involved. Thus, the occurrence of these secondary phases in the first stages of weathering of trachytes in Azores Islands indicates a high porosity of these rocks allowing an effective water-rock interaction. The mineralogical transformations (dissolution/ precipitation), including the nature of secondary phosphate phases, could contribute to the degradation of the stones, with an increase of the physical constraint and consequently the fragility of the stones in monuments. 5. Acknowledgements Supported by the Fundar para a Ci~ncia e Tecnologia (Portugal) through PRAXIS XXI - project n~ 2/2.1/CSH/254/95 and CCA-CT/FCT-R&D Contract-Program. 6. References Braun J.J. 1991. Comportement g6ochimique et min6ralogique des terres rares, du thorium et de l'uranium dans le profil lat6ritique d'Akongo (Sud-Ouest Cameroun). Ph.D. thesis, Universit6 de Nancy. 236 pp.
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Burt D.M, 1989. Compositional and phases relations among rare earth dement minerals. In B.R. Lipin & G.A. McKay, Eds. Geochemistry and mineralogy of rare earth elements. Reviews in mineralogy, 21,259-307. Henderson P., 1986. Rare earth element geochemistry. Developments in Geochemistry 2, Henderson ed., Elsevier, 510 pp. Nasraoui M., 1996. Le gisement de Nobium de Lueshe (Nord Est du Zaire): 6volution g6ochimique et min6ralogique d'un complexe carbonatitique en contextes hydrothermale et supergene. Ph.D. thesis, Ecole des Mines de Paris. 250 pp.
171 COMPARISON BETWEEN TRADITIONAL AND CHAMBER ACCELERATED AGEING TESTS ON GRANITIC ROCKS
Rivas, T.*I; Prieto, B.*; Silva, B.*; Birginie, J.M.** *" Dpto. Edafologia. Fac. Farmacia. Universidad de Santiago. 15706 SPAIN **: Laboratoire de Construction Civile et Maritime. IUT. 17026, La Rochelle. FRANCE. ABSTRACT Comparison was made of the results of seven artificial weathering tests carded out on granites traditionally used in historical monuments in NW Spain. The aim of the comparisons was to determine which of the f'Lxed parameters in each test and which of those related to the rock had most influence in the deterioration processes. The study furthermore aimed to establish which analytical techniques give the most information about the provoked weathering mechanisms. Seven tests were carried out: two using sodium sulphate, four using sodium chloride and one test using sea water. Six of the tests were based on the standardized tests described by Rilem (1978) or were modifications of these, the seventh test was carried out in a controlled atmosphere chamber. Results indicated that the tests based on the Rilem standards are useful for comparing the resistance of different rocks to soluble salts and to different treatment products, but that they do not provide information about the mechanisms of deterioration that are provoked. Of the analytical techniques used, the descriptive ones give most information about the triggered mechanisms.
Keywords: granitic rocks, salt deterioration, artificial ageing test, sea-salt spray. INTRODUCTION Soluble salts are very active agents in the weathering of granites (Evans, 1969; Robert et al, 1992). This fact is of particular importance when the granites are used for construction, as buildings can be exposed to soluble salts from a wide range of sources (from soil, atmospheric contamination, different building materials, etc.), while the weathering processes that are important in natural environments, are of minimal importance. Laboratory accelerated weathering tests are extremely useful for investigating in depth the mechanisms of action of the salts, and for predicting their effects in the medium-long term, thereby establishing criteria for assessing the durability of rock material (Mirwald and Briiggerhoff, 1997; Esbert et al, 1997) The artificial weathering tests traditionally used are those proposed by organisations such as CNR, RILEM, UNE and ASTM. In these tests, which are carded out under reproducible conditions, one or two factors acting at an elevated frequency to accentuate the deterioration processes, are fixed. Interpretation of the results is relatively easy as few parameters are involved. In other tests, including those carried out in controlled atmosphere chambers, materials are subjected to conditions that are as close to natural conditions as possible, although their action is superelevated. The complexity of these tests, involving more than two parameters, means that the results are more difficult to interpret. However, the advantage of these tests is that they have more practical application compared to the standardized tests. The fact that the conditions to which materials in buildings are subjected to can be reproduced in the laboratory allows 1Authorto whomcorrespondence should be addressed
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testing of conservation products under as natural conditions as possible. In some studies, a series of techniques are used with the aim of analysing and quantifying the deterioration. Which of these tests are used depends to a large extent on the specific aims of the study being carried out. In this study, comparison was made of the results of a series of artificial weathering experiments carried out on granitic rocks commonly used in historical monuments in NW Spain. The aim of these experiments was to investigate the mechanism of deterioration by soluble salts, which are the agents that cause the most severe effects in granitic rocks (Rivas, 1997; Casal, 1989; Silva et al, 1994). Comparison of the results of these tests allowed us9 to determine the most appropriate tests or conditions to use in the laboratory in order to reproduce the most common forms of weathering associated with soluble salts, that occur in buildings. 9 to establish which analytical techniques provide the most useful information on the mechanisms of deterioration. MATERIALS AND METHODS Granites
The following Galician granites were selected for this study: Figueiras (F), Roan (R) , Axeitos (AX), Muros (M) and Barbadelo 03). Before carrying out the ageing tests, the mineralogical composition of the five granites was determined by light microscopy and X-ray diffraction analysis. Test samples were cut in the form of blocks, taking the bedding plane of the quarry as the reference plane. Thin sections were cut from each test sample in the three orthogonal directions relative to the reference plane and were visualized by petrographic and fluorescence microscopy (see Fig. 1). In the latter case the sections were impregnated with resin containing the fluorescent dye Rodamine B in order to visualize the fissures. Finally, cubes (with 5cm sides) of each granite were used to determine the open porosity following the procedures of RILEM (1980). Figueiras is a migmatitic granitoid containing xenoliths and showing signs of flow structure. It comprises medium to coarse grains with marked orientation, in particular of biotite crystals. Fluorescence microscopy reveals that this granite is affected by an intense fissural network comprising of inter, intra and transgranular fissures. The latter are associated with the orientation of the biotites and are orientated approximately perpendicular to the reference plane (see Fig. 1). Roan is a medium-free grained two-mica granite with flow structure, xenoliths and no apparent mineral orientation. Axeitos is a pink, post-Hercynian granite comprising of medium grains, and is fairly homogeneous. Under fluorescence microscopy, this granite shows weak intra and transgranular fissures, the latter orientated parallel to the reference plane (Fig. 1). Muros is a medium to fine grained, two mica anatexic granite with slight orientation of its mineral components. Fluorescence microscopy reveals weak intra, inter and transgranular fissures. The transgranular fissures are clearly orientated perpendicular to the bedding plane (Fig. 1). Barbadelo is a two mica, medium to fine grained granite with an inequigranular allotriomorphic texture and iron oxyhydroxide segregations. The mineral orientation is mainly marked by the biotites and is also reflected by the transgranular fissures, which run perpendicular to the bedding plane (Fig. 1). All the granites have a similar mineralogical composition. Analysis by X-ray diffraction revealed the presence of traces of caolinite and hidroxialuminic vermiculite, which indicates
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a fairly advanced state of weathering in the granite samples when collected from the quarries. The characteristics of the granites are briefly summarised in Table 1. Table 1" Open porosity (OP, %) grain size, predominant fissure type observed under fluorescence microscopy and mineralogical composition by x-Ray Difraction (XRD)(Q: Quartz; F: feldspars; M: Mica; K: kaolinite; V: Vermiculite; semiquantitative analysis: ++++: >50%; +++: 50-30%; ++: 30-10%; +: 10-3%; tr: traces; -: not detected). Roan Figueiras , ~Axeitos . . . . Barbadelo Muros 6P 4.33 1.96 2.90 2.05 3.50 Type of fissures XRD Q F M K V
Inter and insular
Inter, intra and transgranular
Intra and transgranular
inter,'intra and ,transgranular
+4+ -r
+++
++ +++
+++
tr
tr
tr
tr
tr
tr
tr
,~,~| t~t Tq
tr tr
|
9
Inter, iTntraand transsrmmlar +++
Figure 1 9Orientation of transgranular fissures relative to the reference plane (bedding or horizontal plane of the quarry), as observed by fluorescence microscopy in Roan, Figueiras, Axeitos, Muros and Barbadelo granites. Salt crystallization tests The conditions of the series of salt crystallization experiments, including the salt solutions used, test sample sizes, drying chamber conditions, etc. are outlined in Table 2. In the first two experiments 14% (w/w) sodium sulphate was used and this solution was absorbed by the test prims by capillary action. The granite test prisms were orientated in three different positions during absorption of the solution, in order to determine whether the direction of absorption of the salt solution relative to a reference plane (the horizontal plane of the quarry, represented by the shaded area in the diagrams in Table 2) influenced the durability of the granite. Five samples each of R, AX and F were tested in each position in both
Table 2: Details of the salt crystallization tests. The shaded face of the granite blocks corresponds to the horizontal plane of the quarry and A,C and D the orientation of the samples during; the tests. i Experiment
1
Solution
14% Na2SO4
Granites
Test sample
Axeitos Figueiras Roan
Drying Chamber conditions
Time
Temperature of drying
Humidity of drying
7h 5h
20~ 60~
80%RH 40%RH
Analyses
Study of thin sections by fluorescence Microscopy
=r
g~ o
c) o
2
14% Na2SO4 2h partial immersion
Axeitos, Figueiras Roan
4% NaCI 2h total immersion
Figueiras
4
4% NaCI 2h total immersion
Figueiras
16% NaCI 2h total immersion
Figueiras
1' sea-salt spray
60~ 20~
40%RH 80%RH
Determination of mass and open porosity after every 10 cycles.
i'D
3
16% NaCI 2h total immersion
16h 16h
o~ i'D r~ r~ o
Roan
Roan
5x5x5cm
20h
20~
80%RH
Determination of mass and open porosity after every 5 cycles.
o
5x5x5cm
10h 10h
60~ 20~
40%RH 80%RH
Determination of mass and open porosity after every 5 cycles.
o <
Roan
Roan
5x5x5cm
20h
20~
80%RH
Determination of mass and open porosity after every 5 cycles.
5x5x5cm
10h 10h
60~ 20~
40%RH 80%RH
Determination of mass and openporosity after every 5 cycles.
5x5x10
29'
40~
50%RH
Determination Of mass and thin section study
Figueiras Roan
Muros Barbadelo i
o
o
< f~ | b~
b~
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experiments as follows: In Expt. 1, the faces of the test blocks (5x5x10 cm) were rendered impermeable with a plastic resin. The blocks were then placed in the salt solution and allowed to absorb it continuously while being subjected to seventy alternating cycles of, 20~ with 80% relative humidity (RH) and 40~ with 60% RH. At the end of this experiment, thin sections were cut perpendicular to the evaporation surface and examined by petrographic and fluorescence microscopy. In Expt. 2, untreated test blocks (5x5x5 cm) were subjected to 60 alternating cycles consisting of 2 hours partial immersion of the sample in the salt solution, 16 h at 60~ and 40% RH, and 16 h at 20~ and 80% RH (RILEM, 1978). The mass of each test sample and its open porosity were determined atier every l0 cycles. The following four experiments were carried out using sodium chloride solutions: Expts. 3 and 4 with 4% (w/w) NaC1 solution and Expts. 5 and 6 with 16% (w/w) NaC1 solution. Five cubes (5x5x5 cm) each of R and F were used in Expts. 3 and 4 and five cubes (5x5x5 cm) each of R, F, M and B in Expts. 5 and 6. The blocks were fully immersed in the salt solution for 2 hours and then dried for 20 hours in the climatic chamber: at 20~ and 80% RH in Expts. 3 and 5, and alternating between 10 hours at 60~ and 40% RH and 10 hours at 20~ and 80% RH in Expts. 4 and 6. The mass of each test sample and its open porosity were determined atter every 5 cycles. Finally, we subjected samples of R, B and M granites to a marine salt-spray ageing test in a chamber that was electronically progranuned to produce cycles of 1 min of saline spray followed by 29 min of drying by forced air at 35-39~ and 50%RH, as described by Auger (1988). The saline spray was produced by passing a constant flow of air through a capillary tube supplied with sea water, connected to a standardized spray-gun. The test blocks were placed on a revolving stand, which made four complete turns during spraying of the salt solution so that all samples were exposed to similar amounts of the solutions (in the order of 0.4 g/sample). These tests were carried out using test prisms (5x5x10 cm) of R, M and B granites. In order to monitor deterioration during this test, the following measurements were made. Weight loss was determined at the start of each experiment, after each 48 cycles, and at the end of the test. Thin sections were also made from fragments cut parallel to each face of the prisms, maintaining the edges of adjoining faces throughout the cutting and preparation of the thin sections. The thin sections were examined under fluorescence microscopy in order to visualize any possible modifications in the fissures of the samples. RESULTS
Salt crystallization tests with sodium sulphate The type of deterioration that was provoked in Expts. 1 and 2, was sand disaggregation. In Expt. 2, the sand disaggregation was apparent at an earlier stage and was much more intense than in Expt. 1, although in both experiments it was found that the more porous the granite, the more intense the disaggregation was. In Expt.1 sand disaggregation was observed on the tops of all test blocks, while the surface in contact with the solution remained intact. In Expt. 2, sand disaggregation was seen on all faces of the test samples. In Expt. 1, scaling was also observed on the tops of the Axeitos granite samples orientated in position A and in the Figueiras granite sample orientated in position C. Fluorescence microscopy of thin sections of these samples showed them to have fissures and cracks that developed during the tests and which may have been associated with the
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
shedding of the surface layers. In the Axeitos granite, the cracks were parallel to transgranular fissures that were present in the unweathered rock and that lay parallel to the horizontal plane of the qtmr~. In these samples (orientation A) the horizontal plane of the quanT was parallel to the surface of evaporation (see Fig. 1). In the Figueiras granite, however, scaling was perpendicular to the mineral orientation plane. Efllorescences were deposited on samples during the drying cycle of both experiments: in Expt. 1 on the top surfaces from which the solution evaporated, and in Expt. 2 on all the faces of all the samples. The effiorescences observed on samples in Expt. 2 formed hard crusts. The gradual deterioration of the samples during Expt. 2 is reflected by the progressive loss of mass (Fig. 2a), which was greatest in the most porous granite (Figueiras). Measurements of porosity showed the Figueiras granite to be slightly more porous at the end of the test.
Figure 2: Changes in weight loss (left) and open porosity (right) in R, F and AX granite samples during Expt. 2 (based on RILEM (1978)). Salt crystallization tests with sodium chloride In Expts. 3, 4, 5 and 6, where NaCI was used as the deterioration agent, effiorescences of this salt only formed on the samples that were subjected to drying cycles at 60~ and 40% RH (Expts. 4 and 6). In these cases the salt was uniformly distributed over all the faces of the test samples. During sea-salt spray simulation (Expt. 7), the test prisms have a damp appearance even throughout the drying cycles, and efflorescences were not deposited. Deterioration was slower in the sea-salt spray simulation test than in the tests using NaCI, and the morphology also differed. In the test using sea-salt, small crusts formed on the surface that were later shed in the form of small rocky fragments or clusters of mineral grains so that the decay resembled scaling rather than sand disaggragation. In contrast, in the test using NaCI, the disaggragation was due to grain by grain loss of material that caused rounding of the edges and an evenly distributed loss of volume of the test prisms. The scaling produced in the sea-salt spray simulation test was also observed by fluorescence microscopy. In the three granites tested, the artificial weathering conditions induced the formation of discontinuous transgranular fissures that ran parallel to the faces of the test prisms at a depth of 6000. In the Muros and Barbadelo granites there already existed transgranular fissures running perpendicular to two of the four decayed faces (Photograph 1), but it is worth noting that the formation of the fissures in the test was always parallel to the evaporation surfaces and was independent of the orientation of preexisting fissures.
9th International Congresson Deterioration and Conservation of Stone, Venice 19-24June 2000
This shows that the effect of salts is strong enough to cause fissuring parallel to the exposed surfaces and perpendicular to the already existing transgranular fissures in these samples. The changes in weight of the granite samples in Expts. 3, 4, 5, 6 and 7 are shown in Fig. 3. Comparing the results of Expts. 3, 4, 5 and 6, we found that: 9 for a given concentration of NaC1 solution, the greatest weight loss was in the samples dried at 60~ 9 for a given set of temperature and humidity conditions, the weight loss was greater in the samples in the experiments using the more concentrated NaCI solution (16%) than in those using 4% NaCI solution. 9 in all four experiments, the rate of weight loss was generally highest in the most porous granite, i.e. Figueiras. The porosity values during the tests (Fig. 3) remained constant throughout in Expts. 3 and 4; showed an initial increase before stabilising in Expt.5, and showed only a slight increase from initial values in Expt. 6.
177
Photograph 1: The photograph shows the transgranular fissures, visualized under fluorescence microscopy, which are formed parallel to the deteriorated surface of Muros granite and perpendicular to the original wansgranular fissuration.
Comparing Expts. 3, 4, 5, and 6 with Expt. 7, the most noticeable differences was that in Expt. 7, the test prisms underwent an initial sharp increase in weight that, in the case of the Roan and Muros granites, became more gradual as the test progressed. The same initial increase occurred in the Barbadelo granite, but after 15 days there was a decrease in the weight of the samples. In contrast, in Expts. 3, 4, 5 and 6 using NaC1 solution, there was no increase in weight.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
1,5 -
......
-
i
....... 6
0,5
5
.-. -0,5
~
~
-1,5
3
-2,5
~. 2
-3,5
1
-.4,5
0
0
-5,5
20
40
60
80
Cyc~
-6,5 0
20
40
60
80
C ~ - - 4 P - R ( 5 ) --B---F(5) R (S) ---.ae-- B (S) ---I1-- F (3) ---O-- R (4)
--e-.-.-R(6) - - ' B - - F ( 6 ) --+--- M (S) ---o-- R (3) ---E}-- F (4)
Figure 3 : Left - changes in weight loss in R, F granite samples during Expts. 3 -R(3), F(3),4-R(4), F(4)-, 5 -R(5), F(5)- and 6-R(6), F(6) and changes in weight loss in R, M and B granites during the sea-salt spray simulation -R(S), M(S) and B(S). Right - changes in open porosity of R and F granite samples during Expts. 5 and 6 (using 16% NaC1 solution). DISCUSSION AND CONCLUSIONS Regarding the experiments using sodium sulphate solution, the following conclusions were made. The conditions of Expt. 2, in which 14% Na2SO4 was used (RILEM, 1978), had a strong effect on the granites tested as intense sand disaggregation was produced on all faces of the prisms. This test demonstrated that the susceptibility of the different granites to the salt solution depends on the porosity of that granite, i.e. the more porous the rock the more rapid and intense the deterioration. The test may thus be extremely useful for comparing different rocks, and above all for evaluating the effectiveness and durability of consolidating treatments. However, it did not provide information about the mechanisms of deterioration provoked by the test itself, nor did it allow evaluation of the differences in intensity or forms of weathering on the different faces of the test prisms, which would be of great interest in this type of study with granites. It has been shown (Rivas et, 1999) that granite rocks are anisotropic in terms of transport of fluids and thus it is clear that the mobilization and evaporation of salt solutions differs in different planes. In Expt.1, which is a modification of Expt. 2, the salt solution is taken up by capillary action and evaporation is produced on only one face of the test blocks. In addition to sand disaggregation, which was less intense than in Expt. 2, small scales developed on the evaporation surfaces of some of the granites. In our opinion, this experiment was more realistic than Expt. 2, for two reasons: fn'stly because scaling developed and this is the most commonly occurring form of weathering in granite buildings in the presence of different kinds of sulphates (Rivas, 1997; Casal et al, 1989; Silva et al 1996b). Secondly, the design of the experiment allowed the anisotropy of the granites, in terms of movement of the salt solution and thus in terms of the weathering produced by the salts, to be demonstrated. In two of the three granites tested, scales formed in only certain directions relative to the reference plane. The experiments using NaCI produced much less deterioration of the samples than those using Na2SO4. Only sand disaggregation was produced in all four of these experiments (3, 4, 5 and 6). This corroborated the results of previous studies that have related the morphology of deterioration to the predominant salt species (Silva et al, 1996a, 1996b), sand disaggregation
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always being associated with the presence of NaCl as the predominant species. The sea-salt simulation test also gave rise to sand disaggregation, however, the appearance of the granites during and at the end of the test was similar to the appearace of the same granites in buildings exposed to the action of marine aerosols i.e. they appear damp and lack effloresences. This can be attributed to the different wetting, drying cycles to which the samples were exposed during the test, which gave rise to a different mechanism of deterioration than in the other tests. Thus, in Expts. 3, 4, 5 and 6, the total immersion of samples in the salt solution meant that they quickly became saturated and the prolonged drying cycles allowed the NaCl to move, in solution, towards the surface and to be precipitated there in the form of efflorescences. None of the samples in Expts. 3, 4, 5 and 6 increased in weight, showing that drying was complete. An increase in weight would have indicated gradual accumulation of the solution in the rock. In Expt. 7 the saline solution was applied in the form of short bursts of a saline spray that were frequent enough to allow the samples to absorb the solution gradually. The short drying cycles at a lower temperature avoided rapid drying of the samples and rapid precipitation of salts. The equilibrium between wetting, mobilization of salts and drying was reflected in the initial weight increase of the samples. Only when the deterioration was sufficiently advanced did the loss of material by disaggregation exceed the increase produced by the gradual saturation with the salt solution. Another factor that is important in determining the kind of deterioration produced in Expts. 3-7 is the nature of the solution used. Although NaCl is the predominant salt in seawater, the presence of other ionic species modifies its solubility and thus the dynamics of its mobilization and precipitation. In the sea-salt simulation test, NaCl precipitated below the surface rather than on it, while in Expts. 3,4,5 and 6, NaCl was able to reach the surface and was deposited in teh form of efflorescences. The following conclusions were made regarding the methodology used to quantify the weathering effects of the salts: 9 The open porosity did not give an accurate estimate of weathering as deterioration mainly affects the outermost layers of the granite. Furthermore the method for detem~ing porosity involves submerging the test prisms in water in order to extract salt from inside the rock, and this process causes additional deterioration and loss of material. 9 The study of thin sections by microscopy - especially fluorescence microscopy - provided useful information. This technique allowed us to demonstrate that salt crystallizmion caused an increase in porosity of the surface layers due to the formation of discontinuous transgranular fissures running parallel to the surface. The technique also allowed us to show that the fissures are always formed parallel to the evaporation surface, independently of preexisting fissures. 9 The study of the change in weight loss of test samples was useful in that it allowed the differences in the deterioration processes produced in each experiment to be established, especially in the test with NaCI and sea-salt spray.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
REFERENCES Auger, F. (1988).- Simulation acceler6e de la d6gradation de mat6riaux de construction en ambiance a6rienne saline. G6ologie de l'ing6nieur appliqu6e ax travaux anciens, mumuments et sites historiques. Marinos and Koukis (Ed.), 1988, Balkema, Rotterdam, vol. 2, 797-804. Casal, M. ; Silva, B.; Delgado, J. (1989).- Forms and factors of weathering in granitic rocks used in monuments. European Symp. Science, Technology and European Cultural Heritage, Bologna (1989). Baer, N.S.; Sabbioni, C.; Sors, D.I. (Eds.), 439-442. Esbert, R.; Ordaz, J. Alonso, F.J.; Montoto, M. (1997).- Manual de diagnosis y tratamiento de materiales p6treos y cerfimicos. Collegi d'aparelladors y Arquitectes T6cnics de Barcelona (De.), 1997. Cap. 5, 55-66. Evans, I.S. (1969).- Salt crystallization and rock weathering: a review. Revue de g6omorphologie dynamique. XIXeme ann6e, n~ 153-177. MArwald, P.W.; Briiggerhoff, S. (1997).- Requirements for an interpretation of accelerated and field testing. In, Saving Our Architectural Heritage, The Conservation of Historic Stone Structures. Baer, N.S. and Snethlage, R. (Ed.) (1997). John Wiley and Sons Ltd. Chpt. 14. 255268. RILEM (1978).- Crystallization test by total immersion (Test V. 1). Crystallization by partial immersion (Test V.2). Proc. Int. Symp. Deterioration and Conservation of Stone Monuments (UNESCO-RILEM), Paris, 1978. RILEM (1980).- Recommandations provisoires, essais recommand6s pour mesurerl'alt6ration des pierres et 6valuer refficacit6 des m6thodes de traitements. Materiaux et Constructions. Vol. 13. n~ 75. Test II.1. Porosit6 accesible/l l'eau. Rivas, T. (1997).- Mecanismos de alteration de rocas graniticas utilizadas en la construccion de edificios antiguos de Galicia. Doctoral Thesis. Servicio de Publicaciones e Intercalbio Cientifico, Universidad de Santiago de Compostela, 307pp. Rivas, T.; Prieto, B.; Silva, B. (1999).- Influence of rift and bedding planes on physicomechanical properties of granitic rocks: implications for the deterioration of granitic monuments. Building and Environment 00 (1999), 1-10. Robert, M.; Verg6s-Belmin, V.; Jaunet, A.M.; Hervio, M.; Bromblet, P.H. (1992).- Mise en 6vidence de deux microsyst6mes d'alt6ration (chimique et physique) dans les monuments en granite (Bretgane). Proc. VII Int. Symp. On Deterioration and Conservation of Stone. Lisboa (1992). Delgado, J.; Henriques, F.; Telmo, F.; vol. 1,129-139. Silva, B.;. Casal, M.; Prieto, B.; Rivas, T.; Guitifin, F. (1994).- Forms and factors of weathering in the Cathedral of Santiago de Compostela. Proc. VII Int. Symp. On The Conservation of Monuments in the Mediterranean Bassin, Venecia, Julio, 1994. 743-748. Silva, B. ; Rivas, T. ; Prieto, B. (1996a). Relation between type of soluble salt and decay forms in granitic coastal churches in Galicia (NW Spain). In European Commision Research Workshop Origin, Mechanisms and Effects of Salts on Degradation of Monuments in Marine and Continental Environments. DGII Protection and Conservation of the European Cultural heritage, research Report 4, pp 181-190, 1996. Silva, B.; Rivas, T.; prieto, B.; Delgado, J. (1996b).- A comparison of the mechanisms of plaque formation and sand disaggregation in granitic historic buildings. In Degradation and Conservation of Granitic Rocks in Monuments. M.A. Vicente, J. Delgado, J. Acevedo (Eds.) European Commision DGXII (Pubis.). Report n~ 269-274.
ACKNOWLEDGEMENTS
This work was founded by an EC Project ENV-4 CT95-0100.
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PHYSICAL PROPERTIES AND DURABILITY OF FRESH AND IMPREGNATED LIMESTONE AND SANDSTONE FROM CENTRAL SWEDEN USED FOR THIN STONE FLOORING AND CLADDING Torgny Sahlin* G6teborg University, Earth Sciences Centre; Geology, P.O. Box 460, SE-405 30 G6teborg, Sweden Katarina Malaga-Starzec G6teborg University, Department of Inorganic Chemistry, SE-412 96 G6teborg, Sweden Jimmy Stigh G6teborg University, Earth Sciences Centre; Geology, P.O. Box 460, SE-405 30 G6teborg, Sweden Bj6rn Schouenborg SP, Swedish National Testing and Research Institute, P.O. Box 857, SE-501 15 Bor~s, Sweden
Abstract Rocks differ in physical and chemical properties, depending on geochemistry, grain size, grain shape and porosity. Physical properties crucial for thin stone flooring and cladding have been investigated on fresh and impregnated J~imtland Limestone and Dala Sandstone. The tests performed were three-point load bending strength, uniaxial compressive strength, abrasion resistance, water absorption (including density), effective porosity and airpermeability. The physical properties were correlated to a chemical, weathering test simulating natural stone material corrosion, due to acid rain. The fresh sandstone showed higher bending strength, compressive strength, abrasion resistance, water absorption and porosity, but lower permeability, than the fresh limestone. The impregnated limestone showed much higher bending strength than the fresh limestone, whereas no significant difference in bending strength were shown between impregnated and fresh sandstone. For thin stone flooring and cladding the fresh sandstone is more suitable than the fresh limestone since it was less vulnerable to mechanical stress and less sensitive to acid rain. The impregnated limestone showed improved bending strength and chemical properties compared to the fresh limestone, but impaired water absorption, porosity and permeability. Fresh and impregnated sandstone did not show any distinct differences in physical and chemical properties.
Keywords: impregnated, sandstone, limestone, physical properties, durability, acid rain.
1. Introduction Rocks differ in physical and chemical properties, depending on geochemistry, grain size, grain shape and porosity. In order to investigate differences of some physical properties, a sandstone and a limestone were selected. The rocks tested are of sedimentary origin and the chosen Dala Sandstone is siliceous whereas the J~imtland Limestone is calcareous. When
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
using the rocks for flooring and cladding, the most important difference between these two rocks concerns the durability. The most crucial durability parameters are related to mechanical strength and weathering. The red-coloured fine-grained middle Proterozoic (900-1600 Ma) Dala Sandstone clastic sequence is about 800 m thick (Lindstr6m et al., 1991). The sequence has a continental origin and is overlaying the Dala porphyries and the Dala granites and also the even older Svekofennian (~ 1900 Ma) bedrock. Primary structures such as cross beddings and ripple marks are common (A1Dahan, 1985). The rock used in this study is quarried in M~ngsbodarna in the county of Dalarna, central Sweden. The mineralogical composition constitutes mainly quartz (~ 70 %), feldspar (~ 15 %), rock fragments (~ 10 %) and muscovite/sericite (~ 2 %) (Hjelmqvist, 1966) and displays a quartzitic character. The mineral grains are well rounded due to the clastic origin (Fig. la). The Ordovician (437-510 Ma) Jamtland Limestone is quarried in the Brunflo area of J~imtland, central Sweden. The limestone is very fine-grained and contains mainly calcite (80 %), some quartz (~ 10 %) and hematite which gives the rock a brownish-red colour (Karis and StrSmberg, 1998) (Fig. lb). Trilobites and brachiopods do occur. The conventional natural stone tile, mainly used as building material, is untreated and at least 10 mm thick. A patent has been obtained on a new production method, which makes it possible to produce natural stone tiles only 4 mm thick. The tiles are treated with potassium-based water-glass diluted with water, colloidal silica and Berol 048 (non-ionic surfactant), using vacuum technique including repeated cycling between vacuum and atmospheric pressure. One purpose is to increase the mechanical strength and the durability of the stone material. Another purpose is to produce more tiles from a stone block. This leads to fewer transports which is an advantage not only in economical aspects but also from an environmental point of view. In addition, the products are easier to handle due to their reduced weight. During the vacuum impregnation process it is believed that the impregnating agent fills the open spaces between the grains. However, to what depth is presently not known. It is also unknown what transport path the liquid takes; through pores, cracks, between grains etc. The tiles aim to be used as exterior cladding panels of buildings, on indoor floors, and as interior decoration in bathrooms and kitchens etc. Interior decoration in lifts and on passenger ships could also be possible due to its lower weight compared to the traditional thicker tiles. The tiles will be applied using tile fixative and mortar or adhesives. The aim of the study was to investigate differences in physical parameters of the fresh and the impregnated limestone and sandstone which are important when using these materials for thin stone flooring and cladding. For more specific data concerning the impregnation chemical see Table 1.
2. Experimental Both fresh and impregnated rectangular and cubic prisms of varying sizes were used. A chemical, weathering test simulating natural stone material corrosion, due to acid rain (SO2, NO2, humidity), has been performed for the limestone and the sandstone (Malaga-Starzec et al., in press). The physical tests performed in this study were three-point load bending strength, uniaxial compressive strength, abrasion resistance, water absorption (including density), effective porosity and air-permeability.
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Figure 1" Thin section microphotographs of (a) fresh Dala Sandstone and (b) J/imtland Limestone in polarised light with crossed polars.
Table 1: Components of the impregnation chemical. Concentration (vet %) Components Density (kg/m3) ** Potassium-based water-glass 1200 64.6 (SiO~K20) 8.5 Water 1000 26.9 Colloidal silica 1200 Berol 048 1020 *0.786 g is added per litre impregnation chemical solution. **After the hardening process the density of the impregnation chemical is approximately 2100 kg/m 3.
2.1 Bending strength The three-point load bending strength was measured according to DIN 52112-A, using an INSTRON 1253/8500 testing machine. The applied load rate was 1.18 N/s. Rectangular prisms 200 x 100 x 4 mm of the rocks were used.
2.2 Compressive strength The uniaxial compressive strength was measured according to DIN 52105, using a TONI COMP III testing machine. Applied pressure rate was 1.0 MPa/s. 27 mm cubes were used in the test.
2.3 Abrasion resistance The abrasion resistance test was carried out according to CEN TC 246AVI 014, using a wide wheel abrasion machine (modified Capon wheel) with corundum as abrasive material. The flesh samples were 100 x 100 x 10 mm and the impregnated 100 x 100 x 4 mm quadratic prisms respectively.
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2.4 Water absorption and density The water absorption and the density were measured according to DIN 52103-A and DIN 52102-RE, VA, respectively. Quadratic prisms 40 x 40 x 10 mm were used.
2.5 Effective porosity The effective porosity was calculated combining the total volume from the water absorption and the density tests with the volume obtained from a Helium pycnometer. The pycnometer (Micromeritics AccuPyc 1330) measures the volume of the open pore systems. The samples used for the pycnometer measurements were the same as the ones used for the water absorption and density tests.
2.6 Air-permeability The air-permeability was measured using a Sch6nlin-Apparatus connected to a vacuum pump. Quadratic prisms 200 x 200 x 10 mm were used. The air-permeability coefficient were calculated using the formula: (Plk -
(ta- t0)(Pa
P0)Vs - (Pl
-
1 P0) / 2) A
where k is the permeability coefficient, p l chamber at the end and at the beginning atmospheric pressure, tl - to is the duration vacuum chamber, l is the thickness of the specimen.
(1) and p o are the pressure inside the vacuum of the measurement respectively, Pa is the of the measurement, Vs is the volume of the specimen and A is the cross section of the
3. Results and discussion The fresh sandstone showed much higher bending strength and much lower permeability compared to the fresh limestone. The compressive strength and the abrasion resistance were higher for the fresh sandstone compared to the fresh limestone. The limestone showed more cracks and had much lower silica content than the sandstone which could be the main reason for these results. The fresh sandstone showed slightly higher water absorption than the fresh limestone, which is somewhat confusing since the limestone has more cracks, but on the other hand, the sandstone has higher porosity than the limestone, which probably is the most crucial parameter for the total water absorption. The impregnated limestone showed two times higher bending strength compared to the fresh limestone, whereas no distinct difference in bending strength between impregnated and fresh sandstone could be detected. This is due to the increase of the Si/Ca ratio of the limestone after the impregnation process. The compressive strength test and the abrasion resistance test showed no significant differences between the impregnated and the fresh sandstone and limestone. The impregnated sandstone showed lower permeability than the fresh sandstone. On the contrary, the impregnated limestone showed higher permeability compared to the fresh limestone. However, since the limestone is mechanically weaker than the sandstone, the crack density may be increased during the impregnation process, which in turn should lead to the higher permeability. This needs to be studied in more detail. The water absorption and the porosity were slightly lower for the impregnated sandstone compared to the fresh sandstone, but were higher for the impregnated limestone compared to the fresh limestone. The slightly lower water absorption ability and the porosity for the
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impregnated sandstone compared to the fresh limestone do not show the same trends as the results from the other physical properties. However, the differences are very small which could be due to heterogeneity of the samples. The acid rain test (Malaga-Starzec et al., in press) showed the highest adsorption of corrosive gases on the fresh limestone samples. Lower reactivity was shown for the impregnated limestone. The lowest reactivity was found for the for the fresh and the impregnated sandstone.
Table 2: Physical test results of the fresh and the impregnated Fresh Impregnated Physical tests sandstone sandstone Bending strength 24.0 20.7 (MPa) Compressive strength 247.2 254.1 (MPa) Abrasion resistance 13.5 14.0 (mm) Water absorption 0.3 / 0.7 0.2 / 0.6 (wt %) / (vol %) Density (kg/m 3) 2631 2632 Effective porosity (%) 1.3 1.1 Permeability 5.3 * 1 0 -9 2.9 * 1 0 -9 coefficient (m2/s)
sandstone and limestone. Fresh Impregnated limestone limestone 9.1
17.1
189.5
172.0
20.5
22.0
0.2 / 0.5
0.3 / 0.9
2710 0.6
2705 1.5
1.6 * 10 .8
3.8 * 10-8
4. Conclusions For thin stone flooring and cladding the fresh Dala Sandstone is more suitable than the fresh J~imtland Limestone since it is less vulnerable to mechanical stress and less sensitive to acid rain. Fresh and impregnated Dala Sandstone did not show any distinct differences in physical and chemical properties. The impregnated limestone showed improved bending strength and chemical properties compared to the fresh limestone, but impaired water absorption, porosity and permeability.
5. References A1Dahan A.A., 1985. Mineral diagenesis and petrology of the Dala Sandstone, central Sweden. Bulletin of the Geological Institutions of the University of Uppsala N.S., 12, 1-48. CEN TC 246/WI 014. Determination of abrasion resistance. 1999. DIN 52102. Testing of natural stone and mineral aggregates; Determination of absolute density, dry bulk density, compactness and porosity. 1988. DIN 52103. Testing of natural stone and mineral aggregates; Determination of water absorption and saturation coefficient. 1988. DIN 52105. Testing of natural stone; Compression test. 1988. DIN 52112. Testing of natural stone; Bending test. 1988. Hjelmqvist S., 1966. Beskrivning till berggrundskarta 6ver Kopparbergs l~in. Sveriges geologiska unders6kning. Ca 40. 217 pp.
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Karis L. and Str6mberg A., 1998. Beskrivning till berggrundskartan 6ver J~imtlands l~in. Del 2: Fj~illdelen. Sveriges geologiska unders6kning, Ca 53:2, 363 pp. Lindstr6m M., Lundqvist J., Lundqvist Th., 1991. Sveriges geologi fr~n urtid till nutid. Studentlitteratur, Lund, Sweden. Malaga-Starzec K., Sahlin, T., Lindqvist, O. (in press). Laboratory investigations of weathering behaviour of flesh and impregnated limestone and sandstone from central Sweden. Submitted for publication in the Proceedings of the 9 th International Congress on Deterioration and Conservation of Stone. Venice, Italy.
6. Materials The raw sandstone material used in this study is quarried by Wasasten AB, M~ngsbodarna, SE-796 99 A_lvdalen, Sweden. Tel: +46 251 540 00, fax: +46 251 540 10, email: [email protected]. The raw limestone material is quarried by AB J/imtlandskalksten, Box 25, SE-834 21 Brunflo, Sweden. Tel: +46 63 21860, fax: +46 63 22595, e-mail: info(~jamtlandskalksten.se. The impregnated 4 mm natural stone tile products used in this study has been developed by two companies; Eka Chemicals AB (Eka Chemicals AB, SE-445 80, Sweden. Tel: +46 31 587000, fax: +46 31 587400, e-mail: [email protected]) and Techstone AB (Techstone AB, SE-471 99, Sweden. Tel: +46 304 676560, fax: +46 304 676569, e-mail: [email protected]). For the composition of the impregnation chemical, see Table 1. The compositions of the stone materials are described under Introduction. The trade name for the sandstone is Alvdal Quartzite, and for the limestone J/imtland Limestone. The impregnated 4 mm products have the traditional trade name including Techstone |
187 STRESS FROM CRYSTALLIZATION OF SALT IN PORES George W. Scherert Princeton University, Civil & Env. Eng., Princeton Materials Inst., Eng. Quad. E-319, Princeton, NJ 08544 USA
Abstract Crystallization pressure results when a growing crystal encounters a pore wall. The maximum stress that a crystal of salt can exert is related to the supersaturation of the pore liquid, but lower limits are set by the interfacial energies of the crystal and the wall, the pore size and the pressure in the liquid. We review the equilibrium thermodynamics of crystallization pressure, then consider a nonequilibrium case, where evaporation drives the liquid/vapor meniscus into the gap between a crystal and the pore wall. If a large pore is nearly filled with salt, then the gap between the crystal and the wall effectively constitutes a small pore, and we find that large stresses can develop in that region. Therefore, even stone that has no small pores can experience high crystallization pressure once the pores fill with salt. Keywords: Crystallization pressure, disjoining pressure, supersaturation, curvature, Laplace pressure, solubility
1. Introduction
A solution of crystal of A in liquid B comes to equilibrium with excess A when the solution contains the equilibrium mole fraction of A, x o. If the concentration of x exceeds x o, then the solution is supersaturated, and the crystal tends to grow until the excess solute is removed. The growth of the crystal can be prevented, even if it is in contact with a supersaturated solution, if it is subjected to a pressure p, given by (Correns, 1949) as
Rg T ln(___x/ P= Vc \Xo,)
(1)
where Rg is the gas constant, T the absolute temperature, and VC is the molar volume of the crystal. The pressure given by eq. (1) is commonly associated with the crystallization pressure, but that is not correct, as explained in a recent review (Scherer, 1999); the tensile stress created in the pore wall by a crystal growing in the pore is closely related to p, but is not equal to it. Recently, Benavente et al. (1999) criticized eq. (1), and argued that the crystallization pressure is given by
t Author to whom correspondence should be addressed. Phone: 1-609-258-1563, Email: [email protected]
1-609-258-5680, FAX:
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
P=
~ l n
x
To
(2)
m
where Vc is the partial molar volume of the solute. As we shall see, this is also incorrect.
2. Disjoining pressure When the surface of a crystal touches the pore wall, a new crystal/wall interface is created with energy 7cw; at the same time, the crystal/liquid and wall/liquid interfaces are eliminated, whose energies are 7CL and 7WL, respectively. As Correns (1949) pointed out, pressure must be applied to force the crystal and wall into contact if A 7 = 7 c w - 7CL- 7WL > 0. That is, if a crystal is growing in a pore in a saturated solution, and the materials are such that A 7 > 0, then the crystal will resist touching the wall and will exert pressure against it. On the other hand, if A 7 < 0, then the crystal will be able to reduce the energy of the system by touching the wall, so it will grow into contact without generating any crystallization pressure. The crystal senses the approach of the pore wall via dispersion, hydrogen bonding, hydration, and electrostatic forces that reach across the intervening film of liquid; it is the interaction of these forces that constitute the disjoining pressure, Pa, that opposes contact. If the crystallization pressure reaches Pcl, then the crystal is forced into contact with the wall; therefore, an upper botmd on the crystallization pressure is set by Pet, which is related to A 7- To get an estimate of the limiting pressure, suppose that the disjoining pressure is given by Pa = Po e-a/~
(3)
where S is the distance from the surface of the crystal to the surface of the wall, and Po and are constants. The work that has to be done to bring area A of the interfaces together is
.
.
.
.
p dV = - ~~ A d8
(4)
Substituting eq. (3) into eq. (4) leads to po =
A7
(5)
The disjoining forces become important at short range, so if we estimate ~ = 2 nm and assume A 7-- 0.05 J/m 2, then Po --" 25 MPa; that is, the crystal could exert 25 MPa of pressure against the wall before the surfaces would be forced into contact. It has been repeatedly demonstrated (Lavalle, 1853; Becker and Day, 1916; Taber, 1916; Correns, 1949) that crystals grow while under load, indicating that there is a film of solution between the crystal and the obstacle. The film is sustained, because the disjoining pressure opposes contact, but if the supersaturation is high enough, then the crystallization pressure will exceed Po and the film will be eliminated (i.e., the solid surfaces will touch). Thus, the crystallization pressure has an upper bound determined by A 7. The role of the interracial energy might
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explain the observation that sodium sulphate is more destructive than sodium chloride: it has been observed (Rodriguez-Navarro and Doehne, 1999) that the sulfate crystallizes under the surface of the solution, whereas the chloride tends to nucleate at the air/water interface. This suggests that the sulfate has a stronger tendency to preserve a liquid film at its surface.
3. Supersaturation Suppose that a crystal of A is in equilibrium with a solution of A in liquid B, and let x be the mole fraction of A in the solution. The Gibbs-Duhem equation (Lyklema, 1991) describing equilibrium for the solution is ( 1 - x)dlur. + xdt.t c = V s dps - S s dT
(6)
where/gL and/gc are the chemical potentials of the liquid and crystal, respectively, Ps is the pressure in the solution, and Vs and S s are the molar volume and entropy of the solution. The chemical potentials can be written in terms of the activity, a, of each component. For the crystal, d/2c = d/20c + R g T d l n ( a c )
(7)
There is pure crystalline material present, and the activity of that component must be the same in every phase in equilibrium; since the activity of the pure solid is unity, the activity of A in the solution must be a ~ = a~o~ = v~ @~ - s~ a r (s) where P c is the pressure inside the crystal, and V c and S c are the molar volume and entropy of the crystal. The analog of eq. (7) for the solution is dll L = dl.lor + R s T d l n ( a r ) = dlaor + R g T d l n ( 1 - x)
(9)
where the approximation is valid for an ideal solution (i.e., where Raoult's law applies); for the sake of simplicity, we will assume that the solution is ideal. The differential of the chemical potential for the pure liquid, d/20L, can be found from the Gibbs-Duhem equation, so eq. (9) becomes a~,. = v,. @,. - s,. d r - l, 1 - x ) &
( 1 O)
In the following, we assume that the temperature is constant, so the entropy terms vanish. The molar volume of the solution is related to the partial molar volumes of the components by Vs=(1-x)Va+xV c (11)
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The pressure in the liquid, PL, in eq. (10) is equal to PS' but the pressure in the crystal, Pc, in eq. (8), is given by the Laplace equation (Defay and Prigogine, 1966): Pc = Ps +
7CLrCcL
(12)
where I~CLis the curvature of the crystal/liquid interface; for a spherical crystal with radius r, tCCL= 2/r, whereas for a cylindrical crystal with radius r, K'CL= 1/r. Substituting eqs. (8) and ( 1O) into eq. (6), and making use of eqs. (11) and (12), we find - R g T dx = A V s dps - x V c d(~,CLtCcL)
(13)
A V s = V s - [ ( 1 - x ) V a +xVc] = x(Vc - Vc)
(14)
where
The second equality results from the fact that the partial molar volume in an ideal solution is equal to that of the pure component (Wall, 1965, p. 348). When a large fiat crystal is present, so that rCCL= 0, then eqs. (13) and (14) lead to the well-known result (Wall, 1965, p. 353) for the pressure dependence of the solubility"
dps
(15)
R~T
Integration of eq. (15) leads to eq. (2), but it does not represent the crystallization pressure; it describes the change in solubility when the crystal and liquid are subjected to the same pressure. In the case of crystallization pressure (see below), the pressures on the crystal and liquid are not equal. For many salts, V c - Vc < 0, so the solubility increases with applied pressure; in an unsaturated body, the capillary pressure is negative, so the solubility decreases in the pores. Integrating eq. (14) over the appropriate limits, we obtain Ps
~'CL K'CL
Pe
0
RJidln(x)=-;(Vc-Vc)dp,+ Xo
; Vcd(Tcr.tccr.)
(16)
where Pe is the equilibrium pressure at which the solubility x o is measured. When the pressure in the liquid is atmospheric, so Ps = Pe, eq. (16) reduces to the Freundlich equation:
~'c,. ~:c,. = Vc
'17
which means that a crystal with a curvature of I~CLis in equilibrium with a supersaturated solution. For a crystal to enter a cylindrical pore with radius rp, it must adopt a curvature of tcCL = 2/rp, and this is only possible when the liquid in the pore is supersaturated by the
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amount given by eq. (17). The pressures are usually not high enough to affect the molar volumes significantly, so eq. (16) can be integrated to obtain
RgTln(k,XoJ X-~-I=-[Vc-Vc](Ps-Pe) Vc
(18)
The Laplace equation requires that
Ps
= Pe + ~'LVIqLV
(19)
where YLV and ~cLVare the energy and curvature of the liquid/vapor interface, so eq. (18) can be written as
Yc,
IVCL
RxT l n ( X / +
-~
~,Xo;
v~
YLV ]~LV
(20)
At any relative humidity below 100%, tcLV < O; thus, if Vc - Vc < O, the tension in the liquid raises tCCL, which allows the crystal to enter smaller pores.
4. Crystallization pressure We are finally ready to quantify the pressure exerted by a crystal on the pore wall. Consider the situation shown in Fig. 1, where a crystal is in equilibrium in a cylindrical e = 2~(re 6), where t~ is the pore. The hemispherical end of the crystal has curvature tCCL thickness of the gap between the crystal and the pore wall (which exists as a result of disjoining forces). There is negative pressure in the liquid that is controlled by the curvature, tcLV, of the liquid/vapor meniscus in the pore entry. At equilibrium, the concentration of solute in the pore liquid is given by eq. (20), and the internal pressure in the crystal is found from eqs. (12) and ( 19): Pc = Pe + ~tLVICLV + ~CLJ~CL
( 21)
s = l l ( r p - b'), so it Along the cylindrical sides of the crystal, the curvature is only KCL appears that the crystal is not in mechanical equilibrium. However, the additional pressure is provided by the disjoining pressure at the pore wall, Pd: Pc = Pe + )'LV KLV + YCL~CSL+ Pd
(22)
The magnitude of the disjoining pressure is found by comparing eqs. ( 21) and ( 22): S
~CL
pa =YCL(KCL--lCCL)= r p _ 6
(23)
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Fig. 1 A crystal is in equilibrium in a portion of a cylindrical pore with radius r e. The pressure in the liquid is fixed by the negative curvature, tq.v, of the liquid/vapor meniscus that resides in the pore entry, where the radius is r E. There is a gap with thickness between the crystal and the pore wall. where the second equality applies for a crystal in a cylindrical pore, as in Fig. 1. The quantity in eq. (23) is the crystallization pressure; that is, it is the pressure that the wall must exert on the crystal to prevent it from growing. It is related to the supersaturation through eq. ( 20); for a crystal in a cylindrical pore, it reduces to
Pa =
2
-2 L--~-c
"~0 "Jr"
VC
7 LV llfLV
(24)
If the supersaturation increases, then the crystal will grow; when it reaches the pore entry (see Fig. 1), it will adopt a curvature such that eq. (20) is satisfied, or it will pass through the entry if x / x o is high enough to permit ~r to exceed 2 / ( r E - 6). If the pores are large, then eq. (23) indicates that the crystallization pressure is not large; if the pores are small, then the pressure can be quite large, but cannot exceed the maximum disjoining pressure, which is given schematically by eq. (5). Now we have the pressure exerted by the crystal, but further analysis is required to find the stress that leads to cracking. The radial stress on the pore wall, o"r, is given by (Scherer, 1999) O'r "-" - P s - P d + ?'wt ~r
(25)
which includes contributions from the pressure in the liquid (controlled by the curvature or the liquid/vapor interface, which in turn depends on the relative humidity), the disjoining pressure (owing to the proximity of the crystal), and the curvature of the wall/liquid interface (tCWL = 1/rp); the negative signs appear because of the convention that compressive
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stresses are negative, while compressive pressures are positive. Eq. (25) represents the compressive stress exerted normal to the wall. The destructive tensile stress is the circumferential (or hoop) stress, ao; if the porosity is not very high, then a o = - a r (Scherer, 1999), so eqs. ( 23)-(25) lead to S O'O= ~tLV]C~LV"I-~fICL(IC~EL~ ]C~CL )~ ~/tWL~r
(26) =
~cc ~LVICLV+ - 2 V c
\XoJ
rp
where the second equality applies only for a crystal in a cylindrical pore, as in Fig. 1.
5. Crystallization in a gap
Consider the case shown in Fig. 2, where evaporation has driven the liquid/vapor meniscus into the gap between the crystal and the wall, so that tcLV-~ 1/(8/2) = 2/8. In this case, the side and the end of the crystal are no longer in equilibrium, because they are no longer joined by liquid through which ions can diffuse. To analyze the equilibrium in this case, eq. (12) must be replaced by eq. ( 22); then proceeding in the same way, we find that eq. (18) is replaced by
RgTID(kXOJ X"I~--IVc T~t --Vc)(PS Cr -Pe)"~TCLIc~SCL
(27)
From eqs. (22), (25), and (27), we find that the tensile stress in the pore wall surrounding the gap is = Vc
\ x0 )
~
7Lv tcLv- YcLtCcr - YwdcwL
(28)
Fig. 2 Evaporation has driven the liquid/vapor meniscus into the gap between the crystal and the pore wall.
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s L and Ir If the pore and the salt crystal are both large, then the curvatures K'C ble, and the tensile stress reduces to (~gap .... RgT
- Vc
In
+
~
7LV ~LV
are negligi-
(29)
which means that the stress is bounded only by the disjoining pressure, Pc/" This is an important result, because it means that large pores are effectively converted into small pores when they are filled with salt, so that high crystallization pressure can occur in stone with coarse pores. In particular, the situation in Fig. 2 could describe the stress created at the end of a columnar crystal bridging a large pore. However, this stress can occur only if the meniscus lies entirely within the gap; if the liquid extends to the end of the crystal, then that region will grow and the pressure will be limited by eq. (26).
6. Conclusions A review of the thermodynamics of crystallization pressure supports the theory of Correns, with regard to the pressure in the crystal; however, the tensile stress in the pore wall is estimated to be about half that large. When the crystal is not in mechanical equilibrium, then high stresses can occur in large pores. This is possible when the pore is nearly filled with salt, and the liquid/vapor meniscus retreats into the gap between the crystal and the pore wall (in which case the gap acts as a small pore). 7. References Becker G.F., Day A.L., 1916. Note on the linear force of growing crystals. J. Geology XXIV [4] 313-333 Benavente D., Garcia del Cura M.A., Fort R, Ordofiez S.,1999. Thermodynamic modelling of changes induced by salt pressure crystallization in porous media of stone. J. Crystal Growth, 204, 168-178 Correns C.W., 1949. Growth and dissolution of crystals under linear pressure. Disc. Faraday Soc. 5,267-271 Defay R., Prigogine I., 1966. Surface Tension and Adsorption. Wiley, New York. Lavalle J., 1853, Recherches sur la formation lente des cristaux ~ la temp6rature ordinaire. Compte Rend. Acad. Sci. (Paris) 36, 493-495 Lyklema J., 1991. Fundamentals of Interface and Colloid Science, Volume 1. Fundamentals. Academic, London. p. 2.35 Rodriguez-Navarro C., Doehne E., 1999. Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern. Earth Surface Processes and Landforms 24, 191-209 Scherer G.W., 1999. Crystallization in pores. Cement Concr. Res. 29, 1347-1358 Taber S., 1916. The growth of crystals under external pressure. Am. J. Sci. 41, 532-556 Wall F.T., 1965. Chemical Thermodynamics. Freeman, San Francisco.
195
STONE MATERIALS USED IN THE MASONRY OF ORTIGIA (SIRACUSA, SICILY) A.Calia 1, A.M.Mecchi CNR - Is.C.O.M., Lecce, Italy. L. Scudeler Battelle Dipartimento di Mineralogia e Petrologia- Universit/l Padova, Italy
Abstract
In this paper, the study of the natural stones used as constructional materials in the buildings of Ortigia is described. This looks at: a) identification and classification of lithotypes used and knowledge of their places of origin; b) macroscopic survey of their state of conservation; c) determination of porosity characteristics and possible presence of soluble salts, in relation to their state of conservation. With these aims in mind, samples of surface materials in a variety of states of conservation were taken from different types of buildings, in different parts of the area under study. As a means of establishing provenance, samples of living rock were also taken from the outcrops and quarries, extant or in disuse, in various parts of the province. The following studies were carried out on the collected samples: mineralogical and petrographic analysis by observation of thin sections and by X R analysis; quantitative analyses by atomic absorption spectrophotometry, porosimetric analyses; measurement of soluble salts content by ions cromatography. These studies have lead to the identification of various calcareous building materials, showing different intrinsic characteristics and levels of conservation. Key-words: constructional stones, stone decay, calcareous porous stones, soluble salts. 1. Introduction
Ortigia is an island on which the historic part of the town of Siracusa (Sicily) developed. It was the first nucleus of the ancient Greek town, before it was extended to the hills on the dry land. It is mainly made up of buildings dating from the 17th to 19th centuries, most of which in fact date from the reconstruction of the town after the earthquake in 1693. The historical sector of Ortigia comes under a conservation programme promoted by the municipal authorities. This project, conducted under the joint aegis of the municipal authorities of Siracusa (Comune di Siracusa) and the National Institute for Cultural Heritage (Istituto Nazionale di Beni Culturali), has the purpose of drawing up preliminary detailed inventories of the materials used, as well as of checking the reliability and efficiency of the conservation methods and modus operandi with a view to drawing up a code of practice for rehabilitation works. The study of the stone materials is presented in this paper. It was applied to the identification and classification of lithotypes used in the buildings, as well as to the evaluation of Author to whom correspondence should be addressed.
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9th International Congresson Deteriorationand Conservationof Stone, Venice 19-24June 2000
their state of conservation. It also is aimed to the identification of their places of origin,by comparison with materials taken from geological formations in the region. With those cognitive and preservative aims, samples of materials taken from the buildings themselves, and from outcrops and quarries were examined.
2. Experimental part The study was organised along the following lines: a) the macroscopic survey of building materials and their states of conservation. Observed morphologies of decay were classified according to the lexis Doe. Normal 1/88 (Doe. NORMAL 1/88, 1990). b) the collection of samples (n. 90) in various states of conservation, from different buildings at various points in the study-zone. (fig. 1). c) the collection of samples (n.30) from outcrops and quarries, extant or in disuse, located in Ortigia and in various part of the province (fig.2). The sample sites were chosen on the basis of the geological formation of the area (Carbone Set al., 1987). d) mineralogical and petrographical analyses, by observation of thin sections through polarised light microscopy (on all collected samples). e) XRD analyses (Philips PW 1710 Diffractometer, 20KV, 40mA) - on 15 samples from masonry and 15 from outcrops and quarries. f) determination of insoluble residual content, quantitative analyses by atomic absorption spectrophotometry (Perkin-Elmer 5000 spectrophotometer), determination of Ca/Sr ratio alter stoichiometric calculus of Ca content - on 12 samples representative of different consituent lithotypes of the buildings. The chemical attack of samples and preparation of solutions were made following Veizer procedure Fig. 10rtigia: sites of collection of the samples (*). (Veizer J. et al, 1978).
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g) measures of integral open porosity (Pi) and porosimetric distribution by mercury porosimetry (Carlo Erba 4000 porosimeter) according to procedures described in the document Normal 4/80, 1980 (Doe. NORMAL 4/80, 1980) - on 15 samples from buildings. h) measures of specific weight (~'r) by means of a Ruska Instrument helium pychnometer, measures of bulk density (qCa)by means of a Chandler Engineering mercury pyehnometer, calculus of Total porosity as Pt=Tr%/Tr, - on 8 samples representative of different lithotypes inside the buildings. i) determination of soluble salts content by ions chromatography (Dionex 300 ions chromatograph). The results for each sample are expressed as percentages in weight. Each value is the average of three measurements taken on a solution prepared in the following way. The sample is ground into a fine powder; 100 ml of bidistilled water are then added to 100 mg of dried powder. The solution is agitated for 2 Fig.2. Sites of collection of samples from living rock.
hours, left to deposit for 1 hour
and then it is filtered through a "black band" filter; measures of conductibility were made on the same solution. The analyses were made on: 34 samples taken from the surface of masonry in various parts of the study-zone; 5 cores up to 4 cms deep, from just one building; 10 samples from living rock. The samples were mainly taken at man height; only in the case of the cores were sampies taken at heights corresponding to the first floor of the building, in positions protected from rainwater by scaffolding but exposed to the effects of heavy traffic.
3. Results and discussion 3.1 Macroscopic survey Before proceeding to laboratory tests, a careful on site inspection was carried out in the various districts that make up Ortigia; it led to the macroscopic identification of different building materials in different states of conservation.
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The most commonly used material is a finely-grained and evenly-structured biocalcarenite called "Palazzolo Stone". Its state of conservation is very variable depending on: a)- different original lythological characteristics of the facies of which the stone is made up; b)- building repairs such as replacements, not always properly documented; c)- different exposure conditions. Generally speaking, this stone suffers the most damage lower down in the masonry which are affected by capillary rising damp. In such cases the observed morphologies of decay are alveolisation and erosion. Some buildings, particularly those more exposed to sea spray are badly damaged; they show deep erosion which spreads up to higher levels, with loss of material some centimetres deep. In the same way, in certain parts of the buildings, especially those below balconies where a strong channelling of rain water takes place, crumbling of material is observed. Some buildings of "Palazzolo Stone", especially those of the 20th century, have the footing made of a compactly-structured fine-grained white-coloured calcareous stone, apparently more resistant and in a good state of conservation, if compared with previous materials. Oolitic calcarenites, more or less fossil-bearing of a somewhat spongy appearance with massive or layered structure are also employed. Their state of conservation is better than that of "Palazzolo Stone". Certain porous-looking types show erosion and sometimes superficial decohesion, while those with more compact structure show only superficial signs of dissolution.
3.2 Mineralogical and petrographical analyses Stone materials recognised inside the buildings of Ortigia, as well as those coming from outcrops and quarries, were classified on the basis of petrographical observations, following the Dunham terminology (Dunham R.J., 1962), updated by Embry & Klovan (Embry A.F. & Klovan J.E., 1971). The results of the observations on the samples taken from the buildings are: - the so-called Palazzolo stone is made of fine and and coarse packstone-wackestones (respectively Pf and Pc groups) - the stone often used for the footings of buildings is also a fine packstone-wackestones (Co
group);
- oolitic calcarenites include: normal oolithic grainstones, grainstones with miliolidae, fine oolitic grainstones (Op group), compacted oolitic grainstones (Oc group). It is important to note some characteristics concerning the fabric in order to try to explain the behaviour of the material on site. The stones of the Pf and Pc groups are made of a poor cemented calcareous detritus (fragments of rocks and fossils). The cement is calcitic and mainly intergranular, with fine texture (microsparite) and mixed with micrite; the intragranular variety is made of larger crystals (ortosparite). The texture of those stones is compact, and their porosity is high, widespread and made up of small size pores (not measuring above a few dozen microns), due both to the poor quantity of the original cement and post diagenetic dissolution processes to which the stone underwent. The lithotypes of the Cc group also possess a clastic-organogenic texture, made of calcareous detritus, with a fine texture and strictly mixed with micrite. They differ from the previously described variety in that they contain a greater quantity of micrite and a finer
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granular structure. Moreover, they are considerably more compact and, as a result, display a much lower level of porosity with very small pores (no greater than a few microns). The oolitic calcarenites, in their different sub-types, are mainly made of oolitic grains, cemented by spatic calcite. Inside their structure there is an intercrystalline porosity which interests the cement and an intragranular one, with larger sizes (from over 50 to 300 microns) which is due to the dissolution of the oolitic nuclei. The calcarenites of the Oc group has a higher density of the grains as a result of the compactation, a higher degree of cementation and less dissolution effects than the Op group. From the observations on the samples taken from quarries and outcrops, the following listed lithotypes have been identified (collection sites are placed in brackets alongside); they are grouped according to their source geological formations. Palazzolo Formation: fine packstones-wackestones (surroundings of Palazzolo). Monti Climiti Formation: grainstones-rudstones (CanicattinL Punta Arenella); rudstones with rhodolites (Capo della Tonnara, Epipoli, Latomie Siracusa); waekestones with miliolidae, rudstones with gastropods, floatstones with red algae incrustations ~orte Vigliena). Monte Carrubba Formation: wackestones-packstones (Penisola della Maddalena); fine oolitic grainstones (Punta Arenella); oolitic grainstones with bivalves (Capo Ognina, Capo S.Croce); rudstones with or without red algae (Puma Arenella,, Punta Izzo, Capo Ognina); fioatstones with or without red algae (Penisola della Maddalena). As had been previously observed on thin sections, the diffractometric analyses confirmed the presence of calcite as a fundamental component; the dolomite in both the packestones-wackestones and the oolitic grainstones is sometimes present. The aragonite was also found on samples of oolitic grainstones taken from outcrops. Apart from lithological characteristics, traces of sodium chloride and gypsum were also frequently found on sampies. These two dements are undoubtedly the result of recent superficial accumulations as they are incompatible with the formation of the samples under study. The mineralogical and petrographical comparisons between samples from buildings in Ortigia and those from geological formations present in the region but also the examination of the hypothesis of paleoambiental reconstruction reported in the literature (Pedley H.M. et al., 1992) point out: a) from the two identified sub-types of the so-called "Palazzolo stone", the Pf variety seems to be attributable to the geological Formation of Palazzolo, while the Pc one could well originate from the Monte Climiti geological Formation; b) Cc group (minute packstones- wackestones) also seems to be attributable to the Monte Climiti geological Formation; c) both Op and Oc groups of the oolitic grainstones seem to belong to the geological Formation of Monte Carrubba.
3.3 Insoluble residual and analyses by atomic absorption spectrophotometry The percentage of insoluble residue (i.r.), the content of Mg, Fe, Sr, Na, K, Mn, expressed in p.p.m., and the CaJSrx1000 ratio are listed in table 2.
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Table 2. Amounts of insoluble residual and some chemical elements. samples Pt2 Plq4 Pfl6 Pc45 Pc39 Pc51 Pc68 Cc47 Op23 Oc40 Oc~l Op65
% i.r
Mg
p.p.m,
1 0.87 1.28 3.11 1.08 1.01 1.69 4.61 0.18 0.i5 0.27 0.21 ....
5909 6359 663i 6459 13915 6669 5459 4482 ' 2092 2547 3518 2955
Fe
Sr
Na
1116 2750 2091 1694 1581 1954 3324 1921 1233 3984 i622 1777 3045 3632 1768- .... 333 3662 243 3182 797 2021 421 2648
K
1320 4458 1280 1149 1181 1295 6061 572 ' 602 664 936 289
xl000 Sr/Ca
Mn
889 15 7.09 1221 47 4.37 5.07 848 37 5.07 1845 76 ~o.58 549 8 4.6 788 42 9.42 4137 35 956 111 .... 3.04 9,24 210 50 8.04 153 21 5.13 465 16 196 " ' i 8 . . . . 6.7 ,
,
....
,
The samples of "Palazzolo Stone"(Pf and Pc groups) show higher quantities of Fe which account for the markedly yellowish colour of this material; the high amount of Mg found in sample 39P derives from the presence of dolomite, already identified by means of XRD analyses. On the other hand, the considerable contents of Mg found in the other samples cannot be adduced to the presence of this mineral. The (Ca/S0 ratio, which is an index of the diagenetie processes that lead to the transformation from incoherent deposits to solidified rock, registers high values in all the samples. They indicate the precocity of the diagenetie processes, whose effects were different in terms of compacting and cementation of the components of each lythotype, as has been observed by microscopic study on thin sections. 3.4 Porosity characteristics
The table 3 sets out total and integral open porosity values (respectively Pt and Pi) and the porosimetric distribution of each samples of different lythotypes. Table 3. Porosit,r values and porosimetric distribution. samples Pt
Pi-
(%) (%)
on
i.
36
Pt3 Pfl6 Pf21 Pc39 Pc51 Cc47 Cc64 0p22 0p23 0P42 0p65 .
.
.
.
.
.
.
37 37 36
.
.
oc4o oc4i 0c43
0-0.05 0.05-0. 2.8 30 1.2 30 3.7 3.5 31 3.2 4.2 29 4.6 4.1 33 3.6 2.5 34 3.3 4.7 10 30.8 37.4 17 19.3 40 37 11.8 5.7 31 5.1 3 33 14.8 2.8' 37 15.5 4 23 23.7 4.2 22 ~ 15.9 16.5 28 42.7 19.9
10 31 33 39
-
,
.
.
.
.
Pore radius (microns) 2-4 4'-10 10-50 0,i-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1 1-2 7.6 7.2 '5.9 38'.5 2O.6 0.5 0 5.7 10 7.9 7.8 7.5 44.1 5.9 9.9' 7.5 0.8 1.6 5.2 4.0 3.4 15.7 28.5 20.4 0 '7.3 8.1 5.4 4.4 3.9 19.9 ~34.9 3.2 3.7 7.3 8.8 40.4 11.2 0.8 3.3L 5.7 513 7.3 4.7 25.1 37.4 18 1.5 3.9 3.7 2.7 15.5 3.8 5.4 0'4 0.6 0 0.2 0.4 0 0.4 28.5 1.4 3.29 2 2.5 3.5 20.9 22.9 6.4 3 213 20.3 15.7 3.5 2.5 10.2 16.8 4.8 4.7 4.0 25.7 1'2.6 6.3 2 . 1 10.2 9.4 6.1 6.6 13.1 25.6 17.2 4.5 4.3 6.5 7.1 7.4 3.7 6.'2 21'.'7 16.7 5.5 2.2 6.1 9.1 7.1 6.6 5 . 5 1415 10.6 10.9 '11 6~15.3 3.5 5.8 4.5 9.8 6 . 5 4.1 ' 4.3 14.1 13.2 6.9 5 3.8 318 3.9 3.7 7.0 6.4 5.9 3.0 2.0 2.0 .
.
.
.
,
.
.
.
,
.
,
.
.
.
.
.
.
.
.
. . . .
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The samples of the Pf group all show similar if not identical Pi values; as is the case with the porosimetric distribution which follows a bimodal cline with a heavily accented maximum value around 1-4 microns. The samples of the Pc group register slightly higher Pi values than those above, with a lower percentage of pores measuring less than 1 micron. The samples of the Cc group have much lower Pi levels and notedly smaller pores. The Op group show a higher Pi value and a mainly consistent distribution of pores sizes; the Oc group has lower Pi levels and a more variable distribution of pore sizes but which, anyway, fall within the range of smaller sizes. The comparison between Pt and Pi values leads us to make various comments on the materials under study. "Palazzolo stone" (both Pf and Pc groups) registers higher Pt values than Pi. Beating mind observations made under microscope which did not show up pores of any great size, this is probably due to the presence of very small pores which cannot be identified by mercury porosimetry. The porosity levels of the oolitic calcarenites are fairly high and consistent. As already found in other materials containing a large number of macropores (Mecchi A.M. et al., 1998), one can expect a higher Pt value than Pi, as a result of the considerable number of pores exceeding 75 microns which are shown up by the microscope but outside the range of measurement by mercury porosimetry. The absence of this disparity suggests that these pores have the shape of a bottleneck and, for this reason, mercury would have entered them, thereby classifying them as having dimensions below 75 microns. On the other hand, the hypothesis that those pores are closed does not stand up on examination of thin sections of which the observed porosity is comparable with the registered Pt.
3.5 Soluble Salts Analyses Measurements were taken for the following ionic species: F, CI, NO2, NO3, PO4=, SO4, C204=, Li +, Na +, NH4 +, K +, Mg ++, Ca ++. Only those with highest amounts are shown in the table 4. Table 4. Soluble salts content
cond CINOa PO4-S04= Na § K§ Ca ++
8 Samples ' 0-50~tS average min max 44 38 48 0.30 0.08 0.81 0.10 0 0.37 0.16 0 0.59 0.20 0103 0.39 0.i4 0.05 0.24 0.12 0.05 0.15 0.80 0.63 1.04
buildings 19 samPles - 50- lOolxs 7 samples- 10o- 163~ts average rain max average min max 71 51 98 137 99 163 0.75 0.18 2.14 1.40 0.48 3.36 0.56 0 4.15 0.90 0.15 2.13 0.22 0 0.77 0111 0 0.34 0.94 0.04 1.14 2.26 0.05 4.43 0.39 0.07 1.66 1.77 0.09 3.46 0.13 0.06 0.27 0.20 0.05 0.36 1.01 0.64 1.40 1.10 1.07 2.62
living rock 10 samples- 0-50itS average min max 46 34 88 0.38 0.08 1.19 0.09 0.01 0.19 0.02 0 0.08 0.16 0.01 1.14 0.19 0.06 0.59 0.08 0.05 0.14 1.22 0.65 1.54
As the contents of the various ionic species have proved to be extremely heterogeneous in the various samples, these have been grouped together according to three ranges in conductibility. On account of these wide differences, the standard deviation appears of no relevance; as a result, the minimum and maximum measurements are noted for each ionic species. Chlorides and sulphates are in the highest amounts, with a predominance of one or the other in different cases; nitrates and phosphates are also present to a lesser degree. Traces of F,C20~,NH4 +, Mg ++ are also sometimes found. NA +, K +, Ca ++ are the most abundant
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abundant cationic species. The high level of correspondence between the amounts of CI, SO4-and Na § Ca++ leads us to suspect the presence of halite and gypsum, previously identiffed by XRD analysis. The content of soluble salts measured at different depths inside the cores do not differ greatly from the previously discussed surface measurements. An observation of the distribution of values of each ionic species, moving from the outride of the cores to the inside, does not reveal a homogeneous tendency either towards an increase in values or a decrease of same. Nevertheless, their presence is up to a depth of 4 cms. and sometimes at greater amounts than on the surface. It should, however, be pointed out that the overall indices of presence (in both superficial samples and cores) are not high. These results compare with those registered in the cases of other stones from Southern Italy (Laurenzi Tabasso et al., 1989; Laurenzi Tabasso et al., 1992; Zezza F. et al., 1995). The levels of soluble salts found in samples taken from living rock - quarries and outcrops - are low and fairly evenly distributed throughout the different samples; only in two cases does the presence of CI" and SO4- proves to be approximately four times the average of the levels of presence encountered.
4. Conclusions
Different types of stones used as building materials have been identified in buildings in Ortigia. Initially distinguishable at a macroscopic level, they have been subsequently classified on the basis of mineralogical and petrographic characteristics as well as in terms of porosity structure; they also demonstrate different levels of conservation which can be related to their intrinsic characteristics. The so-called "Palazzolo stone", in its two varieties (Pf and Pc groups) seems to suffer markedly from processes related to the presence of water and salts as is evident from the poor state conservation especially in those buildings affected by capillary rising damp or exposed to sea spray. This behaviour seems to be related to its textural and porosimetric characteristics (poor level of cementation, high porosity and predominant presence of small pores). The oolitic ealearenites of the Op group, although macroscopieally somewhat similar to "Palazzolo Stone" and with a comparable porosity, manifest a better state of conservation. This could be due to either their textural characteristics (essentially the greater presence of crystalline cement) or their porosimetfic structure: if one considers the hypothesis drawn in the discussion of the porosity results valid (see Paragraph 3.4), they could have the predominant presence of larger pores. The other types of materials studied (Ce and Oc groups) do not seem to be affected by pulverisation and their deterioration takes the form of slight erosion as can be explained by their more compact nature. The importance of the study carried out on the constituent stones of Ortigia lies in the documentation of the historically used building materials and with regard to the choices concerning future conservation works. It will be necessary to be bear these intrinsic characteristics of the materials in mind in the selection of both methods and products to be used in their conservation or their replacement. Substitute materials could be looked for among the geological formations in the surroundings of Siracusa. On the basis of the mineralogical and petrographic characteristics and by comparison with samples of living rocks, the building materials used in Ortigia have, in fact, been attributed to certain geological formations
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outcropping in the territory surrounding Siracusa. It would be possible to arrive at a more precise idea of their provenance making use of historical studies of the old quarries. References Carbone S., Grasso M., Lentini F., 1987. Lineamemi geologici del Plateau Ibleo (Sicilia S.E.). Presentazione delle carte geologiche della Sicilia Sud-Orientale. Memorie Societa Geologiea Italiana, 38. 127-135. Doe. NORMAL 4/80, 1980. Distribuzione dei pori in funzione del loro diametro, C.N.R., I.C.R., Roma. Doe. NORMAL 1/88, 1990. Alterazioni macroscopiehe dei materiali lapidei: lessico, C.N.R., I.C.R., Roma. Dunham R.J., 1962. Classification of carbonate rocks according to depositional texture. Classification of carbonate rocks. Mem. American Association Petrology and Geology, 1, W.E. Ham Ed. 108-121. Embry A.F. & Klovan J.E., 1971. A late Devonian reef tract on Northeast Banks Islands Northwest territories, Bullettin Canadian Petrology and Geology. 19. 730-781. Laurenzi Tabasso M., Di Pierro D., Guidi G., Di Bartolomeo A., Pierdominici F., 1989. Lo stato del paramento lapideo del Palazzo dei Celestini di Lecce: risultati delle indagini chimico-fisiche. The conservation of monuments in the Mediterranean Basin, Proc. Of the First International Symposium, Bari, Grafo Edizioni. 209-212. Laurenzi Tabasso M., Santamaria U., 1992: La biocalcarenite di Lecce: un metodo di valutazione di alcuni trattamenti conservativi, Materiali e Strutture - Problemi di conservazione, 2.45-57 Mecchi A.M., Calia A., Quarta G., 1998. Caratterizzazione di un materiale da costruzione della Puglia: il carparo. Recuperate l'edilizia, Milano, Alberto Greeo Edizioni, I, 3.3337. Pedley H.M., Cugno G., Grasso M. 1992: Gravity slide and resedimentation processes in a Miocene carbonate ramp, Hyblean Plateau, southeastern Sicily, Sedimentary Geology. 79. 192-202. Veizer J., Lemieux J., Jones B., Gibling M.R., Savelle J., 1978. Paleosalinity and dolomitization of a lower Paleozoie carbonate sequence, Somerset and Prince of Wales islands, Arctic Canada. Canadian Journal of Earth Sciences, 15. 1448-1461. Zezza F., Garcia Pascua N., Macri F. 1995. Rising damp and soluble salts in the weathering processes of biocalcarenites. Case study of cathedrals, churches and buildings of Leccese baroque, Actes Congr6s LCP "Conservation et restauration des biens culturels", Montreux. 161-174.
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CONTROL OF MARBLE WEATHERING BY THERMAL EXPANSION AND R O C K FABRICS S. Siegesmund * Institut ~ r Geologie und Dynamik der Lithosphare, Goldschmidtstr. 03, 37077 G6ttingen, Germany T.Weiss Institut ~ r Geologie und Dynamik der Lithosphere, Goldschmidtstr. 03, 37077 G6ttingen, Germany E.K. Tschegg Institut ~ r Angewandte und Technisehe Physik der TU Wien, Wiedner Hauptstr. 8-10, A1040 Wien
Abstract
Marbles as building stones as well as in their natural environments show complex weathering phenomena. The most important damage scenario is based on the highly anisotropic thermal dilatation coefficient a of calcite, i.e. extreme expansion parallel and contraction normal to the crystallographic c- axis. Due to thermally induced stress incompatibilities the grains loose their cohesion, and the final stage is a sugar-like disintegration of the marble. The rock fabric and especially the lattice preferred orientation (texture) of calcite and/or dolomite as the predominant mineral phases in marbles can have a significant influence on this mechanical weathering. Textures of marbles from six different locations have been investigated. The textures observed vary significantly in strength and type. The directional dependence of the experimentally determined dilatation coefficient is clearly controlled by the texture and, thus, can be predicted from texture measurements. Some of the samples show a residual strain after thermal treatment indicating, that thermally induced weathering started already after one heating cycle. Unfortunately, the residual strain is not unequivocally linked to the type and strength of the texture. However, a basic observation is that the directional dependence of (i) the thermal dilatation coefficient and (ii) of the residual strain is large in marbles with a strong texture. The Rosa Estremoz marble, with a distinct texture, shows a larger residual strain parallel to the direction of maximum dilatation than parallel to the direction of minimum dilatation. In contrast, one of the Carrara marbles with a weak texture exhibits a uniform crack formation. But the texture alone gives no unequivocal evidence for large or small residual strains and their directional dependence. There are strongly and weakly textured marbles which exhibit no residual strain. The Kauffung marble with a strong texture and one of the Carrara marbles with a weak texture do not show any residual strain. Both of them are characterized by a fabric with an irregular grain shape geometry but their grain size is remarkably different. Thus, a comprehensive approach is required to assess the quality and durability of a marble as a building stone. Keywords: Marble, Building stone, Physical weathering, Thermal dilatation, Rock Fabrics 1. Introduction
Marble has been used as a building stone since more than 5000 years. However, numerous cases of damage on sculptures, architectural heritage or facade stones made of marble indicate that the deterioration of building stones mainly depends on the climate. * Author to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservationof Stone,Venice 19-24June 2000
Those parts of marble which are exposed to weathering suffer not only by the atmospheric degradation, but in particular by permanent changes of temperature and moisture. Most spectacular examples for proceeded weathering are completely destroyed facade claddings of the Finlandia Hall in Helsinki (Ritter 1992; Fig. l a). Such phenomena are also frequently reported from ancient gravestones (Grimm 1999; Fig. l b). The reasons for the observed deformations are still in discussion. Kessler (1919) found that repeated heating may lead to permanent dilatations due to microfracturing. Bortz et al. (1988) and Thomasen & Ewart (1984) concluded that a variation in moisture contents may be responsible for the deformation. Although marble has a very simple mineralogical composition, the mechanical weathering of marbles due to its extremely anisotropie physical properties seems to be essential. The rock fabric, which includes grain size, grain aspect ratios, grain shape preferred orientation, lattice preferred orientation (texture) and the microcrack populations, controls the materials behaviour.
Figure 1: Marble decay: a) Deformed facade cladding made of Carrara marble from the Finlandia Hall in Helsinki and b) bent gravestone (Carrara marble) from the cemetery Montmartre in Paris. Marbles with distinctively different fabrics were selected to investigate the relationship between the anisotropy of the thermal expansion and the residual dilatation behaviour after heating and cooling to identify constraints on observed types of deterioration.
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2. Experimentals For the texture measurements (i.e. crystallographic preferred orientation) the neutron diffraction was applied (for details see Leiss & Ullemeyer, 1999; Weiss et al. 1999). The quantitative texture analysis was carried out by means of the iterative series expansion method (Dahms & Bunge 1989). Anisotropic physical properties like thermal dilatation can be modeled on the basis of the texture (e.g. Siegesmund & Dahms 1994; Siegesmund, 1996). For the modeling, the single crystal data published by Kleber 1959 for calcite (see Fig. 2) were used.
Figure 2: Relationship between crystallography and thermal dilatation coefficient of calcite. Rhombohedral cell with twinning planes and coefficients of thermal expansion in the directions of the crystallographic c- and a-axes (data from Kleber, 1952). Thermal expansion measurements were performed by using a triple dilatometer (for details see Widhalm et al. 1996). The specimen size was 10ol0oS0mm The starting temperature for the heating was 20~ and the upper temperature limit was fixed at 80~ for the TU, RE, WU, WA and RE marbles (for abbreviations see Chapter 3.1). The CA1, CA2 and KA marbles were measured up to 120~ In order to guarantee thermal equilibrium in the sample during heating a heating rate of 1~ was selected. Only one heating/cooling cycle was performed since the orientation and magnitude of a first thermally induced deterioration increment should be determined. 3. Results
3.1 Mkrofabric The marbles investigated in this case study originate from six locations and possess remarkably different microfabrics: Even the two specimens from the Carrara area (CA1 and CA2) exhibit different grain fabrics. The sample CA1 shows irregular grain boundaries with small grains at the rims of large grains and bulging as evidence for grain boundary migration (Fig. 3a). The average grain size is about 130t~m, but there exist more coarse and more fine grained areas. In contrast, CA2 shows straight and regular grain boundaries and an average grain size of 150pm (Fig. 3b). Twins or open cleavage planes can be observed. Diffuse bands of finer grained material are randomly distributed in both samples (Weiss et al. 1999). Besides the two Carrara samples following marbles were investigated: Turkish marble (TU, grain size 3001~m), Rosa Estremoz marble (RE, grain size 7001~m), Wachau marble (WA, grain size 4001~m), Wunsiedel marble (WU 5, WU 15 grain sizes 1601~m, WU7, grain
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size 11001am) and Kauffung marble in Poland (KA, grain size 801am). The RE and TU marbles show highly irregular grain fabric, occasionally with small recrystallized grains along the grain boundaries, and evidence for grain boundary migration. Sample WU 7 shows a weak foliation marked by alternating coarse and fine grained layers. Mineralized cracks occur at high angle to the foliation. Generally, the grain boundaries are straight but a beginning grain boundary migration is visible.
Figure 3" Mierofabrics of different marbles (long side of the photograph corresponds to 700~tm). Left: Carrara marble (CA2) with straight grain boundaries (so-called "foam structure"); Middle: Carrara marble (CA1) with irregular grain boundaries, a bimodal grain size distribution with small recrystallized grains and large relic grains can be observed; Right: Kauffung marble (KA) with elongated grains showing irregular grain boundaries. The macroscopieally visible foliation is parallel to the long side of the photograph. The WU 5 and WU 15 marbles are characterized by older relic grains with irregular grain boundaries which are surrounded by small recrystallized grains (Siegesmund et al. 1999). The KA marble exhibits a fine-grained but inequigranular structure with partly polygonal and partly interlobating grain boundaries (Fig. 3e; Siegesmund et al, 1997; Weiss et al., 1999). Diffiase dolomitic veins mainly parallel to the macroscopically visible foliation are frequent. 3.2 Textures
For all of the marbles texture measurements were performed. There is a continuous sequence from weakly textured marbles (CA1 and CA2) to strongly textured marbles (WA and WU; Fig. 3). Most of the marbles exhibit single maxima of the c-axis perpendicular to the foliation, i.e. the polefigures are similar to that of the WU 5 marble (c.s Fig. 3a). Exceptions are the TU and and WA marble (Fig. 4c), which show polefigures of the c-axes in a girdle distribution or with submaxima, respectively. However, the exceptionally high intensity of the polefigure of WA marble is caused by single crystal reflexes rather than by a bulk preferred orientation and, thus, has to be treated with care. A good example for a strong texture without single crystal peaks is the WU 5 marble (Fig. 4a).
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It can be supposed, that the anisotropy of the thermal dilatation coefficient caused by the texture is for this marble very large. Since the KA marble contains a significant amount of dolomite in veins the texture measurements were exclusively performed in the ealeitie parts of the samples.
Figure 4: C-axes [006] polefigures of the WU5 (a), WA (b) and CA1 (e) marble. The minimum (leg) and maximum (fight) intensities are given in multiples of random distribution (mrd), equal area projection, lower hemisphere. The maximum intensity of all investigated samples is summarized in (d) in nard.
Figure 5: Relationship between a) texture (e-axes polefigure, equal area projection, lower hemisphere) and b) experimentally determined thermal dilatation and residual strain of Rosa Estremoz marble. Note the directional dependence of residual strain (RS).
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.3 Thermal dilatation and residual strain
Within the limited temperature interval of AT=60~ (RE, TU, WU, WA) or AT=100~ (CA1, CA2, KA) used for the dilatation experiments, the calcite single crystal coefficients of thermal dilatation can be treated as linear. Thus, the thermal dilatation r [mm/m] observed in the experiments should be closely linked to the texture strength of the respective sample. The coincidence between texture and anisotropy of thermal dilatation is illustrated for the RE marble (Fig. 5). The thermal dilatation of the sample pararallel to the c-axes maximum (Fig. 5a) is larger than for the direction parallel to the a-axes maximum (not shown here). A significant amount of residual strain can be observed for this marble at~er heating up to 80~ Parallel to the c-axis the residual strain (0.2mm/m) is twice as large as parallel to the a-axis (0. l mm/m). At lower temperatures the dilatation coefficient is only controlled by the texture. However, beginning from a certain temperature it is superposed with an irreversible increase in length of the sample due to thermal cracking. 1.0
l
@ experimental
0.8 0.6
9 ,~
9
.... [ ] t e x t u r e
..............................
............................................................................... 9
9
[] .........................
[]
0.4
............................................................................................................
0.2
.................................... n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0.0
.........................
-0.2
9
9.........................
~
"0
[]9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
.D ................................................
.....................................................................................................
-0.4 -~ o
~
D ~
o 3
sample Figure 6: Anisotropy of the thermal dilatation coefficient calculated from the texture (open squares) and determined experimentally (filled circles). "13
It might be suspected that the texture controls both, magnitude and directional dependence of residual strain. If this holds true, calculated texture-based dilatation coefficients should be similar to those obtained in experiments. At first glance, this holds true since the anisotropy (AT) of the calculated thermal dilatation coefficient is proportional to the anisotropy of r observed experimentally (Fig. 6). A clear exception is the WA marble, but its texture is characterized by single crystal reflexes and, thus, must be excluded from this consideration. But also the two specimens from Carrara indicate that the proneness to thermal weathering is dependent on more than the texture. Both samples (CA1 and CA2) have a very similar texture and similar grain size but exhibit a completely different magnitude of the residual strain after heat treatment up to 120~ The sample CA2 (Fig. 6b) exhibits a large and the sample CA1 (Fig. 6a) small residual strain after heat treatment. According to the weak texture of both samples, the directional dependence of the thermal dilatation coefficient is small.
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The corresponding curves are almost linear with when the temperature is raised for CA1, but for CA2 the slope increases when approximately 60-70~ are reached (dotted line in Fig. 7b). This indicates that i) thermally induced cracks are generated at a certain critical crack initiation temperature (CCIT) or ii) the total thermal dilatation coefficient is buffered by preexisting crack systems at temperatures lower than the CCIT. Thus, the CCIT can serve as a parameter to characterize the marble's resistance against thermal treatment. Another exceptional example is the KA marble, which exhibits a strong texture comparable to that of the RE marble (see Fig. 5). The directional dependence of the thermal dilatation coefficient of both marbles is similar, but for the KA marble no residual strain even at~er heat treatment up to 120~ can be observed and the dilatation increases almost linearly with temperature. Accordingly, the slope of the thermal dilatation curves is quite linear.
Figure 7: Experimentally determined thermal dilatation as a function of thermal treatment up to 120~ a) Carrara marble (CA1), b) Carrara marble (CA2) and c) Polish marble (KA). Note the considerable residual strain of the CA2 marble while the other Carrara marble shows a very small deterioration due to thermal treatment. The sample directions corresponding to the curves are given in the first graph.
4. Discussion and Conclusions
A basic need for the utilization of marble as a building stone is the assessment of its proneness to weathering. The residual strain aRer heat treatment is supposed to be the first mechanism leading to a decohesion of the grains. The pore space produced by this mechanism provide pathways for fluids which chemically attack the internal structure of the rock in the next stage. Parameters controlling the mechanical weathering of a marble can be the texture, the grain size and grain shape, preexisting microcracks but also stresses in the marble under built-in conditions. The texture clearly controls the directional dependence of the thermal dilatation coefficient. Thus, texture measurements can be used to predict directions of large and small dilatation, i.e. to avoid deformations of fixed in a confined position. However, the texture induced part on thermal dilatation is superposed by a permanent length-change due to thermal cracking. A critical parameter for the formation of thermally induced microcracks may be the grain size. Marbles with larger grain sizes show thermal cracking at significantly lower temperatures (e.g. Widhalm et al. 1997). It is obvious that the ratio between grain size and grain boundary area leads to a significantly lower possible crack porosities in the ease of
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large grain sizes. Thus, an internal damage of a coarse grained marble is less easy to detect than that of a finer grained marble. However, the grain size can not be the only important parameter. Two Carrara samples with very similar grain sizes exhibit completely different residual strains after heat treatment. Thus, the grain boundary geometry, which is largely caused by recrystallization processes, signitieantly controls the weathering behaviour of a marble. Marbles with straight or only slightly curved grain boundaries (e.g. CA2; see Fig. 3a) are much less resistant against thermal treatment than those with strongly curved, interlocking grain boundaries (e.g. CA1, see Fig. 3b). Also the consideration of two strongly anisotropic marbles (KA and RE) gives evidence for the importance of the grain boundary geometry. In this ease the larger grain size of the RE marble may be responsible for the thermal degradation. The small grain size and the irregular grain shape of the KA marble does not produce internal stresses between adjacent grains in the sample exceeding the threshold of cohesion. The critical crack initiation temperature, i.e. the temperature at which thermally induced crack nucleation and propagation starts, and the total residual strain after heat treatment are important measures to characterize the proneness to thermal weathering of a marble. But also the relative humidity will influence thermal microcraeking~ since water can act as a catalyst. Thus, all of these data sets (temperature, sample sizes, humidity conditons, fabric characterization, etc.) have to be standardized in the future. Weathering phenomena of marble range from a superficial disintegration to a complete loss of cohesion along grain boundaries due to thermal treatment and, subsequently, due to chemical attacks. The final stage is the total decay of the material. It is obvious that there is no uniform deterioration scenario. Even marbles from one locality can have an extremely different proneness to weathering, as it was demonstrated by comparing the two Carrara marbles. Thus, a clear and comprehensive fabric analysis, besides petrophysical investigations, is an indispensable tool for the assessment quality of a rock as a natural building stone.
Acknowledgements S.S. thanks the German Science Foundation for the Heisenberg fellowship (Si 438/10-1) and T.Weiss for a postdoctoral fellowship We 2234/1-1. The research on the weathering phenomena is supported by the Deutsche Bundesstifhang Umwelt (DBU) and the Sonderforschungsbereich 468. References Bortz S.A., Erlin B., Monk C.B. Jr., 1988: Some field problems with thin veneer bulding stones. New stone technology, design and constretion for exterior wass system. ASTM STP 996, 11-31. Dahms M., Bunge H.J., 1989: The Iterative Series-Expansion Method for Quantitative Texture Analysis. I. General Outline. J Appl Cryst, 22, 439-447. Grimm W., 1999: Beobachtungen und Obedegungen zur Verformung von Marmorprojekten dureh Gefiigeauflockerung. Z. dt. Geol. Ges., 150 No. 2, 195-236. Kessler D.W., 1919: Physical and chemical tests of the commercial marbles of the United States. Technologic Papers of the Bureau of Standards No 123; Washington D.C. (Govenment prining Office).
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Kleber W., 1959: Einftihrung in die Kristallographie. VEB Verlag Technik, Berlin Leiss, B., ULLEMEYER, K., 1999: Texture characterisation of carbonate rocks and some implications for the modeling of physical anisotropies, derived from idealized texture types. Z. dr. geol. Ges., 150,:259-274. Ritter H., 1992: Die Marmorplatten sind falsch dimensioniert. Stein, 1, 18-19. Siegesmund, S., Dahms, M., 1994: Fabric-controlled anisotropy of elastic, magnetic and thermal properties, In Textures of geological materials (eds. Bunge, H.J., Siegesmund, S., Skrotzki, W. and Weber, K.)(DGM Informationsgesellschaft Veflag), pp 353-379. Siegesmund S., 1996: The significance of rock fabrics for the geological interpretation of geophysical anisotropies. Geotekt. Forsch., 85, 1-123 Siegesmund S., Weiss T., Vollbrecht A., Ullemeyer K., 1999: Marble as a natural building stone:rock fabrics, physical and mechanical properties. Z. dr. geol. Ges., 150, 237257. Siegesmund S., Vollbrecht A., Ullemeyer K., Weiss T., Sobott R., 1997: Anwendung der geologischen Ge~gekunde zur Charakterisierung natiiflicher Werksteine - Fallbeispiel: Kauffunger Marmor. Int. J. f. Restoration of Buildings and Monuments, 3,269-292 Thomasen S.E., Ewart C.S., 1984: Durability of thin-set marble. Proc. 3rd Int. Conf. on Durability of Build. Mat. and Components. ASTM, 313-323. Widhalm C., Tschegg E., Eppensteiner W., 1996: Anisotropic thermal expansion causes deformation of marble cladding. J. of Performance of Constructed facilities, ASCE 10, 5-10. Widhalm C., T schegg E., Eppensteiner W., 1997: Acoustic emission and anisotropic expansion when heating marble. Journal of Performance of Constructed Facilities, ASCE, 11, 35-40. Weiss T., Leiss B., Oppermann H., Siegesmund S., 1999: Microfabric of fresh and weathered marbles: Implications and consequences for the reconstruction of the Marmorpalais Potsdam. Z. dt. Geol. Ges., 150 No. 2, 313-332.
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THE RELATIONSHIP BETWEEN DETERIORATION, FABRIC, VELOCITY AND POROSITY CONSTRAINT
Thomas Weiss* Institut ftir Geologie und Dynamik der Lithosph~ire, G6ttingen, Germany Siegfried Siegesmund Institut ffir Geologie und Dynamik der Lithosph~ire, G6ttingen, Germany Patrick N.J. Rasolofosaon Institute Francais du Petrole, Paris, France
Abstract
Velocities of different marbles from Italy and Poland have been investigated to determine the interaction between deterioration, porosity and ultrasonic wave velocities. The marbles differ widely in their fabric (grain size, grain shape, lattice preffered orientation, etc.). Some of the marbles are characterized by straight and regular grain boundaries while others exhibit strongly irregular grain boundaries. Similarly, the grain sizes are distinctly different. Ultrasonic velocities have been measured on spherical samples to gain data on their directional dependence (anisotropy). It was found that anisotropy is an important parameter for any interpretation of ultrasonic velocities since the directional dependence of ultrasonic velocities can approach up to 30% at dry sample conditions. Ultrasonic velocities on dry samples vary in a wide range (- 1 km/s - 6.9 km/s) depending on marble type and state of deterioration. The corresponding range of porosity is only 0-1 Vol.%. At water saturated sample conditions the variability of ultrasonic velocities is much smaller (5.31 km/s7.17 km/s). Model calculations for the observed strong velocity reduction within a limited porosity range have been performed. Therefore, ellipsoidal cracks with a certain quotient between short and long axis of the ellipsoid (aspect ratio) have been assumed. The velocity reduction can be theoretically explained by cracks with an aspect ratio of about 0.005. This prediction coincides with measurements of the effective pore radii by mercury porosimetry. Most of the cracks in weathered marble from Carrara (Italy) and Prieborn (Poland) have a diameter of about 1gm. Assuming a crack length of about 200gm this gives an aspect ratio close to 0.005 which coincides with the theoretical prediction. Thus, cracks with a very small aspect ratio are very effective in decreasing the ultrasonic velocities. In general, the type and dimension of microcracks can be predicted from a comprehensive fabric analysis. Thus, detailed fabric investigations can help to predict the proneness to weathering of different marbles and to assess on-site the state of deterioration. 1. Introduction
Sculptures and monuments made of marble are often subjected to a strong degradation within a limited time span. The final stage of this weathering is frequently characterized by a sugar-like disintegration of the marble, i.e. the cohesion between the grains is completely lost. In the beginning of weathering, thermally induced microcracks are supposed to play an important role in degradation due to the strong directional dependence of the thermal dilatation coefficient ot of calcite. When the stresses caused by this mechanical weathering exceed the threshold of cohesion, thermally induced microcracks are generated between adjacent grains (e.g. Tschegg et al., 1999). The result is a so-called "crack porosity".
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Figure 1: Ultrasonic wave velocities in marble: a) Monument at the tomb of Michael von Wagmueller on the old north cemetery of Munich (c.f. Grimm, 1999). The ultrasonic velocities at different parts of the monument are according to K6hler (1993). b) Single crystal velocities of compressional waves of the calcite single crystal in respect to the crystallographic axes (after Dandekar, 1972). The complete loss of some cultural and historically important buildings or monuments and the tremendous costs for conservation or replacement of degraded marbles requires more elaborated methods to detect structural disintegration. Since many years ultrasonic measurements are used as a non-destructive tool for the assessment of the quality of a natural building stone (Fig. 1a). The basic assumption for the assessment of the quality of a natural building stone on the basis of ultrasonic measurements is that a decrease in the velocity of compressional waves (Vp) is correlated with a certain stage of deterioration of a marble. A classification of the state of deterioration of Carrara marble and an empirically derived correlation function between Vp and porosity was presented by K6hler (1991). f
Vp = 1 / _ ~ x/'*"
(1)
Table 1 Structural damage classification on the basis of Vp for marble from KOhler (1993). The porosity corresponding to the respective Vp was calculated using equation 1.
Damage class Class 0 Class I Class II Class III Class IV
Vp [~l/sl
condition
porosity ~ [%]
> 5.0 km/s 3.0 km/s - 5.0 km/s 2.0 km/s- 3.0 km/s 1.5 km/s- 2.0 km/s < 1.5 km/s
fresh increasingly porous sugar-like disintegration fragile crumbling rock
< 0.5 1.3 - 0.5 3.0- 1.3 5.3 - 3.0 > 5%.
This study evaluates the relationship between ultrasonic velocity, porosity and anisotropy of marbles using laboratory measurements. The aim is to gain a more
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comprehensive method for rock diagnosis. Laboratory measurements are performed under better defined conditions than field measurements on e.g. sculptures and, thus, the interpretation of data is more confident. At first, the effect of anisotropy on ultrasonic marble diagnosis will be investigated. The elastic properties of a rock are controlled by a number of physical (temperature, pressures, pore pressure, etc.) and lithological (chemical composition, fabric, pore space) parameters (Duerrast et al., 1999). A directional dependence (anisotropy) of elastic wave velocities is a frequently observed characteristic of almost all sedimentary, magmatic and metamorphic rocks (see compilation in Siegesmund, 1996). It is caused by a lattice preferred orientation (here referred to as texture) of anisotropic minerals and can be altered, under low confining pressures, by microcracks (e.g. Siegesmund, 1996). In particular calcite shows an extreme anisotropy of petrophysical properties (e.g. compressional wave velocities, thermal dilatation coefficient c~; Fig. lb) Marbles in the open country can be more or less water saturated. Thus, we investigate the effect of the two different pore fluids air and water on elastic wave velocities. Finally, petrophysical data and theoretical models are combined to characterize the pore space which leads to the velocity decrease during weathering. The results of the ultrasonic investigations are correlated with microstructural characteristics of the respective marble type to gain more suitable and comprehensive parameters for the quality assessment of a marble.
2. Experimental methods For the ultrasonsonic measurements spherical rock samples with a diameter of 50mm and an accuracy of 0.02ram have been prepared. Spherical samples allow measurements in all spatial directions, i.e. a complete determination of anisotropy. We measured transient times of ultrasonic pulses (piezoceramic transducers, resonant frequency 1 MHz) in 90 directions using the pulse transmission technique (Birch 1960, 1961). The measurements were performed at dry and completely water-saturated samples to simulate conditions found in the field. For measurements under pressure cylindrical samples (30o30mm)have been used. All specimens were oriented according to macroscopically visible fabric elements (e.g. metamorphic foliation). The porosity of the marbles was determined by buoyancy weighting. Therefore, the spheres for the ultrasonic measurements have been used. For two strongly weathered marbles the pore space distribution has been determined by mercury porosimetry. Therefore, samples were mounted in a vessel filled with mercury which allows a simultaneous application of hydrostatic pressure. The amount of mercury incorporated in the pore space is measured as a function of pressure. The basic principle is that a higher pressure is required to press the mercury in narrow pores than in large pores. The amount of mercury at a given pressure can be inverted in a volumetric number characterizing pores with a certain dimension. Fabric analyses were carried out on standard thin sections. Quantitative fabric properties (grain size distribution, grain shape, grain shape anisotropy, etc.) were obtained using digital image analysis. High resolution fractographic images from controlled cracked specimens were investigated with a SEM to characterize the mechanical strength in the initial condition of the samples.
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3. Sample description Marbles from different localities in Italy (Carrara, two samples; Lasa, three samples) and Poland (Kauffung, Prieborn, Grosskunzendorf) have been used for the investigations. Their fabric properties are shown in detail in Weiss et al. (1999, except Lasa marble) and are summarized in Table 1. Table 1 Summarized fabric properties of the investigated marbles (for explanations see text) Marble type sample grain size microstructure composition condition [gin] Lasa marble I flesh ~-400pm Type I/II calcite Lasa marble II flesh -400pm Type II calcite fresh Lasa marble III -400gm Type II calcite Carrara marble I flesh -~95gm Type Ill calcite Carrara marble II flesh -~130pm Type Ill calcite Carrara marble III flesh -150pm Type I calcite Carrara marble IV weathered ---140pm Type I calcite Prieborn marble I weathered -150~tm Type I calcite Kauffung marble I flesh -80~tm Type III calcite/dolomite Kauffung marble II weathered -80pm Type III calcite/dolomite Kauffung marble III weathered -80pm Type Ill calcite/dolomite Kauffung marble IV weathered ---80pm Type Ill calc ite/d o lom ite Grosskunzendorf flesh -1500gm Type IV calcite marble I Grosskunzendorf weathered -~1500pm Type IV calcite marble II Some of the specimens were from the quarry (fresh samples), others are weathered and have been replaced in the buildings. The different marbles cover a broad range of textural and microfabric types with different states of preservation (Weiss et al., 1999). All of the marbles with the exception of the Kauffung marbles are more or less pure calcitic marbles. The Kauffung marble has dolomitic veins predominantly parallel to the macroscopically visible metamorphic foliation (Weiss et al., 1999). Some of the marbles show an equilibrated microstructure with straight grain boundaries comparable to that of Carrara Statuario marble (microstructural Type I). Others show serrated grain boundaries (Type II) or a bimodal grain size distribution with small recrystallized and large relic grains with irregular grain boundaries (Type III) or a microstructure with evidence for grain boundary migration (Type IV). Of course, the classification into four fabric types requires some simplification of the naturally very heterogeneous rock fabric. Thus, the prevailing presence of one of the above mentioned fabric characteristics does not necessarily exclude the others.
4. Results A deteriorated rock shows a certain amount of micro- and macrocracks as a consequence of weathering. In particular open microcracks decrase ultrasonic velocities (see compilation in Siegesmund, 1996; Siegesmund et al., 1999). The effect open cracks can be best demonstrated using ultrasonic measurements under increasing confining pressure. With increasing pressure microcracks are closed and the velocities increase strongly (Fig. 2).
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At high confining pressure, the elastic properties of a rock are close to those of a noncracked rock (Fig. 2). The increase in velocity as a consequence of confining pressure is very similar to that of a water saturation. The interaction between porosity, pore fluid, velocity and anisotropy is exemplary shown for weathered Kauffung IV (Fig. 3) and Prieborn marble (Fig. 2,3).
Figure 2: Relationship between pressure and elastic wave velocities of Prieborn marble. Notice the strong increase in ultrasonic velocities (-2.6km/s) with increasing pressure. Onsite, a uniaxial load e.g. on columns) can produce the same effect in certain sample directions.
Figure 3: Directional dependence of Vp for Kauffung (a-c) and Prieborn marble. The velocities of the water-saturated (a,d) and dry samples (b,e) are given as well as their differences (c,f) in an equal area projection, lower hemisphere (isolines in kin/s). Maximum and minimum Vp are given in the bottom at the right and left side and the corresponding anisotropy (Avp=(Vpmax-Vpmin)/Vpmax 100) is given at the top of the polefigures.
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These marbles exhibit significant differences in fabric and petrophysical properties (c.f. Table 2, 3). The Kauffung marble has a small grain size, irregular grain boundaries and a low porosity. In contrast, the Priborn marble exhibits a significantly larger grain size, an equilibrated microstructure and a larger porosity. Accordingly, fracture patterns determined with the scanning electron microscope (SEM) of the two marbles are completely different. The Kauffung marble shows mostly intragranular (cleavage) cracks while the Prieborn marble is characterized by intergranular (grain boundary) cracks (Weiss et al., 1999b). The on-site damage scenario for Kauffung marble is characterized by break-outs along preexisting fractures, the prevailing part of the rock remains intact. In contrast, the Prieborn marble shows a penetrative degradation very similar to that proposed for some equilibrated types of Carrara marble. Table 3 Petrophysical properties of the investigated marbles (for explanations see text).
Lasa marble I Lasa marble II Lasa marble III Carrara marble I Carrara marble II Carrara marble III Carrara marble IV Prieborn marble Kauffung marble I Kauffung marble II Kauffung marble III Kauffung marble IV Grosskunzendorf marble I Grosskunzendorf marble II
0.43 0.37 0.38 0.20 0.14 0.44 0.94 0.77 0.23 0.32 0.26 0.27 0.31
5.39 6.42 6.53 3.45 1.54 3.03 6.58 6.34 6.97 6.72 5.05
4.61 6.16 6.41 2.67 1.43 2.11 5.43 5.04 5.99 5.84 4.37
14.62 4.13 6.26 22.5 7.39 30.12 17.78 20.44 14.11 13.05 13.59
6.50 6.76 6.83 6.14 5.55 5.65 7.17 6.97 6.95 7.00 6.83
6.09 6.62 6.61 5.94 5.35 5.31 6.31 6.19 6.08 6.19 6.48
6.35 2.12 3.26 3.46 3.53 6.11 12.04 11.22 12.57 12.57 5.18
0.46
4.59
3.63
20.81
6.42
6.10
5.09
4.1 Velocity reduction due to structural disintegration The damage type of the respective marble can be clearly identified in the Vp polefigures. The weathered marble from Kauffung shows relatively high Vp in the range of 6.0-7.0 km/s under dry sample conditions. In contrast, the velocities for Prieborn marble are significantly lower (Fig. 3b,e). Accordingly, the Kauffung marble would correspond to the damage Class 0 and the Prieborn marble to Class II from Koehler (1991). Both marbles are from the same building with almost the same time in built-in condition. However, it should be kept in mind that the effect of break-outs can not be considered in the laboratory scale and, therefore, a detailed on-site mapping of damage structures is indispensable for a comprehensive expertise. 4.2 Effect of anisotropy Both samples exhibit a pronounced anisotropy which approaches even 30% under dry conditions (Prieborn marble, Fig. 3b). Velocities measured on a column of Prieborn marble can range between 2.2km/s and 3.0km/s (Fig. 3e). Notice that almost the entire Class II (Vp from 2.0km/s to 3.0kin/s) from
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the damage classification of K6hler (1991) is covered by only one dry and penetratively weathered marble in different directions.
Figure 4: Average compressional wave velocities for different marble samples as a function of porosity and sample condition: a) dry samples, b) water-saturated samples. The anisotropy of the respective marble is given as error bars. The velocity/porosity-curve of Koehler (1991; bold line) and theoretical predictions according to the models of O'Connel & Budiansky (1974; hatched lines) are added for comparison. For the latter model calculations, the aspect ratio of the cracks assumed in the computations are given. 4.3 Effect of fluid saturation
Marbles can be very sensitive on the type of pore filling medium (i.e. water or air). The difference of compressional wave velocities in the water-saturated (Fig. 3a) and dry (Fig. 3b) condition of weathered Kauffung IV marble is remarkably low (less than lkm/s, Fig. 3c). The corresponding porosity is about 0.27%. In contrast, the Prieborn marble shows very low velocities (-2.6km/s) at dry condition (Fig. 3e). The corresponding porosity is about 0.77% (Tab. 2). At a water-saturated condition (Fig. 3d) velocities increase up to 5.5km/s. The large differential velocities between the water-saturated and dry sample condition of about 2.9km/s (Fig. 3f) account for a strong degradation of this marble. 4.4 Vp as a function of porosity?
The velocity data compiled for all the marbles is shown in Fig. 4 and Tab. 2. At dry sample conditions (Fig. 4a), the porosity of the samples never exceeds 1Vol%. However, the compressional wave velocities cover a broad range from 6.5km/s down to less than l km/s. Thus, the pore space is small but very efficient in reducing the velocities. Note the very different ultrasonic velocities for the Carrara II and Carrara III marble at dry conditions considering that both marbles are fresh from the quarry. All of the marbles exhibit water-saturated velocities within the range of 5.5 to 6.9km/s. The Vpmaxof the Carrara IV marble (weathered) is for example close to the Vpminof the Carrara III marble (fresh) and, thus, these 0.4km/s are within the accuracy of the measurement. However, at dry sample conditions the Vp of the respective marbles differs remarkably.
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4.5 Theoretical prediction of the Vp/porosity relation In order to find constraints for the magnitude and shape of this pore space we modeled the velocity reduction as a function of crack geometry using the well known theoretical prediction of O'Connel & Budiansky (1974). The basic principle is that a given porosity is formed by certain types of ellipsoidal cracks. The crack geometry is only defined by the aspect ratio (i.e. the ratio between small and large axis of the ellipsoid) of the cracks. Spherical cracks have an aspect ratio of about 1 flat cracks of smaller than 1. The model calculations reveal that strongly decreasing Vp as a function of porosity, as it is observed experimentally, can only be caused by extremely flat cracks with an aspect ratio of about 0.005 (see Fig. 4). 5. Diskussion and conclusions A clear interpretation of Vp in terms of rock degradation deserves a comprehensive knowledge of rock fabrics and petrophysical properties of the marble types under investigation. A number of parameters has to be considered: The basis for any interpretation of ultrasonic data must be a comprehensive knowledge of the rocks fabric. Macroscopic and microscopic fabric properties are responsible for the type and magnitude of weathering of a marble. To quantify degradation on new monuments or sculptures the initial situation has to be documented since the quality of fresh marbles from the quarry can be significantly different.
Figure: 5 Distribution of the effective pore radii of extremely weathered Prieborn (a) and Carrara (b) marble. Thermal cracking is supposed to be the first step of marble weathering. Weathering increases the pore spaces due to microcrack generation and subsequent solution/precipitation activities. Thus it is important to know for a given marble type the proneness to thermal cracking and its promoting factors which is controlled by grain size, grain shape and preexisting open or healed cracks (Siegesmund et al., this volume). The result is a sugar-like disintegration like it is observed for some types of Carrara marble. Preexisting microcrack systems can be activated by weathering leading rather to a partial loss of larger parts of monument due to break-outs than to a total disintegration. This effect is on-site hard to detect when no superficial evidence for cracks is observed but it can be predicted when macro- and microfabric data are available (Weiss et al., 1999b). On-site ultrasonic velocities measurements have to be treated with care. Anisotropy is a typical characteristic of rocks. The Vp-anisotropy can account up to 30% and, consequently, a large difference in Vp can not unequivocally be explained with locally restricted disintegration. Even for Carrara marble, which is generally assumed to be isotropic, the Vp-anisotropy can be about 22% (Carrara III dry, Tab. 3).
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But also the anisotropy in water-saturated marbles can be considerable as it was shown for the marbles from Kauffung. The tremendous velocity reduction within a very limited porosity range of only 0-1% (see Fig. 4) can only be explained by very flat pores with an aspect ratio of about 0.005. For calcite rocks it is well known that at relatively low temperatures (i.e. below 200~ grain boundary cracks are the predominant crack types (e.g. Fredrich & Wong, 1986). The socalled "pore throat diameters distributions" of weathered Carrara and Priborn marble give a maximum of the pore throat diameters close to l gm. A facet of a calcite grain can easily reach 150gm and, thus, the quotient between the pore throat diameter (i.e. the height) and the lateral dimension of the supposed crack (i.e. the crystals grain boundary) is close to the aspect ratio of 0.005 which was estimated from modeling. However, specimens in the open country are probably never completely water saturated. When the samples are only partially saturated the corresponding velocities approach rapidly those shown for the dry samples. Thus, it is very important to get information about the degree of water saturation of a specimen under investigation.
References
Birch, F., 1960: The velocity of compressional waves in rocks up to 10 kilobars, Part I. J. Geophys. Res., 65, 1083-1102. Dandekar 1968: Variation in the elastic constants of calcit with pressure. AGU Trasactions, 49 (1), 323pp. Duerrast, H., Siegesmund, S. & Prasad, M, 1999: Schadensanalyse von Naturwerksteinen mittels Ultraschalldiagnostik: M6glichkeiten und Grenzen. Z. dr. geol. Ges., 150, 2, 359374. Frederich, J.T., Wong, T.f., 1986: Micromechanics of thermally induced cracking in three crustal rocks. J. Gephys. Res., 91 B12, 12,743-12,764. Grimm W., 1999: Beobachtungen und lJberlegungen zur Verformung von Marmorprojekten dutch Geffigeauflockerung. Z. dt. Geol. Ges., 150 No. 2, 195-236. O'Connell, R.J., Budiansky, B., 1974, Seismic velocities in dry and saturated cracked solids, J. Geophysical Res., 79(35), 5412-5426. Siegesmund S., 1996: The significance of rock fabrics for the geological interpretation of geophysical anisotropies. Geotekt. Forsch., 85, 1-123 Siegesmund S., Vollbrecht A., Ullemeyer K., Weiss T., Sobott R., 1997: Anwendung der geologischen Geft~gekunde zur Charakterisierung nat~irlicher Werksteine - Fallbeispiel: Kauffunger Marmor. Int. J. f. Restoration of Buildings and Monuments, 3,269-292 Siegesmund S., Weiss T., Vollbrecht A., Ullemeyer K., 1999: Marble as a natural building stone:rock fabrics, physical and mechanical properties. Z. dt. geol. Ges., 150, 237-257. Tschegg, E.K., Widhalm, C., Eppensteiner, W., 1999: Ursachen mangelnder Formbest~ndigkeit von Marmorplatten. Z. dt. geol. Ges., 150(2), 283-297 Weiss T., Leiss B., Oppermann H., Siegesmund S., 1999a: Microfabric of fresh and weathered marbles: Implications and consequences for the reconstruction of the Marmorpalais Potsdam. Z. dt. Geol. Ges., 150 No. 2, 313-332. Weiss, T., Siegesmund S., Leiss B., Oppermann H., 1999b: Microfabric of fresh and wathered marbles and its implication on weathering phenomena observed at the Marmorpalais in Potsdam (Germany). Proceedings Eurocare/Euromarble 1998, Bayerisches Landsamt f~ir Denkmalpflege, Forschungsbericht, 17, 4-15
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SALINE POLLUTION IN ISLANDS (PORTUGAL).
TRACHYTE
MONUMENTS
OF
THE
AZORES
C. A. S. Alves* Centro de Ci~ncias do Ambiente/Dept. Ci~ncias da Term, U.M. 4700-320 Braga, Portugal, e-mail: [email protected]. M. A. Sequeira Braga Centro de Cidncias do Ambiente/Dept. Ci~ncias da Terra, U.M. 4700-320 Braga, Portugal. A. Trancoso INETI, Estrada do Pa~;o do Lumiar, 1649-038 Lisboa, Portugal.
Abstract
The decay aspects of trachyte stones applied in churches from Ribeira Grande (Sao Miguel Island) and Angra do Heroismo (Terceira Island), both in the Azores Islands, were studied in order to characterise the associated soluble salts and to discuss contamination sources and decay processes in these monuments. Granular disintegration, scales and flakes are the main pathologies affecting the trachyte stones on the facades. The aqueous extracts compositions of these pathologies have a clear trend towards the chloride and sodium poles, and halite and gypsum were identified. Sodium salts also dominate the efflorescences, which occur on diverse building materials. The decay patterns and the mineralogical and chemical results suggest that rainwater is the main saline pollution source. The pollution by rainwater and the high precipitation contribute to the intense deterioration of trachyte stones applied in these monuments of the Azores Islands. Key words: trachyte stones, saline pollution, Azores Islands monuments
1. Introduction
Soluble salts are recognised as an important agent in the decay processes that affect historical monuments. The sources of the soluble salts are varied (Arnold and Zenhder, 1989), including geogenic sources (the stone itself, rainwater, groundwater and sea-spray) and sources related to anthropogenic activities and products (atmospheric pollution, mortars, organic wastes, etc). In order to adopt the appropriated conservation measures, the salt systems and the pollution sources must be identified. Papers dealing with the decay of volcanic stones are rare, being most of them dedicated to volcanic tuffs, a group of rocks common in some European regions and that are also applied in the famous Eastern Island monuments. Papers dealing with trachytes are rarer (Fitzner, 1994; Laue et al., 1996). The scarcity of trachyte stone decay studies is explained by the scarcity of the trachyte rock and, therefore its rare use as building stone. "Author to whom correspondence should be addressed.
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In the Azores Islands trachyte has been, historically, an important building resource, due to its abundance in the islands and its lighter aspect, when compared with the other rocks found in these islands. However, the trachyte stones applied in the Azores monuments show intense decay. In some buildings the stone was rendered with mortars, lime and paintings. However the decay has affected also the rendering products. As consequence, the use of trachyte in building facades has declined and other darker rocks are now been preferred, with the consequent disruption in the building traditions of the islands. The present paper attempts to characterise the saline pollution that affects selected monuments of the two main islands of the Azores archipelago: S~.o Miguel e Terceira. The discussion of salt systems, pollution sources and decay consequences is also attempted.
2. Materials and methods
The decay aspects of several selected churches, built with trachyte stones, were studied in localities of Sao Miguel and Terceira Islands (fig. 1). In Sao Miguel Island, were studied monuments in the village ofRibeira Grande: the Espirito Santo, Matriz and Nossa Senhora da Conceigao churches. In the capital of the Terceira Island, Angra do Heroismo (UNESCO world heritage), were selected the Cathedral and the Nossa Senhora da Concei~ao church. Both localities are placed near the coast (fig. lb and lc). Yearly rainfall values (mean values for the period 1961-1990 from the portuguese Instituto de Meteorologia) are very high: 1125.6 mm for Angra do Heroismo and 1027.1 mm for Ponta Delgada (climatic station in Sao Miguel Island).
Figure 1: Localisation of a) Azores Islands; b) Ribeira Grande in S. Miguel Island and c) Angra do Herofsmo in Terceira Island.
A survey of the decay features (pathologies) of the monuments was conducted, in order to define a sampling program. Granular disintegration, scales and flakes are the most important decay forms affecting the trachyte stones, but there are also the occurrence of efflorescences on several building materials. Efflorescences were sample in all the churches and, to obtain a regional view of the salt systems, also in the Casa da Cultura of Ribeira Grande. The other decay forms (granular disintegration, scales and flakes) were collected in the following buildings: Espirito Santo and Matriz churches (S. Miguel) and Angra do Heroismo Cathedral (Terceira). Samples from old quarries in both islands and from a stair stone, without decay evidences, in the interior of Espirito Santo church were also collected for comparison.
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Effiorescences were studied by optical microscopy (immersion method, following the recommendations of Arnold, 1984), X-ray diffraction (XRD) and scanning electron microscopy with EDS analysis system (SEM/EDS). Granular disintegration, scales and flakes were also studied by SEM/EDS and chemical analysis of the aqueous extract. The cations (Na +, Ca2+, K § and Mg 2+) were determined by flame atomic absorption spectrometry and the anions (CI, NO3 and SO42) by ion chromatography.
3. Results and discussion 3.1. Field study of decay aspects Intense deterioration has been observed in the trachyte stones applied in the facades of the selected monuments, but there are some differences regarding the pathologies. In the facades of the Angra do Heroismo churches, scales and flakes (with thickness between 1 mm and 18 mm) are the dominant decay forms affecting trachyte stones, but granular disintegration is also present. These decay features have a very wide distribution from the base to the top of the facades (fig. 2a). In the Ribeira Grande churches fa~;ades, the decay is mainly linked to granular disintegration, which in the Espirito Santo church is concentrated at the higher zones of the main Fa~;ade (fig. 2b,c). In the Matriz church, besides granular disintegration, there are also thin flakes (between 1 mm and 3 mm) and a discrete occurrence of effiorescences in the main fa~;ade. Inside the monuments were not found evidences of stone physical deterioration, but there are occurrences of efflorescences. The efflorescences are found on the wall rendering mortar (leading to the disruption of the wall painting), in mortar joints between stones and in a tile panel (in the mortar joints between tiles and in places of the files were the glazing has peeled off). Discrete occurrences of efflorescences in trachyte stones (that are covered with cement) were found inside the churches of Angra do Heroismo and in the N. S. da Concei~o church of Ribeira Grande.
3.2. Characterisation of pathologies In the efflorescences of the several churches were identified the saline minerals presented in table 1. With the exception of the Matriz church in Pdbeira Grande, all the efflorescences were found indoors. Sodium minerals are clearly dominant in the efflorescences. Inside the monuments the efflorescences mineralogy is monotonous, dominated by either mirabilite (Na2S04* 10H20) or sodium carbonate (trona and natron). However, inside the Angra do Heroismo churches, in stones that are covered with cement, halite and gypsum (Cathedral) or gypsum (N. S. Concei~o church) were identified. Halite and gypsum are also the saline minerals present in the efflorescences of the main facade of the Matriz church (Ribeira Grande). Calcite crusts were found on mortar joints in the churches of Angra do Heroismo, being probably a carbonation product of the mortar and, therefore, are not considered in the discussion of the soluble salts in effiorescences.
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
Figure 2: Trachyte stone decay aspects: a) deterioration by granular disintegration, scales and flakes in Angra do Heroismo Cathedral; b) and c) granular disintegration and erosion of decorative features in the Espirito Santo church of Ribeira Grande.
In the samples of granular disintegration, scales and flakes that affect trachyte stones, SEM/EDS studies (fig. 3)~showed the presence of halite and calcium sulphate that in some samples was possible to confirm, by XRD, as gypsum. The chemical analyses of the aqueous extract show enrichment on the soluble salts (determined by the sum of all the ions analysed, in %) in the trachyte stone pathologies, when compared with samples from the quarry and from the stair stone that was inside the Espirito Santo church (Table 2).
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Table 1- Saline minerals found in the effiorescences of the studied monuments. Saline minerals (with indication of substrate) Church Locality Mirabilite (wall mortar rendering) Espirito Santo Ribeira - Halite + gypsum (trachyte) Matriz Grande - Mirabilite (trachyte covered with cement) N. S. Concei~ao (Sao Miguel) - Natron (mortar joint; trachyte covered with cement) - Mirabilite (mortar joint; trachyte covered with cement Casa da Cultura - Mirabilite (wall mortar rendering; mortar joints) Cathedral - Natron (tiles; mortar joints between tiles) - Halite + gypsum (trachyte covered with cement) Angra do Heroismo - Mirabilite (wall mortar rendering) N. S. Conceigao (Terceira) - Trona (mortar joint) - Natron (wall mortar rendering) - Gypsum (trachyte covered with cement)
Figure 3 - SEM/EDS studies of soluble salts in trachyte stone pathologies. Examples from Angra do Heroismo Cathedral: a) halite crystals (h) in feldspar (f) fractures in a trachyte scale; b) gypsum aggregates in the separation interface of flakes.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Table 2 - Soluble salt amount (as sum of ions analysed, in %) in trachyte samples (number of samples in bold between parenthesis). Zions (%) Locality Type of sample 0.0214 (1) Ribeira Quarry 0.022(1) Grande Stone from inside Espirito Santo church (Sao Miguel) Granular disintegration (Espirito Santo church) 0.6634-1.6405 (5) 0.449- 1.786 (8) Granular disintegration (Matriz church) 0.189- 1.106 (7) Flakes (Matriz church) 1.5197-6.15(3) Mortars (Espirito Santo church) 0.0268 (1) Angra do Quarry 0.643- 1.552 (4) Heroismo Granular disintegration (Cathedral) (Terceira) Scales and flakes (Cathedral) 0.1405- 1.742 (14) 1.473- 4.3403 (3) Mortars (Cathedral) The miliequivalent proportions of anions and cations in the aqueous extract of stone pathologies samples show a clear trend towards the chloride and sodium poles (fig. 4). There are however, some samples in the Ribeira Grande churches facades that clearly approach the calcium and sulphate poles. Nitrate is the less important anion in all the samples (always less than 30% of the anions determined).
c~2+
a)
CI-
NO 3
Na+ Ca2+
b)
C1-
K+ + Mg2+
NO 3
Na+
K+ + Mg2+
Figure 4: Proportions of main anions and cations (in meq) in the soluble extract of samples of granular disintegration (e) and scales and flakes (o) from a) Ribeira Grande churches and b) Angra do Heroismo Cathedral.
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In the Matriz church of Ribeira Grande and in the Cathedral of Angra do Heroismo was possible to collect stone pathologies samples at diverse heights from the floor, allowing to study the evolution of the salt content with height. It is visible (fig. 5) that there is no relation between the height of the sample from the floor and its soluble salt content. When the miliequivalent proportions of the different anions and cations (considering separately the anions and the cations) are considered, instead of the total soluble salt content, there are also not chemical trends with height (fig. 6), excepting the nitrate, that seems to show a weak trend to decrease with height. _
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3.3. Considerations on salt systems and pollution sources
The extensive distribution of the decay aspects in the facades and the similarity of chemical characteristics (salt contents and proportions of the different ions) indicate a pollution source that affects the whole of the monuments fagades in a similar way. The chemical and mineralogical characteristics of the stone pathologies indicate a chloride and sodium dominated pollution source, presumably rainwater with an important oceanic influence. The high rainfall in the islands contributes to the intense decay of the trachyte stones. However, some dispersion is observed towards the sulphate and calcium poles, which could indicate some contribution from other pollution sources like automobile traffic or the products that were used for the rendering of the trachyte stones. The mineralogy of the efflorescences indoors is also dominated by sodium salts, mainly sulphates and carbonates. These results seem linked to the interaction between the sodium and chloride rich solutions from the outside salt system (linked to rainwater) with the mortars applied in the walls. Similar observations were made by Gurrera et al. (1994), who referred the formation of thenardite, trona and aphthilite as a consequence of the reaction between sea-spray and cement compounds. Alves and Sequeira Braga (1999) also observed the zoned evolution of sodium salts by interaction between solutions from a deposit of common salt and the wall mortars.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
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The monotony of the saline mineralogy in the efflorescences of these Azores monuments is deafly different from what has been observed in other Portuguese monuments affected by several pollution sources (Alves and Sequeira Braga, 1999). In those monuments, the variety of saline minerals allowed the authors to identified several saline systems in the same monument, while in the Azores Islands the saline mineralogy is similar in both localities (placed in two different islands), indicating a common salt system. The soluble salts characteristics are similar in the different types of pathologies. Therefore, in order to understand the variations in the pathology type and in its morphology other factors must be investigated.
4. Conclusions The decay patterns and the chemical and mineralogical characteristics of the decay products indicate similar salt systems in these trachyte monuments of the Azores islands and a saline pollution mainly linked to geogenic sources (rainwater with an oceanic component). The pollution effect of rainwater and the high rainfall values in these islands contribute to the intense deterioration of trachyte applied in the monuments facades.
5. Acknowledgements Supported by the Funda~ao para a Ci~ncia e Tecnologia (Portugal) through PRAXIS X X I - project n ~ 2/2.1/CSH/254/95 and CCA-CT/FCT-R&D Contract-Program.
6. References 9Alves, C.A.S. and Sequeira Braga, M.A. (1999) Soluble salts in pathologies of granitic monuments of Braga (Northwest Portugal). Ninth Annual V.M. Goldschimdt Conference, pp. 5-6. 9Arnold, A. (1984) Determination of mineral salts from monuments. Studies in Conservation, 29, 129-138. 9Arnold, A. and Zehnder, K. (1989) Salt weathering on monuments. 1st Int. Syrup." The Conserv. of Monuments in the Mediterranean Basin, Bari, 31-58. 9 Fitzner, B. (1994) Volcanic turfs: the description and quantitative recording of their weathered state. Lavas and Volcanic Tufts, Int. Meeting, Eastern Island, Chile, pp. 33-51. 9Gurrera, M.A., Raventos, X.D., Bou, V.E., Perez,J.L.P., Vifias, R.R., and Horta, A.V. (1994) Degradation forms and weathering mechanisms in the Ber/t Arch (Terragona, Spain). 3rd. Int. Symp.:The Conservation of Monuments in the Mediterranean Basra, Venice, 673-679. 9Laue, S., B6hm, C.B., Jeannette, D. (1996) Saltweathering and Porosity - Examples from the Crypt of St. Maria in Kapitol, Cologne. 8th lnt. Congr. on Deterior. and Conserv. of Stone, Bedim, pp. 513-522.
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TRACHYTE STONES IN MONUMENTS OF THE SAO MIGUEL AND TERCEIRA ISLANDS, AZORES (PORTUGAL). M.A. Sequeira Braga CCA/CT, Universidade do Minho, 4700-320 Braga, Portugal M.O. Figueiredo Inst. Investiga~.o Cientifica Tropical, AI. Afonso Henriques, 41, 4~ 1000 Lisboa, Portugal. M.I. PrudSncio Instituto Tecnol6gico e Nuclear, Aptdo. 21, 2686-953 Sacav6m, Portugal J. Delgado Rodrigues* Laboratorio National de Engenharia Civil, Av. Brasil, 101, 1799 Lisboa Codex C.A.S. Alves CCA/CT, Universidade do Minho, 4700-320 Braga, Portugal D. Costa Laborat6rio Nacional de Engenharia Civil, Av. Brasil, 101, 1799 Lisboa Codex T. Silva Inst. Investiga~o Cientifica Tropical, A1. Afonso Henriques, 41, 4~ 1000 Lisboa, Portugal. M.J. Trindade, J.C. Waerenborgh, M. Nasraoui and M.A. Gouveia Instituto Tecnol6gico e Nuclear, Aptdo. 21, 2686-953 Sacav6m, Portugal
Abstract Among the volcanic rocks from Azores Islands, trachytes have been preferentially used through centuries in many monument fagades, mainly due to their colour and softness. However, aider a few centuries the decay stone of monument stones is remarkable. Angra do Heroismo Cathedral, in Terceira Island, and Miseric6rdia Church, in Sao Miguel Island, were the monuments selected for the present study on degradation causes and mechanisms. The same methodology was applied to quarry and monument samples from both Islands by using petrographic, mineralogical, chemical and petrophysical techniques. Well-marked differences were noticed between the trachytes from Sao Miguel and Terceira Islands but within each island, outcrops or the monument building stones, show several similarities. However, some textural aspects observed in the field showed some variability. The stones have a pore-type porosity of genetic nature. The values of porosity accessible to water are very high for monument samples and higher than the values for quarry samples. The samples of Miseric6rdia Church show a high porosity, dominated by large pores (radius > 1 lam). It was concluded that these highly porous materials trachytes are very susceptible to degradation, namely by salt crystallisation mechanisms. Keywords: stone decay, trachytes, monuments, Azores Islands 1. Introduction Volcanic rocks are the typical building materials used in the Azores Islands. Among these rocks, trachytes have been used through centuries in many monument facades mainly due to their colour (the so-called white stone) and softness (easy to work). However, time
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
has shown that trachytes have one of the worse behaviours as building materials in those islands. Two monuments were selected for the present study. The Cathedral of Angra do Heroismo is located in Angra do Heroismo (Terceira Island, Azores), a city included in the World Heritage List by UNESCO. Its building began in 1570 on the site of a 15th century church and was completed in 1618. The Cathedral was badly damaged by an earthquake in 1980. The Misericrrdia Church (also named Espirito Santo Church) in town of Ribeira Grande (S~o Miguel Island) exhibits in its main facade one of the most important sculpture works in Baroque style. Terceira and S~o Miguel (fig. 1) are two of the nine volcanic islands comprise by the Azores Archipelago located near the Mid-Atlantic Ridge, between 36~ 35'N and 39 ~ 43' N (latitude) and between 25 ~ and 31 ~ W (longitude). High annual values of rainfall have been recorded: 1125.6 mm/yr in Tereeira (mean values for the period 1961-1990, according to the Portuguese Institute of Meteorology) and in Sao Miguel between 3000 mm/yr at the Lagoa do Fogo to 1000-1500 mm/yr in the dryer part of this Island (Ricardo et al., 1977).
Figure 1: Location of Azores archipelago. Several publications report on the geology of the Terceira Island (Zbyszewski et al., 1971; Self, 1973; Forjaz et al., 1990) and of the Sao Miguel (Zbyszewski et al., 1958, 1959; Moore, 1990, 1991). The oldest formations of each island are Pliocene in age and the most recent are Quaternary. Some historic eruptions have occurred in both islands. Rocks of the volcanic complexes from Terceira Island consist essentially of lava flows, pyroclasts and ignimbrites. In S~o Miguel Island these rocks comprise trachytes (lava flows and domes), basalts and pyroelastic deposits. Trachyte building stones in the Azores monuments, in particularly in S~o Miguel and Terceira Islands, show an intense decay state. Alves et al. (2000) attempted to characterise the saline pollution that affects some monuments of these islands. Regarding the Misericrrdia Church in Ribeira Grande, the stone decay was mainly linked to granular disintegration that is concentrated in the higher zones of the main facade. The decay state of the trachyte building stone in the Angra do Heroismo Cathedral is intense and widespread by several facades.
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In this work a comparison of trachyte rocks from quarries and monuments was carried out by using petrographic, mineralogical, chemical and petrophysical techniques. The main goals of the present study are: (1) to characterise the trachyte from the quarry and from the monument; (2) to point out similarities and differences, in order to investigate the building stone provenance and (3) to contribute to the understanding of the decay processes. 2. Materials and methods Angra do Heroismo Cathedral, in Terceira Island, and Misericordia (or Espirito Santo) Church, in Ribeira Grande, from S~.o Miguel Island - themonuments selected for study (fig. 2) - were both monuments built with trachyte stones. The field survey in the Terceira Island showed that the rock in the Grota dos Calrinhos quarry, located about 2 km Northeast of Angra do Heroismo, has macroscopic similarities with the monument stones from South and East facades. In this quarry, trachyte lava flows show some textural and chromatic variability and are associated with Santa Barbara Volcanic Complex (Forjaz et al., 1990). Samples were collected from Grota dos Calrinhos quarry and from decayed building stones (scales and granular disintegration) in the monument. In S~o Miguel Island, samples were collected in nine outcrops of lava flows and domes between Porto Formoso and Ribeira Grande. In this attempt of covering the potential places of extraction of trachyte, it should be remarked that old quarries (known by the older local habitants) are today inaccessible. A sample from one of these old quarries that was stored in the so-called Casa da Cultura was studied. The sampled trachyte outcrops are related to precaldera units of Agua do Pau stratovolcano (zone 3 - Moore, 1991). The samples showing more macroscopic similarities with the monument stones were those from Porto Formoso and Lameiro trachytes. Samples of the monument were collected on a stone fragment from a fallen decorative element of the main facade (fig. 2) and on a stone previously used as an altar step. The same methodology was applied to quarry and monument samples from both islands. Mineralogical, petrographical and chemical characterisation were developed by optical microscopy, scanning electron microscopy with EDS analytical system (SEM-EDS), X-ray diffraction (XRD) of the whole rock and of the <2 ~tm fraction, electron microprobe (EMPA) and X-ray fluorescence spectrometry in wave length dispersive mode(XRF-WDS) analysis. The following physical properties were characterised: porosity, real mass density, pore size distribution by mercury intrusion porosimeter, ultrasonic velocity and swelling strain. Porosity accessible to water was determined through hydrostatic weightings with saturation under high vacuum conditions. Porosimetry was carded out in a Quantachrome 60 instrument. Swelling strain was determined in prismatic prisms at 48h-immersion time. Ultrasonic velocity was measured with a Steinkamp instrument in well-defined conditions of saturation or dryness. All the dry conditions were obtained by placing the specimens in a ventilated oven at 60~ during 72h. 3. Results and discussion 3.1. Petrographic, chemical and mineralogical data The trachyte samples from Grota dos Calrinhos quarry and from the building stones in Angra do Heroismo Cathedral are hemicrystalline, porphyritic, with small phenocrysts of alkali feldspar in a mesocratic fine-gained groundmass. Their texture is slightly vesicular (small vesicles, bellow lmm). Some samples show a banded structure resulting from
23 8
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
alternation of dark and light flow layering. The massive samples show chromatic variations from grey and greenish-grey (main colour) to brownish. These colour variations are related to the presence of glass, clay minerals and weathering products. Samples display a typical trachyte texture. a
b
Figure 2: Azores monument: a) Angra do Heroismo Cathedral; b) Miseric6rdia Church. Alkali feldspar, straddling the anorthoelase-sanidine compositional boundary is the dominant phase in both phenocrysts and groundmass. Sodie-ealcie amphiboles, as brownyellowish microerystals and and clinopyroxenes are the magic minerals. Ilmenite, magnetite, erystobalite and apatite are also present. Smectites, rare calcite and goethite are the secondary minerals identified in these samples. Volcanic glass is found in the groundmass, occasionally displaying spheroidal cracking. SEM and SEM-BSE images (fig. 3) show peculiar petrographic features of the samples from the quarry and from the monument, namely: (1) mieroporosity; (2) large pores (_< 50~m) with infiUings of smectite and finegrained silica; (3) smectite coatings on alkali feldspar; (4) crystobalite and (5) volcanic glass. XRD analyses showed that smectites are well crystallised, but they occur in very small amount. A summarised petrographic and chemical study of Porto Formoso (S~o Miguel Island) trachyte samples from the quarry was presented by Prud~ncio et al., (1998). Further data show that the composition of the alkali feldspar straddles the anorthoclase-sanidine boundary. These feldspars are the dominant phase in both phenoerysts and groundmass. Green clinopyroxene, showing a augite-diopside compositional range, brown-yellowish sodic-ealeie amphibole and biotite occur as microcrystals. The traehyte samples from Lameiro outcrops, also in S~o Miguel, are porphyritic with phenocrysts of alkali feldspar in a mesocratie fine-grained and vesicular groundmass. Sound samples display a trachyte
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texture and are grey in colour while weathered ones show a brownish tim, that affects even the alkali feldspar phenocrysts. Some xenoliths and a light flow layering structure occur both in the Lameiro outcrop samples and in the building stones of the monument, but these aspects were not observed in the Porto Formoso samples.
Figure 3: SEM images of trachytes: Grota dos Calrinhos quarry samples [a (SEM-BSE image) and c; b is a detail from a]; stone monument fragment (d). A = amphibole; C = crystobalite; F = alkali feldspar; G = glassy matrix; S = smectite; V = large pore. Alkali feldspar is the dominant phase in both phenocrysts and groundmass from Lameiro outcrops. Green clinopyroxene (augite-diopside), rare brown-yellowish sodic-calcic amphibole and biotite also occur as microcrystals in the groundmass. Plagioclase, ilmenite, magnetite, apatite and a silica polymorph (possibly trydimite) are also present in the groundmass. A high microporosity is associated with the presence of abundant large pores of different size. All these main petrographic features were also observed in the building stones of the monument. Some brownish stains or even opaque products are dispersed in the groundmass of both Lameiro and Porto Formoso samples as well as in the monument stones. XRD analyses of the whole rock and of the < 2 ~tm fraction showed the presence of halloysite 10 A and goethite, both in the quarry and monument samples. These secondary minerals have low crystallinity and occur in very small amounts. Data from the whole rock chemical analysis (Table 1) show similar values for the quarry and monuments samples in the Terceira Island. Chemical data for S~.o Miguel Island show
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that the Lameiro outcrop samples are more similar to the monument samples than those from the Porto Formoso quarry. In the TAS diagram (fig. 4), the samples are plotted very close: i) in the field of trachydacites for Terceira Island samples and ii) in the field of trachytes for the samples of S~o Miguel. However, the TAS diagram must be used with caution in altered samples (LeMaitre, 1989). As a general rule, this author suggests that only analyses with H20 <2% and CO2< 0.5% should be used which seems to be the case, since L.O.I values are always less than 1.5%. The variability of L.O.I. values in Table 1 may be related to the amount of amphiboles and clay minerals present.
1 - FOIDITE 2 - PHONOLITE 3- TEPHRIPHONOLITE 4 - PHONOTEPHRITE 5 - TEPHRITE 6 - PICROBASALT 7 - BASALT 8- TRACHYBASALT 9 - BASALTIC TRACHYAHDESITE 10 - BASALTIC ANDESITE 11 - AHDESITE 12 - TRACHYANDESITE 13 - TRACHYTE 14 - TRACHYDACITE 15 - DACITE 16 - RHYOLITE 17 - SILEXITE
Figure 4 - Total alkalis
versus
SiO2 plotted in the TAS diagram (Middlemost, 1994).
Table 1" Whole rock chemical analysis in studied samples (quarries and monument stones) from S~o Miguel and Terceira Islands. Terceira Island
S~lo Migue! Island Lameiro LI' Porto Formoso (mean of 4 Casa da (7 samples) samples) Cultura (% w/w) Sio2
A1203 Fe203*
MgO CaO Na20
i~o
TiO2
too5 MnO L.O.I. * - Total iron
(% w/w)
(% w/w)
62.52 15.91 4.'76 2.94 1.98 4.47 5.76 0.98 0.20 0.15 0.35
65.56 16.59 4.12 0.44 1.06 4.86 6.31 0.69 0.12 0.16 0.09
, ,
.... Monument (15 samples)
.
.
.
.
.
.
.
.
.
Monument (8 samples) (% w/w)
(% w/w)
(% w/w)
66.28 - 67.24 62.66 - 65.57 1 6 . 0 2 - 16.61 ' 1 6 . 0 4 - 19.60 3 . 2 4 - 3.65 3 . 7 0 - ~,125 0.21 - 0 . 3 9 0.15 - 0 . 5 3 0.20 - 0.62 1 . 0 2 - 2154 4 . 9 6 - 5.33 4.12 - 5.41 6 . 0 7 - 6.7-1 5.98 - 6.32 0 ' 7 8 ' 6.81 0.66 - 0.71 0.06 - 0 . 1 0 0.11 - 0 . 1 5 0.16 - 0 . 2 0 0.14 - 0 . 1 7 0 . 0 2 - 0.71 0 . 0 2 - 1.62
Quarry
(18 samples)
.
64.24 - 67.17 1 4 . 2 4 - 16,52 5 . 7 8 - 6.41 0.15 - 0 . 5 0 0152 - 0.83 4.40 ' 5.i'2 4.99 - 5.16 '4 0.63 - 0 . 6 8 0.04 -0.07 0.21 - 0 . 2 8 0 . 0 6 - 1.28 .
.
64.33 - 65.96 1 5 . 0 0 - 17.04 4.75 - 6 . 0 9 0.41 - 0 . 5 4 0 . 7 6 - 1.11 4 . 7 8 - 5.17 4.87 - 5.14 0.62 - 0 . 6 6 0.05 - 0 . 1 1 0.19-0.26 0.26 i . 1 8
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In general, mineralogical, petrographical and chemical data exhibit well-marked differences among the trachyte samples from the two islands. Within each, the chemical and mineralogical data, either from the outcrops or the monument building stones, show similarities. However, some textural aspects, in particular those observed in the field, showed some variability, namely the abundance of phenocrysts. For example, Berthois (1948) studied a trachyte outcrop in the centre of Angra do Heroismo (today concealed below urban housing), referring the abundance of anorthoclase phenocrysts. In fact, this petrographic feature is rare in the Grota dos Calrinhos trachyte and has been observed in several stones from Angra do Heroismo Cathedral. In S~o Miguel Island, the results showed that the sample (L 1) from the old quarry (kept stored in the Casa da Cultura) is more similar to the monument stones. Future research must be carried out to confirm the provenance of this sample, since it represents the best indicator of a possible source quarry.
3.2. Physical properties
Table 2 and 3 show the values of porosity accessible to water and Table 4 show the porosity determined by mercury intrusion in quarry and monument samples from both islands. Samples from Tereeira Island (Grota dos Calrinhos quarry) have values from 3.6 to 13.9%, showing that there is a large heterogeneity even at the level of a single outcrop. Samples from S~o Miguel Island come from different quarries and they show a similar range of variation (4.7-13.6%). Samples from Ribeira Grande Church are much more porous than the ones from local quarry samples. The tested samples from the monument were taken at a certain depth and from their cohesion and texture we can exclude that their porosity had been significantly incremented by degradation during exposure. Therefore, it seems reasonable to conclude that the porosity values higher than 20% can be ascribed to a genetic type of porosity. In fact optical and SEM observation of the quarry and monument samples has pointed out that a significant weathering inherited from the quarry of the trachyte can be excluded. Samples from Angra Cathedral are also significantly more porous than most quarry samples. Sample Ge9 has the highest porosity accessible to water among the quarry trachyte samples and it is macroscopically distinct from all the other quarry samples, namely for its much fighter colour. For its macroscopic aspect and porosity this sample shows some resemblance to the monument samples, but its colouring and the scarcity of phenocrysts allow to exclude it as a potential indicator of the quarry source. Table 2. Results of porosity measurements in quarries and monuments samples of Tereeira Island. Quarries ' Angra Cathedral Samples Porosity (%)
(a)
A
B
9.1
3.6
8.2
4.0
2671
2627
G~4)"
Go(3)
6.9
Go'9
Sa(2)
13.9
17.1
Na(4)
, ,
(b) Real density (Kg.m3)
14.4
12.1 2676
2673
16.3
2652
(a) Accessible to water; (b) determined by mercury intrusion. The subscript (i) indicates the number of distinct samples for calculating the listed mean value. A, porous and B, compact, trachytes from Grota dos Calrinhos; Ge, other samples from Grota dos Calrinhos; Sa, thick plates and Na, thin lamella, from monument stones.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Table 3. Results of porosity measuremems in quarries and monument samples of S~o Miguel Island. Quarries Miseric6rdia Church Samples Porosity (%)
L1
L9.1
Pt~5)
Rg2
4.7
9.9
29.9
(a)
Rg3.8
25.3 . . . . .
(b) .
15.0
,
Real density (Kg.m3)
,
|
15.0
3.9 , |
Rg(6)
.
.
.
.
.
12.8
.
2700
2638
2642
2658
(a) Accessible to water; (b) determined by mercury intrusion. The subscript (i) indicates the number of distinct samples for calculating the listed mean value. L, Lameiro; Pf, Porto Formoso; Rg, Ribeira Grande (Miseric6rdia Church). Table 4 summarises the results of porosity, linear swelling strain and ultrasonic velocity obtained in two quarry blocks from Terceira Island. Since the latter two tests require large samples, they could not be carried out in the monument samples. The results of porosity and the ultrasonic velocity show a similar trend. The small differences between the velocity in dry and saturated conditions suggest that these stones have pore-type porosity. The presence of large pores detected by SEM observation corroborates this conclusion. The swelling strain is very low in sample B, a very compact material, and it is slightly higher in sample A. The better accessibility of water conferred by the higher porosity and a possible higher smectite content may account for the slightly higher linear swelling strain. Graphs in Fig. 5 show the pore size distribution of some quarry and monument samples. The very compact variety of Grota dos Calrinhos trachyte (sample B) has pore radius lower than 0.11xm while the more porous one (sample A) has a clear bi-modal distribution and one mode with values around 1~tm. The remaining quarry samples have their main mode in the range between 0.1-10~tm. Trachyte varieties taken from Angra Cathedral (Fig. 6) show a highly prevalent mode in the range of large pores (1-10~tm) and some may show a second mode at lower pore radius. Samples from Ribeira Grande Church (Fig.7) have very high porosity, predominantly as large pores (radius larger than 1lam). Among the quarry samples, the one kept stored in Casa da Cultura (L1) (Fig.7) shows extensive similarities with those collected in the monument confirming it as the best indicator of the source quarry. Table 4. Results of porosity of quarry and monument samples (Terceira Island) determined mercury intrusion. Porosity Samples
(%)
A
Linear strain due to water absorption
Ultrasonic velocity
(m/s)
(x lO -4t
dry
saturated
9.1
2.26
4010
4300
3.6
1.00
6230
6330
,
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Figure 5: Pore size distribution of Grota dos Calrinhos samples. 4. Conclusions The natural variability presented by volcanic rocks, the abandonment of old quarries and the dense vegetation covering the Azores Island may account for the impossibility of identifying the source quarries, despite the extensive sampling carried out. Some samples from the Grota dos Calrinhos are not very different from the monument stones, but the macroscopic petrographic features allowed to exclude them as indicators of the original quarry. Bibliographic references about old quarries that are no more available for sampling suggest that the main source quarry for the building stones of Angra Cathedral could be situated not far from the monument, within the limits of the city historic centre.
Figure 6: Pore size distribution of samples from Angra do Heroismo Cathedral.
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Figure 7: Pore size distribution of samples from Miseric6rdia church (left) and from local quarries (fight). In the monument, highly porous materials are very susceptible to degradation, namely by salt crystallisation mechanisms. When clay minerals are present (even in a small amount) the decay rates increase and degradation is more extensive. The very high porosity of the samples taken from the Ribeira Grande Church with prevalence of large pores turns them very susceptible to decay and this is in agreement with the extensive degradation visible in the exposed facades. The outcrops sampled for this study do not represent the quarry source of the material of this monument. However, one sample kept stored and provided by the local authorities show great similarities, from the geochemical, petrographical and physical points of view, but the research team could not have access to the exact place of its provenance in order to fully certify this statement. 5. Acknowledgements Supported by the Funda~o para a Ci~ncia e Tecnologia (Portugal) through PRAXIS XXI - project n~ 2/2.1/CSH/254/95 and CCA-CT/FCT-R&D Contract-Program. The following institutions have participated: Instituto Tecnologico e Nuclear, Universidade do Minho, Instituto de Investiga~o Cientifica Tropical, Centro de Conserva~o e Restauro dos Ar and Laborat6rio National de Engenharia Civil. 6. References Alves, C.A.S., Sequeira Braga, M.A. and Trancoso, A. (2000) Saline pollution in trachyte monuments of the Azores islands (Portugal). Submitted for publication at the 9th Int. Cong. Det. Cons. Stone. Berthois, L. (1953) Contribution/t l'6tude lithologique de l'Archipel des Agores. Comun. Serv. Geol. Portugal, Lisboa, T. XXXIV, p.p. 5-198. Forjaz, V.H., Serralheiro, A., and Nunes, J.C. (1990) Carta vulcanol6gica dos Ac~resGrupo Central, na escala 1 2 0 0 000. Univ. dos A~ores e Centro de Vulcanologia (INIC). LeMaitre, R.W. (1989) A classification of igneous rocks and glossary of terms. Blackwell Scientific [Publications, Oxford, 193 p.
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Middlemost, E.A.K. (1994) Naming materials in the magma/igneous rock system. Earth Sei. Rev., 37, p.p. 215-224. Moore, R.B. (1990) Volcanic geology and eruption frequency, S~o Miguel, Azores. Bull. Volcanol., 52, p.p. 602-614. Moore, R.B. (1991) Geology of three late Quaternary stratovoleanoes on S~o Miguel, Azores. U.S. Geol. Survey Bull., B-1900, 41 p. Prud~neio, M.I., Waerenborgh, J.C., Gouveia, M.A., Trindade, M.J., Alves, E., Sequeira Braga, M.A., Alves, C.A., Figueiredo, M.O. and Silva, T. (1998) Degradation processes of traehyte in monument facades, Azores, Portugal. WRI-9, Arehart and Hulston (eds). Balkema, Rotterdam, p.p. 391-394. Rieardo, R.P., Madeira, M.A.V., Medina, J.M.B., Monteiro Marques, M., Sanehes Furtado, A.F.A. (1977) Esbo~o pedol6gieo da Ilha de S. Miguel, A~ores. Anais do Instituto Superior de Agronomia, Lisboa, 37, p.p. 275-385. Self, G. (1973) Recent volcanism on Tereeira, Azores. PhD thesis, Imperial College, London, 236 p. Zbyszewski, G, Almeida, F.M., Veiga Ferreira, O. and Torre de Assun~o, C. (1958) Carta Geol6giea de Portugal, na escala 1:50 000. Notieia explieativa da folha B de S. Miguel (A~ores). Servi~os Geol6gieos de Portugal, Lisboa, 37 p. Zbyszewski, G, Medeiros, A.C., Ferreira, V.O. and Torre de Assun~o, C. (1971) Carta Geol6giea de Portugal na eseala 1:50 000. Notieia explieativa da folha da Ilha Tereeira. Servi~os Geol6gieos de Portugal, Lisboa, 43 p. Zbyszewski, G., Veiga Ferreira, O. and Torre de Assun~,o, C. (1959) Carta Geol6giea de Portugal, 1:50 000. Notir explieativa da folha A de S. Miguel (A~ores). Servi~os Geol6gieos de Portugal, Lisboa, 22 p.
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DETERMINATION OF STRUCTURAL ANISOTROPY OF CARRARA MARBLE WITH ULTRASONIC MEASUREMENTS Florije Sheremeti-Kabashi* Institute of Geology, University of Munich, Germany Rolf Snethlage Bavarian State Conservation Office, Munich, Germany
Abstract
The application of ultrasonic measurements for determining the structural anisotropy of Carrara marble is described. Measurements were carried out on sic 20 x 20 x 20 cm Carrara marble cubes which have been exposed in Munich since 1991 under the frame of EUROMARBLE project. Using ultrasonic tomography a remarkable anisotropy of the ultrasonic velocity distribution was found which requires to take into account the orientation of calcite crystals in the marble for assessing its weathering behaviour. Ultrasonic velocity measurements are compared with determination of the optical c-axis determined with universal stage. The position of contour lines of the maximum and minimum ultrasonic velocties plotted in the Schmidt Net corresponds very well with the orientation of the optical c-axis. Key words: structural anisotropy, marble, unltrasonic velocity
1. Introduction
In all Europe, since antiquity marble is used for different kinds of monuments, buildings and sculptures. A major part of the cultural heritage of every nation is formed from marble. However, since the beginning of our century, the rate of decay of marble is obviously increasing. Typical deterioration phenomena appear to be dependent on the climatic conditions and the amount of air pollutants. In particular, the entire structural disintegration is a dangerous type of decay which can cause the breakdown of a whole sculpture. The bending of marble plates is not only observed on historic tombstones, but also on modem buildings like Finlandia Hall in Helsinki (Ritter 1992) or Amoco Tower in Chicago (Trowhitt & Tuchmann 1988).The causes of such kind of destruction are intensively discussed. According to several authors (Neumann 1964, Quervain 1967, Widhalm 1996) the anisotropic thermal expansion of marble is responsible for the weakening of the marble structure. The structural anisotropy is moreover enhanced by the shape of the calcite crystals and the texture (Siegesmund et al. 1997). The calcite crystal shows an extreme anisotropic thermal expansion, with values ct = 26 x 10.6 K "~ parallel and ct = -6 x 10.6 K ~ perpendicluar to the c-axis (Kleber 1959). The irregular expansion and contraction of calcite crystals during heating and cooling causes a detachment of the grains and eventually the disintegration of the structure. On the other hand, in the calcite crystal ultrasonic velocity shows a maximum of Vp = 7,73 km/s parallel to the a-axis and a minimum OfVp = 5,71 km/s parallel to the c-axis. Ultrasonic velocity allows to determine the orientation of calcite crystals in the marble structure and to evaluate the degree of deterioration because ultrasonic
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
velocity decreases with increasing loosening of the crystal contact planes. Universal stage is a very well known method for determining the orientation of optical c-axis of minerals. It is the aim of this investigation to find out whether both methods give consistent or deviating results and whether ultrasonic velocity can be used as a reliable non-destructive method to determine calcite crystal orientation.
2. Materials and Methods 2.1 Sample material For the investigations carrried out Carrara marble cubes of 20 x 20 x 20 cm (,,Carrara Arabescato") were made available. The cubes have been exposed in Munich since 1991 within the frame of EUROMARBLE exposure program (Snethlage & Simon 1992). In the text, figures and tables, cubes are designated with the following abbreviations: P6: reference marble cube, unweathered, kept indoors in Institute of Geology, University of Munich since 1991 P1, P2, P3, P4, P5: weathered marble cubes, exposed in the open air on the roof of Institute of Geology since 1991 2.2 Ultrasonic measurements On each cube, an arbitrarily chosen coordinate system with X, Y and Z designating the main axes was plotted. Along the orthogonal main planes XY, XZ and YZ of each cube 180 measurements were carried out to obtain a three dimensional ultrasonic tomography. Altogether 1080 single measurements were performed to determine the spatial distribution of ultrasonic p-wave velocity within the six marble cubes (see fig. 1). All measurements were carried out with a USME-C from Krompholz/Pirna using an emitter with 46 KHz frequency.
Figure 1: Coordinate axes X,Y, Z with the three orthogonal main planes of the test cubes and directions of ultrasonic measurements. With the help of maximal and minimal ultrasonic velocities the anisotropy coefficient was calculated using the formula Vmax- VmjVm~ (see e.g. (~esnokov 1977, in Schrn 1983). In order to prove the results obtained on the cubes, drill cores (diameter 4,5 crn, length 7 cm) were taken from each cube which were oriented parallel to the maximum of the e-axis
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distribution which has been already determined by the above mentioned ultrasonic measurements. Then, in three planes parallel to the X-Z plane of each drill core ultrasonic velocity has been measured in radial direction proceeding with an angle of 30 ~. For explanation, the methodology of measurement on the drill cores is depicted in figure 2.
Figure 2: Position of the ultrasonic measurement directions in the drill cores.
2.3 Stereo Net For determining the orientation of crystals in a stone structure stereographic projections are used. The most frequently used way of depicting the orientation is the projection into the lower half sphere. For statistical evaluation the frequency of piercing points per unit area was measured and plotted in contour lines. The data were calculated with the help of SHERISTAT, a PC computer program. 2.4 Universal stage To prove the orientation of calcite crystals obtained from ultrasonic measurements, the orientation of the optical e-axes of calcite crystals was determined using an optical universal stage were performed. Thin sections were made from samples taken from the oriented drill cores. 150 - 170 optical axes per thin section were determined. The results were calculated with the help of SPHER/STAT. 3. Results 3.1 The spatial distribution of ultrasonic velocity As shown in table 1, each marble cube has a different anisotropy coefficient which is highest in cube P1 and lowest in cube P2. This result, however, does not simply mean a high or low degree of orientation of calcite crystals. The anisotropy coefficient only provides information on the structural heterogenity or on the quality of crystal contacts within a marble body, which in our ease is high within P1 and low in P6. It is not appropriate, however, to conclude to strong or weak orientation of calcite crystals as will be shown later. It is much more influenced by the loosening of crystal contacts and can therefore be interpreted as a measure for decay evolution (Zezza 1990). In case of the cubes P1 to P6, in fact cube P6 has the lowest anisotropy coefficient because it has been kept indoors and has not undergone any weathering.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Table 1: Anisotropy coefficients oftest cubes Pl to P6. Marble cube P1 P2 P3 P4 P5 P6
Anisotropy coefficient 0,5 0,3 0,4 0,2 0,4 0,2
K6hler (1988) introduced ultrasonic velocity for assessing the degree of weathering of marbles. He established the following scale: quarry flesh marble: Vp > 5 km/s good state: vp = 4 - 5 km/s acceptable state Vp = 3 - 4 km/s beginning destruction vp = 2 - 3 km/s endangered state Vp = 1,5 - 2 km/s total structural disintegration Vp < 1,5 km/s As measurments show, us-velocity of the reference marble cube P6 which was kept indoors lies in the field of "quarry flesh marble". Almost 60 % of the measured velocities plot in the range of 5,0 - 5,49 km/s. Contrary to P6, in the case of cube P2 which is exposed since 1991 in the open air, us-velocity is decreased by ca. 1 km/s. The cube now groops into the field of good state marbles; 56 % of measured values are within the range of 4,0 - 4,49 km/s. The comparison between cubes P2 and P6 is shown in figure 3.
Figure 3: Statistical comparison between us-velocities of test cubes P2 and P6.
3.2 Determination of calcite crystal orientation by us-measurements As can be seen from figures 4 a + b and 5 a + b, the maxima of the minimal and maximal us-velocities of cubes P2 and P6 are exactly shifted by an angle of 90 ~ It can also be clearly seen from the figures 4c and 5c that the optical c-axes of both P2 and P6 show a strong maximum ( P 2 : 3 1 5 ~ ~ and P6: 16,7~176 Streaking and dipping of Vm~x are: 94,80/0,40 and of Vain: 4,80/0,4 ~ in case of P6 and Vmax: 211 ~ ~ and Vn~: 301 ~ ~ in case of P2. The orientation of the minimal us-velocities corresponds very well with the orientation of the optical c-axes. This result is in agreement with the properties of the calcite crystal in which us-vdocity is minimal in direction to the c-axis.
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Figure 4: Distribution of us-velocities and optical c-axes of calcite crystals in marble cube P2. 4a+b: Maxima and minima of ultrasonic velocities, 4c: Maximum of optical c-axes distribution. The correspondance of minimum of us-velocities (fig. 4b) with position of optical c-axes indicates a good orientation of calcite crystals in marble cube P2.
Figure 5: Distribution of us-velocities and optical c-axes of calcite crystals in marble cube P6. 5a+b: Maxima and minima of us-velocities, 5c: Maximum of optical c-axes distribution. The correspondance of minimum of us-velocities (fig. 5b) with position of optical c-axes indicates a good orientation of calcite crystals m marble cube P6.
3.3 Determination of anisotropic us-velocity distribution In a plane parallel to crystallographically oriented calcite crystals a clear dependence of the us-velocities from the direction of transmission should be observed, in other words the disribution of us- velocities should be significantly anisotropic. The experimental setup is explained in figure 2. The directions of maximal and minimal us-velocities differ by 90 ~ and should be coincident with streaking and dipping of the plane of orientation. If the Z-axis is chosen in direction of Vp,max and the Y-axis in direction of Vp~, the coordinate system obviously defines the reference system for the elastic properties of the investigated material and allows to determine possible anisotropy of us-velocities. Figure 6 shows the results of measuring the us-velocity parallel to the plane of orientation of calcite crystals in an oriented drill core (Fig. 6a). In this case, a clear dependence of the measured us-velocity on the angle of transmission is observed.When measurements are carried out in a plane parallel
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
to XZ-axis which is not oriented to calcite crystal orientation, the distribution of usvelocities forms a random distribution without a clear meximum (Fig. 6b). According to figure 6a it can be concluded that within the marble cubes P2 and P6 the calcite crystals are very well oriented because the us-velocity shows a clear dependence from the angle of transmission. The maximum coincides with the Z-axis.
Figure 6: Distribution of us-velocities in drill cores taken from marble cubes P2 and P6.6a: direction of us-measurement in an oriented drill core parallel to plane of orientation, 6b: direction of usmeasurement in a not oriented drill core parallel to XZ-axis.
4. Discussion The investigations demonstrate that the methodology of measuring the us-velocity is appropriate to detect the orientation of calcite crystals in marble. The method, however, requires tomographic measurments in all directions of a marble cube or sphere. A high anisotropy coefficient is not necessarily consistent with a high orientation of calcite crystals because it is much influenced by inhomogenities like small cracks or structural disintegration. To prove a orientation of the calcite minerals, a clear dependence of the usvelocity from the angle of transmission through oriented samples must be observed. The results obtained from us-measurements correspond very well with measurements of the optical c-axes carried out with the universal stage. Besides a few degrees of deviation the maxima of optical c-axes orientation coincide with the minima of us-velocity which is minimal in c-direction of the calcite crystal.
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In spite of the short exposure time of 8 years the avarage us-velocity within cube P2 has dropped by 1 km/s in comparison with the unweathered reference cube P6 which was kept indoors. This results underlines the scale of Krhler (1988) with the help of which the state of marbles in the open air can be assessed. It also confirms that even the moderate temperature changes of the Munich climate in cooperation with changing humidities can cause crystal detachments and decreasing us-velocity. On the other hand, in the case of well oriented marbles, the us-velocity can remarkably differ in different directions. The question whether a decreased us-velocity can be ascribed to enhanced weathering or good orientation can only be answered by perfoming a sufficient number of us-measurements which, however, have to be correlated to a fixed chosen coordinate system. As a general rule, a scattering of at least 0,5 km/s should be admitted before changes of us-velocity can be ascribed to enhanced weathering. 6. Acknowledgement The authors like to thank Dr. Ettl & Dr. Schuh for generously providing the ultrasonic device. The work was financially supported by DAAD. 7. References Kleber W., 1959. Einftihrung in die Kristallographie. VEB Verlag Technik, Berlin Krhler W., 1988. Preservation Problems of Carrara-Marble Sculptures in PotsdamSanssouci (,,Radical Structural Destruction" of Carrara-Marble). Proceedings vlth Intern. Congress on Deterioration and Conservation of Stone, Torfin 12, 653-662 Neuman R., 1964. Geologic ftir Bauingenieure. Verlag Wilhelm Ernst & Sohn, Berlin Mtinchen Quervain F., 1967. Technische Gesteinskunde. Verlag Birkhauser, Basel Ritter H., 1992. Die Marmorplatten sind falsch dimensioniert. Stein, 1, 18-19 Siegesmund S., Vollbrecht A., Ulemeyer K., Weis T., Sobott R., 1997. Die Anwendung der geologischen Ge~gekunde ~ r die Charakterisierung nat0rlicher Werksteine Fallbeispiel Kauffunger Marmor. Int. J. f. Restoration of Buildings and Monuments 3, 269292 Snethlage R., Simon S., 1992. EUREKA Project EU 496 EUROCARE-EUROMARBLE. Proc. Of the 7~ Intern. Congr. On Deterioration and Conservation of Stone, Lisbon, 21-27 Schrn J., 1983. Petrophysik-Physikalische Eigenschatten von Gesteinen und Mineralien. Enke Verlag, Stuttgart Trewhitt J., Tuchmann J., 1988. Amoco may replace marble on Chicago headquarters. Engineering News Record, 11-12 Widhalm C., Tschegg E., Eppensteiner W., 1996. Anisotropic thermal expansion causes deformation of marble cladding. J. of Performance of Conctructed facilities, ASCE, 10, 5-10 Zezza U., 1990. Physical-mechanical properties of quarry and building stones. Advanced workshop ,,Analytical methodologies for the Investigation of Damaged Stones", VENIALE & ZEZZA ed., Pavia, 20
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THE STONE OF PIRAEUS AT THE MONUMENTS OF THE ACROPOLIS OF ATHENS
P. Theoulakis, Ministry of culture, Athens, Geece M. Bardanis Conservator, Athens, Geece
Abstract This article presents the study of the stone of Piraeus (HetpGtiK6g ~i0og) at the ancient monuments of the Acropolis of Athens. Hereafter matters related with the history of the use and the archaeology of the stone, as well as the geology of the peninsula of Piraeus will be studied. Our aim is to provide the necessary background about the mineralogical composition and the properties for the varieties of the Piraeus stone in order to continue with the research on the causes and mechanisms of decay. Keywords: Ancient building stones, Acropolis of Athens, Stones in ancient monumental architecture, Stone of Piraeus, Aktites stone.
1. Introduction The stone of Piraeus belongs to the group of stones, except marbles, were used during the ancient times to build the city of Athens. Among the stones of Eleusis (dark limestone), Aegina (porolithos), Karea (travertine), Acropolis (limestone) and the one known simply as conglomerate (arouraios, Gtpoupaiog) quarried between Ilissos river and mount Hymettus, the stone of Piraeus is considered to have been used in great measure (Orlandos, 1958, Dermetzopoulos, 1988). Regarding the monuments on the Athenian Acropolis, several kinds of stone were employed for the construction of the buildings during the Archaic period, but the stone of Piraeus was the main building material (fig. 1). Later on, into the Classical and Hellenistic periods the Piraeus stone still remained into use, but in a relatively smaller degree and mainly as a second hand material, coming from the demolished structures of the Archaic Acropolis. In general, stone of Piraeus was very important for the Athenian architecture. It is assumed that its use was totally even larger than that of the famous Athenian marbles from mountains Pentelikon and Hymettuso
2. The name of the s t o n e - Terminology The terms that have been used, during the time, to name the stones come from the area of Piraeus are: a. Aktites stone (Axri~" 2i0o~'). This term is ancient and found in a number of ancient inscriptions (I. G., 1873-1927). It came from the name (Akte, AKzfl) of the west part of the peninsula, where the hard dolomitic limestone is the most commonly found stone. Sometimes, today, the term referred both to the soft and hard stones of Piraeus. b. Porofithos of Piraeus (17etpatr6r rccop62tOo~). Porolithos and poros are terms today used to characterize mostly calcareous sandstones. Wrongly, during the nineteenth and early twentieth centuries archaeologists and architects called like that many kind of
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stones other than marbles, used in Athens and all over the Greece. The term porolithos of Piraeus was used specifically for the stone of Piraeus. When the term Aktites stone is adopted for the hard stones, porolithos of Piraeus refers only to the soft, marly stones of the area.
Figure 1: Capitals and segment of a drum of the "Ancient Neos" nearby the stones of North Wall (left), stones at Arrephorion where samples were taken from (right)
3. Quarries and quarrying Ancient Greeks used stones from all the area of the peninsula of Piraeus: from the Akte, the hill of Mounychia, the Eetioneia and other adjacent areas (fig. 2). Quarries were established at the continental peninsula (inland), as well as at the coast. Their number during the ancient times was really great. Today most of those (the quarries) which are still visible, are the coastal ones and that because the peninsula is densely populated. Eickstedt has recorded all the quarries known from the archaeological excavations at the area, totally 131 locations (Eickstedt, 1991). It is important to note that their exploitation yielded stone with a remarkable variety in its lithological character and mechanical properties (Wycherley, 1978). The archaeological research has revealed that blocks were quarried on steps from the surface. The depth of the quarries was great and sometimes further than ten meters. On the contrary, their surface dimensions (occupation) were not quite large and so, the pits could characterised relatively small (fig. 3). A controversy is about the employment or not the underground quarrying technique. Even if there is not any archaeological found which can support this opinion, there are important testimonies which are at least evidences - if not proofs- for the existence of underground quarries in the area of Piraeus: Xenophon narrates that Athenians imprisoned the crew of three triremes, during the Peloponnese war, at the galleries of the underground quarries of Piraeus (Loicq-Berger, 1967). Far more later E. Dodwell (1819), referred to surface quarries bat also underground galleries, where bovines had found protection from the hot Greek sun. Actually, he is so charmed of the view that compares them with the underground quarries of Syracuse in Sicily, famous for their beauty. After ancient times it seems that quarrying from the Piraeus peninsula almost stopped, even if there are few monuments of the Byzantine era built by this stone. A revival occurred, far more later, during the nineteenth and early twentieth centuries, when the Neoclassical Athens was being built and the need for new building materials was great (Travlos, 1993).
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Today the area of Piraeus is densely populated and only a few ancient surface quarries can be seen.
Figure 2: Geological map of the Piraeus peninsula, (IGME, 1982) 3.1. Transportation The stone first transported by boats, from the peninsula to the port of Phaleron and from there to Athens by land. This happened because ancient Geeks preferred to avoid the passage through the marshy and impassable Alipedon, the area between Athens and Piraeus (Korres, 1996). Later, in Neoclassical Athens, the plinths were transferred directly from Piraeus to Athens through the Piraeus street.
Figure 3: Stepped extraction in one of the quarries on Piraeus peninsula (Archaeological Bulletin, 1976)
4. The archaeological use of the Piraeus stone The stone of Piraeus has been used to a large extent for the construction and restoration of the Athenian Acropolis monuments, from the Archaic period till the Turkish occupation. During the 7 th and 6th century B.C. it was used as the main building material for all the parts of the monuments. "H building" and "ancient Neos" are characteristic works of this
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period. In particular, M. Korres reports that "ancient Neos" is built by stone of inferior quality, i.e. less hard and durable, compared to that of"H building" (Korres, 1996). From the Classic period the use of marble superseded entirely the stone of Piraeus in the upper parts of the buildings and its use restricted consequently in the construction of foundations. Parthenon, Erechtheum, Temple of Athena Nike and Propylaea are some of the most remarkable monuments that belong to this category. The stone of Piraeus was also used to a large extent for the construction of the Acropolis Walls, fortification and retaining walls. A detailed list with all the locations on the Acropolis hill where monuments or architectural features made of Piraeus stone found is out of the aim of this article. In cases where the stone was used in the visible, superstructure of the buildings, the hard, durable limestone (already named aktites) was almost always preferred. On the contrary, the soft, marly kind of Piraeus stone (stone of Mounychia) was selected when used for the substructure and the foundations of the buildings (parts lower of the euthynteria). This choice based of course on the fact that the marly limestone or sandstone of Piraeus are easier and finally more economical to be quarried and dressed (Korres, 1988). Large proportion of the stone first used in the Archaic period was reused later, during the construction activity of subsequent periods. In general, the Piraeus stone has been used to some degree in almost all the Acropolis monuments (with very few exceptions).
5. The geology and stratigraphy of the peninsula of Piraeus The peninsula of Piraeus is a sedimentary area. It is believed that it was firstly an island. During the ages the mainland and the island were connected due to the rising ground movements, the action of the Kefissos river and the local torrents, with the transportation and deposition of alluvial materials (Charalambakis, 1952). From historical sources it is also known that the area between the hill of Mounychia and the Phaleron region was a lagoon, which landfilled during the age of Kimon. The geological formation of Piraeus is called in general "Marl o f Piraeus" and belongs to the Pliocene period of Neogene (fig. 2). The research until now have shown that the peninsula is constituted by several layers, which composition vary and depend on factors such as the ratio between calcite and clay, the presence of dolomite, the fossils, the granulometric gradation and the impurities. All the kinds of stone found in Piraeus form actually a series of similar lithological types but the very hard dolomitic limestones and the soft marly lime- stones and sandstones can be consider as different stones from the view of building technology.
6. Mineralogical composition and properties of the stone of Piraeus and its categories The aim of this chapter is to present the laboratory research that was carried out in order to determine the mineralogical composition as well as the physical and mechanical properties of the Piraeus stone. A number of representative samples (totally 18) were taken from ancient monuments on the Acropolis hill: 9 Four samples from a group of architectural members (mostly capitals) nearby the Parthenon worksite (No 1-4).
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Figure 4, left: Comparison between a stone specimen from Akte and the capitals to the south of the Parthenon worksite Figure 4, right: Comparison between a stone specimen (with macro-fossils) from Akte and a plinth from the tower of the temple of Athena Nike
Figure 5, left: Comparison between a stone fragment from the area of Mounychia and a stoneplinth from the tower of the temple of Athena Nike Figure 5, right: Comparison between a stone fragment from the area of Mounychia and a plinth at the Arrephorion building
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9 Five samples from architectural members gathered at the area of Chalkotheke (No 59). 9 Four samples from the foundation of Arrephorion (No 10-13, fig. 1) and, 9 Five samples from the cistern of Propylaea (No 14-18). Samples were also collected from 4 characteristic lithotypes of Piraeus stone at the peninsula: 9 The very hard whitish stone of Akte. 9 A fossiliferous variation from the same area. 9 A sott, marly limestone from the Mounychia area. 9 A very sott, clayey sandstone of Mounychia. Selected samples were examined under stereomicroscope, polarizing microscope and scanning electron microscope, and were analyzed by means of X-ray diffraction technique and electron probe micro-analysis. Measurements of porosity (mercury porosimetry), ultrasonic velocity, mechanical strengths and water absorption coefficient were also performed. From the polarizing microscopy, X-ray diffraction analysis, scanning electron microscopy- microanalysis (SEM - EDX) and mercury porosimetry the following varieties of these rocks have been recognized (tab. 1-3, fig. 6-8): 9 Dolomitic limestone, hard, compact, whitish to creamy-colored, with low to medium porosity, small grain size and good values of mechanical strength and weathering resistance. Apart from calcite and dolomite, very small quantities of fine-grained quartz and leaflets of sericite were observed (fig, 4, le~). 9 Fossiliferous limestone, yellowish to light grey-colored, rich in macrofossils (shells) and microfossils, with high porosity and mostly low values of mechanical strength and weathering resistance (fig. 4, right). 9 Marly limestone/dolomitic limestone with oolitic texture, brownish, yellowish to light grey-colored, with low to medium porosity and low values of mechanical strength and weathering resistance. The calcitic oolites are connected with little cementing material, something which justify the relatively high micro-porosity of the stone and its poor mechanical properties. Numerous grains of clastic quartz are found in the dolomitic matrix (fig. 5, lett). 9 Sandstone (Neogenic to Pleistocenic clastics), fine to coarse-grained, yellowish, brownish to light grey-colored with high porosity and low mechanical strength and weathering resistance. The terms "poros" and "porolithos", used by architects and builders, include quite otten not only the last variety but also the marly limestones and especially the oolitic ones (fig. 5, right). The mechanical strength and weathering performance of the marly limestones, in general, are very much associated with clay content (Lampropoulos, 1992). Uniaxial, unconfined compressive strength test and flexural (bending) test were carried out. Samples A gave relatively high compressive and tensile strength values in contrast with samples B, F and A (tab. 4). Water absorption coefficient (tab. 4) found too small for samples A, ranged between 0.30.4x10 "3 g/cm 2t 1/2 . Samples B, F, A gave by far higher values (25.00-55.00x10 3 g/cm2t 1/2.
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Ultrasonic velocity (across and in parallel to the bedding o f the rock) o f samples A and B measured higher than that o f samples F and A, indicating once more the difference between the two stones. Table 1 X-ra, Sample Quarries A A Monuments 3 6 13 12 15 17
diffraction analysis results Quartz Calcite Dolomite +
+ ++++
++++ ++++
+
++++
+
+
Kaolinite
Gypsum
+
+
Chlorite i
+
+
++++ ++ ++++
++++ ++ ++++
+
+
+ + +
+
Table 2 Electron 9robe microanal,,sis results Sample Ca % Mg % Si % A! % Quarries A 26.17 24.58 5.60 4.90 B1 30.14 28.28 1.91 3.62 B2 28.09 26.16 4.59 3.97 F 19.03 10.67 20.80 5.35 A 16.43 10.96 23.40 4.25 Monuments 2 34.72 21.61 3.22 4.24 7 ++++ ++ ++ ++ 11 ++++ +++ ++ ++ 12 ++++ +++ ++ ++ 18a ++++ +++ +++ ++ 18b ++++ +++ +++ ++ Table 3: Mercury porosimetry results Sample Total porosity Spec. surface area Quarries A B F A Monuments 3 7 13
lllite
(%)
(m2/g)
" ~ersive Anal, K% S
is) C!
Na
1.15 +
+
0.88 0.63
++ +
++
++
++
++
0.57 +
+
++
+
++
++
+
+
++
++
+
++
+
+
Pore radius average (pm)
Bulk density
(~cm3)
21.90 22.41 16.95 24.86
1.59 2.34 0.08 1.20
5.61 37.65 9.71 4.08
2.77 2.71 2.08 2.66
9.91 22.39 16.35
2.42 1.00 1.30
0.06 4.12 1.76
2.77 2.68 2.12
7. C o n c l u s i o n s The peninsula o f Piraeus presents considerable vertical differentiation. As a result, the term Stone of Piraeus does not include a unique kind o f stone but in contrast a quite great variety o f sedimentary stones. In general, all the stones extracted from the area o f Piraeus should be classified into two main types:
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a. The hard limestones and dolomitic limestones found mainly in the area Akte (AKrfl), the west part of the peninsula, and b. The soft marly (clayey) limestones and sandstones of the Mounychia area, the east part of Piraeus called today Kastella. Here, the term Stone of P#'aeus is proposed for the entirety of the lithological types can be found at the peninsula of Piraeus. Two further subdivisions (of the term) are also used. Aktites stone is called the hard dolomitic or not limestone, because that kind of stones came especially from the area of Akte. With the term Stone of Mounychia we referred to the soft marls and sandstones, found mainly in the area of Mounychia. Table 4: Physical and mechanical properties of the quart, t stones Quarry Compressive Tensile Water Water saturation strength absorption samples strength ft (Kp/cm2) fc (Kp/cm 2) coeff.(g/cm2t lrz) coeff. (%w) 0.41 x10-3 0.44 162.80 A1 1132.00 0.38 x10-3 183.80 1.13 1032.00 A2 0.28 x10"3 954.00 116.80 1.43 A3 << 49.00 xl0 -3 118.00 11.32 B1 55.00 xl0 3 149.00 73.5O 9.38 B2 31.00 xl0 -3 142.00 49.20 11.04 B3 7.50 xlO"3 F1 156.00 43.70 11.94 27.00 xlO-3 165.00 50.30 12.26 F2 51.00 xlO-3 44.60 13.05 121.00 F3 26.00 xlO"3 122.00 42.00 13.26 A1 32.00 xlO"3 244.00 29.00 6.00 A2 35.00 xlO-3 115.00 73.50 17.16 A3
Ultrasonic velocity (cm/Its) _L // 0.53 0.52 0.50 0.51 0.48 0.50 0.31 0.40 0.35 0.45 0.33 0.45 0.28 0.29 0.27 0.28 0.24 0.27 0.31 0.24 0.19 0.18 0.20 0.22
8. References Charalambakis S., 1952. Contribution in the study of the Neogene in Attica. Annales Geologiques de pays Helleniques, 1e Serie T. IV- 1952. Dermetzopoulos T., Mimides T., Davi E., Karas S., Perraki T., Sachpatzis K., 1988. Ancient monuments in Attica, an outline engineering geology and protection. The Engineering Geology of Ancient Works, Monuments and Historical Sites, Proc. of an International Symposium, Athens, Marinos & Koukis (eds), 619-629. Dodwell E., 1819. A classical and topographical tour through Greece during the years 1801, 1805 and 1806. Vol. 1, Printed for Dodwell and Martin, London. Eickstedt K.V., 1991. Beitrage zur Topographie des Antiken Piraeus. Library of the "Archaeological Society in Athens", No 118. Inscriptiones Graecae, 1873- 1927. Volymminis II et III, 292-297, 300-304. Korres M., 1988. The geological factor in ancient Greek architecture. The Engineering Geology of Ancient Works, Monuments and Historical Sites, Proc. of an International Symposium, Athens, Marinos & Koukis (eds), 1779-1793. Korres M., 1996. Topographic matters of the Acropolis, Archaeology of the city of Athens. National Foundation of Research, Athens. Lampropoulos V.N., 1992. Deterioration and conservation of stone, Athens. Loicq P. M . - Berger, 1967. S y r a c u s e - Histoire Culturelle d' une Cite Grecquel Collection Latomus, Volume LXXXVIII, Latomus, Revue d' etudes Latins, Bruxelles. Orlandos A. K., 1958. The building materials of ancient Greeks. Vol. II, Athens (in Greek).
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Travlos I., 1993. The urban development of Athens. KAPON, Athens (in Greek). Wycherley R. E., 1978. The stone of Athens. Princeton University Press, Princeton, New Jersey.
Figure 6: SEM micrographs, quarry sample A 400x (left) and 750x (right)
Figure 7: SEM micrographs, quarry sample B 750x (le~) and 750x (right)
Figure 8: SEM micrographs, quarry samples F, 100x (left) and A, 400x (right)
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PETROPHYSICAL PROPERTIES MODIFICATIONS C A T H E D R A L SANDSTONE BY BLACK CRUSTS
OF
STRASBOURG'S
C. Thomachot* Louis Pasteur University, CNRS, Strasbourg, France D. Jeannette CNRS, Strasbourg, France
Abstract
Two kinds of sandstone, covered with "glossy" black crusts, were taken during works on the Cathedral of Strasbourg. Yellow sandstone with oxide and hydroxide brown aureoles and a 19% water porosity as well as pink sandstone with a 20% porosity and the same granulometry. In each case, these kinds of sandstone have normal petrophysical parameter values for Buntsandstein sandstone. Being covered by glossy black crusts that cling to the stone, these same types of sandstone show modifications of some petrophysical values : Weaker mercury porosity and pore access distribution more widely spread without threshold. Slower and weaker capillary absorption, with a relative increase of the dynamic trapped porosity, Slow dryings, with evaporation occurring under the crust ; Slower adsorption kinetics through crusts, but adsorption isotherms not much modified. These modifications result from a weak moistening of the crust and the sandstone next to it. According to what is observed on embedded stones, these modifications justify, among other things, that these crusts : Keep slightly thick because their hydrophobia limits their alimentation and thus their accretion ; Cause slab fracture. Keywords: sandstone, glossy black crusts, porosity, capillary absorption, adsorption, moistening. 1. Introduction
In sandstone monuments, in Alsace and particularly in Strasbourg's Cathedral, we notice the presence of black thin crusts with a "glossy" aspect, thin and greatly adhering to the stone (Jeannette 1981, Gross 1978). These thin crusts are distinguishable from usual black crusts characterised by an important thickness, a spongy aspect and detachments and which cover surfaces become friable by gypsum. Contrary to these thick crusts which develop in wet but unwashed zone, glossy crusts cover surfaces exposed to rain. Thus we observe them at the top of pinnacles, of hand-rails and sometimes of belfries giving them a black and glossy aspect. They give to sandstone a sort of impermeability and even hydrophobia. Under these crusts, stones are coherent and don't show visible weathering. In some case, a miUimetric thick slab of sandstone in which black crust adheres comes off in a parallel direction to the outside surface of the stone.
* Author to whom correspondence should be addressed.
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By using samples of these same sandstone covered or not by black crust, we have studied possible petrophysical parameter variations and analysed the influence of these variations in weathering developments. 2. Studied sandstone 2.1 Description Two types of thin sandstone covered by black crusts were taken during works on the Cathedral of Strasbourg. The first block (fig. l b) is a fenestration element in a yellow type of sandstone with oxide and hydroxide brown aureoles that was put into place in the 14th century. Facing south, exposed to rain, this sandstone is covered with a glossy black crust. The crust adheres to a 1,5 mm thin sandstone slab which comes off in a parallel direction to the outside surface of the stone. The second block (fig. l a) was taken from a fine pink sandstone hand rail that was put into place during restoration works in 1950. Facing south, its upper weathered part is covered with a thin glossy black crust that adheres well. In the lower part corresponding to an area protected from running water, the stone is covered with a thick blistered crust corresponding to the usual black crusts.
Figure 1: Diagrams of the blocks analysed in their original positions : a) a fine pink sandstone weathered handrail covered with a glossy black crust over the parts exposed to rain, and with a thick black crust over the parts protected from running water , b) fenestration element of a fine yellow sandstone, which, being weathered is covered with a glossy black crust that is progressively being detached from the base of the block upwards. A new black crust develops on the part made bare by the detachment of the initial slab.
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2.2 Petrography The two types of the sandstone being analysed are of the < type that spreads over the summit of upper Buntsandstein. They are fine types of sandstone with an often visible bedding as they are underlined with interpolated finer, more silty layers of a darker colour due to the presence of more iron oxides and hydroxides. Under a microscope, the yellow and pink types of the analysed sandstone are hardly different. They contain quartz, ovoid potassic fedspars of mean diameters of 150 to 2001am. All the intergranular intervals are filled with irregularly edged large pores that may be more than 2501am wide. On the edges these pores shrink to little channels that make up a network of micropores around the grains and the polycristalline masses. However a large part of the microporosity is within the polycristalline masses, the corroded fedspars and the concentrated clay. 2.3 Petrophysical properties The petrophysical measures (see tab. 1) carried out on the unspoilt parts of the 2 blocks have pointed out on the first and second cases, for yellow sandstone and pink sandstone respectively to: Middle capillary transfer kinetics for Buntsandstein type of sandstone : B = 1,6 et 2 crn/h v2 ; 14 and 20% mercury porosity and 0,5 and 3,61am pore threshold ; Drying kinetics corresponding to a surface evaporation ; Same water adsorption isotherms in spite of different specific surfaces (1 m2/g and 0,6 m:/g) ; Table 1 9Comparative table of the main petrophysical properties of the yellow and the pink types of sandstone with and without glossy black crust. In percentage Of Pink ' ' Pink sandstone Yellow Yellow sandstone sandstone with with black the sample volume sandstone black crust crust 19,513 19,5 20,3G 20,3Fq Wate'r total ' Nt ' ii
p0r0s~
2
'1i2
'
,
Capillarity Drying
) Critical saturation 6,3 .
ii
.
i
.
.
Middle threshold ra (laln) Ss (m2/g)
,
i
,i
i
,
,i
i
i
1,4
Sc (%) NHg (%)
Mercury porosimetry
Specific surface Adsorption at 95% R.H.
.
,
0,15
A (g/cm/h ) I/2
ii
i,
0,12
0,18
0,13
1,2 /
1,6
0,8 /
20,1 3,7
17,6 2
016288
Ads (in % of dry 1,079 weigJ~t)
i
i
t5,~ Jl
i
'
i
i6,7 0,55
14,1 0,2-5
0,5846'
1,0540......
1,0212
],468
i,076
' ' 0,78'4
3. Petrographic modifications of black crusts surfaces The remarks already made on this type of black crusts have been confirmed by petrographic analysis (Fefix 1992).
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3.1 Coloured thin sections The outer surface of this type of sandstone is covered with a black glossy crusting that clings to the sandstone. Under a microscope, the crust, 8 to 12 lam thick most of the time, fits the forms of all the superficial grains even the micas and the phyllitic masses (ph. la). Within this film of almost constant thickness, it has not been possible to identify any components through transmitted or reflected light. Under this slightly thick crust (hardly more than 1 mm), the sandstone is sometimes neatly enriched with oxides and iron hydroxides which surround some grains, filling in some narrow areas and cluttering the biggest pores with intertwined microporous areas of phyllites and oxides (ph. l b). No significant difference has been noticed between the two types of sandstone. Under this film, at the bottom of the iron oxides-enriched area, a developing fracture has been noticed several times, that determines the detachment of all the transformed zone.
Photo 1: Thin section view of the yellow sandstone glossy black crust: a) On surface, grains are covered with an iron oxide and carbonaceous matter layer of 10 to 20 microns, b) Along 1 mm under the surface porosity is reduced and oxides are in big quantity. 3.2 Chemical analysis and RX For the two types of sandstone, chemical and X-ray analyses show that from the heart toward the surface covered with a glossy black crust, we have gypsum, iron and carbonaceous matter concentration increase. An analyse of trace elements allows to display strontium, barium, copper and zinc proportions which are more important in the black crust than in sandstone mass. 3.3 SEM Glossy black crusts of the pink and the yellow sandstone defer when we observe them under a scanning microscope. The yellow sandstone glossy black crust appears like a sort of thin and granulous film (grains of few microns) which covers quartz and feldspar grains which we cannot differentiate (ph.2). The analyse shows silica, gypsum, iron, manganese, chlorine, sodium, potassium and phosphorus. In the transformed zone, through 1 to 1,5ram under the crust, pores are filled with clayey felting associated with more important iron oxide and hydroxide concentrations than in the rest of the stone. No salt has been found in depth in the transformed zone. The pink sandstone glossy black crust is made of well crystallised and very imbricated gypsum crystals of few ten microns (ph. 3). These crystals
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are covered here and there with crystalline clusters (of few ten microns) made of gypsum crystals in the region of the micron agglomerated into a Si, CI, K, Fe and Cu mixing. Under the crust, in the transformed zone, pores are also filled with phyllitic clusters with few iron oxides and with few gypsum which concentration decreases quickly with depth.
Photo 2 : SEM pictures of the yellow sandstone glossy black crust : a) General crust aspect ; grains seem covered with a voile; b) Granulous voile's view at a bigger scale predominating mixing of Si, Ca, S, A1 with Fe, Mg, Mn, CI, Na, K and P.
Photo 3 : SEM pictures of the pink sandstone glossy black crust : a) Main black crust aspect composed of imbricated gypsum crystals ; b) View of a mass enclosing a mixing of: Si, Ca, S, AI, CI, K, Fe, Cu.
4. Modifications of the petrophysical properties by black crusts. By its continuity and its surface properties and in spite of its thin thickness, this crust can modified capillary and evaporation transfers and adsorption power (tab. 1). 4.1 Water total porosity and mercury porosity In spite of the presence of a black crust and subjacent modifications, total porosity (Nt) doesn't vary because transformation volume is insufficient at the measured sample scale
(50ee).
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Mercury porosity has been determined on samples (12 co) cut from the block mass (unspoilt sandstone) and at the surface in the glossy black erust's level. The black erust's porosimetric curve obtained is more widely spread and it is no more possible to determinate a threshold. These values show porosity structure modifications near the black crust.
Figure 2 : Pink sandstone mercury porosimetry curves on undamaged stone and on stone with black crust.
4.2 Capillary absorption For capillary absorption experiments, 11 cm cylindrical samples with crusts in the upper face were taken from blocks. They were cut into two to have two comparable samples of 5,5 cm with and without black crust. Absorption goes from the non weathered face to the black crust. We find out (fig. 3 and tab. 1) a capillary weight catch kinetic decrease when the stone is covered with a black crust. These different absorption kinetics already perceptible from the sample base show porosity structure modifications of several centimetres under crusts. This absorption reduction corresponds to a connectivity reduction and the threshold absence. This evolution toward a more heterogeneous porous network is accompanied with an increase of the trapped porosity.
Figure 3 : Yellow sandstone capillary absorption kinetics with and without black crust.
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4.3 Drying kinetics ARer capillary absorption, these same 5,5 cm high samples with and without crust are isolated in a water-proof sheath except for the upper face covered or not with a black crust which is the macroscopic drying surface. For each type sandstone, kinetics (fig. 4) show that drying is slower when the stone is covered by a glossy black crust. Unspoilt sandstone drying curve is characterised by a first phase during which the flow doesn't vary very much. The surface is wet because water capillary transfer toward the surface is enough to equilibrate the loss by drying (Hallaire 1958, Tournier 1998). At the end of this phase, the porosity still occupied by water corresponds to critical saturation (Sc). Beyond critical saturation, we have water vapour diffusion toward the porous network. With a black crust we notice that the drying surface dries immediately and that there isn't any first phase and critical saturation (Sc). The crust acts like a barrier preventing capillary transfers toward the surface and drying occurs in depth under the crust by diffusion toward the porous network.
Figure 4 : Yellow sandstone drying kinetics with and without glossy black crusts at 55% of R.H..
4.4 Adsorption kinetics and adsorption isotherm Into the weathered blocks, covered in surface by a black crust, we take eight times two successive cylindrical slides of 1,5 cm thick. Each slide preliminary dried is isolated by teflon. Only the upper surface is let free. Thus what we measure is water vapour penetration kinetic from the surface toward the depth of the porous network. For a sample serie the free surface is the sane sandstone, for the other one the free surface is the black crust. Obtained results show that for each sandstone, presence of the black crust has the effect of decreasing water vapour adsorption kinetics (fig. 3a) without modifying isotherms (fig. 3b).
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figure 5 : a ) Adsorption kinetics of the yellow sandstone with and without black crust at different relative humidity (R.H.) ; b) Adsorption isotherm of the pink sandstone with and without black crust.
4.5 Moistening Contact angle measurements have been done in glossy black crust of the two sandstone and in sane sandstone. In the yellow sandstone, drop penetration in the crust is slower than in the sane stone but not enough to measure a contact angle. In the pink sandstone's black crust we measure a middle contact angle of 24 ~ when it can't be measured on the sane sandstone because of too fast drop penetration. These measurements confirm on the one hand the decrease of permeability and on the other hand the decrease of moistening. 5. Conclusion So much by as their aspect condition than their composition and morphology, glossy black crusts owe for their formation to mechanisms different from the one usually proposed of justifying the formation of thick black crusts which develop in areas protected from running water. Surfaces which become overcast glossy black crusts are exposed to rain and to running water which soak the sandstone. It is by these same surfaces that evaporation occurs during dry period. During their back drainage and their evaporation, solutions concentrate clays and iron oxides and hydroxides into pores near the surface and precipitate gypsum which cements atmospheric particles at the surface. As exposure conditions, precipitation and superficial deposits are submitted to leaching and dissolution. After each absorption-drying cycles, there may be lef~ the sandstone surface only a weak part of crystallisation and deposits in spite of the weak solubility of gypsum (Arnold 1996) , carbonaceous matter not much soluble being comparatively spared. For these crusts, these exposures justify a slow evolution and a reduced thickness. Further more, at each state of their formation, permeability and moistening reduction and capillary and evaporation transfer properties limit solution penetration and then the crust accretion. At their ultimate state of evolution, solutions contained in the sandstone could pass through the crusts. This confinement would justify the development of other weathering mechanisms responsible for the detachment of little slabs under the crusts (frost, hydric dilatation...).
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6. References Arnold A., 1996, Evolution des sels solubles dans l'alt6ration et la conservation des monuments, La Pietra dei monumenti del suo ambiente fisico ; Instituto Poligrafico e Zecca dello strato, 195-214, Felix C., Maravelaki P., 1992, Black crusts with different origins on the Istrian stone in Venice, 7~ International Congress on Deterioration and Conservation of Stone, 1,267-276, Gross J.J., 1978, Caract6risation et 6volution de l'alt6ration des gr6s de la Ctah6drale de Strasbourgo Th6se de 3~e cycle, Universit6 Louis Pasteur de Strasbourg, 102 p. ; Hallaire M. et Henin S., 1958, Dess6chement du sol et 6volution des profils hydriques, Acad6mie des Sciences, 2151-2153 ; Jeannette D., 1981, Modifications superficielles de gr6s, Sci. G6ol. Bull., 34, 4, 193-208 ; Tournier B., Sizun J-P., Jeannette D., 1999, Influence of pore structures and evaporating surfaces on drying kinetics of stone samples, European Union of Geosciences, 4, 589.
7. Acknowledgements We acknowledge the Oeuvre-Notre-Dame to have supplied us black crust covered blocks of Cathedral's sandstone and for its support.
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FREEZE-THAW RESISTANCE OF THE YAZILIKAYA TUFFS Tamer Topal* Middle East Technical University, Ankara, Turkey Burak Srzmen Middle East Technical University, Ankara, Turkey
Abstract The Midas monument is an impressive cult facade carved with meander ornaments, pediment decorations, and inscriptions during Phrygian times. The monument is formed within nonwelded white and slightly welded pink Yazdlkaya tufts. The monument shows some signs of deterioration. Freeze-thaw activity is quite effective in the region where the monument is located. Therefore, freeze-thaw tests are carried out to assess the freeze-thaw resistance of the tufts. Some physico-mechanical propeties such as weight loss, effective porosity, dry unit weight, water absorption under atmospheric pressure, uniaxial compressive strength (UCS) and sonic velocity of both white and pink tufts are recorded at different test cycles, and compared with those of the flesh samples. The test results reveal that although the pink tuff is found to be more resistant to freeze-thaw activity, both white and pink tufts are adversely affected from the freeze-thaw tests. Therefore, the Yazd~kaya tufts should be protected from freeze-thaw activity. Keywords: tuff, deterioration, freeze-thaw, physico-mechanical properties. 1. Introduction The Midas monument is an impressive cult facade located to the south of Eski~ehir province in Central Anatolia, Turkey (Fig. 1). It is dated BC 600 (Ayday and Grktan, 1990; 1993). The monument is about 17 m wide and 20 m high. The facade is carved with meander ornaments and pediment decorations. The inscription strips on the fagade are in the Phrygian alphabet. The monument is formed within Yazlhkaya tufts. In the monument, the Yazlhkaya tufts have two different units. These units are distinguished on the basis of color differentiation and strength. The lower part of the monument is formed within white tuff whereas the upper part of the monument is formed within pink tuff. They are the products of successive volcanic eruptions. The field observations reveal that although the white tuff is non-welded, the pink tuff is slightly welded. The Midas monument, ancient Midas city, other monuments and tombs make this region attractive from both historical and touristic points of view. However, there is evidence of deterioration in the tufts. Therefore, understanding the processes, which cause deterioration of the tufts, is essential for the purpose of conservation. In the region, the continental climatic conditions prevail. The winters are cold with rain and snow, and the summers are hot and dry. The number of freeze-thaw cycles throughout the year is considered to be about 20 (Binal et al., 1997; 1998). However, it is found to be around 50 in Cappadocia region where similar climate dominates (Topal, 1998). Thus, in the region, freeze-thaw
*Author's to whom correspondence should be addressed.
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processes are quite effective. Therefore, freeze-thaw tests up to 52 test cycles are performed to assess the freeze-thaw resistance of the tufts in this study. Some physico-mechanical properties of both white and pink tufts are recorded at different test cycles, and compared with those of the fresh samples. The relative changes of the properties are used to assess the effects of the freeze-thaw tests on the tufts.
Figure 1: Location map of the study area.
2. Method of Study For the assessment of freeze-thaw resistance of the Yazdlkaya tufts, 20 fresh block samples were taken from the field. For both white and pink tufts, 50 cylindrical core samples (NX size) with length to diameter ratio of 2.5 were prepared in the laboratory. The samples were subjected to freeze-thaw tests in accordance with RILEM (1980). Freeze-thaw tests attempt to reproduce the stresses, which may arise inside the stone when ice crystals are formed. Those effects are generally obtained by varying temperature under and above 0 ~ on samples containing a known amount of water (Rossi-Doria, 1985). For the freeze-thaw tests, the samples were immersed for 6 hours in distilled water at 15 to 20 ~ The samples were then placed in a deep freeze cabinet at -15 + 2 ~ for 6 hours period of freezing in the air. This procedure was repeated 52 times. The weight, effective porosity, dry unit weight, water absorption under atmospheric pressure, uniaxial compressive strength (UCS), and sonic velocity of the samples were recorded at 10, 20 40 and 52 test cycles and compared with those of the flesh samples. For the determination of these properties, the procedures suggested by RILEM (1980), ISRM (1981), and TS699 (1987) were followed.
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3. Test Results and Discussion
Test results associated with the change in physico-mechanical properties of both white and pink tufts for different freeze-thaw test cycles are presented in tabs. 1 and 2. They are the mean values of five samples. The variations of the physico-mechanical properties mentioned above are shown in figs. 2 and 7. The fresh sample is represented by 100% for all variables and the others are normalized with respect to the flesh sample. Table 1" Test results for the white tuff Number of Cycle
Weight
Effective Porosity
0 10 20 40 52
100.00
39.65 40.70 39.61 40.92 41.50
(%)
Dry Unit Weight
(%)
99.86 99.51 98.49 85.61
Water Absorption
( k N / m 3)
(%)
UCS (MPa)
12.04 12.23 12.09 11.88 11.99
23.63 24.42 23.76 24.42 25.75
10.00 9.64 9.31 9.00 7.16
Dry Unit Weight (kN/m3) 14.37 13.97 14.55 14.16 14.46
Water Absorption
Sonic Velocity (m/see) 1932.42 1933.42 1920.75 1827.72 1424.40
Table 2 Test results for the pink tuff Number of Cycle
Weight
Effective Porosity
0 10 20 40 52
100.00
33.75 34.77 33.06 35.06 33.36
(%)
(%)
99.98 99.82 99.69 99.19
(%)
Sonic uCS (MPa) Velocity 16.95 16.20 15.86 15.84 15.59
18.35 19.60 17.80 19.16 17.97
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Figure 7 Variations of the sonic velocity of the tufts after freeze-thaw tests Fig. 2 shows that no significant change in weight occurs at the end of 20 freeze-thaw test cycles for both white and pink tufts. Slight weight losses are observed only in white tuff at the end of 40 test cycles. Weight loss is very significant in white tuff after 40 test cycles. It is in the form of disintegration and is mainly concentrated at the upper and lower corners of the white tuff samples. At the end of 52 test cycles, weight loss in the white tuff is reached to 14.4%, although it is about 0.2% in the pink tuff. Effective porosities of both tufts are also not changed at the end of 20 test cycles (fig. 3). It is increased by 5.7% in white tuff and 2% in pink tuff at the end of 52 test cycles. Similar variations are observed in dry unit weight and water absorption values of both tufts (figs.4 and 5). Effect of freeze-thaw tests in UCS and sonic velocity of the tufts is very significant. UCS is decreased by 5.6% in the white tuff and 4.4% in the pink tuff, at the end of 10 test cycles. The loss in UCS is more pronounced at~er 40 test cycles. UCS is dropped by 29.4% in the white tuff and 9% in the
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pink tuff at the end of 52 test cycles (fig. 6). Sonic velocity of the tufts also decreases as the number of test cycles increases. Decrease in sonic velocity in the white tuff (2.4%) is almost the same as the pink tuff (1.9%) at the end of 20 test cycles. However, sonic velocity is much more reduced in the white tuff as the number of test cycles increases. Reduction in sonic velocity is 5.6% in the white tuff and 2.2% in the pink tuff, at the end of 40 test cycles. It is 23.8% in the white tuff and 2.6% in the pink tuff at the end of 50 test cycles (fig. 7). In general, except the dry unit weight, all the other physico-mechanical properties of both tufts are influenced as the freeze-thaw test cycles increased. The change in the physico-mechanical properties of the white tuff is more than that of the pink tuff. Therefore, the pink tuff is more resistant to freeze-thaw activity than the white tuff. The field observations also reveal that the pink tuff is more durable than the white tuff. Most of the ornaments and pediment decorations carved in BC 600 in the pink tuff can be easily seen even today. Considering the fact that the pink tuff is also slightly affected from the freeze-thaw cycles, both tufts should be protected from freeze-thaw activity.
4. Conclusions
The Midas monument formed within nonwelded white and slightly welded pink Yazfl~kaya tufts, shows some signs of deterioration. Freeze-thaw tests are carried out to assess the freeze-thaw resistance of the tufts. The physico-mechanical propeties such as weight loss, effective porosity, dry unit weight, water absorption under atmospheric pressure, uniaxial compressive strength (UCS) and sonic velocity of both white and pink tufts are recorded at different test cycles, and compared with those of the fresh samples. Based on the findings of this study, except dry unit weight, all the other properties of the tufts are found to useful to assess the damage. However, deterioration of the tufts by freezethaw tests can be better followed by UCS and sonic velocity measurements. Although the pink tuff is found to be more resistant to freeze-thaw activity, both white and pink tufts are adversely affected from the freeze-thaw tests. Therefore, the Yazfl~kaya tufts should be protected from freeze-thaw activity.
5. References
Ayday, C. and G0ktan, R.M., 1990. A preliminary engineering geology study directed to the conservation of Midas monument, Proc. International Earth Sciences Colloquium on the Aegean Region (IEASCA), GOll0k-Izmir, Turkey, 102-108. Ayday, C., and G0ktan, R.M., 1993. Yazlhkaya (Midas) anm civarmda g0zlenen kaya blok devrilme ve kayma mekanizmalan, Tiirkiye Jeoloji Kurultayl B01teni, 8, 155-159. Binal, A., Kasapo(glu, K.E., and GOk~eo(glu, C., 1997. The surficial physical deterioration behaviour ofNeogene volcanosedimentary rocks of Eski~ehir-Yazfl~kaya, NW Turkey, Proc. Int. Cong. on Engineering Geology and the Environment, Athens, Balkema, Rotterdam, 3065-3069. Binal, A., Kasapofglu, K.E., and G0k~eo~lu, C., 1998. Variation of some physical and mechanical parameters of the volcanosedimentary rocks around Eski~ehir-Yazfl~kaya under freezing-thawing effect, Yerbilimleri, 20, 41-54. ISRM, 1981. Rock characterization, testing and monitoring, International Society for Rock Mechanics Suggested Methods, Pergamon Press, Oxford.
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RILEM, 1980. Recommended tests to measure the deterioration of stone and to assess the effectiveness of treatment methods. Commission 25-PEM, Materials and Structures, 13, 175-253. Rossi-Doria, P.R., 1985. Laboratory tests on artistic stonework. The Deterioration and Conservation of Stone. Studies and documents on the cultural heritage. No. 16, 23 5-242. Topal, T. and Doyuran, V., 1998. Analyses of deterioration of the Cappadocian tuff, Turkey, Environmental Geology, 34, 1, 5-20. Balkema, Rotterdam, 2939-2944. TS699, 1987. Methods of testing for natural building stones (in Turkish). Ttirk Standartlarl EnstittisO, Ankara.
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AN EVALUATION OF GEOLOGY AND WEATHERING IN THE PRESERVATION OF MARL OBJECTS
Metaxia Ventikou* Sculpture Conservation, Victoria and Albert Museum, London, UK. Chris Halls Royal School of Mines, Imperial College of Science, Technology and Medicine, London, UK. William Lindsay Conservation Unit, Department of Palaeontology, The Natural History Museum, London, UK. Meryl Batchelder Department of Mineralogy, The Natural History Museum, London, UK. Charlotte Hubbard Sculpture Conservation, Victoria and Albert Museum, London, UK.
Abstract
The deterioration of an Italian marl fireplace in the Victoria and Albert Museum led to the research described in this paper. The purpose was to study the geology and weathering of marl in order to explain the poor state of preservation of such objects and to develop a suitable conservation strategy. Marl is an argillaceous carbonate rock rarely encountered in works of art. The mineralogical and geological characteristics described here are particular to the sample examined, but these properties can be considered typical for all marls. The fireplace marl consists of clay minerals and calcite and the rock has a characteristic fabric. Natural weathering, combined with the effect of the conditions, under which the fireplace has been used and stored, were identified as the cause of its partial disintegration. Among the factors governing deterioration, atmospheric humidity has played a major role and is the one most likely to affect the condition of marl objects. Experiments were made in which a sample was exposed to various levels of relative humidity and the resulting dimensional changes were measured. The outcome of this research was to establish a deterioration model confirming that variations in ambient relative humidity are the main cause of weathering in a marl artefact. Keywords: marl, sedimentary, delamination, weathering, relative humidity, displacement.
1. Introduction
Marl, due to its composition and conditions of formation, is a sedimentary rock highly susceptible to weathering. Although marl is not a common material in sculpture or architecture, when used, it tends to show marked deterioration which poses significant problems for conservation. The sixteenth-century Italian fireplace, in the Victoria and Albert Museum (inv. no. 72531861), provides a case study (Fig. 1). On acquisition, in 1861, it was recorded as originating from a house in Savona, North Italy. Until the present study revealed it to be marl, it was *Sculpture Conservation,Victoria and Albert Museum, CromwellRoad, LondonSW7 2RL, UK.
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believed to be carved from black slate (or pietra di lavagna). The fireplace consists of 11 pieces of various dimensions. All pieces show delamination, parallel to the bedding of the rock, which is most severe at the carved surface. Many of the carved details do not survive and those still intact are very friable, or even detached from the substrate. The geology of marl is very important in understanding the material and thus, crucial in establishing a conservation treatment. Marl has been fully described in the geological literature, but because it is rarely used as a sculptural medium, it has not been broadly characterised in conservation terms. In addition, the term 'marl' has been used to describe a variety of rocks and its classification depends on several parameters. It was therefore necessary to establish a suitable definition of the material before proceeding to study weathering mechanisms and potentially suitable methods of preservation.
2. The geology of marl 2.1 Definition Marl is a sedimentary rock with a composition between that of claystone and carbonate rocks (Millot 1970, Cornell and Aksoyoglou 1990). Specifically, marl is a mixture of clay and carbonate minerals, the latter between 35 and 65% of the total composition (Greensmith 1989). However, any sedimentary rock with significant clay and calcite content may be further classified to one of the marl types given by Kirsch (1968), ranging from marly clays to marly limestones. It should also be noted that marls are heterogeneous rocks, a feature common to many sedimentary formations. In geological publications that include compositional analyses of marl, the carbonate content is found in various percentages ranging from 20 to 80%. (Cornell and Aksoyoglou 1991, Antoine, Giraud, Meunier and Van Ash 1995.). Marl is further defined by its petrology. The term marl is applied to chemical and biogenic sedimentary rocks originating from unconsolidated calcareous or dolomitic mud which, if it contains clay minerals and calcite in the above percentages, when consolidated will become marl (Greensmith 1989). The texture of marls is governed by the rate of deposition of the sediments and local variations in the proportions of the clay and carbonate components. 2.2 Identification of the fireplace marl The properties of the fireplace material were identified by optical microscopy, scanning electron microscopy and quantitative x-ray diffraction. The samples used for the analyses were fragments of unknown original position already detached from the surface of the fireplace. The results from the quantitative XRD analysis are given in Table 1. In particular, clay minerals constitute 41-52% of the stone and the smallest percentage of calcite detected was 31%. Given this mineralogical composition, the rock can be classified definitely as marl. The clay minerals were found to be of sedimentary origin and have not undergone significant alteration in the diagenetic environment. Among the clay minerals present, kaolinite is well crystallised. During XRD identification, heating to temperatures above 500~ does not alter the illite structure. Although illite may coexist in mixtures with smectite in sedimentary rocks, the treatment with glycol during the same analysis did not indicate any swelling phenomena. The presence of muscovite indicates a late diagenetic process, but its coexistence with illite and chlorite does not suggest significant prograde recrystallization or alteration. Finally, chlorite in the marl samples is well-crystallised and its complete structure is confirmed by the stable XRD peak when treated with ethylene glycol. Spectrum 1 shows the detected clay minerals and illustrates their stability under different treatments. The fireplace
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marl does not contain expandable clay minerals of the smectite group. Table 1. Minerals and their percentages identified in the fireplace marl Mineral
Weight (%)
Kaolinite Illite Muscovite Chlorite Calcite Gypsum Pyrite Quartz Total
3-5 23-27 4-5 11-15 31-33 3-4 1-2 19-21 100
Figure 1. XRD spectrum of minerals in a sample from the marl fireplace. A 550~ 2 hours, B 400~ 2 hours, C Ethylene Glycol, D Air dried. The first peak corresponds to chlorite, the second to illite and the third to kaolinite.
In thin section, marl would be expected to show a planar stratification corresponding to the gradual deposition of the sediment. Instead, foliations of clay minerals and carbonates are observed to form lenticles around carbonate domains. Clay minerals exhibit a layer structure that is easily arranged in a shape-preferred orientation. In argillaceous sedimentary rocks like shales, for instance, clay minerals show quite well developed planar arrangement as a result of deposition and compaction (Weaver 1989). Under late diagenetic conditions, clay minerals are recrystallised to form larger structures, whereas in metamorphic states, minerals are transformed into completely new assemblages and the fabrics and preferred orientation from the original rock are not readily distinguished (Weaver 1989). Because of the thin, layered structure of clay minerals, they are visible in thin sections only as crystal aggregates and foliations. Grains consisting of chlorite/muscovite aggregates and individual flakes of muscovite reaching sizes of approximately 55/L m were observed in marl from the fireplace. The presence of foliated crystals suggests a mechanism different from ordinary sedimentation and, in the case of this marl, the foliated fabric is attributed to the effect of pressure exerted by overlying sediments, causing diagenetic growth of clay minerals with a lattice-preferred orientation along the foliated planes of bedding. Since the minerals do not show significant metamorphic modification, the rock acquired its properties at a late stage of diagenesis (Fig.2). The formation of foliations is further assisted by the general behaviour of calcite and carbonate minerals during diagenesis and compression. The stress differences generated during burial and diagenesis produce elongated and lenticular structures from the aggregates of carbonate. Burial overpressure causes partial dissolution, redistribution and re-precipitation of the soluble carbonates which thus form lenticular domains parallel to the bedding planes. These are surrounded by insoluble clay minerals and other carbonaceous organic material, all of which are moulded around the carbonate lenticles. The conclusion is that the rock acquired its foliated texture at a late stage of diagenesis but it can be characterised as marl on the basis of its dominantly sedimentary features and the clay and calcite composition.
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Figure 2. Marl fireplace piece 7253.7-1861 (from view) Figure 3. Chlorite aggregate in the foliated arrangements of clay minerals and calcite in a thin cross section from the fireplace marl, under transmitted polarised light (field width 550 ~t m)
3. Weathering mechanisms of marl Until recently removed for study, the fireplace has remained in the same store for as long as records have survived. The conditions in the store were generally stable, as appropriate to sculpture collections. However, it is evident by comparing the present state of the fireplace with a photograph taken of the piece 7253.1-1861 in 1899 that its condition has deteriorated progressively over the last one hundred years. The exposed surfaces of the marl fireplace, particularly those carved in relief, are splitting and becoming detached. The decision was therefore taken to determine the composition of the fireplace and establish the weathering mechanisms responsible for this breakdown. According to conservation terminology, the fireplace has been subject to extensive delamination which has taken place parallel to the bedding of the rock. This is most extreme on the carved surface. The present state of the marl fireplace can be attributed to a combination of mechanisms that have acted on the rock and the clay minerals in it from the time when it was brought to the surface by erosion and quarried from its place of origin. The main causes of deterioration can be classified as follows.
3.1 Weathering due to mineralogy The combination of clay minerals and calcite makes marl a very soft stone to carve. It has low strength and is susceptible to shrink-swell behaviour. In consolidated rocks, the existence of clay minerals significantly contributes to the degree of water penetration and swelling. Water entering the rock due to the presence of clay minerals is a cause of deterioration. Two main mechanisms govern the absorption of water by clay minerals. These are surface adsorption and the attraction of water molecules to the crystal lattice resulting in expansion. Lattice absorption does not occur in the fireplace marl because the clay minerals present are not expandable As far as adsorption is concerned, all clay minerals attract water to their surfaces. When water molecules approach the mineral surfaces they become adsorbed to form a molecular film which has a different density and viscosity compared to that of liquid water (Grim 1968, Kirsch 1968). Adsorption of water by clay minerals is a characteristic phenomenon and is the main response of those minerals to water (Mitchell 1993). In addition, water may dissolve the carbonates and thus alter the chemical composition and
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porosity of the rock. In particular, water containing carbon dioxide can dissolve and carry away calcium carbonate from calcareous argillaceous rocks, including marl. Calcite becomes more soluble at high pressures of carbon dioxide and low temperatures (Deer, Howie and Zussman 1991). Some porosity can be created by this process in marls in contact with sedimentary waters during burial and diagenesis and later, when in contact with carbonic meteoric waters during exhumation as erosion of the land surface proceeds. The porous fabric of some marls, with carbonate domains and void systems, is attributed to the dissolution and precipitation of carbonate minerals in this way. Decalcification during weathering would also occur along planes of weakness created by material discontinuities and fractures where water gains access more readily (Hawkins and Pinches 1992).
3.2 Wetting-drying cycles and temperature variations Temperature plays a very important role in the weathering of rocks by affecting the state and chemical action of water, the solubility of salts, the rate of chemical reactions and by causing thermal expansion and contraction. When the effects of temperature and humidity are combined, the mechanisms governing deterioration of rocks become even more complex. The generally heterogeneous behaviour of minerals during wetting-drying cycles and temperature variations under ambient conditions can cause stone to disintegrate. However the fireplace may have been exposed to extreme variations when hot and dry conditions alternated with cool and humid conditions during seasonal domestic use. Relative humidity must have contributed to the weathering mechanism. The use of the fireplace, presumably on a daily basis during winter, would have resulted in frequent and intense RH changes in the environment of the marl. Since RH depends on temperature, when the surface of the marl cooled, water would be adsorbed on the surface of the fireplace, penetrating the outer layer of the marl as the stone cooled. When the temperature increased again as a result of fire, moisture would evaporate and the cycle would be repeated. Temperature variations also cause deterioration because of the mineralogy of the rock. It has been reported that swelling of clay minerals takes place more rapidly if water is absorbed under dry conditions (Price 1995). During drying, clay minerals shrink and their structures progressively break down. Shrinkage during drying becomes even more destructive in rock masses like marl which show textures in which voids are interspersed with closely compacted clay mineral aggregates and carbonate grains (Mitchell 1993). Consequently, both adsorbed and free water will be lost during drying and the rock must have been strongly affected by wetting-drying cycles. 3.3 Weathering due to fabric and overconsolidation All sedimentary and consolidated rocks may suffer some expansion, and even softening, when pressure is reduced during the removal of overburden and stored strain energy is released (Cripps and Taylor 1981). This stress relief readily causes expansion. Fractures open in a direction parallel to the release of force, and separation of foliations and bedding planes in the rock can occur. As a result, water absorption increases because of the increased permeability and opening of fractures (Price 1995). The state of preservation of the fireplace marl and the extensive delamination observed on the outer surface, are primarily attributable to the effects of unloading of the rock in combination with the effects of the humidity and temperature variations described above. In addition, for at least fifteen years, the fireplace was subject to the weight of a marble fireplace of similar dimensions which rested on it due to a dense storage arrangement and the misidentification of the fireplace material as slate. The storage was improved in 1995 after
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concerns about these unsatisfactory conditions led to the removal of the outmoded system of storage. The weight of marble would have imposed a stress which, when removed, would have caused small-scale expansion added to that induced by removal of the original geological overburden. There is the added possibility that shear stresses imposed by this loading during storage could have facilitated delamination, given that the carved relief of the surface cuts across the sedimentary laminae which lie parallel to the principal plane defined by the slabs of which the fireplace is formed.
4. Analyses of the effect of relative humidity on the fireplace marl 4.1 Aim of experiments Of the main weathering mechanisms discussed, variations in humidity had the most dramatic influence on the degradation of the fireplace during its existence, and can be expected to continue to have an effect in the future. Extreme temperature variations are no longer like in the museum environment and the fracturing due to stress release which accompanied geological unloading must have been completed at the site of origin during the past. To confirm the role of relative humidity and measure its impact on the marl, a series of experiments were conducted. The aim was to determine the response of the fireplace to humidity and thus establish appropriate guidelines for conservation and determine treatment appropriate for the preservation of the fireplace and other marl artefacts.
4.2 Experimental procedure Experiments were designed in order to examine the response of the marl sample to extremes and cycles of relative humidity. The tests were performed in the Palaeontology Conservation Unit of the Natural History Museum. The experimental arrangement consisted of a micro-climate generator that provided the relative humidities and a measuring device for recording dimensional change. The micro-climate generator can accurately control the RH by conditioning and recirculating the appropriate amount of humid air in order to maintain the value set by the operator. The generator is equipped with software that simultaneously monitors the RH in the case and enables the user to program values from 10 to 90% RH. The measuring device used was a displacement transducer connected to a digital LED indicator. The temperature is not controllable but is monitored and remained at 23~ with occasional variations of _+ I~ The transducer responds to dimensional changes of _+2500x10 -4 mm, which are displayed in real time. A sample of volume 1.5cm 3 was taken from the marl fireplace piece 7235:13b-1861. The sample was placed inside the sealed case of volume 33736cm 3, with the marl foliations parallel to the level of the base. The transducer was adjusted to record the response of the laminations. The case was connected to the micro-climate generator at the RH set to 35%. A sensor inside the case sends the values of temperature and RH to be processed by the recorder in real time The dimensions of the sample were allowed to stabilise under the relatively dry conditions of 35% RH. The dimension in that state was taken as a standard zero with any subsequently induced expansion or contraction registering as positive or negative values respectively.
4.3 Results and discussion Experiment 1: From an initial environment of 35% RH, the sample was gradually exposed over a two hour period to relative humidities up to 75%. It was held at 75% RH for 75 minutes
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when the RH was progressively decreased over a period of two hours, to 35%. Under these conditions, RH changed by 1% every three minutes. Comparable values have been recorded for some periods in the storeroom where the fireplace was kept. As illustrated in Figure 4, displacement and RH show a direct positive correlation. The marl sample expands as the RH rises, and it contracts as the RH falls. The response to the RH changes is rapid, although there is some delay in the change which takes place as RH is reduced. During contraction the dimensional changes are smaller than the expansive changes which accompany increasing RH, and the sample does not regain its original dimensions. Experiment 2: The micro-climate generator was programmed to provide a RH of 35% and when the above condition was achieved, the RH was increased as rapidly as possible to 75%. After the RH inside the case reached 75%, it was held at that level for six hours in order to examine the maximum displacement that could occur in the sample under constant high RH. During the second experiment, as shown in Figure 5, the sample responded almost immediately and the rate of displacement is fast when the RH change is rapid. The displacement tends to slow down or stop when the RH stabilises at a high level. Moreover, it is notable that the sample showed a displacement of 71x10 ~ mm, the maximum measured experimentally. The sample was left under 75% RH for six hours, though the expansion reached a maximum and stabilised after five hours. This time is therefore taken to be the time needed for the marl to respond to equilibrate under conditions of high humidity. Experiment 3: The third experiment involved the exposure of the same sample to repeated changes of relative humidity within the range of 40 to 60%. These values correspond to the ambient RH under which the fireplace is kept in storage. Given that the first and second experiments show that the sample continues to change its dimensions after RH has stabilised, in this case the sample was not allowed to reach dimensional equilibrium as the RH was varied. This experiment was designed to determine whether these short cycles of expansion and contraction had a permanent effect on the rock. The displacement curve in Figure 6 shows a very clear response to the RH changes. The pattern of displacement is repeated during the second cycle, confirming the consistent effect of short-term variation of RH on the dimensions of the sample. The high RH was maintained for less than 20 minutes and the sample showed a maximum displacement towards the end of that period. The abrupt halt in dimensional expansion suggests that further deformation would be experienced had the RH continued to increase. The sample presented the same pattern of displacement during both contraction and expansion. Experiment 4: The sample was stabilised in 50% RH and wetted with a brush to determine the possible response caused by wetting of the fireplace. The RH inside the case was set to 80% for two hours so that the wet condition was maintained. Figure 7 illustrates the behaviour of marl under these extreme conditions. During the first 5 minutes after wetting the fastest displacement took place. Thereafter the sample continued to expand rapidly for 15 minutes, followed by a slower dimensional increase. The sample reached the maximum expansion (180xl 0 -4 mm) measured in these experiments. These experiments demonstrate the susceptibility of marl to changes in relative humidity and the effect of wetting. While it is apparent that the sample deforms in response to RH changes, further study is required to establish the extent to which the dimensional changes are permanent. Moreover, given that the sample was much smaller than the object, it can be assumed that changes in RH would have less impact on the fireplace as a whole and that dimensional changes would be slower. Because adsorption and penetration of humidity depends on the area exposed, once delamination has begun, the rate of disintegration will increase. However, the experiments confirm that marl responds to ambient RH variations in
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the museum environment and is especially susceptible to wetting by liquid water. The response of the fireplace to ambient humidity and water demonstrates that the effective preservation of the fireplace and related marl objects requires an environment in which RH is kept relatively constant and that water should not be used during conservation treatment. Figure 4 Displacement and RH vs time (experiment 1)
Figure 6 Displacement and RH vs time (experiment 3)
Figure 5 Disolacement and RH vs time (exoeriment 2)
Figure 7 Displacement vs time (experiment 4)
5. Conclusions
Marl is an uncommon sculptural medium and therefore the study of its constitution and behaviour in a museum environment contributes to the limited references from the point of view of conservation. Marl is susceptible to deterioration because of the synergism of the factors involved. The mineralogical composition of the rock and the geological conditions under which it formed and consolidated have an irreversible effect on its preservation once taken from the ground. The condition of the marl fireplace in the Victoria and Albert Museum confirms the continuing deterioration of the rock. The characterisation of the material has proved crucial in determining a strategy for conservation. The study of weathering of the fireplace marl provided significant information that can be used both for restraining deterioration and for improving its stability. Specifically, deterioration had begun before the rock was quarried due to its geological nature and continued when the fireplace was used in its architectural setting. During storage the process continued as a result of a variety of factors in the domestic and museum environment. Marl is particularly responsive to fluctuations in relative humidity. Under ambient environmental conditions, it is subject to deformation as a result of gradual or abrupt changes in relative humidity, even within a narrow range. Thus, the primary aim in conservation
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should be to establish and maintain a constant relative humidity in the environment where marl artefacts are stored and displayed. 6. Acknowledgements The research was carried out under the auspices of the V&A/RCA post-graduate Conservation Course, in collaboration with the Sculpture Conservation and the Sculpture Department of the Victoria and Albert Museum as part of their on-going conservation programme. We are indebted to Mr Martin Gill, Ms Elisabeth Morris and Mr Dick Giddens from the Royal School of Mines, Imperial College of Science, Technology and Medicine, to Mr Adrian Doyle from the Palaeontology Conservation Unit, The Natural History Museum, and to Mr Pedro Gaspar from the RCA/V&A Conservation Course who assisted with the technical preparation of material, analyses and scientific advice. 7. References Antoine, A., Giraud, A., Meunier, M., Van Ash, T., 1995. Geological and geotechnical properties of the "terres noires" in Southeastern France: weathering, erosion, solid transport and instability, Engineering Geology, 40, 223-234. Cornell, R. M., Aksoyoglou, E. S., 1991. Simultaneous determination of the cation exchange capacity and the exchangeable cations on marl. Clay Minerals, 26, 567-570. Cripps, J. C., Taylor, R. K., 1981. The engineering properties of mudrocks. Quarterly Journal of Engineering Geology, 14, 325-346. Deer, W. A., Howie, R. A. and Zussman, J., 1991. An Introduction to the Rock-Forming Minerals, Essex, Longman Scientific & Technical. Greensmith, J. T., 1989. Petrology of the Sedimentary Rocks (7 th edition), London, Unwin Hyman. Grim, R. E., 1968. Clay Mineralogy (2na edition), New York, McGraw-Hill. Hawkins, A. B., Pinches, G. M., 1992. Engineering description of mudrocks. Quarterly Journal of Engineering Geology, 25, 17-30. Kirsch, H., 1968. Applied Mineralogy (translated by K. A. Jones), London, Chapman and Hall Ltd. Millot, G., 1970. Geology of Clays (translated by W. R. Farrand and H. Paquet), New York, Springer-Verlag. Mitchell, J. K., 1993. Fundamentals of Soil Behavior, New York, John Wiley & Sons. Price, D. G., 1995. Weathering and weathering processes. Quarterly Journal of Engineering Geology, 28, 243-252. Weaver, C. E., 1989. Clays, muds and shales. Developments in Sedimentology 44, Amsterdam, Elsevier. 8. Equipment Micro climate generator: Microclimate Technology Inc., Preservation Equipment Ltd. Displacement transducer: Model D5/10G8, RDP Electronics Ltd. Displacement indicator: Model E309, RDP Electronics Ltd.
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Theme 2 External factors of decay" environmental influence on stone
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TOPOCLIMATIC CONSERVATION: PORTUGAL
MAPPING, A TOOL FOR C U L T U R A L HERITAGE THE CASE OF THE R O M A N THEATRE OF LISBON,
Lufs Alres-Barros Lab. Mineralogy and Petrology, Mining Dept., Av. Rovisco Pais, 1049-001, Lisbon, Portugal Am61ia Dionfsio Lab. Mineralogy and Petrology, Mining Dept., Av. Rovisco Pais, 1049-001, Lisbon, Portugal
Abstract In this paper some preliminary results regarding the microclimatic survey that is being made at Lisbon's Roman Theatre are presented 9 Some of the variables that are being monitored at different points in the archaeological site are near-surface relative humidity, dew point, air temperature and surface stone temperature. Preliminary conclusions show that it is imperative to take measures in order to maintain and preserve this site, since high variations of relative humidity, air temperature and stone surface temperature occur daily and along the year. Besides, and according to the actual conditions it rains in several parts of the Theatre, which can severely damage the artefacts. The most critical areas of the Roman Theatre are the SW comer and the central zone where are usually obtained the highest values of relative humidity and the lowest of dew point spread. These seems to be the areas that are more prone to form condensation and to allow micro biological life and weathering to occur. Key-words: microclimatic survey, topoclimatic mapping, conservation, Roman Theatre.
1. Introduction The Roman Theatre of Lisbon (Portugal), constructed or rebuilt during the 1~t century AD, was one of the most important parts of the Roman city Felicitas Olisipo Julia, and was dedicated to the emperor Nero. It is located on the hillside of St. George Castle, in the vicinity of Lisbon's Cathedral, slightly NE (fig. 1 and fig. 2). The space occupied by the Roman Theatre is located in a very populated urban area surrounded by buildings, in the confluence of two streets. The ruins of the Theatre were discovered fight after the big earthquake that occurred in Lisbon in the 18 Ih century (1755) and then again buried during the rebuild of the city. Only in our century, in the 60's decade, they were "'rediscovered" (fig. 3). The sector already excavated occupies approximately 285 m 2. According to archaeological studies this theatre is supposed to have a diameter of almost 60m. During the excavation works performed in the 60"s different types of artefacts (made of limestone, sandstone and marble) like columns, shafts, bases, statues, tiles, elements from the proscaenium and coins were discovered.. Some of these elements remain in this Author's to whom correspondence should be addressed
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archaeological space in their original places. The remaining were stored in a warehouse and at Lisbon's Township Museum.
'Figure 1 (left): General view of the SW part of the Roman' s Theatre Ruins (Moita, 1994). Figure 2 (fight): Partial plant of Lisbon's city with indication of the Roman Theatre (Hauschild, 1990).
Figure 3: Plant of the Roman Theatre, after 1966-1967 excavations (Hauchild, 1990), with location of the points where the indoor microclimatic survey is being done. One of the most important and original parts of this theatre is the orchestra ground. This ground has a pattern shape, where different kinds of limestones with different colours were used (fig. 4). However only a small amount of this mosaic can be, observed nowadays, and most of the tiles present severe decay phenomena (fig. 5).
Figure 4 (left): Reconstitution of orchestra ground according to Hauschild, 1990. Figure 5 (fight): Two elements of orchestra's mosaic showing severe decay phenomena.
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Since 1966, the area exposed and studied by the archaeological team is partially covered with a metal shed, that semi-protects it from the direct action of the weathering agents. The north and east elevations have no protection against meteoric agents. One of the main problems that needs to be solved by the people running this monument is not only the conservation of this space, where different types of materials coexist, but also to allow visitors without damaging the Roman monument. To evaluate possible causes of damage and to predict future deterioration, a microclimatic study is being carried out since October 1998 at the Ruins of Lisbon's Roman Theatre by our laboratory. This study addresses: 9 Evaluation of weathering decay phenomena and their intensity (through a qualitative method - visual assessment and through a quantitative method - direct ultrasound method. The results already obtained allow us to say that most of these artefacts are sound, slightly or moderately damaged. 9 Characterisation of air pollutants levels, rainwater properties, temperature and relative humidity, solar radiation, wind speed and direction of the outdoor environment (since these ruins are in a semi-sheltered regimen). Mostly of these data are obtained at Lisbon's Cathedral where our microclimatic monitoring station is located. 9 Characterisation of indoor environment through thermo-hygrometric parameters like near-surface relative humidity, dew point, air temperature and stone surface temperature that are being monitored non continuously at different points. The study of their spatial distribution enables the elaboration of topoclimatic maps. Through these maps, singularities like anomalies, intensity and shape of gradients can be visualised. It is also possible to study diurnal or seasonal variations. It is precisely this last theme that will be developed and discussed in this paper. As atmospheric variables continually fluctuate in a short period of time what is intended with this type of survey is to obtain the main trends, for example analyse if diurnal or seasonal variations occurs and check which are the most deleterious areas. The results and conclusions are preliminary. In what regards the indoor environment, it is also being continuously monitored the relative humidity and air temperature, at two different vertical levels (approximately at 2m and 5m).
2. Lisbon's environmental conditions Lisbon experiences a temperate maritime climate. During the year the temperature does not show great variations. The coldest months are January and February (mean minimum value 10~ and the warmest are July and August (mean maximum value 23~ The rainfall is scarce in Summer and very abundant in Winter, when monthly mean values reach 1 ! lmm. The pH and conductivity range values are comprised between 5.3 -7 and I-8.7 ~S, respectively. The average chemical composition of rain water is presented in tab. I. Table 1" Average mineral content of Lisbon's rain water (units are mgl -~) Na K Ca cr NO~ SO42 Mg Si 7.50 0.50 8.00 12.00 7.50 5.00 1.30 0.75
NH4 + 1.20
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In what concerns the wind direction, it is mainly SW during winter whereas in summer is NW ("nortada" wind). Regarding other factors that can damage this archaeological site it must be considered not only the influence of marine spray (tab. 2), through the effects of wet and dry deposition on stones surface but also the air pollutants levels (fig. 6). Table 2" 85 percentile for the daily deposition rate (units are mg cm-2d-I) for dry deposition of the principal marine spray's ions (Dionfsio, 1999). NO3" ] SO4 z Ca Na K Mg CI 11.00 3.52 I 6.62 5.50 5.91 0.59 0.79
Figure 6: Hourly averaged concentration for relevant gases.
3. Methodology and analysis of the topoclimatic maps In order to get a better knowledge and to create the most suitable microclimate for conservation of this monument some thermo-hygrometric parameters (air and stone temperature, relative humidity, dew point, difference in degrees between the air temperature and the dew point, i.e., the dew point spread) are being analysed and monitored at different points of this archaeological site (fig. 3). The points (located on stone artefacts) are distributed without following a regular grid, but they cover approximately all excavated area. With exception of the sampling point n~ 6, all the points are in the same horizontal cross section. The survey it is performed not only in different days but also at different hours. To perform this type of discreet measurements it is being used a psychrometer positioned near the artefact surface, equipped with a thin insulating disk, to avoid the perturbation of the local air and a surface temperature probe. As a first approach it is assumed a simple geometry for the sampling area, i.e., without intermediate architectural structures. For the construction of the two-dimensional maps (topoclimatic maps), it was used the triangulation method with linear interpolation.
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In fig. 7, 8, 9, l 0, 11, 12, 13 and 14 are presented some of the topoclimatic maps for the mean values of two variables - relative humidity and dew point spread - obtained in different days at different hours (the black balls corresponds to the sampling points that are precisely located at fig. 3).
Figure 7 (left): Near-surface relative humidity (%) at Lisbon's Roman Theatre. Measurement taken the 11 October 1999 at l 3.15. Figure 8 (right): Dew point spread (~ at Lisbon's Roman Theatre. Measurement taken the l I October 1999 at 13.15.
Figure 9 (left): Near-surface relative humidity (%) at Lisbon's Roman Theatre. Measurement taken the 14 October 1999 at 14. l 0. Figure 10 (right): Dew point spread (~ at Lisbon's Roman Theatre. Measurement taken the 14 October 1999 at 14.10.
Figure l l(left): Near-surface relative humidity (%) at Lisbon's Roman Theatre. Measurement taken the 7 December 1998 l 1.00. Figure 12 (right): Dew point spread (~ at Lisbon's Roman Theatre. Measurement taken the 7 December 1998 l 1.00.
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Figure 13 (left): Near-surface relative humidity (%) at Lisbon's Roman Theatre. Measurement taken the 9 February 1999 at 10.45. Figure 14 (fight): Dew point spread (~ at Lisbon's Roman Theatre. Measurement taken the 9 February 1999 at 10.45. These graphics correspond to the main trends that seems to occurred at this monument, i.e., the central and SW area are the ones that usually have the smallest dew point spreads and highest relative humidity. The zones having the smaller dew point spread are probably the most deleterious since they are more prone to form condensation and to allow microbiological life and weathering to occur. The variations of the termo-hygrometric parameters during each survey at the different points, are not remarkable, for instance, the variation of relative humidity or dew point was always lower than 10% and 5%, respectively. However, at different days or at different hours in the same sampling point there are significant variations. The values are not kept homogeneous, which induces internal stress on the artefacts and contribute to their deterioration. Regarding the central area of the Theatre where most of the times it is attained the highest values of relative humidity and the lowest of dew point spread, it corresponds approximately to the area where an metallic element of the shed is missing and when it rains all this area is wetted. The SW area where the same phenomena occurs it is in the vicinity of one of the surrounding buildings it is also the area where the artefacts classified as moderately damaged are located.
4. Conclusions In this paper is presented the methodology that is being applied at Lisbon's Roman Theatre to describe its actual microclimate and to recommend, if necessary, the modification of some parameters, to properly conserve this ancient monument of our city and to allow the entrance of visitors. The results and conclusions here presented are preliminary and mainly correspond to the analysis of the isoline maps. Their analysis shows that it is imperative to take urgent measures to maintain and preserve this archaeological site. During this sampling period it was possible to verify that the indoor ambient conditions showed great variations in terms of air and stone surface temperature, dew point and air relative humidity. So, the first need for the conservation of this monument is to maintain it in a steady state climate.
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According to the actual ambient conditions, the most deleterious areas of the Roman Theatre seems to be the SW comer and the central zone. It was in the central area that most of the times the highest and lowest values of relative humidity and dew point spread respectively, were obtained. The metal shed that is partially covering the excavations does not avoid great variations of air and stone temperature and relative humidity during the day or during the year. Besides, the ruins have two elevations that are directly exposed to weathering agents, which contributes to monument's damaging (through, for instance, the run-off and wetting of artefact's surface). These microclimate measurements will continue for a longer period (at least more six months) to be statistically representative and thus to give a more complete and accurate description of the Roman's Theatre environment variability.
5. Acknowledgements This study was partially financed by project PRAXIS XXI/P/ECM/12012/1998 and by the Township of Lisbon.
6. References Article reference: Dionisio A. et al., 1999. Deposiqfio de aerossol marinho na ~ e a urbana de L i s b o a - Um factor determinante no decaimento geoquimico das rochas dos monumentos. II Congresso lb6rico de Geoquimica/Xl Semana de Geoquimica, 157-160. Book reference: Camuf~b D., 1998. Microclimate for Cultural Heritage. Developments in Atmospheric Science, 23. Hauschild T., 1990. Das R~mische Theatre von Lissabon. Planaufnahme 1985-88. Verlag. Moita, I., 1994. Das origens pr6-hist6ricas ao Dom/nio Romano. O dom/nio romano, in O Livro de Lisboa, cap/tulo ll-B. Livros Horizonte, 35-68.
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CHARACTERIZATION OF SURFACE MORPHOLOGY OF CARBONATE STONE AND ITS EFFECT ON SURFACE UPTAKE OF SO2
ElizaBeth A. Bede University of Delaware, 303 Old College, Newark, DE, 19716, USA
Abstract This laboratory study evaluates the role of receptor surface variables in the dry deposition process. It focuses on the effect of surface variables (i.e., porosity, texture, roughness, and effective surface area) on SO2 (g) uptake in ambient outdoor conditions (50 ppb; 65% RH; 4 m/s; 25~ Experiments are undertaken in a custom-built recirculating environmental deposition chamber (Spiker, 1992(1)). The primary components of this project include developing a surface characterization methodology and evaluating the deposition velocity of SO2 (g) onto limestones. Four U.S. domestic limestones (Salem; Cordova Cream; Cottonwood Top Ledge; Tennessee Pink) and one imported limestone (Monks Park, GB) are utilized in this study. Both polished and simulated weathered surfaces are examined to gauge the effect over a range of surface variables. The understanding of the role of surface morphology in the pollutant uptake process from this study will be used to develop a methodology to assess the long-term effects of surface treatments (i.e., cleaning, consolidation) of buildings and outdoor sculptures. Key words: dry deposition, sulfur dioxide, limestone, surface morphology
1. Introduction The deterioration of carbonate stone is greatly accelerated by the action of air pollutants such as SO2,NOx, H2SO4,HNO3, 03 and particulates (Amoroso 1983; Hoffmann 1986; Butlin 1991; Haneef 1992). While the deleterious effects of these atmospheric pollutants on stone was first cited over a century ago (Voelcker 1864), the apparent increase in stone degradation has been attributed to the increase in anthropogenic pollutants (Shaffer 1932; Babu Rao 1983; Livingston 1983). This is supported by observations of damage much more severe in urban than rural areas (Feddema 1987; Vella 1996). Of these pollutants the sulphurous compounds have been identified as playing a major role in the deterioration of carbonate stone (Winkler 1966; Spedding 1969; Braun 1970). Dry deposition is governed by the mass transfer in the gas phase and by adsorption and absorption at the surface. In the case of carbonate stone the latter results in an irreversible chemical reaction. Of primary concern to architectural conservators is the formation of the alteration product, gypsum, resulting from this reaction. This mechanism of stone decay occurs in protected areas such as under stone sills and cornices, or in less protruding portions of sculptures or monuments. The effect of dry deposition in these protected areas is a slow continuous process that eventually leads to catastrophic surface losses from spalling and delamination. Simplistically, the overall dry deposition process is often presented in terms of three resistance steps. In the first step, the pollutants are transported from the lowest levels of the atmosphere into the very thin quasi-laminar sublayer, sometimes referred to as the viscous sublayer, that surrounds each object. This is termed as the aerodynamic resistance, ra, and is
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governed by wind speed and air turbulence. The second step, known as the boundary layer resistance, rb, requires just that, breaching the boundary layer turbulence and molecular diffusivity. The final step is the physical and/or chemical capture/reaction of the pollutant with the receptor surface and is termed surface uptake resistance, re. Surface chemistry, wetness, roughness, and porosity control this resistance. Each step may be rate limiting and occur at varying speeds depending on the characteristics of the system. The sum of these three resistances is inversely proportional to the deposition velocity and can be stated as: Vd - - ( r a + r b + rc) "1
(1)
ra and rb Can be estimated by micrometeorological data and chambers have been constructed in order to define and control these resistances (Spiker 1989; Preston 1972; Johnson 1990; Lewry 1992; Girardet 1996(1)(2)). rc is dependent on the surface properties of the stone and is relatively poorly understood (Wu 1992). Hence, it is the magnitude of re that distinguishes the rate of dry deposition for different materials. Methods for measuring deposition velocities on materials are reviewed by Lipfert (1989(2)). Primary dry deposition of 8 0 2 onto carbonate stone has been shown to vary from one to two magnitudes of order (Lipfert 1989(1); Furlan 1992). It is dependent on the environmental factors and the characteristics of the receptor surface. More specifically, dry deposition of SO2 onto carbonate stone is intimately related to: 9 SO2 concentration; 9 boundary layer characteristics (i.e., temperature, moisture content, turbulence); 9 temperature and humidity gradients of the receptor surface; 9 the presence of environmental and/or surficial catalysts; 9 and surface morphology (i.e., roughness, porosity, effective surface area). These parameters and their subsequent damage have been well documented in field studies. In addition, numerous laboratory studies have been undertaken to isolate the various environmental components in order to determine their contributions to primary dry deposition process. However, to date the interdependence of re and morphological properties have only been tangentially investigated and are poorly understood. This study focuses on the effect of some surface and bulk properties of carbonates stone (primarily porosity, texture, roughness and effective surface area) o n SO2 uptake in simulated outdoor conditions. The long-term aim of this research is to gain an understanding of this relationship that will enable conservators to evaluate conservation treatments more effectively. Conservation treatments, such as consolidation and cleaning, change the effective surface. An understanding of how this may or may not affect the long-term pollutant uptake of the stone will aid in choosing appropriate treatments.
2. Research Goals And Parameters The primary goal of this research is twofold:
".9 To determine the most appropriate methodology for characterizing surface morphology variables (e.g., surface texture parameters; effective surface area; porosity; pore size, shape and spatial distribution; permeability; capillarity). ".9 To utilize quantitative surface uptake resistance data to evaluate the effect of these
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variables on primary deposition of SO2 under controlled ambient conditions. The overriding design parameter is to simulate field conditions whenever possible. The choice of test specimens, surface textures, sample preparation and chamber conditions are dictated by this criterion.
3. Sample Preparation 3.1 Stone types Five commercially available limestones that are commonly utilized as structural or ornamental elements in outdoors cultural resources were chosen. Since the focus of this study is to evaluate the effect of the physical properties of the surface on pollutant uptake it is desirous to limit the number and types of chemical interactions occurring on the surface. Therefore, the limestones considered were limited to one category -- calcitic. One imported and four domestic United States limestone types were chosen. These are: 9 Salem limestone (Bedford, Indiana) 9 Cottonwood Top Ledge Limestone (Chase County, Kansas) 9 Cordova Cream Limestone (also known as Austin stone) (Austin, Texas) 9 Tennessee Pink Marble (highly crystalline limestone; orthomarble) (Knoxville, Tennessee) 9 Monks Park Limestone (also known as Bath stone) (Wiltshire, Great Britain) Salem limestone was utilized for the US NAPAP studies and for similar international studies. In addition, in depth petrographic (McGee 1989) and porosity (Leith 1996) analysis are available. Monks Park Limestone was chosen since it is a standard test limestone in researched sponsored by the UNECE. In addition it has been widely utilized and characterized by research conducted by Great Britain's National Materials Exposure Program. Inclusion of this limestone type will allow for correlation and comparison with similar international dry deposition studies.
3.2 Texture categories In the initial phase, two texture categories are utilized: a smooth and a rough texture. The smooth and rough surface textures are achieved by polishing and acid etching respectively. Etching was chosen since it most closely simulates the preferential attack of the carbonate grains and matrix of weathered surfaces under field conditions. The goal was to achieve a similar surface roughness parameter (Ra) for each texture category. The roughness parameter is determined by 3-D non-contact laser profilometry (Proscan 1000, Micro Photonics). The limestones are cored utilizing a water-cooled thick-walled drill bit and cut to approximately 1/4" (0.64 cm) thickness. Due to possible variations within the stone, cores are taken as close together as possible. In order to remove all previously deposited and inherent sulfate the test specimens are placed in a constant temperature deionized water bath (43 C) until a constant sulfate background level is attained. The deionized water was changed daily and sulfate levels were determined biweekly by ion chromatography (Dionex DX-500). Up to six months of bathing was required for some limestones to reach background. All test sample surfaces are hand-polished lightly with successive grit sized silicon carbide paper to remove saw marks or protruding inclusions and to provide a level surface for polishing
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or etching. Polishing residue is removed by three successive 15-minute ultrasonic baths in deionized water followed by a 5-minute bath in methanol. Test specimens are then dried in an oven at mild temperatures. To achieve the 'smooth' texture a polishing wheel with various grades of polishing cloths was employed. To etch the test specimens in the rough texture category a 23% solution of glacial acetic acid in water was utilized. In order to insure a uniform etch across each individual surface a stainless steel apparatus was designed. It allows the simultaneous etching of up to eight test specimens. Each limestone type required a different etching time to achieve a universal roughness parameter for all the test specimens in the rough texture category. At the completion of these processes each sample was rinsed thoroughly for five minutes in deionized water. The test specimens were then placed in an ultrasonic bath with deionized water for three successive baths at 15-minute intervals and followed by oven-drying overnight at a mild temperature. The surface morphologies of these test specimens were characterized utilizing the methods described below.
4. Surface Morphology Evaluation The surface morphology of a stone strongly influences the uptake of SO2. Porosity and microporosity affect the manner in which moisture and pollutants are transported through the stone, as well as, influence both the development of moisture films and the sites of reaction. Even for dry stone, the more porous the surface the greater the reaction with pollutants. In addition, the total surface area available for uptake and reaction of pollutants increases with increasing surface roughness. However, the dry deposition mechanisms at work on nonhomogeneous stone surfaces have not been systematically studied. It is the aim of this research to study the interactive relationships of surface morphology parameters (e.g., porosity, roughness, and surface area) with uptake rates in order to correlate a better insight into the SO2 deposition process. The first step towards this goal is the identification and utilization of techniques to evaluate pore structure and surface texture. 4.1 Pore structure evaluation The following methods are utilized to analyze pore structure and geometry of the limestone test specimens. Specifically the size, shape and distributions of the pores in relation to open porosity. Meng (1993) has developed a similar characterization for sandstone.
Thin Section Analysis utilizing epifluorescent microscopy (Leith 1996) 9 evaluate pore network structures (inter- vs. intragranular) 9 quantify and map spatial distribution of macropores (> 50 nm) 9 determine pore shape (i.e., round, inkbottle) and distribution 9 Scanning Electron Microscopy 9 evaluate fine pore network structures (inter- vs. intragranular) 9 quantify and map distribution of mesopores (2-50 nm) and micropores (< 2 nm) 9 determine pore shape (round; inkbottle) and distribution # Photomicrographs 9 illustrate pore geometry and pore connectivity [ 1]
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Mercury Intrusion Porosimetry 9 determine pore entry size distribution 9 quantify pore surface area 9 relate pore surface area to pore volume
r
Nitrogen Adsorption Porosimetry 9 determine pore size and distribution 9 quantify surface area distribution of smallest pores
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Pore-Surface Fractal Measurements (Mossotti 1992) [2] 9 define the effective surface capacity 9 determine pore type 9 ascertain distribution of pores and mass
4.2 Surface Texture Characterization The following were utilized to quantitatively characterize surface roughness and surface area in order to evaluate qualitatively and differentiate the surficial parameters affecting pollutant uptake rates. Nitrogen Gas Adsorption 9 quantify surface area and specific surface area (SBET) 3-D Non-contact Laser Profilometry 9 generate a quantitative topographic map 9 quantify surface parameters (i.e., roughness (Ra); peak to valley height (Rz); peak spacing (Rsm); peak count (Pc); material ratio (tp) Surface Fractal Measurement [2] 9 calculate surface roughness
5. Primary Deposition Study Primary deposition of S02 on a variety of stone surfaces was conducted under controlled ambient conditions in an environmental deposition chamber. The surface uptake resistances and their corresponding surface morphology characterizations for each sample are compared with the goal of identifying those surface variables that dominate dry deposition mechanisms.
5.1 Deposition chamber The experimental environmental deposition chamber utilized for this study was designed by Spiker et al. (1989). The chamber is essentially a recirculating flow wind tunnel where ra + rb is defined and constant within the design parameters. Temperature, relative humidity, wind speed, and pollutant (SO2, NOx, O3) concentration are computer controlled and monitored within the chamber by commercially available data acquisition cards and computer software (LabTech). These values are utilized to calculate rc and subsequently Yd. The elliptical chamber is approximately 15' (4.6 m) in length, 7' (2.1 m) wide and stands approximately 6' (1.8 m) high. It utilizes an electric steam generator to produce and maintain
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relative humidity; an industrial recirculating cooling unit for temperature control; an industrial fan for circulation and wind speed; and a pump pack (Monitor Labs 8551) for gaseous SO2 introduction. The custom-design airfoil test specimen shelf allows for analysis of eight test specimens per run (four on top; four on bottom). The test specimens are discs of 1.5-inch diameter. An SO2 analyzer monitors SO2 levels in the chamber with an ultraviolet fluorescent detector (Monitor Labs 8660). A PITOT tube assembly (Baratron) measures the wind speed in the tunnel. Dew point cells and temperature probes gauge relative humidity and temperature. 5.2 Environmental conditions Based on previous studies and in an attempt to replicate, as closely as possible, ambient outdoor conditions, the following parameters are monitored in the chamber: Relative humidity: 65% Temperature: 25 C SO2: 50 ppb Wind speed: 4 rn/s These parameters replicate the general northeastern United States environment. These conditions remain constant throughout each 24-hour exposure run. 5.3 Overall methodology To degrease the surface and lower its surface tension the test specimens are uniformly sprayed with methanol. Test specimens are dried in an oven at mild temperature (less than 50 C) for a minimum of an hour followed by equilibration to 65% RH in a desiccator with conditioned silica gel for a minimum of 24-hours. Nine test specimens comprise a run. Eight are exposed in the chamber and one remains in the desiccator as a blank. The eight test specimens exposed consist of two limestone types and the two texture categories. For example a typical run might contain: 2 smooth textured Monks Park Limestones; 2 rough textured Monks Park Limestones; 2 smooth textured Salem Limestones; and 2 smooth textured Salem Limestones. Each of these test specimens is run in each position on the chamber shelf- a total of eight runs per test specimen group. This sample placement compensates for any anomalies of exposure along the airfoil shelf and for fluctuations in the environmental conditions over the 24-hour period. [3] At the completion of the 24-hour run the test specimens are removed expeditiously from the chamber and placed in 60 ml. screw top containers. 30.0 ml 0.6% H202 solution added to each container to oxidize and leach the sulfur deposited on the surface during exposure. The blank is removed from the desiccator and also placed in a 30.0-ml solution. The nine test specimens are placed on a Reax 3 platform mixer for 24 hours. The asymmetrical movement of this mixer causes differential pressures within the pores of the stones as the leachate levels rise and fall thus providing effective and thorough washing of the stone's substructure. The leachate is poured off and a P81 filter paper (Whatman) is placed in the leachate to provide solid phase cation exchange. This pre-filtering was necessary in order to reduce the number of calcium ions in the solution prior to analysis by ion chromatography. The leachate is placed again on the platform mixer for an additional 24 hours. An additional 30.0-ml H202solution is added to the original containers with test specimens and a second 24-hour leach is conducted followed by the same 24 hour filtering process. Simplex Optimization was utilized to develop this protocol. [4] Ion chromatography is performed on leachate to determine the ppb of the SO42. Sulfate levels of both washes are corrected in accordance with the established background levels of the individual test specimens and then added to provide the total amount of deposited
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sulfate. The depositional velocity (Vd) and the surface resistance (re) are calculated.
6. Conclusions The correlation and comparison of this data with the surface morphology characterizations is currently underway. Preliminary investigations suggest that deposition increases with increasing roughness. Furthermore it appears that the characteristics of porosity are paramount factors in the deposition process. Preliminary analyses demonstrate that numerous factors seem to act, not independently, but rather in a complicated system of mutual interferences. It is however, the task of conservation scientists to unravel these systems and decipher the role of each dominant variable. Through this understanding effective mitigating procedures and/or appropriate treatments are developed.
7. Acknowledgements Funding for this research was generously provided by the National Center for Preservation Technology and Training, Materials Research Program and the University of Delaware, Art Conservation Research Program. This paper presents portions of an in-progress dissertation towards the Doctorate of Philosophy, University of Delaware, Newark, DE, USA.
8. Endnotes [1 ] To date there is not a method for quantitatively assessing these features. Since they are conceptually highly significant in controlling SO2 uptake and subsequent gypsum formation rates, photomicrographs are utilized to illustrate these properties and a descriptive methodology is under development. [2] MORPH-I and MORPH-II are components of a software package that analyzes SEM micrographs for the assessment of the fractal dimension of pores and a surface edge respectively. Modifications of these programs were made for the purposes of this research to enable the assessment of thin sections. (Mossotti, V., Eldeeb, R., 1998. USGS Open File Report 98-248; http://caldera.wr.usgs.gov/OF98-248.) [3] Evaluation of the data produced from these runs in underway with the assistance of a Ph.D. statistician. The design of future runs, if necessary will follow this evaluation. [4] Rebus Simplex Optimization is a multivariate, non-parametric, non-linear computer software program for response optimization. (Simplex Optimization, WindoChem Software, Inc., USA, 707-864-0845)
9. References Amoroso, G., Fassina, V., 1983. Stone Decay and Conservation: Atmospheric Pollution, Cleaning, Consolidation, and Protection. Elsevier, New York. Babu Rao, G., 1983. Effect of pollution by sulphur dioxide on marble and sandstone. Journal of Archaeological Chemistry: 1, l, 31-38. Baedecker, P. A., et al., 1990. Effects of acidic deposition on materials. NAPAP Report 19, Acidic Deposition: State of Science and Technology. NAPAP, Washington, DC.
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Braun, R. C., Wilson, M., 1970. The removal of atmospheric sulphur by building stones. Atmospheric Environment, 4, 371-378. Butlin, R. N., 1991. Proceedings of the Royal Society of Edinburgh: 97B, 255-272. Camuffo, D., M. Del Monte, and C. Sabbioni, 1983. Origin and growth mechanisms of the sulfated crusts on urban limestone. Water, Air and Soil Pollution, 19, 351-359. Fassina, V., 1988. Environmental pollution in relation to stone decay" Air Pollution and Conservation: safeguarding our architectural heritage. Elsevier, New York, 133-174. Feddema, J. J., Meierding, T. C., 1987. Marble weathering and air pollution in Philadelphia. Atmospheric Environment, 21, 1, 143-157. Furlan, V., Girardet, F., 1983. Considerations on the rate of accumulation and distribution of sulphurous pollutants in exposed stones. Materials Science and Restoration: proceedings of the international congress, Filderstadt, Lack und Chemie, 285-290. Furlan, V., Girardet, F., 1992. Atmospheric pollution and reactivity of stones. Proceedings of the 7th Intemational Congress on Deterioration and Conservation of Stone, Lisbon, Laborat6rio Nacional de Engenharia Civil, 153. Gilardi, E. F., 1965. Absorption of Atmospheric Sulfur Dioxide by Clay Bricks and Other Building Materials. Unpublished doctoral dissertation, Rutgers State University, NJ. Giradet, F., et al., 1996(1). Experimental study of sulfation of a limestone and an calcareous sandstone in the atmospheric chamber of Laussanne. The 8th International Congress on Deterioration and Conservation of Stone, Berlin, 349-358. Giradet, F., et al., 1996(2). Reactivity of stones to atmospheric SO2: study in simulation chamber and correlation with measurements in situ. The 8th International Congress on Deterioration and Conservation of Stone, Berlin, 341-347. Hamilton, R. S., et al., 1995. Sulphur and nitrogen particulate deposition onto building surfaces. The Science of the Total Environment: 167, 57-66. Haneef, S. J., et al., 1992. Effect of dry deposition on NOx and SO2 gaseous pollutants on the degradation of calcareous building stones. Atmospheric Environment, 26A, 16, 29632974. Hoffmann, M. R., 1986. Fog and cloud water deposition. Materials Degradation Caused by Acid Rain, Washington, D.C., 64-91. Honeyborne, D. B., Harris, P. B., 1958. The structure of porous building stone and its relation to weathering behavior. Colston Papers. The Structure and Properties of Porous materials: proceedings of the 10th symposium of the Colston Research Society: 10, New York: Academic Press. Johnson, J. B., et al., 1990. Laboratory exposure systems to simulate atmospheric degradation of building stone under dry and wet deposition conditions. Atmospheric Environment, 24A, 10, 2585-2592. Leith, S. D., et al., 1996. Limestone characterization to model damage from acidic precipitation: effect of pore structure on mass transfer. Environmental Science & Technology, 30, 7, 2202-2210. Lewry, A. J., et al., 1992. A chamber study of the effects of sulphur dioxide on calcareous stone. Proceedings 7th International Congress on the Deterioration and Conservation of Stone, Lisbon, Laborat6rio National de Engenharia Civil, 641-650. Lipfert, F. W., 1989(1). Atmospheric damage to calcareous stones: comparison and reconciliation of recent experimental findings. Atmospheric Environment, 23, 2, 415-429. Lipfert, F. W., 1989(2). Dry deposition velocity as an indicator for SO2 damage to materials. Journal of Air Pollution Control Association: 39, 446-452.
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Livingston, R. A., Baer, N. S., 1983. Mechanisms of air pollution-induced damage to stone. Proceedings of the 6th World Congress on Air Quality, Paris, SEPIC. McGee, E. S., 1989. Mineralogical studies of the Shelburne Marble and Salem Limestone. U. S. Geological Survey Bulletin, Denver, GPO. Meng, B., 1993. Characterization of pore structure for the interpretation of moisture transport. Conservation of Stone and Other Materials: Proceedings of the International RILEM/UNESCO Congress, New York, E & FN Spon, 155-162. Mossotti, V. G., Eldeeb, A. R., 1992. The fractal nature of Salem Limestone. Proceedings of the 7th International Congress on Deterioration and Conservation of Stone, Lisbon, Laborat6rio Nacional de Engenharia Civil, 621-630. Preston, P. E., 1972. An industrial atmosphere test chamber. Transactions of the Institute of Metal Finishing, 50, 125-131. Serra, M., Starace, G., 1978. Study of the reactions between gaseous sulphur dioxide and calcium carbonate. Deterioration and Protection of Stone Monuments, Paris, Reliure. Shaffer, R. J., 1932. The Weathering of Natural Building Stones, DSIR Building Research Special Report 18, London, HMSO. Spedding, D. J., 1969. Sulphur dioxide uptake by limestone. Atmospheric Environment, 3,683-684. Spiker, E. C., et al., 1989. Environmental chamber for study of the deposition flux of gaseous pollutants to material surfaces. Open-File Report 89-296. Washington, DC. Spiker, E. C., et al., 1992(1). Environmental chamber for study of the deposition flux of gaseous pollutants to material surfaces. Atmospheric Environment, 26A, 16, 2885-2892. Spiker, E. C., et al., 1992(2). Dry deposition of SO2 on limestone and marble: the role of humidity. Proceedings 7th International Congress on the Deterioration and Conservation of Stone, Lisbon, Laborat6rio Nacional de Engenharia Civil, 397-406. Spiker, E. C., et al., 1995. Laboratory study of SO2 dry deposition on limestone and marble. Water, Air and Soil Pollution, 85, 4, 2679-2685. Vella, A. J., Camilleri, A., Adami, J. P., 1996. Limestone surfaces in built-up environments as indicators of atmospheric pollution. Environmental Geochemistry and Health, 18, 165-170. Voelcker, J., 1864. On the injurious effects of smoke on certain building stones and on vegetation. Winkler, E. M., 1966. Important agents of weathering for building and monumental stone. Engineering Geology, 1, 5, 381-400. Wu, Y. L., et al., 1992. Aerosol Science and Technology, 16, 65.
10. Materials
Conditioned silica gel: Art Preservation Services, 235 East 85 th Street, Suite B2, New York, NY 10028; (212) 988-3869 Proscan 1000 Non Contact 3D Profilometer: Micro Photonics, PO Box 3129, Allentown, PA 18106; (610) 366-7105; www.microphotonics.com
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SEA WATER ABSORPTION, PERMEABILITY EVOLUTION AND DETERIORATION ASSESSMENT OF BUILDING STONES SUBJECTED TO
MARINE EXPOSURE Jean-Marc Birginie Laboratoire de Construction Civile et Maritime, Universit6 de La Rochelle (IUT), La Rochelle, France
Abstract
The deterioration effect developing on building stones subjected to marine exposure, results mainly from the salt crystallisation, which occurs during the repeated drying and wetting phases. This phenomenon can be artificially re-created on samples in salt spray dynamic simulators. By recourse to these accelerated ageing tests, it is possible to characterise the general form of the evolution of the stone regarding the seawater accumulation, the incubation time before deterioration and the intensity of degradation. In this paper, the effectiveness of two non destructive techniques used to quantify, on one hand, the stone deterioration (visual scanning of the surface) and, on the other hand, the transfer properties evolution (measurement of permeability to air), is shown in the case of Richemont, Tuffeau, and Sireuil, three calcareous stones from West of France. The experimental results emphasise an acceleration of seawater accumulation before the developing of deterioration. It is also shown that the evolution of the stone is very dependent on the salt spray quantity received by the samples during each cycle of ageing. In order to anticipate the decay of monument stones due to the marine pollution, a general approach consists in determining the critical salt content which creates the surface disintegration, according to the time of exposure, as well as the distance from the sea. By associating the results obtained from accelerated ageing tests and from sampling on site, this general presentation of the evolution of the stone may be determined for representative lithotype in order to provide an assessment tool useful for the intervention on monuments. Keywords : building stone deterioration, permeability to air, accelerated weathering.
marine
exposure,
degradation
analysis,
I. Introduction
The deterioration of building stones subjected to atmospheric pollution, such as marine salt, depends mostly on the time of exposure, as well as on the distance of the monument from the pollution source (Auger, 1991). Several other factors concerning the stone itself, mainly the porosity and the permeability, and the climatic parameters play an important role on the deterioration evolution (Auger, 1996). The eharacterisation of lithotypes with respect to their initial microstructure and their initial transfer properties, can provide us information regarding the sensitivity of materials to atmospheric pollution (Meng, 1994; Parrott, 1994). It is also important to follow the evolution of the above mentioned characteristics during the exposure because, for example, transfer properties modifications are usually precursory of the deterioration processes. In
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particular, near the marine zones, the sea salt accumulation at various concentrations in the stone, causes irreversible transformations on the microstructure which affect the kinetics of mass transfer. The deterioration effect by salt crystallisation that results from repeated wetting and drying phases, can be greatly amplified or reduced. When the environmental conditions are optimal, severe sand disintegrations can develop on the stone surface, favouring depth damages (Auger, 1996; Birginie, 1999). Ageing tests carried out in salt spray dynamic simulation (Auger, 1988), confirm that the disintegration intensity developing on the surface is very dependent on the micro-structural aspect of material and its fluid transfer properties such as liquid water progression (wetting phase) and vapour diffusion (drying phase) In this paper, three non destructive methods are proposed to assess the evolution of porous building material, with respect to the mass absorption and the surface deterioration, and their effectiveness are compared through the results of ageing test by salt spray concerning three French limestone : Richemont, Tuffeau and Sireuil. On the basis of this results and previous works (Auger, 1991), a global approach is then proposed with the objective to forecast the salt accumulation and the decay in the stones.
2. Accelerated ageing test and sampling The weathering in dynamic simulation consists in creating cyclic atmospheric conditions by repeated drying and salt spray phases, so that the disintegration phenomena by salt crystallisation are developed quickly on the surface of the stone. In order to accelerate the deterioration from a natural exposure, the temperature in the simulator is maintained at 40~ and the time of cycle reduced to half hour, that corresponds to an average cycle of one week under the South European climate. The cycle in simulation includes one minute of salt spray and 29 minutes of drying. The ageing procedure is explained in detail in (Auger, 1998) and has received the recommendation from the AFREM (French association of material testing ) in 1996. Core samples were extracted from blocks of two fine grain calcareous stones, Richemont (open porosity : 25%) and Tuffeau (porosity : 45%), and a coarse grain limestone, Sireuil (porosity of about 35%). The cylindrical samples of 50 mm diameter and 100 mm high, have been exposed to dynamic simulation with five different salt spray intensities corresponding to the following seawater quantities received, per cycle, by each sample : 0.3, 1, 2, 5 and 8 mg/cm 2. The evolution of material is appraised from the use of three non-destructive analysis: weight variation, surface analysis by camera-laser scanning and permeability measurement.
3. Non destructive analysis 3.1 Mass variation of samples In an ageing simulation, the weight evolution of samples can be checked during the test. The provided results give information about the solution accumulated into the samples. In fact, when the surface disintegration occurs, the weight variation corresponds to the difference between the mass gain due to the solution absorption, and the mass loss due to the loose grains on the surface of samples by effect of salt crystallisation. For this reason, it is difficult to deduce, in all case, the solution content evolution using the weight variation
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measure. If the sequence of cycles is constant in the time, the beginning of disintegration could be approximately located on the point of mass curves where the sample weight reaches a maximum value before decreasing. Graphic of Figure 1 shows that, in the case of Richemont stone, the mass variation is very dependent on the solution quantity received per cycle, by the stone surface. A high salt spray pulverisation (8 mg/cm 2) leads to the quick saturation of the stone, preventing the salt crystallisation. The optimal pulverisation that favours a fast disintegration in depth seems to be situated between a level of 1 to 3 mg/cm 2 per cycle.
Mass evolution according to the received salt spray (Richemont)
Figure 1 : Influence of salt spray quantity received by the Richemont samples on the evolution of mass. Continuous lines : supposed mass curves without the loss due to the disintegration
3.2 Evolution of surface aspect (visual analysis) A more direct method to quantify the disintegration consists in a surface analysis by using a camera-laser scanning system (Birginie, 1999). The system provides a relief matrix (topographic data) and a laser light reflection matrix (evolution of reflection properties of the surface such as colour change). The principle of the relief analysis is based on the use of a triangulation technique between the laser light source, the CCD camera and the surface to be analysed. In previous works (Birginie, 1999), the authors showed that it is possible, by the use of the above mentioned device, to characterise objectively the degradation morphology. In other respects, the deterioration can be quantified computing global statistical parameters from matrix, such as the standard deviation. Regarding the relief data, the standard deviation corresponds to a surface roughness criteria.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 a) Evolution of surface disintegration (Richemont)
Figure 2 a-b 9Detection of the stone deterioration threshold from the visual analysis of the surface roughness" a) Richemont, b) Tuffeau
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This global statistical parameter variation is linked to the evolution of degradation developing on the surface during the simulation (Birginie, Rivas, 1999). For example, figure 2 a-b compares, by means of this statistical criteria, deterioration suffered by the Richemont and Tuffeau samples for the intensities of salt spray that have favoured the sand disintegration effect. These graphics shows that the evolution of deterioration is very dependent on the salt spray pulverisation and follows different steps of progression. By a fixed threshold of roughness (initial roughness + 0.2 ) the significance of disintegration can be considered. At that point, it is easy to locate, for each salt spray intensity, the corresponding number of weathering days need for the disintegration phenomena to develop of significant manner.
3.3 Evolution of permeability to air
Measurement of permeability to air gives a very precious result, as this transfer property of the stone is linked to the pore obstruction due to the solution accumulation. Modifications which happen on the sea water penetration process, influence directly the evolution of the permeability to air. This physical property is measured by letting pressurised air on core samples and by gauging the inlet pressure P and air flow Q. A suggested formula including P, Q, the stone dimensions and the gas viscosity vl, gives the global permeability of the sample in m s. The fact that the measurement method is easy and fast to achieve, is very important to prevent the micro-structural transformations due to the air flow into the material. Unlike the weight measurement, the permeability is much less dependent on the disintegration effect and it varies essentially according to the presence of salt solution in the pores. Graphic of figure 3-a shows the evolution of permeability in the case of Richemont stone exposed in dynamic simulation to different salt spray intensities. These curves well emphasise the incubation times followed by a decreasing of permeability corresponding to the acceleration of salt accumulation due probably to the hygroscopic effect of salt. After these two steps, the samples tend to saturate when they receive a strong salt spray and seem to reach a stability zone with respect to the permeability property. Figure 3-b tends to show the same evolution feature in the case of lithotype Tuffeau but, due to its higher open porosity, the decrease of permeability began later and this stone reaches the saturation more slowly than for Richemont. In order to deduce the solution accumulated and salt content in stone from the permeability measurement, it is necessary to establish an empirical curves and a mass transfer modelling. These physical data require several previous test achieved on each considered lithotype.
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a) Evolution of permeability to air according to the received salt spray
Figure 3 a-b: Influence of the salt spray quantity received by samples, on measurement of permeability to air" a) Richemont, b) Tuffeau
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4. Global approach of the marine salt accumulation effect 4.1 General presentation of results The susceptibility of the three stones subjected to different seawater spraying in cyclic conditions, can be characterised by two types of parameter, taken from the preceding analysis: - variation of permeability and roughness at 35 days of ageing test - day of the simulation corresponding to a significant variation of roughness and permeability.
Table 1: Characterisation of evolution of the three limestone studied, from the visual analysis and the permeability measurement. Visual analysis (roughness) Spraying 0.3 mg/cm2
1 mg/cm2
3 mg/cm2
5 mg/cm2
8 mg/cm 2
Sat. Richemont 0.3 / 26 1.1 / 14 1.5 / 4 Sat. Sat. Tuffeau 0.1 / 48 1.3 / 21 2.2 / 10 3.9 / 2 Sat. Sireuil 0.3 / 17 0.9 / 17 1.5 / 8 1.1 / 8 First value : deterioration at the 35 m day of simulation test (Threshold, Fig. 2) ( = roughness - initial roughness ) Second value : days of simulation at 10% increase from the initial roughness Permeability Spraying 0.3 mg/cm2
1 mg/cm2
3 mg/cm2
5 mg/cm2
Richemont 10% / 50% / 23 85% / 9 Sat./5 Tuffeau 0% / 20 % / 45 50% / 28 Sat./18 Sireuil 0% / 30 % / 31 50% / 26 70% / 17 First value 9Permeability drop (in %) at the ~35m day of the simulation test Second value : days of simulation at 30% decrease of permeability
8 mg/cm2 Sat.~3 Sat./ 9 Sat./ 7
Through these results, it appears that the salt spray quantity which optimises the sand disintegration on Richemont and Sireuil is about 2 to 3 mg/cm 2 per cycle, and 5 mg/cm 2 for Tuffeau. Beyond these spraying levels, the material saturates, that prevents the disintegration phenomenon. The less porous the stone (Richemont, 25% of porosity) the more rapid the saturation. The more porous (Tuffeau, 45% of porosity) the more depth and rapid the deterioration. When the permeability of stone reduce to 30% before the first ten days of simulation, it means that the sample is going to saturate without disintegrating.
4.2 Relationship between natural exposure and simulation On site, the distance from the coast is a determining factor to forecast the quantity of salt present into the material, when exposed to salt contamination that originates from marine spray. Due to the fact that the quantity of salt provided by the atmospheric environment is
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cumulative in the time, the exposure duration is also a fundamental factor to describe the evolution of building stones. In a preceding paper, Auger (1991) proposed the use of a three-dimensional diagram including distance from the sea and time, in order to anticipate the possible quantity of marine salt found in monument stones, and the resulting deterioration. Considering that the experimental data available on site are very insufficient, the proposed numerical approach is more an extrapolation based on experience, some localised experimental data and the knowledge of the stone behaviour regarding the diffusion phenomena, than an exact modelling. This 3D plot could be extrapolated from the preceding results of permeability measurement, associating the number of cycle of accelerated ageing to the real time of exposure and the received salt spray quantity to the distance from sea. The analogy between simulation and natural exposure from the sea in our region can be defined by the following linear correspondence : - one day in simulation (48 cycles) is equivalent to one year in natural exposure - the relationship between the intensity of pulverisation and the distance from the sea depends on the specificity of site of exposure, in particular the wind direction and celerity. This analogy is mainly established on the base of the comparison of deterioration observed on site on samples aged in simulation. Experience shows that the sand disintegration can appear when the salt concentration reaches the value of about 500 mg per 100 g of dry stone (Auger 1991). We underline that the porosity and the transfer properties of the stone can influence a lot this critical salt content. In order to make a systematic study with respect to the specific characteristics of each lithotype and exposure conditions, it is necessary to work on samples subjected to accelerated ageing in a salt spray simulator with controlled atmospheric conditions.
5.
Summary
and
conclusions.
In the case of accelerated weathering test achieved in laboratory, the evolution of material subjected to salt spray can be effectively checked with the help of three different non destructive analysis : - the weight variation which corresponds mostly to a difference between solution accumulated and mass loss due to the surface disintegration - the visual scanning of the surface to quantify the sand disintegration degree - the measurement of permeability to air that gives an estimation, by means of an empirical relationship, of the solution quantity accumulated into the samples. Through the experimental results, three steps can be clearly distinguished in the evolution of a fine grain limestone such as Richemont during the exposure to salt spray: - an incubation time where the salt penetrates slowly without appreciably affecting the material structure, - an acceleration phase of the seawater absorption, mainly due to the increasing of salt content in the stone (hygroscopic effect, reduction of evaporation process),
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- finely the stone reaches a more stable state, which corresponds to the saturation of the stone or the development of a progressive sand disintegration, according to the received salt spray intensity. The association of visual analysis and permeability measurements seems to constitute an objective non destructive experimental methodology to deduce the critical conditions that create an optimal disintegration. The salt content could then be deduced from the accumulated solution by implementing a mass transfer model between the stone and the environment. But, an experimental method, the electro-physic spectroscopy, represents also a promising non destructive technique to detect and quantify the salt content into the material. The relationship between the deterioration and the salt penetration kinetic in the depth of the stone has to be confirmed too by destructive chemical analysis. In order to assess the analogy between the real time ageing and the simulation, according to the climatic zone and the lithotype, an important campaign of tests conceming several stones selected with respect to their initial porosity and transfer properties, is planned now. These results may contribute to generate sufficiently information to forecast the deterioration effect by salt crystallisation on building stone.
Acknowledgements This work was founded by an EC Prject ENV-4 CT95-0100
References Auger F., 1991. Vieillissement par alt6ration atmosph6rique des mat6riaux de construction- Etude comparative in situ et en simulation. Proc. of Int. Symp. on the Deterioration of Building Materials, La Rochelle 12-14 june 1991, 115-128. Auger F., 1996. Durabilit6 des pierres calcaires utilis6es dans le patrimoine architectural, M6m. Soc. G6ol. France, 169, 415-420. Meng B., 1994. Calculation of moisture transport coefficients on the basis of relevant pore structure parameters, Materials and structures, 27, 125-134. Parrott L. J., 1994. Moisture conditioning and transport properties of concrete test specimens. Materials and structure 27, 460-468. Auger F., 1988. Simulation acc616r6e de la d6gradation des mat6riaux de construction en ambiance a6rienne saline, Proceeding of IAEG Conference on The engineering Geology of Ancient Works, Monument and Historical sites, Athens, 19-23 september, 797-804. B irginie J.-M., Auger F., 1999. Caract6risation visuelle de l'alt6ration d'6chantillons carrot6s de pierre, vieillis en simulation dynamique aux brouillards salins, Mat6riaux et Constructions, 32, 584-592. Kollek, J.J., 1989. The determination of the permeability of concrete to oxygen by the Cembureau method - a recommendation. Materials and Structures, 22, 225-230. B irginie J.-M., Rivas T., Auger F., 1999. Comparaison de l'alt6rabilit6 au brouillard salin de deux pierres calcaires de construction au moyen de mesures pond6rales, acoustiques et par traitement d'images. Submitted to Materiales de Construccion in september 1999.
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C O L O U R CHANGES AND REACTIVITY TO SO2 OF SOME CLADDING STONES AT THE "GRAN TEATRE DEL LICEU" (BARCELONA; SPAIN) Carlota M Grossi; Rosa M Esbert*; Francisco J Alonso; Luis Valde6n; Jorge Ordaz; Francisco Diaz-Pache Area de Petrologia y Geoquimica. Dpto. de Geologia. Universidad de Oviedo. Jesfis Arias de Velasco S/N, 33005 Oviedo, Spain.
Abstract Some ornamental building stones (sedimentary and metamorphic) have been pre-selected to be used as cladding material for the restoration of the facades of the "Gran Teatre del Liceu" of Barcelona (Spain). In order to assist the final selection these were subjected to a climatic chamber SO2 exposure. A way to evaluate the effect of SO: was to measure colour changes after exposure. The methodology and the results are presented in this paper. Although no visual colour changes were observed, significant colour changes were detected by colorimetry measurements. These changes were related to stone reactivity to SO2.
Keywords: Ornamental stones, SO2 reactivity, Colour measurements, Stone conservation.
1. Introduction The main scope of the study was to select the most suitable cladding stones for the Great Theatre "Liceu" of Barcelona (Spain) from a series of pre-selected stones. In this sense, some durability tests were carded out to reproduce some of the main decay agents that can affect those stones once have been used in the building. Among the trials carried out, this paper shows the results of a SO2 polluted atmosphere exposure test. This test was selected because even very low atmospheric concentrations of SO2 can lead to decay of building stones, mainly those of carbonate nature. The test was evaluated by means of different techniques, such as binocular (low-medium power) microscopy, scanning electron microscopy (SEM) and microanalysis (EDX). Moreover, qualitative and quantitative colour measurements were undertaken both previously and after testing using a colorimeter. Colour determination is now a common practice in the field of stone conservation, mainly in studies of stone decay and treatment (Garcia Pascua et al, 1996, Ginell and Coifnan, 1998). Colour can be described by three attributes that correspond to the perceptions of hue, chroma and value (McAdam, 1985). Hue is defined by the terms blue, green, red and yellow. It creates the colour wheel. That corresponds to the normal term of colour. Chroma (saturation) refers to the degree of coloration, that is the purity of colour. It is related to the amount of white radiation that exists in the radiation of a particular colour. Colour is more or less saturated depending on the degree of dilution with white/grey. It refers to the terms "vivid" or "dull".
*Author to whom correspondence should be addressed.
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Value (lightness or luminosity) indicates if the colour is "light" or "dark" and varies from white (maximum reflectance) to black (absence of light). Colour measurements were given in the CIE L*a*b* and CIE L*C*h systems. The system CIE L*a*b* is frequently used to measure colour differences because it represents better than others human sensibility to colour. L* is the variable lightness, which varies from 0 black to 100 white; a* and b* are the chromatic coordinates: +a* is red, -a* is green, +b* is yellow and -b* is blue. In the system CIE L*C*h, L* is again ligthness, C* is the chroma or saturation and h is the hue angle. They can be calculated by the equations (1) and (2). C* = (a*2+b*2) 1/2
(1)
h = tan-~(b*/a *)
(2)
Colour differences can be determined as follows: A L * = L * l - L * o ; A a * = a * l - a * o ; A b * = b * l - b * o ; A C * = C*I-C*0
(3)
Were: L* 1, a* l, b* 1 C* 1are the final values L* 0, a* 0, b* 0 C* 0 are the original values Total colour difference is determined as follows: AE* = (AL*2+Aa*2+Ab*2)1/2
(4)
2. Materials Six different stones were pre-selected: three light coloured sedimentary and three dark coloured metamorphic stones. All stones were honed finished. Additionally flamed specimens of two sedimentary stones were available for testing. Geological classification, mineral composition determined by X-Ray diffraction, visual colour and surface finishes are summarised in table 1.
3. Experimental methodology 3.1 Exposure to SO2 atmospheres Several nominal 50mm x 50mm x 10mm stone slabs were subjected during eight days to simulated polluted atmospheres in a climatic chamber Heraeus, which allows control of type and flow of gas, temperature and relative humidity. The gas was SO2 in a concentration of 2ppm. Temperature and relative humidity were 25~ and 90%, respectively. Samples were placed horizontally in the chamber, so that the honed or flamed surfaces were permanently exposed to SO2.
3.2 Test Evaluation The evaluation was carried out as follows : 9 Visual and low-medium power microscopy examinations. 9 Surface analysis by scanning electron microscopy and microanalysis SEM-EDX.
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9 Quantitative measurements of colour. Colour measurements were carried out with a MINOLTA CR-200 colorimeter which possesses a xenon lamp that produces a beam of diffuse light illuminating a target area of 8 mm diameter. Colour was measured before and after testing in four specimens (50ram x 50mm surface) of each of the selected stones. The systems used were CIE L*a*b* and CIE L*C*h. The number of shots necessary to obtain a representative colour was selected taking into account the differences between two successive cumulative averages of each of the parameters L*, a* and b* (LNEC, 1994). 16 shots per specimens were selected for all the stones and 25 in the case of the gneiss, which was more heterogeneous in colour. Therefore, a total of 64 and 100 colour measurements were carried out before and after testing. The significance of colour differences was evaluated by the Mann-Whitney non parametric test. Table 1: Stone characteristics
4. Results and Discussion Table 2 summarises reaction products and colour changes during testing (Esbert et al, 1997). Values of the parameters L*, a*, b*, C* and eolour differences AL*, Aa*, Ab* and AE* are shown in this table. Differences in chroma (AC*) are graphically exhibited in fig. 1, which also indicates the significance of the differences (critical level V= 0.05). After testing, a small deposition of sulphur was detected on all samples under SEMEDX. This is almost imperceptible with the unaided eye and low-medium power microscopy (magnifications x120). No visual colour changes were observed. Sulphur distribution on the surface of the specimens was related to surface topography. Honed specimens showed a uniform distribution. Sulphur concentration was higher around
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surface irregularities such as cavities or fissures. F l a m e d surfaces s h o w e d differential distribution o f sulphur favoured by the surface r o u g h n e s s o f this type o f finish. SO2 chemical attack w a s only detectable o n the gneiss surface. After testing, whitish salt efflorescence w a s o b s e r v e d on one o f the maffic minerals (scapolite). SO2 reacted with the calcium o f that mineral to f o r m gypsum. Table 2: Results o f S O Stone Test SEM EDX analysis Lim 1 pre . . . Honed post S deposit Lim 2 pre . . . Honed post S deposit Lim 2 pre . . . Flamed post S deposit Lim 3 pre . . . Honed post S deposit Lim 3 pre . . . Flamed post S deposit Serp 1 pre . . . Honed post S deposit Serp 2 pre . . . Honed post S deposit Gneiss pre . . . Honed post s deposit.
:st Visual Colour changes . NO . NO . NO . NO . NO . NO . NO . NO
L*
a*
74.30 2.16 73.60 L 2.37 60.86 6.53 60.46 6.71 6 7 . 0 5 5.19 65.94 5.64 65.34 3.68 65.63'3.42 70.76 4.99 70.09!| 5.34 32.74 -4.42 33.13 | -4.48 38.63 -5.63 39.74 | -5.55 47.48 -3.16 49.26 -3.27
b*
C*
AL*
15.88 16.99 17.29 18.13 13.46 14.66 21.19 21.88 15.76 16.80 0.48 0.47 0.53 0.30 2.90 2.88
16.03 17.16 18.53 19.39 14.47 15.75 21.51 22.14 16.55 17.65 4.45 4.52 5.65 5.56 4.43 4.51
.... -0.70 . . -0.40 .... -1.11 . . 0.29 . . -0.67 . . 0.39 .. 1.11 . . 1.78
Aa*
Ab*
i -0.21 l 1.11 . . . . 0.18 0.84 i "" 0.45 | 1.20 . . . . -0.26 0.69 . . . . 0 . 3 5 1| . 0 4 . . . . -0.06 1 -0.01 . . . . .1i 0.08 | -0.23 . . . . -0.11 -0.02
AE*
1.33
r
__
0.95 -.
1.70 ..
0.79 __
1.29 ..
0.39 __
1.14 -.
1.78
Gypsum from
reaction
with
scapolite
Chroma difference 1,5
Yes
I-, Ye~
1
~9
Yes
Yes
0,5 0 L1-H
L2-H
Yes
I
L2-F
L3-H
L3-F
~
$t -H
I
i
i
S2-H
I
i
'
i
G-H
-0,5
Specimen Figure 1: Chroma variations (AC*) after SO2 testing. Positive AC* means more saturate or pure colours whereas negative AC* indicates less saturate colours. The word "yes" means that the difference in values prior and after testing is significant (level cz=0.05). Chroma changes are significant in all the light limestones varying to more vivid or pure colours.
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In the light limestones, appreciable colour changes were detected by colour measurements although no visible colour changes were observed (table 2). These stones had a substantial yellow component (positive and high b* values) and the change was mainly due to and increase in b* values (yellow direction), which led to a chroma increase (C*). Colour became more vivid or pure. That variation was similar in all the limestones. Lightness variations (AL*) were, in general, less significant. Total colour difference AE* was thought to be related to SO2 deposition and was higher in limestone 1 (which had more surface cavities) than in limestones 2 or 3 (with smoother surfaces). AE* was also higher in flamed finished (rougher) than in honed finished (smoother) surfaces. Overall, values of AE* corresponded to grey scale values from 4 to 5 (BS EN ISO 105A05, 1997), 4.5 being approximately the limit of visual appreciation. (Grey scale values vary from 5: no difference to 1 maximum difference). Neither visual colour changes nor significant chroma differences were detected in the dark metamorphic stones. The only significant change was found in lightness values (AL*) in the serpentinite 2. This difference was positive indicating, then, a change to a lighter colour. The gneiss showed higher absolute differences but these were not significant because of the poly-chromatic appearance of the stone.
5. Conclusions Colour measurements were useful to indicate degree of reaction to or deposition of SO2 in the case of mainly monochromatic building stones. In this way : No visual changes were appreciated in some light coloured limestones subjected to artificial SO2 polluted atmospheres, however significant colour differences were measured with a colorimeter. Colour differences also indicated that these limestones would with time turn to a more saturate yellowish colour due to SO2 action. Colour differences seemed to be higher in rougher surfaces, which could be related to a higher deposition of sulphur. However a quantification of sulphur is necessary to assess this supposition. From these results limestones 2 and 3 seemed to be more resistant to decay by SO2 than limestone 1. Serpentinite 1 appeared to be the most resistant among the dark metamorphic stones.
6. Acknowledgements The authors wish to acknowledge the financial support of this research to DragadosOSHSA U.T.E., CICYT (projects CC95-SEC05-01 and 1FD97-0331-C03-01) and FICYT (project PB-REC96-98). To Joan Ard~vol and Oriol Escolfi, from the Executive Direction of Restoration Works ("Gran Teatre del Liceu"). Also to Mr Richard Tews for revising the English and STATS Consultancy (St. Albans, UK) for the time and facilities allowed to complete this paper.
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7. References
BS EN ISO, 105-A05, 1997. Test for Colour Fastness. Part A05. Instrumental assessment of change of colour for determination of grey scale rating. Esbert RM., Valde6n L., Alonso FJ., Ordaz J., Grossi CM., Diaz-Pache F., 1997. Estudio de la Durabilidad de las Piedras Preseleccionadas para el Revestimiento de las Fachadas del "Gran Teatre del Liceu". Unpublished Report, Universidad de Oviedo. Garcia Pascua N., S~.nchez de Rojas MI., Frias M., 1996. The important role of the colour measurement in restoration works. Use of consolidants and water-repellents in sandstone. 8th International Congress on Deterioration and Conservation of Stone, Berlin, 1351-1362. Ginell WS., Coffman R., 1998. Epoxy resin-consolidated stone : appearance change on aging. Studies in Conservation, 43,242-248. LNEC (Laboratorio Nacional de Engenharia Civil), 1994. Medi~oes colorim6tricas em rochas heterocronfiticas. Relatorio 89/94-GERO. I&D Geotecnia, 171. McAdam DL., 1985. Colour Measurements. Theme and Variations. Springer-Verlang.
329
EARLY MECHANISMS OF DEVELOPMENT OF SULPHATED BLACK CRUSTS ON CARBONATE STONE
Patrick Ausset*, Roger A. Lef'evre, Laboratoire Intertmiversitaire des Syst~mes Atmosph6riques, Universit6 Paris XII, 94010 Cr6teil, France. Marco Del Monte, Dipartimento di Scienze della Terra e Geologico-Ambientali, Universit~ di Bologna, 40127 Bologna, Italy.
Abstract
Experimental conditions characteristic of the urban pollution in many European cities over the last decades were reproduced in a simulation chamber in which samples of limestone were exposed for a period of 12 months, both naked or sprinkled with carbonaceous fly-ash. The development of gypsum crystals was observed overall in close proximity of fly-ash anchoring them to the limestone surface. Samples of the same limestone exposed in the field in a polluted environment for the same period of time led to similar results. The preliminary mechanisms leading to the genesis of sulphated black crusts in polluted environments were thus highlighted. Because of their roughness the embryonic black crusts increase the development of the crust by trapping new particles. This trapping is also facilitated by the wetness of the stone surface leading to the development of hydrated mineral (gypsum) in the water meniscus between fly-ash and stone surface. .(eywords: black crusts, limestone, sulphur dioxide, carbonaceous fly-ash, gypsum, simulation chamber, field exposure.
Introduction
Sulphation with the development of authigenic gypsum crystallisation below the surface of materials affects carbonate stones exposed to atmospheric pollution (Girardet and Furlan, 1983). This mechanism has been experimentally reproduced, revealing the important role played by SO2 (Spedding, 1969), enhanced by the presence of NO2 (Johansson et al., 1988), 03 (Haneef et al., 1992) and high relative humidity (Johansson et al., 1988; Spiker et al., 1992). The sulphation progresses with decreasing intensity from the surface towards the interior of the material (Ausset et al., 1996). On buildings surfaces, generally on those sheltered from direct rainfall or washout, along with sulphation products formed below the surface, one also observes the presence of black gypsum crusts above this surface containing numerous particles, particularly fly-ash, emitted into the atmosphere due to the combustion of coal and mineral oils (Fassina et al., 1979; Camuffo et al., 1982, 1983; Del Monte et al., 1981; Del Monte and Sabbioni, 1984; Ausset et al., 1994). Carbonaceous fly-ash, particulary those emitted by heavy fuel oil combustion, have a very strong physico-chemical reactivity. They contain many sulphured chemical species, in particular sulphates along with metals such as vanadium, iron and nickel. Indeed, it has been demonstrated that:
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 9 carbonaceous fly-ash adsorb atmospheric SO2, triggering its oxidation into sulphate (Novakov et al., 1974) 9 this reaction is intensified by the presence of NO2 and 03 (Cofer et al., 1980; 1981) 9 and by a high relative humidity (Tartarelli et al., 1978).
The reactivity of carbonaceous fly-ash in the presence of H20 or the reactivity of carbonate stones in the presence of SO2 and H20 are well known. By contrast, experiments that bring the four (fly-ash, stone, SO2 and H20) together within a single system are rare and have yielded contradictory results: some suggest that fly-ash play a slightly intensifying role in the sulphation process (Cheng et al., 1987; Ausset et al., 1996; Sabbioni et al., 1996), while others point to a completely negligible effect (Hutchinson et al., 1992). In fact the really or directly effect of carbonaceous fly-ash or other aerosol particulate matter had never been place in a prominant position. This paper tends to explain the role and the contribution of carbonaceous fly-ash in the nucleation of gypsum crystals and in the development of incipient sulphated black crust on carbonate stone. This goal is achieved by comparing simulation chamber data with those obtained in the field. Embryonic black crusts forming over 12 months through interaction between carbonaceous fly-ash and samples of Jaumont limestone in the controlled atmosphere of a simulation chamber (Lausanne Atmospheric Simulation Chamber - LASC, Ausset et al., 1996) are compared with those forming in the field on the same carbonatic stone, over the same time period in a real polluted atmosphere.
1. S i m u l a t i o n chamber observations 1.1. Materials
9 Fly-ash from heavy fuel oil combustion were collected from the electrostatic filters of an electrical power plant. The granulometric fraction lower than 100 ~tm, obtained by dry sieving, was used for the experiment. These particles are in the same size range as those found in samples collected from the atmosphere, far from their sources near the material surfaces (Ausset et al., 1992; Derbez and Lef'evre, 1996) or from within sulphated black crusts (Del Monte et al., 1981). Carbonaceous fly-ash are black and more or less round in shape with spongy (fig. la)or porous morphology (fig. lb).
Figure 1: a) spongy and b) porous carbonaceous fly-ash particles both emitted by heavy fuel oil combustion collected fromthe electrostaticfilter of a power station (Porchevillepower plant, France).
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*Bulk chemical analysis, Raman Spectrometry and X Ray adsorption spectrum (XANES) of this fraction show that the main element is carbon (graphite), accompanied by small concentrations of sulphur, sulphates, vanadium, silicon and iron (Ausset et al., 1999). 9 The Jaumont limestone had been chosen because of its widespread use as a building material. This limestone is made up of 94% calcite and 2.5% quartz and has a water porosity of 23%. It presents macropores of 200-500 ~tm in diameter, which are observed on the surface once the stone has been cut. The fly-ash spreaded on the Jaumont limestone revealed a tendency to collect within the superficial open macropores.
1.2. Experimental procedure The Jaumont limestone samples (0.1 x 0.1 x 0.02 m) were placed inside the LASC, either naked or sprinkled with fly-ash at the concentration of 7.5 g.m-2. The operating principle of the LASC (fig. 2) is described in Ausset et al. (1996). We simply mention here the following experimental conditions: temperature 13 ~ relative -3
-3
humidity 79 %; [SO2] = 340 ~tg.m (125 ppb); [NO2] = 98 ~g.m (50 ppb). These conditions reproduced those which have existed in Milan, the temperature and relative humidity being the annual average in this city from 1931 to 1960, and the 1972 annual average for SO2 and NO2 concentrations, years when the pollution peaks were very high. Such conditions are analogous to those observed in intensely industrialised regions in the seventies and eighties. In all cases, the values chosen for this study were far lower than those utilized during most of previous simulation experiments (Braun and Wilson, 1970; Judeikis and Stewart, 1976; Johansson et al., 1988; Haneef et al., 1992; Coboum et al., 1993).
Figure 2: Schemeofone ofthe 10 cells and its nmning: gas injection system (1 to 5), main part (6 to 11) and measurement system (12 and 13) (modifiedfromAusset et al., 1996 and Girardetet al., 1996).
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The samples were removed from the simulation chamber and studied after 3, 6, 9 and 12 months of exposure. The reaction products forming on the limestone surfaces, on fly-ash and on the stone-particle interface were studied by Analytical Scanning Electron Microscopy (ASEM, Jeol 6301F fitted with an EDS elemental analysis system Oxford Link-Isis).
1.3. Results and discussion 1.3.1. Evolution of the Jaumont limestone and of the fly-ash deposited on its surface
In a previous work (Ausset et al., 1996), it was shown how Jaumont limestone, either naked or sprinkled with fly-ash, after 12 months presented sulphation reaching a depth of 600 to 800~tm, of decreasing intensity as the depth increased. Observations by SEM also revealed the presence of small acicular gypsum crystals on the surface of the naked samples. However, even after a year of experimentation, these gypsum crystals did not cover the whole surface. In the case of the limestone sprinkled withfly-ash, the two above-mentioned phenomena, sulphation above and below the surface, are found with increasing intensity. In fact, the following observations were made: 9 small lanceolate gypsum crystals (a few ~tm), isolated or occasionally in small clusters, formed on the surface, in areas not in direct contact with the carbonaceous fly-ash (fig.3).
Figure 3: SEM micrograph of the surface of the Jaumont limestone sprinkled with carbonaceous fly-ash exposed in LASC after 3 months of exposure. Lanceolate gypsum crystals are visible in areas not in direct contact with fly-ash.
9 acicular crystals (20 x 1 lam) or tabular crystals (10 x 3 ~tm) (fig. 4a) or ~ desert rosette~ crystals (fig. 4b) developed directly on the surface of the fly-ash. EDS analysis of all the crystals revealed the presence of calcium and sulphur, with a S(Ca ratio (0.7-0.8), close to that of anhydrite (CaSO4), bassanite (CaSO4, 0.5H20) or gypsum (CaSO4, 2H20). The presence of high relative humidity in the LASC and the characteristic morphology of the crystals indicate a highly probable presence of gypsum. Among the 165 crystals individually analysed, 65% consist of gypsum (acicular, tabular or occasionally "desert rosette" in shape), the other 35% were juxtaposed micronic fine lamellar crystals composed of sulphur and iron associated with low content of sodium, vanadium and nickel or lenticular crystals composed of sulphur and sodium, with a S/Na ratio (0.7-0.8) close to that calculated for thenardite (NaESO4) or mirabilite (Na2SO4, 10H20). All of the described
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crystals invariably contain sulphur, and a single fly-ash particle can be the site o f different crystalline t y p e s .
Figure 4: SEM micrographs of different shapes of gypsum crystals developped on the carbonaceous fly-ash deposited on the Jaumont limestone after three months of exposure in LASC: a) acicular in shape; b) desert rosette in shape.
Figure 5: SEM micrographs of gypsum crystals (Gyp.) grown on the contact between a fly-ash (FA) particle and the Jaumont limestone substrate (Cal.) a/ier 12 months in the LASC: a) general view ; b and c) blow up ofacicular gypsum, attached to the fly-ash particle (FA), anchoring it to the surrounding limestone substrate 9 regardless o f the crystals developing on the surface o f the carbonaceous fly-ash and on that o f the limestone substrate between these particles, only g y p s u m crystals were observed at the fly-ash-limestone interface. These acicular and tabular g y p s u m crystals, which appear to anchor the fly-ash to the substrate, develop on the limestone substrate
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encircling the fly-ash basis (fig. 5a, b, c). The gypsum is clearly observed at a distance of up to 50 ~tm. Alongside the parallel experiments in the simulation chamber, some of the same fly-ash particles were placed inside a hermetically sealed opaque phial away from air, light and relative humidity. During the 12 months experimental period, they were regularly studied under ASEM at three-month intervals. No morphological transformation or crystal growth appeared and the chemical composition remained stable. It would therefore seem that carbonaceous fly-ash only become reactive in specific environmental conditions, such as those imposed inside the LASC.
2. Field observations 2.1. Materials and methods Parallelepipedic samples of Jaumont limestone (20 x 10 x 2 cm) were exposed vertically, sheltered from rainwater and washout in Milan for one year. During this period (May 1986/ May 1987), the average content of the air in SO2 was 107 lag.m"3, approximately 3 times weaker than that having existed in 1972 and than that imposed in the LASC (Furlan and Girardet, 1988). 2.2. Results and discussion The observation by ASEM reveals the following points;
9 many microparticles of industrial origin are visible on the surface of the Jaumont limestone exposed in Milan at the average density of 90 particles per square centimeter. The most abundant are carbonaceous spongy and porous fly-ash (72% in number), similar in shape and granulometry and comparable in chemical composition to those utilized during the the experiment in the LASC. Alumino-silicated spherical (18%) and ferriferous dendritic (10%) fly-ash originating probably mainly from coal combustion, are also represented. Small gypseous crystallizations appear on the surface of some fly-ash, always less numerous and less well developed than in the case of the fly-ash deposited on stone exposed in the LASC.
Figure 6: SEM micrographs of gypsum crystals grown on a fly-ash particle and at the contact between the particle and the Jaumont limestone substrate exposed in Milan during one year : a) general view ; b) blow up of small acicularcrystals of gypsum growingon the fly-ashparticle (FA) and largertabular crystals of gypsum (Gyp.) anchoringit to the surroundinglimestome substrate (Cal.).
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While in the LASC many species of crystals develop, only gypseous crystallizations are observed on the fly-ash surface in Milan. This result can be explained by the higher solubility of many salts (i.e. sulphate of sodium, of iron...) compared to those of calcium sulphate. In the LASC the relative humidity was stable at the average relative humidity of 79%. Moreover, in the field, the soluble salts are removed by condensation water (smog, fog) and only gypsum remains on material surfaces. 9 Gypseous crystallizations are also visible on the surface of the limestone, in regions not covered by fly-ash. 9Finally, small gypsum crystals are present at the interface between fly-ash and stone surface (Fig. 6) as in the experiment.
3 - Conclusions
The above results allow us to highlight the following main phenomena: 9 Jaumont limestone exposed naked in the presence of SO2 and humidity in the LASC, as well as undergoing sulphation below the surface, also reveals a moderate degree of authigenic gypsum formation above the stone surface. 9 On Jaumont limestone sprinkled with fly-ash, one observes a combination of the two above-mentioned phenomena: predominantly gypsum crystals appear on the fly-ash, while only gypsum crystals are encountered on the limestone surface between the fly-ash particles. However, the third most original phenomenon occurs at the limestone-fly-ash interface and consists of the fixing of these particles to the material surface through the intermediate growth of authigenic gypsum crystals. This phenomenon marks the beginning of the development of an embryonic black gypsum crust, the colour of which is given by the particle content. 9 The field samples also revealed fly-ash adhering to limestone by means of a crown of gypsum crystals. The gypsum crystals observed on the surface of limestone samples between carbonaceous particles are less numerous. 9 On the basis of simulation chamber and field data obtained over 12 months, the study of the morphology, mineralogy and chemical composition of the deposits and associated neocrystallisations indicates that they represent the first stage of black crust development. Although accounting for only a modest fraction, the fly-ash appear to play a crucial role leading to the formation of black crusts, since they facilitate the precipitation of gypsum which constitutes the predominant mineral in the black crusts. 9 The deposition of the fly-ash on the stone surface is easier when this surface is wet. It is highly probable that a <<meniscus >>of water is forming at the interface of the wet surface stone and the wet fly-ash particle. Thus, the evaporation of the water leads to the crystallization of gypsum that anchors the particle to the substrate. 9 Finally the development and thickening of the black crust from its embryo proceeds through the continued deposition of new fly-ash, the fLxation of which is strongly enhanced by the local increase in surface roughness. This phenomenon, which is a continuous deposition in the field, was impossible to reproduced in the simulation chamber.
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Aknowledgrnent : this work was supported by the European Commision, programme <<Environment and Climate ~, contract n~ EV5V-CT92-0116, and by the Regional Council of lie de France, programme ~ S6same >>. 4. References Ausset P., Bannery F. and Lef'evre R. (1992). Les microparticules dans l'air et dans une crofite noire de Saint-Trophime d'Arles. 7th International Congress.on Deterioration and Conservation of Stone, Lisbon, vol. 1,325-334. Ausset P., Lef'evre R., Philippon J. and Venet C. (1994). Pr6sence constante de cendres volantes industrielles dans les crofites noires d'alt&ation superficielle de monuments fran~ais en calcaire compact. Comptes Rendus de l'Acaddmie des Sciences., Paris, t. 318, s6rie II, 493-499. Ausset P., Crovisier J.L., Del Monte M., Furlan V., Girardet F., Hammecker C., Jeannette D. and Lef'evre R.A. (1996). Experimental study of limestone and sandstone sulphation in polluted realistic conditions: the Lausanne Atmospheric Simulation Chamber (LASC). Atmospheric Environment, 30, 18, 3197-3207. Ausset P., Del Monte M. and Lef'evre R.A. (1999). Embryonic sulphated black crust in Atmospheric Simulation Chamber and in the field 9role of the carbonaceous fly ash. Atmospheric Environment, 33, 10, 1525-1534. Braun R.C. and Wilson M.J.G. (1970). The removal of atmospheric sulphur by building stones. Atmospheric Environment, 4, 371-378. Camuffo D., Del Monte M. and Sabbioni C. (1983). Origin and growth mechanisms of the sulfated crusts on urban limestone. Water, Air and Soil Pollution, 19, 351-359. Camuffo D., Del Monte M., Sabbioni C. and Vittori O. (1982). Wetting, deterioration and visual features of stone surfaces in an urban area. Atmospheric Environment, 16, 22532259. Cheng R.J., Hwu J.R., Kim J.T. and Leu S.-H. (1987). Deterioration of marble structures. The role of acid rain. Analytical Chemistry., 59, 2, 104-106. Coboum W.G., Gauri K.L., Tambe S., Li S. and Saltik E. (1993). Laboratory measurements of sulfur dioxide deposition velocity on marble and dolomite stone surfaces. Atmospheric Environment, 2, 193-201. Cofer W.R. III, Schryer D.R. and Rogowski R.S. (1980). The enhanced oxidation of SO2
by NO2 on carbon particulates. Atmospheric Environment, 14, 571-575. Cofer W.R. III, Schryer D.R. and Rogowski R.S. (1981). The oxidation of SO2 on carbon particles in the presence of 03, NO2, and NO 3. Atmospheric Environment, 15, 1281-1286. Del M onte M. and Sabbioni C. (1984). Gypsum crust and fly-ash particles on carbonatic outcrops. Archives for Meteorology, Geophysics and Bioclimatology, Ser-B35, 105-111. Del Monte M., Sabbioni C. and Vittori O. (1981). Airborne carbon particles and marble deterioration. Atmospheric Environment, 15, 645-652. Del Monte M., Sabbioni C., Ventura A. and Zappia G. (1984). Crystal growth from carbonaceous particles. The Science of the Total Environment, 36, 247-254. De Santis F. and Allegrini I. (1992). Heterogeneous reactions of SO2 and NO 2 on carbonaceous surfaces. Atmospheric Environment,16, 3061-3064. Derbez, M. and Lef'evre, R.A (1996) - Le contenu microparticulaire des crofites gypseuses de la Cath6drale Saint-Gatien de Tours. Comparaison avec l'air et la pluie 8 th International Congress on Deterioration and Conservation of Stone, Berlin, 359-370.
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Fassina V., Lazzarini L., Biscontin G. and Calogero S. (1979). Influenza del materiale particellare atmosferico sui processi di degradazione della pietra a Venezia. 3rd International. Congress on Deterioration and. Conservation of Stone, Venice, 43-53. Furlan V. and Girardet F. (1988)- Vitesse d'accumulation des compos6s atmosph6riques du soufre sur diverses natures de pierre. 6th International Congress on Deterioration and Conservation of Stone, Torun, 187-196. Girardet F. and Furlan V. (1983). Mesure de la vitesse d'accumulation des compos6s soufr6s sur des 6prouvettes de pierre expos6es en atmosphere rurale et urbaine. 4th International Congress on Deterioration and Conservation of Stone, Louisville, 159-168. Girardet F., Furlan V., Ausset P., Del Monte M., Jeannette D. and Lef'evre R.A. (1996). Etude exp6rimentale de la prise en soufre d'un calcaire et d'un gr~s caleareux dans la chambre de simulation atmosph6rique de Lausanne. 8th International. Congress on Deterioration and. Conservation of Stone, Berlin, 349-358. Haneef S.J., Johnson J.B., Dickinson C., Thompson G.E. and Wood G.C. (1992). Effect of dry deposition of NO x and SO 2 gaseous pollutants on the degradation of calcareous building stones. Atmospheric Environment, 16, 2963-2974. Hutchinson A.J., Johnson J.B., Thompson G.E., Wood G.C., Sage P.W. and Cooke M.J. (1992). The role of fly-ash particulate material and oxide catalysts in stone degradation. Atmospheric Environment, 15, 2795-2803. Johansson I.J., Lindqvist O. and M angio R.E. (1988). Corrosion of calcareous stones in humid air containing SO 2 and NO r Durability of Building Material, 5,439-449. Judeikis H.S. and Stewart T.B. (1976). Laboratory measurement of SO2 deposition velocities on selected building materials and soils. Atmospheric Environment, 10, 769-776. Novakov T., Chang S.G. and Harker A.B. (1974). Sulfates as pollution particulates : catalytic formation on carbon (soot) particles. Science, 186, 259-261. Sabbioni C., Zappia G. and Gobbi G (1996). Carbonaceous particles and stone damage in a laboratory exposure system. Journal of Geophysical Research, 101,621,627. Spedding D.J (1969). The rate of sulphur-35/sulphur dioxide released in a laboratory. Atmospheric Environment, 3, 341-346. Spiker E.C., Hosker R.P, Comer V.J., White J.R., Were Jr R.W, Harmon F.L., Gandy G.D and Sherwood S.I. (1992). Environmental chamber for study of the deposition flux of gaseous pollutants to material surface. Atmospheric Environment, 16, 2885-2892. Tartarelli R., Davini P., Morelli F. and Corsi P. (1978). Interactions between SO 2 and carbonaceous particulates. Atmospheric Environment, 12, 289-293.
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PAST AIR POLLUTION RECORDINGS ON STONE MONUMENTS: THE HEADS OF THE KINGS OF JUDA STATUES FROM NOTRE-DAME CATHEDRAL (PARIS)
Patrick Ausset*, Roger A. Lef'evre, Laboratoire Interuniversitaire des Syst6mes Atmosph6riques, Universit6 Paris XII, 94010 Cr6teil, France. Marco Del Monte, Dipartimento di Scienze della Terra e Geologico-Ambientali, Universit~ di Bologna, 40127 Bologna, Italy. St6phanie Thi6bault, Arch6ologies et Sciences de l'Antiquit6, M.A.E., CNRS, 92023 Nanterre, France.
Abstract A pollution linked to the combustion of wood is a characteristic of the atmosphere of the cities in the past. It led to the development of thin grey crusts on the surface the stone of monuments. The grey crusts discovered on the Heads of Kings of Juda Statues, present on the western facade of Notre-Dame in Paris from the 13th Century to 1792, are the material witnesses of the effects of this ancient air pollution. The particles of unburnt wood included inside these grey crusts confirm that the burning of wood was the main cause of air pollution. The high position where the statues were sited suggests that this development was not the result of a local or punctual phenomenon but the result of a general pollution of the air of Paris at that time. Keywords: Heads of the Kings of Juda, Notre-Dame Cathedral in Paris, past air pollution, grey crusts, charred wood residues, polychromy, calcite, gypsum, ASEM, DRX, anthracology.
1. Historical introduction The remains of the Heads of the Kings of Juda, exhibited as a group at the Mus6e National du Moyen Age of the H6tel de Cluny in Paris since 1980, are those of the Heads of statues that originally adorned the western fafade of Notre-Dame Cathedral in Paris (Fig.l). The statues stood there from around 1240 until 1792, when they were thrown down along with all other statuary adorning the fafade. Their remains were heaped together in the parvis of Notre-Dame until 1796, when they were cleared away by a building contractor (Fleury in Giscard d'Estaing et al., 1977). It can be supposed that the statues were not 'decapitated' until their removal in order to facilitate transport. However, it cannot be entirely excluded that the heads had broken off when the statues were knocked down. Whatever the case, the group of sculptures was dispersed among different sites in Paris and the surrounding areas. It was not until 1977, that twenty-one of the twenty-eight Heads of the Kings were accidentally brought to light during earthworks on the foundations of the French Bank of Foreign Trade in rue de la Chauss6e d'Antin (Giscard d'Estaing et al., 1977).
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Figure 1: Western Facade of Notre-Dame Cathedral in Paris in 1699 by Antier (French National Library, Stamps department). The Gallery of Kings of Juda Statues is well visible above the three portals.
Figure 3: Headnumber 16. Note the presence of the grey crust forming an almost vertical strip from the crown down to the spacebetweenthe eyes.
2. Description of the Heads of the Kings of Juda These statues were sculpted in a free Miliolidae limestone (Middle Eocene) frequently employed in the statuary and buildings in Paris (Blanc and Lorenz, 1992). Traces of polychromy dating back to the early 13th Century are visible; indeed, the height at which the statues were erected (16 m) and the consequent lack of access to them is sufficient to discard the possibility that any maintenance, cleaning or restoration had subsequently been performed (Erlande-Brandenburg, 1982). Apart from the polychromy, the surface of the Heads locally shows a grey crust, generally away from the damaged areas. In particular, they are absent from the surfaces of major breaks.The literature makes no mention of the presence of these grey crusts. On comparison with other similar cases studied in Aries (Ausset and Lef'evre, 1994) and Bologna (Ausset et al., 1998), it is reasonable to think that the grey crusts on the Heads bear witness to the air pollution in Paris, at least at the time of the French Revolution and during the period immediately before it. The hypothesis favouring the atmospheric origin of the grey crusts is substantiated by their absence from the surfaces of major fracture sections, as mentioned above. That means that they formed while the Heads were exposed to the Paris atmosphere and not during their long period of burial from 1796 to 1977.
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This study should be seen within an archaeological-environmental perspective and contributes to research on the character and evolution of urban air pollution during the recent past. These results will also be compared with those deriving from studies on the modem industrial black crusts.
3. Sample collection and preparation The samples were obtained by scraping the surfaces with a scalpel and took the form both of tiny scales of millimeter size and powder. Firstly, all samples were studied raw, without undergoing any particular preparation procedure. Then, the scales were set within a polyester resin to study their stratigraphic section. The powders underwent hydrolysis by HCI (6M), in order to dissolve the sulphates and carbonates and isolate the solid particles insoluble in the acid. Solid particles have been then washed with distilled water. Among the twenty-one Heads, samples of grey crusts were taken from four (fig. 2): Head 4 : centre forehead; Head 8: around the lips and back of the scalp on the leit; Head 12 : centre forehead and nose break; Head 16: from a grey crust forming an almost vertical strip from the crown down to the space between the eyes (fig. 3).
4. Analytical methods Several analytical techniques were used to highlight the main physico-chemical and mineralogical characteristics of the grey crusts: differences in colour between ancient and modem crusts were measured by colorimetric technique (Munsell Color Chart); the determination of the mineral phases present in the stone, the cement matrix and particles in the crusts and pigment layers was performed by X-Ray Diffraction (XRD, Philips PW1710). The morphological, granulometric and elemental characterisation of the isolated grains and stratigraphic sections were performed by Photon Microscopy (Leica-Wild M10 Stereomicroscope and Zeiss 2 Axiophot) and Analytical Scanning Electron Microscopy (ASEM, Jeol JSM 6301F fitted with a Link-Isis device for semi-quantitative analysis by XRay Energy Dispersive Spectrometry, EDS). 5. Results 5.1. Raw sample analysis The colorimetric analyses performed on the powders revealed a grey colour with shades running from yellow to light green. The grey crusts surface is transparent and microcrystalline, like that of alabaster. Large, solid gypsum crystals are easily identified and are highly characteristic. The crust is composed of a mixture of calcite (CaCO3) as the main constituent (65 %)and a smaller quantity of gypsum (CaSO4, 2H20) (35 %) and, less frequently, of a mixture of larger quantities of gypsum and smaller quantities of calcite, associated with traces of quartz and, in only one case, traces of weddeUite (CAC204, 2H20). Residues of the underlying stone scraped off during sampling are locally attached to the crust.
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5.2. Analysis of the stratigraphic sections The stratigraphic sections show the following succession (fig. 4): 1. Miliolidae limestone; 2. a discontinuous white layer of a few tens of ~tm thickness, composed of white lead (cerusite : PbCO3 or hydrocerusite: 2PbCO3, Pb(OH)2), constituting a preparation layer; 3. the upper grey layer of a few hundred micrometres thickness (400 to 500 ~tm), composed of a calcite-gypsum matrix, containing numerous black particles and grains of quartz.
Figure 4: Scanning Electron Micrograph ofa stratigraphic cross section of the grey crust surrounding the Head number 12 : a) Secondary electron image : this sample is composed of three layers, from bottom to top, (1) Milliolidae limestone (2) - discontinuous intermediate layer; (3) - homogeneous upper layer, b) Distribution image of silicium (Si) : SiO2 grains (quartz) are distribuated in the limestone and in the upper layer, c) Distribution image ofsulfur (S) and lead (Pb) : the intermediate layer (2) is constituted ofPb (W.L : White Lead) and the upper layer (3) contains S in the gypsum form. d) distribution image of calcium (Ca) : calcite in the limestone (layer 1), and a mixture of gypsum and calcite in the grey crust (layer 3). The above sequence shows that the grey crust can only have formed after the decoration of the sculptures (1240). This chronology supports the hypothesis of the grey crust formation may be the result of subsequent atmospheric deposition.
5.3. Analysis of particles isolated by acidic attack Different particle types were identified after dissolving the powders in hydrochloric acid: black particles and pigment grains. They were studied and analysed by ASEM.
5.3.1. Black particles The grey colour of the crusts is due to the presence of numerous black particles, which are elongated, prismatic, longitudinally striated and, in some cases, presenting small pits
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regularly distributed over the surface. The black particles are essentially composed of carbon associated with traces of Si, Ca, K, A1 and, occasionally, Na and/or Mg. These particles are encountered in the grey crusts removed from the unbroken surfaces of Heads 4, 8, 12 and 16 and from the breakage of the nose on Head 12. In addition, they were observed within the black patch on the lower fracture of Head 17, but not in the black patch of the vertical fracture of the same Head. The size of the particles (from a few tens to several hundreds of microns) is compatible with their transport within atmospheric aerosols. Identical particles of comparable size have been observed and measured in the grey crusts sampled on other monuments in Aries (Ausset and Lef'evre, 1994) and Bologna (Ausset et al., 1998) and have been identified as the debris of wood incomplete combustion. The identification of these wood fragments was attempted by comparing them with present-day collections of burned wood and with atlas of wood anatomy (Boureau 1956; Metcalfe and Chalk 1950; Greguss 1955, 1959; Jacquiot 1955; Jacquiot et al., 1973; Schweingruber 1978, 1990). In spite of their very small size, some characteristic anatomical structures have been recognised. It would appear that the wood debris originate from the combustion of angiosperms and gymnosperms (conifers). The three anatomic planes of wood (transversal, longitudinaltangential and longitudinal-radial) are visible on some to the samples observed using ASEM. In fact, the micrograph in figure 5 shows, in the longitudinal-tangential plane, the section of a vessel and the presence of a uniseriate ray, probably attributable to an angiosperm, as indicated also by the details of the pits on the vessel visible in figure 6. Figure 7 shows a detail of a uniseriate ray cell. A further example, presented in figure 8, shows on one side the presence of a tracheid-ray cross field in the longitudinal-radial plane and on the other a large fenestriform pit in cross-field, which cannot fail to suggest the Scotch pine (Pinus sylvestris). All of the observed samples present uniseriate rays. According to the anatomic charts, only some tree species possess such uniseriate rays" gymnosperms in general and a few angiosperms, for example, the chestnut (Castanea sativa), willow (Salix sp.), poplar (Populus sp.). Others present a combination of uni- and pluriseriate rays, like the oak (Quercus sp.) and certain Betulaceae (birche family). However, the presence of homogeneous ray cells, coupled with the absence of spiral thickenings and micro-pits in the pores tend to exclude the Betulaceae, willow and poplar. The identification of wood fuels used in Paris has been achieved by charcoal analysis from the archaeological excavations of Napol6on (Thi6bault, 1986) and Carrousel Squares in the Louvre (Solari and Thi6bault, 1991). It indicated that, among the numerous species used as domestic and craitmen fuels, the deciduous oak is the most frequently encountered. The other most commonly employed tree species were the poplar, willow, chestnut, birch (Betula sp.), hornbeam (Carpinus betulus) and hazel tree (Corylus avellana). Gymnosperms have been very rarely identified, although they are present in filigree in anthracological analysis starting from the 16th Century, the fir (Abies alba) and Scotch pine being those most frequently observed. The attribution of a definite origin to the plant residues contained in the crusts on the Heads is made more difficult by the very small size of the samples, compared to those collected from archaeological excavations. However, it is possible to attribute certain fragments to angiosperms which could belong to the oak or chestnut and others to a gymnosperm species such as the Scotch pine.
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Finally, spherical particles are sometimes found stuck to the wood fragments, which are colourless or with slight hints of light green or brown; ranging from 1 to 5 ~tm diameter, they are composed of Si, and less often, of Si and AI. Although more rarely, these spherical particles can also be found isolated within the grey crusts. Both these features have already been observed within ancient grey crusts (Ausset and al., 1998) as well as in the microparticulate of smoke from experimental wood combustion.
Figure 5: Scanning Electron Micrograph of a vessels' section and presence of a uniseriate ray in the longitudinal-tangential plane of a fragment attributable an angiosperm.
Figure 6: Scanning Electron Micrograph of a pit of a vessel (detail of figure 5).
Figure 7: Scanning Electron Micrograph of a detail ofuniseriate ray cell.
Figure 8: Scanning Electron Micrograph of a large fenestriform pits in cross-field in the longitudinalradial section attributable to the Scotch pine (Pinus
Sylvestris).
5.3.2. Pigments As mentioned above, the Heads were painted. Indeed, the evidence suggests that the grey crust formed above of the painted surface. Pigments of different colours are observed: red pigments of cinnabar (HgS); yellow to brown pigments of oxides (hematite, Fe203) or ferrous hydroxides (goethite, FeO-OH, or limonite, FeO-OH, nH20), the constituent minerals of ochres; green pigments originate from green clays, whose chemical composition varies according to the presence and amount of minerals such as glauconites ((K,Ca,Na)_l.6(Fe 3+, Al, Mg, FeE+)4Si7.3Alo.7OEo(OH)4), celadonites (K(Mg, Fe, A1)2(Si, A1)4Olo(OH)2) or serpentines
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(Mg3[Si2Os](OH)4), along with metallic grains of gold associated with impurities of Ag, Cu and Zn.
6. Discussion and conclusion
Many of the characteristics of the ancient grey crusts of the Heads of Kings of Juda directly contrast with those of the present-day black crusts (Del Monte et al., 1981) observed on the buildings of Paris, while they suggest comparison with other ancient grey crusts observed in different cities (Aries and Bologna). These characteristics are colour, texture, thickness, chemico-mineralogical nature of the crusts and of the prismatic or spherical particles embedded in the matrix. The grey crusts on the Heads are far lighter in colour than that of the present-day black crusts observed (very dark grey to black). Finally, the ancient crusts have a fraction of a millimetre thickness, whereas the modem crusts can reach to about one centimeter. Diffractometric analysis of the modem black crusts highlights the presence of the same minerals as those found in the ancient crusts of the Heads, but in different proportions 9 greater amounts of gypsum than calcite, followed by quartz and weddellite (oxalic acid secreted by lichens). But the main difference in the mineralogical composition of the two crusts lies in the lower gypsum/calcite ratio of the ancient crusts. In addition, the ancient grey crust is composed of gypsum crystals of three-dimensional growth, while gypsum of the modem black crusts presents lamellar crystals of two-dimensional growth. This means that the conditions of their crystallisation were not the same, particularly the humidity of the ambience and the SO2 concentrations. The studies of the genesis of modem sulphated crusts (Braun and Wilson, 1970 ; Camuffo et al., 1983) suggest that the origin of the gypsum is to be found in the atmospheric contribution of sulphur and calcium in various forms, associated with urban air pollution (Del Monte and Rossi, 1997). These results coincide with those obtained on ancient grey crusts from Bologna (calcite : 70% ; gypsum : 30%), although they differ slightly from those obtained on another grey crust, this time more ancient, observed on the Roman portal of Saint-Trophime in Arles. Here, the grey crust is mainly composed of calcite associated locally with acicular gypsum crystals of micron size (Ausset and Lef'evre, 1994 ; Ausset et al., 1998). A further major difference between the ancient grey crusts and the modem black crusts lies in the kind of particles contained in the gypsum-calcite cement. While the grey crusts only contain the residues of incomplete wood combustion, the modem crusts embed microspheres which turn out to be fly-ash released into the atmosphere by the combustion of coal or heavy fuel (Del Monte M. and Sabbioni, 1987; Ausset et aL, 1994). These microparticles, of highly characteristic granulometry, morphology and chemical composition, are excellent tracers of modem industrial pollution. Large quantities of fly-ash are always found within modem black crusts, unlike the residues of wood burning, which are very rarely observed and, when so, always only at their base. Indeed, the absence of industrial flyash confirms that the grey crust is ancient. Moreover, the presence of particles from wood combustion is proof that the Paris air, during the Revolution and in the years or centuries prior to it, was polluted by smoke originating from wood combustion. The body of observation and analyses are proof that the grey crusts locally encountered on the Heads originate from a phenomenon of atmospheric deposition on the surface of stone. It also
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shows that the atmospheric alteration of monumental stones is not an exclusively modem phenomenon, appearing with the on-set of air pollution of industrial origin. Medieval and Renaissance cities also experienced air pollution, due, not to coal or oil combustion, but to the burning of wood and vegetal matter in general. Acknowledgements. This work received the financial support of the European Commission, contract ENV4CT 95-0092: "Archaeometric study to reconstruct the pollution and climate of the past and their effects on Cultural Heritage" and of the Ue-de-FranceRegional Council, Programme "Sesame 1995". We acknowledge particularly Mrs Huchard, Director of the National Museum of Middle Age of Paris and Mrs Lagabrielle, Conservator, for facilitiesof sampling. 7. References
Ausset P. and LeFevre R. (1994). Ddbris de bois imbrfilds dans une couche grise ddposde entre les 126me and 176me si6cles sur la pierre de Saint-Trophime d'Arles (France). 3rd
International Symposium for the Conservation of Monuments in the mediterranean Basin, Venice, 243-249. Ausset P., Lef6vre R., Philippon J. and Venet C. (1994). Pr6sence constante de cendres volantes industrielles dans les crofites noires d'alt6ration superficielle de monuments frangais en calcaire compact. Comptes Rendus de l'Acaddmie des Sciences, Paris, t. 318, s6de II, 493499. Ausset P., Del Monte M., Bannery F. and Lef'evre R.(1998). Recording of pre-industrial atmospheric environment by ancient crusts on stone monuments. Atmospheric Environment 32, 16, 2859-2863. Blanc A. and Lorenz C. (1992). Ile-de-France et Champagne; Paris et Versailles, in Terroirs et Monuments de France, BRGM ed., Orl6ans, 111-118. Boureau E. (1956). Anatomie v6g6tale. 3 vol., Presses Universitaires de France. 752p. Braun R.C. and Wilson M.J.G (1970). The removal of atmospheric sulphur by building stones. Atmospheric Environment, 11, 1157-1162. Camuffo D., Del Monte M. and Sabbioni, C. (1983). Origin and growth mechanisms of the sulfated crusts on urban limestone. Water, Air and Soil Pollution, 19, 351-359. Del Monte M., Sabbioni C. and Vittori O. (1981). Airbom carbon particles and marble deterioration. Atmospheric Environment, 15, 5,645-652. Del Monte M. and Sabbioni C. (1987). Characterization of individual fly-ash particles emitted from coal and oil-fired power plants. Atmospheric Environment, 21, 12, 2737-2738. Del Monte M. and Rossi P. (1997). Fog and gypsum crystals on building materials. Atmospheric Environment, 31, 1637-1646. Del Monte M., Ausset P., Lef'evre R. and. Thi6bault S. (1999). Evidence of pre-industrial air pollution in Paris from the Heads of Kings of Juda Statues from Notre-Dame Cathedral.
Archaeometry (submitted). Erlande-Brandenburg A. (1982). Les sculptures de Notre-Dame de Paris au Mus6e de Cluny, Ed. R6union des Mus6es Nationaux, Paris, 133pp. Giscard d'Estaing F., Fleury M. and Erlande-Brandenburg A. (1977). Les Rois retrouv6s, Cu6not, Paris, 80p. Greguss P. (1955). Identification of Living Gymnosperms on the Basis of Xylotomy. Budapest, 263 p.
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Greguss P. (1959). Holzanatomie der Europa'fschen Laubh61zer und Straficher. Akad6miai Kiado Budapest, 330p. Jacquiot C. (1955). Atlas d'anatomie des bois des conif'eres. Centre Technique du Bois. Paris 135p, 64 pl. 2 vol. Jacquiot C., Trenard Y. and Dirol D. (1973). Atlas d'anatomie des Bois des angiospermes. Centre Technique du Bois, Paris, 175p. 72 pl. 2 vol. Metclafe C.R. and Chalk L. (1950). Anatomy of the dicotyledons. Clarendon Press, Oxford, 2 vol., 1500p. Schweingruber F.H. (1978). Mikroskopische Holzanatomie. Ztircher a.g. zug, 98p1., 226p. Schweingruber F.H. (1990). Anatomie Europa'icher H61zer. w.s.l.f.n.p, haupt. 800p. Thi6bault S. (1986). Une approche du pal6oenvironnement v6g6tal par l'6tude des charbons de bois : l'anthracologie, 30 -33 et premiers r6sultat anthracologiques : le fait 3 de la zone 10 74-78. Pal~oenvironnement etfouilles urbaines, f6vrier 1986, Grand Louvre, Cour Napol6on. Solari M.E. and Thi6bault S. (1991). Les fouilles du jardin du Carrousel, r6sultats pr61iminaires de l'analyse anthracologique in : Van Ossel : Les jardins du Carrousel ~ Paris, fouilles 1989-1991, S.R.A. lle de France, vol. III, 47-56.
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L A B O R A T O R Y I N V E S T I G A T I O N S OF W E A T H E R I N G B E H A V I O U R OF FRESH AND I M P R E G N A T E D L I M E S T O N E AND S A N D S T O N E F R O M C E N T R A L SWEDEN
Katarina Malaga-Starzec* GOteborg University, Department of Inorganic Chemistry, SE-412 96 G/3teborg, Sweden Torgny Sahlin GOteborg University, Earth Sciences Centre; Geology, P.O. Box 460, SE-405 30 G/3teborg, Sweden Oliver Lindqvist G6teborg University, Department of Inorganic Chemistry, SE-412 96 G0teborg, Sweden
Abstract The weathering of natural stone depends on its chemical and morphological properties. Two sedimentary rocks of different mineralogy quarried in Central Sweden were used in this study, sandstone and limestone. The main purpose of the project was to investigate differences in chemical weathering behaviour between fresh and impregnated samples. Impregnation material used for the study was potassium-based water-glass diluted with water, colloidal silica and Berol 048. The experimental part consisted of corrosion experiments in laboratory. The simulation of acid rain condition was performed in two atmospheric corrosion apparatus, suitable for short-term and long-term exposure. The rocks" sensitivity to chemical corrosion was correlated to results from physical tests: threepoint load bending strength, uniaxial compressive strength, abrasion resistance, water absorption, effective porosity and air-permeability. The results from chemical experiments showed significant sulphation of both fresh and impregnated limestone surfaces while no changes on sandstone surfaces were observed. Physical tests showed very small or no changes between fresh and impregnated sandstone while impregnated limestone showed higher bending strength, water absorption and air permeability compared to fresh samples. It could be concluded that impregnation material did not improve properties of the sandstone while a small improvement was noticed for the limestone.
Key words: Acid rain, Chemical weathering, Limestone, Sandstone, Laboratory.
1. Introduction Most natural stones found near the surface of the earth are formed under high temperature and pressure conditions and are not thermodynamically stable. Exposure to the chemical weathering, particularly water and dissolved gases, decomposes the original rock into substances that are stable in the surface environment. The weathering of natural stone depends on its chemical and morphological properties. The conventional stone tile used as building material, is untreated, except for cases of surface treatment, and at least 10 mm thick. A new method makes it possible to produce natural stone tiles only 4 mm thick. The natural stone material used in the study was
* Author to whom correspondence should be addressed.
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impregnated with a potassium-based water-glass using vacuum technique including repeated cycling between vacuum and atmospheric pressure. The purpose of the impregnation process was to increase the mechanical strength and the durability of the stone material. The limestone and the sandstone are aimed to be used as exterior cladding panels of buildings, on indoor floors, and as interior decoration in bathrooms and kitchens due to its low weight compared to the traditional thicker tiles. In order to analyse the effect of an accelerated air pollution impact on the sandstone and the limestone climatic chambers for stone-air pollution-humidity simulation have been used. Results from physical studies were used for evaluation of impregnation material's efficiency for improvement of rocks properties (Sahlin et al., in press). The aim of the project was to investigate differences in chemical weathering behaviour between fresh and impregnated natural materials. Efficiency of impregnation material examined during chemical tests was analysed and correlated to results from physical tests. Image analyses of thin sections and prisms were expected to express the rate of the stone decay as a function of the different variables (corrosive gases, humidity, temperature, mineralogy and porosity).
2. Experimental 2.1 Sample preparation The red-coloured fine-grained Dala sandstone, quarried in M~ngsbodama, and the very fine-grained red J~imtland limestone, quarried in the Brunflo area, both from central Sweden, were used in this study. The mineralogical composition for sandstone had quartzitic character (quartz -~70%, feldspar- 15%, rock fragments ---10%, muscovite/sericite -~2%) and for the limestone had carbonaceous character (calcite ---80%, quartz -~10%, hematite, fossils). Samples used for analysis were both fresh and impregnated with potassium-based water-glass diluted with water, colloidal silica and Berol 048 non-ionic surfactant. Colloidal silica has been developed by Eka Chemicals in Sweden, and used for material consolidation. It consisted of very fine amorphous silica particles (500 nm) in dispersion form that easily penetrates into pores and cracks. Amorphous silica is highly reactive pozzolan. It is completely inorganic material and thus environmentally friendly. Three different sample sizes were used in the study, small prisms 30 x 30 x 4 mm and 30 x 20 x 4 mm, and thin sections. The prisms were polished in water with silicon carbide abrasive paper to 500 meshes on all sides and thereafter placed in the high purity water and washed in an ultrasonic bath 3 times for 15 rain. The washed samples were vacuum-dried in a desiccator with a drying agent for one week and equilibrated at the relative humidity for another week. Thin sections were equilibrated at the same relative humidity as the prisms. Prior to exposure, a 0.12 mm thick nylon thread was bound around the sample for suspension in the exposure chamber. One sample at the time was used in each on-line exposure while eight samples in separate chambers were used in long-term experiment.
2.2 Corrosion chamber Short-term on-line gas analysis of SO2 adsorption catalysed by NO2 was performed in a single corrosion chamber (fig.l) and for long-term exposure to corrosive gases an apparatus, of the same type as short-term set-up, with eight separate chambers was used. The atmospheric corrosion testing apparatus for short-term (-~ 20 hours) analysis consisted of: molecular sieve preceded by an air drier, needle valves, humidifier, vessels for SO2 and
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NO2 permeation tubes, mixer, thermometer, corrosion chamber, and thermostated water tank. The main difference between short-term and long-term corrosion testing apparatus was that the latter one consisted of eight single corrosion chambers, which were open sequentially, in order to attain equal flow through all chambers, and was not connected to on-line gas analysis. The long-term exposure lasted for circa five weeks. The utilisation of corrosion chambers was ideal for the determination of deposition velocities for single and multi-pollutant gas mixtures using ppm and ppb concentrations and for investigations of chemical reaction mechanisms.
Figure 1: The experimental on-line set-up for short-term exposures. The main advantage of using corrosion chambers was the high accuracy in the control and regulation of temperature, gas flows, relative humidity (RH) and concentrations of corrosive gases such as SO2 and NO2. The presence of oxidants, such as NO2, was found to enhance the corrosion process strongly, since they catalyse oxidation of the four-valent sulphur, or calcium sulphite, to sulphate (Johansson et al. 1991, Elfving et al. 1994). The experimental conditions used in the study are presented in tab. 1. Table 1: The experimental conditions. NO2 802 (ppm) (ppm) Exposure ~ . . 1.8 0.841 0.345 1.8 Short-term 0.143 1.8 1.8 0.061 0.902 0.193 Long-term
RH (%)
Air flow rate (L/min)
T~
95
22
95
22
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3. Results and Discussion 3.1 Deposition rates of SO2 The deposition rates of the SO2 were measured with an on-line SO2 fluorescence instrument (Environment s.a.A.F. 21M). The results for tWO sedimentary rocks, sandstone and limestone, showed significant differences in reaction with corrosive atmospheres. Impregnation material, the potassium-based water-glass contained high amounts of silica, which was expected to increase resistance to acid rain and to improve physical properties of the rock material. Sandstone, both fresh and impregnated proved to be resistant to the impact of SO2 catalysed by the presence of NO2 (fig.2-4). The Dala sandstone consisted mostly of quartz (---70%), which is one of the least reactive minerals. Variation of the input concentration of SO2 (0.841, 0.345, 0.143, 0.061 ppm) did not influence significantly the adsorption on the surface. Impregnation material improved neither chemical nor physical properties of the sandstone. Fresh limestone, which consisted mostly of the very reactive calcite, CaCO3, showed higher adsorption of SO2 compared to the impregnated limestone and both sandstones. The level of adsorption of SO2 was dependent on the concentration of SO2 (fig.4). The highest difference for the adsorption between fresh and impregnated limestone was detected for the highest concentration of SO2. Also the highest adsorption was found when concentration of SO2 was highest (fig.2). The difference in adsorption of SO2 between fresh and impregnated samples was decreasing with decreasing concentration of SO2. For the lowest concentration of SO2 used in this study, 0.061 ppm, no difference occurred in adsorption between fresh and impregnated limestone and between fresh and impregnated sandstone (fig.3).
Time of exposure (h) Figure 2: Deposition of SO2 on fresh and impregnated limestone and sandstone. Input concentration of SO2 was 0.841 ppm.
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Time of exposure (h) Figure 3: Deposition of 802 on fresh and impregnated limestone and sandstone. Input concentration of SO2 was 0.061 ppm.
Figure 4: Trends for the deposition rate for the limestone and the sandstone after 20 hours exposure.
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3.2 Optical changes The thin films and samples from long-term exposures were optically analysed with a polarising microscope. In order to illustrate the surfaces changes a series of images were taken before the samples" exposure in the corrosion chamber and compared with the images taken at the same locations after exposure to corrosive gases. The results for fresh and impregnated sandstones showed no optical changes after exposure while image analysis of limestone indicated severe changes on the surface areas. For the fresh limestone the corrosion products were more abundant than for impregnated (fig.5). The dark areas corresponded to the corrosion products, gypsum, CaSO4 2H20, and mostly calcium sulphite hemihydrate, CaSO4 1/2H20. The white areas on Figure 5-2c indicated points resistant to corrosion that could correspond to the natural content of quartz in the rock in combination with the impregnation material.
Figure 5: Thin section microphotographs of fresh (1) and impregnated (2) limestone before exposure in the corrosion chamber (a and b) and after exposure (c) to atmospheres containing 0.841 ppm SO2 and 1.8 ppm NO2 and 95 % R.H. (a) in polarised light with crossed polars; (b) and (c) luminated from above in plane-polarised light.
3.3 Corrosion product characterisation The Environmental Scanning Electron Microscopy connected to an X-ray detector (ESEM-EDX) and X-ray diffractometry were used for characterisation of corrosion products obtained during short- and long-term exposures. The results from ESEM-EDX showed clear differences between concentrations of adsorbed SO2 on fresh and impregnated limestone after exposure (fig.6). The sulphur content was not detectable on the fresh
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limestone before the exposure. No differences between fresh and impregnated sandstone were detected. The results from X-ray diffraction analysis indicated formation of calcium sulphite hemihydrate and gypsum on the fresh and impregnated limestone. The Secondary Ion Mass Spectroscopy (SIMS) technique was used for detection of impregnation material. The impregnation material is very difficult to detect because it is amorphous. By using SIMS technique it was possible to see a slight trend in silica concentration along the pores and grain boundaries compared to the fresh samples.
Figure 6: ESEM-EDX elements mapping of fresh limestone before exposure (1) and fresh (2) and impregnated (3) limestone after long-term exposure.
4. Conclusions The chemical degradation of the studied sedimentary rocks was a complex phenomenon depending on a number of factors. The mineralogical composition of the natural material was the major factor responsible for the natural variety in stone reactivity. The calcium carbonate-rich limestone was naturally more reactive than quartz-rich sandstone under the same environmental conditions. The adsorption of SO2, and thereafter production of
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hemihydrate and gypsum, was dependent on the corrosive gases concentration. The effectivity of impregnation material for the sandstone could not be observed while both chemical and physical properties of the limestone became improved.
5. References Elfving, P., Panas, I., Lindqvist. O., 1994. Model study of the first steps in deterioration of calcareous stone II. Sulphate formation on calcite. Applied Surface Science 78, 83-92. Johansson L-G., Lindqvist O., Mangio R., 1991. Corrosion of Calcareous Stones in Humid Air Containing SO2 and NO2. Durability Build. Mater. 5 439-449. Sahlin T., Malaga-Starzec K., Stigh J., Schouenborg B., (in press). Physical Properties and Durability of Fresh and Impregnated Limestone and Sandstone from Central Sweden Used for Thin Stone Flooring and Cladding. Submitted for publication in the proceedings of the 9 th International Congress on Deterioration and Conservation of Stone. Venice, Italy.
6. Materials The raw sandstone material used in this study is quarried by Wasasten AB, M&ngsbodama, SE-796 99 Alvdalen, Sweden. Tel: +46 251 540 00, fax" +46 251 540 10, email" [email protected]. The raw limestone material is quarried by AB J~imtlandskalksten, Box 25, SE-834 21 Brunflo, Sweden. Tel: +46 63 21860, fax" +46 63 22595, e-mail" [email protected]. The impregnated 4 mm natural stone tile products used in this study has been developed by two companies" Eka Chemicals AB (Eka Chemicals AB, SE-445 80, Sweden. Tel: +46 31 587000, fax" +46 31 587400, e-mail" [email protected]) and Techstone AB (Techstone AB, SE-471 99, Sweden. Tel" +46 304 676560, fax: +46 304 676569, e-mail" [email protected]). For the composition of the impreganation material see tab.2. The trade name for the sandstone is Alvdal Quartzite, and for the limestone J~imtland Limestone. The impregnated 4 mm products have the traditional trade name including Techstone|
Table 2" Components of the impregnation material. Density (kg/m 3) Components Potassium-based water1200 glass (SiO2/K20) Water 1000 Colloidal silica 1200 Berol 048 1020 *0.786 g is added per litre impregnation material solution.
Concentration (Weight %) 64.6 8.5 26.9
357
THE INFLUENCE OF BUILDING ORIENTATION ON CLIMATE WEATHERING CYCLES IN STAFFORDSHIRE,UK. David J. Mitchell* School of Applied Sciences, University of Wolverhampton, Wolverhampton WV11SB, UK David P. Halsey Gyford House, Hereford, HR96EX. UK Karl Macnaughton School of Applied Sciences, University ofWolverhampton, Wolverhampton, UK David E. Searle Built Environment Research Unit/School of Applied Sciences, University of Wolverhampton, Wolverhampton, UK. Abstract
Climate or meteorological induced cycles have been associated with weathering processes of building stone for a long time. Freeze-thaw cycles can have severe effects on stone disintegration. Although less dramatic, other cycles such as heating-cooling and wettingdrying will create similar stresses in stone. Diurnal and seasonal climatic cycles from standard meteorological measurements lack detail on the effects of short-duration rates of change, variations in subsurface gradients and aspect control. During certain synoptic conditions building orientation can have a great influence on climatic extremes of different facades. The use of sensors and data loggers has, to a large extent, opened up the potential for in-depth investigations of general climatic monitoring of the exterior of buildings and cyclic changes in temperature and moisture in stone. Using temperature and humidity sensors located on the four cardinal faces of the tower of Lichfield Cathedral, Staffordshire, UK, the frequency of heating-cooling, wetting-drying and freeze-thaw cycles have been analysed. For most of the cycles, west and south faces have the highest frequency especially the west. In contrast, the north and east have the lowest values, with the north having the least. Although this is a simplified interpretation, more climatic processes are operating on the south and west faces than the east and north faces. These could be loosely termed the 'maritime' and 'continental' faces respectively. In a parallel study of 30 sandstone churches in the West Midlands, the occurrence of 18 forms of weathering with respect to aspect were recorded. Granular disintegration, spalling, multiple flaking, total case hardened stone and total autotrophic stone were all found to be the greatest on the north aspect and, to some extent, on the east aspect. In contrast, relief weathering and total blackened stone were the greatest on the south and west aspects. Keywords: weathering cycles, heating-cooling, wetting-drying and freeze-thaw cycles, Triassic sandstone.
*Author to whom correspondence should be addressed.
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1. Introduction Temperature and moisture conditions are key parameters in mechanical weathering processes of building stone. Rather than extreme meteorological conditions, cyclic changes have greater effects on stress and strains in stone and hence disintegration. Detailed temperature and moisture measurements, using sensors and data acquisition systems, are required to examine the changes oecurring as a result of mechanical weathering processes. The aim of this paper is to assess the influence of orientation on the frequency of climatic cycles. In order to review the potential of detailed monitoring, using sensors and data acquisition systems, a case study at Lichfield Cathedral, UK will be used (Halsey 1996, Halsey et al., 1998). 2. Methodology To assess the effects of aspect on climatic parameters, temperature and humidity sensors were installed 37 m above ground level on the central tower of Lichfield Cathedral, Stafford shire, England (fig 1).
Figure 1 Central tower of Lichfield Cathedral Steel sheathed thermistor probes and 'Vaisala' relative humidity probes were installed on the four cardinal faces of the tower, which is composed of Triassic sandstones (fig. 2). The thermistors (4 mm diameter) were inserted parallel to the exposed face 5 mm from the surface and held in place by thermally conductive adhesive to ensure thermal contact with the stone. The relative humidity probes (25 mm diameter) were inserted in 25 mm deep holes, normal to the surface. Silicon sealant was used to provide airtight seal so that the R.H. of a pocket of air, trapped to a depth of 25 mm beneath the surface, was recorded. Raw data from each sensor was recorded at 15 minutes intervals on a Unidata data logger. The large data set provided a detailed record of the temperature and relative humidity of the four cardinal faces of the tower from January 1994 to November 1996. Furthermore, the time intervals enabled shorter cycles to be calculated besides diurnal changes. Using
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mathematical and logic functions, heating-cooling, wetting-drying and freeze-thaw cycles were derived (tab. 1). To calculate these factors, it is assumed that when the sandstone RH is _>80%, moisture is present in the stone. This is based on the findings of Sereda (1974), which show at inland locations plastic and metal surfaces were wet at a RH of =80%. This assumption has also been used to measure the time of wetness by Henriksen et al., (1993). Climatic data for the same period (January 1994 to November 1996) were extracted from the 'Weather Log" for Elmdon, 24 km south of Lichfield Cathedral.
Figure 2. Temperature and relative humidity sensors in position Table 1. Factors calculated using temperature and relative humidity data, and their ....... descrip tions Factor Description " Rates of temperature Temperature changes per 15 minutes. change (monthly mean, maximum and minimum) Heating-cooling cycles (number month- 1)
Cycles consist of temperatures increasing and then decreasing. When temperatures start to rise again a new cycle begins.
Wetting-drying cycles (number month- 1)
Cycles consist of relative humidity increasing and then decreasing. When relative humidity starts to rise again a new cycle begins.
Time of wetness (minutes month -1 )
The length of time relative humidity is >_80%.
Freeze-thaw cycles (number month- 1)
Freezing occurs when relative humidity is >_80% and temperature is _<0~ A cycle is a period of freezing folowed by a thaw caused b~, a rise in temperature.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Results
Besides orientation, seasonal variability of the climate for the studyperiod had an impact on the climatic cycles. Generally, the seasonal weather pattern for the three years were similar (tab. 2). The 1994-5 winter was very wet with more than 61 raindays and 285 mm precipitation for the three-month period. Usually wet winters tend to be mild, but in this winter 19 air frosts and 31 ground frosts occurred. The 1995-6 winter was drier but colder with a total of 44 air frosts and 56 ground frosts during the three months. The 1994 spring was mild and wet, while spring in the other two years were cold (18-19 air frosts) and dry (30-31 raindays). All three summers were dry and sunny with 86, 90 and 90 sunshine days for 1994, 1995 and 1996 respectively. In all three years the dry summers were followed by wet autumns, especially 1994 with 238 mm precipitation. Table 2: Seasonal climatic data for Elmdon Season Highest Lowest No. Air Temp ~ Temp ~ Frogs 1994
13.1
winter (2 mths)
Sprms
1994-5 ,
1995-6
Summer Autumn Winter Spring Summer Autumn Winter Spring Summer Autumn
.
20.5 31.1 21.1 15.2 25.8 32.2 23.5 11.9 23.8 30.6 22.7 .
" .
-6.9
23
38
Total Sun S~ne Hours 143
-1.5 4.4 -1.5 -7.5 -5.5 1 -5.6 -9 -4.2 2.4 -4.1
3 ..... 0 3 19 19 0 9 44 18 0 15
32 3 21 31 31 7 19 56 46 11 26
431 659 277 196 564 743 341 151 366 709 339
.
,
.
.
.
No. Ground F~s
.
.
.
.
.
Sun s~ne Days
Rain Days
42
Total Rain~11 mm 131
80 86 70 64 66 90 75 46 70 90 78
181 108 238 285 99 68 197 177 98 110 133
51 31 47 61 31 22 43 45 30 37 43
,
.
.
.
.
.
35
.
. . . .
, ,
Seasonal monthly averages for heating-cooling, wetting-drying and freeze-thaw cycles have been calculated for each orientation of the Cathedral tower as shown on figures. 3, 4 and 5 respectively. The greatest number of heating-cooling cycles occurred in spring and summer 1995, probably due to the particular sunny conditions. In both these seasons the greatest number of heating-cooling cycles occured on the east fasade. Generally the greatest number of heating-cooling cycles occured on west facing facades, followed by the south facing fasade. This pattern is repeated nine out of the twelve seasons with the north and east facing facades being numerically very similar. Complete results for wetting-drying cycles are only available from summer 1994 because of initial problems with the humidity sensors. The lowest number of wetting-drying cycles occurred during the 1995-6 winter. Although the winter was moderately wet, the number of sunshine days were low (46 days) and the greatest number of freeze-thaw cycles occurred. With these conditions, wetting occurred but the cycle was not completed by a drying phase. In contrast, spring and summer 1995 were dry with only 31 and 22 rain days respectively, but drying processes were assisted by the sunny conditions. As found with the heatingcooling cycles in these two seasons the wetting-drying cycles were the greatest on the east
Average monthly heating-cooling cycles
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362
Average monthly wetting-drying cycles
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Average monthly freeze-thaw cycles
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fa~}ade. As expected, during autumn, westerly synoptic conditions increased the number of wetting-drying cycles on the western facade of the tower. The number of freeze-thaw cycles are far less than the other two cycles because of the relatively mild winters. As expected, the greatest number of freeze-thaw cycles occur in the winter months, with coldest winter of 1995-6 having the greatest number of cycles. As expected, freeze-thaw is prominent on the north faqade, but equally numerous, on occasions on the west fa~;ade. Whereas the shaded north face remains cold, the west face can complete more cycles in response to changing synoptic conditions and direct insolation. 4
Discussion
Heating and cooling are important in insolation weathering ( Smith 1977). Occurrence of heating and cooling rates, show marked differences associated with seasons and aspect (fig. 3). As expected, rates of heating and, in most cases, cooling, occur least on the northern face, because of no direct insolation. The other faces respond to the diurnal passage of the sun, but the average number per month of heating and cooling periods are much greater on the west than the east face, except for winter, spring and summer 1995. With maximum summer temperatures >30~ heating-cooling cycles establish temperature gradients in stone, creating compressive and tensile stresses, as recorded by Warke and Smith (1994). Besides obvious seasonal differences, the frequency of heating-cooling cycles are influenced by aspect. Heating is dominated by direct insolation, but ambient temperatures are also important as illustrated by the occurrence of cycles on the shaded north-facing surface. In western margin temperate climates, numerous causes can result in surface cooling, such as changes in shade, precipitation and wind speed and direction. These controls as expected have greater influences on the south and west aspects, causing greater number of cycles in all four seasons (fig. 3). In this case study, wetting-drying cycles have a similar pattern to heating-cooling cycles with the greatest frequency during summer (fig. 4). It is reasonable to assume that wettingdrying cycles in Lichfield Cathedral will correlate closely with heating-cooling cycles because the heating process will aid drying. The frequency of wetting-drying cycles are probably much greater in the south and west, than the north face, due to the effects of driving rain. As found in some early simulation experiments, moisture plays a significant role in insolation weathering. Therefore, the common association of these two cycles may lead to greater stresses in the stone. With the mean monthly change in relative humidity being small and problems associated with the probes, analysis of these results are limited. Changes in stone temperature and moisture content are dominant conditions for physical salt weathering mechanisms to occur on the Cathedral stone. Temperature and relative humidity probes enable the measurement of freeze-thaw cycles to be calculated. Due to the mild winter of 1994-5, the number of freeze-thaw cycles were relatively low (fig. 5). For most of the cycles west and south faces have the highest frequency especially the west. In contrast the north and east have the lowest frequency of cycles. With the exception of freeze-thaw cycles, the north has the least active cycles. Although this is a simplified interpretation, more climatic processes are operating on the south and west faces than the east and north faces. These could be loosely termed the 'maritime' and 'continental' faces respectively.
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In a parallel study of 30 churches, built of ferruginous sandstone, in the West Midlands, Halsey (1996) recorded the occurrence of 18 forms of weathering with respect to aspect. Granular disintegration, spalling, multiple flaking, total case hardened stone and total autotrophic stone were all greatest on the north aspect and, to some extent, on the east aspect. In contrast, relief weathering and total blackened stone were greatest on the south and west aspects.
5. Conclusions This study of Lichfield Cathedral demonstrates the value of sensors and data loggers in monitoring climatic cycles in relation to building orientation. Over 35 months data from eight sensors generated variable results for the four cardinal faces of the tower. The study illustrates that even in a temperate period, with few extreme conditions, detailed monitoring can identify the multitude occurrence of many cycles, although low in magnitude. Further work in progress will measure the frequency of high magnitude cycles which have greater effects on stone deterioration. Acknowledgements We are grateful to the UK Engineering and Physical Science Research Council for funding this research. Martin Stancliffe of Martin Stancliffe Architects Ltd kindly allowed the use of Lichfield Cathedral for monitoring purposes and provided financial assistance with equipment. We are grateful to Fred Handy for help with the photographs.
References Halsey, D.P. (1996): The Weathering of Sandstone, with Particular Reference to Buildings in the West Midlands, UK. Ph.D. thesis, University of Wolverhampton. Halsey D.P., Mitchell D.J. and Dews, S.J. (1998): Influence of climatically induced cycles in physical weathering.- Quart. J of Eng. Geology. 31, Pt 4:359-368. Henriksen, J. et al (1993) Monitoring of the wetness impact on buildings by means of a new instrument for continuos recordings. In Theil, J (ed.) Conservation of stone and other material Vo|. 2 784-791. E & F N Spon, London. Sereda, P. (1974) Weather factors effecting the corrosion of metals. In Corrosion in Natural Environments, ASTMSTP 558 7-22. Smith, B.J. (1977): Rock temperature measurements from the northwest Sahara and their implications for rock weathering. Catena. 4:41-63. Warke, P. & Smith B (1994): Short-term rock temperature fluctuations under simulated hot desert conditions: some preliminary data in Robinson, D and Williams, R (Eds.) Rock Weathering and Landform Evolution. J. Wiley & Sons, Chichester, 57-70
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CORROSION OF LIMESTONE IN HUMID AIR CONTAINING SULPHUR AND NITROGEN DIOXIDES: A MODEL STUDY Beatrice Moroni*, Giampiero Poli Department of Earth Sciences, Perugia, Italy
Abstract
Laboratory experiments were performed by exposing limestone samples to the corrosive action of SO2 (lppmv) and N O 2 (6ppmv) at constant temperature (25~ relative humidity (about 100%) and dynamic flow conditions (300cc/min) within a testing apparatus simulating dry deposition of pollutants. The obtained results point to a marked slowdown of the sulphation process in the short time and to an apparent resumption of sulphation after about twenty days from the beginning of the experiments. The trend of the experimental points was approximated by means of two different fitting curves, with logarithmic form in the initial stage and simple linear form in the subsequent stage. This led to some considerations on the relative rates of formation of the reaction products, calcium sulphite hemihydrate and gypsum, at different pollutants concentrations. A multistep genetic model was formulated by taking into account the influence of nucleation and growth of the reaction products in the progress of sulphation. Key words: limestone sulphation, laboratory experiments, liquid chromatography, X-ray diffraction, fitting functions, genetic model 1. Introduction
Dry deposition of pollutants, such as SO2 and NO2, is the most active process in urban areas because it affects large extents of material for long periods of time (Haneef et al. 1993). Laboratory tests have been performed on different carbonate rocks in order to study the influence of the gas mixture reacting with the stones (Haneef et al. 1992; Yerrapragada et al. 1994), with special interest to the role of NO2 in sulphation (Johansson et aL 1988; Vassilakos & Salta 1993; Elfving et aL 1994a, b). Other studies have been focused on the influence of the intrinsic properties of the exposed materials, particularly the texture and the presence of adsorbed or condensed humidity (Gauri et aL 1982/1983; Spiker et aL 1992a, b; Kozlowski et aL 1992), on the rate and extent of sulphation attained. A few efforts have been made also to derive a kinetic model of sulphation (Kulshreshtha et aL 1989; Yerrapragada et al. 1994). The aim of the present study is to describe in more detail the mode of interaction of SO2, alone or combined with NO2, with limestone and to derive a general model of sulphation. Previous, short-term laboratory experiments (Moroni & Poli 1996) established a marked slowdown of the sulphation process after a short period of reaction. New long-term experiments have been performed in order to check the intrinsic validity of this observation and to interpret the kinetic behaviour of the material. The results of these new laboratory investigations are the subject of the present paper.
*Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
2. Experimental
Laboratory experiments were performed by exposing fresh samples of limestone to constant environmental conditions within a special corrosion testing apparatus simulating dry deposition of pollutants. The complete experimental procedure is described elsewhere (Moroni & Poli 1996). The experiments were performed at constant temperature (25~ _+0.1~ and :7:100% relative humidity. The pollutant atmosphere was a mixture of air and SO2 alone (lppmv :~0. l ppmv) or combined with NO2 (6ppmv _ 0.Sppmv) in dynamic flow conditions (300co/rain -+30cc/min). The duration of the experiments was from about sixty to about ninety days. The samples were removed from the reaction vessel at fixed times and analyzed by means of liquid chromatography, X-ray diffraction and scanning electron microscopy to monitor the progress of sulphation. Liquid chromatography was performed on solutions obtained after oxidation of the dried and hand grinded samples with H202 in water (6%) in ultrasonic bath and filtering of the solutions. The validity of the method was tested by analyzing the precipitate of the solution through X-ray powder diffraction analysis. The sole presence of calcite, quartz and clay minerals, which are the constituents of the original limestone, within the precipitate evidenced that complete leaching, oxidation and dissociation of the reaction products was attained. The analytical precision is better than 5%. X-ray diffraction was performed on the bulk solid samples using a Bragg-Brentano diffractometer equipped with graphite curved-crystal monochromator in the diffracted beam, 1~ divergence and anti-scatter slits and 0.1 ~ receiving slit. Step-scan data (step width 0.02 ~ counting time 15 seconds per step) were collected over the range 20-60 ~ 20 and treated by the Rietveld quantitative phase analysis structure refinement method (Rietveld 1969) using the LS1 computer program by Lutterotti et al. (1992). Precision is better than 5% for the most abundant phases (> 50 wt%), and better than 10% for the other phases. Scanning electron microscopy was performed on the external surface of the samples after graphite coating. The textural details under consideration, such as the mode and extent of development of the reaction products upon the surface, were evidenced by secondary electron observations and EDX sulphur distribution maps.
3. Results
The results of the new long-term experiments confirm the initial slowdown of the sulphation process observed in the previous short-term experiments, but point also to an apparent resumption of sulphation aiter about twenty days from the beginning of the experiments. Besides, they confirm the presence of calcium sulphite hemihydrate and gypsum as reaction products. Reproducibility was tested by comparison with homologous data from a previous short-term experiment performed at lppmv SO2 concentration. Reproducibility of chromatographic data is quite good in the short time, but progressively decreases in the long term. Reproducibility of X-ray diffraction data is quite low, ranging from 10 to 30% for sulphite and from 25 to 50% for gypsum, quite stable with time for sulphite, and decreasing with time for gypsum (fig. 1).
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000 600,
|
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,
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400 a[sdl (%) 300
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4 23/33% ~
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/~....
200 100
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(a) t 24 ,
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.... 1 24days
Figure 1: Reproducibility of chromatographic (a) and diffractometric (b) experimental data. Short-term and long-term experiments performed at l ppmv SO2 concentration. In (b), solid symbols and lines for sulphite, open symbols and dot lines for gypsum, reproducibility values reported for sulphite and gypsum in the order. In spite of these limitations, and in consideration of the complexity of the physical-Chemical system reproduced in the laboratory simulations, we tried to apply an empirical approach in the kinetic treatment of the experimental data by means of a trial-and-error technique of purely mathematical manipulation of the curve best-fitting method. Two empirical fitting equations, with logarithmic form and simple linear form, were determined. The former is to describe the initial period, whereas the latter fits the subsequent period of resumption of sulphation. Comparison between the fitting curves describing the chromatographic experimental data (tab. 1; fig.2) shows that addition of NO2 at the given concentration leads to a change from a deceleratory to a faintly acceleratory process of ion sulphate production in the initial period (n from 0.2 to 1.03), and to a 25% increase of the rate of sulphate production in the subsequent resumption period (b from 20.09 to 24.67). Table 1" Fitting parameters of the best-fit curves of chromatographic data y=kx n y=a+bx _, SO2 NO2 k n R a b 1 142 0.2 0.65 38.39 20.09 1
6
8.25
1.03
0.96
-2.56
24.67
R
0.96 0.86
X-ray diffraction shows that calcium sulphite hemihydrate is the main reaction product in the presence of SO2 alone, whereas gypsum is the only reaction product in the presence of SO2 and NO2 (fig. 3). Examination of the fitting parameters (tab. 2) and mathematical derivation of the fitting cuves shows that in the experiment performed in the presence of SO2 alone the rate of
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
sulphite formation is always higher than the rate of formation of gypsum, but the ratio between the rates changes from 4:1 at the end of the initial period to 5:1 in the resumption period. In the experiment performed in the presence of SO2 and NO2, instead, the rate of formation of gypsum is 1.5 times lower than the rate of gypsum formation in the presence of SO2 alone at the end of the initial period, but drastically increases in the resumption period up to a value which is 5 times higher than the rate of formation of gypsum, and similar to the rate of formation of sulphite in the experiment performed in the presence of SO2 alone. The products of reaction form in preference on the micritic matrix rather than on the sparitic cement of the limestone. They are so small in size in the initial period that they cannot be 2500 observed directly by scanning electron A microscopy, but only evidenced indirectly by 2000 EDX sulphur distribution maps. Visible grains a .."" 9 few microns in size can be observed only in the 1500 resumption period. ~ ...- " ' .
.
.
.
.9
1000
Figure 2: Percent variation of retained sulphate ion contents as a function of the exposure time for samples exposed to air containing SO2 alone (solid symbols and line) or combined with NO2 (open symbols and dot line).
A
500 /X ~A/IJA |
0
,
/" I
,, J
20
time(days) |
40
|
I
|
60
I
80
Table 2: Fitting parameters of the best-fit curves of X-ray diffraction data y=a+bx y = k xn (lny = Ink +n lnx) SO2 NO2 k n R a 0.31 1 sulphite 0.47 0.58 0.70 -3.44 0.06 gypsum 0.18 0.68 0.59 -0.30 1
6
sulphite gypsum
. 0.72
.
. 0.2
. 0.69
-1.99
,
i
I00
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0.96 0.78
0.95
0.29
4. Discussion
The obtained results are in general accordance with those obtained in the previous, shortterm laboratory experiments performed at higher SO2 concentrations and different SO2/NO2 ratios (Moroni & Poli 1996), so evidencing that the processes active in sulphation are the same independently from the concentration of the pollutant gases in the environment. In particular, two different reaction mechanisms have to be taken under consideration. The first mechanism, which is active in the presence of SO2 alone, is characterized by the formation of calcium sulphite hemihydrate as intermediate product in the transformation of calcite into gypsum: 1
1
CaC03 +S02 +-~H20 --+CaS03 "-~H20 +C02
(1)
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
1 3 CaS03 " H 2 0 + -~02 + -~ H z O
~
371
(2)
C a S O 4 92 H 2 0
The second mechanism, which is active in the presence of SO2 and NO2 in the reaction vessel, is characterized by direct formation of gypsum from calcite: CaCO 3 + SO 3 + 2 H 2 0 --->CaS04 . 2 H 2 0
(3)
+ CO 2
It is strictly related to preliminary oxidation of sulphur dioxide (SOz) to trioxide (SO3) by NO2. 2o
|
9
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,
!
,
!
,
|
,
i
!
,
!
wt%
!
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!
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!
,
I
!
,
25
[lppmv SO2 + 6ppmv NO2 I
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0
,
I
10
,
I
20
,
I
i
i
30
40
50
,
i
60
,
i
l
70
0
i
I
20
i
I
40
60
,
I
80
,
100
Figure 3" X-ray diffraction quantitative data as a function of time for samples exposed to air containing SO2 alone or combined with NO2. Solid symbols for sulphite, open symbols for gypsum.
Application of the logarithmic fitting function to the previous short-term experimental data and plotting of the exponent of these curves versus the corresponding SO2 concentrations and SOJNO2 ratios gives interesting results (fig. 4). In fact it shows that in the presence of SO2 alone in the reaction vessel the formation of sulphite is an acceleratory process (n>l) at very high SO2 concentration, whereas the process of formation of gypsum is acceleratory only in the range 5-10ppmv SO2. In the presence of SO2 and NO2 in the reaction vessel, instead, direct formation of gypsum (reaction 3) is practically the only reaction path for SO2/NO2 ratios lower than 25, the formation of sulphite is an acceleratory process for SO2/NO2 ratios lower than 50, whereas the formation of gypsum is, surprisingly, acceleratory only for a 25 SO2/NO2 ratio. This is of particular interest since ambient levels of NO2 may now exceed the concentration of SO2 in many parts of the world (Yerrapragada et al. 1994). Application of the simple linear fitting function to the resumption period in the new longterm experiments shows that addition of NO2 has greatest effects on the rate of formation of gypsum, and leads to the shortening of the initial deceleratory period for an early activation of the resumption period. This is an evidence of the strong oxidizing properties of NO2 at humid
372
9th I n t e r n a t i o n a l C o n g r e s s on D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f Stone, Venice 19-24 J u n e 2000
conditions (Elfving et aL 1994b). In any case it is clear from the results that the rates of formation of the reaction products drastically increase in this period independently on the reaction mechanism. This particular occurrence may be explained with a change of the leading process of sulphation from the deceleratory to the resumption period. 0
Figure 4: Fitting parameters of the logarithmic form equations versus SO2 concentrations and SOjNO2 ratios for the previous (Moroni & Poli 1996) and present experiments. Solid symbols for sulphite, open symbols for gypsum; solid lines for the experiments performed in the presence of SO2 alone, dot lines for the experiments performed in the presence of SO2 and NO2.
10
i
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20
l
30
,
40
|
50
so~zNo~
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I
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4
6
8
10
12
14
16
The obtained results suggest that nucleation alternates with growth as leading processes in the development of sulphation. In particular, we observed from scanning electron microscopy sulphur mapping that the products of reaction are not visible till the resumption period. This occurrence may be explained assuming that nucleation of the reaction products is the leading process in the initial period of sulphation, whereas growth of the products is the leading process in the subsequent period of resumption of sulphation. Moreover, the logarithmic form of the fitting function of the experimental data in the initial deceleratory period is a typical equation describing a multi-step nucleation process (power law; Bamford & Tipper, 1980). Consideration of the influence of nucleation and growth processes during sulphation leads to the derivation of a genetic model describing the total process of sulphation. In the first period, described by the logarithmic form function, pollutant gases and ambient humidity are rapidly adsorbed on the surface of the material. The gases dissolve in the adsorbed film of water where they react with the solid substratum following the mechanisms already described. In this period the polycrystalline system resulting from the chemical reactions is not in thermodynamic equilibrium owing to the different dimensions of the crystals, and minimization of the surface free energy of the solid phase is attained through dissolution of the smaller crystals and growth of the larger crystals (ripening; Morse & Casey 1988). This period is terminated by the development of stable nuclei. The second period of sulphation, described by the simple linear form function, starts with the development of stable nuclei and is characterized by the growth of such nuclei.
Acknowledgements We are grateful to A. Dipaola for the helpful co-operation in the experimental and analytical work. This study was supported by C.N.R. of Italy (Comitato per la Scienza e la Tecnologia dei Beni Culturali and Progetto Finalizzato Beni Culturali).
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
373
References
Bamford C.H., Tipper C.F.H., 1980. Comprehensive chemical kinetics Vol.22, pp. 41-113. Elsevier, Amsterdam. Elfving P., Panas I., Lindqvist O., 1994a. Model study of the first steps in the deterioration of calcareous stone I. Initial surface sulphite formation on calcite. Applied Surface Science, 74, 91-98. Elfving P., Panas I., Lindqvist O., 1994b. Model study of the first steps in the deterioration of calcareous stone II. Sulphate formation on calcite. Applied Surface Science, 78, 83-92. Gauri K.L., Popli R., Sarma A.C., 1982/1983. Effect of relative humidity and grain size on the reaction rates of marble at high concentrations of SO 2. Durability of Building Materials, 1, 209-216. Haneef S.J., Johnson J.B., Dickinson C., Thompson G.E., Wood G.C., 1992. Effect of dry deposition of NOx and SO2 gaseous pollutants on the degradation of calcareous building stones. Atmospheric Environment, 26A, 2963-2974. Haneef S.J., Johnson J.B., Thompson G.E., Wood G.C., 1993. Effects of dry deposition of pollutant gases on the degradation of pentelic marble. Corrosion Science, 35, 743-750. Johansson L.G., Lindqvist O., Mangio R.E., 1988. Corrosion of calcareous stones in humid air containing SO2 and NO2. Durability of Building Materials, 5, 439-449. Kozlowski R., Hejda A., Ceckiewicz S., Haber J., 1992. Influence of water contained in porous limestone on corrosion. Atmospheric Environment, 26A, 3241-3248. Kulshreshtha N.P., Punuru A.R., Gauri K.L., 1989. Kinetics of reaction of SO2 with marble. Journal of Materials in Civil Engineering, 1, 60-72. Lutterotti L., Scardi P., Maistrelli P., 1992. LS1- a computer program for simultaneous refinement of material structure and microstructure. Journal of Applied Crystallography, 25, 459-462. Moroni B., Poli G., 1996. Corrosion of limestone in humid air containing SO2 and NO2: results aiter short-term laboratory experiments. Science and Technology for Cultural Heritage, 5,7-18. Morse J.W., Casey W.H., 1988. Ostwald processes and mineral paragenesis in sediments. American Journal of Science, 288, 537-560. Rietveld H.M., 1969. A profile refinement method for nuclear and magnetic structures. Journal of Applied Crystallography, 2, 65-71. Spiker E.C., Comer V.J., Hosker R.P., Sherwood S.I., 1992a. Dry deposition of SO2 on limestone and marble: role of humidity. Proceedings of the VIIth International Congress on Deterioration and Conservation of Stone, Lisbona. 397-406. Spiker E.C., Hosker R.P., Comer V.J., White J.R., Werre Jr. R.W., Harmon F.L., Gandy G.D., Sherwood S.I., 1992b. Environmental chamber for study of the deposition flux of gaseous pollutants to material surfaces. Atmospheric Environment, 26A, 2885-2892. Vassilakos C., SaRa A., 1993. Synergistic effects of SO2 and NO2 in their action on marbles studied by reversed flow gas chromatography. Conservation of stone and other materialsVolume one: causes of disorders and diagnosis. Proceedings of the International RILEM/UNESCO Congress, Paris. 99-106.
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Yerrapragada S.S., Jaynes J.H., Chirra S.R., Gauri K.L., 1994. Rate of weathering of marble due to dry deposition of ambient sulfur and nitrogen dioxides. Analytical Chemistry, 66, 655659.
375
THE D O R I A P A M P H I L J E X H I B I T I O N ENVIRONMENTAL CONDITIONS
GALLERY:
A
STUDY
OF
THE
Domenico Artioli, Annamaria Giovagnoli*, Maria Pia Nugari Istituto Centrale per il Restauro, Rome, Italy Alessandra Ivone Graduating in Chemistry at the University of Rome "La Sapienza", Rome, Italy Giorgia Lonati Piazza Baldini 13.00141 Rome, Italy
Abstract This work concerns a study of the air quality in some rooms of the Doria Pamphilj Gallery in the centre of Rome, from a chemical and a biological point of view. The Doria Pamphilj Gallery is an exhibition gallery of historical value, not only because it contains a precious painting collection but also because it is intimately connected with the history of the collection itself. In fact, the gallery is inside the historical private residence of the Doria Pamphilj family and for this reason the building can not meet all the requisites for a right conservation of works of art. The aim of this work is threefold: a) to define the state of conservation of the artefacts as regards the environment, b) to determine if it is necessary to make changes in the building (for example concerning the window frames or the lighting, etc.) c) to fix a permanent maintenance project. The programme provides a series of environmental monitoring campaigns relative to chemical and biological aggressors carried out in different seasons to put into evidence the influence of the climatic parameters on the internal pollution charge. The study has been carried out in two rooms, the fifteenth century and the seventeenth century rooms, that are the most significant because in the last two years they have undergone improvements and adaptations to the indoor museum standards and because they face a street with heavy car traffic. The method and the primary results obtained are presented.
Key words: air quality, aerobiology, environmental monitoring, gallery, museum, dangerousness, suspended particulate.
I. Introduction The control of the air quality of museum environments still represents a complex problem and needs the intervention of experts of different disciplines. The difficulties are often represented by the fact that the researches regard environments and structures built for purposes different than those of expository ones that, in time, have undergone readaptations and modifications whose characteristics are often unknown. The case of the Doria-Pamphilj Gallery represents an example of a private gallery opened only successively to the public. For this reason, in the past numerous maintenance interventions and readaptations were deemed necessary for a more suitable fruition of the works of art and to respond to the changes brought about by the presence of visitors. The gallery is located in the centre of Rome on the first floor of an historical
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
building and one of the four sides of this building faces Via del Corso, a road of heavy car traffic and lined on both sides by buildings (an urban Canyon). For a correct conservation of artefacts exhibited in a museum, particular attention must be given to the monitoring and to the control of the precursory factors of deterioration, for example the thermohygrometrical parameters, the lightening and the quality of the air from a chemical and a biological point of view (De Santis, 1997). Environmental modifications of the mentioned parameters could depend on various factors including heating, cleaning, management and even flow of visitors. To ensure right conditions of conservation it is necessary to know if these factors interact between themselves and if they exercise a negative action on the materials in the museum (Brimblecombe, 1990; De Bock et al., 1996; Pasquariello et al., 1998; Nugari et al., in press). Although a standardised methodology does not exist, we can specify some guidelines on the modalities of investigations. In particular, monitoring must consider: - the rooms exposure; - internal-external interchange (openings of doors and windows); the opening to the public; the maintenance modalities; - the heating cycles. The monitoring of the air quality should let us to know the risk of microbial contamination and chemical attack, to determine the quality and quantity of the aerodispersed species, to evaluate the dangerousness of the environment on the exhibited materials. Consequently it is possible to reduce the levels of risk, compatible with the limits imposed by an historical building, also identifying some easy and at low cost interventions to carry out. Air is an important medium in the diffusion of aerodispersed pollutants (suspended particulate, fungi and bacteria). Their significant presence in the air of indoor environments could cause damages to artefacts, other than that of human health. A high concentration of particulate could determine in fact, if the mechanisms of deposit are efficient, a blackening of the surfaces and consequent deterioration of the materials. The biological component of the particulate, composed mainly by fungi spores, represents one of the most frequent microbiological causes of deterioration to paintings and other organic materials, as long as the microclimatic conditions are favourable to their development and reproduction (Sorlini., 1993; Ranalli et al., 1995; Pasquariello et al., 1998; Sbaraglia et al, 1999). With regard to the project "Map of Cultural Heritage", a programme has been developed for the control of the environmental conditions of the Doria Pamphilj Gallery in relationship with the state of conservation of the works of art, in order to produce a maintenance chart based not only on the vulnerability of the materials exhibited and their state of conservation, but also on the environmental-air dangers (Ministero dei Beni Culturali ed Ambientali - Istituto Centrale per il Restauro, 1996).
2. Materials
and
Methods
In this study, the investigations were carried out in two rooms, the room known as the '400 and that called the '600 one, for two reasons. The first because they face a road with heavy car traffic and the second, because recently some interventions were
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carried out to adapt these rooms to the exhibition standards (application of screen to reduce sun light, lighting system, new arrangements of the exhibition of canvas and panel paintings). The project provides four campaigns of seasonal monitoring for chemical and biological parameters and a continuous survey of the microclimatic ones. In particular, sampling is carried out on the total suspended particulate (TPS) and on the aerodiffused micro flora. The investigations were performed outside and inside of the gallery, considering that the opening hours of the gallery are from 10 a.m. to 6 p.m., every day except Thursdays. For the chemical analyses, the sampling of the TPS was carried out on Millipore filters (cellulose acetate), O 47 mm and 0,45 pm of porosity, with a speed of suction of 20 litres/minute. On each sample the following analysis were conducted: gravimetric analysis for the total particulate; - PIXE analysis for elemental characterisation of the particulate; - ionic chromatography for the soluble species. For PIXE analysis the samples are taken in two different time sections, before the opening to the public (7 - 10 a.m.) and after closure (7 - 10 p.m.); for the ionic chromatography analysis, the sampling was done in a daytime and a night-time period (8 a . m . - 8 p.m. and 8 p . m . - 8 a.m.). For aerobiological analysis the sampling was carried out by the Surface Air System (S.A.S.), collecting 20 litres of air on suitable cultural media; for the isolation of bacteria Plate Count Agar (PCA) was used whilst for the fungi Czapek Yeast extract Agar (CYA) and Rose Bengal Agar (RBA) the last one restricts the growth of fungi and aids the isolation of slow growing species. To verify the contamination induced by visitors, a quantitative determination of the air concentration of Staphylococcus aureus is carried out by the coagulase test (Staphylococcus aureus coagulase +). The detection of microbiological parameters is performed before (9 a.m.) and during the opening hours (12 p.m.) of the museum to point out the effects of the visitors on the bacteria charge. At the same time the environmental monitoring on the outside is followed out by a survey mobile unit for four seasons. The data obtained will be utilised for the elaboration of a microscale model of urban pollution. Portable X-fluorescence at low and high energy will be used to identify the characteristics of the particulate deposited on the surface of the works of art. During the time of monitoring, a survey of the state of conservation of the artefacts is executed by means conservation data cards.
3.
Results
At present, there is not sufficient data and information available, because the study is still in progress. Only at the end of the monitoring will be possible to compare statistically significant data and to make some definitive hypotheses on environmental dangerousness. However, from the results obtained of the analysis of the first monitoring campaign carried out between the spring and summer of 1999, it seems possible to identify the trends and to make comparisons that show synergetic effects of various
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
factors of the air quality. Useful observations may be also done for a better aimed planning with respect to the specific characteristics of examined rooms. In order to suspended particulate collected outside and inside of the gallery the chemical results (tabs. 1 and 2) have pointed out that the values of the fine-dust vary from 14,2 to 83,7 lxm/m3 inside (the maximum corresponds to the closure day of the gallery), whilst from 76,4 to 258,6 lxm/m3 outside with a constant day trend superior to the night one (the value of 42,5 l.tm/m3 recorded on the outside is relative to a rainy day). As regards the elemental analysis of the particulate the presence of two components clearly distinguished was observed: one component of natural origin (AI, Si, Ca, Ti, Fe) and one from anthropogenic sources (S, Cu, Zn, Br, Pb), besides the presence of elements due to marine aerosol (C1, Na) (tabs. 1 and 2). Table 1: Outdoor data PIXE. (lag/m3)
Elements Na K C1 S Ca Si Ti Fe Cu Br Pb TSP
P2/7-1Oam P3/7-1Opm P4/7-1Oam P5/7-1Opm P6/7-1Oam P7/7-1Opm 0.59 1.21 1.36 2.08 8.29 5.28 0.10 4.59 0.23 0.10 0.36 132.04
0.62 1.77 1.30 2.72 6.75 6.96 0.11 6.57 0.32 0.18 0.22 137.99
0.63 2.20 2.15 3.97 11.88 7.74 0.39 8.28 0.34 0.08 0.40 168.52
0.63 2.59 2.07 4.33 12.17 11.26 0.56 7.57 0.29 0.15 0.45 140.57
0.64 2.68 3.31 5.52 10.85 11.50 0.40 6.19 0.24 0.22 0.56 258.62
0.63 2.49 2.81 6.60 9.38 8.73 0.41 5.97 0.28 0.15 0.57 141.46
Table 2: Indoor data PIXE. (lag/m3)
Elements Na K C1 S Ca Si Ti Fe Cu Br Pb TSP
P2/7-1Oam P3/7-1Opm P4/7-1Oam P5/7-1Opm P6/7-1Oam P7/7-1Opm 0.36 0.31 1.37 0.53 0.46 0.71 0.07 0.33 0.02 0.03 0.08 26.87
0.36 0.29 1.21 0.77 0.49 0.64 0.07 0.23 0.02 0.03 0.08 26.98
0.36 0.33 1.29 0.93 1.06 0.94 0.07 0.53 0.02 0.03 0.08 27.75
0.36 0.30 1.67 1.25 0.99 1.18 0.07 0.44 0.02 0.03 0.08 83.71
0.36 0.32 1.27 1.11 0.96 1.42 0.07 0.66 0.02 0.03 0.08 27.01
0.36 0.20 1.70 1.48 1.07 1.31 0.07 0.40 0.02 0.03 0.08 27.02
The analysis of the soluble salts in the particulate (tabs 3 and 4) put into evidence that during the day the anthropogenic component is more evident than during the night and that during the closure the particulate is enriched by sodium and potassium probably due to the detergents used in cleaning operations.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Table 3: Outdoor data Ion Chromato :raphy. (~tg/m 3) GC2 night GC3 day GC4 night GC1 day Ions 1.29 0.69 3.35 Na 2.59 K 0.70 0.19 0.24 0.58 C1 3.93 2.65 2.67 0.90 SO42 5.56 2.64 3.35 1.91 Ca 3.56 1.94 3.44 1.89 NH4 + 0.00 0.00 0.00 0.37 NO3 3.84 2.65 4.33 1.84 PST 110.18 76.40 124.60 42.53 Table 4: Indoor data Ion Chromatogr ~phy. (~tg/m3) Ions GC1 day GC2 night GC3 day GC4 night 0.29 0.17 Na 0.00 0.00 K 0.16 0.18 0.00 0.00 Cl 0.46 0.75 0.76 0.00 S0421.74 0.41 0.43 0.75 Ca 0.00 0.00 0.00 0.00 NH, § 0.18 0.00 0.00 0.00 NO30.84 0.00 0.25 0.00 PST 35.19 14.17 35.19 21.22
GC6 day 0.26 0.23 1.27 3.75 2.92 0.71 3.47 156.68
GC6 day 18.02 12.93 1.86 1.08 2.34 0.34 0.81 35.37
379
GC7 night 0.20 0.61 1.26 5.01 3.54 1.10 2.23 128.83
GC7 night 5.31 4.37 2.68 1.43 0.00 0.08 0.00 14.21
The aerobiological investigation has put into evidence that the major total microbial charge, on the inside and the outside, is more evident during the first hours of the day rather than the middle hours: this is an antithesis with what is a normally detected in non-urban environment with a low pollution level.
hours and days Figure 1: Fungal charge trend inside
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
The fungal charge varies from 325 to 1825 CFU/m 3, the bacterial one from 50 to 500 CFU/m ~ inside of the gallery, whilst outside the former from 525 (relative to a rainy day) to 2400 CFU/m 3, and the latter from 100 to 500 CFU/m 3. The fungal charge trend inside the gallery follows on the average that surveyed outside: a reduction in the middle hours of the day was detected. Moreover, differences were observed in relation to the rooms examined: the '600 room, which is a passing-through room and communicates with a large salon, seems to be the most disturbed as demonstrated by the variable presence of fungi (fig.l). The count of the mesophile bacteria demonstrated on the other hand, and as foreseen, an increase corresponding to the hours when there is a maximum flow of visitors (fig.2).
hours and days Figure 2" Bacterial charge trend inside The presence of Staphylococcus aureus seems not to vary significativelly in relation to the flow of visitors although it is necessary to emphasise the fact that during the period of investigations the number of visitors was not high Concerning the fungal species, there exists at qualitative level a significative diversities between the species identified outside and those inside; in fact, a predominance of biodeteriogen for the canvas paintings strains is evident inside (Aspegillus flavus, Aspergillus fumigatus, Penicillium spp.); this can be connected to the presence of a fungi attack on some artefacts positioned in a nearby room to the one being examined. In fact, during the investigations on the state of conservation of artefacts, the presence of fungi colonisation on some of them was identified. The comparison between the chemical and the biological data shows that the increase of the anthropogenic component in the particulate corresponds to a decreasing of the fungi spore concentration. The maintenance operations that are carried out during the closure day determine an increase not only of the particulate
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concentration but also of the microbial charge observed yet again during the first hours of the successive day (tabs. 2 and 4, fig. 2).
4. Conclusions From the analysis of the results obtained it is observed that, owing to the complexity of the studies of the air quality of the exposition spaces, it is fundamental to carry out orientative preliminary investigations, to optimise times and modalities for the monitoring procedure. For example, the two different period chosen for the sampling are insufficient to emphasise the trend of the monitored species, with regard to the management of the gallery; the only elemental analysis of the particulate, if not associated with the morphological study, does not permit a clear identification of its origin. The research of the Staphylococcus aureus, which indicates the microbial pollution due to the visitors, must be carried out in the period of the maximum presence of the public or in correspondence to the manifestations that determine situations of major environmental risks. Although principally the pollution in an internal site depends on air exchange between outside and inside, this research shows that it is necessary to consider particular inside sources that can play a negative rule on a pollution level not only in a continuous way but also in a discontinuous one (for example: the use of solvents for cleaning, the presence of sporified fungi development, the use of the rooms for parties or other activities, etc.). On the basis of the obtained results, and keeping in mind that pollution of a chemical kind is normally low during the season examined, the quality of the air in the inside of the gallery is to be considered on an average-high level (the maximum value detected is of 83.7 lam/m3) if compared to the data available in literature (De Santoli et al., 1997; Thomson, 1986). Also regarding the biological aspect, even though data is not available for the comparison of museum environments but only of churches and hypogea, the microbial presence (the maximum value of which is of 1825 CFU/m 3) seems to have reached levels of average-high risks for works of art. 5. Acknowledgements We wish to thank the Director, Dr. Massimo Floridi, and the scientific trustee, Dr. Andrea G. De Marchi, of the Doria Pamphilj Gallery for their availability; our thanks also go to the custody personnel. A particular thank for scientific contribution to Dr. A. Ventura ofEco Vema s.r.l., and the consultants Dr. A. Papa and Dr. Lucia Zambonelli.
6. References Brimblecombe P., 1990. The composition of museum atmospheres. Atmospheric Environment, vol.24b, No. 1, Great Britain, l- 8. De Bock A.L., Van Grieken R.E., Camuffo D., Greme G.W., 1996. Microanalysis of museum aerosols to elucidate the soiling of paintings: case of the Correr Museum, Venice, Italy, Environmental Science & Technology, vol. 30, n.11, 3441-3350. De Santis F.,1997, Effects of atmospheric pollution on works of art conserved inside museums, Italian Society for the progress of science, Notes of the LXlV
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
Reunion of Rome 16-18/10/1997 - The science of cultural heritage, 211-221. De Santoli L., Moncada Lo Giudice G., 1997 Caratterizzazione e monitoraggio della qualit~ dell'aria nrgli ambienti museali, AICARR, Seminarial day Florence 7/2/97, 27-3 7. Ministero dei Beni Culturali ed Ambientali - Istituto Centrale per il Restauro, 1996, Carta del Rischio del patrimonio Culturale, vol 1, a cura di A.T.I. MARIS, Bonifica, Rome Nugari M.P, Roccardi A., (in press), Aerobiology to project and control the conservation of works of art. Aerobiology. Pasquariello G., Maggi O., 1998. Museums, Aerobiology and Cultural Heritage, Methodologies and Measuring techniques, Eds G. Caneva and P. Mandioli, Nardini Editore, Fiesole (Florence), 215-227. Sbaraglia G., Bellezza T., Bon di Valsassina C., Garibaldi V., Giraldi M., Pitzurra L., Bistoni F., 1999. Microbial environment monitoring of museums. An International Conference on Microbiology and Conservation (ICMC '99) of Microbes and Art, Florence, Italy, 102-108. Sorlini C., 1993 Aerobiology: general and applied aspects in the conservation of art works, Aerobiologia, 9, 109-115. Ranalli G., Coppola R., Sorlini C., 1995" Preliminary investigations on airborne microorganisms in indoor environments of artistic interest. 3rd. International Conference on Biodeterioration of Cultural Property, Bangkok, Thailand, 267-271. Thomson G., 1986, II ed. The museum environment, Butterworths, London.
383
ANALYTIC M E T H O D O L O G I E S FOR C A R B O N C O M P O U N D IDENTIFICATION: LEANING T O W E R AND BAPTISTERY OF PISA
Cristina Sabbioni* Istituto ISAO-CNR, via Gobetti 101, 40129 Bologna, Italy. Nadia Ghedini Dipartimento di Scienze Farrnaceutiche, Bologna, Italy. Giancarlo Gobbi Dipartimento di Scienze dei Materiali e della Terra, Ancona, Italy. Carlo Riontino Istituto ISAO-CNR, Bologna, Italy. Giuseppe Zappia Dipartimento di Scienze dei Materiali e della Terra, Ancona, Italy.
Abstract
Several analytic methodologies were developed and used for the characterisation of carbon materials in black crust specimens sampled on the Leaning Tower and Baptistery of Pisa. Since black crusts are the accumulation areas of material damage and atmospheric deposition, the discrimination and measurement of the carbon components is of crucial importance in the partitioning of pollutant sources, damage mechanism identification, maintenance of modern buildings and protection of ancient masonry. Cx were obtained by combustion of the bulk samples, while CNC and CE were quantified after elimination of Cc and Co, respectively. Carbonate carbon and organic carbon were then calculated. An investigation on the organic fraction was performed by IC technique. With scanning electron microscopy carbonaceous particles were identified. The results obtained indicate that this approach permits to discriminate and quantify the carbonaceous products of stone damage, obtain precise information on damage mechanisms, identify the pollutants sources and can provide important information for a correct safeguard planning of the Cultural Heritage. Key words: black crust, carbonaceous particles, carbon compounds, elemental carbon, Leaning Tower. 1. Introduction
The atmospheric deposition of gas and aerosols on outward facing surfaces is one of the main causes of damage on buildings, masonry and monuments (Rossval, 1988). The study of damage processes due to atmosphere-materials interaction is of crucial importance for a correct planning of restoration and conservation works and, in particular, of intervention on pollutants sources. External building surfaces constitute the interface where material damage processes occur. Among the various of damage typologies (physical, chemical and biological), the areas affected by the formation of black crusts (areas of atmospheric deposition not subject to wash out ) can be considered the accumulation points of deposits and products of chemical reactions occurring on material surfaces (Sabbioni, 1995). *Author's to whom correspondence should be addressed.
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The principal mineralogical constituent of black crusts is gypsum (CaSO4-2H20), a product of the reaction between the sulphuric acid of atmospheric pollutants and the calcium carbonate of building materials (Camuffo et al., 1982). During growth, the gypsum crystals embed the products of atmospheric deposition (Sabbioni and Zappia, 1992), including carbonaceous particles which are responsible for the blackening of the degradation layer that seriously impairs the appearance of monuments (Baer et al., 1991). These black particles are a complex system consisting of elemental carbon, organic compounds, sulphur and small quantities of diverse dements, including heavy metals; owing to their composition, such particles act as catalysts in the damage process of sulphation affecting stone monuments (Benner et al., 1982). Carbonaceous particles are emitted by the combustion of fossil fuels, oil and coal combustion, and their presence in the atmosphere has been reported by various authors (Leysen et al., 1989). 1.1 Carbon compounds in black crusts
Alongside sulphur, carbon is the main element of anthropic origin presents in the damage layers affecting monuments and historic buildings. Carbon compounds can have four different origins: a) carbonates, deriving almost exclusively from the underlying carbonate materials (Zappia et al., 1993); b) deposition of atmospheric particles containing elemental and organic, primary and secondary compounds (Saiz-Jimenez, 1993; Turpin and Huntizcker, 1995); c) biological weathering due to the action of micro-organisms, such as fungi and lichens, which produce oxalic acid that reacts with the underlying materials, leading to the formation of calcium oxalate (Sabbioni and Zappia, 1991; Saiz-Jimenez, 1995); d) surface treatments (oils, waxes, proteins, etc.), frequently used in the past to protect historic masonry (Rossi Manaresi, 1996). Total carbon (CT) presents in the black crusts can be considered as being composed of three main fractions: CT-- C c + C o + C E
Cc is carbonate carbon, basically due to the underlying material, Co the organic carbon of biogenic and anthropic origin and CE is the elemental carbon, which is predominantly a product of combustion processes. Therefore, the CE content can be considered a quantitative index of the carbonaceous particles deposited onto or embedded within the damage layers. The Co plus CE constitute the noncarbonate fractions (CNc) of total carbon. The measurement of noncarbonate carbon, its discrimination into elemental and organic carbon and the characterisation of the organic fraction are essential for a complete identification of the major components of the damage layers on monuments and for the characterisation of pollutant sources. Especially important is the measurement of organic and elemental carbon of natural and anthropic origin. Since elemental carbon, also referred to as black carbon or graphite carbon, mainly results from combustion processes, several authors have used it as a tracer for primary organic carbon (Turpin et al., 1991). Some authors have used the Co/CE ratio to indicate the presence of secondary organic aerosol (Turpin and Huntzicker, 1995). Afterwards, a complete carbon balance is of vital importance in studying the effects of the interaction between atmospheric pollutants and the environment, including those on human health and the conservation of Cultural Heritage (Masuda and Takahash, 1990). The literature contains a wide variety of carbon speciations, but very little on the identification and measurement of the carbon constituents in the damaged layers on monuments, where they are present in different ratios from those in the atmosphere.
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2. Materials and Methods 2.1 Sampling To study and evaluate the part played by of atmospheric pollutants in materials damage, black specimens were sampled (PI) on stones located in the external walls of the outer walkway of the Leaning Tower (fig. 1) and on the external capitals (BA) of Baptistery (fig. 2), two important parts of the architectural complex called Piazza dei Miracoli in Pisa town centre, proclaimed a "World Heritage Site" by UNESCO. After sampling, the specimens were dried and stored at 20 ~ in a nitrogen inert environment until the time of analysis. Before undergoing the analytic procedure below, they were ground in an agate mortar.
Fig. 1 - The Leaning Tower of Piazza dei Miracoli in Pisa.
Fig. 2 - External capital on the Baptistery of Piazza dei Miracoli (Pisa) with black crusts.
2.2 Analytic procedures All the experimental measurements of carbon were carried out by means of combustion analysis (CHNSO) using a Carlo Erba Analyzer. Total carbon was obtained by burning the bulk samples, while noncarbonate carbon was measured after eliminating the carbonates by treatment with HCI vapours, following a methodology developed and described in a previous work (Zappia et al., 1993). In order to determine the elemental carbon content of our samples, we developed a specific methodology which was controlled on the basis of preliminary analyses performed on specially prepared standard samples; this technique involves the elimination of the inorganic matrix and organic species, prior to the determination of the residual CE. The procedure adopted, described in detail in a previous paper (Ghedini et al., 2000), requires the decomposition of carbonates and the complete removal of CO 2. This is achieved by treating a suitable quantity of ground black crust (from a minimum of 100 mg to a maximum of 0.5 g) with HC1 37% until the effervescence stops, heating the suspension
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at 40-50~ followed by centrifugation. The breaking up of silicates and elimination of low soluble salt was performed by subsequent treatment of the residue with HCI 37% and Na:CO3 saturated solution in an airtight tube at 140~ followed by eentrifugation. The attack and dissolution of organic materials and the dissolution of the amorphous silica was obtained by submitting the residual samples to five alternate treatments at 140~ C, in an airtight glass tube, carried out with KOH 30% and HCI 37%, each followed by centrifugation and rinsing. The sample was finally dried at 180~ for 2 11, cooled in a drier, weighed and analysed by combustion to evaluate the elemental carbon content. Carbonate carbon and organic carbon were then calculated. The quantification of anions were carried out by means of ion chromatography (IC) using a Dionex Ion Chromatograph (model 4500i), equipped with conductivity detector (Dionex CDII) In order to quantify gypsum, the main product of stone degradation, and to compare carbonate and oxalate content measured with another analytic technique, differential and gravimctric thermal analysis (DTA-TGA), by Netzsch STM, was performed. Finally, the characteristic crystal growth patterns and the carbonaceous particles included were also observed by means of a scanning electron microscope Philips XL 20, linked with a dispersive energy microanalyser (SEM-EDX).
3. Results
The CHNSO and DTA-TGA data, shown respectively in Tab. 1 and Tab. 2, clearly reveal that carbon (with mean value of 5.15~ and sulphur (average 9.1%) are the main atmospheric deposition elements contained in the deterioration layers on stone buildings.
Table 1 - Relative concentrations of total carbon (Car), carbonate carbon (Cc), noncarbonate carbon (CNc), organic carbon (Co) and elemental carbon (Cz), measured by CHNSO analysis, in samples collected from the Leaning Tower and Baptistery in Pisa. Sample
CT
Cc
CNc
Co
C~
PIe
4.14
2.84
1.30
0.74
0.56
Pld
6.81
5.39
1.42
0.58
0.84
BAc
6.73
5.34
1.39
0.81
0.58
BAd
2.91
1.47
1.44
0.67
0.77
The sulphur content mean value, obtained by thermal analysis, was calculated as if all the sulphates present were CaSO4-2H20; this approximation was adopted because the data reported in the literature indicate that more than 95% of the sulphur is present as gypsum (Sabbioni et al., 1998). The carbon and sulphur values found in the samples are typical of sites with significant pollution levels. The discrimination of the different carbon components present in the black crusts is reported Tab. 1. Noncarbonate carbon (CNc) shows mean concentrations of 1.39% and accounts for 27.0% of Car. The high mean Cc content measured (3.76% 3 is due to the presence of many calcite fragments originating from the underlying carbonate stone, embedded within the crust during its growth.
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The mean value of Co is 0.70% and represents 50.3% of Cnc. There is a wide range of possible organic carbon sources and its measurement is of fundamental importance for evaluating the contribution of atmospheric deposition (in particular anthropic) and establishing the pollutant sources responsible for the formation of the deterioration layers. Elemental carbon, a quantitative index of the carbonaceous particles deriving from the incomplete combustion of fossil fuels, is found to be present in the black crusts, with a high average value (0.69%). The quantity of CE found, that represents about 49.6% of Cnc, indicates a higher combustion-generated aerosol deposition on monument surfaces in Pisa. The amounts of oxalates, acetates and formates found in black crusts, detected by IC technique, are shown in Fig. 3. Such organic anions may play an important role in damage processes affecting materials exposed to urban atmospheres.
Figure 3 - Organic anions (ppm) measured by ionic chromatography in the black crusts sampled on the Leaning Tower and Baptistery (Pisa). The mean oxalate concentration is about 596 ppm and its carbon content (Cox) accounts for 2.9% of Co. Calcium oxalates (weddeHite and whewellite) are frequently encountered on building surfaces and their origin is still the subject of controversy, the literature proposing a variety of different causes (Realini and Toniolo, 1996). Sources of oxalate in black crusts can be: (a) the transformation of organic materials used in the past as protective and/or aesthetic treatments, (b) biological weathering (lichens, in fact, produce oxalic acid), (c) the deposition of primary pollutants due to the incomplete combustion of fossil fuels and secondary pollutants forming due to the photochemical oxidation of olefin compounds. Our data are not sufficient to exclude any of the possible origins suggested. Acetate is the main organic anion detected by IC, its mean concentration is 1077 ppm, the CAC content average (carbon due to acetates) accounts for 5.7% of Co. Acetate can be due to primary anthropic aerosol deposition, especially that emitted by combustion processes, i.e. only from direct source emissions (Nolte et al., 1997). Formates, with mean values of 438 ppm, originate from biogenie and anthropie primary and secondary pollutants (Sakugawa and Kaplan, 1995, Nolte et al., 1997) and their carbon content average (CFoR) represents 1.4% of Co.
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DTA-TGA analysis (Tab. 2) indicate gypsum ranging between 41 and 68%, and carbonate varying between 7 and 42%. The differential and gravimetric thermal analyses confirms, in all the specimens analysed, the presence of oxalate anions. Table 2 - Mineralogical quantification (%) of the samples by DTA-TGA analysis. Sample
Gypsum
Calcite
Pie
43
30
Pld
44
42
BAc
41
39
BAd
68
Ca-Oxalates
= poor + = trace Scanning electron microscope observation of black crests evidence, as reported in Fig. 4, the widespread reaction between the sulphur due to atmospheric deposition and the stone surface, leading to the growth of a well-developed crust of interlocking gypsum crystals including carbonaceous particles (cenospheres).
Figure 4 - SEM micrograph of a carbonaceous particle observed in a sample of the Baptistery of Pisa.
4. C o n c l u s i o n s
Since black crusts can be considered the areas where both the products of the chemical transformation of the stone and the deposition of atmospheric gas and particles accumulate, the identification and measurement of the carbon components is of crucial importance in the partitioning of pollutant sources and identification of damage mechanisms. Such knowledge is important in planning the safeguard and restoration of the cultural heritage, as well as in the maintenance of modem buildings.
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The results obtained from analysing the specimens of black crust sampled from the surfaces of the Leaning Tower and Baptistery of Pisa, indicate that this approach satisfactorily distinguishes between carbonate, organic and elemental carbon and allows a reliable evaluation. Our data show that, aider sulphur, total carbon is the main anthropic component of atmospheric deposition present in damage layers on buildings. The characterisation and quantification of the carbonaceous species present in the black crust analysed revealed that Cx represents on average 5.15% of the total mass and that approximately 73% of it is composed of Cc, originating from the carbonate substrate, 14% of Co, of both natural and anthropic origin, and 13% of CE, tracer for combustion processes. The samples show a high elemental carbon content with respect to total carbon. Since CE is almost exclusively a product of combustion processes and represents a good marker for combustion-generated aerosol deposited on stone surfaces, this result indicates a significant pollution level in the areas around the said monuments. In black crusts CE is mainly due to the deposition of atmospheric carbonaceous particles and, as such, constitutes a quantitative index of their abundance. The mean Co/CE ratio turns out to be 1.02, a typical value for urban sites with intense traffic circulation (values close to unity). All of the samples analysed contain varying amounts of formates, acetates and oxalates, which are organic anions found in the water-soluble fraction of organic carbon. These organic anions, measured with the IC technique, may play an important role in damage processes affecting materials exposed to urban atmospheres. The carbon due to oxalates, acetates and formates (Cox + CAc +CFoR) represents about the 10% of the organic carbon. Electronic microscope observations show that degradation layers have the structure typical of the so-called black crusts, a fraction composed of anthropic materials (gypsum and carbonaceous particles) and a carbonaceous fraction linked to the substrate. 5. Acknowledgements This research was jointly supported by the EC-STEP Programme and the National Research Council (CNR) within the Programme "Progetto Finalizzato Beni Culturali Subproject 2". 6. References Baer N.S., Sabbioni C., Sors A., 1991. Science, Technology and European Cultural Heritage (edited by Baer N.S., Sabbioni C., Sors A.). Butterworth-I-Ieinemmm, Oxford. Benner W.H., Brodzinsky R., Novakov T., 1982. Oxidation of SO2 in droplets which contain soot particles. Atmospheric Environment, 16, 1333-1339. Camuffo D., Del Monte M., Sabbioni C., Vittori O., 1982. Wetting, deterioration and visual features of stone surfaces in an urban area. Atmosferic Environment, 16, 2253-2259. Ghedini N., Gobbi G., Sabbioni C., Zappia G., 2000. Determination of elemental and organic carbon on damaged stone monuments. Atmospheric Environment (in press). Leysen L., Roekens E., Van Grieken R., 1989. Air pollution-induced chemical decay of a sandy-limestone Cathedral in Belgium. Science of the Total Environment, 78, 263-287. Masuda S., Takahash K., 1990. Aerosol: Science, Industry, Health and Environment. Pergamon Press, Oxford. Nolte C.G., Solomon P.A., Fall T., Salmon L.G., Cass G.R., 1997. Seasonal and Spatial Characteristics of Formic and Acetic Acids Concentrations in the Southern California Atmosphere. Environmental Science and Technology, 31, 2547-2547.
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Realini M., Toniolo L., 1996. The oxalate films in the conservation of works of art (edited by M. Realini and L. Toniolo). Editeam Publishers, Milan. Rossi Manaresi R., 1996. Oxalate patinas and conservation treatments. The oxalate films in the conservation of works of art, Proc. of the Second International Symposium, Milan, (edited by M. Realini and L. Toniolo), Editeam Publishers. 113-127. Rossval J.,1988. Air Pollution and Conservation. Elsevier, Amsterdam. Sabbioni C., Zappia G., 1991. Oxalate patinas on ancient monument: the biological hypothesis. Aerobiologia, 7, 31-37. Sabbioni C., Zappia G., 1992. Atmospheric-derived element tracers on damaged stone. Science of Total Environment, 126, 35-48. Sabbioni C., 1995. Contribution of atmospheric deposition to the formation of damage layers. Science of the Total Environment, 167, 49-55. Sabbioni C., Zappia G., Ghedini N., Gobbi G., Favoni O., 1998. Black crusts on ancient mortars. Atmospheric Environment, 32, 215-222. Saiz-Jimenez C., 1993. Deposition of airborne organic pollutants on historical buildings. Atmospheric Environment, 27B, 77-85. Saiz-Jimenez C., 1995. Deposition of anthropogenic compounds on monuments and their effects on airborne microorganism. Aerobiologia, 11, 161-175. Sakugawa H., Kaplan I.R., 1995. Stable carbon isotope measurements of atmospheric organic acids in Los Angeles, California. Geophysical Research Letters, 22, 1509-1512. Turpin B.J., Huntzicker J.J., Larson S.M., Cass G.R., 1991. Los Angeles summer midday particulate carbon: primary and secondary aerosol. Environmental Science and Technology, 25, 1788-1793. Turpin B.J., Huntzicker J.J., 1995. Identification of secondary organic aerosol episodes and quantification of primary and secondary organic aerosol concentrations during SCAQS. Atmospheric Environment, 29, 3527-3544. Zappia G., Sabbioni C., Gobbi G., 1993. Noncarbonate carbon content on black and white areas of damaged stone monuments. Atmospheric Environment, 27A, 1117-1121.
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THE EFFECTS OF COAL AND DIESEL PARTICULATES ON THE WEATHERING LOSS OF TWO MAJOR BUILDING STONES IN THE UNITED K I N G D O M - A COMPARATIVE MICROCATCHMENT STUDY. David E. Searle* University of Wolverhampton, Wolverhampton, England David J. Mitchell University of Wolverhampton, Wolverhampton, England David P. Halsey Gyford House, Ross-on-Wye, Hereford, England. Stephen J. Dews University of Wolverhampton, Wolverhampton, England John P.Smith University of Wolverhampton, Wolverhampton, England Abstract Due to reductions in domestic usage, legislation and changes in fuel use, coal derived particulates in the UK urban atmosphere have been significantly reduced. However, a large increase in road usage and an expansion in the use of diesel engines, has meant that the majority of particulate, now present in the urban atmosphere, originate from vehicle exhausts. Particulate matter, resulting from coal combustion, has been recorded as being present in black patinas observed on some historic stone buildings and monuments and has been associated with accelerated weathering of stone surfaces as a result of enhanced gypsum formation. In contrast, the effects of particulate resulting from vehicle exhaust on stone are much less understood. To investigate this, a comparative study was undertaken using the technique of microcatchments under ambient atmospheric conditions. This compared the elemental composition and volume of precipitation runoff from two stone types coated with three different particulate treatments. The stone types used consisted of a ferruginous Triassic sandstone (Hollington Sandstone) and a oolitic Jurassic limestone (Portland Limestone) both of which have been extensively used in historical buildings and monuments in the UK. Treatments consisted of coal and diesel particulates, both separately and in combination. Combining these treatments attempts to investigate any synergistic effects that may occur when coal derived particulate is overlain by layers formed by particulates from more contemporary sources. It was found that diesel coated Portland Limestone samples showed a significant reduction (p<0.05) in both the rate of weathering loss and the volume of precipitation run-off when compared to untreated samples. The samples treated with a combination of both particulate types demonstrated a highly significant increase (p<0.01) in the volume of precipitation runoff from the sandstone microcatchments when compared to all other treatments. The work should contribute to an understanding to how current and future particulate pollution may affect stone structures that have a cultural significance. Key words: coal particulate, diesel particulate, microcatchments, weathering loss.
* Author to whom correspondence should be addressed.
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I. Introduction 1.1 Changes in sources of urban particulate A definite change has been evident in the sources of urban particulate matter in the U.K. during the last thirty years. Large reductions have occurred in emissions of particulate matter now classified as PM10 (all airborne material with an aerodynamic diameter smaller than 10 l.tm) from the usage of coal for domestic purposes. This has decreased from 210 kilotonnes in 1970 to 28 kt in 1994, a change from 40% to 12% of total emissions over 34 years (QUARG, 1996). The emissions from coal burning power stations (the other major coal emission source) remained relatively constant during this period but have, since declined. It is expected that this trend will continue as other energy sources, such as gas, continue to replace coal both for domestic use and in power generation. Associated with this decrease in coal derived particulate, diesel emissions from motor vehicles accounted for approximately 20% of all PMl0 emissions nationally, increasing by 13% from 1970 (QUARG, 1996). In urban environments percentage increases are even higher. In 1993, approximately 70% of the PM10 value for Greater London was attributed to diesel exhaust emissions (QUARG, 1996). Future trends of diesel emissions are unclear. A reduction is possible due to the implementation of European legislation controlling emission limits for new diesel vehicles (91/542/EEC, 94/12/EEC, 93/59/EEC), however, such forecasts are very dependent on both magnitude for road usage and the proportion of new diesel powered car sales. It is probable that exhaust emissions from diesel vehicles will continue to be the dominant source of urban particulate matter for the foreseeable future. Consequently, the current and future deposition of anthropogenically derived material on stone structures in the UK will be primarily traffic derived (Mansfield et al., 1991). The apparent lack of published research into the effects of these contemporary particulates on stone surfaces, provides the impetus for the research described here. 1.2 The role of particulate in stone deterioration processes Coal-derived particulate emitted during combustion significantly contributes to stone deterioration processes (Halsey,1996; Sabbioni and Zappia, 1992; Sabbioni et al., 1996; Warke et al., 1996; Zappia et al., 1993). Consisting principally of carbonaceous material, coal particulates have been considered to be responsible for the blackened surface patina, observed on many old stone buildings and monuments. In addition to this aesthetic degradation, coal particulates may also change moisture/thermal regimes and enhance the sulphation of calcite into gypsum by a catalytic action attributed to their transition metal content (Sabbioni and Zappia, 1992). However, this potential enhancement of sulphation by coal particulates is the subject of an ongoing debate. In work carried out by Hutchinson et al. (1992), they concluded that there was no evidence that coal or oil particulates had any significant effect on the promotion and development of gypsum.
A Similar debate exists concerning the role of diesel particulates as a potential catalyst for the promotion of sulphation. Studies by Ausset et al., (1996) and Johnson et al., (1996), found little or no evidence for such a role but in contrast Rodriguez-Navarro and Sebastian (1996) found that limestone slabs coated with diesel particulate formed significantly more gypsum (CaSO4.2H20) than untreated control samples when exposed elevated levels of SO2..
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1.3 Study background Published research on the influence of diesel particulates on stone decay involve the use of atmospheric simulation chambers in an attempt to accelerate natural processes to determine cause and effect of certain chemical species on stone. A natural extension to these studies would be to investigate these processes in a wider context under 'natural' conditions and different stone types. In the context of stone decay research, chamber experiments offer an effective method for examining the role of a limited number of pollutants. The ability to accurately control certain environmental parameters facilitates comparative experiments, which can demonstrate relatively small changes in chemical species. It is unsuitable, however, for recreating the wide range of cycles, natural controls and composition of atmospheric gases, which exist in the natural environment. To further this area of study and to investigate the effect of such particulate on other factors relating to the weathering of stone, building stone with different particulate surface treatments has been exposed to ambient atmospheric conditions in a research study currently underway at the University of Wolverhampton. 2. Methodology Slabs of Hollington Sandstone and Portland Limestone were artificially 'loaded' with coal and diesel particulates, both separately and in various combinations (tab. 1). These slabs were then exposed to atmospheric conditions utilising the microcatcbanent technique. Any chemical changes occurring as a result of the treatments, are determined by comparison with an untreated stone control. Table 1 - Stone/treatment combinations Stone Only
Hollington Sandstone Portland Limestone
r162 r162162
Stone + diesel particulates
Stone + coal particulates
Stone + diesel/coal particulates
r
r162
j,j,j'
j'r162
j'r162
j'r162
J'= single microcatchment (dimensions : 200mm(W) x 200mm(L) x 45mm (D) The inclusion of coal particulates in the study facilitated a comparison of pre and post 1970 pollution induced weathering rates and also any synergistic effects that may result when layers of contemporary pollution (ie primarily diesel derived) overlay older black deposits of coal particulate. Coal particulate (pulverized fuel ash, PFA) was collected from the electric precipitators of a local coal-fired power station. Equipment and methods were developed to sample large numbers of diesel particulates from an exhaust line of a large passenger transport vehicle. A method was developed to evenly deposit particulates onto stone surfaces in known quantities. This involved the use of a vacuum technique with the particulate in a distilled water suspension. A loading value for the diesel/coal treatments was determined to provide a local deposition rate equivalent to approximately 11 years.
2.1 Microcatchment study First developed by Jeffrey et al., (1985) and further refined by Cooper et al., (1992), a microcatchment consists of a stone slab fitted with an upright Perspex surround (fig.l) The
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slab and surround is then exposed to ambient atmospheric conditions. Precipitation run-off from the microcatchment is collected and chemically analysed. This method, combined with environmental monitoring, is described as being suitable for the statistical determination of any associations which may exist between stone weathering, climate, acid precipitation, acidic gases and dry deposition ( J e f f r e y et al., 1985). As such, the technique is well suited for the purposes of a comparative experiment in the current study. The study site location was on the roof of a building at an elevation of approximately 25 metres. A support frame was designed to carry 35 microcatchment units, each located with the stone surface at an angle of 15~ to the horizontal with the inclined surface facing south-west (fig. 1). In addition to the treatments (tab. 1), Three microcatchments consisting of roughened glass plate were used to monitor wet and dry deposition (Jeffrey et al., 1985).
Figure 1 - Microcatchment units in position at the University of Wolverhampton
2.2 Sample collection and analysis Runoff was initially sampled weekly but this period was extended later in the study dependent on precipitation volume. After determination of pH and mass, the run-off was sub-sampled and filtered through a 0.45 ~tm pore size cellulose nitrate membrane filter. The filter paper was then dried at 40~ and the mass of material retained obtained. To see if gypsum was being formed, the calcium and sulphate content of the run-off was determined. Calcium was determined using a Thermo-Jarrell Ash 'Iris Advantage inductively coupled plasma emission spectrophotometer and sulphate by a DIONEX Ion chromatograph. The results from chemical analysis for each microcatchment were expressed as a concentration in ppm and were converted into a value for mass lost or gained for each analyte from each microcatchment as follows:
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Mex =
((CexV/1000)- M G e x ) 2 5 . 2 2 8
395
(1)
: Mass of element (x) lost or gained per square metre of the stone surface (mg m -z) Cex : concentration of element (x) in filtrate sample (ppm) V : Volume of precipitation runoff from sampling event (ml) MGex : mass of element (x) present in precipitation runoff from glass microcatchments (mean of three results) (mg) Mex
3. Results Results for the volume precipitation run-off and the mass of solid material >0.45 lam retained are reported for 64 weeks (14/8/98-11/1/99). Chemical analysis determined from ICP and Ion chromatography is for 40 and 18 weeks respectively. 3.1 Precipitation run-off Table 2 shows the results obtained for cumulative precipitation runoff from the two stone types. When all four treatments on the limestone samples were compared using an ANOVA and subsequent post-hoc analysis, there was strong evidence (P<0.001) that the volume of runoff from the diesel coated samples was significantly less than the coal and coal/diesel combination treatments (P=0.001). In addition there was also some evidence (P<0.05) that this also occurred in comparison to the untreated control (P=0.023). Table 2: Cumulative precipitation run-off volume (mean of three microcatchments) StoneType/ Cumulative Mean Precipitation Run-off Volume (mi) Weekl Weekl0 Week 20 Week31 Week 40 Week 49 Week 60 Week 64 Treatment Hollington Sandstone Untreated control 679 5356 10977 16156 18846 21910 29784 31103 Diesel particulate 1025 5866 11259 15969 18384 20821 28853 30238 Coal particulate 822 5717 11166 16590 18862 21441 29680 31056 925 6220 1 1 8 1 1 17653 20468 23605 32032 33483 Coal + diesel - p Portland Limestone Untreated control 738 5083 10753 16058 19068 22130 30361 31728 Diesel particulate 742 4667 10029 15124 17757 20758 28656 29963 692 5286 11045 16861 19904 22811 31432 32810 Coal particulate Coal + diesel - p 731 5376 11151 16595 19854 23203 31450 32902
In contrast, the results from the sandstone showed strong evidence (P_
3.2 Material loss >0.45 lxm & Chemical Analysis Loss of material from both stone types over the duration of the study (64 weeks) is shown in fig 4. There were no significant differences (P=0.05) between any of the treatments on the Hollington Sandstone. It is seen however, that a negative loss (gain) of material is observed for all treatments for this stone type. For Portland Limestone, there was some evidence (P=0.045) that less material was lost from the diesel treatment in comparison to
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the untreated control samples. Table 3 lists the results for two different time periods for Ca and SO4.
T i m e (weeks) ----o--- Portland Limestone - control - - ~ - Portland Limestone + diesel particulate - ~ - P o r t l a n d Limestone + coal particulate -- 0 - - Portland Limestone + coal/diesel particulate -- Hollington Sandstone - control .... Hollington Sandstone + diesel particulate . . . . . . Hollington Sandstone + coal particulate .... Hollington Sandstone + coal/diesel particulate
Figure 2: Mean cumulative material loss >0.45~tm from Portland Limestone and Hollington Sandstone microcatchments (n=3)
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4. I)iseussion
For runoff to occur on a microcatchment, the rate of precipitation must be greater than the rate of infiltration, or the stone is in a saturated condition (Steiger et al., 1993). It could be argued, therefore, that any agent present on the surface of the stone, which restricts infiltration, should result in an increased volume of runoff. This is generally reflected in the results, with the greatest volume on both stone types resulting from the coal/diesel combination treatment, however, the significantly reduced volume that was observed on the limestone coated with diesel particulate contradicts these results. Precise reasons for this are presently unclear. To reduce run-off volume it could be argued that the following changes are required in certain physical properties of the stone: (i) an increase in the rate of drying, (ii) an increase in the water storage capacity of the stone, (iii) an increase in the permeability of the stone. It is possible that the relatively small size of the diesel particulate (<2 ktm) enables them to move down into the pores of the limestone, changing the nature of the pore network and the capillary sorption. Figure 2 shows a difference between the material loss from the two stone types. The gain in material observed on the sandstone is probably due the open texture of the sandstone, which appears to reduce loss of material in the runoff and 'trapping' material from atmospheric deposition of material. In contrast, the limestone shows a characteristic loss of material, usually due to its natural solubility and the buffering effect on acid rain (Webb et aL, 1992, Cooper et al., 1992). Although all the treatments appear to be reducing material loss on the limestone, only the diesel treatment is significant at the 90% level for both for solid particulate loss and for calcium loss in the run-off. This may be due in part to the treatments acting as a consolidant to the surface layer binding material together. Grossi et al., (1995) observed that surface recession correlated strongly with open porosity, therefore, if the treatments are reducing the area of stone/precipitation interface this could be partly responsible for a reduction in the dissolution of C a C O 3 . In addition, the significant reduction in material loss observed between the untreated limestone and the diesel treatment may be related to the similar significant reductions recorded in the runoff volume. The rate of weathering loss for the untreated limestone was approximately 110 mg m 2 d ~, this compares well with values of 160 mg m "2 d "1 (Webb et al., 1992) and 62-80 mg m "2 d -l (Cooper et a/.,1992) recorded for Portland Limestone at similar urban sites during comparable time periods. The lack of a significant value for an increase in sulphate content on the limestone when compared to the glass control results during the 0-18 week period (tab 3), indicates that no gypsum is being formed. The exception to this is the coal/diesel treated sample, which, although significantly higher than the glass control, is not significantly different to the other treatments. This may reflect sulphate present in the coal particulate on the surface. In contrast, significantly extra calcium and sulphate are being lost from the sandstone when compared to the glass, although the only difference occurring between treatments is that the diesel is significantly reducing that loss. This indicates that although some gypsum may be forming, this appears to be related to the stone type itself and not the treatment.
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Table 3" Chemical analyses of precipitation run-off: results Soluble elemental loss (rag m 2) I
Period i (weeks) .
.
.
.
.
.
!
Control
Diesel
199.3 i 336.6 619.3 413.5 556.3 843.6 849.9 983.7 1284.8
!
Coal
Coal/ Diesel
54.7 23.5 30.1 275.8 266.1 250.7 244.5 322.0 188.4
369.1 366.0 363.6 660.1 605.3 636.3 703.7 906.1 956.0
280.5 409.8 240.4 576.0 613.2 451.9 538.1 905.7 711.1
2391.7 3270.3 3183.8 5560.8 6641.0 6499.5 63.6 292.8 133.5
3649.1 3697.2 3490.7 7675.6 7206.9 7337.0 256.4 218.8 524.3
2901.8 3583.8 3921.3 6174.1 7067.6 7632.6 447.1 282.8 401.0
Significance (Tukeys post hoc test after ANOVA)
.
Hollington Sandstone
0-18 Calcium 0-37
Sulphate
0-18
P<0.000, diesel-t < control P<0.000, diesel-t < coal P=-0.001, diesel-t < coal/diesel P=0.006, diesel-t < control P=0.003, diesel-t < coal P--0.009, diesel-t < coal/diesel P=0.002, diesel-t < control P=-0.008, diesel-t < coal P--0.032, diesel-t < coal/diesel
Portland Limestone
0-18 Calcium 0-37
Sulphate
O-18
374112 3451.7 3665.2 7462.4 7340.8 7171.4 258.8 355.0 199.0
No significant differences
P=0.099, diesel-t < control P=0.074, diesel-t < coal
No significant differences
Glass
0-18
625.3 578.3 628.1
N/A
N/A
N/A
0-37
962.7 871.5 918.9
N/A
N/A
N/A
Calcium
639.7 692.4 N/A N/A 709.7 HS = Hollington Sandstone, PL = Portland Limestone Sulphate
0-18
N/A
P=0.002, glass < control (HS) ! P=0.006, glass < coal (HS) P=-0.003, glass < coal/diesel (HS) P<0.001, glass < control (PL) P<0.001, glass < diesel (PL) P<0.001, glass < coal (PL) P<0.001, ~lass < coal/diesel (PL) . P<0.001, glass < control (HS) P=0.011, glass < diesel (HS) P<0.001, glass < coal (HS) P<0.001, glass < coal/diesel (HS) P<0.001, glass < control (PL) P<0.001, glass < diesel (PL) P<0.001, glass < coal (PL) P<0.001, glass < coal/diesel (PL) . P<0.000, glass < control (HS) P=0.001, glass < coal (HS) P=0.003, glass < coal/diesel(HS) P=0.033, glass < coal/diesel (PL)
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5. Conclusions It is highly likely that future particulate pollution deposited on historic buildings and structures in UK urban areas, will continue to be, primarily, traffic derived and that diesel particulates will form the majority of such deposition. Understanding their role in altering the 'natural' weathering and soiling processes will contribute to the development of transport and conservation strategies and improvement of cleaning methods. The paucity of published research demonstrates the need to increase research in this area and to widen the range to encompass other physical and biological factors. This paper shows the value of studying the effect of such particulate under actual atmospheric conditions. It has shown that the presence of diesel particulate on certain stone types can affect weathering rates and that further work is required to understand the processes and mechanisms, causing these effects. Acknowledgements The Built Environment Research Unit and the School of Applied Sciences, University of Wolverhampton for funding and Mr F.R. Handy for photographic reproduction and printing assistance
6. References Ausset P., Crovisier J.L, Del Monte M., Furlan V., Giradet F., Hammecker C., Jeannette D., Lefevre R.A., 1996. Experimental study of limestone and sandstone sulphation in polluted realistic conditions: the Lausanne Atmospheric Simulation Chamber (LASC). Atmospheric Environment, 30, 18, 3197-3207. Cooper T.P., O' Brien P.F., Jeffrey D.W., 1992. Rates of deterioration of Portland Limestone in an urban environment. Studies in Conservation, 37, 228-238. Grossi C.M., Murray M., Butlin R.N., 1995. Response of building stones to acid deposition. Water, Air and Soil Pollution, 85, 2713-2718. Hutchinson A.J., Johnson J.B., Thompson G.E., Wood G.C., 1992. The role of fly-ash particulate material and oxide catalysts in stone degradation. Atmospheric Environment, 26A, 15, 2795-2803. Jeffrey D., 1985. A test rig for determining short term weathering rates of building materials under urban environmental conditions. IN The effects of air pollution on historic buildings and monuments. Padua 30/9-2/10/85.83-95. Johnson J.B., Montgomery M., Thompson G.E., Wood G.C., Sage P.W., Cooke M.J., 1996. The influence of combustion-derived pollutants on limestone deterioration: 2, The wet deposition of pollutant species. Corrosion Science, 38, 2, 267-278. Mansfield T, Hamilton R., Ellis B., Newby P., 1991. Diesel particulate emissions and the implications for the soiling of buildings. The Environmentalist, 11, 4, 243-254. QUARG, 1996. Airborne Particulate Matter in the United Kingdom. Third report of the Quality of Urban Air Review Group. Institute of Public and Environmental Health, University of Birmingham. December 1993. Rodriguez-Navarro C., Sebastian E., 1996. Role of particulate matter from vehicle exhaust on porous building stones (limestone) sulfation. The Science of the Total Environment, 187(2), 79-91. Sabbioni C., Zappia G., 1992. Decay of sandstone in urban areas correlated with atmospheric aerosol. Water, Air and Soil Pollution, 63,305-316.
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Sabbioni C., Zappia G., Gobbi G., 1996. Carbonaceous particles and stone damage in a laboratory exposure system. Journal of Geophysical Research, 101, D 14, 19,621-19,627. Steiger M., Wolf F., Dannecker W., 1993. Deposition and enrichment of atmospheric pollutants on building stones as determined by field exposure experiments. IN Thiel M.J., Conservation of Stone and Other Materials.E&FN Spon, London, 1, 35-42. Warke P.A., Smith B.J., R.W. Magee, 1996. Thermal response characteristics of stone: implications for weathering of soiled surfaces in urban environments. Earth Surface Processes and Landforms, 21,295-306. Zappia G., Sabbioni C., Gobbi G., 1993. Non-carbonate carbon content on black and white areas of damaged stone monuments. Atmospheric Environment, 27A, 7, 1117-1121.
401
EVALUATION OF THE ENVIRONMENTAL INFLUENCE ON SULPHATE SALT FORMATION AT MONUMENTS IN DRESDEN (GERMANY) BY SULPHUR ISOTOPE MEASUREMENTS
Heiner Siedel* Institut f0r Diagnostik und Konservierung an Denkmalen, Dresden, Germany Werner Klemm Institut FOr Mineralogie, TU Bergakademie Freiberg, Germany
Abstract
Sulphur isotope measurements have been performed on samples from gypsum crusts and sulphate salt efflorescence as well as on rain water, SO2 and dust in the city centre of Dresden. The comparison of the values from monuments and from environmental sources shows the dominating influence of air pollution on salt formation. The location of Dresden in the Elbe valley, the use of lignite for energy production and the lack of filters in industrial plants and power stations in the past resulted in isotopic heavy crusts which are strongly influenced by aerosol particle deposition. In a case study from the Frauenkirche where efflorescence occurred at the surface of the rebuilt facade the detailed investigation of 834S for the possible sulphur sources lead to a better explanation of the phenomenon. Keywords: sulphur isotope analysis, environmental pollution, gypsum crusts, efflorescence, mortars
1. Introduction
Lots of damages on porous building materials as natural stone and mortar are related with salt attack. Sulphates of different composition are often predominant in the salt mixtures of efflorescence. In the black crusts high amounts of gypsum are found. Although the global relation between dry and wet deposition of sulphur, the formation of sulphate salts and damages on building materials seems to be evident, the detailed interpretation of the causes of damages at one special building is more complicated. The relevant processes might be dry deposition of sulphur, rain attack and runoff water as well as chemical interaction of water with several (historic and modem) building materials or rising damp with possible influences of soil and ground water. In a particular case the sources of sulphate salts could be different from only anthropogenic environmental influences. The isotopic composition of sulphur can be used as a ,,fingerprint" to identify its origin. The method has been successfully applied in the geosciences and for environmental studies (Hoefs 1997). In several case studies it has already been tested in the field of material deterioration at historic monuments (Buzek et al. 1991, R6sch & Schwarz 1993, Toffs et al. 1997). The following local study presents results from the city of Dresden (Saxony). They are part of regional investigations in Saxony which aim to get a set of data for the variation of sulphur isotopic composition in salts at monuments and in the environment. *Author to whom correspondence should be addressed.
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2. Sulphur isotope chemistry Sulphur has four stable isotopes (32S, 33S, 34S, 35S), but usually only the ratio of the two most abundant ones (32S: 95,02 %, 34S: 4,21%) is considered to study its isotopic effects. These effects are expressed as differences in isotopic ratio 34S/32S related to the standard Canyon Diablo Troilite (CDT) in the unit 634S [permill, %o]:
5348 "-- [(34S / 32S)sample / (34S / 32S)standard - 1] x 1000
(1)
The partial separation of sulphur isotopes in nature by different isotope effects results in a broad range for 634S of about 150 %o (-65 to +90). Within this global range there are smaller variations for sulphur from several natural or environmental sources / processes (Nielsen 1970) with any possible effect on sulphate salt formation at monuments: ocean sea spray (+20 %o), burning of coal and lignite (-0,5 to + 20 %o), burning of oil (-5 to + 30 %o), melting of sulfidic ores (-25 to + 25) and others. The local variation for 834S of these potential sulphur sources is again much smaller than the global one quoted above. To evaluate the sources for sulphate formation at a certain historic monument or at monuments in a certain city, one must know the regional or local variation of the 834S values for natural and environmental sulphur sources. As already shown by other studies, changes in 534S caused by oxidation reactions of sulphur on the way from the air to the building surface (e.g. SO2 to SO3-and to sulphate) are rather small (about +1%0, Buzek et al. 1991). For this reason, the ~34S values of possible sulphur sources and salts at monuments can be directly compared. Differences could be mainly interpreted as mixed effects between several sulphur sources.
3. Methods of analysis Investigations on the isotope ratios of sulphur have been made on various kinds of samples (efflorescence, gypsum crusts, rainwater, dust and atmospheric sulphur collected by filters). Sulphur was precipitated as barium sulphate from solution and then converted to SO2 for analysis. Sulphate was dissolved by HEObidest. from efflorescence and air filters. The sulphur from crusts and mortars has been dissolved by cooking the samples for 20 minutes in a soda solution (10%)Rain water samples have been evaporated to concentrate sulphate before precipitation (for further details see Klemm & Siedel 1999). The isotope ratio 34S/32S was determined by a gas mass spectrometer Delta VE (Finnigan MAT). Water soluble sulphate contents in rainwater and in water extracts were determined by ion chromatography (Metrohm IC 690). The sulphur from soda extracts was analysed by gravimetric determination (precipitated as BaSO4). Total sulphur contents were determined by elementary analysis with a Heraeus Vario EL System. In addition, some samples from efflorescence were investigated by X-ray diffraction. 4. The city of Dresden - monuments and environmental situation The historic city centre of Dresden is dominated by buildings in the Renaissance and the Baroque style. The most important ones are the Zwinger (1711-28), the Residence Castle (16. - 19. cent.) and the churches Hoikirche (1739-55) and Frauenkirche (1726-1738). The latter was destroyed by bombs in 1945 like many other historic buildings and has been a ruin
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until 1991, when the reconstruction began. Most of the monuments are built of Cretaceous sandstone from the Elbe valley region. Dresden is located in the Elbe valley graben and has been influenced by an intensive atmospheric environmental pollution in the past. In the last decades especially the burning of lignite in power plants, industry and households produced a high imission rate of SO2 (mean for the year 1989:105 ~tg/m3). The surfaces of historic buildings were strongly affected by the formation of gypsum crusts and sulphate salts which caused an intensive weathering of building sandstones. After the political changes in 1989 / 90 the imission rates for SO2 decreased drastically (mean values for 1998 are nearly one third of those measured in 1989). Fig. 1 shows the imission concentrations in the city centre for the last years.
5. Results of sulphur isotope analysis and discussion 5.1 Aims of the investigation and sampling procedure Samples have been taken from crusts and efflorescence of building surfaces, from rainwater, dust, SO2 of the atmosphere and from building materials to evaluate the environmental influences on sulphate salt formation at historic buildings in Dresden. Rainwater and SO2 from the air have been collected over a period of at least one year on the Zwinger wall in the very city centre, the latter with filters impregnated with K2CO3 and exposed to the atmosphere (sheltered from rain) for about 3 month (cf. Torfs et al. 1997). Groundwater could be taken from a borehole at the construction site of the Frauenkirche. One sample of dust was taken from a sheltered position at the Zwinger. Samples of crusts and efflorescence have been collected from the Zwinger and the Hofkirche. While rebuilding the Frauenkirche from the ruin, problems arose with new formed salt efflorescence which contained sulphate compounds. To explain the mechanism of salt formation in this special case, further samples from efflorescence and possible sources (mortars, building stones) were taken at the Frauenkirche. The results of these measurements should demonstrate the practical relevance of sulphur isotope investigations. 5.2 Salts from Zwinger, Hofkirche and atmospheric sulphur compounds The samples from Zwinger and Hofl
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figure 1
Range for ~348 [%0] of salt efflorescence and crusts from Hofldrche and Zwinger
3
I crust
"6 2
!
[3 efflorescence l
! I
i l
i l
t I
I I
!~-I i I
I
[ I
II
I I
~
range of ~a4S The ~348 ratios of SO2 in the atmosphere are characterised by lower values in the range of +0,3 to +4,5 %0 (see tab. 1). Sulphate in rainwater varies between +4,4 and +7,7 %0 (one single value is +9,1%0, fig. 3). For the dust sample 534S was +l 1,7 %0. The three groups of values can be differentiated in the following way: 534S(SO2) < ~348(8042 rainwater) < ~534S(dust). The latter single value is confirmed by previous analyses of filter dust from lignite burning in the range of 7,3 to 14,7 (Arndt 1986). Table 1
~348 for air filter samples and deposition rate on filters, Zwinger
Number
period of filter exposure
804 [mg/m~d]
~348 1~1
1 2 3 4
June 15th -September 4 th, 1997 September 4th -November 26 th, 1997 December 9th, 1997-March 9th, 1998 March 9th- July 7th , 1998
3,3 5,5 9,7 3,3
+4,5 +2,3 +0,3 n.d.
The measured ~348 ratios for efflorescence and crusts (+5,4 to +10,1%0) correspond well with the total range of all atmospheric sulphur components (+ 0,3 to +11,7 %0). For the discussion of recently measured values for atmospheric sulphur components in comparison with values for sulphate salts on monuments (which have been formed over years in the past) the above mentioned changes in the environmental situation after 1989 must be taken into account. Although the imission rates for SO2 and dust have been decreased drastically since this time (especially caused by the installation of filter systems in industry and power plants) and the contribution of oil and gas heating to energy production is rising step by step lignite is still a very important source of energy in this region. In January
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figure 2
405
Variation of monthly mean SO2 imission between June 1996 and December 1998 in the city centre of Dresden (data from Sachsisches Landesamt fOr Umwelt und Geologic)
120 T 100 --
~E
80 -
=,
60
(:3 m
40 20 0
I
r
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month / year
Sulphur isotopic ratio ~34Sand concentration of sulphate in rainwater in the city centre of Dresden between October 1996 and June 1998 (horizontal lines: mean ~534Sof SO2 from the air in the same place).
Figure 3
60 50-
40 E
'
30-
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.
-10
~34 S
9
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406
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
1997, within the heating period a mean imission concentration for SO2 of still about 105 pg/m 3 was reached in Dresden (fig. 2). Isotopic patterns of the single sulphur components from the air (SO2, sulphate from rainwater and dust, still produced mainly by lignite burning) should not have been changed even if their total and relative amount is different from that of earlier times. With respect to this conclusion and to the general correspondence of ~534S from atmospheric components and salts on monuments the results will be discussed together. The 534S ratios in crusts and efflorescence can in general be interpreted as mixed values from several environmental influences. They are in the best correspondence with the range for sulphur in rainwater which itself can be regarded as an isotopic mixture of sulphur from SO2 of the air and from aerosol. The highest ~534Svalues can be found in crusts while the sulphate from efflorescence has lower ~534Sratios. Crusts contain particles from aerosol as well as gypsum formed by the reaction with SO2 and rain water. The contribution of sulphate particle deposition to crust formation is still under discussion and can be hardly proved by only microscopic and chemical analyses. The high ~534Sratios of some gypsum crust samples from the city of Dresden can be explained by a high particle deposition rate at building surfaces in the past. The particles have been washed away by rain and run-off water and redeposited and accumulated in rain sheltered areas where the formation of gypsum crusts takes place. The formation of isotopic heavy crusts seems to be in relation to the geographic situation of the inner city of Dresden at the bottom of the Elbe Valley. Samples of crusts taken from the Meissen Cathedral about 20 km north-west of Dresden in the same industrial region show only ~534Sratios < 8 %0. The values for sulphur from efflorescence are in the same range as in the samples from Dresden. The Cathedral is situated on a hill over the Elbe river, where the influence of particle deposition is lower than in the valley. Salt efflorescence has mainly been formed by dry deposition of SO2 or chemical reaction of rain and run-off water at the surface of mortars and sandstone. Therefore the isotopic ratios of sulphate salts from efflorescence are in their tendency more related to SO2 and rainwater. The single value for each sample from the building is the result of several influences like the deposition rate of sulphur from the air and from aerosol or rain as well as microclimatic influences, position at the building surface, effects of run-off water etc. This leads to the scattering of single values within a range of 634S ratios which is characteristic for the situation in the city centre in general. The good correspondence to the 634S range for sulphur fi'om environmental pollution shows again the dominating role of the environmental situation for the sulphate salt formation at monuments.
5.3 Salt efflorescence from Frauenkirche The walls of the Frauenkirche are reconstructed with a mixture of original sandstone (as far as available from remnants) and new sandstone from quarries in the Elbe valley. The building site is sheltered from rain under a roof. The mortar is a lime mortar with pozzolanic additive (,,trass", a volcanic ash from the Eifel region). It contains high amounts of soluble alkali (total alkali contents up to 10 % Na20 equivalent). A short time after building the walls in some parts of the sandstone surface thin white layers of salt efflorescence could be observed. The salts were analysed as a mixture of carbon-
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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ates and sulphates (calcite, thenardite, aphtitalite, thermonatrite, gaylussite and trona) dominated by carbonate compounds. The concentration of efflorescence near the mortar joints lead to the assumption that soluble components of the mortar are involved in the process of salt formation. Relations between efflorescence of alkali sulphate and alkali carbonate and mortars containing trass are known from other buildings where porous sandstone was used. While the alkali content in efflorescence has certainly moved from mortar pore solution to the stone surface the origin of sulphate compounds is not totally clear. It might be either an effect of the reaction of alkali carbonate or hydroxide with SO2 from the air or an effect of sulphate migration from the binding agent of the mortar. In addition, sulphate in the (original and new) sandstone and in the water used for processing of the mortar should be considered. Sulphur isotope investigations were made on efflorescence from various position at the building wall and on all materials mentioned above. The results are given in tab. 2 and 3. The 634S of mortar, tap water and new sandstone do not fit in the ~34S range for efflorescence (+4,8 to +8,4 %o). In order to control if there are reactions that might change the isotope ratio of sulphur on the way from mortar compounds to efflorescence an efflorescence test was made on laboratory samples. Mortar prisms were dived with the bottom 1 cm deep in distilled water for 24 hours and then dried for 48 hours. Efflorescence was scratched off the top after 10 and 20 cycles of wetting and drying. The isotope ratios (tab. 3) are nearly the same in efflorescence and mortars but show a clear difference to the values measured for efflorescence on the building walls. The latter corresponds best to the range of sulphur from rain water and from sulphate salts in crusts and older salt efflorescence (Zwinger, Hoikirche, Frauenkirche). Table 2
6348 and contents of sulphur in building materials from the Frauenkirche Material
joint mortar grouting mortar pure trass tap water (used for mortar processing) new Posta type sandstone, quarry Mtihlleite original sandstone, crusts and thin black layers at the surface
~34S [~,] + 10,4 to + 11,8 + 11,4 + 17,5 + 0,9 to + 1,0 - 4,3 +5,7 to +6,4
S [weight-%] 0,1 0,08 0,01 70 mg/1 0,006 0,22 to 13,1
The results can be explained in the following way. Efflorescence at original sandstone is mainly caused by the reaction of alkali components from the mortar with ,,old" sulphate salts within the stone and on its surface (e.g. gypsum). Those salts have been formed by environmental influences in the past. Therefore the reaction products show the isotopic patterns of environmental sulphur. In efflorescence on the original stones the sulphate component is predominant in the carbonate / sulphate mixture. In contrast efflorescence on the surface of new sandstone is dominated by carbonate compounds. Due to the roof which shelters the construction site from rain the sulphate com-
408
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
pounds should have formed only in contact with SO2 from the air. The recently measured 834S are somewhat lower (see tab. 1). Thus, the formation of sulphate salts on new sandstone could be discussed as a combined effect of (little) sulphate migration from mortar and sulphatisation of alkali carbonate by SO2 from the air. Table 3
~348 and contents of sulphur in efflorescence from the Frauenkirche wall and from laboratory tests
efflorescence from wall outside wall inside laboratory test samples of mortar (10 wet/dry cycles) laboratory test samples of mortar (20 wet/dry cycles)
mortar for test samples
~34S 1~1 + 4,8 to + 8,4 + 6,0to + 7,8 + 9,5 to + 9,9 + 9,3 to + 10,3 + 10,5
S [weight-%] 0,59 to 7,82 0,16 to 1,86
The reaction of more or less ,,stable" sulphate (as gypsum) from original sandstone with alkali components from the mortar to alkali sulphate (mainly thenardite) is dangerous to the porous fabric of sandstone because Na2SO4 can produce hydration pressure in the system thenardite / mirabilite. The fast reaction of alkali carbonate with SO2 to sulphate as shown on new sandstone will also contribute to this process. Even if the efflorescence seems to disappear when the facade is in contact with rain water, the salts might be accumulated elsewhere (maybe at the bottom of the wall). To reduce the effect of salt formation, alkali contents in the mortars should be minimized.
6. Conclusions Sulphur isotope analyses have shown the enormous influence of air pollution by lignite buming on the formation of sulphate salts at monuments in Dresden in the past. The measured 834S of salt efflorescence and gypsum crusts can be interpreted as mixed values that represent influences from rain, SO2 and dust. The tendency to higher ~34S ratios in crusts is remarkable and can be explained with a high contribution of aerosol particles to their formation due to Dresden's geographic situation at the bottom of the Elbe valley. Even if the imission rates of SO2 and dust have decreased reactions of material surfaces with sulphur from the environment are still possible as shown in a case study from the rebuilt facade of the Frauenkirche. At the same time, this case study should demonstrate the practical benefit of the method. Knowing the 834S range for the local environmental background and for building materials, the origin of sulphate salts can be explained or at least some possibilities of salt formation can be excluded. Thus, the sulphur isotope analysis is a useful tool to investigate the causes of stone deterioration by sulphate salts.
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7. Acknowledgements The authors wish to thank the Deutsche Bundesstittung Umwelt, Osnabrtick for financial support (Az 07843). The isotope measurements were performed in the laboratory for isotope geochemistry of the Institute for Mineralogy, TU Bergakademie Freiberg.
8. References Arndt I., 1986. Schwefelisotopenbestimmung in Aerosolen. Unpublished, TU Bergakademie Freiberg. Buzek F., Cerny J., Sramek J., 1991. Sulphur isotope studies of atmospheric S and the corrosion of monuments in Prague, Czechoslovakia. In: Krouse H.R., Grinenko V.A (eds.). Stable isotopes, natural and anthropogenic sulphur in the environment. Wiley & Sons, Chichester. 399-405. Hoefs J., 1997. Stable isotope geochemistry. Springer, New York, Berlin, Heidelberg. Klemm W., Siedel H., 1999. Schwefelisotopenanalyse von bausch~idlichen Sulfatsalzen an historischen Bauwerken. Wiss. Mitt. Inst. Geol. TU Bergakademie Freiberg, 8. Nielsen H., 1970. Sulphur isotopes in nature. In: Wedepohl K.-H. (ed.). Handbook of geochemistry 16, B 1-40. Springer, Berlin. RSsch H., Schwarz H.J., 1993. Damage to frescoes caused by sulphate-bearing salts: Where does the sulphur come from? Studies in Conservation, 38, 224-230. Torfs K. M., van Grieken R., Buzek F., 1997. Use of stable isotope measurements to evaluate the origin of sulfur in gypsum layers on limestone buildings. Environ. Sci. Technol., 31,2650-2655.
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GRANITIC BUILDING STONE DECAY IN AN URBAN ENVIRONMENT:A CASE OF AUTHIGENIC KAOLINITE FORMATION BY HETEROGENOUS SULPHUR DIOXIDE ATTACK N. Schiavon Dpt. of Earth Sciences, University of Cambridge, Downing St., Cambridge, U. K.
Abstract
Under natural acid and wet conditions, one of the main weathering processes affecting granitic rocks is the kaolinisation of Na, Ca and K-feldspar minerals by H20 + CO2 attack. We here report the occurrence of authigenie kaolinite on the surface of an 18th century granitic monument covered with sulphate-rich weathering patinas. We suggest that, in humid mesothermic climates, anthropogenically derived gaseous SO2 from air pollution is responsible for accelerated kaolinisation of feldspars in an urban environment; SO2 from air pollution thus plays a dual role in the weathering of silicate rocks being responsible for the well known sulphation of Ca-bearing materials leading to the formation of sulphate salts such as gypsum as well as the weathering of feldspar minerals to kaolinite. The kaolinisation reaction weakens the granite mierofabrie leading to enhanced decay of the building stone. Keywords: granite, urban environment, sulphur dioxide, feldspar, kaolinite, weathering. 1. Introduction
Natural weathering processes can lead to the transformation of primary minerals in granitic rocks (s.l.) such as micas and feldspars into secondary crystalline and amorphous products. In wet, acid conditions, atmospheric attack on feldspar minerals is responsible for the formation of secondary clay minerals such as kaolinite (A14(OH)8[Si4Olo]) (Stoch and Sikora, 1976; Yatsu, 1988; Blum, 1994); in a CO2 + H20 rich atmosphere, the idealised stoichiometry of the kaolinisation reaction for orthoclase (K[AISi3Os]) and albite (Na[AlSi308]) may be written as follows (Me = K, Na): 4Me[A1Si308] + 4H20 + 2CO2 ~=> AI4(OH)8[Si4Olo] + 2Me2CO3 + 8SIO2 In a recent review on feldspar weathering, Blum (1994) subdivides the feldspar weathering process into two main stages, dissolution and precipitation; he states that "...feldspar weathering occurs via dissolution of all components, with the subsequent precipitation of secondary minerals from solution". Dissolution rates for feldspars are very slow and these rates are determining the overall weathering reaction rate. Feldpars of all compositions have dissolution rates that increases with decreasing pH at pH<6. Other factors such as feldspar surface area (including internal surface area) and initial adsorption/exchange reactions also play an important role in the dissolution reaction. The weathering of feldspars under natural conditions is believed to be a process requiring 100,000 of years to complete (Blum 1994). * Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
SO2 attack on Ca-bearing porous building materials (such as, for example, limestones and/or lime mortars) with gypsum precipitation as an end product is well documented (Schiavon 1991, 1992; Fobe et al. 1995; Schiavon & Zhou 1996); although gypsum crystallisation on granitic building stone surfaces has also been ascribed to SO2 air pollution, the detailed pathway of the chemical reactions leading to stone decay in low porosity materials which contains less Ca (such as granitic stones) and are exposed to urban air pollution is less well undertood (Schiavon et al. 1994, 1995). As part of a wider investigation into the role played by SO2-enriched urban atmospheres in the weathering of granite-forming silicate minerals (with special reference to feldspars), samples of surface patinas on granite walls from the 18th century S. Jorge Church have been collected in the town of La Corufia, Galicia, NW Spain. The dark crusts sampled are composed of a framework of gypsum crystals (CaSO4 ~ 2H20) with fly-ash and airborne soil particles (quartz and feldspar) as minor components. In this study, Scanning Electron Microscopy (SEM) with Energy-Dispersive Spectroscopy (EDS) and Fourier-Transform Infrared Spectroscopy (FT-IR) have been combined to analyse in detail the weathering products and decay processes in the surface patinas of the S.Jorge church. One of the aims of the project was to assess whether gaseous SO2 from air pollution can be directly responsible for the onset of chemical weathering reactions in feldspars and for corrosion of granitic building stones. 2. Materials And Methods
20 patinas samples were collected from the granitic plinth at the base of the S-SW wall at approximately l m height. The stone is a fine grained leucogranite with polycrystalline quartz, xenomorphic K-feldspar, idiomorphic plagioclases and minor muscovite; plagioclase are more abundant than K-feldspars, biotitic mica is absent. On the outskirts of the city of La Corufia, a high-sulphur lignite burning power plant is currently operational and air quality data for La Corufia province for 1986 show a mean SO2 value of 75~g m-3. The climate in the region is humid-mesothermic. Both rough specimen surfaces and polished thin sections of the granitic chips spanning the contact stone-patinas were microscopically examined. The thin sections were hand polished down to a thickness of 60-70ktm (thicker than the standard 30ktm used in routine petrographical analyses to account for differences in hardness between rock substrate and weathering patinas). Atter sputter coating with a thin carbon (thin sections) or gold (rough specimens) layer, samples were examined in a Jeol 820L SEM (with a Robinson back-scatter detector) interfaced with a Link 860 EDS system. Back-scattered electron imaging was used for thin-section work as it provides better image resolution when studying materials with a complex chemical/mineralogical composition such as the weathering patinas under investigation. Powdered samples obtained by scraping with a stainless steel knife layers of black crusts and granitic substrate at increasing depths from the patinas-substrate interface were analysed by Fourier-Transform Infrared Spectroscopy (NICOLET 205 FT-IR Spectrometer). Infrared absorption spectra were obtained using KBr disks prepared by adding 1.5 mg of a pre-ground sample to 300 mg of potassium bromide (Aldrich FT-IR grade) and pressing it at a pressure of 9 tons for 4 minutes to form a 13mm diameter disk 1.5 mm thick. FT-IR analysis provides information about the chemical nature of unknown compounds by recording the amount of stretching and bending vibrations of chemical bonds caused by the applied infrared radiation.
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3. Results
Under SEM, sulphate patinas appear to be composed of a continuous, highly porous network of acicular, tabular and platy gypsum crystals. Within the gypsum framework, airborne iron-rich and aluminosilicate spherical particles and carbonaceous eenospheres derived from the combustion of fossil fuels can be seen together with mineral fragments detached from the rock substrate and soil dust (mainly well-rounded quartz grains). Although occasionally gypsum crystal enueleation seems to occur on the surface of carbonaceous anthropogenic particles typical of oil-fired power stations emissions, the bulk of sulphate precipitation does not show any correlation with the presence of these particles; furthermore their abundance in the sulphate patinas is very low. Physical weathering by gypsum crystal growth is evident, particularly on micas (muscovite) (fig. 1); pre-existing fractures on quartz crystals are further enlarged by the enucleation and growth of gypsum crystals. Gypsum erystallisation is observed down to a depth of a few millimeters from the original granite/atmosphere interface where it marks the inward boundary of the weathering front (fig. 2).
Figure 1 S . J o r g h e church, La Coruna; granitic stone surface. Crystallisation of gypsum crystals along basal cleavage planes of mica mineral leads to phisycal decay of the stone. SEM micrograph, secondary image. Figure 2 S.Jorghe church, La Coruna; interface granitic substrate/sulphate crust. Gypsum crystallisation occurs deep into the stone substrate enlarging preexisting fractures in granitic minerals, particularly feldspars (center of picture). SEM micrograph, back-scattered image. Authigenic crystals of NaCI with a distinctive cubic habit may occasionally be found within the sulphate crust. F eldpars grains are generally absent from sulphate patinas and the weathered surface of the underlying granitic substrate. Where found, feldspar grains show the development on their surface of elongate etch trenches, striations and prismatic etch pits producing a pseudo-perthitic texture (fig. 3). On the surface of the weathered granite and within the gypsum framework, micron-size poorly crystallised kaolinite occurring in aggregates and often displaying the distinctive booklet habit is common (fig. 4) ; in EDS plots, these aggregates show an elemental spectrum with a low Si-AI peak ratio consistent with kaolinite chemical composition (fig.5). Bulk X-ray diffraction analysis of sulphate patinas and of powdered samples obtained by scraping the outer surface of weathered granitic substrate confirms the presence of poorly crystallised kaolinite.
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FT-IR results are summarised in table 1, where a series of analytical wavenumber values (in cm-1) of absorption bands from the FT-IR spectra of reference standards (gypsum, kaolinite, quartz, albite, orthoclase) and of powdered samples taken at increasing depths from the interface atmosphere/granitic surface (i.e. from black sulphate patinas down to unweathered granitic substrate) are listed. A typical example of FT-IR spectra of black sulphate crusts is shown in fig. 6. By comparing FT-IR wavenumber values, relative intensities and peak shapes of unknown samples with the ones typical of pure compounds, we can establish whether the samples and the standards have (or have not) identical or very similar molecular structure and so verify the likely presence (or absence) of standard compounds in the unknown samples (Socrates 1994).
Figure 3 S. Jorghe church, La Coruna, interface granitic substrate/sulphate crust. Higly weathered feldspar surface. SEM micrograph, secondary image. Figure 4 S. Jorghe church, La Coruna; granitic stone surface. Cluster of micron-size kaolinite crystals showing the typical booklet habit.
< 0.9
keV
11.1
Figure 5 Energy Dispersive Spectroscopy plot of cluster of kaolinite cryistals of fig. 4
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
S.Jorge Cathedral
o~. ~o rn,-
415
~ ~ c/
22
~
II
I
I
8I
~.
I--
o
o
, I
c~
~ eqm
o "--
4000
'3600
'3200
'2800
'2400
'2000
'1800
I1600
t1400
~ 200
~m
'1000
'800
'600
O0
Wavelenghts (cm-1)
Figure 6 S. Jorghe church, La Coruna. Typical FT-IR spectrum of black sulphate crust. Numbers are wavenumbers in cm"~ Table 1 shows the presence of kaolinite, gypsum and quartz (SiO2) in samples 6 to 11 corresponding to black sulphate crusts (6), to the interface black crust/granitic substrate (7) and to samples at increasing distance (up to 2-3 mm) from the interface (8-11). The peak at co = 3695 cm -1 is characteristic of kaolinite and it is due to O-H stretching frequencies associated with the hydroxyl ions. A diagnostic pair of doublets for kaolinite (1035 vs/1010 vs cm-1 and 940 m(sh)/914 s cm "1) is also present; the first one is due to Si-O and AI-Si-O bonding while the second one represents A1-O-OH bending of kaolinite (Lyon and Tuddenham, 1960). Gypsum diagnostic peaks (which are interfering with main kaolinite peaks at co = 1112 s cm-1 and at 1139 vs/1117 vs cm-l) are at co = 3547 vs, 3407vs cm-1 (OH stretching), 1685w, 1621s cm "1 (O-H-O bending of the crystallisation water) and at 1144 vs (br, sh), 1114 vs, 670m, 600m(sh) cm -1 corresponding to the sulphate ions. Analytical wavenumber bands for silica (SiO2) are in the range 690-800 cm-1 and represent the bending vibrational mode of the -Si-O-Si- bonds in the polymeric (SiO2)n molecule. Within this range, there are differences between different silica compounds; Rao (1963) reports the following analytical wavenumbers: quartz = 694 cm-1 ; quartz in industrial dust = 800 cm-l; quartz in rocks = 781,694 cm -1. The reference values for quartz used in table 1 (798m, 780m, 695w cm -1) derive from our own FT-IR analysis of a quartz standard. -Si-OSi- bonds are also present in the kaolinite lattice between adjacent SiO4 tetrahedra sharing oxygens and the absorption bands at 788w, 696m cm-1 in the kaolinite standard may be attributed to the vibrational bending mode of these bonds. On the other hand, the band at
3548vs 3407vs
1685m 162 ls
670s
1143vs 1117vs
3697s 3620s
1103vs
1033vs lOOgvs
788w
937m 914s 798
1139vs 1139vs
10 11 12 13 14
3695vs 3547vs 362 lvs 3407vs 3697vs 3548vs 3620vs 3406vs 3696vs 3547vs 3620vs 3406vs 3696s 3540vs 3620s 3406vs 3696s 3547vs 3620s 3406vs 3696m 3545s 3620m 3406s 3696w 3544s 3620m 3408s 3696w 3620m 3410s
1685w 1622m 1686w 1621m 1684w 162 lm 1684wl 1621m 1684w 1621m 1684w 1621m 1684vw 1621mw -
l144vs 1114vs l146vs l116vs l147vs 1116vs 1144sh 1114vs l146vs 1117vs 1144vs l116vs l144vs 1143vs l137vs
1031vs lO12vs 1053vs lO14vs 1035vs 10 lOvs 1032vs lOllvs 1034vs 101 lvs 1034vs lO09vs 1034vs lO09vs 1034vs 1010vs 1096vs 1036vl lO16vs 1095vs 1035vs 1013vs 1093vs 1054vs,sh 1041vs lO19vs
602
696m 781
694
1094vs
('1)
770m
0
788m
694m
670m
601sh
788m
694m
671m
602m
787m
695w
670m
601m, s
693w
671m
601m, s
786m
693w
671m
602s
786m
694w
671w
797w
787m
695w
670w
797w
787m
695w
940w 914s 919s 919sh
780 914s
0
r~ r~ 0 (1) 0
0
915s
0
916s 919sh 914s
0 (/3 0
798m
780m
695w
Table 1. Absorption band values (wavenumbers in cm "1) from FT-IR spectra of samples: 1 standard gypsum; 2 standard kaolinite; 3 standard quartz; 4 standard albite; 5 standard orthoclase; 6 black sulphate crust; 7 interface black sulphate crust/granitic substrate;8 granitic substrate (0.5-1mm from interface);9 granitic substrate (1-1.5 mm from interface),10 granitic substrate (1.5-2 mm from interface); 11 granitic substrate (23 mm from interface); 12 granitic subtrate (3-4 mm from interface); 13 granitic substrate (5mm from interface); 14 unweathered granitic substrate (> 5ram from interface), w = weak, s = strong; vw = very weak; vs = very strong; m = medium; sh = shoulder.
<
i
b~
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417
787 cm -] can also be ascribed to amorphous silica formed during kaolinisation of feldpars (Blum 1994) as it will be discussed below in the comments to table 2. In sample 12 (3-4mm deep) kaolinite absorption bands are still present whereas gypsum bands decrease in intensity; at this depth, a well defined feldspar (albite) absorption band at 1096vs cm -1 appears for the first time together with a crystalline quartz band at 797 cm -1. The first appearance of bands typical of granitic minerals shows that only partial kaolinisation occurred at this depth. In sample 13 (4-5 mm deep) gypsum bands disappear. At a depth of >5mm from the interface patinas/granite (sample 14, corresponding to the unweathered granite), the disappearance of kaolinite bands is associated with the appearance of well developed absorption bands typical of albite (1093vs cm-1), of orthoclase (1054vs, sh cm -1) and of crystalline quartz (798m, 780m em -1) as the main constituents of the unaltered granitic stone. Although plagioclases, being part of a solid solution series between a calcic and a sodic end members (anorthite=Anl00/Ab0 and albite=An0/Abl00 respectively) show a continuous compositional variation, we have experimentally observed, analysing plagioelase standards of various composition, that when An < 70%, only absorption bands typical of albite show up in FT-IR spectra. The mainly sodic composition of plagioelases in the granite used in the S. Jorge church thus explains the absence of anorthite bands in our FT-IR results corresponding to the unweathered granitic stone. Spectrum
Sample
3696(7) cm -1 670 cm -1
%T
%A
%T
%A
787(8) cm -1
%T
%A
58.3
41.7
2
Std kaolinite
28.3
71.7
6
black sulphate crust (bsc)
31.9
68.1
30.5 69.5
37.1
62.9
7
interface (if) bsc/substrate
33.8
66.2
20.9 79.1
17.4
82.6
8
substrate 0. 5-1mm from if
35.6
64.4
12.9 87.1
18.4
81.6
9
substrate 1-1.5 m m f r o m i f
42.5
57.5
25.7 74.3
25.0
75.0
10
substrate 1.5-2 mm fromif
45.4
54.6
28.2 71.8 28.2
71.8
11
substrate 2-3 mm fromif
59.3
40.7
38.5 61.5
36.5
63.5
12
substrate 3-4 mm from if
66.0
34.0
62.2 37.8
58.4
41.6
13
substrate 5 mm from if
68.0
32.0
63.0
37.0
-
-
Table 2. Trend of absorption band's intensity with increasing distance from interface atmosphere/granitic stone surface of characteristic bands of kaolinite (3696-7 cm-1), gypsum (670 cm -1) and of amorphous silica + kaolinite (787 (8) cm -1). T = Transmittance; A = Absorbance. Spectrum numbers as in table 1. Bands intensity for kaolinite standard included for comparison. For discussion see text. Table 2 reports the variation in intensity values (derived from transmittance values) along the weathering depth profile for selected absorption bands, chosen as representative of kaolinite (3696-7 cm-1), of gypsum (670 cm -1) and of amorphous silica + kaolinite (787 cm1); absorption wavenumber values for kaolinite standard are presented for comparison. The
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kaolinite band at 3696-7 cm-I decreases in intensity from surficial sulphate patinas to a depth of 5ram from the interface gypsum patina/granite (samples 6-13). The gypsum band at 670 cm"1 shows a different trend: absorbance (i.e. intensity) increases up to a depth of lmm (samples 6-8); this is in agreement with SEM observations which show the depth of penetration of gypsum crystallisation (fig. 2); the band's intensity then gradually decreases until it disappears at 5ram from the interface (sample 13); it is important to note that, by contrast, kaolinite bands are still present at this depth showing how kaolinisation weathering fronts may penetrate deeper into the stone substrate than sulphate weathering fronts. The absorption band at 787 cm-1 which we interpret as representative of kaolinite + amorphous silica increases from the outer weathering patinas to the interface patina/granite (samples 6-7) and it then decreases to a depth of 5ram (samples 8-13). The increase in band intensity in samples 6 to 7 could be ascribed to the presence, beside kaolinite, of amorphous silica released from weathering of feldspars (Blum 1994). 4. Discussion
The kaolinite found on samples of granitic stone in the cathedral of S.Jorge in the town of La Comfia could have three main origins: a) deposition of kaolinite-bearing airborne soil dust and/or surface wash on the building surface; b) natural weathering in the original granite predating its use as a building stone; c) authigenic formation as a result of weathering processes operating since the emplacement of the granite in the cathedral and its exposure to the urban atmosphere. The identification from FT-IR analysis of kaolinite absorption bands at depths of up to 4-5ram from the interface surficial patinas-granitic stone rules out a soil dust or surface wash origin. On the other hand, the decreasing trend of kaolinite abundance in an inward direction from the surface of the granitic building stone until its disappearance at depths > 5ram (table 2) suggests that the kaolinite does not derive from weathering processes occurred during the granite's geological history. The presence of kaolinite in S.Jorge church samples is then due to surface weathering of granitic building stone occurred after the emplacement of the stone in the cathedral. Kaolinization may affect both mica (biotite and muscovite) and feldspar minerals (Stoch and Sikora 1976, Blum 1994). The absence of biotite and the accessory nature of muscovite in the granite used in the building of S. Jorge, suggests that feldspars are the most likely "reactants" in the kaolinisation reaction. SO2 air pollution in a humid climate may be responsible for direct silicate weathering via heterogeneous attack of feldspars either by the aeriform mixture SO2(gas) + H20(vap) adsorbed at the surface of the granite walls or by SO2(aq) in aqueous solution. The reaction pathway may be subdivided in three steps and in the case of Cafeldspar may proceed as follows: a) 2Ca(AI2Si208) + 2SO2 +2H20 r 2CASO3 + 2(A12Si2Os)-- + 4H + b) 2(A12Si208)-" +4H + r 2H2(A12Si208) c) 2H2(A12Si208) +2H20 r AI4(OH)8(Si4Olo)
fast
very fast very very slow
Steps a) and b) are in reality a unique fast reaction of ionic exchange between the cations Ca2+ and H + leading to to the formation of calcium sulphite and of an acid aluminosilicate less stable than the reagent Ca-feldspar and has been reproduced in experimental weathering tests on Ca-rich feldspars (anorthite) whose results will be presented soon (Schiavon 2000,
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in preparation). The Ca 2+ ions interleaving between the structural double layer of the silicate mineral, are esacoordinated with three oxygens atoms of one layer and with three oxygen atoms of the second layer. The calcium ions form six coordination bonds whereas the two H + do not and are then responsible for the metastable character of the acid aluminosilicate as compared with the feldspar. Step c) is the slow rearrangement reaction of the acid aluminosilicate to a basic silicate of aluminum (kaolinite). Oxidation of the calcium sulphite in step a) to sulphate (gypsum) may then ensue. Part of the gypsum present on sulphate crusts may then derive from sulphation of Ca-beating minerals in the granite and not from reaction with lime mortars and/or limestone architectonic elements (Schiavon et. al. 1995). If we assume the attack to procede via SO2(aq), the reaction mechanism may be expected to follow a similar pathway to the one advocated for a CO2(aq) controlled weathering in natural systems, i.e. dissolution by aqueous, aggressive pore solutions and precipitation of kaolinite (Blum 1994); the stoichiometry for the latter reaction would indeed be similar with CO2 substituting for SO2. Simply to substitute CO2 for SO2 in the equation above, however, does not necessarily mean that the respective reactions need following identical pathways; the acid strengths of the dioxides are indeed different and experimental evidence is forthcoming in showing differences in the reactivity of CO2 as compared with SO2 in the simulated weathering of feldspar minerals (Schiavon 2000, in preparation). In a CO2(aq) eontrolled weathering meehanism the formation of kaolinite as one of the final products is believed to require 100.000 of years (Colman and Dethier, 1984; Blum 1994); the reactivity differences mentioned above may influence the rate of the kaolinisation reaction and thus explain why in this study kaolinite is already present as a weathering product to a depth of 5mm from the atmosphere/granitic stone interface after less than 100 years of exposure to a SO2 aggressive atmosphere (corresponding to the time of significant SO2 release in the Galicia region in northern Spain). Alternatively, to explain the presence of the final product of the reaction (i.e. kaolinite) in such a short time span, the decay reaction pathway may be thought as having been proceded through an heterogeneous attaek by an aeriform mixture of SO2 (gas) + H20 (vapour) adsorbed at the surface of the solid granite and not by SO2(aq). Kaolinite is found at depths of up to 4-5 mm from the grantic wall surface and the low porosity nature of granitic building stone (typieal values for open porosity in granite are 2-3% in volume as opposed to values of up to 30% for limestones) and its low permeability is indeed unlikely to have allowed free circulation within the stone pore spaces of aggressive aqueous solutions in the same short time span considered in this study. Although microporosity has been shown to commonly exists in many unweathered feldspars (Walker 1990), the isolation of a large proportion of feldspar surface area in isolated micropores has been advoeated to explain the one to three order of magnitude slower rate of feldspar natural weathering in field studies as compared with experimental studies (Veldel 1993); this further confirms how "geological" time is usually assumed to be needed for complete weathering to occur under a CO2(aq) aqueous solution driven mechanism. The corrosion mechanism by an aeriform mixture SO2(gas) + H20(vap) here proposed may offset the inhibition effect on the rate of weathering caused by the above mentioned isolated nature of the microporosity and by preferential fluid flow considerations in feldspar minerals when dealing with dissolution in pore solution systems (Veldel 1993, Blum 1994). In summary, in a SO2 polluted environment such is the case here considered, an aqueous
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
solution does not need to be a necessary condition for the initiation of chemical weathering on feldspars and of granitic stone decay. The chemical and mineralogical transformation from aluminosilicate (feldspar, hardness=6-6.5 on the Mohs scale) to basic silicate of aluminum (kaolinite, hardness=2-2.5 on the Mohs scale) through the corrosion mechanism outlined above leads to important physical changes and significant weakening of the stone surface. The presence of minor kaolinite in well cemented quartz sandstones is known to be responsible for a decrease in the compression strenght and bulk density of the building stones (Sramek 1992). Kaolinisation of feldspars by SO2 action acts together with gypsum crystallisation to promote loss of cohesion and spalling or flaking of the stone surface. The identification of kaolinite as a weathering product up to 4-5 mm from the stone/atmosphere interface beyond the level at which gypsum is found suggests that kaolinisation may penetrate even deeper into the stone substrate causing major stone decay. Recognition of this process has thus important applications in conservation science. 5. Conclusions Authigenic kaolinite has been found on surface samples of granitic building stone in the town of LaComfia in northern Spain. Depth profiling of kaolinite abundance from the stoneatmosphere interface by FT-IR analysis suggests that kaolinite formed from weathering of the granite after exposure of the stone to the SO2-enriched urban atmosphere in the last 100 years. A model for the accelerated kaolinisation of feldpar minerals in granite is proposed which involves corrosion of the building stone via heterogeneous attack by an aeriform mixture of SO2(gas) + H20(vap) adsorbed at the surface of the granitic building stone. Taking into account the low porosity nature of granitic building stone, this reaction mechanism is preferred as opposed to the one promoted by SO2(aq) and is believed to better explain the presence of well formed kaolinite on the surface walls of a 200 years old monument which have been exposed to significant SO2 attack only for the past 100 years. In the weathering of granitic building stone, SO2 plays a dual role promoting both sulphate precipitation and kaolinisation of feldspars. Some of the Ca++ ions needed for gypsum crystallisation may derive from plagioclase weathering, in laboratory simulated SO2 attack on Ca-feldspar, Ca-sulphite and its oxidation product Ca-sulphate was obtained. Both processes have a profound effect in weakening the stone surface causing exfoliation, spalling and pulverisation. Further research on SO2 attack on granite is needed to establish whether kaolinisation is a general phenomenon in urban environments; future work will also include simulation experiments of granite weathering under laboratory controlled SO2 concentrations. 6. Acknowledgements I would like to thank Prof. Benita Silva-Hermo of Departamento de Edafologia, University of Santiago de Compostela for useful discussions and help with the logistics of sampling.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
7. Reference list
421
Blum A.E. (1994) Feldspars in weathering, in Feldspars and their reactions (ed. Parsons, I) pp.595-630, Kluwer Academic Publishers, The Netherlands. Colman S.M. and Dethier D.P. (1984) Rates of chemical weathering of rocks and minerals, pp.603, Academic Press, London. Fobe, B.O., Vleugels, G.J., Roekens, E.J.,Van Grieken, ILE., Hermosin,B., OrtegaC a l v e , J.J., del Junco, A.S., Saiz-Jimenez, C. (1995) Organic and inorganic components in limestone weathering crusts from cathedrals in southern and western Europe. Environmental Science & Technology 29, 1691-1701. Lyon R.J.P. and Tuddenham W.M. (1960) Infrared determination of the kaolin group minerals. Nature 185, 835-836. Rao C.N.R. (1963) Chemical Applications of Infrared Spectroscopy pp.543, Academic Press, London-New York. Schiavon, N. (1991) Gypsum crust formation and "stratigraphy" in weathered building limestones: a SEM study of stone decay in the UK. In C.Sabbioni, N.S. Baer and A.J. Sors (eds.) Proceedings of the European Symposium "Science & Technology for European Cultural Heritage", Bologna, 447-451. Schiavon, N. (1992) BSEM study of decay mechanisms in urban oolitic limestones. In Robin G.M. Webster (ed.) Stone cleaning and the nature of soiling and decay mechanisms of stone. Donhead Publ. Edimburgh, 141-151. Schiavon,N., Chiavari,G., Fabbri,D. & Schiavon,G. (1994). Microscopical and chemical analysis of black patinas on granite. In V. Fassina, H.Ott and F. Zezza (eds.) Proceedings 3rd Int. Symp. The conservation of monuments in the mediterranean basin, Venice, p. 9399. Schiavon N., Chiavari G., Schiavon G. and Fabbri D. (1995) Nature and decay effects of urban soiling on granitic building stones. Sci. Tot. Envir. 167, 87-101. Schiavon,N. & Zhou,L.P. (1996). Magnetic, chemical and microscopical characterization of urban soiling on historical monuments. Environmental Science & Technology 30, n. 12, 3264-3629. Socrates G. (1994) Infrared characteristic group frequencies. 2nd ed., John Wiley & Sons, New York. Sramek I. (1992) Kaolinitic quartz sandstones. The influence of mineralogy on physieomechanical properties and durability, in Proceedings of the 7th International Congress on Deterioration and Conservation of Stone, LNEC Lisbon, 1, pp.67-76. Stoeh L. and Sikora W. (1976) Transformation of micas in the process of kaolinisation of granites and gneisses. Clays and Clay Minerals 24, 156-162. Velbel M.A. (1993) Constancy of silicate mineral weathering rate ratios between natural and experimental weathering:implications for hydrologic control of differences in absolute rates. Chem. Geol. 105: pp.89-99. Walker F.D.L. (1990) Ion microprobe study of intergrain micropermeability in alkali feldspars. Contrib. Mineral. Petrol. 106: pp.124-128. Yatsu E. (1988) The nature of weathering, pp. 624, Sozosha, Tokyo.
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425 POLYSACCHARIDES AS A KEY STEP IN STONE BIO-EROSION Albertano P.*, Bruno L., Bellezza S., Paradossi G. Department of Biology and ~Department of Chemical Sciences and Technology, University of Rome "Tor Vergata", via della Ricerca seientifica, 00133 Rome, Italy; E-mail: [email protected] Abstract Cyanobacterial polysaccharides were studied in Leptolyngbya sp. isolated from Roman hypogea in order to gain preliminary information on their physico-ehemical characteristies. The contribution of released (RPS) and capsular (CPS) polysaccharides to total biomass was calculated and circular dichroism spectra of the three extractable polysaccharide fractions were analysed. All fractions showed the presence of uronic acids, and CPS of sulphated residues as well. No evidence of temperature dependence was found, whilst low pH values caused an irreversible change in the polysaecharide molecular conformation. Key words: Roman hypogea, biofilms, cyanobacteria, polysaccharides, circular dichroism. 1. Introduction Sciaphilous epilithic cyanobacteria and microalgae have been studied in a number of Roman Catacombs and Necropolis in Rome (Italy) to understand the ecophysiological and structural mechanisms that allow stone colonisation and cause deterioration of the archaeological surfaces (Albertano 1991, 1993, 1998; Albertano et al. 1991a, 1994, 1995; Albertano & Grilli Caiola 1989). Development of biofilms formed by phototrophic microorganisms was usually favoured by the climatic conditions of the sites, that are characterised by a limited air circulation, an even temperature throughout the year, and a high level of humidity. Biofilms were mainly composed of chroococcal and filamentous cyanobacteria associated to green algae and diatoms, and developed on stone surfaces thanks to the light gradients occurring in proximity of entrances and artificial lamps (Albertano et al. 199 l b, 1991e). Although irradiances available for photosynthetic activity were estremely low, the growth of phototrophs caused evident problems for the conservation of art works in most of the sites, and mainly in those exposed to massive influx of visitors. Terrestrial cyanobacteria and microalgae in Roman hypogea are possibly the first colonisers of the exposed surfaces and their extensive development is supported by the mineral composition of the substrata and facilitated by the porous nature of most calcareous surfaces. The strategies for the adhesion to the stone seemed to be generally based on the production and secretion at the cell surface of mucilaginous compounds. Exopolymeric substances (EPS) secreted by the microorganisms (glycocalyx, sheath or envelope) act in sticking the cells to the substratum, and their adhesive properties contribute to the formation and cohesion of biofilms. A polysaccharide matrix containing cell debris and significant amounts of inorganic material adsorbed from the substrate makes up most of the cyanobacterial films to which airborne particles, bacteria, and spores adhere increasing masking effects, transformation and corrosion of the surfaces (Albertano 1998). In addition, the anionic nature of exopolymers maintains highly hydrated the fibrous matrix, strongly adsorbs cations and dissolved organic molecules from the minerals, and stabilises dust particles (Decho 1993; Gloaguen et al. 1995). Calcium ions are easily subtracted and precipitated on polysaccharidic sheaths of cyanobacteria in form of calcium carbonate
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(Arino et al. 1995, Schneider & Le Campion-Alsumard 1999), and to a greater extent macronutrients as nitrogen and phosphorus are mobilised from the substrate and metabolised or stored into the cells (Albertano 1995, 1997; Albertano & Compagnone 1999). Moreover, the photosynthetic activity that sustains the production of new biomass into the ecosystem, supports the development of numerous populations of heterotrophic bacteria and fungi that graze on cyanobacterial and algal exopolysaccharides, metabolites and cell debris, therefore increasing the deterioration of stone by a synergistic action (Albertano & Grilli Caiola 1990; Albertano et al. 1991c, Albertano & Urzi 1999; Krumbein 1987). Cyanobacterial polysaccharides are still poorly known and extensive research was recently started mainly focusing on sugar composition and presence of sulphated residues (Bertocchi et al., 1990, De Philippis & Vincenzini, 1998, Gloaguen et al., 1995), whilst no data are yet available on their structure and physico-chemical properties. Variation in pH, temperature and ion concentration in the microenvironment could, in fact, influence the polysaccharides behaviour within the biofilms. Therefore, studies on polysaccharide fractions of selected cyanobacterial species from Roman hypogea were performed in order to gain preliminary information on their physico-chemical characteristics using circular dichroism.
2. Experimental Methods Cyanobacterial biofilms were collected at the Catacombs of St. Sebastian in Rome (Italy), where 90% relative humidity, 18 ~ constant temperature and irradiances < 1 l~mol photon m-2 s1, favoured the development of photosynthetic microbial communities on plaster and marble. Samples were observed either as flesh material or fixed in situ in 2.0% glutaraldehyde in 0.2 M phosphate buffer at pH 7.2 and subsequently processed for scanning and transmission electron microscopy (Albertano et al., 1991c). SEM and TEM observations were performed using a Zeiss DSM 950 at 10 kV and CEM 902 at 80 kV respectively. Cultures of a red pigmented Leptolyngbya sp, strain CSS6-3, previously isolated from the natural biofilms (Albertano & Bruno 1995, Bruno and Albertano 1999), were grown in BG11 medium (Rippka et al., 1979) at 17 _+ 1 ~ under photosynthetic photon flux density (PPFD) of 5 ~tmol m2 s"1with a dark-light cycle of 10:14 hours. After harvesting of cultures and culture media by centrifugation, polysaccharide extraction was performed according to Forni et al. (1998) to obtain three fractions: the polysaccharides in solution, termed released polysaccharides (RPS) and the envelope polysaccharides, termed capsular polysaccharides (CPSc = cold extract and CPSh = hot extract both from the cell pellets). Circular dichroism (CD) measurements of the the three fractions were carried out with a JASCO J600 spectropolarimeter. Concentration of 0.05 % (w/V) was used for the measurements with quartz cells of 0.1 cm.
3. Results and Discussion The results of the light microscopy observations were confirmed by SEM and TEM images that evidenced the presence of abundant polysaccharide material in the biofilms (Figs. 1-4). Oscillatorialean filamemous cyanobacteria were the most abundant phototrophic microorganisms in the community. Most of the bacteria and cyanobacteria appeared to be surrounded by individual capsules and sheaths made up of fibrils running in parallel. These structures may act in the adhesion of one cell to the other and contribute to the common mucilagineous matrix together with other excreted compounds. Total polysaccharides obtained after the extraction procedure on the Leptolyngbya sp., strain CSS6-3, were 3.4 % of flesh weight. The 1 . 1 % yield of extractable released polysaccharide (RPS) and of 2.3 % capsular polysaccharides (CPSc + CPSh) showed that
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Figure 1. SEM micrograph of green biofilms adhering to a marble surface inside the 'Cubieulum of symbols' in the Catacomb of St. Sebastian in Rome (Italy). Filamentous cyanobacteria and bacteria are held together by the EPS matrix, the outside face of which is clearly visible (arrow). Bar = 10 lam. Figure 2. TEM micrograph of a sample from the 'Cubiculum of symbols' at the St. Sebastian's Catacomb in Rome (Italy). Transverse section of the biofilm reveals filaments of Leptolyngbya sp. (arrow) and bacteria embedded in the common EPS matrix made up of several empty cyanobacterial sheaths (e). Bar = 5 ~tm.
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Figures 3, 4. TEM micrographs of a sample from the 'Cubiculum of symbols' at the St. Sebastian's Catacomb in Rome (Italy). Fig. 3. Longitudinal and cross sections of Leptolyngbya trichomes (L) inside the individual multilayered sheaths (arrow) interspersed among polysaccharide fibrils (arrow) and mineral precipitates. Fig. 4. Detail of Leptolyngbya triehomes showing the typical arrangement of thylakoids inside the cells, and mineral particles tightly adhering to the sheaths. Bars = 1 lam.
9 t h I n t e r n a t i o n a l C o n g r e s s o n D e t e r i o r a t i o n a n d C o n s e r v a t i o n o f S t o n e , V e n i c e 19-24 J u n e 2 0 0 0
I
I
I
429
I
RPS .....
CPSc
-- -- - C P S h
I--4 eXO
i i
'X::I
2r
-2
~
,
-4
200
t
t
220
~'
,,
t
240
I
t
260
280
300
(nm) Figure
5. Circular dichroism spectra of all fractions of extractable polysaccharides from
Leptolyngbya sp., strain CSS6-3, at neutral pH.
the latter represented a much more abundant proportion of biomass. CPSc and CPSh fractions represented the 29.9 % and 37.7 % of total polysaccharides respectively. Circular dichroism spectra of the three polysaccharide fractions are shown in Figure 5. The absence of any ellipticity in the region from 300 nm to 260 nm, particularly evident in CPSc spectrum, revealed that proteic material was completely eliminated during the purification steps. In the range from 250 nm to 200 nm a strong ellipticity was detected and , attributed to the n -, n electronic transition of the carboxylic groups embedded in the chiral saccharidic moiety. The broadness of this absorption spanning over more than 40 nm was indicative of an overlapping of contributions relative to different uronic residues present in the polysaccharidic chain. The high quantity of acidic sugars in the macromolecules accounted for the anionic nature of Leptolyngbya sp. polysaccharides, a feature common to almost all the cyanobacteda studied so far (De Philippis & Vincenzini, 1998). The independence of the dichroie absorption from the temperature, as shown in Figure 6, was indicative of the absence of a structured conformation at room temperature. This finding was in agreement with the behaviour of chemically similar polysaccharides from other cyanobacteria (Cesaro et al, 1990) and from macroalgae (Paradossi et al., 1999). Moreover, the change of the spectral features upon lowering of the solution pH (Fig. 7) proved to be irreversible since a back neutralisation of the polysaccharide solution did not cause a recover of the original CD spectrum.
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Figure 6 Fraction CPSc of extractable polysaccharides from CSS6-3. Dependence of ellipticity from temperature.
Leptolyngbya sp., strain
Figure 7 Fraction CPSc of extractable polysaccharides from CSS6-3. Dependence of ellipticity from pH.
Leptolyngbya sp., strain
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Sulphated groups did not interfere in the range of the UV spectrum explored with CD analysis. In addition, cytochemical staining of Leptolyngbya sp. (Albertano, pers. comm.) indicated the presence of sulphated groups in the polysaceharide sheath of this species as it has been previously evidenced for 17 Oscillatoriacean strains, mainly of marine origin (Gloaguen et al., 1995). Sulphatation of the macromoleeules will increase the high anionic density due to the uronic acids and the affinity of polysaccharidie chains for the adsorption of calcium and other cations. The biological mobilisation of the dements from the substratum would be, therefore, favoured by the presence of this type of polysaccharides. In conclusions, our results indicate that further and extensive investigation on polysaccharides produced by terrestrial cyanobacteria is necessary as well as the understanding of the role played by EPS in the interactions among bacteria, cyanobacteria, algae and the substrata. On the other hand, quantification and identification of the chemical composition of the EPS that are produced by these microorganisms would offer new possibilities for the eradication and control of biodeteriogenie agents through factors, i.e. enzymatic hydrolysis (Decho, 1993), affecting the cohesiveness and stability of the exopolymeric matrix that characterises biofilms in Roman hypogea. 4. Acknowledgements This work was supported by the financial contribution of the National Research Council of Italy, C.N.R.- Progetto Finalizzato Beni Culturali, grant 97.00578.PF36. We gratefully thank Pros F. Bisconti and Dr. R. Giuliani of the "Pontificia Commissione di Archeologia Sacra" in Rome for the fruitful collaboration and the permission to sample inside the Catacombs. 5. References Albertano P., 1991. The role of photosynthetic microorganisms on ancient monuments. A survey on methodological approaches. Journal of European Studies on Physical, Chemical, Biological and Matemathical Techniques applied to Archaeology, PACT 33, 151-159. Albertano P., 1993. Epilithic algal communities in hypogean environment. Giom. Bot. Ital., 127, 385-392. Albertano P., 1995. Application of ESI and EELS analysis to the study of microalgae. Microscopia Elettronica 16, Suppl. 2, 165-167. Albertano P., 1997. Elemental mapping as a tool in the understanding of microorganismssubstrate interactions J. Computer Assisted Microscopy, 9, 81-84. Albertano P., 1998. Deterioration of Roman hypogea by epilithic cyanobacteria and microalgae. In: A. Guarino et al (eds.) Science and technology for the safeguard of cultural heritage in the Mediterranean basin, vol 2, Palermo, CNR Editions. 1303-1308. Albertano P., Bruno L. 1995. Photosynthesis, pigments and ultrastmcture of an acclimating Leptolyngbya sp.. Giorn. Bot. Ital., 129, 1285-1287. Albertano P., Compagnone D., 1999. Ultrastmctural and analytical approaches to the study of stone microbial communities. In: M. Monte (ed.) Eurocare-Euromarble Proceedings EU 496/8, Rome, CNR Editions. 89-93. Albertano P., Grilli Caiola M., 1989. A hypogean algal association. Braun Blanquetia, 3, 287-292.
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Albertano P., Grilli Caiola M., 1990. Bacteda/Lyngbya association in nature and in culture. Giom. Bot. Ital., 124, 642-643. Albertano P., Kovacik L., Grilli Caiola M., 1994. Preliminary investigations on epilithic cyanophytes from a Roman Necropolis. Arch. Hydrobiol., Algological studies, 75, 71-74. Albertano P., Kovacik L., Marvan P., Grilli Caiola M., 1995. A terrestrial epilithic diatom from Roman Catacombs. In: D. Marino and M. Montresor (eds.). Thirteenth Diatom Symposium, Bristol, Biopress Ltd. 11-21. Alberta.no P., Luongo L., Grilli Caiola M., 199 la. Ultrastructural investigations on algae deteriorating roman frescoes. In: N. Baer, C. Sabbioni and A.I. Sors (eds.). Science, Technology and European Cultural Heritage, Oxford, Butterworth-Heinemann Ltd. 501-504. Albertano P., Luongo L., Grilli Caiola M., 1991b. Influence of different lights on mixed cultures of microalgae from ancient frescoes. International Biodeterioratiort, 27, 27-38. Albertano P., Luongo L, Grilli Caiola M., 1991c. Observations on cell structure of microorganisms of an epilithic phototrophic community competing for light. Nova Hedwigia, 53, 369-381. Albertano P., Urzi C., 1999. Structural interactions among epilithic cyanobaeteria and heterotrophic microorganisms in Roman hypogea. Microbial Ecology, 38, 244-252. Arifio X., Hernandez-Marine M.., Saiz-Jimenez C., 1997. Colonization of Roman tombs by calcifying cyanobactefia. Phycologia, 36, 366-373. Bertocehi C., Navadni L., Cesaro A., Anastasio M., 1990. Polysaccharides from cyanobacteria. Carbohydrates Polymers, 12, 127-153. Bruno L., Albertano P., 1999. Photoacclimation of sciaphilous epilithic cyanobacteria isolated from Roman hypogea. Arch Hydrobiol., Algological Studies, 94, 89-103. Cesaro A., Liut G., Bertocchi C., Navarini L., Urbani R., 1990. Physicochemical properties of the exocellular polysaccharide from Cyanospira capsulata. Int. J. Biol. Macromol., 12, 79-84. De Philippis R., Vincenzini M., 1998. Exocellular polysaccharides from cyanobacteria and their possible applications. FEMS Microbiol. Rev., 22, 151-175. Decho A. W., 1993. Molecular-scale events influencing the macroscale cohesiveness of exoploymers. In: W. E. Krumbein, D. M. Paterson and L. J. Stal (eds), Biostabilization of Sediments, Oldenburg, BIS. 135-148 Forni C., Haegi A., Del Gallo M., 1998. Polysaccharide composition of the mucilage of Azolla algal packets. Symbiosis, 24, 303-314. Krumbein W.E., 1987. Microbial interactions with mineral materials. In: D.R. Hougton, R.N. Smith and H.O.W. Eggins (eds.). Biodeterioration 7, London & New York, Elsiever Applied Science. 78-100. Gloaguen V., Morvan H., Hoffmann L., 1995. Released and capsular polysaccharides of Oscillatoriaceae (Cyanophyceae, Cyanobacteria). Archly ftir Hydrobiologie, Algological Studies, 78, 53-69. Paradossi G., Cavalieri F., Pizzoferrato L., Liquori A.M., 1999. A physico-chemical study on the polysaccharide ulvan from hot water extraction of the macroalga Ulva. Int. J. Biol. Macromol., 25, 309-315. Rippka R., Deruelles J., Waterbury J.B., Herdman M, Stanier R.Y., 1979. Generic assignements, strain histories and properties of pure cultures of cyanobacteria. J. Gen. Microbiol., 111, 1-61. Schneider J., Le Campion-Alsumard T., 1999. Construction and destruction of carbonates by marine and freshwater cyanobactefia. Eur. J. Phycol., 34, 417-426.
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THE TEMPLES OF THE ARCHAEOLOGICAL AREA OF PAESTUM (ITALY): A CASE STUDY ON BIODETERIORATION Altieri Antonella*, Pietrini Anna Maria, Ricci Sandra, Roccardi Ada Istituto Centrale del Restauro, P.zza San Francesco di Paola 9, 00184 Rome - Italy Piervittori Rosanna Dipartimento di Biologia Vegetale, Universit/t di Torino, Turin- Italy
Abstract
A study on biodeterioration of the temples of Athena, Neptune and Basilica in the archaeological area of Paestum has been performed. In order to characterize the kinds of deterioration, a procedure of reconnoitering, mapping out and taxonomical identification of biodeteriorating agents was carried out. On the basis of the distribution and the frequency of the different taxa, what emerged was that the various biological colonizations were connected essentially to the kind of stone to its state of conservation and to the different microclimatic situations present on each of the three monuments. The travertine surfaces, the principal material in the structural elements, were colonized prevailingly by epilithic and endolithic lichens and higher plants and, to a lesser and more localized degree, by phototrophic microflora (cyanobacteria and algae) and bryophytes. Key words: Paestum, travertine biodeterioration, algae, lichens, mosses, higher plants. 1. Introduction
The restoration of the temples of Athena, Neptune and Basilica, situated in the archaeological area of Paestum, has been the occasion to carry out a complete study of biodeterioration of the stone materials that make up the three architectural structures. The ancient town of Paestum (Salemo, Italy) is on top of a rocky bank roughly 20 m above sea level, about one kilometre from the seashore. This area has a mediterranean climate, with summer drought and rainfalls occurring mostly in autumn and spring. The temples have been built with two kinds of stone material: local travertine, made up mostly of architectural elements and sandstone, employed in architraves, in correspondence with parts decorated in relief. The aim of the present work has been to study the variability and the distribution of different biological communities, so as to verify the incidence of environmental factors and the role played by the substrata on the growth of organisms. Each architectural complex has been examined in its entirety so as to create a relationship between the colonisation present on the various structural parts with exposure, its quota, the materials which constitute the structures and their state of conservation. The need for a separate study of the various groupings arose, due to the heterogeneous nature of the phenomena of biological degradation, as well as the peculiarities of the individual groups of organisms.
*Author's to whom correspondence should be addressed
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2. Results 2.1. Autotrophie mieroflora A point of departure for the study of microbe colonisation has been the thorough survey of alterations of certain or probable microbiological origin. On the basis of visual observation, it has been found out that the growth of microflora manifested itself with diverse forms of alteration and that they were present on the travertine, never on the sandstone. This may be explained by considering the structure of the two constituent materials. Travertine is a calcareous stone created by the chemical precipitation of calcium carbonate, non-homogeneous in structure. Such characteristic has determined the formation of many micro-environments with peculiar thermo-hygrometric conditions which favoured attachment and subsequent proliferation of epilithic photoautrophic microflora. The absence of biological alterations on the sandstone parts of the temples can be explained by the tendency to break up of this material, constantly exposing new surfaces, not favouring the development of potential biodeteriorating agents. In the course of surveys have been noticed the following kinds of alterations: patinas of a soft consistency and of a green colour, localised in some of the cavities in the travertine and distributed on all the sides of the temple; globular incrustations, fragile, of a blackish colour on the exterior and dark green on the interior, placed mainly undemeath the capitals, along all the sides of the temple; incrustations of a grey colour, more or less accentuated, extended on all the vertical travertine surfaces. The green patinas have been found to be made up of mixed populations of cyanobacteria and microalgae. In particular, an abundant number of individuals belonging to the Cyanophyceae and traceable to the Gloeocapsa, Nostoc, Lyngbya, Chlorogloea and Myxosarcina genera, together with some examples of the Bacillariophyceae and Chlorophyceae, this latter present with the Chlorococcum and Scenedesmus genera. It is for the most part ubiquitous micro-organisms, commonly found in stone surfaces, whose lifecycle and related diffusion are favoured by the presence of water (Ricci et al., 1989). This explains why such a population of algae was localised uniquely inside those travertine cavities where there was less sun and where the accumulation of earth and the slow evaporation of the water determined a constant humidity factor. Such epilithic photoautrophic communities initially formed slight layers made up of a few taxa and then evolved towards more complex biocoenosis. The surveys carried out during the year showed how the populations undergo even seasonal changes, conceming principally the number of individuals. This increases substantially in the hot season with peaks in spring (April-May) and at the end of the summer (September-October) in relation to the milder temperature and the presence of rain. The globular incrustations have resulted as being formed by thin mixed calcareous layers, and at times regularly altemated with a rather heterogeneous microbe population, constituted by Cyanophyceae (Chlorogloea microcystoides Geitler, Lyngbya sp., Chroococcus sp.) Bacillariophyceae and Chlorophyceae (Chlorococcum sp. and Scenedesmus sp.). This type of alteration, very similar to that found frequently on fountains, may be due to the infiltration of rain water coming from the upper structures of the temples. Water, flowing through preferential paths, comes out in fully localised places, where it forms carbon deposits, due to the constant water-drops. On them are found cyanobacteria and microalgae which, due to the high humidity, find an ideal ground for growth. The repetition of such a phenomena determines a characteristic layering of calcareous patinas of algae.
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The grey incrustations have been found to be forms of algae in a process of lichenization, constituted by Chlorophyceae, strictly intertwined with fungal iphae of a dark colour. The examination of morphological characteristics of the photobiont brought to the recognition of the Trebouxia genus (fam. Chloroccocaceae) even if in some samples it has not been possible to identify with certainty since this algae modifies its morphology when it becomes lichenized. This type of association has been frequently found on stone material, in conditions of high ventilation and scarce humidity of the substrata. An analysis of the results has shown substantially similar situations in the three temples both in terms of conditions of growth (substrata, environmental factors) and for quality and quantity characteristics of the biocoenosis present. The colonisation of the algae on the various architectural parts does not reveal to be influenced in any significant way by the exposition, but rather by the quantity of water present in the material, which was shown to be variable in relation to the orientation, but above all to the structure of the travertine and the internal channelling of the water. On the basis of the ecological characteristics of the taxa found it has been possible to associate the presence of populations of cyanobacteria and algae in the areas of the temples with the greatest humidity and the forms of lichenisation in the driest areas of the stone material. 2.2. Lichens The presence of epilithic lichens and endolithic ones on the three temples has been found relevant and different for each one. In relation to travertine surfaces, the sandstone ones were without lichen colonisations, except in some limited areas. Surveys carried out in the temple of Athena have privileged above all the columns and have been carried out in such a way as to be representative of the different situations found out. In general, a strict correlation has been found between the distribution of the species and exposure: colonisation has been found more abundant on the lower portions of the columns. If the presence of epilithic lichens revealed a considerable visual impact, the same could be said, in terms of stone degradation, of the endolithic ones, which formed continuous and extended mosaics. Amongst the epilithic species were most conspicuous, in terms of frequency and degree of covering, Dirina massiliensis which formed whitish incrustations, converging, thick and of a cretaceous aspect, localised above all on the surfaces facing north and north-west. This lichen usually prefers vertical surfaces or those protected by rain, scarcely eutrophic and in general not exposed to direct sunlight. It is often found on stone artworks, where it can cause, aside from indubitable aesthetic damage, also considerable chemical alterations of surfaces. Thalli, impregnated by calcium oxalates, may leave micropitting of surfaces, more easily attacked by polluting and environmental agents (Nimis 1992; Seaward et al., 1990). For this temple what emerged as a significant factor was also the presence of the crusty endolithic Bagliettoa parmigera, and crusty epilithic species Acarospora glaucocarpa, Caloplaca aurantia and Lecania eryside (tab. 1). On Neptune's Temple, the upper parts of the trabeation presented, regardless of the exposition of the surfaces, a considerable and diffused colonisation on the part of Bagliettoa parmigera, with a cover which can be assessed as being between 30 and 50%, in particular on horizontal surfaces. It is interesting to note that, wherever B. parmigera was present, the underlying substrata was more protected by erosive phenomena due to the action of meteoric waters, caused by a bioprotecting action.
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Along the vertical surfaces of the columns, D. massiliensis showed a different degree of cover which increased progressively in the upper parts towards the inferior ones. In the superior areas the colonies assumed a typical 'poured' aspect, related to the presence of higher plants which colonised the capitals and abaci.
Table 1 - Lichen taxa surveyed on the three templa of Paestum. Growth Species* Form* Ecological features* *
Substrate*
L'
A carospora glaucocarpa
Cr
on calciferous rocks and base-rich Sax siliceous substrata in sunny nutrientenriched situations Bagliettoa parmigera Cr. end in nutrient-poor situations, on Sax (J. Steiner) Vezda and Poelt limestone and dolomite Caloplaca aurantia Cr. pl on calcareous rocks, on man-made Sax (Pers.) Helb. substrata Caloplaca teicholyta Cr on base-rich siliceous rocks and Sax (Ach.) Steiner man-made substrata Collema crispum (Huds.) i Fol. b on base-rich soil, in fissures, on Sax-Terr F.H. Wigg. walls Collema tenax (Sw.) Ach. Fol. b on base-rich soil, in fissures, on Terr walls Dirina massiliensis Cr on limestone and siliceous rocks, Sax Durieu and Mont rather shaded habitat Lecania erysibe Cr on nutrient-enriched, more or less Sax (Ach.) Mudd. calcareous rocks and man-made substrata Lecanora muralis Cr. pl on limestone, base rich siliceous Sax (Schreb.) Rabenh. rocks, sometimes acid siliceous rocks, on man-made substrata Squamarina periculosa Sq in fissures of calcareous rocks, often Sax (Schaer.) Poelt in rather shaded habitat Verrucaria nigrescens P e r s . . Cr on a variety of substrata Sax * according to Nimis 1993; ** according to Nimis 1999. (Cr = crustose; Cr. end = crustose endolithic; Cr. pl = crustose placodiomorph; Sq = squamulose; Fol. b = foliose broad-lobed; Terr = terricolous; Sax = saxicolous) (Ach.) Korb.
Surveys revealed the presence of a diffused colonisation of the Squamarina periculosa on the eastern, northern and southern sides, along internal vertical walls of the trabeation, on surfaces in the shade. It is a lichen with a squamulose thallus, of a green colour, which prefers to colonise calcareous rock fissures or small cavities in the shade. It is therefore often associated to the presence of upper vegetation which can insure, through the shading, a sufficient degree of humidity. The same lichen was at times associated with Lecanora muralis, which tends to form continuous and consistent placodioid thalli: its presence can start relevant phenomena of physical and chemical degradation. Also on vertical surfaces exposed to the north of the Basilica, the most evident alterations have shown themselves to be caused by the D. massiliensis species. On the horizontal and
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vertical surfaces of the trabeation exposed to the south have been found abundant cover of Verrucaria nigrescens, a crusty epilithic species, forming thalli of a dark brown colour, often mixed with moss cushions and Bagliettoa parmigera, less evident macroscopically but extensively diffused on stone surfaces. Occasional thalli of lichen were also present of the Squamarina genus and Caloplaca teicholyta and Caloplaca aurantia. Here also, on the topmost part of the temple, a relevant bioprotective effect was noticeable, produced, in this case, by thalli of F. nigrescens. In relation to what was observed on the other two temples, the alteration which concerned very extended surfaces was represented by gray-green incrustations, distributed along the columns, referred to algae in the process of lichenisation. The alterations at the base of the three temples were very different, since the floristic richness increased and the colour contrast on the surfaces also increased. The predominant species which gave the substrata a dark brown colouring was Ferrucaria nigrescens; amongst the most diffused species, which gave an intense orange colouring, was Caloplaca
aurantia. Lecanora muralis, Squamarina periculosa, Collema crispum, and Collema tenax were also found. These last two species are frequent on stone substrata with accumulation of earth (tab. 1).
2.3 Bryophytes Surveys of the flora have been carried out in different seasonal periods, so as to verify both the gametophytic and sporophytic generation. Assessment in the field of bryophytic growth has been carried out by employment of growth-forms, in which the species are placed in their typical habitat, where they are normally present in the most favourable ecological conditions for development (Gimingham and Birse, 1957). Bryophytes observed in the stone structures of the temples of Paestum presented themselves with the following growth-forms: cushions, of a round shape with radiating shoots; short turfs, with shoots placed in parallel alignments; mats, with shoots extending horizontally over the substratum. The growth-forms showed up to be strongly influenced by the kind of substrata: turfs and cushions predominated on the stone material whilst mats, including liverworts, were more frequent on the accumulations of earth inside the travertine cavities. As far as relations between the growth-forms and microclimatic parameters, it can be indicated that the most arid zones (tops of trabeations and of abaci) showed prevailingly cushions and turfs, since such structures are the most effective in containing water loss. In the dampest, shadiest areas, such as cavities, fissures and parts of the base, were found very favourable microclimatic conditions which allowed for the development of all the growthforms, amongst which also of mats, set up both by mosses and liverworts Marchantia polymorpha (L.) and Lunularia cruciata (L.) Duru. Colonisation appeared to be more diffused on horizontal surfaces of the trabeation and of the tops of the abaci. Almost all moss species identified showed up to be xerophylous or meso-xerophylous and eliophylous. The presence, in fact, of the only sciaphylous and mesophylous species, Rynchostegiella tenella showed up to be limited only to a few shady and damp areas. The number of identified species is rather limited (tab. 2). The restricted wealth of flora is in strict relation both to the microclimatic situation present on the architectural structures of the temple, and to the characteristics of the stone material, which, even if full of cavities in which bryophytes can fit in, it is subject to a fast flowing of water inside hollow structures, and to a quick drying up.
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The most frequent species found in floristic surveys have been Tortula muralis and Barbula convoluta. The presence of T. muralis, in particular, is well adapted to the microclimatic characteristics of the architectural structures examined: it represents an emblematic example of moss, capable of surviving drying up. Physiological studies carried out on this species have in fact demonstrated that its capacity for survival with lack of water is particularly high, especially with low values of related humidity (about 30%): moreover, it has been demonstrated that, even after drying up, individuals are capable of fully reestablishing their ftmctions within 15 hours of rehydration (Gimingham and Birse, 1957). These physiological characteristics have allowed T. muralis to colonize also the most exposed stone surfaces and the driest in the temples, where the sun irradiation and ventilation cause a quicker drying up of the stone. In some areas was found the laying out of calcareous incrustations above moss gametophytes, showing the presence of dripping of water rich in carbonated water, probably deriving from the dissolution at the top of the travertine.
Table 2. Moss taxa from the three temples. Species*
Ecological feature
Growth
Substrate
form xerophylous, saxicolous, pH turfs mortar, concrete, basic indifferent, cosmopolitan rocks, walls Barbula convoluta Hedw. xerophylous, saxicolous, turfs soil, walls, old calcicolous, heliophylous . buildings Trichostomum crispulum xerophylous, saxi-terricolous, turfs soil, rocks, mortar of Bruch. neutrophylous walls, in basic areas Fissidens viridulus (Sw.) meso-xerophylous, turfs soil, rocks, in shady Wahlenb. terricolous, acidophylous, i places photo-heliophylous Bryum capillare Hedw. ubiquist, cosmopolitan cushions rocks, walls Homalothecium sericeum meso-xerophylous, saxicolous mats basic rocks, walls, in (Hedw.) B.S.G. pH indifferent, heliophylous . . dry and exposed places Brachythecium rutabulum ubiquist, cosmopolitan mats soil, rocks, walls, in (Hedw.) B.S.G. shaded habitat Rhynchostegiella tenella mesophylous, saxi-terricolous, mats basic rocks, walls, in (Dicks.) Limpr. . neutrophylous, sciaphylous . shaded habitat *According to Cortini Pedrotti (1992). Tortula muralis Hedw.
The columns, in the base and in the middle portions, have showed up as being almost deprived of colonisation in the three temples, plausibly due to the rapid loss of water, to which these vertical structures are subject. The temples showed signs of colonisation by bryophytes in more or less similar ways. The colonisations of the temples of Athena and Basilica have resulted in any case more relevant, both on a floristic and cover level. For what concerns the temple of Athena this result has been to lead essentially the worst state of conservation of travertine which presented a greater presence of cavities with earth accumulations. The Basilica, instead, whilst its travertine was in the best state of conservation, presented a greater number of colonisable surfaces, due to a better maintained architectural whole.
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2.4 Higher plants The presence of higher plants was for the greatest part on the top portion of the three temples as well as at the base. Qualitative and quantitative analyses were carried out, the latter both by phytosociological methodology, adopting the indexes of the Braun-Blanquet (1928), and by counting individuals for each species, on homogenous surfaces, as far as orientation and size. The study has been limited only to trabeations, to the various parts of the capital and to the upper drum of the columns since, being surfaces placed at elevated heights and not easily reached, they should not have been the subject to repeated weeding activities, which would have been the case with the base. In tab. 3 are listed the different species found and, for each of the three temples, the class of presence was also indicated; such index, calculated on the phytosociological relev~s, allows for a useful comparison between the temples. From the surveyes of the species can be observed a scarce floristic diversity, to be attributed in part to the kind of rocky habitat and in part to the winter period, in which the investigations have been carried out. It has not been possible to integrate floristic data withsamples in the spring-summer period, due to the beginning of restauration activities, which had as an initial phase the weeding out of any flora. All identified species are typical of rocks and some of them are characteristic of coenosis of the Parietarietea and Asplenietea classes (Hruska, 1979; Caneva et al., 1995). From a conservation point of view most of the species include herbaceous plants, biennial or perennial (hemicryptophytes) or small trees (chamaephytes), whose growth can determine a static-structural damage. On the basis of qualitative and quantitative data, the presence of Umbilicus rupestris is highlighted, recurrent in the three temples. The fern Ceterach officinarum is frequent on the trabeation of the Temple of Athena, less frequent instead on Basilica and absent altogether on Neptune. Antirrhinum majus, common on the temples of Neptune and Basilica (class of presence IV and V) is absent on the temple of Athena. Taking in consideration ecological needs of the species, it is possible to relate the differences found in the three temples with the state of conservation both in the constitutive material and in the entire architectural complex. In fact, the temple of Neptune, in which the different elements at the top (gable, architrave, frieze, cornice) have kept their architectural integrity, presents a greater number of chamaephytes distributed on the most exposed surfaces, such as the abaci and the summit of the trabeation, where there is greater exposure to the sun and a greater quantity of rainwater. Their highest frequency (tab. 3) allows to notice the existence of more arid conditions on such a temple compared to the one of Athena, where instead U. rupestris and C. officinarum fern prevail, both species typically
Family*
Species*/Phytosociological classes
Life form* [9
Temple
shadow and humid rocks rocks shadow and humid rocks
Basilica [ Athena I Neptune number of relev~s 9 9 12 I IV I IV I IV V III
Asplenietea rupestris Aspleniaceae Crassulaceae Crassulaceae Urticaceae Urticaceae Scrophulariaceae Moraceae
Ceterach officinarum DC. Sedum dasyphyllum L. Umbilicus rupestris (Salisb.)Dandy Parietarietea diff usae Parietaria diffusa M. et K. Urtica dioica L. Antirrhinum majus L. Ficus carica L.
H ros Ch succ G bulb H scap H scap
Chfrut P scap
II
Habitat
calcareous and sunny rocks ruderal and nitrophylous rocks, stony, debris, walls shadow rocks, walls
I V
I~ -
-
~. o
==,. ~ o ~=
I
~ o
other species Cruciferae
-~ =
II IV
-
0
=
Lobularia maritima (L.) Desv.
H scap/ waste land, rocks, walls IV IV II Ch suffr Sonchus oleraceus L. T soap walls, at the roadside II II II Compositae Liliaceae Allium sp.(cfr, neapolitanum Cyr.) G bulb humid and shadow walls I II I Graminaceae spp. nd I II I Chenopodium album L. T scap ruderal, weed environment IV I Chenopodiaceae Amaranthus retroflexus L. T scap ruderals, debris II Amaranthaceae Labiatae Micromeria cfr. graeca (L.) Bent Ch suffr rocks II II Cruciferae Alyssum saxatile L. Ch suffr calcareous rocks I I I Crassulaceae Sedum sediforme (Jacq.) Pan. Ch succ rocks, stony, walls I I I Cerastium ligusticum Viv. T scap ruderal I I I Caryophyllaceae Geraniaceae Geranium rotundifolium L. T scap waste land, walls I I Boraginaceae spp. nd I I ' T a b l e 3 -List of tlae plant species surveyed (on January 1996 and 1997) on the upper structures of the three temples at Paestum with the presence class index (I = 1-20%; II=21-40%; III=41-60%; IV=61-80%; V=81-100%). (nd = not detectable). *The nomenclature follows Pignatti (1982).
~ ~. o ~= ~. o ~ < g. o = o o < o-~. ,~ ~ t'D t',J
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found in damp or shady rocks. In particular, U. rupestris is usually inside the cavity of the travertine: its greater diffusion on the surfaces of the temple of Athena can be traced to a greater degradation of such material, which was observed in the temple. It is interesting to note the fact that the Basilica may present a habitat with intermediate characteristics compared to the other two temples, which may be synthetized in the recurrent presence of a species, A. majus, which tolerates arid conditions, together with U rupestris and C. officinarum, species which belong to damper environments. So as to highlight the role of the factor of inclination in the selection of the diversity, and the degree of cover of the different species, phytosociological surveys on horizontal and vertical surfaces were carried out. The fact that, while both surfaces presented extreme floristic poverty (4-5 species), the degrees of cover varied (50% on horizontal surfaces, 20% on vertical ones).It is also interesting to note the preferential presence of U. rupestris, Parietaria diffusa and Sedum dasyphillum on vertical surfaces. Another selective factor, above all on vertical surfaces, has been exposure. Exposures south and west showed a greater percentage of cover and in part also a greater floristic diversity in all three temples. In fig. 1 is marked the frequency (%) of the number of individuals shown for each of the recurrent species in the four principal expositions, on the columns of the temple of Athena. Analysing the specific composition of such a survey, the U. rupestris was shown to have been the species with the highest number of individuals, followed by S. dasiphyllum and P. diffusa.
Umbilicus rupestris Sedum dasyphyllum Parietaria diffusa Sedum tenuifolium Urtica dioica Lobularia maritima Ceterach officinarum
28
20
26
1
6
ll
37 15
6
5
ll
3
-
5
6
-
-
-
5
3
-
2
3
2
-
2
1
3
1. Surveyes of higher plants on different exposures of the upper surface of ten columns: a) frequency (%) of the individuals for each exposure; b) list of the species more frequently surveyed and number of individuals for each of them.
Figure
3. C o n c l u s i o n s
Microflora and vegetation present on the temples showed characteristics of rocky habitats and seem to be affected considerably by environmental factors. Taking into consideration the different groups of biodeteriorating agents, a reduced floristic diversity was found, in comparison to preceding surveys carried out in archeological areas (Roccardi and Bianchetti, 1988; Garcia-Rowe and Saiz-Jimenez 1991; Altieri and Ricci, 1994; Caneva et al., 1995 Aleffi et al., 1997; Mouga and Almeida, 1997)
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and on monuments. This can be due both to the kind of habitat and to the dominating presence of only one stone substratum, the travertine. In fact, the presence of materials of a heterogeneous nature may favour the development of species with different ecological needs regarding pH and mineral content. The sandstone was revealed to be without biological colonisations, excepting some lichen species. This can be due not so much to mineral composition of such stone material, as to its characteristic of dismantling superficially. It is interesting to note how a different layer of conservation of the architectural structures of the temples, as well as a differing degree of degradation of the stone substratum, has determined a substantial difference in the development of the various biodeteriorating agents. The temple of Neptune, which has kept a greater architectural integrity, above all on the upper levels, showed in fact a very limited development of the microflora and bryophytes, and a majority of xerophylous plants. Amongst the various environmental factors, water represented the most selective one in relation to biodeteriogenous species. In particular, photosynthesizing microflora resulted being linked to the presence of water the most in the stone structure, since its development occurred only in the dampest areas. At times microflora presented itself associated to bryophytes, probably due to the greater and more constant water tenure provided by moss cushions as opposed to stone surface. Lichens, moss and plants have responded instead to the differing degree of water with different needs. The absence of superior structures of protection clearly influenced the flow of meteoric waters, both inside and outside the material, which led to a specific localization of biological colonisations. As far as the exposure of the surfaces is concerned, it has been found that microflora is not greatly influenced by this factor; its development in any case is favoured by less sunny exposures (north and east) which guarantee a greater stagnation of humidity. As far as plants are concerned, instead, exposures to the west and south were the ones that showed a greater cover and floristic diversity; the presence of a radical apparatus, which develops inside the stone structure, allows plants to suffer less from water evaporation in the more superficial layers of the substratum. Lichens have colonised almost all the exposures. Dirina massiliensis, the most diffused species on the three temples, showed nevertheless a marked preference for surfaces facing north. The study of the characterization of the various biodeteriorating agents, carried out before the restauration, allowed to direct specific restaurations of the architectural structures and to point out the products and the methodologies which were more appropriate for the control of biological deteriorating agents. Such an analitic and thorough knowledge of the main biodeteriogens is a useful basis to verify, in the medium and short term, the efficacity of the restaurations carried out and will allow to plan in the future the most apt maintenance interventions. 4. References Aleffi M., Altieri A., Cortini Pedrotti C., Ricci S.,1997. Flora briologica di siti archeologici della citt/t di Roma e considerazioni ecologiche sul ruolo delle briofite nel deterioramento dei manufatti lapidei. Informatore Botanico Italiano, 29 (2-3), 239-257. Altieri A. and Ricci S., 1994. I1 ruolo delle briofite nel biodeterioramento di materiali lapidei. III Intern. Symp. on the Conservation of monuments in the Mediterranean Basin, Venezia 22-25 June, 329-333. Braun-Blanquet J., 1928. Pflanzensoziologie. Springer Verlag, Wien.
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Caneva G., De Marco G., Dinelli A., Vinci M., 1995. Le classi Parietarietea diffusae (Rivas Martinez 1964) Oberd. 1977 e Adiantetea Br.-B1. 1947 nelle aree archeologiche romane. Fitosociologia, 29, 165-179. Cortini Pedrotti C., 1992. Check-list of the Mosses of Italy. Flora Mediterranea, 2, 119221. Garcia-Rowe J. and Saiz-Jimenez C., 1991. Lichens and Bryophytes as Agents of Deterioration of Building Materials in Spanish Cathedrals. International Biodeterioration, 28, 151-163. Gimingham C.H. and Birse E.M., 1957. Ecological studies on growth-form in bryophytes. J. Ecol., 45, 533-545. Hruska K., 1987. Syntaxonomical study of italian wall vegetation. Vegetatio, 73, 13-20. Mouga T.M. and Almeida M.T., 1997. Neutralisation of herbicides. Effects on wall vegetation. Intemational Biodeterioration and Biodegradation, 40, 141-149. Nimis P.L., 1993. The lichens of Italy. Monografia XII. Torino. Nimis P.L., 1999. Lichen database of Italy, 1.0, Univ. of Trieste, Dept. of Biology, INI 0/99 (http://biobase.kfunigraz.ac.at/flechte/owa/askitalflo). Pignatti S., 1982. Flora d'Italia. Edagricole, Bologna. Ricci S., Pietrini A.M., Giuliani M.R., 1989. A contribution to the knowledge of the algal flora of archaeological remains: the Foro Romano. Braun-Blanquetia, 3 (2), 319-320. Roccardi A., and Bianchetti P.L., 1988. The distribution of lichens in some stoneworks in the surroundings of Rome. Studia Geobotanica, 8, 89-97. Seaward M., Giacobini C., Giuliani M.R., Roccardi A., 1990. The role of lichens in the biodeterioration of ancient monuments with particular reference to Central Italy. Intemational Biodeterioration Bulletin, 25, 49-55.
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BIOLOGICAL PATINAS ON THE LIMESTONES OF THE LOCHES ROMANIC T O W E R (TOURAINE, FRANCE) M. Zagari* Via Tortolini, 7 - 00040 Ariccia - Roma, Italy F. Antonelli Laboratorio di Analisi dei Materiali Antichi - Dip. Storia dell'Architettura- I U A V Venezia, Italy C. Urzi Istituto Policattedra di Microbiologia- Facolta di Scienze- Universit/l di Messina, Italy
Abstract The weathering of the Romanic tower of Loches (Touraine, France) has been investigated. The building material, a porous siliceous limestone also called "Mica Chalk", showed alterations such as scaling, alveolization, detachment. The original white colour of the limestone turned yellow and/or orange in the superficial layer associated with a biological patina. Microbiological investigations carried out as support for previous mineralogical, petrographic and chemical data, showed that calcicolous lichens were the most important group colonizing the outer side of the facade; algae were dominant in the inner side not exposed to the direct sunlight irradiation. Stone surfaces also supported a heavy colonization of a microbial community (bacteria, actinomycetes, fungi), whose establishment and activity were enhanced by the lichens and algae colonization (outer and inner part respectively). Bacterial and fungal strains were able to produce yellow or pink endo- and exo-pigments contributing to the colour change of the superficial layer of the stone. A correlation between the distribution of calcium oxalate dihydrate (weddellite) and the occurrence of lichen colonization was also observed. Keywords: biodeterioration, biological patina, lichens, limestone, microbial community, oxalate film. 1. Introduction The presence of calcium oxalate on stone surfaces is often found both in natural outcrops (Del Monte, 1989; Watchmann, 1991; Russ et al., 1999) as well as on stone monuments (Realini and Toniolo, 1996). It concurs to the mineralogical composition of most of patina studied as mineral in traces or as one of the most abundant constituent (Lazzarini and Salvadori, 1989). In monuments, the presence of calcium oxalate can be attributed both to anthropogenic origin as a result of man-made protective treatments (Franzini et al., 1984; Gratziu & Melucco Vaccaro, 1989) or of atmospheric pollution (Saiz-Jimenez, 1989) or to a biological origin (Del Monte e Sabbioni., 1987). In the present work we report the finding of oxalate patina associated to lichen colonization on the Romanic tower of Loches. The tower, built in the 11th century, stands in the valley of Loire (France), in a small village, 230 Km far from the Atlantic ocean, in a rainy and windy climate, with dominant winds blowing from the south/west; temperature ranges from -18 ~ to 41~ moisture from * Author to whom correspondence should be addressed.
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62 to 94% and annual rainfall is about 676 mm. Conservation and restoration treatments were reported in the 18th century and atter the second world war. Antonelli and Dessandier (1994) found that the building material used for the tower is the so-called "white tuffeau" of Touraine or "Mica-Chalk", a porous siliceous limestone belonging to the Late Cretaceous (Middle Turonian) of the Paris Basin. It is characterized by the occurrence of cherts (siliceous concretions) and a texture with debris dipped in a cryptocrystalline concrete made of micrite (70%) and of small spheres (10-15 microns of diameter) of opal-CT (15-20%). The detrital fraction is represented by angular quartz with minor feldspar, muscovite and glauconite. Among bioclasts, lamellibranchia, ostracoda, echinoderma, briozoa and foraminifera could be found. Alterations described as scaling, alveolization, detachment (Commissione Normal, 1990), were chiefly linked to the crystallization of salts, in particular gypsum and halite and to the high porosity of rocks (Antonelli and Dessandier, 1994; Antonelli et al., 1997). In addition, a biological patina covered most of the surfaces of the tower and in particular the north facing walls: the outer side of this one was entirely affected by lichen colonization, while in the inner side, not exposed to direct sunlight irradiation, algae were predominant. The aim of our research was to investigate the relationships between the biological colonization and the state of the decay of this historical building. 2. Material and methods
Samples were taken both from the outer and the inner side of the north-northwest oriented facade of the tower, at heights ranging between 12 and 36 meters above ground level. As control, samples from non evident deteriorated stone were also examined. In laboratory, samples were sorted for XRD analysis of stones and patinas (carried out by a Rigaku Geigerflex diffractometer; CuK_/Ni) and for microbiological characterization of samples both by direct microscopic evidentiation as well as by cultural analysis. Characterization of biological components of patina were carried out as follows: 1. lichen identification was done using the identification keys reported by Nimis et al., 1992); 2. quali-quantitative analysis of photoautotrophs (algae and cyanobacteria) and heterotrophic (chemoorganotrophic bacteria, fungi) microorganisms and preliminary identification of bacteria and fungi were carried out as described by Urzi and Realini (1998). 3. Results
The mineralogical composition of stone showed that: 1. calcite, quartz, opale-CT, smectite and clinoptilolite, derived from the substrate examined, 2. halite and gypsum were components in all patinas examined; 3. calcium oxalate dihydrate (weddellite) was detected in all patinas taken from the outer side of the facade and it was absent in the patina of samples collected in the inner side. The occurrence of gypsum on the patina examined indicate that sulphation (CaCO3 CaSO4 -2H20) was taking place, caused by sulphuric acid (H2SO4), which in turn is formed by sulphur dioxide (SO2) oxidation, a reaction catalyzed by carbon particles and photochemical reactions (Ciccioli e Cecinato, 1992). Sulphate aerosols could be related both to anthropogenic factors (oil and coal combustions due to domestic heating systems, vehicular emissions, etc.) and natural factors, such as the influence of marine aerosols
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Figure 1. Outer part of the North facing wall of the tower. Particular of sample LOB 2. Lichens colonization by Dirina massiliensis occurs mainly along the mortar joints and also on the stone surface. Figure 2. Outer part of the North facing wall of the tower. Particular of sample LOB 6 (height 36 mt). Lichen colonization was supported by several types (Lecanora crenulata, Caloplacaflavescens, Xanthoria calcicola, plus non identified strain).
Figure 3. Inner part of the above mentioned wall. A green biological patina covered almost all the surface except were detachment phenomena occurred. Figure 4. Sample LOB 8 taken from the inner side of the tower. It is well evident the algal colonization and the slime production. Magnification 16X.
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(Zezza e Macri, 1995). Rain-water operated a selective dissolution of superficial layer, due to the higher solubility of gypsum compared to calcite. The occurrence of halite, unexpected in an area so far from the sea (about 230 Km), provides evidence that the influence of the Atlantic sea aerosols is still working as reported by Martinet (1988). Calcium oxalate was strictly associated to the heavy lichens colonization. In fact all samples taken from the outer side of the facade showed a severe colonization by lichens. Lichens were endolithic and epilitic species with a large ecological distribution, able to colonize a large variety of substrates. They produced different degree of attack on stone materials. Their finding at different height of the tower was in agreement with their ecological behaviour. Dirina massiliensis, was found mainly at the basements (Fig. 1). Its distribution was usually on vertical north-oriented surfaces, protected from rain and not directly irradiated. Samples in which this kind of lichen was found showed a bigger amount of calcium oxalate. Caloplaca saxicola, Caloplaca flavescens, Xantoria calcicola were predominant in samples taken from the higher part of the facade (about 24-36 meters above the ground level) (Fig. 2). They are calcicolous lichens with nitrophilic and photophilie exigences. Their distribution in the upper part of the tower is in agreement with the occurrence of nitrous substances (i.e. guano, dry deposition rate of airborne pollutants such as particulate NO3", etc.) and the exposition to direct sunlight irradiation. In one sample (LOB 6) also mosses were found indicating an high humidity of the substrate. Due to the height (36 mr) it is presumable the presence of percolating water. As associated to the lichen colonization, a microbial community of chemoorganotrophic microorganisms was observed, mainly constituted by ubiquitous air- and soil-borne microorganisms, such as Gram-positive bacteria (mainly Bacillaceae, and Actinobacteria) and as fungi, like Penicillium or black fungi with meristematie growth. Microscopic investigations showed that algae and chemoorganotrophic microorganisms were in a close contact with the stone particles (Fig. 3). All samples taken from the inner side of the facade, where no calcium oxalate was found, showed a biological patina due to a more or less homogeneous superficial algal colonization (Fig. 4). Unicellular and filamentous green algae, Cyanobacteria (such as members of the Pleurocapsa and Nostocaceae group), were favored by the indirect sun exposure and to the high degree of humidity. In some eases (LOB 7) also some lichens were present. Stones heavily colonized by algae were soft and wet. The occurrence of ehemoorganotrophie microorganisms as Bacillus, Gram positive rods and cocci (mainly Actinobacteria) and Penicillium and Ulocladium species was also detected. Thus concerning the associated microflora in the outer and inner facade of the North facing wall, no differences were seen. However, their finding in both eases, stressed the existence of close interactions between inorganic and biotic components and indicates that in this habitat the input and output of organic matter occur from and to the different members of the microbial community. In addition, most of bacteria found are known for their ability to precipitate mineral phases (Urzi et al., 1999) and thus could be connected with the diffuse crystal precipitation observed in almost the totality of samples (Fig. 5). 4. Conclusions Alteration patterns found on the limestones of the Romanic tower of Loches are due to the synergistic action of climatic, environmental and biological factors.
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Figure 5. Scotch tape from sample LOB 2 seen under epifluorescence microscopy. It is visible the algal colonization between crystals and dark chain of meristematic growing fungi. Magnification 50X. Figure 6. Sample LOB 1. Surface. A diffuse crystal precipitation is visible on the whole surface. Magnification 32X.
In the outer layer, the occurrence of gypsum, halite and calcium oxalate is undoubtedly related to neoformed mineral phases, as these salts results absent in the composition of the original stones (Antonelli and Dessandier, 1994). Sulphatation occurring on the surface of limestones could be only partly related to the impact of air pollution, mainly due to the aeolian transport of pollutants from urban or industrial areas upwinds in that zone. The climate basically oceanic seems to be the main factor responsible for the neoformation of salts (gypsum and halite): the Atlantic sea aerosols influence is linked to the main winds blowing from southwest, easily reaching the inland because of the particular geomorphological conditions, mainly the lacking of mountains (Martinet, 1988). Sulphate and chloride usually act together, with a disaggregating action both directly on the surface of the stone and within microfractures, causing severe physical disruption and leading to the detachment of large stone chips (Zezza e Macri, 1995). The formes of decay also depended by the sedimentary and petro-physical characteristics of the limestone: principally their high porosity and the bad quality of joints of grains (Antonelli and Dessandier, 1994, Antonelli et al., 1997). The occurrence of calcium oxalate was always associated to an intense colonization of lichens (mainly Dirina massiliensis), which were the most important group colonizing the examined facade of the Tower. They were dominant in the outer side, while algae were dominant in the inner side, not exposed to direct sunlight irradiation.
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Lichens and phototrophic microflora found covered almost all the North facing walls causing an aesthetic damage; they supported the growth of chemoorganotrophic microbial community, enhancing the deteriogenic action. Endolithic algae and some of the lichens (Dirina massiliensis) contributed to the physico-chemical decay by the penetration of cells and hyphae in the depth, while the other species of lichens could have protected the stone surface from further detachment and scaling phenomena. Most of the microbial strains were able to develop survival strategies (i.e spore production, pigment production, pleomorphism, metabolic versatility, etc.) that allow them to grow under adverse conditions. Their ability to produce yellow or pink endo- and exopigments by most bacterial and fungal strains isolated, could be related to the colour changes of the superficial layer of the stone (Urzi and Realini, 1998; Urzi et al., 1999). Another factor is the possibility to function as precipitation nuclei of neoformed mineral phases, and especially in the micritic formation as already demonstrated in laboratory conditions, in quarries and in monuments (Urzi et al., 1999).
5. Acknowledgements We greatly acknowledge the support of the Dr. Daniela Pinna of the Soprintendenza per i Beni Artistici e Storiei in Bologna for the identification of lichens. The present research was carried out with the contribution of European Community (projects n~ ENV4-CT98-0704 and n~ ENV4-CT98-0707), CNR (Finalized project Beni Culturali) and MURST 60%. 6. References Antonelli F., Dessandier D. 1994. Caratterizzazione petrografica e stato di conservazione delle pietre della facciata principale (N-NE) del DonJon gomanieo di Loehes (Turenna, Francia) - Mineralogica et Petrographica Acta, Vol. XXXVII, pp. 387-406. Antonelli F., Dessandier D., Rasplus L. 1997. Identification and petrographic, physical and mechanical characterization of stones used in the chevet of the Royal Abbey in Fontevraud Maine et Loire, France). Comparison with rock materials proposed for restoration. Science and Technology for Cultural Heritage, 6 (1), pp.1-12, CN1L Istituti Editoriali e Poligrafici Intemazionali, Pisa. Ciccioli P., Cecinato A. (1992) - Advanced methods for the evaluation of atmospheric pollutants relevant to photochemical smog and dry deposition. In: J.O. Nriagu (Ed.). "Gaseous Poll. Characterization & Cycling", Commission of the European Communities. F. Guyot SA. Bruxelles - Chap. 11: 461-534, John Wiley & Son, New York. Commissione Normal 1991. Raccomandazioni Normal: 1/88 Alterazioni macroscopiche dei materiali lapidei: lessico. C.NR. - I.C.R., Roma. Del Monte M. 1989. I monumenti in pietra e licheni. Rass. Beni Culturali, VI, 3. Del Monte M.,Sabbioni C. 1987. The so-called "scialbatura" on Roman imperial marbles. Studies in Conservation, 32, 114-121. Franzini M., Gratziu C, Wicks E. 1984. Patine ad ossalato di calcio su monumenti marmorei. Rend. Soc. Ital. Miner. Petrol:, 39, 59-70. Gratziu C., Melucco Vaccaro A. 1989. Patine a ossalato di calcio: un problema di metodologia scientifica. I Convegno Intemazionale "Le pellicole a ossalati: origine e significato nella conservazione delle opere d'arte", Milano,
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Lazzarini L. and Salvadori O. 1989. A reassessment of the formation of the patina called scialbatura. Studies in Conservation, 34, 20 - 26. Martinet G. 1988. Inventaire des tuffeaux en oeuvre darts la Cath6drale de Tours. DEA, Universit6 d'Orleans et de Tours, p.65. Nimis P. L., Pinna D., Salvadori O. 1992. Licheni e Conservazione dei Monumenti. CLUEB, Bologna. Realini M. and Toniolo L. (eds) 1996. The oxalate films in the conservation of works of art. Proceedings of the II International Symposium. ED1TEAM s.a.s., Milan. Russ, J., Kaluarachchi, W. D., Drummond L. and Edwards H.G.M. 1999. The nature of a whewellite-rich rock crust associated with pictographs in southwestern Texas. Studies in Conservation 44, 91 - 103. Saiz-Jimenez C. 1989. Biogenic vs anthropogenic oxalic acid in the environment. In: Alessandrini G. (ed.), I ~ Convegno Internazionale "Le pellicole a ossalati: origine e significato nella conservazione delle opere d'arte", Milano. Urzi C., Garcia-Vall6s M.T., Vendrell M., Pernice A. 1999. Biomineralization processes on rock and monument surfaces observed in field and in laboratory conditions. Geomicrobiology Journal 16, 39-54. Urzi C., Realini M. 1998. Colour changes of Noto's Calcareous sandstone as related with its colonization by microorganisms. Intern. Biodeterioration & Biodegradation 42, 45-54. Watchman, 1991. Age and composition of oxalate-rich crusts in the Northern territory, Australia. Studies in Conservation 36, 24 - 32. Zezza F., Macri 1995. Marine aerosol and stone decay. The Science of the Total Environment 167, 123-143.
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CHEMIOLITHOTROPHIC BACTERIA ON STONE MONUMENTS: CULTURAL METHODS SET UP M. Bartolini* ICR- Istituto Centrale per il Restauro, piazza S. Francesco di Paola 9, Roma, Italy M. Monte CNR- Centro Conservazione Opere d'Arte, via Monte d'Oro 28, Roma, Italy
Abstract Chemiolithotrophic prokaryotes, sulphur and nitrifying bacteria can cause severe damages to stone materials by the release of their metabolic end-products such as sulphuric acid, nitrous and nitric acid. The importance of chemiolithotrophic bacteria in the process of stonework decay is an open question. Nevertheless, their involvement in the degradative phenomena is evident since sulphur and nitrifying strains have been detected from some kinds of stone alteration. For this reason, it is very important to find specific and careful methods for the qualitative and quantitative analyses of these bacteria. In this experimental work, several cultural analysis methods for enumeration and isolation of viable sulphur and nitrifying bacteria from stone were compared. This study was carried out on decayed marble samples taken from Arco di Tito in Rome. The determination of the cell counts was made by most-probable-number technique (MPN). The microbial growth into the media was assessed by metabolic substance determination (nitrite, nitrate, sulphate), pH variation and measurement of total biomass through ATP bioluminescence assay. The results of analyses showed that the stone surface was colonised by lithotrophic bacteria with values ranging between 103 and 105 per gram of sample. Some cultural media showed to be suited for bacteria enrichment while others to be better for culture maintenance. Keywords: Sulphur-oxidising bacteria, Ammonia-oxidising bacteria, Nitrite-oxidising bacteria, Biodeterioration, Cultural methods. 1. Introduction Sulphur-oxidising and nitrifying bacteria are able to colonise stone material and to determine biodeterioration processes (Pochon and Jaton 1968). These chemiolithotrophic micro-organisms use, as energy source, reduced sulphur and ammonium compounds that are oxidised to sulphates and nitrates. The degradative action is due to the release of their autotrophic metabolism ending products as sulphuric acid, nitric and nitrous acids. The degradation caused by these bacteria on stone is similar to that due to atmospheric chemical pollutant in urban areas, therefore, clarify their importance in stone degradative processes, is still an open problem (Reddy et al. 1985). Nevertheless, their involvement in degradative phenomena is confirmed by several studies in which chemiolithotrophic bacteria presence is detected in higher quantity in decayed stone than in sound stone (Sila and Tarantino 1981; May and Lewis 1988);
* Author to whom correspondence should be addressed.
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moreover the corrosive activity of bacteria isolated from degraded stone, has been verified in laboratory experiments under controlled conditions (Monte M. et al 1999). Since microbiologic analysis represent the only way to detect specifically the sulphuroxidising and nitrifying bacteria on the stone, it become very important to optimise the cultural procedures with the aim to reach certain and comparable results. The cultural analysis of these bacteria is complicated by several factors as: i) long incubation time since they are characterised to have a growth speed rather slow also in culture; ii) high sensibility to nutrient concentration (Meincke et al. 1988); iii) difficulty to evaluate their growth in culture because it is indirectly detected by metabolite analysis (Sarathchandra 1979). Furthermore, it must be considered that the techniques used have been developed for bacterial analysis in the soil while the stone, as building material, represent an environment with different ecological characteristics (water content, temperature, pH value, salt concentration). These factors can determine such a selection and a metabolic adaptation of the species living on stone that make difficult their growth in traditional cultural media. The Aim of the present work has been to evaluate the presence of chemiolithotrophic micro-organisms on degraded marble of Titus Arch in Rome comparing several methods of cultural analysis for the quantification of nitrifying and sulphur bacteria. Particularly cultural media with different mineral composition have been compared to individuate those more efficient as enriching media. Several techniques to determine the cultural bacterial growth have been also compared to select those with higher sensitivity and more practical use. 2. Material and methods 2.1 Sampling procedure The study was carried out on altered marble sample drawn from Titus Arch in Rome. Marble showed a compact crust dark grey coloured under which the stone showed pulverisation phenomena. Samples have been drawn by a sterile lancet and quickly transferred in the laboratory to be analysed because a long interval time between sampling and analysis could lead to underestimate the microbial quantity (Lewis 1985). An aliquot of sample was pulverised in a sterile mortar and diluted 1:10 in physiologic solution. To favourite the bacteria detachment from stone fragments Tween 80 (0,05%) was added to the suspension and it was shacked with a magnetic stirrer for 10 minutes. The suspension was diluted 10-fold steps. For the determination of cell count a three tube mostprobable number (MPN) techniques were employed using several media. Bacteria developed in positive tubes were transferred in fresh media to produce maintenance cultures. 2.2 Cultural media Several cultural media have been compared to individuate those more efficient for the chemiolithotrophic bacteria development on marble samples. The culture for sulphur-oxidising bacteria were obtained using two mineral media, in according to Normal (Normal 9/88), characterised by different sulphur reduced source: 1)basal medium according to Pochon e Tardieux containing sulphur flowers; 2) medium in use at the American Type Culture Collection (ATCC) containing thiosulphate. The ATCC medium was used at two different pH values (pH 5 and 7). The cultures were incubated at 30~
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For the ammonia-oxidising bacteria three media were compared: 1) Sarathchandra medium (Normal 9/88); 2) Knmamel and Harms medium (Koops and Moller 1992); 3) Stanier medium (Normal 9/88). The first two media contain a pH indicator, the red phenol and the red cresol respectively, and are lightly buffered. These markers permit to evaluate the medium pH variations induced by the production of acidic substances due to microorganism metabolic activity. For nitrite-oxidising bacteria, sensitive to nitrites concentration, Stanier and Bock media have been utilised (Normal 9/88, Bock and Koops 1992). The two media are characterised to have different nitrite ions concentration. All cultures have been placed in the dark at 30~ 2.3 MPN estimates
Bacterial growth in serial dilutions were checked after 30, 60 and 90 days by drawing, in sterile conditions, a medium rate from each tube. The standard methods utilised are based on chemical analysis to determine the disappearance of specific nutritive substances or the presence of ending products of autotrophic metabolic processes. Sulphur-bacteria growth was evaluated in Pochon medium, by the analysis of sulphate appearance through the barium sulphate precipitation (Normal 9/88); for cultures in ATCC medium the disappearance of thiosulphate has been observed through iodimetric analysis (Normal 9/88). In the media with pH indicator, the ammonia-oxidising bacteria development has been evaluated by both the pH variation and nitrite analysis using the Greiss-Ilosvay reagent (Normal 9/88). Nitrite-oxidising bacteria have been determined evaluating the disappearance of nitrates and the nitrites consumption (Normal 9/88). At the end of incubation period in all the dilution steps the bacteria presence has been directly verified determining the bio-mass by the ATP bioluminescent dosage. The nucleotide analysis were carried out using a Biocounter 2500 luminometer (Lumac B.V. Netherland), on a 100 ktl aliquot from each tube. ATP was extracted adding a nucleotide releasing reagent and measured utilising the firefly luminescence reagent Lumit PM (Lumac B.V. Netherland). Luminescence were measured in Relative Luminescence Units (RLU), then converted in ATP quantity according to a calibration curve obtained from pure standards. Most probable numbers were calculated using the ATP analysis results and the values were compared with the MPN obtained from the cultural metabolites analysis. 3. 3. Results
In table 1 the quantitative analysis results for sulphur-oxidising and nitrifying bacteria are compared. The results show the presence of chemiolithotrophic bacteria in the marble sample. The quantity of sulphur-oxidising bacteria in Pochon medium was 105 per gram of sample. These bacteria showed to be very sensitive to the sulphurate compound present in the medium. In fact they developed only in the medium containing elementary sulphur while no growth has been detected in ATCC medium with thiosulphate.
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Table 1- MPN estimation in different cultural media Microorganisms Media
Evaluation methods
Sulphur
Pochon
SO42 production
ATCC pH 5
Thiosulphate desappearance
ATCC pH 7
Thiosulphate desappearance
Stanier
NO2- production
2 , 5 x l 03
Sarathchandra
NO2- production
4,5xl 0 3
pH variation
2,5xl 03
oxidising
r
Ammonia oxidising
Knnnmel
Nitrite oxidising
Stanier
NO2production
I
L
N.D.
pH variation
4,5 x 103
NO3 production-
2,5xl 03
NO2 desappearance Bock
Estimation , (MPN/g) 1,5 x 10s
2xl 02
NO3- production
4,5x 103
NO2- desappearance
1,4x 103
N.D. (not detectable ) This datum indicates that the development of sulphur-bacteria on decayed marble seems to be favourited by sulphur compounds with low oxidation state as elementary sulphur. These bacteria showed to be able to also utilise thiosulphate, as energy source, after an initial phase of growth in a sulphur containing medium. In fact bacterial growth after the transfer of cultural aliquots from positive tube into fresh ATCC solid and liquid medium was measured. With regard to nitrifying bacteria, it can be observed that the used media resulted good for both the growth of ammonia and nitrite-oxidising bacteria present in the sample. The cell number calculated with the MPN has been about 103 per gram of sample in all the media tested. For nitrite-oxidising bacteria only a little difference in bacteria quantity in the two media has been detected. The best result has been obtained with Bock medium: 4,5 x 103 cells per gram of sample, evaluated through nitrate production in serial dilutions. The test based on NO2 disappearance showed not to be so sensible, determining an underestimation of bacteria present in the samples. For the ammonia-oxidising bacteria, the evaluation of pH variations permits to reveal the presence of these micro-organisms by just observing the medium colour changing. The accuracy level of this method is comparable to that obtained with the nitrite disappearance. In Krummel medium cultures, the result was unclear because of the interference between the induced colour from the reagents and that due to the pH indicator present in the medium. Figure 1 shows the bacteria number, expressed in log l 0, calculated after 30, 60 and 90 incubation days in those media that gave the best growth results. It can be observed that the
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incubation time had a considerable effect on micro-organisms estimation. For all the three bacterial groups examined the maximum MPN has been calculated after three incubation months. Figure 1: Effect of incubation time on estimates of sulphur and nitrifying bacteria
Particularly for nitrite-oxidising group the development level after 2 months resulted much less than that calculated after 90 days. This behaviour has been observed also in the sulphur-oxidising bacteria which, even if developed quicker than the nitrifying ones in the tubes at lower dilution, in higher dilution have been detected only at the end of incubation time. 3.1 M P N estimated by ATP measures
ATP dosage through bioluminescence is a very sensitive technique that permits to detect ATP quantity around the picogram. Therefore this method permits to determine the presence of a bacterial strain since the first phases of its development. Table 2 shows the bacteria most probable number calculated by ATP evaluation in serial dilution. The sulphur-oxidising and ammonia-oxidising bacteria number calculated with the ATP method coincide with the quantitative datum obtained with the metabolite analysis. For nitrite-oxidising bacteria, a MPN equal to 1,5xl 04 cells per gram of sample has been detected, it is sensitively higher compared with that obtained with traditional methods. The ATP dosage permitted to assess the micro-organisms development also in tubes negative to the nitrate assay. This because of its higher sensitivity that lead to detect
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bacterial presence in culture in the first stages of growth when the nitrate quantity produced, probably, was to low to be detectable with classical methods. Table 2: MPN calculated by ATP evaluation Micro-organisms
Media
Ammonia-oxidising
Stanier
2500
2500
Krummel
4500
4500
Bock
4500
15000
Stanier
2500
11500
Pochon
150000
150000
Nitrite-oxidising Sulphur-oxidising
MPN estimated by MPN estimated by catabolic analysis ATP content
This datum indicates that, also after 3 months incubation the bacterial development, in higher dilutions, can be still considered in an initial phase. For this reason to calculate the MPN of nitrite-oxidising bacteria by means of the catabolic analysis, longer incubation time could be necessary. 4. Conclusions
Results obtained with cultural tests pointed out a significant chemiolithotrophic bacteria presence on Titus Arch corresponding to decayed stone. Sulphur-bacteria are present with values ranging around 105 per gram of sample. They developed only in cultures containing elementary sulphur and not in those with thiosulphate. Therefore it has been observed that bacterial growth started in medium with thiosulphate after the inoculum of positive culture aliquots previously developed with elementary sulphur. Probably only the starting cultures, coming from the stone inoculun, are unable to utilise the thiosulphate. This behaviour can be explained as a need of a metabolic adaptation phase. For this reason the two tested media must be used for different purpose: Pochon medium is good as enrichment medium while ATCC medium can be used only for maintenance cultures. To calculate the highest quantity of micro-organisms, 3 months of incubation were necessary. The ATP detecting techniques, confirmed the quantitative values obtained with the sulphate dosage; this demonstrate that the incubation time was long enough for the maximum growth in serial dilution. Ammonia-oxidising bacteria were present with values of 4,5xl 03 per gram of sample and with an incubation time ranging between 2 and 3 months. As for the sulphur bacteria, also in this case the ATP analysis confirmed the results obtained through the metabolites dosage. Among the tested media, Krummel and Sarathchandra showed to be equivalent; regarding the growth detecting method, the pH variation, detected by an indicator, showed the same sensitivity of nitrite dosage. For this reason the pH variation would be preferred in the cultural analysis to speed the microbiological analysis procedure.
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Regarding nitrite-oxidising bacteria, the greatest quantity, with values of 4,5x103 per gram of sample, has been detected utilising Bock medium. Bacterial growth detection by nitrate disappearance showed to be more sensitive than that based on the nitrite disappearance. Nitrite-oxidising bacteria growth resulted slower compared to the other two analysed groups. The graphic shows, in fact, that the development in culture after 60 days was much less compared to that of 90 days. Furthermore, the ATP analysis, being very sensitive, lead to stabilise that, after 3 months, the micro-organisms growth in the tubes having higher dilution were still going on. This means that the incubation time, needed to calculate the number of these bacteria, can exceed 90 days. The tests done, besides giving information about the best procedures to quantify chemiolithotrophic bacteria present on marble, permitted the isolation of several strains with probable biodeteriogenic action. These strains will be used to prepare experimental tests, in controlled conditions, with the aim to evaluate their corrosive activity in marble samples. Thanks
The authors thank Dr. Giuseppina Del Signore for reviewing the English text. 5. References
Bock E., Koops H.P., 1992. The genus Nitrobacter and relate genera. In: The Prokaryotes, v. III, 2302-2309, Springer-Verlag, New York. Koops H.P., Moiler U.C., 1992. The lithotrophic ammonia-oxidizing bacteria. In: The Prokaryotes, Vol. III, 2625-2637, Springer-Verlag, New York. Lewis F., May E., 1985. Isolation and enumeration of autotrophic and heterotropic bacteria from decayed stone. Deterioration and Conservation of Stone, Proc. of the 5 th International Congress, Lausanne, Presses Polytechnique Romandes.633-642. May E. and Lewis F.J., 1988. Strategies and techniques for the study of bacterial population on decaying Stonework. Deterioration and Conservation of Stone, Proc. of the VI International Congress, Torun, Nicholas Copernicus University Press Depatment. 59-70 Meincke M., Ahlers T., Krause-Kupsch E., Krieg C., Meyer F., Samuluck W., Wolters B., Bock E., 1988. Isolation and characterization of endolithic nitrifier. Deterioration and Conservation of Stone, Proc. of the V I th International Congress, Torun, Nicholas Copernicus University Press Depatment. 15-23. Monte M., Del Signore G., Persia F., 1999. Damage caused by microorganisms on marble samples. Workshop on Microbial Corrosion, Proc. of the Fourth International European Federation of Corrosion, Lisboa, in press. NORMAL 9/88 (1988). Microflora autotrofa ed eterotrofa: tecniche di isolamento in coltua. ICR-CNR, Comas Grafica, Roma. Pochon J., Jaton C., 1968. Biological factors in the alteration of stone. Biodeterioration of Materials. Waiters A.H., Elphick J.J. (eds), Amsterdam, Netherlands, Elsevier. 258-268. Reddy M.M., Sherwood S., Doe B., 1985. Limestone and marble dissolution by acid rain. Deterioration and Conservation of Stone, Proc. of the 5 th International Congress, Lausanne, Presses Polytechnique Romandes. 517-533. Sarathchandra S.U., 1979. A siplified method for estimating ammonium oxidising bacteria. Plant and soil, 52, 305-309
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Sila M.M, Tarantino G., 1981. The metabolic state of microorganisms of the genus Thiobacillus on stone monumentes. The Conservation of Stone II, Proc. of the IIth International Symposium, Bologna, Rossi-Manaresi, R. 117-138.
461 NEW METHODS TO STUDY THE DETRIMENTAL EFFECTS OF P O I K I L O T R O P H MICROCOLONIAL MICROMYCETES (PMM) ON BUILDING MATERIALS
Thomas Dornieden* Carl von Ossietzky Universitaet Oldenburg, D-26111 Oldenburg, Germany Anna A. Gorbushina Carl von Ossietzky Universitaet Oldenburg, D-26111 Oldenburg, Germany
Abstract Poikilotroph microcolonial micromycetes (PMM) were isolated from various monuments and natural rock outcrops in the Mediterranean Basin. Pure cultures and mixed cultures were inoculated on artificial glass and standardised marble surfaces. The aim of the study was to analyse chemical and mechanical effects of the fungal flora on the materials studied. Temperature flow, heat as well as subsequent dilatation were measured. Further some simple techniques to detect mechanical effects of the PMM on the substrate were developed. Tuned lasers were used as well in order to analyse surface changes by the PMMs. Another set of experiments aimed at differential penetration of gasses and substances into the materials analysed. Microscopic and spectroscopic techniques were also applied in order to verify chemical and physical changes of the materials by the growth of PMMs. As a result it is stated that mechanical abrasive damage by PMM is considerable and may be more important than chemical corrosive activities. Cell rigidity, pigments embedded in the cell walls, turgor pressure and directional growth seem to play the most important role in the mechanical damage functions. Biopitting and bioexfoliation are the most conspicuous effects of the presence of PMMs on rock materials.
Keywords: poikilotroph microcolonial micromycetes, mechanical effects, biopitting, bioexfoliation 1. Introduction The destruction of marble monuments and sculptures under the influence of time and environment (including physical, chemical and biological factors) is proceeding very fast in special cases. As the restoration of an already destroyed building is always an expensive venture, many researchers investigate the mechanisms of stone destruction (e.g. Franzini 1995). Microbiological destruction of rock is regarded as a remarkable and important phenomenon. Among many groups of micro-organisms contributing to the rock destruction, micromycetes are one of the most important (Leznicka et al. 1988). Recently a special group of rock dwelling melanised fungi with slowly expanding colonies attracted attention of researchers (Gorbushina et al., 1993; Sterflinger, 1995; Wollenzien et al., 1995). These yeast-like microcolonial fungi are the real specialists for stone destruction). Often their specific in-situ morphology and dark pigmentation were the reasons for confusion with the deposition of soot and dust (Diakumaku et al. 1994; Wollenzien et al., 1995). *Author to whom correspondence should be addressed.
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Their influence on the rock substrate is ranging from colour changes caused by melanin production and excretion (Gorbushina et al., 1993; Diakumaku et al. 1995) to spectacular mechanical penetration of natural spaces between calcite grains in marble resulting in pitting of the rock surface (Sterflinger & Krumbein 1997). Different properties of marble are strongly influenced by fungal growth and our present research concentrates on physical changes in substrate caused by the development of the melanised fungal colonies. It was convincingly demonstrated that fungal growth on the rock surface influences the reflection of sunlight and the heat absorption of marble and other rock materials (Dornieden et al. 1997). Similar results were obtained by Garty (Garty 1989) for cyanobacteria and lichen growth on mortar. In our previous investigations (Dornieden et al. 1997) it was also demonstrated that the fungal biofilm was responsible for additional heat transmission into the deeper rock layers. Since fungal colonies naturally develop a patchy cover on the rock surface, different temperatures will be reached in different parts of the stone. As a consequence the structure of the stone can be locally weakened. Recently this hypothesis was confirmed by a computer simulation model (Sadouki & Wittmann 1998). Like the situation is with most deterioration processes, the problem with experimenting with fungi lays in the time scale, as these organisms are very slow growing. The problem for other experiments with fungi is the time scale like it is for most deterioration problems. In our experiments different ways to simulate the development of slow processes are used to shorten the experimental time scale. In this paper the methods for quantification and demonstration of physical influence of fungal growth on the substrate, as well as some running experiments with first qualitative results will be described.
2. Direct fungal action The main objective of the studies in our laboratory presently is to measure and quantify the direct action of the melanised slow growing fungi through their growth pressure during the hyphal tip extension and penetration into the substrate. This task can be subdivided into the characterisation of mechanical properties like turgor quantification in hyphae of the fungi in question and cell wall mechanical stability measurements, which are undertaken on the colonies and allow the quantification of additional passive strength existing in the crack after the penetration was successful. Another aspect involves the visualisation of fungal growth pressure in the substrate by surface monitoring with the help of extremely sensitive optical methods. 2.1 Turgor and cell wall The most obvious physical factor is the direct action of the fungal hyphae expansion into the substrate namely the growth pressure. The growth pressure of fungi allow them to penetrate very hard substrates, e.g. plant cuticles (Howard & Valent, 1996). It was convincingly demonstrated (Sterflinger, 1995; Diakumaku 1996; Domieden et al., 1997) that fungal hyphae can penetrate the stone through little fissures and cracks, which are often widened or even created by the physical growth action. By penetrative growth and colony expansion inside the stone they can damage the substrate by pushing away the grains. In order to prove this hypothesis it is important 1. to quantify the inner pressure of the fungal growing cells (i.e. turgor pressure) in rock inhabiting fungi, 2. to quantify the strength of the cell wall of a fungal colony
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the morphology of the PMM colony under different environmental influences i.e. nutrients or other stress factors. The turgor is the hydrostatic pressure inside a cell that is driven by the osmolarity influencing factors like salt concentration in a space surrounded by a semi-permeable membrane. This means water can penetrate into but no bigger ions. The turgor is the reason that plants can hold their shape and that fungi can penetrate substrates. It was demonstrated that phytopathogeneic fungi can only penetrate a substrate if the turgor is high enough to pierce the hard mechanical barrier (Howard et. al 1991, Money 1995). There are well established data on mechanical properties of different stones (i.e. Carmichael 1982) or building stones (i.e. Christaras 1991) and to damage a stone the fungi just have to produce a force comparable with mechanical strength of the material (stone). Although it is not an easy task to exactly measure and determine the turgor, because of the microscopic scale of the organisms in question, there are some techniques developed, i.e. turgor can be calculated from the difference between the external milieu and the osmotic potential of the protoplasm (i.e. Money 1990). Surprisingly the turgor in a fungal hyphae can reach a value of 8.0MPa (Howard et. al 1991, Jennings & Lysek 1996). This value is in ranges of different stone parameters, i.e. intact marble. The compressive strength of marble differs between 79 and 206 MPa, the torsion strength between 12 and 26 MPa and the tensile strength lies at 3.9 MPa. One can see that the turgor normally existing in fungal hyphae is high enough for mechanical marble destruction. But the turgor is not enough to damage a stone or rock because the turgor is founded on liquid and liquid has no solid form above 0~ So there should be a mechanical barrier able to withhold the turgor pressure from inside and mechanical resistance of the substrate. This role is played by the cell wall, which is very hard and multilayered in this group of rock inhabiting fungi. The first approach to determine the mechanical strength of cell wall in a colony is to use bigger colonies (2 to 6 mm in diameter and 1 to 4 mm height) and a constant pressure surface. With these restrictions an experimental set-up was constructed (fig. 1) which has given interesting results. The colonies measured were able to resist a pressure of 1.2 MPa. It is near the range of the tensile strength. In the experimental set-up one could see that not the whole surface of the stamp was used, which means that the real pressure and thus the actual mechanical strength/resistance of cell wall in fungal colony must be higher. To get quantitative data the set-up will be changed to a variable pressure surface with optimal shape for each colony. A second step is to minimise the stamp to measure smaller colonies. The final goal of our attempts is to measure the cell wall resistance of particular cells at a microscopical scale. The last point is the determination of the growth and pressure phases and their dependence on humidity and nutrients. First results show that the rock inhabiting fungi develop compact and mechanically resistant colonies when growing in the air under unfavourable humidity and nutrient supply (fig. 2). Similar results of compact colonies formation were already demonstrated for salt and temperature stress (Sterflinger & Krumbein 1995), but the mechanical resistance of the fungal structures formed in the air exposed conditions was measured by us for the first time. The colonies developed in submersed culture with abundant nutrients are growing much faster and their mechanical fast growth with soft cell walls when growing. The pressure created by the growing structures is also connected with the size and shape of the penetration hyphae. Some studies were done on the appressoria formation by phytopathogenic fungi (Howard & Valent, 1996), but the question of the change in size,
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shape and turgor of penetration structures by rock inhabiting fungi is currently under development in our laboratory.
Figure 1: Set-up for the determination of cell wall strength
Figure 2: A single cell with a thick wall (Transmission electron microscopy image)
2.3 Visualisation of fungal growth A second way to proof the ability of fungal colonies to alter the rock or stone mechanically is to use a set-up that can allow us to observe the alterations in stone directly during the growth and development of fungal colonies. The knowledge of the turgor and cell wall strength is not enough to proof mechanical damage inside stones, because the turgor measurements are carried out in vitro and some processes cannot be extrapolated to in situ conditions. For simulating the conditions in situ one needs strictly and directly controlled climate conditions in which the stone with growing colonies is investigated.
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Furthermore a possibility to observe changes on a microscopic scale i.e. at a resolution of 500nm is very important, because one cannot expect fast changes with a very slow growing fungal group. A method of this high resolution is called electronic speckle pattern interferometry (EPSI) and is presently used for high resolution observation of rough surfaces (Gtilker et. al 1992). The laboratory set-up is shown in Figure 3. Such measurements can be also carried out in the field, because there is a version for field observations that could be mounted directly on surfaces (Gtilker et. al 1996). To get the information of surface changes over a defined period images will be taken. A computer analysis of the images is used; whereby the computer calculates a difference signal where contour lines can be seen when the deformations occur (fig. 4a). Another form of presentation is the three dimensional one (fig. 4b). Results can be got at any time during the experiment and thus allow monitoring of surface changes over different time periods.
Figure 3: ESPI set-up
Figure 4a: Difference image (height lmm) Figure 4b: Shaping image
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For the experiment little marble slabs (2 x 2 x 0.5 cm 3) with a little hole in the middle are used. The holes are inoculated with different fungi. After nine month of incubation (it was shown that 9 month of growth can produce considerable effects on the material (Sterflinger et. al 1997, Dornieden et. al 1997)) the slabs will be put in the climate chamber of the ESPI. The observation time will be about 4 days or longer depending on the results. If there are any surface changes observed, no doubts will be left of the physical influence of fungi on the substrate, because all the other external influences on the material are eliminated in such a controlled climate chamber.
3. Observation of indirect action The growth of melanised fungal colonies on the stone surface also causes significant changes in spectral properties of the stone and can change the absorption of sun irradiation by the material. The patchy growth of fungal colonies is followed by patchy changes in the material. The effect of additional heating followed by weakening of stone caused by microorganisms mentioned in the introduction demands further investigations of indirect effects. To observe these effects a small climate chamber (fig. 6) was constructed (13 x 13 x 19 cm 3) where almost every environmental factor can be simulated and controlled
Figure 5: Climate chamber All important parameters like humidity (0 to 100 % rH), temperature (-30 to 90~ wind, wind with different temperature and different radiation i.e. light can be changed relatively fast and are fully under control. The lid is changeable and is easily modified for different applications and sensors. With this chamber experiments were started to quantify the results (Dornieden et al., 1997). With the same chamber we are currently investigating the limiting conditions at which the fungal colonies in/on rock or stone will be no longer able to stay viable and grow. These experiments are very closely connected with biodeterioration and conservation treatments of stone monuments where these organisms grow. The important role of physical protective measures That is an important point because this group of fungi can live can live at very different conditions and survive at more harder condition in an inactive state (Gorbushina & Krumbein 1999; Sterflinger, 1999).
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Conclusion It is very difficult to investigate the non-chemical actions of fungi, because of the microscopical scale of the colonies. The proof of a chemical substance is much more easier because there are well established very sensitive methods. To determinate direct and indirect physical and mechanical influences of fungi new approaches and experimental setups are necessary. This article has shown some ways to fulfil these demands. It could be shown that fungi can have a very hard cell structure which mechanical resistance values are comparable with the values of stone or rock parameters.
Acknowledgements We acknowledge the help of EC financial support through the project "Novel molecular tools for the analysis of unknown microbial communities of mural paintings and their implementation into the c__onservation/restoration practice" (ENV4-CT98-0705). Further discussions with W. E. Krumbein and K. Sterflinger are gratefully acknowledged.
References Article references Christaras B., 1991. Weathering of natural stones and physical properties, Wheathering and air pollution, I Corso Lago di Garda (Portese) - Venezia- Milano, 169-174 Diakumaku E., Ausset P., Sterflinger K., Wollenzien U., Krumbein W.E., Lef6vre R., 1994. On the problem of rock blackening by fly-ash, fungal and other biogenic particles, and their detection in Mediterranean marbles and monuments, Proc. of the 3rd International Conference on the Conservation of Monuments in the Mediterranean Basin, 305-310 Diakumaku, E.; Gorbushina, A.A.; Krumbein, W.E., Panina, L. and S. Soukharjevski, 1995. Black fungi in marble and limestones - an aesthetical, chemical and physical problem for the conservation of monuments, Sci. Total Environment, 167, 295-304 Dornieden T., Gorbushina A.A., Krumbein W.E., 1997. Changes of the physical properties of marble as a result of fungal growth, International Journal for Restoration of Buildings, 3, 441-456 Franzini M.,1995. Stones in monuments: natural and anthropogenic deterioration of marble artifacts, European Journal of Mineralogy, 7, 735-743 Garty J., 1989. Influences of epilithic microorganisms on the surface temperature of building walls, Canadian Journal of Botany, 68, 1349-1353 Gt~lker G., Haack O., Hinsch K.D., H61scher C., Kuls J., Platen W., 1992. Twowavelength electronic speckle-pattern interferometry for the analysis of discontinous deformation fields, Applied Optics, Vol. 31, 22, 4519-4521 Gtilker G., Helmers H., Hinsch K.D., Meinlschmidt P., Wolff K., 1996. Deformation mapping and surface inspection of historical monuments, Optics and Lasers in Engineering, 24, 183-213 Gorbushina A.A., Krumbein W.E., Hamann C.H., Panina L., Soukharjevski S., Wollenzien U., 1993. Role of black fungi in colour change and biodeterioration of antique marbles, Geomicrobiology Journal, 1,205-222 Gorbushina A.A., Krumbein W.E., 1999. The poikilotrophic micro-organisms and it's environment. Microbial strategies of establishment, growth and survival, J. Seckbach (ed.), Enigmatic micro-organisms and life in extreme environments, Kluver, Dordrecht, 177-185.
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Howard R.J., Ferrari M.A., Roach D.H., Money N.P., 1991. Penetration of hard substrates by a fungus employing enormous turgor pressures, Proc. Natl. Acad. Sci. USA, Vol. 88, 11281-11284 Howard R.J., Valent B., 1996. Breaking and entering: host penetration by the fungal rice blast pathogen Magnaporthe grisea, Annual Review of Microbiology, 50, 491-512. Leznicka S., Strzelczyk A., Wnadrychowska D., 1988. Removing fungal strains from stone-works, IV International Congress on Deterioration and Conservation of Stone, Vol.2, 102-110 Money N.P., 1990. Measurement of hyphal turgor, Experimental Mycology, 14, 416-425 Money N.P., 1995. Turgor pressure and the mechanics of fungal penetration, Canadian Joumal of Botany, 73, 96-102 Sadouki H., Wittmann F.H., 1998. Simulation of temperature gradients and stresses in natural stone plates under solar radiation, International Journal for Restoration of Buildings, 4, 53-72 Sterflinger K., Krumbein W.E., 1995. Multiple stress factors affecting growth of rockinhabiting black fungi, Botanica Acta, 108, 467-538 Sterflinger K., Krumbein W.E., 1997. Dematiaceous fungi as a major agent for biopitting on Mediterranean marbles and limestones, Geomicrobiology Journal, 14, 219230 Book references Carmichael R.S., 1982. Handbook of physical properties of rocks, CRC Press Inc., Boca Raton, Florida Jennings D., Lysek G., 1996. Fungal Biology: Understanding the fungal lifestyle, BIOS Scientific Publisher Ltd, Oxford, UK
469
DIVERSITY OF HETEROTROPHIC BACTERIA ISOLATED FROM THREE EUROPEAN MURAL PAINTINGS
Jeroen Heyrmanl'*, Joris Mergaert I and Jean Swings1' 2 1. Laboratorium voor Microbiologie, Universiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium 2. BBCM/LMG Culture Collection, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
Abstract Three sites, Carmona (Spain), Herberstein (Austria) and Greene (Germany) were sampled to study the diversity of heterotrophic bacteria present on severely damaged mural paintings. Of the four-hundred twenty-eight isolated strains, three-hundred eighty-five were characterized by fatty acid methyl ester analysis (FAME). This technique allowed a grouping of the isolates into 41 clusters on the basis of their FAME-profiles, 20 isolates remained ungrouped. FAME revealed the presence of the following bacterial heterotrophs on mural paintings: Bacillus sp., Paenibacillus sp., Micrococcus sp., Arthrobacter sp., Staphylococcus sp., nocardioform actinomycetes and Halomonas-like organisms. For each cluster, representative strains were chosen for further identification by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and 16S rDNA sequencing. ARDRA is used for the identification of the bacilli, for which an extensive database is available in the laboratory. By using this technique clusters were further identified as B. circulans, B. firmus, B. similibadius, B. niacini and B. licheniformis. Strains characterized by 16S rDNA sequencing were closest related to Micrococcus luteus, Bacillus marismortui, B. macroides, B. cohnii, B. megaterium, Arthrobacter sp. and A. crystallopoietes. Key words: mural paintings, biodeterioration, bacterial heterotrophs, FAME, ARDRA, 16S rDNA sequencing 1. Sampling and sample treatment In the scope of the European project "Novel molecular tools for the analysis of unknown microbial communities of mural paintings and their implementation into the C__Qnservation/restoration practice" (ENV4-CT98-0705), the biodiversity of heterotrophic bacteria occurring on mural paintings is being investigated. From three European sites, mural paintings showing visible deterioration by microorganisms were sampled: the Roman necropolis of Carmona (Spain), the St. Catherine chapel of the castle Herberstein (Austria) and the St.-Martins church of Greene (Germany). In total eleven samples were taken by scraping off the top layer with a scalpel and homogenized in physiological water using a Stomacher blender. Dilution series were plated using a Whitley Automatic Spiral Plater. To isolate a large diversity of bacteria, eight different agar media were used, two of which contained 10% NaCI. All media were supplemented with 0.03% w/v cycloheximide (Sigma) to inhibit fungal growth. The inoculated plates were incubated aerobically at 28~ Total counts and isolations were carried out over a period of three weeks. For eight samples, total counts of heterotrophic aerobic bacteria on media without 10% NaC1 were in the range of
* Author to whom correspondence should be addressed.
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103-107 CFU per gram. For the remaining three samples (one of Herberstein and two of Greene) the total counts were below the detection limit of 2000 CFU/gram. On the media supplemented with 10% NaC1, total counts were also in the range of 103-107 CFU/gram for samples from Carmona and Greene. The samples of Herberstein however had total counts up to l09 CFU/gram on these media. In total 428 isolates were collected, 162 from the samples of Carmona, 127 of Herberstein and 139 of Greene.
2. Fatty Acid Methyl Ester Gas Chromatography (FAME) For the first characterization of this large amount of isolates, FAME was used (Heyrman et al. 1999). FAME fingerprints were identified with the Microbial Identification Software (MIS, MIDI) using the TSBA database (Microbial ID, Inc., Newark, Del., U.S.A.). The data were analyzed numerically using the BioNumerics software (Applied Maths, Kortrijk), and clustering was achieved by UPGMA of the Canberra metric coefficients, calculated between each pair of profiles. In total, 385 FAME profiles (90% of the strains) were used for grouping, 41 clusters were delineated at 80% Canberra metric coefficient similarity and 20 strains remained ungrouped. Thirty-six clusters contained Gram positive bacteria, and comprised more than 90% of the isolates. The major clusters were identified as Bacillus licheniformis, Bacillus megaterium, Bacillus pumilus, Micrococcus luteus and Arthrobacter sp.. Four clusters contained Gram negative bacteria and included isolates that did not grow on media without added salt. By comparing their FAME-profiles to those of reference strains, two clusters could be identified as Halomonas sp. and Methylobacterium extorquens, respectively. One cluster contained actinomycetes, which could not be identified by FAME.
3. Amplified Ribosomal DNA Restriction Analysis ARDRA was used for further identification of the bacilli, for which an extensive database is available in the laboratory. FAME-clusters that were identified by the TSBAdatabase as belonging to the genera Bacillus, Paenibacillus or Brevibacillus, were further investigated on spore-formation. If spore-formation was recorded, representative isolates were chosen for ARDRA. After growth on TSA for 24h at 28~ total genomic DNA was purified according to the DNA extraction method of Pitcher et al. (1989). DNA quality was verified by measuring the absorbance ratio 260/280 nm and by electrophoresis in agarose gels. Polymerase chain reaction, restriction digestion of the amplified 16S rDNA with five restriction enzymes and gel electrophoresis was performed as described by Heyndrickx et al. (1996). The digitized gel images were analyzed using the GelCompar software version 4.2 (Applied Maths, Kortrijk Belgium) and compared with the laboratory database. Using the ARDRA technique it was shown that the FAME-grouping is more accurate if clusters are delineated at a Canberra metric similarity of 85% instead of 80. In this case there are 60 clusters and 46 ungrouped isolates. Using the ARDRA technique it becomes clear that the diversity of bacilli living on mural paintings is high. Clusters were further identified as B. circulans, B. firmus, B. similibadius, B. niacini and B. licheniformis. The success of the genus can be explained by the fact that bacilli are able to survive for very long periods as spores. Small populations of bacilli present on mural paintings over a long period of time can give very high numbers of spores. Sampling and isolation will therefore give an overestimation of the number of viable cells present on the paintings (Heyrman et al., 1999). Still, the high species diversity found is an indication of a successful growth of bacilli on mural paintings.
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4. 16S rDNA sequencing For 16S rDNA sequening of the isolates, the total DNA was purified as described above. Of the total DNA, a fragment of the 16S rRNA gene (corresponding to positions 8-1541 in the Escherichia coli numbering system) was amplified by PCR using conserved primers (5' AGAGTTTGATCCTGGCTGAG 3' and 5' AGAGTTTGATCCTGGCTGAG 3'). The PCR products were purified using a QIAquick PCR Purification Kit (Qiagen), according to the manufacturer's instructions. Sequencing was performed using an Applied Biosystems 377 DNA Sequencer and the protocols of the manufacturer (Perkin-Elmer) using the ABI Prism Dye Terminator Cycle Sequencer Ready Reaction Kit. The sequencing primers used were previously described by Coenye et al. (1999). Sequence assembly was performed using the program Auto-Assembler (Perkin-Elmer). The closest related sequences were found using the FASTA program. Strains characterized by 16S rDNA sequencing were closest related to Micrococcus luteus, Bacillus marismortui, B. macroides, B. cohnii, B. megaterium, Arthrobacter sp. and A. crystallopoietes. All of these species belong to genera frequently isolated from mural paintings (Ciferri, 1999). One cluster, which contained isolates restricted to one sample of the church in Greene, was most similar to the genus Nocardioides. Of the nocardioform actinomycetes, only members of the genus Nocardia were previously isolated from mural paintings (Giacobini et al., 1988). 5. References Ciferri, O., 1999. Microbial degradation of paintings, Applied and Environmental Microbiology 65,879-885. Coenye, T., Falsen, E., Vancanneyt, M., Hoste, B., Govan, J.R.W., Kersters, K., Vandamme, P., 1999. Classification of Alcaligenes faecalis-like isolates from environment and human clinical samples as Ralstonia gilardii sp. nov., Intemational Journal of Systematic Bacteriology 49, 405-413. Giacobini, C., De Cicco, M. A., Tiglie, I., Accardo, G., 1988. Actinomycetes and biodeterioration in the field of fine art, p. 418-423. In D.R. Houghton, R.N. Smith and H.O.W. Eggings (Eds.), Biodeterioration, vol.7. Elsevier Applied Science, New York, N.Y. Heyndrickx, M., Vauterin, L., Vandamme, P., Kersters, K., De Vos, P., 1996. Applicability of combined amplified ribosomal DNA restriction analysis (ARDRA) pattems in bacterial phylogeny and taxonomy, Journal of Microbiological Methods 26, 247-259. Heyrman, J., Mergaert, J., Denys, R., Swings, J., 1999. The use of fatty acid methyl ester analysis (FAME) for the identification of heterotrophic bacteria present on three mural paintings showing severe damage by microorganisms, FEMS Microbiology Letters 181, 5562. Pitcher, D.G., Saunders, N.A., Owen, R.J., 1989. Rapid extraction of bacterial genomic DNA with guanidium thiocyanate. Letters in Applied Microbiology 8, 151-156.
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A STUDY OF BIOLOGICALLY DECAYED SANDSTONE WITH RESPECT TO CA AND ITS DISTRIBUTION.
M. S. Jones Roslyn Associates, 19, High Street, Kemnay, Aberdeenshire. Scotland, AB51 5NB. email:[email protected] *R. D. Wakefield, G. Forsyth. Opto electronics Research Centre, Black Friars Street Building, School of Applied Science. The Robert Gordon University, Aberdeen, Scotland.AB251FR.
Abstract
Examination was carried out of decayed spalled stone taken from a Scottish 13th Century sandstone castle colonised predominantly by Trentepohlia A u r e a and a number of bacteria, fungal species and blue green algae. Previous work by FTIR had identified deposits of monohydrocalcite in the Hermitage sandstone pores, and associated with the microbial community. To explore the potential of the microorganisms to solubilise Ca from the sandstone, individual microbial species were isolated from the decayed stone and systematically screened for their potential to dissolve small amounts of Ca from fresh Hermitage stone, in culture, under conditions of Ca starvation. Many of the species of bacteria and fungi were capable of releasing varying amounts of Ca from the stone though algal cultures of T. a u r e a were not found to be capable of causing Ca dissolution from the stone. The production of the polyol mannitol by cultures of T. a u r e a was also examined and small amounts of the polyol were found following osmotic shock of T. aurea. Keywords: T r e n t e p o h l i a aurea, biodeterioration, calcium, sandstone decay. 1. Introduction During the period 1994-1996 Hermitage Castle in the Scottish Borders was examined in an U.K-EPSRC funded case study investigating the role of stone micro-organisms in decay. Field work was carried out in conjunction with various laboratory tests. Hermitage Castle was the focus of the study because of the spalling of surface stone in small areas of 0.5 to 5.0 cm dia. and 1 to 2 mm in depth. These decayed areas appeared to be associated with the distribution of a mixed microbial community, of which the predominating species was T r e n t e p o h l i a a u r e a (Wakefield and Jones, 1996). The decay affected extensive areas of the castle and T. a u r e a was found to varying degrees on all aspects of the castle. Below the stone surface the algal filaments were green in colour, becoming orange at the stone surface through the accumulation of globules of carotenoid oil. Examination by scanning electron microscopy (SEM), light and epifluorescence microscopy showed that, while bacteria and cyanobacteria were also present in the spalled stone, the filaments of T. a u r e a were the major contributors to mechanical degradation of the stone surface. The distribution of the algae was synonymous with extensive spalling of the surface of the stone. One of the major factors of the stone decay process is the potential for solubilisation of cations by micro-organisms by the production of various chelating agents. Previous researchers have identified various organic acids associated with stone decay (Eckhardt, *author to whom correspondence should be addressed
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1985; Jones and Wilson, 1985; Griffin, et al., 1991; Jones et al., 1996). Biochemical damage to stone caused by algae through the production of extracellular organic acids, chelating agents and carbonic acid from respiratory carbon dioxide, have been found to cause dissolution of minerals and salt crystallisation (Caneva, et al., 1990; Krumbein and Dyer, 1985). Studies on Hermitage stone by SEM, energy dispersive x-ray analysis (EDX) and Fourier transfer infra red spectroscopy (FTIR), found that large amounts of Ca in the form of monohydrocalcite were present in association with the microbial community (Jones et al, 1999). Since Ca concentrations in fresh unweathered stone from the same building were relatively low, the microbial community (including the principle organism present, T. aurea and associated bacteria, fungi and cyanobacteria) was clearly able to accumulate Ca from the surrounding environment. One factor protecting cells against dehydration is the accumulation of osmotically active molecules within the cell. Such molecules may leak from the cell during wetting after a period of drought and may contribute to the stone decay process either directly, by chelation, or indirectly as a nutrient source for heterotrophic organisms. Considerable amounts of organic solutes or salts may accumulate in the cell during times of matric or osmotic stresses. In particular the algal genus Trentepohlia is aknown to accumulate large amounts of the polyol mannitol (Feige and Kremer, 1980), which very probably acts as an osmoregulator (Reed and Wright, 1986). To investigate further the decay process of Hermitage stone, a series of experiments were devised to determine the ability of microbial isolates from decayed Hermitage stone to solubilise Ca from fresh unweathered Hermitage sandstone. A preliminary experiment to determine the presence of mannitol in solution after sudden wetting of decayed stone samples and algal cell cultures is also presented. 2. Methodology 2.1 Specimen observation and isolation and culture of microorganisms Specimens of spalled stone from Hermitage Castle were carefully removed, made into polished thin sections and analysed using a polarising microscope and SEM/EDX to identify some elements present in the specimens. Specimens of spall (flakes of stone colonised by Trentepohlia) were removed from the north facade of the building into sterile bottles containing 1.0cm 3 physiological saline or 1/4 strength Ringers solution. In the laboratory, specimens were ground in a sterile pestle and mortar before being re-suspended into dispersant solutions of Tween 80 and peptone (0.01%:0.05%) or Tween only (0.01%) (Weirich and Schweisfurth, 1985) and shaken for 10 minutes before serial dilutions and spread plates were made. Various solid culture media were made to encourage the growth of both copitrophic and oligotrophic bacteria and fungi. Low nutrient media of 1/50 strength of Malt Extract and Czapek Dox agar were made up for oligotrophic fungi, with full strength of the same media for copiotrophs. Plates of full strength and 1/50 dilution of Nutrient Agar and Nutrient Agar with soil extract were made for copiotrophic and oligotrophic bacteria respectively (Weirich and Schweisfurth, 1985; Warscheid et al., 1988). R2A agar, used in the isolation of bacteria in treated potable water, was used in addition diluted media for the isolation of bacteria growing under nutrient limited conditions. Bolds Basal and BG11 liquid and solid medium were made up for the culture of algae. 2.2 Determination of bacteria/fungal isolates to solubilise Ca. The potential of isolated bacteria, fungi and algae to bring about dissolution of Ca was determined by culture of a selection of isolates with stone after the method first described in Jones and Wakefield (1998). Ca free minimal salts media (containing glucose as a carbon
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source and adjusted to pH 7.8, the pH of Hermitage stone), containing either 1.0 g sand or 1.0 g of crushed Hermitage sandstone was used. The use of acid washed sand in stone-free control samples resulted in similar cell densities in inoculated media {MM} (sand-free media did not yield high cell densities). Fresh Hermitage stone was crushed and passed through a sieve (420gm) and both sand and stone were acid washed with 0.02M HC1 and then rinsed several times with MM to remove exchangeable cations (Schatz, 1963). Acid washing was to ensure that Ca present in solution after incubation was as a result of slower desorption from less readily exchangeable sites, or as a result of interaction between microbial cells/by products. All glassware used in the experiments were similarly acid washed using 0.6M HC1 to remove contaminants. Prepared minimal salts media were inoculated with one of 14 bacterial or fungal isolates. Cultures were also prepared with axenic T. aurea obtained from a culture collection (Sciento). The methodology for determination of total Ca concentration released from Hermitage stone during the culture period by the action of the microbial community is summarised in fig. 1. 2.3 Determination of the prescence of organic acids in spent culture media. Gas chromatography-mass spectrometry (GCMS) was used in the determination of the presence of organic acids in filtered spent growth media from bacterial and fungal isolates cultured in the presence of stone/sand. A MM extract was also taken from decayed Hermitage spall and prepared for GCMS. Aliquots were removed from spent MM media, filtered through 0.2~tm to remove microbial cells, the cell free solutions acidified by addition of conc. HC1 and extracted in ether. Tert-butyldimethylsilyl (tBDMS) derivatives of organic acids present were made after the method described by Cromholm and Norsten (1985). Tert-butyldimethylsilyl derivatives were made of standard solutions containing a mixture of oxalic, citric, D-gluconic and lactic acids in minimal salt medium. Determination of organic acids in spent culture media was carried out using a HRGC 5160 Carlo Erba GCMS system where l~tl of sample was introduced to the GC and a heating cycle of 100~ for 5 mins; 60~ to 290~ for 1 min. carried out prior to introduction to the MS system. The mass spectra of spent culture media from a number of bacterial samples were compared with those of the standard organic acid samples to identify if any of the selected acids were present. 2.4 Determination of the polyol mannitol in algae cultures and extracts from decayed Hermitage stone. Trentepohlia, and other types of aerophilic algae are known to accumulate mannitol in the cell. Like bacterial cells, they may undergo some loss of their osmotically active molecules into the surrounding environment on sudden wetting following a period of drought. To simulate a period of drought, 50mL of a liquid culture of T. aurea was passed through a Wattman 45 filter paper of known weight so that the algae were deposited onto the surface of the filter. This was done in duplicate. The dry weight of algae deposited on the filter papers was determined by taking the weight of the papers after filtration and again periodically over a period of 24 hours during drying at 23~ in a fan-assisted incubator until no more weight loss occurred. Similarly, a specimen of decayed Hermitage spall were broken with minimal force in a pestle and mortar and 2g of the material were then deposited onto each of two Watmann 45 filter papers. A duplicate blank was prepared using acid washed sand. All filters were subjected to similar conditions of drying at 23~ over a 24 hour period. After the samples were air dry, each filter paper was placed onto a
Inoculation of: nutrient broth with bacteria or Czapecs dox/malt extract broths for fungi/Bold's basal with T.aurea ,b Shake incubation at 23~ until mid log phase reached Sub-cultures removed and washed several times in minimal medium (MM) by centrifugation to remove residual calcium ,b Cell pellets re-suspended in MM and used as inocula for MM containing sandstone/sand Cultures incubated (shake culture, 23~ to stationary phase and pH of media taken ,b Replicate I0 mL aliquots of cell culture removed and centrifuged to remove particulates Addition of 100 ~tL EDTA and pH of supernatant adjusted to pH 9 (optimum EDTA chelation) & Precipitate removed by passing through 0.2 ~m Millipore filter ,k Calcium determination by flame absorption spectroscopy (standard method) against calcium standards made using cell-free procedure described above. Calcium in culture extract was determined by the following calculation: 4,
O 0"Q r~ r~ O
O 0
0
~.,. 0
([Ca] in M M + cell-free stone) + ([Ca] in M M + inoculated sand) - [ C a ] in inoculated stone.
Figure 1" Methodology for Calcium determination in microbial cultures isolated from decayed Hermitage stone.
0
Figure 2a: SEM micrograph o f thin sectioned sandstone with Trentepohlia aurea living in the
stone surface (to the right of micrograph).The bright areas in the
top right SEM denote the biological community, calcium and clays in the stone pores.
Figure 2b: Back scattered electron
Figure 3: SEM micrograph of thin
micrograph showing porosity (black areas within the stone), bright dots indicate zirconium silicate, light
section
grey areas are feldspar, dark grey is quartz. Note the parting o f grains in the right hand side o f the micrograph where the Trentepohlia aurea is present
of
weathered
sandstone
showing a calcium rim within a pore, l m m away from the top surface. The calcium may be sourced by dissolution from the lime mortar with re-precipitation in
0
<
|
4~
the pores. t,J
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filter unit without suction. Ten mL of distilled water was added to each sample and the sample gently agitated for a few minutes before the suction was turned on and the filtrate collected. Mannitol in filtrates was determined by the method described by Kirst (1988). In this method sodium periodate solution was added to downshocked algal extracts. The mannitol present is oxidised within 1 minute by the periodate. Other polyols and sugars take longer to oxidise. Periodate in the samples was determined by absorption at 260nm. The concentration of periodate is proportional to the amount of mannitol present. The concentration of mannitol in each extract was determined against mannitol-periodate calibration.
3. Results and Discussion 3.1 Examination of decayed stone Previous work showed the overall composition of the stone to be of grains of quartz, potassium feldspar, and trace amounts of iron oxides, calcite, futile, mica, goethite, illite, chlorite and kaolinite. The stone is cemented by siliceous overgrowths, produced by pressure solution during the original formation of the rock (Jones et al., 1999b). Figure 2a and b are scanning electron micrographs which show the photosynthetic community associated with the decayed spalled stone and the intact stone underneath. An increase in porosity of the spall is clearly visible on figures 2a and b. Mercury porosimetry also supported this observation, since spalled stone examined by this technique was 28.14%, compared to fresh stone which was 14.23%, indicating a substantial porosity increase at the spalled surface (Jones et al; 1999). Examination by SEM/EDX of thin sections of spalled sandstone and other samples of weathered sandstone at higher magnification shows rims containing the element Ca round the edges of some of the pores (e.g. fig.3). Ca can also be seen in association with the photosynthetic community. The pore in fig.3 is situated approximately l mm away from the top surface. The sandstone block from which the sample was taken was cemented in place by lime mortar. It was suggested by Jones et al., 1999a, that the original Ca source was dissolution of the lime mortar (containing 18.23% Ca according to XRF). The Ca then migrated into the stone pores. Previous work (Jones et al., 1999a) utilised FT-IR and XRD and identified the Ca in the spall to be in the form of monohydrocalcite. A search of the literature showed that since monohydrocalcite is metastable with respect to calcite and aragonite, calcite is more likely to be re-precipitated (Hull and Turnbull, 1973). However, Mg can also inhibit the formation of calcite in preference to monohydrocalcite (Hull and Turnbull, 1973) under certain circumstances and Mg was found in the spall, and in the mortar samples taken from Hermitage Castle (Jones et al., 1999a).The monohydrocalcite in Hermitage stone appears to be associated with the biological community and this maybe due to a variety of processes acting singly or synergistically, though it was recognised that further research would be required to substantiate the precise genesis of the monohydrocalcite. However, since Ca is the most vulnerable of the mineral elements to be chelated by organic compounds (Leadbetter and Riding, 1986) its apparent accumulation may also be indicative of a biomediated chelation process where the biological community re-works the Ca to form biogenic monohydrocalcite and this was the hypothesis put forward in Jones et al,. 1999a. 3.2 Culture of micro-organisms from decayed spalled stone Culture of the micro-organisms from decayed stone resulted in the isolation of 31 colonies of bacteria and fungi. Plate counts showed that highest bacterial and fungal numbers were
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9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
obtained using Tween 80 and peptone as a dispersant. The use of low nutrient media and media with diverse energy supplies encourages the growth of slow growing organisms and slows down growth of more competitive species enabling a better representation of the diversity of species present in nutrient starved environments. Relatively large numbers of bacterial and fungal species were selected using low nutrient media. Czapek Dox was favoured by fungal isolates from stone at both 1/50 th and full strength concentrations used. For epilithic bacteria, media containing low nutrients such as R2A and more complex nutrients as supplied by soil extract, were most favoured and found to encourage the most growth. Growth in Bolds Basal and BG11 liquid media indicated the presence of cells similar in appearance to Chlorococcum, and green filaments of Trentepohlia. Solid media showed small, discrete colonies of the cyanobacteria Nostoc embedded in mucilage and short filaments resembling Callothrix. 3.3 Determination of bacterial and fungal isolates to solubilise Ca from Hermitage stone Incubation of the majority of fungal and bacterial isolates with Hermitage sandstone resulted in elevated concentrations of Ca in spent culture media compared to controls. Fig. 4 demonstrates that the amount of Ca present in the cell-free medium containing He~xnitage sandstone, is lower than that present in medium containing stone and inoculum. The Hermitage stone used was ground, sieved and acid washed prior to addition to the incubation and a total of 15 cell free replicates showed similar amounts of Ca in each case. The mean background Ca concentration was 5.3 + 2.8 ppm. Similarly, the culture containing sand and inoculum demonstrates that for a similar amount of growth, the Ca content associated with the cells alone was minimal compared to that in cultures containing stone and inoculum. Although an amount of Ca does dissolve into the surrounding medium from the stone during the incubation period, approximately double the amount is further released in the presence of the cells. The presence of cells in a culture is expected to influence the pH of the medium and thus influence Ca solubility. The pH of the cultures were taken at the end of the incubation, and plotted together with the Ca concentration present in each case (figs. 5, 6). The amount of Ca present in the spent medium is not correleted with pH. The alga T. aurea from the culture collection did not release Ca from Hermitage stone. 3.4 Determination of the presence of organic acids in spent culture media Gas chromatography mass spectroscopy of spent culture medium from bacterial, fungal, T. aurea and also a water extract of decayed spalled stone showed the presence of lactic, malonic and succinic acids, fatty acids and some unknown organic compounds (fig. 7). Substances present in the culture medium of T. aurea were also derivitised and examined. The spent algal media contained lactic acid and some larger molecules, possibly fatty acids (fig. 8). Some of the extract obtained from wetting of the dried algae, as described in section 2.4 was also derivitised. This was found to differ from the culture medium of the same alga in containing fatty acids and some unknown compounds (fig.9). 3.5 Determination of mannitol in spall extract. The periodate colourimetric test for the prescence of mannitol in solution gave aborbencies of 0.334 and 0.515 corresponding to 0.58 and 0.90 [~tM mannitol in spall extract respectively (fig. 10).
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Figure 4: An example of typical Ca concentrations found in spent bacterial and fungal culture media after incubation with Hermitage sandstone or sand.
Figure 5: pH and Ca concentration in spent cultures of bacteria incubated with Hermitage Sandstone.
Figure 6: pH and Ca concentration in spent cultures of fungi incubated with Hermitage Sandstone.
Figure 7: GCMS of bacterial culture extract with malonic, succinic and lactic acid present.
Figure 8: GCMS of T. a u r e a spent culture extract showing lactic acid present.
Figure 9: GCMS of extract from T. a u r e a following downshock.
480
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
o~~
0.6 0.5 E 0.4 co r 0.3
0.3347"
J
,i
0.2
0.1 Of" 0
0.2
0.4
0.6
0.8
[mannitol] uM
Figure 10: Mannitol concentration in spall extract using the periodate oxidation method. Mannitol was not found in extracts from T. aurea cultures grown in liquid media, nor was it present in extracts from air-dried cultures indicating mannitol is not produced under the culture conditions used. Mannitol is a polyol which may be acting in this case as an osmoregulator, it is also a potential cationic chelating agent due to its many OH groupings and is potentially a factor in biochemical mechanisms of stone deterioration which is mediated by microclimate. Trentepohlia is not the only alga that is known to produce mannitol as an osmotic regulator and the source of the mannitol from the spall is unclear at this stage. The finding of this molecule in the spall extract is an indication that osmoregulators would be released in this case on wetting of the decayed stone. The role of such molecules in stone biodeterioration needs to be explored but the implication is that a rain event, after a period of drought, may prompt consequential stone decay processes. In a mixed microbial population it is possible that a host of different osmoregulators may be released into the stone environs following a rainfall event. This may bring about a localised increase in cation chelation from vulnerable minerals and precipitates within the stone. Further, these molecules also represent a ready source of organic nutrients for heterotrophic bacteria and fungi, which may contribute to the stone decay process. 4. Conclusions. Previous work by the authors has shown that T.aurea contributes by physical processes to biodeterioration. This work has shown that this alga is capable of producing quantities of lactic acid which would also contribute in a biochemical w a y b y chelating divalent cations such as Ca. The results show that Ca could be solubilised by certain members of the microbial community namely the heterotrophic bacteria and fungi. Spent media extracts and extracts of spall showed the presence of organic acids. The spall extract also showed the polyol mannitol to be present. All compounds are able to chelate divalent cations such as Ca and it is possible that these are the factors responsible for the precipitation of the Ca associated with the microbial community as observed by SEM/EDX. The authors recognise the role of cyanobacteria would also be important in decay of Hermitage stone and Ca accumulation, however their study was beyond the scope of this work. 5. Acknowledgments. EPSRC for funding Biodeterioration of Sandstone by Algae and Application of Stone Conservation Methods (Grant Reference GRJ91500). Historic Scotland for access to
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Hermitage Castle. T.Fraser at Macaulay Land Use Institute, Cragiebuckler, Aberdeen for help with the FT-IR and D.Duthie, D. Bain for XRD and XRF results. 6. References.
Eckhardt F., 1985. Solubilisation, transport and deposition of mineral cations by microorganism - efficient rock weathering agents. In: Drever J.I. Ed. The Chemistry of Weathering. D. Reidel Publishing Company. 161-173. Feige G.B., Kremer B.P., 1980. Unusual carbohydrate pattern in Trentepohlia species. Phytochemistry, 19, 1844-1845. Griffin P.S., Indictor N., Koestler R.J., 1991. The biodeterioration of stone: a review of deterioration mechanisms, conservation case histories, and treatment. Intemational Biodeterioration. 28, 187-207. Hull H., Tumbull A.G., 1973. A thermochemical study of monohydrocalcite. Geochimica et Cosmochimica Acta. 37, 685-94. Jones D., Wilson M.J., 1985. Chemical Activities of Lichens on Mineral Surfaces: A Review. International Biodeterioration. 22; 99-104. Jones M.S., Wakefield R.D., 1998. Methodologies and techniques associated with a study of biodeterioration at Hermitage Castle, U.K. Environmental Aspects of Weathering Processes, UNESCO/UISG proceedings ENVIWEATH 96, Bmo, Czech Republic. 100-106. Jones M.S., Wakefield RD., Forsyth G., 1999a. The occurrence of rare minerals on decayed medieval scottish building stone colonised by biological growths. Materiales de Construccion, 49, 256. Jones M.S., Wakefield R.D., Forsyth G., Martin P.J., 1999b. Aspects of microclimate: effects on the distribution of a biological community on Hermitage Castle, U.K. Aspects of Stone Weathering Decay and Conservation, SWAPNET96, Aberdeen, U.K. Ed. Jones M.S., Wakefield R.D., Imperial College Press (ISBN 1-86094-131-1). 90-102. Kaplan D., Christiaen D., Arad S.A., 1987. Chelating properties of extracellular polysaccharides from Chlorella spp. Applied and Environmental Microbiology. 53, 12. 2953-2956. Kirst G.O., 1988. Accumulation of organic compounds with increasing salinity: mannitol accumulation in the unicellular phytoplankter Platymonas. In 'Experimental Phycology' Lobban, C et al. (eds.), Cambridge University Press. 217-221. Leadbetter B.S., Riding R., 1986. Biomineralisation in plants and lower animals. The Systematics Association, Special Vol. 30, Clarendon Press, Oxford. Reed R.H., Wright P.J., 1986. Release of mannitol from Pilayella littoralis (Phaelphyta. Ectocarpales) in response to hypo-osmotic stress. Marine Ecology - Progress Series, 29, 205-208. Schatz, 1963. The pedogenic action of lichens and lichen acids. Journal of Agriculture, Food and Chemistry, 11, 112-118. Wakefield R.D., Jones M.S., Forsyth G., 1996. Decay of sandstone colonised by an epilithic microbial community. Processes of Urban Stone Decay, SWAPNET95, Belfast. Ed. B.J. Smith B.J., Warke P.A., Donhead. (ISBN 1 873394 20 9). 90-99. Warscheid T., Petersen K., Krumbein W.E., 1988. Effect of cleaning on the distribution of micro-organisms on rock surfaces. Biodeterioration, 7, 455-60. Weirich G., Schweisfurth R., 1985. Extraction and culture of microorganisms from rock. Geomicrobiology, 4, No. 1.
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483
MICROBIAL
ENVIRONMENTAL
MONITORING
OF
STONE
CULTURAL
HERITAGE
Lucia Pitzurra,* Monica Giraldi, Giovanni Sbaraglia, Francesco Bistoni Microbiology Section, Department of Experimental Medicine and Biochemical Sciences, University ofPerugia, Perugia, Italy Teresa Bellezza Soprintendenza dei BB. AA. AA. AA. SS. dell'Umbria, Laboratory of Analysis and Restoration, Perugia, Italy Gennaro Spera National Research Council, Rome, Italy.
Abstract
Recently, a new technique for the assessment of microbial contamination on surfaces has been described. Microbial environmental monitoring (MAM from the Italian acronym Monitoraggio Ambientale Microbico) is based on an innovative conceptual approach using new techniques. Surface contamination was evaluated by measuring the microbial build-up (MB) on samples collected using a nitrocellulose membrane. In this study, MAM was employed in microbial monitoring during restoration of the medieval fountain in Priori Square in Narni, Italy. MB was monitored during and after restoration of the fountain to quantify and identify the contaminating microbial flora, bacteria, and fungi and their modifications. The results showed that MAM is suitable for evaluating the efficacy of restoration and offers many advantages with respect to other microbial techniques currently in use. In particular, surface sampling with a nitrocellulose membrane is not destructive and allows for quantitative and qualitative analysis of microbial flora contaminating the surfaces of art works and monuments before and during restoration. Key words: Microbial environmental monitoring, MAM, stone, biodeterioration
1. Introduction The fountain in Priori Square in Narni, Italy dates back to 1300. The fountain is composed of a polygon-shaped marble basin and a bronze basin placed in the center of the fountain (fig. 1). The marble basin consists of 20 panels of pink limestone separated by marble columns. A bronze pillar supports the bronze basin (fig. 1A). On the fountain surfaces, an extensive biological colonization is present, mainly composed of moss and weeds. The colonization is present outside and inside the basin, on the panels, and on the column surfaces (fig. 1B). A new technique to study microbial contamination in air and on surfaces in environments at risk has been described (Pitzurra, 1997a; Pitzurra, 1997b). More recently this technique has been successfully applied in studies on cultural heritage environments (Pitzurra, 1999). The MAM (from Italian acronym Monitoraggio Ambientale Microbico) method involves evaluation of microbial surface contamination by measurement of microbial build-up (MB) on samples collected using a nitrocellulose membrane (Pitzurra, 1997b).
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Figure 1: A: Medieval fountain in Priori Square in Narni. B: Biological colonization on fountain surfaces. MAM was employed in microbial monitoring of the medieval fountain in Priori Square in Narni during restoration. In this study, MB was controlled during and after restoration of the fountain to quantify and identify the contaminating microbial flora and their modification. The results showed that MAM is suitable for evaluating the efficacy of restoration and offers many advantages with respect to other microbial techniques currently in use. In particular, sampling of the surfaces by nitrocellulose membrane is not destructive and allows for quantitative and qualitative analysis of microbial flora contaminating the surfaces before and during restoration.
2. Experimental Methods 2.1 Sampled sites Samples were collected from the surfaces of the stone basins. Five sites were monitored on the surfaces of the external pink limestone panels, five on the marble columns, and five inside the marble basin. The samples were collected before restoration and at completion of restoration. 2.2 Microbial monitoring Microbial monitoring of the fountain surfaces was performed by evaluating the MB index and by scanning electron microscopy (SEM) analysis. MB. MB is the measurement of the number of microorganisms on a surface after an unknown period of time (Pitzurra, 1997b). Briefly, membrane filters of 17.34 cm2 (Sartorius AG, Goettingen, Germany)were pressed against the surface to be tested for 30 seconds (fig. 2A) and then transferred on solid culture media for algae (BG-11, Stainer, 1971), bacteria (Nutrient Agar, Difco, Detroit, MI, USA), or fungi (Rose Bengal Agar base, Difco) in Petri dishes, 60 mm in diameter. The plates were incubated at 25~ in 80% of relative humidity. After incubation
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(i.e. 7-14 days for algae and 2-5 days for bacteria and/or fungi) the microbial colonies grown over the membrane were counted and the results of MB were expressed as colony forming units (CFU)/cm 2 (fig. 2B).
Figure 2" A: Sampling procedure on stone surfaces using a nitrocellulose membrane; B Microbial colonies grown on nitrocellulose membranes. MAM establishes the contamination classes and maximum acceptable levels for a correct interpretation of the results (Pitzurra, 1997a; Pitzurra 1997b). Four classes of MB have been defined: very high, high, middle and low risk and the maximum acceptable levels are 0.06, 1.00, 2.00, and 4.00 CFU/cm 2, respectively. SEM. Specimens were collected under sterile conditions from the surface of the fountain using a scalpel. The specimens were spattered with gold in a low-pressure argon atmosphere as previously described (Guglielmetti, 1994). Ultrastructural analysis was performed using a Philips 505 scanning electron microscope.
2.3 Microbiological procedures The fungal strains were identified by genus using analytical keys, as proposed by Domsch (1980) and Ellis (1976). The bacterial strains were identified by genus and species using analytical keys as proposed by Koneman (1995) or by Sceptor System (Becton Dickinson, Sparks, MD, USA).
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Figure 3: MB evaluation of fountain surfaces before restoration. Samples were taken from panels (A), columns (B), and inside the basin (C). MB values were evaluated as described in Experimental Methods. Horizontal lines indicate the maximum acceptable levels in environment at middle risk. 3. Results The results of microbial monitoring, by evaluation of the MB index, on the surfaces of the fountain showed high levels of contamination on the surfaces of the panels (fig. 3 A) and
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inside the basin (fig. 3C). In particular, all five sampled sites had MB values over 2 CFU/cm 2, the maximum acceptable level for environments at middle risk. In contrast, low levels were observed on the column surfaces (fig. 3B). Furthermore, by comparing the microbial species isolated from different sites, differences were observed between panels and surfaces inside the basin. Bacteria were the predominant contaminating microbe on the panels, while algae were highly represented on the surfaces inside the basin (fig. 3A, 3C).
Figure 4: Comparison of MB indexes evaluated on the fountain surfaces before and after restoration. Cleaning of the surfaces was performed with Preventol RS0 (PRS0) and mechanical removal (MR). MB values were evaluated as described in Experimental Methods. Horizontal lines indicate the maximum acceptable levels for environment at middle risk. Cleaning of the calcareous deposits and moss from the stone surfaces of the basin was performed with Preventol R80 at 3% in dH20 followed by mechanical removal of chemical and biological deposits. Microbial monitoring by MB after treatment with Preventol RS0 showed a marked increase in the MB values on the panels, columns, and surfaces inside the basin with respect to those detected before treatment (fig. 4). This increase in the MB values was drastically reduced after mechanical removal of the deposits (fig. 4). The identification of microbial species isolated from the surfaces of the fountain showed that the observed increase in MB values on all fountain surfaces 60 days after application of Preventol R 80 was determined by overgrowth of the bacterial spp. (fig. 5A, B, and C) Scanning electron microscopy confi/med the results obtained by evaluation of the MB index (fig. 6). Before restoration, microscopic analysis documented the presence of algae on the stone fountain surfaces (fig. 6A). After treatment with Preventol R80 the scanning electron microscopic images revealed the decomposition of algae and the appearance of bacterial and fungal morphologies (fig. 6B). After mechanical removal, no cellular morphologies were observed (fig. 6C).
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Figure 5. Microbial species (A: algae; B: bacteria; C: fungi) isolated from fountain surfaces before and 60 days after the application of Preventol R80 (PR80). MB values were evaluated as described in Experimental Methods. Horizontal lines indicate the maximum acceptable levels for environment at middle risk. 4. Discussion
Air pollutants attack and cause damage to artistic materials (Zanotti Censoni, 1980; Saiz-Jimenez, 1981; Nugari, 1993; Saiz-Jimenez, 1993; Fassina, 1999). Polluted air contains many microorganisms that actively participate in the metabolism of mineral substances. Algae, cyanobacteria, lichens, bacteria, and fungi colonize art works and cause
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A
Figure 6. SEM analysis of biological colonization on fountain surfaces before and after restoration. A: Before restoration; B: 60 days after application of Preventol RS0; C: 60 days before MR treatment. SEM analysis was performed as described in Experimental Methods. corrosion of these substrates (Krumbein, 1978; Krumbein, 1990; Ortega-Calvo, 1991; Bock, 1993; Petersen, 1993, Caneva, 1994; Koller, 1996). For the preservation of monuments and sites of cultural heritage, microbiological methods based on defined standards are needed to evaluate the problems associated with biodeterioration. The routine monitoring of microbial contamination on surfaces is based on quantitative studies. The samples are usually collected by cotton swab or by scalpel, a technique which gives good results and allows for the isolation of a single microbial species (CNR, 1982; Raschle, 1983). However, this sampling procedure is not suitable for quantifying the degree of surface microbial contamination. In this context, the use of nitrocellulose membranes allows the study in parallel of the quantity and the quality of the whole microbial population present on the surface under examination. In particular, surface sampling by nitrocellulose membrane followed by MB index evaluation makes possible a description of
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the dynamics of the microbial population on the fountain surfaces before and during restoration and evaluation of the efficacy after restoration. Furthermore, the samples collected using this well-defined and standardized sampling technique permits the comparison of results obtained in different environments and by different researchers. At the present, there are no official guidelines to define the maximum acceptable MB levels in cultural heritage at risk. In this study, the maximum level of 2.00 CFU/cm 2 was chosen considering that the medieval fountain in open-air is a middle-risk environment. The value of MB detected on all surfaces of the fountain after restoration (<2.00 CFU/cm 2) suggests that MB standardized contamination classes employed in hospitals and industries can also be employed in microbial monitoring of cultural heritage. Studies are in progress to confirm this issue. Preventol R80 was employed in the restoration of the fountain to facilitate the removal of moss and calcareous deposits from the surface of the marble basin. The present data showed that this treatment drastically increased microbial contamination of stone surfaces due to the overgrowth of resistant bacterial species (Vibrio metschnikovii). Once again, this finding emphasizes that the efficacy ofbiocides in removal ofbiofilm from surfaces should be tested in the laboratory and in situ on selected sample surfaces before application to prevent overgrowth of microbes resistant to treatment. The aim of this study was to validate the application of MAM on microbial monitoring of cultural heritage. As shown by our data, the advantages of MAM in microbial monitoring of stone surfaces are: i) the collection of surface samples is not destructive; ii) it permits quantitative and qualitative analysis of the samples; iii) it is easy to perform and inexpensive; iv) contamination classes and maximum acceptable levels allow a correct interpretation of the results.
Acknowledgments The authors thank Eileen Zannetti for editorial assistance, C. Pasquarella for MAM, M. Tosti for SEM, M. Romano for historical documentation of the art works, S. De Turres for information on restoration. This study was supported by Progetto Finalizzato CNR-Beni Culturali, contratto n. 96.01081.PF36 and a grant from the University of Perugia, Italy. 5. References Bock E., Sand W., 1993. The microbiology of masonry biodeterioration. Journal of Applied. Bacteriology 74, 503-514. Caneva G., Nugari M.P., Salvadori O., 1994. La biologia nel restauro. Nardini, Firenze. CNR, Centro di Studio di Milano e Roma sulle cause di deperimento e sui i metodi di conservazione delle opere d'arte. ICR, Istituto Centrale di restauro. 1982. Microflora autorofa ed eterotrofa. Tecniche di isolamento in coltura. Raccomandazioni Normal. ICR, Roma, Eds. Domsch K.H., Gams W., Anderson T.H., 1980. Compendium of soil fungi. Academic Press, London. Ellis M.B. 1976. More dematiaceous hyphomycetes. Comm. Mycol. Inst. Kew, Surrey, England. Fassina V, Marabelli M., 1999. Effects of air pollutants on the decay of frescoes in the Scrovegni Chapel: new results after twenty years of survey. International Conference." Air Quality in Europe Challenges for the 2000s" Venice 19%21 th 1999. Short Paper Book. Cocheo V., De Saeger E., Kotzias D., eds. 102.
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Guglielmetti M., De Guili Morghen C., Radelli A., Bistoni F., Carruba G., Spera G., Carretta G., 1994. Mycological and ultrastructural studies to evaluate biodeterioration of mural paintings, detection of fungi and mites in frescos of the Monastery of St. Damian in Assisi. International Biodeterioration and Biodegradation 31,269-283. Koller M., 1996. Research and care of painted facades - The Eurocare project-492 Muralpaint Fassadenmalerei. Forchungsprojekt Eurocare 492 Muralpaint, Mayer & Comp, Klosterneuburg, Wien, 25-33. Koneman, E.W., et al. 1995. Testo Atlante di Microbiologia Diagnostica. Antonio Delfino, Eds. Italy. Krumbein W.E., Lange C., 1978. Decay of plaster, paintings and wall material of the interior of buildings via microbial activity. Environmental biogeochemistry and geomicrobiology. Proceedings of 3 rd International Symposium on Environmental Biogeochemistry, 2, 687-697. Krumbein W.E., Petersen K., 1990. Mikroorganismen beschleunigen den Zerfall mittelalterlicher Wandgem/~lde. Wandmalerei-Schaoden, Arbeitshef~e zur Denkmalpflege in Niedersachsen 8, 115-121. Nugari M.P., Realini M., Roccardi A., 1993. Contamination of mural paintings by indoor airborne fungal spores. Aerobiologia 9, 131-139. Ortega-Calvo J.J., Hernandez-Marine M., Saiz-Jimenez C., 1991. Biodeterioration of building materials by cyanobacteria and algae, International Biodeterioration 28, 165-185. Petersen K., Hammer I., 1993. Biodeterioration of romanesque wall paintings under salt stress in the Nonnberg Abbey, Salzburg, Austria. Biodeterioration of cultural property." Proceedings of the 2nd bltet~lational Cot~erence, October 5-8, 1992, Yokohama, Japan~ International Communications Specialists, Toshi K., Arai H., Kenjio T., eds., Tokyo, 263277. Pitzurra L., Bellezza T., Giammarioli M., Giraldi M., Sbaraglia G., Spera G., Bistoni F., 1999. Microbial environmental monitoring of the refectory in the monastery of St. Anna in Foligno, Italy. Aerobiologia, 15, 203-209. Pitzurra M., Pasquarella C., Savino A., 1997a. I1 Monitoraggio Ambientale Microbiologico (MAM). Annali di Igiene, 9, 9-14. Pitzurra M., Savino A., Pasquarella C., Paoletti F., 1997b. A new method to test the microbial contamination of surfaces. Hygiene Medicine, 22, 77-92. Raschle P., 1983. Experience of combating moulds during restoration of ceiling paintings in a Swiss baroque monastery church. T.A. Oxley, S. Barry, eds., Biodeterioration 5. Chichester (John Wiley & Sons). Saiz-Jimenez C., Samson R.A., 1981. Microorganisms and environmental pollution as deteriorating agents of the frescoes of the Monastery of Santa Maria de la Rabida, Huelva, Spain. 6t~ Triennial Meeting ICOM Committee for Conservation, Ottawa 1981, 81/15/5-1 81/15/5-14. Saiz-Jimenez C., 1993. Deposition of airborne organic pollutants on historic buildings. Atmosphere Environment 27B, 77-85. Stainer R.Y., Kurisawa R., Mandel M., Choen-Bazire G., 1971. Purification and properties of unicellular blue-green algae (8 ord. Chrooccoccales). Bacterial Review, 35, 171-205. Zanotti Censoni A.L., Bettini C., Giacobini C., Mandrioli P., 1980. Aerobiological research in enclosed spaces of historical and artistic interest. Umwelt Bundes Amt Berichte, 79, 434-438.
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493
THE
S/kO
SEBASTIAO CHURCH OF TERCEIRA ISLAND (AZORES, CHARACTERISATION OF THE STONES AND THEIR BIOLOGICAL COLONISATION PORTUGAL)
P. Romeo Centro de Estudo, Conserva~o e Restauro dos A~ores, Rua de Jesus, n~119, 9700 Angra do Heroismo, Portugal M.I. Prudrncio*, M.J. Trindade, M. Nasraoui, M.A. Gouveia Instituto Tecnologico e Nuclear, EN 10, 2685-953 Sacavrm, Portugal M.O. Figueiredo, T. Silva Instituto de Investigag~.o Cientifica Tropical, A1. Afonso Henriques, 41, 4~ 1000 Lisboa, Portugal
Abstract
The S. Sebastiao Church, the oldest of the Terceira Island of Azores (XV-XVI century), was built with two main type of stones- tufts and trachytes as revealed by chemical and mineralogical analysis. The general state of the surface of the tuff blocks is more preserved than the trachyte. The biological colonisation on the walls of the church is composed by: (a) bacteria; (b) two species of free-fungi (Aspergillus spp.); (c) two species of macro-algae (generous Trentpollia); (d) twenty-four species of epilithic lichens; and (e) one specie of mosses (Grimmia sp.). Lichens are the most frequent organisms in all the stone elements. Eighteen of the twenty-four identified species are crostose and six are foliaceous (Physcia adscendens and five Parmelia sp.). On the east wall a gelatinous specie belonging to the Collema sp. vv. Generous was also detected. Key words: Azores, tufts, trachyte, biological colonisation 1. Introduction
The Sao Sebasti~o Church was the first church built in the Terceira Island of Azores (XV-XVI century), and since then has been submitted to several increases, adaptations and modifications according to the needs and styles of the different epochs (Fig. 1). The church is composed by one bells tower (the oldest part of the building), one nave, the chancel, and one aisle chapel, in a whole of 17 walls in a mixed exposed stone and lime painting. This work has two main goals: (1) to identify the stones used as building materials and (2) to characterise the biological colonisation of the stones. 2. Experimental Methods
The samples used in this work come from the facade and different walls of the S. Sebastiao Church. The chemical analyses were performed by means of the instrumental neutron activation method and X-ray fluorescence. *Author to whom correspondence should be addressed
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Figurel. The S~.o Sebasti~o Church in S~.o Sebasti~.o (Terceira, Azores). 3. Results and discussion
Chemical and petrographic analyses of the stones showed that trachytes are the majority of the exposed stones, except in the tower which is made of mfrs. The whole rock classification using Log (Zr/TiO2) vs SiO2 diagram +show that the church stones have a trachyte composition and clearly trend toward an increase of the SiO2 and Zr/TiO2 ratio. In TAS binary diagram (Cox, 1979) most samples plot in the trachyte field, but some samples are shifted toward a trachy-andesite composition probably as result of alteration inducing K20 and Na20 losses. The general state of the surface of the tuff blocks is more preserved than the trachyte. Tufts and trachytes are well discriminated by the rare earth elements, specially the Ce and Eu anomalies (Henderson P., 1986) (Fig. 2) and other trace elements, such as Cs and Br (Fig. 3).
& 0,9
9Tufts 9Trachyte
~= 0,8 uJ ::3 I.LI 0,7
&
0,6
A W
015
0,6
0
i
i
i
0,7
0,8
0,9
Q
CelCe *
Fig. 2. Ce vs. Eu anomalies for the tufts and trachyte monument samples.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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Fig. 3. Trace elements contents in the tufts (t) and trachyte (tr) monument samples.
3.1. Characterisation of biological colonisation Biological colonisation of S~o Sebasti~o Church is quite homogeneous along all the surface walls and is particularly frequent on the west and east ones The survey that was carried out revealed a biological colony composed by: - bacteria (not studied yet) - two species of free-fungi (Aspergillus spp.), - two species of macro-algae (generous Trentpollia), - twenty-four species of epilithic lichens, - one specie of moss (Grimmia sp.). Lichens are the most frequent organisms in all the stone elements regardless their composition, inclination, orientation, weathering or exposure to sunlight, rainfall and wind. On the south wall of the sacristy, for instance, exposure to sunlight is almost complete during the all day and crustose species are dominant. On the abside, foliaceous species are prevailing and this can be related to the presence of trees on the neighbourhood and the minor stone disaggregation. On the backside of this same space, less exposed to sunlight, rain and wind but with an important alveolition, foliaceous species are the ones that stay on those points where alteration is slower. Eighteen of the twenty-four identified species are crustose and six are foliaceous (Physcia adscendens and five Parmelia sp.). On the east wall, on a small area near the soil and on the neighbourhood of mosses, one gelatinous species belonging to the Collema sp. vv. generous was also detected. The major lichen density is registered on the south and east walls. However, factors like orientation and exposure to sunlight of the surfaces must always be studied together with stone weathering.
Table 1
Ecological variability of the lichen species found on SAo Sebastiao church.
-
Ecological indexes
Lichen specie
Aspicitia
intermutans
' ,
Caloplaca
crenularia
Caloplaca
inconnexa
Candelariella
, var.nesode
.
x
x
x x ,
' . x
x
Lecidella
carpathica conspersa
Parmeiia
loxodes
Parmelia
pulla
Parmelia
saxatilis
Parmelia
somloensis
.
,,'
.
adscendens
.
. .
.
x
x
x
x
, x
.
'
geographicum
.
Sum of' the weight averages ,
. .
. .
.
.
,
x
X
x x
tm mm mm mm
x
x
x ....
x
,
245
x X
x
r~
x
x
x
~
x 9
....
x
~~ .
X,
;
x
X
E"
x
~
x
,
i
,
...........
5 15 11 83 61 28' 166 1'83 112 i
i 6 12
3 17 51
i
.
.
,
8 15" 3 44 83 17 176 415 102
.
.
.
,
m
.
.
.
x
x
x
.
1 i' 6 6 6 ' 12
O
,.,
< ~
x
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x
O
9
x
x
0
'''
X x
x ,
~
x
x
x x
O
,
,
x
x
~ o
x
x
x
o ,
x
mm
x
~"
x
x
,?
x
x
x
5 28 28
Representative value o f the i n d e x
x
x
11 1'5'" 12' ' 89 "1 61 '83' 67 '11 6 183 332 335 66' 42
.
x
x
x
.
,,X
x
x
x
.
x
x
x
X
~D
x
x
x
5 84
x
x
X
x
Su m o f the relative frequencies
.
4
x
x
x
x
x
3 17 34
,,,
3
x
x
x
X
,,.
Sum of the indicative values / class Rdative frequency / class(%) .Weight averase
.
x,
X
x , '
x
.
x
,
atra
x
.
1
x
x
,
X
.
x
6
x
.
x
x.
x
.
.
4
2
x
x X .
x
,,
x,
,,
.
x
4
x
,x
.
3
x
x .
....
2
x
ochroleucum
Parmelia
1
x x
~!phurea,
7' "
x
x
Lecanora
6
x
s actmostomuss
gangaleoidbs
Tephromela
,
,,
Lecanora
Rhizocarpon
" x
s
vitellina
Haematomma
Physcia
x
5
,
Diploic.!a canescens Diploschiste
4
L
H
pH 3
, , , , . , , ,
6 33 99
x
IL
.
14 14 78 78 312 390
0
p <
201
200
167
992
489
756
819
4,05
2,45
4,53
4,07
i
bJ 4~ =
x - Incidence of the values found on literature Relative frequency = (sum of the indicative values/total number of s p e c i e s ) x l 0 0 Weight average = Relative frequency x index value Representative value o f the index = sum of the relative frequencies / sum of the weight averages
b~
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497
3.2. Ecological variability With the results of the survey, maps for the distribution and covering of the lichen species on each wall were constructed and the study of the ecological variability of the place was initiated. Table 1 shows this ecological variability for all the species whose ecological indexes are defined on literature (Nimis et a/., 1987, for instance). Those indexes refer to pH, nitrofitism (N), hygrofitism (H) and photofitism (L) and indicate the substrate characteristics in which species development are depending. The values on the last line of the table define the ecological variability of the place and of the species colonising it: pH=4,05; N-2,45; H=4,53 e L=4,07. According to Nimis et al. (1987), those levels define variability characterised by species quite acidophyle, moderate nitrophyle, mesophyle and quite photophyle. 4. Acknowledgements Supported by the Funda~Ao para a Ci~ncia e Tecnologia (Portugal) through PRAXIS XXI -project 2/2.1/CSH/254/95 and CCA-CT/FCT-R&D Contract-Program. References Cox, K.G., Bell, J.D., Parkurt, R.J., 1979. The interpretation of igneous rocks. George, Allen and Urwin (eds), London, 450pp. Nimis P.L., Monte M., M. Tretiach M., 1987. Flora e vegetazione di aree archeologiche del Lazio, Studia Geobotanica, 7, 12-14. Henderson P., 1986. Rare earth element geochemistry. Developments in Geochemistry 2, Henderson ed., Elsevier, 510pp.
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RAPID DIAGNOSIS OF MICROBIAL GROWTH AND BIOCIDE TREATMENTS ON STONE MATERIALS BY BIOLUMINESCENT LOW-LIGHT IMAGING TECHNIQUE Giancarlo Ranalli* Dept of STAAM, University ofMolise, Campobasso, ITALY Patrizia Pasini, Aldo Roda Dept of Pharmaceutical Science, University of Bologna, Bologna, ITALY
Abstract
A method for rapid diagnosis of microbial growth and response to chemical treatments on stone materials was developed. It allows detecting spatial distribution and activity of residual microflora on the surface of stone artworks after addition of biocides. Bioluminescent lowlight imaging technique was adopted and the ATP assay, as a potential bioindicator of microbial presence on monuments related to cultural heritage, was selected. The peculiarities of this method can be summarized in a not-destructive technique; a reduced processing time (10 min vs. 48 hours if compared with the cultural microbiological analyses); specific response and sensitivity that are favorable in order to distinguish an effective presence of biological risk in act on stones; the spatial distribution and sample geometry of the bioluminescent light presence and quantification of different gradient in relation to the activity of biocide treatments. This method is suggested as a useful for study concerning rapid diagnosis of biodetedogen risks, in restoration and monitoring programme on stones and monuments. Key words: Microbial growth, biocide, stones materials, bioluminescence, diagnosis, monitoring. 1. Introduction
The conservation of artworks and cultural heritages could be affected even by microbial growth (bacteria, fungi, yeasts, algae and lichens) that representing biodeteriogen agents, especially under particular environmental conditions; in fact when high relative humidity and temperature are present, biological deterioration of artworks appear increased by the stimulated growth of microflora and related enzymatic activities and metabolites production, including organic acids and pigments which, cause especially on mural painting, alteration changes and finally damage the appearance. Until today, chemical treatments to prevent and or control microbial growth is considered as one of the practical approaches and effective means for artworks including stone materials (Koestler, 1997). Several characteristics and related techniques should be taken into account in selecting an "adequate" chemical treatment (selection and use of biocides, their effects, toxicity, modes of applications, risk of environmental pollutions. Traditional cultural techniques, based on the counts of different microbial groups (plate * Author's to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
count, enrichment cultures based on MPN estimation), appear today not sufficiently adequate, in detecting the biodeteriogens, in selecting biocides treatment and in monitoring monument after restoration intervention, owing to their limits in the procedure highly specialised, time consuming, long time responses, unsuitable for use by conservators (May, 1995). Usually they are based upon a destructive sampling methods, that otien underestimate the microbial counts and, more, the results could not reflect the real situation but artifacts conditions. In the past decades, numerous rapid techniques have been used to asses stone colonisation, cause and mechanisms of biodeterioration, development and application of control methods; they included direct SEM observation (Warscheid, 1991), light microscopy and fluorescent dyes (acridine orange, INT-2,3,5 phenyl tetrazolium chloride) (Tayler, 1991), colorimetric assay with fluorosceine diacetate-FDA (Quinn, 1984). More recently, enzyme-linked immunosorbent assay (ELISA) (Tayler, 1994) and applications of molecular biological tools based on PCR (Polymerase Chain Reaction) technique have been applied for the detection of bacterial isolates which had shown potential for stone decay and biodeteriogen risks on paint walls and frescoes; but the validity of the PCR method, even showing great potentialities, depends on obtaining representative extracts of nucleic acids from the samples with limitations as incomplete cell lyses, DNA sorption to matrix, loss, degradation or damage ofDNA (Holben, 1997; Miller, 1999); for these reasons, today they don't' appear yet enough easily and routinely when applied to environmental studies. Recently, biodeteriomtion of stones and monuments of cultural heritage have been receiving an increased interest even in area of research that involves non-destructive study methods. The aim of this research was to develop a non-destructive technique, by determination of ATP content, for rapid diagnosis on stone biodeteriorations, to perform and to optimize the biocides selection when chemical treatments in restoration procedures are required and, finally, to monitor their effects after short and long times in conservation on stones and monuments related to artworks. 2. Experimental Methods 2.1 Stone materials Four stone specimens that differ for rock crystalline structures and porosity were tested. In particular, Serem stone specimens, a sandstone ascribable to felspathic greywacke with an abundant clayey matrix and poor cement, extracted from the formation of Macigno (Sorlini, 1991) and used in Italian and especially Florentine buildings (Palazzo Pitti, CmUeria degli U f ~ , Chiesa S. Lorenzo, etc.), measuring 3 x 3 x 0.9 cm; Carrara marble specimens measuring 3.2 x 3.2 x 1.4 cm; Lecce stones and brick specimens, measuring 3 x 3 x 3 cm were utilised. All stone specimens were sterilised in an autoclave at following vapour and stored at room temperature before use, under sterile conditions. Five replicates were performed for each specimens selected. 2.2 Microorganisms and media Four test strains were used in the presem study, including E. coli (ATCC 35346), Pseudomonas fluorescens, Achromobacter sp., and Bacillus subtilis (DISTAAM collection).
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Exponential growth phase of bacterial cells used as inoculum (about Log 7.5 CFU/ml) in Standard Plate Count broth (Oxoid) were obtained in standard laboratory conditions. In order to favorite an homogeneous distribution of inoculurn, an aliquot of 2.0 ml from each bacterial suspension before obtained, onto stone surface of specimens tested by sterile brush were transferred; after addition of cells, stone specimens were maintained at room temperature for 10 min before their use, under sterile conditions. Quantitative determination of viable microbial counts, after addition of biocide solution onto surface of stone specimens tested, were carried out either by cotton swab and replica plating techniques directly on Petri dishes agarised.
2.3 Bioddes Freshly prepared aqueous solution ( 1 % and 2% v/v) of two common biocides namely neo-Desogen (Alkyl- (3,4,-diclorobenzyl) demethylammonium chloride) and Metatin 101 (Lauryl dimethyl benzyl ammonium bromide) were used for the present study. Three different modes of applications of biocides involving spraying, brushing and direct injection were tested, and an equal volume of biocide solutions (1 to 2 ml) to surface of stone specimem tested was added. After 10 rain by biocides treatments, the following bioluminescent assay took place. 2.4 Bioluminescent low-light imaging technique and ATP assay An ultrasensitive CCD-hlminograph (model LB 981, EG&G Berthold), showing a high performance low-light imaging system able to detect luminescem emission (400-700 nm) over a wide range of intensities (sensitivity range 50 plx-10 lx at 490 nm) was adopted. The immediate direct bioluminescent image acquisition from the samples above cited, for differem duration times, ranging from 1 min to 5 min, using a CCD-based luminograph, gives information on the comamination level and spatial distribution on the sample surface (Roda, 1996). The bioluminescent ATP assay were measured in Tris-HC1 buffer solution (0.025 M; pH 7.75) by placing adequate solution of ATP standard (10 l~g) into the black chamber of a portable luminometer Biocounter model P 1500 (Celsis-Lumac B.V.) equipped with a photomultiplier tube (PTM) set at 7,200 RLU with 200 pg ATP in 100 ~l. Calibration of the instrumentations serial dilutions of ATP standard or pure culture of bacterial cells as above performed, were carded out. Adding broth reagents in drops, spraying, or by brush onto surface, all tests on selected stone specimens were performed, before and after placed them in the instrument chamber, under room temperature. Possible interferences due to the different matrices and the light emission quenching were evaluated, when required, both with pure culture of bacterial cells and standard solution of ATP content, at known concentration. More details about bioluminescent method have been extensively reported in a previous work (Ramlli, 1998). 3. Results A linear relationship between bioluminescent signals and dilution of pure culture of bacterial cells adopted as standard (E.coli ATTC 35346) was observed. Furthermore, according with previous results, the strict correlation between the ATP values and the direct bioluminescent image registered using a CCD-based luminograph, appear to be a great
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
possibility in order to development an innovative technique able in rapid diagnosis and monitoring programme for biodeteriogen activity on stone artworks (Ranalli, 1998). The detection limit of bioluminescent signals detected using a CCD-based luminograph (LB 981) is lower (about 1/10) to that achieved with a photomultiplier-based luminometer adopted, as reported in the following Table 1. Table 1: Comparison of detection limits (lower sensitivity) between two bioluminescent detectors adopte~ and pure culture of bacterial cells, E. coli ATTC 35346. E. coli (Log CFU/ml) Detector
5
4 . . . .
3
2 .
, .
CCD + + PTM + + Legend: + detectable;- not detectable. .
.
.
.
+
.
.
.
-
But, until today, when luminometers with PTM tube are used, the ATP assay usually require destructive methods of sampling and analyses, which are not frequent proposable for stoneworks related to cultural heritage. Several trials were carried out in order to evaluate the possible effects of stone matrices on BL image related with ATP assay. All tests on numerous different specimens by adding known volume of bacterial cell dilutions were performed, and immediately repeated with known ATP contents as internal standard in place of cells. The results proved that the geophysical well as geochemical aspects of the stone materials tested could influence strongly the bioluminescence signal induced by luciferin-luciferase system. In fact, in our experimental conditions, stone specimem with low porosity values (marble) showed absence of any interference and quenching, while in stone specimens with high porosity values (brick, Lecce stone and Serena stone) remarkable phenomena of quenching have been registered. These results confirmed both the positive responses in bioluminescent light intensity as index of presence of ATP but the potential influence of the matrices on BL image, according with data of a previous work (Ranalli, 1998). Among the numerous causes of the above phenomenon, we believe that the presence in the matrix of high quantity of mineral colloids -clay-typecould strongly increase the sorption of ATP released from the microbial cells, in similar manner at what noted in soil (Jenkinson, 1979). On other hand, in order to verify the influence of high surface permeability and porosity value of the matrix, several tests were carried out by inducing a longer contact time among ATP assay reagents and stone surfaces; preliminary results obtained both on Lecce stone and brick specimens were not favorable, in fact, no increase in BL signals were registered. Figure 1 shows an example of the innovative technique for rapid diagnosis of biocides treatment based on the ATP-bioluminescent low-light imaging technique applied at a "Carrara marble" specimen enriched with bacterial cells: the live image of marble specimen (a), BL signal of marble specimen (b) and the overlay of both (c).
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(a) Live image
(b) Bioluminescent signal
(c) Overlay after processing bioluminescent image
Legend: 1 Blank (bacterial culture, no biocide treatment), 2 (neoDesogen, 1%), 3 (neoDesogen, 2%), 4 (Metatin, 1%).
Figure 1" Bioluminescence response by detection of ATP content in Carrara marble specimen enriched with bacterial cells E.coli (Log 7.5 UFC/ml), aiter biocides treatment (neoDesogen, Metatin). Different gradient of black/white color ruler on the fight shows the relative light intensity.
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The observation of BL images suggested that the biocides tested, here added by spraying, showed different biocide effect and, as consequence, different successful in inhibition the bacterial growths. In fact, it was noticed that the lowest and the highest BL relative lights intensity were recorded when 2% and 1% neoDesogen solutions were applied, respectively, in comparison with the control (Areas 1, no biocide treatment). The subsequent microbiological analyses supported even by optical microscope observations confirmed low number of viable microflora when neoDesogen (2%) was sprayed (Areas 3), a medium presence of residual viable cells after Metatin addition (Areas 2), and finally, a larger number of surviving bacteria when biocide treatment with neoDesogen (1%) (Areas 4) was used. In this case, the relative efficacy ofbiocide treatments versus bacterial culture tested (in this case, E.coli) could be given as: - neoDesogen (2%) > Metatin (1%) > neoDesogen (1%). Similar results were confirmed by testing the other bacteria selected. By comparing different mode of application of biocides it may be believe that although direct injection method is more precise for quantitative estimation of efficacies both of different BL reagents and biocides in laboratory, distribution by spraying and brushing are more useful for field trials. Finally, aider several applications of biohminescent reagents adopted on stone specimens enriched of bacterial cells, no traces in changing of color surface were observed in presence or absence ofbiocides treatments selected. Preliminary results, in our experimental conditions, were satisfactory and confirm the validity and convenience of employment of bioluminescent low-light imaging technique to evidence efficacy and effectiveness of different biocide treatments on stone materials. The peculiarities of this technique can be focused: i) rapidity (10 min vs. 48 hours if compared with the cultural microbiological analyses); ii) specific response and semitivity (favorable in order to study the dynamics of viable microflora respect to chemical treatments); iii) quantification of the bioluminescent light; iiii) spatial distr~ution and sample geometry that means possibility to localize and distinguish portion on stone surface, examined at different gradient, in relation to the residual biodeteriogen risk after bioeides treatment; ~ ) useful method to evaluate the specific action among short and long time of exposition to biocides of biodeteriogen agents; iiiiii) definition and selection of optimal restoration conditions; iiiiiii) not-destructive technique. This fact means a great advantage if compared with others destructive techniques otien not favorable in monitoring studies of biodeteriogen risks. The routinely utilisation of the bioluminescent low-light imaging technique must be consider of a great support in the study of recovery and monitoring on stone materials related to cultural heritage, especially when biocide treatments are required, but a deep standardisation of this method and the reduction of the eventual influence of the matrix, in terms of intensity of BL signal, are needed. At list, the development and the improvement of this innovative technique will be an in-situ application on the artworks suitable both for a rapid diagnosis and monitoring programme. 4. References
Holben W.E., 1997. Isolation and purification of bacterial community DNA from environmental samples. In: C.J. Hurst, G.R. Knudsen, M.J. McInerney, L.D. Stetzenbach and V.Walter (ed.). Manual of methods in environmental microbiology. American Society for Microbiology, Washington, D.C., pp. 431-436.
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Jenkinson D.S., Oades J.M., 1979. A method for measuring adenosine triphosphate in soil. Soil Biology Biochemistry, 1 l, 193-99. Koestler R.J., Warscheid T., Nieto F., 1997. Biodeterioration: risk factors and their management. In: Baer N.S., Snethlage R. (ed.). Saving our architectural heritage: the conservation of historic stone structures. Chichester, England: John Wiley & Sons Ltd., pp. 25-36. May E., Lewia F.J., Pereira S., Tayler S., Seaward M.R.D., Allsopp D.A., 1993. Microbial deterioratiopn of building stone- a review. Biodeterioration Abstract, 7, 109-123. May E., 1995. Microbial communities on stone: detection, distribution and activity. In: 3rd International Conference on Biodeterioration of cultural property, ICBCP-3, Bangkok, 4-7 July, pp. 154-162. Miller D.N., Bryant J.E., Madsen E.L., Ghiorse W.C., 1999. Evaluation and Optimization of DNA extraction and purification procedures for soil and sediment samples. Applied Environmental Microbiology, 65, 4715-4724. Quinn J.P., 1984. The modification and evaltmtion of some cytochemical techniques for the enumeration of metabolically active heterotrophic bacteria in the acquatic environment. Journal of Applied Bacteriology, 57, 51-57. Ranalli G., Pasini P., Roda A., 1998. Bioluminescent low-light imaging technique as a rapid method to detect spatial distribution and activity of biodeteriogen agents in cultural heritages. In: A. Roda, M. Pazzagli, L.J. Kricka and P.E. Stanley (ed.). Bioluminescence and Chemiluminescence. Perspectives for 21st century. John Wiley & Sons Ltd., Chichester, England, pp. 153-156. Roda A., Pasini P., Musiani M., Girotti S., Baraldini M., Carrea G., 1996. Chemiluminescent low-light imaging of biospecific reactions on macro- and microsamples using a videocarnera-based luminograph. Analitical Chemistry, 68, 1073-80. Sorlini C., Falappi D., Ranalli G., 1991. Biodeterioration preliminary tests on samples of Serena stone treated with resin. Annali di Microbiologia, 41, 71-79. Tayler S., 1991. The seasonality of heterothophic bacteria on sandstone ~om ancient monuments. International Biodeterioration Biodegradation, 28, 49-64. Warsheid T., Oelting M., Knanbein W.E., 1991. Physico-chemical aspects of biodeterioration processes on rocks with special regard to organic pollutants. International Biodeterioration, 28, 37-48. 5. Materials
Cultural media (Oxoid, Hampshire, U.K.). Chemicals: neo-Desogen, CIBA; Metatin 101, Acima Chemicals, srl. Tarquinia, Italy. Reagents for ATP assay: Microbial Biomass Test KitTM and Standard ATP, Celsis-Lumac B.V., Landgraaf, The Netherlands. CCD-luminograph (model LB 980): EG&G Berthold, Wildbad, Germany. Luminometer Biocounter (model P 1500): Celsis-Lumac B.V., Landgra~ The Netherlands.
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THE ACTION OF CALOPLACA CITRINA ON CONCRETE SURFACES: A PRELIMINAR STUDY Vilma G. Rosato* Luis Traversa*, LEMIT (Laboratorio de Entrenamiento Multidisciplinario para la Investigaci6n Tecnol6gica), 52 entre 121 y 122, CC 128, 1900 La Plata. ARGENTINA. T E. 0054- 221483-1141/44. E-MAIL [email protected] Marta N. Cabello Instituto de Botanica "Carlos Spegazzini", Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata. 53- 477, 1900 La Plata, ARGENTINA. TE 0054- 221421-9845
Abstract The aim of this contribution is to assess the importance of the chemical action of the lichen Caloplaca citrina on concrete, and how it changes the substrate's composition. Caloplaca citrina causes the decay of concrete surfaces by the mechanical action of the hyphae that penetrate the substrate. This species is also thought to have a chemical action because Caloplaca citrina produces oxalic acid. Samples have been obtained from a broken concrete piece and prepared as follows: a) substrate with lichen. b) concrete treated with hydrogen peroxide, to dissolve the lichen. c) concrete not covered by Caloplaca citrina The samples have been observed with a scanning electronic microscope and analized with an EDAX microprobe. The concrete attacked by the lichen has lost nearly all the calcium ( 5,31% as CaO). As regards the lichen, high levels of aluminum and potassium have been found, as well as steel, calcium and magnesium. Nevertheless, the calcium percentage is quite low (8, 58 % as CaO). Caloplaca citrina intakes elements from the substrate and causes mierocorrosion through the action of oxalic acid. However, the calcium content is low and the oxalate cristals are scarce. This means that the concrete calcium is mostly dissolved and washed away. The detrimental effect on concrete surfaces has a close relationship with the microdegradation Caloplaca citrina produces. Keywords: Concrete, Biodeterioration, Lichens, Caloplaca citrina, EDAX microanalysis 1. Introduction It has been observed that the lichen Caloplaca citrina (Hofl~.) Th. Fr.causes the decay of concrete surfaces by the mechanical action of hyphae that penetrate the substrate (Traversa &.Rosato, 1998). In the photomicrographs, the absence of cement particles and the presence of sand particles on the surface have been noted. This species may also have a chemical action, which is possible because Caloplaca citrina produces oxalic acid, a substance that degrades various forms of minerals, and posseses oxalate cristals, although scarce (Salvadori & Lazzarini, 1991). Besides, epilithie lichens, for instance Caloplaca
* Author to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
aurantia, are able to incorporate different elements, specially calcium and potassium, and also iron and aluminium (Gorgoni et al, 1992). Calcium incorporation has been pointed out as an indication of biodeterioration (Beth - Anderson, 1984) whereas potassium is found in high concentration in lichens (Hallbauer & Jahns, 1977). Favali et al. (1995) have also studied the action of Caloplaca flavescens and C. aurantia on calcareous substrates and found both species have mechanical and chemical action. Portland cement contains a high calcium concentration (ca. 60 % - Rocha, 1984) and the cement produced at Olavarria (Prov. di Buenos Aires) contains 62,74 % (Bonavetti & Rahal, 1997). So, although calcium is available, whether it is incorporated by the lichen or not has not already been proved. In fact, there are few references concerning the action of lichens on concrete(See Piervitori et al., 1994; 1996; 1998). Caloplaca citrina has a bright yellow, undefined thallus (Fig.l), wholly covered by soredia (vegetative reproduction propagules-Fig.2). It is widely distributed around the world and has been mentioned by several authors, that agree to describe this species as a nitrophilous lichen, with a broad ecological spectrum, prefering eutrophic, neutral to basic substrates. It can be found in shadowed places, but it prefers sunny exposed places. It has been found growing, for instance, on the marble of archeological monuments of the Lazio region (Nimis et al., 1987) on the ruins of Aquileia (Salvadori et Lazzarini,1991) and on other calcareous substrates (Nimis et Salvadori 1997). Nimis et al. (op. tit) also mentioned Caloplaca citrina from cement substrates. This is an important question, because this species has been found on concrete works built in the Buenos Aires Province (Argentina) by Arch. Francisco Salamone, the author of several buildings now considered as examples of the so called "Art D6co" style (Traversa, Rosato & Vittalone, 1999). Therefore, there are doubts about whether the lichen has to be considered only from an aesthetical point of view or any measures should be taken to avoid damages. As a preliminar study to solve this problem, a concrete structure covered with Caloplaca citrina was used to obtain samples to study the importance of the chemical action of Caloplaca citrina on concrete, and how it modifies the substrate's composition. 2. Material and Methods
Samples have been obtained from a broken concrete piece from a rainwater drainage by a rural road at Tandil (Buenos Aires Province, Argentina) and prepared as follows: a) substrate with lichen. b) concrete treated with hydrogen peroxide, to dissolve the lichen. c) concrete not covered by Caloplaca citrina The samples have been observed with a Phillips SEM scanning electronic microscope and analized with an EDAX microprobe.. 3. Results and Conclusions
The results of microanalysis are summarized in the table below (TABLE 1).In order to compare results, data concerning Caloplaca aurantiaca from Gorgoni et al. are also included here.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Fig. 1- Detail of Caloplaca citrina growing on concrete
Fig. 2 SEM photomicrograph of soredia of Caloplaca citrina.
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Table 1- Elements found in Caloplaca citrina (EDAX microanalysis)
Caloplaca citrina
Element (% weight)
Mgo
.
.
.
.
Al203 SiO2 K20 CaO Fe203 ,
,.
,,,
,
1,86 22,35 44,50 12,28 , 8,58 3,42
i
i
i
Deteriora ted
Concrete
Cement '
,
,
0,46 14,90 75,03 2,19 5,31, 2,11
Caloplaca aurantia (Gorgoni et al.)
8,6,1 28,43 1,83 59,44 1,69.
Biocalea renite (Gorgoni et
0,29 0,52 12, 70 0,43 29,00 , ,,
1,20 t' i
al.)
0,42 0,38 22,20 0,12 42,00 1,25
The cement sample contains 59,44% Ca (as CaO). This percentage is near to the normal mimimum (59%) but it is lower when compared to the cement from Olavarria produced in the region near Tandil (62,74 %)). The cement covered by the lichen has lost nearly all the calcium ( 5 , 3 1 % as CaO) whereas silicium (constituting the sand particles) has remained (75 % as Si 02). As regards the lichen, there is a high concentration of aluminum and potassium, as well as iron, calcium and magnesium. This has already been noted in other lichens, but here the percentage of calcium is lower (8, 58 % as CaO), when compared with Caloplaca auramia with 29% calcium on a substrate of biocalcarenite with 4 2 % Ca. Caloplaca citrina incorporates elements present in the concrete, and causes microcorrosion through the accion of oxalic acid, so it has both mechanical and chemical action, as seen in other Caloplaca species (Gorgoni et al., 1992; Favali et al, 1995) However, the calcium contents found are low and the oxalate cristals are scarce . This means that calcium is to a great extent dissolved and washed away from the concrete surface. As a conclusion, Caloplaca citrina produces a superficial microdegradation having a detrimental effect on concrete surfaces, so its presence is not just an aesthetic problem. Although in some modem buildings the bright yellow lichen colonies add a chromatic effect, as stated by Nimis et al. (1987), it should be recomended to remove this species in historic buildings. 4. A c k n o w l e d g e m e n t s
To Dr. O. Salvadori, for her kind invitation and the literature she provided to me ; to Prof. M. A Favali for sending me a copy of her paper; to my brother, Ing. M. A. Rosato and his wife, Arch. G. Barbaro, for helping me to translate the abstract into italian, and to Mr. Mario Shnchez, who helped with the SEM and EDS observations. 5. References
Bech-Anderson, J. 1984 - Biodeterioration of natural and artificial stone caused by algae, lichens, mosses and higher plants, in: Biodeterioration VI. Proceedings of the sixth international biodetrioration symposium 126-131 Bonavetti, V. & V. Rahal .1997- Morteros de cemento portland con adici6n de filler calizo. Hormig6n 30: 37-48.
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Favali M. A., Fossati F., Mioni A., Realini M. 1995- Biodeterioramento da licheni crostosi dei calcari selciferi lombardi. Scienza e Beni Culturali XI. Atti del Convegno ressanone 1995. Libreria Progetto Editore, Padova.201-208. Gorgoni, C., Lazzarini, L .& O. Salvadori 1992- Minero-geoehemical transformations induced by lichens in the biocalcarenite of the Selinuntine monuments, in: Proceedings International Congress on Deterioration and Conservation of Stone.(J. Delgado Rodrigues, F.Henriques & F.Telmo-Jeremias, eds.): 531-539. Lisbon, Portugal, LNEC. Hallbauer, D. K. & H. M. Jahns 1977- Attack of lichens on quartzitic rock surfaces. Lichenol. 9:119-122. Nimis, P. L., Monte, M., Tretiach, M. 1987- Flora e vegetazione lichenica di aree archeologiche del Lazio. Studia Geobotanica 7:3-161. Nimis P. L., Salvadori, O.- La crescita dei licheni sui monumenti di un parco. Uno studio pilota a Villa Manin.. in: I1 restauro delle sculture lapidee nel parco di Villa Manin a Passariano. I1 viale delle Erme.( E. Accomero, Ed.) Restauro nel Friuli- Venezia Giulia. Quaderni di studi e ricerche del Centro regionale di restauro dei beni culturali: 4:109-141 Piervittori R., Salvadori O., Isocrono D 1998: Literature on lichens and biodeterioration of stonework III. - Lichenologist 30(3): 263-277. Piervittori R., Salvadori O., Laccisaglia A. 1994: Literature on lichens and biodeterioration of stonework. I. - Lichenologist 26(2): 171-192. Piervittori R., Salvadori O., Laccisaglia A. 1996: Literature on lichens and biodeterioration of stonework. II. - Lichenologist 28(5): 471-483 Rocha, C. A. 1984- Verificacirn de la aptitud de las cenizas volantes como adicirn a hormigones de cemento portland. 6a. Reunirn Tecnica de la Asoc. Arg. de la Tecnol. del Hormigrn. Salvadori, O. & L. Lazzarini. 1991- Lichen deterioration on stones of Aquileian monuments (Italy). Bot. Chron. 10:961-968. Traversa, P . L , Rosato, V. G. 1988- Algunas consideraciones sobre el crecimiento de los liquenes sobre el hormigrn. Ciencia y Tecnologia del Hormigrn n~ Traversa, P.L, , Rosato, Vilma G., Vittalone, C. 1999- Colonizacirn biolrgica en construcciones de valor histrrico. Actas del Congreso Conpat 99, Vol. 3: 1575-1580, Montevideo, 18-21 October 1999.
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513
ENDOLITHIC
LICHENS
AND
CONSERVATION:
AN
UNDERESTIMATE
QUESTION Daniela Pinna Soprintendenza Beni Artistici e Storici, Laboratorio Scientifico, via Belle Arti 56, 40126 Bologna, Italy Ornella Salvadori Soprintendenza Beni Artistici e Storici di Venezia, Laboratorio Scientifico, Cannaregio 3553, 30131 Venezia, Italy
Abstract
Notwithstanding their spreading on limestone monuments, endolithic lichens are scarcely considered in conservation studies. Their thalli are completely placed inside the stone and, penetrating deeply, they can weaken the stone structure altering considerably the substratum. The physiology as well as the ecology of these organisms have been scarcely studied; many aspects of their growth such as the ways of sprouting and penetrating inside the stone, the growth rate, the penetration depth and the amount of damage are almost unknown. The knowledge of these characteristics for the different species is very important during the preliminary steps of restoration, when it is necessary to plan control operations of the biological growth. Six endolithic species (Acrocordia conoidea, Caloplaca sp., Petractis clausa, Rinodina immersa, Verrucaria baldensis and V. marmorea) were studied. Different techniques were applied to investigate the samples (lichen + substratum): microscopic investigations (optical and scanning electron microscopies) of polished cross and thin sections, X-ray diffractometry, microdiffractometry, and FTIR. These analyses allow to know the depth of penetration in the stone, the position of mycobiont and photobiont compared with stone surface, the morphological aspects of the thallus-substratum interaction and the damage caused by the lichens into the substratum. Keywords: endolithic lichens, limestone, pitting, dissolution.
1. Introduction The interactions between epilithic lichens and monuments have been studied by many Authors (Nimis et al., 1992). The knowledge of their morphology, ecological needs, deteriorative capability on different substrata and the mechanisms involved has been established for many different species. On the contrary literature on endolithic lichens is rare (Nimis and Zappa, 1988; Gehrmann et al., 1992; Gehrmann and Krumbein, 1994, 1996; Tretiach, 1995, 1996). They are frequent colonisers of monuments but they are not easily recognisable by anyone as generally their colour is very similar to the rock one; their thalli are completely immersed in the stone and appreciable only using particular techniques. They are actively involved in weathering processes of the rock and for this reason they are worth studying aspects of their anatomy and ecology related to conservation problems. In fact the knowledge of these characteristics is very important
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during the preliminary steps of restoration, when it is necessary to plan control operations of the biological growth. Moreover the effects of different cleaning methods or biocide treatments on stone colonised by endolithic lichens have been only hypothesised (Nimis and Zappa, 1988) and are almost completely unknown. In this paper we present the results of some studies in progress on various endolithic lichens growing on monuments and natural outcrops in order to examine either morphological features and interactions with stone.
2. Materials and Methods
-
The collecting sites were: Sanctuary of Macereto (Visso, Macerata, Central Italy) (fig. 1). The substratum is a massive biocalcarenite formed by fragments of carbonate rocks and bioclasts, it belongs to the "Scaglia Bianca e Rossa", a geological formation developed in the Cenomanian-Middle Eocene and outcropping near the sanctuary. The sanctuary walls, particularly those faced North and West, were widely colonised by lichens. Besides crustose epilithic lichens (Caloplaca saxicola and Diplotomma epipolium were the most abundant), extensive presence of a grey endolithic lichen was observed (fig. 2). Its colonisation extended until the higher walls zones (20 m high).
Figure 1: South facade of the sanctuary of Macereto. - Trieste Karst (NE, Italy). The substratum is a hard compact, fine-grained, homogeneous Cretaceous limestone belonging to the Eocenic Alveoline-Nummulitic formation. Rock samples colonised by endolithic thalli (Acrocordia conoidea, Caloplaca sp., Petractis clausa, Rinodina immersa, Verrucaria baldensis and V. marmorea) were studied by different techniques. Samples were treated with a solution of hydrochloric acid in order to completely remove the carbonatic rock. The resulting biomass was stained with Lactophenol Cotton Blue and observed with optical microscope. Polished cross-sections and thin sections were observed under optical microscope, in addition some of them were stained with PAS (Periodic Acid Schif0. Other specimens were fixed overnight with 2.5% glutaraldehyde in 0.01M phosphate buffer, serially dehydrated in ethanol, included in
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epoxy resin, and treated with Perenyi solution in order to partially remove the calcareous matrix, then examined with a SEM (Philips SEM 505). The research of biomineralisation products was carried out with: X-ray diffractometry on powdered samples using a Philips 1940 diffractometer, X-ray microdiffractometry on cross-sections taking measures from the surface to a depth of 2 mm at intervals of 100 ktm with a Rigaku instrument, FTIR analyses on KBr micropellets using a Perkin Elmer Paragon 1000PC spectrophotometer.
Figure 2: Orbicular thalli of Caloplaca sp. developing on the sanctuary walls.
3. Results
Most of examined species show many analogies in the anatomical characteristics of the thalli, only Caloplaca sp. is completely different. According to Pinna et al. (1998) the thalli of Acrocordia conoidea, Petractis clausa, Rinodina immersa, Verrucaria baldensis and V. marmorea can be subdivided into three layers: (a) a outer layer, sometimes pigmented, consisting of densely conglutinated hyphae mixed together with microcrystals of calcium carbonate; (b) a photobiont layer, composed of photobiont cells assembled in irregular clusters surrounded by a few enlarged hyphae; in most species the clusters are observed to 100-180 lam from the external surface reaching a depth of ca. 250 l.tm; (c) a inner layer, is formed by a loose web of hyphae poorly delimited towards the interior. The distribution pattern and the depth of penetration of the hyphae vary among species. Usually, there is a more superficial zone where they are more dense and a deeper zone where they become progressively sparser, with thinner and more elongated cells. In the inner layer of all the species there are oil-hyphae. The most typical ones are spherical and arranged as a rosary. In R. immersa a further type is present: the cells are smaller, rather short and slightly inflated. The first type of oil-hyphae are particularly abundant in the shade-tolerant V. baldensis, whose thallus is the deepest and thickest: it penetrate till 2.7 mm from the external surface (fig. 3). In spite of the common features some endolithic lichens, f.e. Petractis clausa and Encephalographa elisae (Tretiach and Modenesi, 1999), form some voids in the stone respectively ca. 30-50 ~tm and 50-80 lam in diameter, distributed in a rather continuous layer located below the photobiont layer, up to a maximum of 1.6 mm in depth. These
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holes are filled with clews consisting of hyphae and large amount of extracellular polymeric compounds (EPS) of mucopolysaccharidic nature (fig. 4).
Figure 3: Resin casts of the thick net of oil-hyphae in the inner layer of Verrucaria baldensis.
Figure 4: Resin casts of the inner layer of Petractis clausa showing the clews formed by hyphae and extracellular polymeric substances filling the holes created in the stone.
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In respect to the above described thallus organisation, the endolithic lichen colonising walls of the sanctuary ofMacereto, Caloplacasp., is an exception. Its thallus is completely embedded in the rock but considerably differs from the others. From microscopic observations of cross sections its morphology appears very similar to that of endolithic algae (fig. 5); only staining and observing the biomass aider stone dissolution could clarify its characteristics and so come to the conclusion that the organism we were studying was actually a lichen. It penetrates inside the stone (0.5 mm in depth) forming small canals, almost perpendicular to the external surface, in which mycobiont together with photobiont are located (fig. 6). In this lichen there are not definite demarcations between the photobiont layer and the inner layer like in the other endolithic species; fungi actively penetrate enclosing small algae groups, oil-hyphae are not present. This particular morphology is clearly shown observing the lichen biomass resulting from HCI treatment and magnifying portions of the thallus. This lichen only rarely forms apothecia and has been recently the object of a taxonomic study that demonstrated it is a species not yet described, both morphologically and ecologically well characterised. It belongs to Caloplaca genus but the species name has not yet been assigned; so in this note it will be named Caloplaca sp. It forms orbicular thalli with endolithic growth in the central zone while in the marginal one there are small white lobes protruding from the substratum. The observation of the cross-sections shows the strong deteriorative capability of Caloplaca sp. which is able to form a concavity on the stone surface, accentuated in the central zone of the thalli. Endolithic lichens cause the biodeterioration of limestone not only with the penetration of hyphae but also by means of the formation of fruiting bodies (apothecia and perithecia) creating a bio-pitting. Notwithstanding hyphae are very efficient in the dissolution of limestone penetrating calcite crystals, none of studied species produces calcium oxalate as biomineralisation product, as the analyses performed by X-ray diffractometry, microdiffractometry, and FTIR demonstrated.
Figure 5 and 6:
Caloplacasp., polished cross section (5) and resin casts of canals of hyphae which surround photobiont cells and penetrate into the stone (6). Scale bars indicate 0.1 mm.
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4. Conclusions The results of this and other recent studies on endolithic lichens show that either morphology or physiology of these organisms need more research to be well known. The sanctuary of Macereto and the outcrops of Trieste Karst represent emblematic study-cases in order to analyse the problems arising in conservation field when a colonisation of endolithic lichens is present on stone. Although a common structure is generally clearly recognisable, for the first time a different kind of endolithic lichenic structure (Caloplaca sp.) has been evidenced. Even if the results of chemical action is similar in the examined species, on the contrary the distribution of hyphae into the substratum is very different. They can spread in different directions forming a web which becomes the more loose the more it expands towards the interior, or they can form compact and clearly delimited agglomerates. In the last case the penetration joins lower depths (ca. 0.5 mm) than in the first (ca. 2-3 mm), but the deterioration is equally high as the canals of penetrating hyphae are all close in such a way they cause a homogeneous decohesion of stone surface following from the dissolution of rock. The biodeterioration of carbonatic rocks by endolithic lichens is characterised not only by the penetration of hyphae into the rock and the formation of biopitting on the surface but also, for some species, by the production of many holes inside the rock at a certain distance from the surface. The formation of pits was well described by Gehrmann et al. (1992). On the contrary the production of holes inside the rock is a recent discovery whose significance in not yet clear; they could determine an increase in the water-holding capacity. Further investigations are necessary to establish in how many species this ability is spread. All endolithic lichens examined do not produce calcium oxalate, whereas this compound is the most common biomineralization product in epilithic lichens. Finally, we wish underline that the growth of endolithic lichens is not limited to the basal part of monuments as seen on the Sanctuary of Macereto where they extend vertically up to 20 m from the ground. This confirms again the widespreading of endolithic communities on monuments and the need of their best knowledge. Acknowledgements We are grateful to Dr Mauro Tretiach (Trieste) for help in taxonomic identification and to Mr Dino Zanella (Soprintendenza per i Beni Artistici e Storici di Venezia) for technical assistance. This study was supported by C.N.R. funds (Committee No. 15). References Ascaso C., Galvan J., Rodriguez-Pascal C., 1982. The weathering of calcareous rocks by lichens. Pedobiologia, 24, 219-229. Degelius G., 1962. lJber verwitterung von kalk- und dolomitgestein durch algen und flechten. In: Hedvall J.A., (ed.), Chemie im dienst der archaologie bautechnik denkmalpflege, Lund, 156-164. Fry E.J., 1922. Some types of endolithic lichens. Ann. Bot., 36, 541-562. Gehrmann C.K., Krumbein W.E., 1994. Interaction between epilithic and endolithic lichens and carbonate rocks. In: Fassina V., Ott H., Zezza F., (eds.), The Conservation of
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Monuments in the Mediterranean Basin, Proceedings of the 3rd Int. Symp., Venice, 311316. Gehrmann C.K., Krumbein W.E., 1996. Biomineralization in epilithic and endolithic lichens. In: Progress and Problems in Lichenology in the Nineties, Proceedings of the 3rd IAL Symposium, Salzburg, 157. Gehrmann C.K., Krumbein W.E., Petersen K., 1988. Lichen weathering activities on mineral and rock surfaces. Studia Geobot., 8, 33-45. Gehrmann C.K., Krumbein W.E., Petersen K., 1992. Endolithic lichens and the corrosion of carbonate rocks. A study ofbiopitting. Int. J. Micol. Lichen., 5, 37-48. Golubic S., Friedmann E., Schneider J., 1981. The lithobiontic ecological niche, with special reference to microorganisms. J. Sedim. Petr., 51,475-478. Golubic S., Perkins R.D., Lukas K.J., 1975. Boring microorganisms and microborings in carbonate substrates. In: Frey R.W., (ed.). The study of true fossils, Springer-Verlag, New York, 229-259. Nimis P. L., Pinna D., Salvadori O., 1992. Licheni e conservazione dei monumenti. CLUEB, Bologna. Nimis P. L., Tretiach M., 1995. Studies on the biodeterioration potential of lichens, with particular reference to endolithic forms. In: De Cleene M., (ed.), Interactive physical weathering and bioreceptivity study on building stones, monitored by Computerized X-Ray Tomography (CT) as a potential non-destructive research tool, Environment/Protection and Conservation of European Cultural Heritage, Research Report, 2, 63-122. Nimis P.L., Zappa L., 1988. I licheni endolitici calcicoli su monumenti. In: Nimis P.L., Monte M., (eds.), Lichens and Monuments. Studia Geobot., 8, 125-133. Pinna D., Salvadori O., Tretiach M., 1998. An anatomical investigation of calcicolous endolithic lichens from the Trieste karst (NE Italy). Plant Biosystems, 132 (3), 183-195. Salvadori O., 2000. Characterisation of endolithic communities of stone monuments and natural outcrops. In: Ciferri O., Tiano P., Mastromei G., (eds), Of Microbes And Art: The Role of Microbial Communities in the Degradation and Protection of Cultural Heritage. Plenum Publishing Corporation, London. 89-101. Tretiach M., 1995. Ecophysiology of calcicolous endolithic lichens: progress and problems. Giorn. Bot. Ital., 129, 159-184. Tretiach M., 1996. Ecophysiology of calcicolous endolithic lichens. In: Progress and problems in Lichenology in the Nineties, Proceedings of the 3rd IAL Symposium, Salzburg, 30. Tretiach M., Modenesi P., 1999. Critical notes on the lichen genus Encephalographa A. Massal. (? Hysteriaceae). Nova Hedwigia, 68, 527-544. Wessels D.C.J., Schoeman P., 1988. Mechanism and rate of weathering of Clarens sandstone by an endolithic lichens. South African J. Sc., 84, 274-277.
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BIOLOGICAL COLONIZATION FEATURES ON A GRANITE MONUMENT FROM BRAGA (NW, PORTUGAL) S. Leite MagalMes Centro de Ci6ncias do Ambiente / Ci~ncias da Terra, U. M., 4700-320 Braga, Portugal M. A. Sequeira Braga Centro de Ci~ncias do Ambiente / Ci~ncias da Terra, U. M., 4700-320 Braga, Portugal
Abstract The Edificio do Largo do Pa~}o, in Braga, built between 14th and 18th centuries, presents several colored patinas and biological colonization on the fa~}ades of the Medieval unit. One of them was matter of a microbiological study in order to understand the microbial activity responsible for the extensive biodeterioration of the granite stones, particularly for its disfigurement. Qualitative and quantitative microbial analyses were done. Complementary mineralogical studies by X-ray diffraction (XRD) and scanning electron microscopy (SEMEDS) of the granite substrate were also made. The analyses revealed the existence of a very large and significant range of stone colonizing organisms : biogeochemical nitrogen and sulfur cycles bacteria, algae, fungi, actinomycetae, heterotrofical microorganisms and sugar fermentative bacteria. This biological colonization is associated with others granite stone pathologies - granular disintegration, scales, flakes and patinas (black, green, brown and brown-reddish). We observed that patinas are biogeneous, mainly formed by biofilms of algae, cyanobacteria and fungi, which cover the stone creating different colors (black, green and some tonalities of brown. Biogeneous round particles were identified. Although the salt crystallization is rare, XRD and SEM-EDS analyses allowed the identification of gypsum underlying scales covered by biogeneous layering.
Key words : Microbiology, granite, biodeterioration, biofilm, patina, monument. 1. Introduction One of the fa~}ades of the Medieval unit of the Edificio do Largo do Pafo (Braga, NW Portugal) was matter of a microbiological stone study. In this monument, Alves (1997) studied the main pathologies (granular disintegration, scales, flakes and efflorescences) and the sources of pollution in detail. Concerning pollution sources, the type and distribution of the soluble salts show that antropogenic pollution sources are more important than natural ones (Alves and Sequeira Braga, 1999). Stone surface color changes has been observed in several monuments, being pointed in literature by several designations, like stains, darkening, crust, coveting and patina. Urzi et al. (1993) presented a redefinition of patina, as being the all-embracing term for all changes brought about at or near the surface of materials by time, climate and the interaction of physical, chemical and biological factors with the material in question. Alves (1997) uses the word patina to point out a colored coating different from the original color of the stone. In this work, the word patina will be used to describe chromatic alterations observed on the stone surface. In lower antropogenic pollution areas, several works have shown that the biological factor could be associated or Author to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservationof Stone,Venice 19-24June 2000
even being responsible for the anaesthetic color change of stone (Caneva et al., 1992; Krumbein, 1992; Urzi et al., 1993; Vendrell-Saz et al., 1996). The aim of this work was characterize biocolonization in a fagade of the monument in order to understand the microbiologic activity responsible for the biodeterioration of the granite stone, particularly for its disfigurement. 2. Materials and methods
The selected historical monument was the Edificio do Largo do Pago (14th-18th centuries) located in Braga, NW Portugal (fig. 1). Three units, from different ages form it : Medieval, Renaissance and Baroque. Like most monuments of this city, it was built with Braga granite, which is a porphyritic two-mica granite, biotite rich, fine to medium grained. Unweathered and weathered granite by parental mineral hydrolysis inherited from the quarry was used as building material of the monument. In this region from NW Portugal, where climate is temperate of humid and warm type, with mean annual rainfall ranging from 1200 to 1600mm, the granite rocks present an intense degree of weathering (Sequeira Braga et al., 1990). The East facade of the Medieval unit presents wide dark colored areas (fig. 1), spreading from the gargoyles that drain rain water from the terrace (Medieval unit roof), till the bottom of the facade. Studied samples were collected in this facade (fig.l) between 1,2 m and 6,5 m (samples 1,6), in biocolonized granite blocks. Samples of an apparently non-colonized granite block (sample 8) and from the nearest soil (sample 7) were also studied.
Figure 1: Location of the studied area (Braga, Portugal) and East facade of Edificio do Largo do Paso Only the results concerning samples collected during November 1997, analyzed under qualitative and quantitative microbiological techniques, are discussed in this paper. The research of algae and biogeochemical cycles bacteria, either nitrogen or sulfur, was made using liquid culture media (Galsomies, 1995). The quantification of the biomass was obtained through the determination of the most probable number (MPN) of microorganisms by gram of stone sample. The presence of fungi, heterotrophic, sugar fermentative bacteria, actinomycetae, Streptococcus and fecal contaminants was analyzed using solid culture media and quantified by counting of colony forming units (CFU) also by gram of stone sample. Samples of the different patinas as well as samples of the algae that developed in
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laboratory were observed through binocular lens and optical and scanning electronic microscopy (SEM). Some algae samples were prepared according to the techniques presented by Ascaso et al. (1988) and observed by transmission electronic microscopic (TEM). 3. Results and discussion 3.1 Microbiological colonization Table 1 shows the results of microbiological stone analyses and also the remain stone pathologies associated to biological colonization. Maximum and minimum amounts of the MPN/g of sample of the different groups of bacteria searched in the stone, allows us to characterize the activity of the microbial colonization. Excluding the non colonized granite block, ammonifying bacteria were detected in high amounts (14xl 06) in all samples studied. These results could be related to the degradation of the organic matter, accumulated on stone surface during the summer. N2-free fixing aerobic bacteria were also detected in significant amounts (14x104), specially in the higher blocks, which means that ammonia is being produced. The N2-free fixing anaerobic bacteria showed a higher presence in the upper blocks (25xl 03) comparatively with the ones near the ground (4.5 to 7.5x102). In a general way it can be said that the activity of these three groups of microorganisms means a great production of ammonia. Concerning nitrifying bacteria, nitrous and nitric, the first ones were detected only in one sample and in small amounts (30), while the second ones were present in all blocks in small quantities (1.1 to 3x102), except the non colonized block, which presented 3xlO 3. The absence of ammonia oxidizers can be related to the high amounts of this substance in the granite, produced by stone colonizing ammonifying and N2-free fixing bacteria. Wilimzig et al. (1992) observed a reverse connection between ammonia and the cell numbers of nitrifyers : the more ammonia was present the lower cell numbers of ammonia and nitrite oxidizers could be analyzed. According to theses authors, this means that if there are high ammonia concentrations, no metabolic turnover of nitrifyers reduce these concentrations. Denitrifying bacteria were only detected in the blocks located near the soil (samples 1 and 2). The absence of these bacteria in the upper blocks could be associated with lower nitrate production due either to the weak presence of nitrifying bacteria, or to the activity of mosses, ferns and Thiobaeilli in these blocks, which compete for nitrate with the denitrifying bacteria. It was observed a weak presence of organic-sulfur mineralizing bacteria in the upper blocks (O to 25xl 02). The absence of these bacteria in the lower blocks seams to be related with the few amount of sulfate reducing bacteria registered in those blocks.
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Table l: Results o f microbiological granite stone analyses and distribution o f associated pathologies (samples 1 to 6 = colonized blocks; sample 7 = soil; sample 8 = non-colonized block).
Biological colonization ~
o .~ ~ ~
~ . ~ ~ o ~s
o
(9 (9 + + + +
N cycle . ~, ~ ~ "~ ~ o ~ =
. ~ ~
] S.cycle
.
~
~ ~ ~
~
~ ~
~, ~:
~
Y
o
~
+ + + + + +++
+
+
+++
|
++
,
++
+
+
+
+
+
+
-
,
-
+
+++
++
++
-
+
+-t-+
-
-H-
(9 (9 ++ ++ +++ ++ ++-~ -
+
+++
-
-I--4- + 4 - + +
+
+
-
+
+++
-
++
+
+
6 (6,5) O (9 (9 + + ++ + + + + + + +++
-
+4-++-
7 (-0,1) n.sn.s n.s ++ n.d + + + +++ +++
-
++ +++ ++ 4 - ~ ++ ++ ++ + +
-
++ ++
2 (1,5) O ~
(9 + + + +
+ + + + + ++-F
3 (4,2) O ~i (9 ++ ++ +++ ++4 + + ,
4 (4,2) ~
5 (6,5) (9 (9 (9
8 (1,5)~G~++
= absent (9 = present
+ ++
+++
n.s n.s
++
n.s
' Other pathologies associated to biological colonization
Z
r~
1 (1,5) ~
~
+++
n.s
+ = 1 to lO s ++ = 10 s to 10 6
+++
-
++
++
+
-t-+++4-+4-4-
-
++ n.s
= > 10 6 - = zero
+
-
Granular disintegration Black and : g r e e n patina Granular disintegration Reddish-brown 9patina Granular disintegration i Hakes Reddish-brown and yellowish patina t Granular ! disintegration Flakes Black and g r e e n 9patina . . . . Granular disintegration Scales Black and . green patin a Granular disintegration Scales G r e e n patina
++ N o t detected
n.s = not searched n.d = not determined
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Regarding sulfur-oxidizing bacteria, this group was detected in all blocks in small quantities (0.06 to 1.5x103), excluding the non-colonized one, being the upper blocks the ones with higher values. These results seam to have some influence in the registered values of sulfate reducing bacteria. The lower value of sulfate-reducing bacteria was registered in the non-colonized block (40). On the blocks near the soil the registered values were 2.5 to 4.5x102 and on the block under less influence from the gargoyle were registered 2.5x102 sulfate-reducing bacteria. All the others showed the presence of this group of bacteria in larger values (0.15 to 1. lx104). The remaining searched groups presemed the following minimum and maximum UFC by gram of sample 9 sugar fermentative (19x103 to 66,9x105) and fungi (4 to16x104). Streptococcus and fecal contaminants were not detected. This absence shows that there is no antropogenie pollution at this level in the fagade. Actinomyeetae and heterotrophie bacteria were registered in too high amounts, and therefore impossible to quantify. The presence of algae and cyanobacteria was detected in significant amounts in all samples (6,5x102 to 14x103), although it was not possible to identify the totality of these organisms. The main algae present are Chlorophyta (Chlorella, Chlorococcum, Klebsormidium, Stichococcus, and Scenedesmus). Most taxa colonizing the granite substrate are green algae (Chlorophyeeae), common in wet rock environments, being the unicellular forms the most representative. This fact agrees with previous results presented by OrtegaCalvo et al (1992) and Seoane & Lastra (1996). According to Ortega-Calvo et al (1992) the extraeelular polymeric substances produced by algae and cyanobacteria can undergo large changes in volume during drying and wetting cycles, thus loosening stone grains. This effect may contribute to granular disintegration of the granite stone. Beside biological colonization, other stone pathologies occur on the studied faq,ade, although rare and with low intensity (tab.l). XRD and SEM-EDS analyses allowed the identification of gypsum aggregates (fig.2) in five blocks (distributed between the bottom and the top of the facade) but only in the surface of separation between the stone and the scales covered by an intense biogenous layering.
Figure 2: SEM images o f : a) gypsum agregates (g) among biotite (b) divages surfaces under scales covered by biogenous layering (bio), detail of gypsum crystals.
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The presence of gypsum in the blocks located near the soil and consequently the scales formation may be explained through the model presented by Arnold (1982) and verified in other places of the Edificio do Largo do Pago by Alves (1997). Gypsum lower solubility and diluted solutions that rise by capillary transfer of the solutions from the ground contribute with sulfates and calcium to the formation of that salt mineral. The potential salts sources are rain water, underground waters, soil and mortars. The results of the microbiological analyses on these blocks, located near the soil showed the absence of organic-sulfur mineralizing bacteria do not allow the development of sulfur oxidizing bacteria and therefore the sulfate liberation. This fact removes the hypothesis of a possible microbial contribution on gypsum formation. The presence of gypsum aggregates on the higher blocks (tab. 1) of the fa~}ade may be explained by the microbial activity involved in biogeochemical cycle of sulfur. The presence of organic-sulfur mineralizing bacteria and sulfur oxidizing bacteria was detected in these blocks. The sulfate resulting from their activity will be used by other stone colonizing organisms as source of sulfur for biosynthesis. Mineralizing bacteria degrade organic matter returning sulfur back to the environment. Nevertheless, the amount of sulfate-reducing bacteria is much lower than the sulfur oxidizing bacteria, leading to higher sulfate availability in the environment. Rain water is the main source of calcium to the formation of gypsum in the upper blocks of the facade. 3.2 Patinas
The widespread presence of patinas with different colors coveting monument stones have been already recognized (Caneva et al., 1992, Krumbein, 1992; Urzi et al., 1993; VendrellSaz et al., 1996;). These authors showed that those patinas have biogenic origin and its coloration can be related to microbial activity namely algae, fungi, cyanobacteria and bacteria, among others. Vendrell-Saz et al. (1996) also verified that colored patinas could occur in all kinds of rocks from the mediterranean, despite the chemistry, mineralogy, porosity or the durability of the stone. Mapping of patinas carried out on the studied facade of the Medieval unit is presented in figure 3. The dark colored areas show a color pattern with a lateral zoning, ranging from the middle to the outside part, from green (5GY5/2; 5GY7/2; 10GY7/2; 10GY4/4), black to reddish-brown (5YR3/2; 5YR4/4; 5YR5/6). In the middle part of these areas occurs an intense and heterogeneous biological colonization (lichens, algae, fungi, mosses and also some ferns). In these colonized areas other stone pathologies (granular disintegration, scales and flakes) were observed, though its little expression. The occasional presence of fly ash particles is not relevant in the composition of these different patinas. Some round particles with porous morphology like those presented by Krumbein (1992) as biogeneous ones, were also observed in the studied facade. Its carbon-rich composition (fig.4) and their occurrence in the patinas confirm a biogenic origin for those round particles. The occurrence of patinas only in the areas under the influence of the gargoyles allows us to consider that their biogenic formation is related to the runoff waters. SEM observations have showed that on the studied fa~}ade patinas are mainly formed by biofilms and bioerusts of algae, cyanobacteria and fungi (fig.4).
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Figure 4: Biofilms at granite surface: a) Hyphae; b) Penetration between packs of biotite; e) and d) biogeneous porous round particle and chemical spectra. 4. Conclusions In the granite stones of the East facade of the Medieval unit of the Edificio do Largo do Pago, in Braga, the presence of important amounts of the biogeochemical sulfur and nitrogen cycle bacteria, as well as other searched groups (algae, fungi, actinomycetae and heterotrophic bacteria) lead or accelerate the stone decay, granular disintegration, scales and flakes, but in particular its disfigurement, favored by microbial growth. The intense microbial activity explains the scarcity of salt minerals under colonized blocks. Gypsum occurrence on scales in higher blocks of the facade seams to be more easily explained by biological weathering than geochemical one. Beside, once the fagade is intensively washed by runoff waters during most of the year, gypsum should only be formed in dry periods of the summer, after the death of the majority of colonizing organisms. The different colored patinas are biogeneous and their origin is related to the stone colonizing microorganisms (algae, cyanobacteria, fungi and bacteria) which forms biofilms covering a large surface of the granite blocks. The formation of these patinas is due to the runoff water that supplies, during a long part of the year, the moisture necessary to microbial populations' development. 5. Acknowledgments This work was supported by the Funda~o para a Ci~ncia e Tecnologia (Portugal) through PRAXIS X X I - project n~ 2/2.1/CSH/254/95 including grant BIC n~ 3189, and CCA-CT/FCT-R&D Contract Program. Thanks are also due to CCMA of CSIC from Madrid, and in particular to Mr. M. Cobelas.
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6. References
Arnold A., 1982. Rising dump and saline minerals. 4th Int. Cong. on Deterioration and Preservation of Stone Objects, Louisville, 11-28. Alves C.A.S., Sequeira Braga M.A., 1999. Soluble salts in pathologies of granitic monuments of Braga (Northwest Portugal). Ninth Annual V. M. Goldschmidt Conf., p.XX.LPI Contribution N~ Lunar and Planetary Institute, Houston, 5-6. Alves C.A.S., 1997. Estudo da deteriorag~o de materiais graniticos aplicados em monumentos da cidade de Braga (Norte de Portugal). ImplicagSes na Conservagao do Patrim6nio Construido. Ph D thesis, Universidade do Minho, Braga. Ascaso, C., Brown, D.I-I, Rapsch, S., 1988. The effect of desiccation on pyrenoid structure in the oceanic lichen Parmelia laevigata. Lichenologist, 20, 31-39. Caneva, G., Nugari, M.P, Ricci, S., Salvadori, O., 1992. Pitting of marble roman monuments and the related microflora. Proc. of the 7th Int. Cong. on Deterioration and Conservation of Stone, Lisboa, 521-530. Galsomies, L., 1995. Le r61e du faeteur biologique dans l'alt6ration des monuments historiques en granite (Bretagne). Ph D thesis, Universit6 Paris XII, Val-de-Mame. Krumbein, E.W., 1992. Colour changes of building stones and their direct and indirect biological causes. Proc. of the 7th Int. Cong. on Deterioration and Conservation of Stone, Lisboa, 443-452. Ortega-Calvo, J., Hernandez-Marine, M., Saiz-Jimenez, C., 1992. Experimental strategies for investigating algal deterioration of stone Proc. of the 7th Int. Cong. on Deterioration and Conservation of Stone, Lisboa, 541-549. Seoane A.N., Lastra A.B.R., 1996. Epilithie ficoflora on two monuments of historicartistic interest from Galicia (N.W. Spain). Degradation and Conservation of Granitic rocks in Monuments, Res. Rep. N~ Vicente M.A., Delgado Rodrigues J., Acevedo J., 417-421. Sequeira Braga, M.A., Nunes J.E.L., Paquet H., Millot G., 1990. Climatic zonality of coarse granitic saprolites ("ar6nes") in Atlantic Europe from Scandinavia to Portugal. Sci. G6ol. M6moire, Strasbourg, 85, 99-108. Urzi, C., Criseo, G., Krumbein, W., Wollenzien, U., Gorbushina, A., 1993. Are colour changes of rocks caused by climate, pollution, biological growth, or by interaction of the three ?. Proc. of Conservation of Stone and other Materials, vol.I " Causes of Disorders and Diagnosis, E&FN Spon, 279-285. Vendrell-Saz, M., Krumbein, W., Urzi, C., Garcia-Vall6s, M., 1996. Are patinas of mediterranean monuments really related to the rock substrate ?. Proc. of the 8th Int. Cong. on Deterioration and Conservation of Stone, Berlin, Germany, 609-624. Wilin~g, M., Fahrig, N., Boek, E., 1992. Biologically influenced corrosion of stones by nitrifying bacteria. Proc. of the 7th Int. Cong. on Deterioration and Conservation of Stone, Lisboa, 459-469.
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EFFICIENCY OF BIOCIDE IN "IN SITU" AND "IN VITRO" TREATMENT. STUDY CASE OF THE "TEMPLETE DE MUDEJAR", GUADALUPE, SPAIN. Clara Urzi*, Filomena De Leo, Mariagrazia Galletta, Paola Salamone Institute of Microbiology, Faculty of Science, Messina, Italy Riccardo Balzarotti PHASE, Florence, Italy
Abstract
The present research investigated different aspects of the treatments with ALGOPHASE | using as case study the situation present in the "Templete de Mudejar", Guadalupe, Spain as follows: a) "in situ" efficiency of ALGOPHASE | after 8 years of treatment; b) "in vitro" efficiency of ALGOPHASE | on microbial suspensions obtained from the samples; c) "in vitro" comparison of the classical formulation of ALGOPHASE | in organic solvent with a new aqueous formulation (pH025/d) not yet commercialised. Results showed that after 8 years from the treatment, colonisation by algae, cyanobacteria, fungi and bacteria occurred on the temple. Cultural analyses showed the presence of Nitrogen-fixing cyanobacteria (mainly Nostoc) localised on the basement up to a height of 50 cm together with black fungi and spore forming bacteria; while only green unicellular algae and bacteria were recovered in the upper part. Thus no inhibitory effects on the microflora were any longer observed. Laboratory tests carried out on the sample suspensions showed that ALGOPHASE | was active against most of those algae, cyanobacteria, fungi and bacteria occurred on the temple. The new aqueous formulation was even more effective, causing a reduction in the presence of fungi of up to 100%. Bacteria were found to be less sensitive with both compounds. Key words: Biodeterioration, algae, biocides, ALGOPHASE | 1. Introduction
Biocide compounds are widely applied before and after restoration and conservative treatments, in order to reduce and/or eliminate the contaminant macro- and microflora (Commissione Normal, 1991). Two main categories of compounds are known: those applied before the treatment, that are removed after their action, and those that should have a preventive effect in order to reduce in time the re-colonisation of restored surfaces. ALGOPHASE | (2,3,5,6-tetrachloro-4 (methylsulphonyl) pyridine) belongs to this latter group and it is applied at the end of conservative treatments. It is a compound effective against algae, cyanobacteria and fungi (Balzarotti et al., 1999). Recent studies demonstrated its activity against photoautotrophic microflora, fungi and lichens up to 5-6 years after the application (Gomez-Bolea et al., 1999; Pietrini et al., 1999). On the contrary very little is known about its effect against bacteria. In the frame of European Project ENV4-CT98-0707, the present research considered different aspects of the treatments with ALGOPHASE | using as study case the situation present in the "Templete de Mudejar", Caceres, Guadalupe, Spain restored in 1991, as follows: a) "in situ" efficiency of ALGOPHASE | after 8 years of treatment; * Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
b) "in vitro" efficiency of ALGOPHASE | on microbial suspensions obtained from the sampling campaign in Guadalupe; c) "in vitro" comparison of the classical formulation of ALGOPHASE | in organic solvent with a new aqueous formulation (pH025/d) not yet commercialised. 2. Material and Methods 2.1 Study case The "Templete de Mudejar" was built in the XIVth century almost entirely from polished lime mortar. The monument is located in the courtyard of the "Real Monasterio de Santa Maria de Guadalupe" in a rural area of the region of the Estremadura about 300 km north from Sevilla (Spain). Before the restoration of 1991 the temple was heavily covered with mosses, lichens and algae. During the restoration, the biological patina was removed and the lower parts (height | of < 3 mt) were treated with the biocide ALGOPHASE . The upper parts above the first cornice (height of > 3 mt) were also treated with the water-repellent product (siliconebased) HYDROPHASE | 2.2 Sampling 14 samples were taken from the different oriented faces and height of the "Templete de Mudejar" (Fig. 1) as summarised in Table 1. Samples were taken with two different modalities depending on the characteristic of the material and the possibility of taking destructive samples: 1) Adhesive tape stripes (Fungi tape DID, Milan, Italy) were used as a non-destructive sampling procedure (Urzi et al., in press) for the survey of microbial colonisation of surfaces. 2) Scalpel technique was used in order to take samples for quali-quantitative microbiological analysis. 2.3 Microscopical observations Each stripe was cut in small pieces and sorted for a direct observations under light and epifluorescent microscopy (DMLB, Leica). Microscopical observations were carried out without any specific preparation using a drop of sterile water or a drop of Amman's lactophenol (Fassatiov~i, 1986), or with the addition of a drop 0.01% sterile Acridine Orange between glass slide and tape and placing a cover glass on the top in order to keep the tape as fiat as possible. 2.4 Isolation of culturable microorganisms In order to check the efficiency of ALGOPHASE | "in situ" after 8 years from the treatment, cultural analysis for chemoorganotrophic bacteria, fungi and photoautotrophic microorganisms were carried out according to the Normal Committee recommendations (Commissione Normal, 1990) as described by Urzi and Realini (1998). Results were recorded after selected incubation times in agreement with each physiological group.
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Figure 1. East Facade of the "Templete deMudejar". The heavy biological colonisation in the lower part is well evident. Figure 2. Adhesive tape stripe from sample TM 8 observed under Light Microscope. Algal patina and black fungal conidia are visible. Magnification 20x. Bar = 20 ~tm. Figure 3. Dematiaceous fungal colonies (Ulocladium sp.) grown on DRBC medium after inoculation of dilution 10-3 of sample TM4 (height of 0-10 cm).
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Figure 4. Amasses of unicellular green algae and filamentous cyanobacteria grown on BG 11 medium. Bar = 10gm. Figure 5. Filamentous cyanobacteria with terminal heterocysts of the genus Anabaena grown on BG 11 medium. Bar = 10gm. Figure 6. Filamentous cyanobacteria of the genus Nostoc enveloped in extracellular polymeric substance (EPS). Bar = 10gm.
2.5 "In vitro" efficiency of biocides ALGOPHASE | and pH025/d The effects of the biocide ALGOPHASE | in ethanol solvent and of the new aqueous formulation (pH025/d) at 5% concentration, were evaluated according to the Normal Committee recommendations (Commissione Normal, 1994) with some modification. 0.1 ml of the rock suspensions (1:10 w/v), in physiological solution + 0.001% Tween 80 obtained from samples with evident algal colonisation (all samples between a height of 050 cm) were inoculated into agarised media BG11, BRII and DRBC for algae, bacteria and fungi respectively, in which a solution of each biocide had previously been distributed on the surface with a sterile cotton swab. Results were recorded after selected incubation times in agreement with each physiological group.
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3. Results 3.1 Microbiological analysis 3.1.1 Samples taken between the height of O-50 cm Direct microscopic observations of the samples taken with adhesive tape revealed the presence of biological colonisation mainly as algal patina and black fungal clusters (Fig. 2). Cultural analysis confirmed the presence of phototrophic and chemoorganotrophic microorganisms (bacteria from 2.5104 to 5.0106 c.f.u./g; fungi from 8.1103 to 1.9105 c.f.u./g) as shown in Table 1. Bacteria were mostly Gram positive, they were mainly red, yellow, pink and orange pigmented cocci (Micrococcus sp. and Staphylococcus sp.) and spore forming rods (Bacillus sp.). Fungi isolated belonged to the ubiquitous dematiaceous genera of Alternaria, Ulocladium and Phoma (Fig. 3). Occasionally black meristematic fungi were isolated. As far as regards phototrophic microflora, unicellular algae (Fig. 4) were detected in all samples, filamentous diazotrophic cyanobacteria of the genera Anabaena (Fig. 5) and Nostoc (Fig. 6) were found in almost all samples, except for TM 4 and TM 6. In the sample TM 13 (taken in the inner part), only chemoorganotrophic bacteria of the genus Micrococcus were isolated.
3.1.2 Samples taken between the height of lO0-150 cm All samples taken at this height and the sample taken at the height of 300 cm did not show any evident microbial colonisation. This fact was also confirmed by direct microscopic observations and by cultural analysis. In fact, cyanobacteria resulted absent and unicellular green-algae (Chlorella-like) were rare as well as bacteria (from 0 to 4.5103 c.f.u./g) (Table 1). These latter, when present, belonged to the genera Micrococcus and Bacillus. Fungi were isolated only from the sample TM 3 (1.0103 c.f.u./g) and were attributed to the dematiaceous genera Ulocladium and Phoma. 3.2 "In vitro" efficiency of biocides ALGOPHASE | and pH025/d The effects of the biocide ALGOPHASE | and the new aqueous formulation pH025/d against the microflora colonising the "Templete de Mudejar" are summarised in Table 2 and Figures 7 and 8.
3.2.1 Activity against phototrophic microflora The biocide ALGOPHASE | was efficient against phototrophic microflora present in most of the rock suspensions tested. In fact, a total inhibition of the growth was observed for samples TM 1, TM 4 and TM 6; there was a reduction of growth around or less than 50% for the organisms of samples TM 2 and TM 8; there was scarcely any or no reduction of algal growth for samples TM 7, TM 9 and TM 11 (Table 2). The biocide pH025/d seemed more efficient than ALGOPHASE | against phototrophic microflora. In fact, inhibition of algal growth was observed in samples TM 1, TM 4, TM 6, TM 7, TM 11; a reduction of algal growth around or less 50% in the samples TM 2 and TM 8 was observed. Only for sample TM 9 the effect of the biocide was scarce (Table 2).
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Table 1. Enumeration of bacteria and fungi is referred as colony forming units per gram (c.f.u./g) and phototrophic microflora as presence/absence. Samples
Height
TM 1 TM 2 TM 4 TM 6 TM 7 TM 8 TM 9 TM 11 TM13
0-50 cm " " " " " " " (Inside)
TM TM TM TM
3 100-150 cm 5 . . . 10 " 12 "
Orientation Chemoorganotrophic Fungi bacteria (c.f.u./g) (c.f.u./~) East 2.0106 1.010" East 9.8105 2.4104 " 4.1105 8.1103 " 5.0106 7.3104 South 2.9106 1.9105 South 2.0105 9.8103 West 4.3105 9.7104 North 5.0106 1.8104 SW Comer 2.5104 0 East . West North
4.5103 0 0 3.5103
Algae and Cyanobacteria
1.1103 0 0 0
+++ +++ +++ +++ ++ +++ +++ +++ 0 + n.d. + +
TM 18 300 cm West 2.510 4 5.8104 ++ +++ = abundant growth; ++ = good growth; + = scarce growth; 0 = no growth; n.d. = not determined; Table 2. Activity of the biocides ALGOPHASE | and of new aqueous formulation pH025/d on the phototrophic microflora. Samples TM 1 TM 2 TM 4 TM 6 TM 7 TM 8 TM 9 TM 11
Control +++ +++ +++ +++ +++ +++ +++ +++
ALGOPHASE ~ + ++ + ++ +++
pH025/d + + ++ -
G r o w t h on the Petri dishes: + + + = similar the control ( 1 0 0 % ) ; + + = >50~ < 1 0 0 % ; + = < 5 0 % ; - = no growth.
-
3.2.2 Activity againstfungi In laboratory conditions, fungi were sensitive to the treatment with ALGOPHASE | In fact, reduction of the fungal growth was observed in all samples with a percentage between 88% and 99.5% (Fig. 7). It is worth noting that the new aqueous formulation pH025/d was more effective against fungi with 100% inhibition of growth in all suspensions tested.
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3.2. 3 Activity against bacteria Both biocides ALGOPHASE | and pH025/d were ineffective against bacteria. In fact, no reduction of the bacterial growth was observed in some samples. In the other cases a percentage of reduction of the growth between 85.2% and 97.6% (Fig. 8) was observed.
Figure 7. Effect of the biocide ALGOPHASE | and of the new formulation pH025/d on the mycoflora and percentage of reduction of the growth.
Figure 8. Effect of the biocide ALGOPHASE | and of the new formulation pH025/d on the bacteria.
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4. Discussion
Microbiological analysis showed that after 8 years from treatment with biocide ALGOPHASE | a re-colonisation of the surfaces of the "Templete de Mudejar" by algae, cyanobacteria, fungi and bacteria for all orientations occurred. Microbial re-colonisation was demonstrated especially in the lower parts (between the height of 0-50 cm) in which a heavy biological patina was evident. Favourable conditions for the growth of phototrophic microorganisms were due to ascending humidity caused by the position of the temple located at the centre of a small pond in the cloister garden, as already reported by Arifio et al. (2000). These Authors reported a list of phototrophic organisms isolated and put into evidence their opportunistic and ubiquitous behaviour. However, laboratory tests showed that ALGOPHASE | was able to dramatically reduce the amount of algae, cyanobacteria and fungi present in the samples suspension. These data seem to demonstrate that the biocide was no longer present (or efficient) "in situ" in the temple. Other Authors' data demonstrated that ALGOPHASE | is able to inhibit the growth of phototrophic microorganisms for a period of 5-6 years (Gomez-Bolea et al., 1999; Pietrini et al., 1999). It is known that different factors could influence the efficiency of biocide treatments; the environmental conditions of exposition of treated materials, among which sunlight radiation and rainfall washing-out, could play an important role (Nugari, 1999). In fact, in this case the "humidity" should be considered as a key factor for the durability of the biocide treatment.
5. Conclusion
We can conclude that application of ALGOPHASE | can be useful to slow down lichens, algal, cyanobacterial and fungal re-colonisation processes, if applied within intervals of time not exceeding 8 years and in environmental conditions relatively free of humidity. Because better results were obtained with the new aqueous formulation pH025/d, particularly against funsal growth, we suggest, when it is possible, to apply it. Concerning bacteria, ALGOPHASE ~ failed to inhibit their growth and thus a specific product against bacteria should be applied. 6. References
Arifio X., Canals A., Gomez-Bolea A., Saiz-Jimenez C. Re-colonisation of the Templete Mudejar, Guadalupe Monastery, Caceres, Spain, after silicone/biocide treatment. The Conservation of Monuments in the Mediterranean Basin Proc. of the 5th International Symposium, 5-8 April, 2000, Seville, Spain. Balzarotti-Kammlein R., Sansoni M., Castronovo A., 1999. An innovative watercompatible formulation of ALGOPHASE | for treatment of mortars. Microbiology and Conservation of Microbes and Art (ICMC '99), Proc. of the International Conference. Firenze. 217-220. Commissione Normal, 1990. Raccomandazioni Normal: 9/88. Microflora autotrofa ed eterotrofa: tecniche di isolamento in coltura. C.N.R. - I.C.R., Roma.
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Commissione Normal, 1991. Raccomandazioni Normal: 30/89. Metodi di controllo del biodeterioramento. C.N.R. - I.C.R., Roma. Commissione Normal, 1994. Raccomandazioni Normal: 38/93. Valutazione sperimentale dell'efficacia dei biocidi. C.N.R. - I.C.R., Roma. Fassatiov~i O, 1986. Moulds and filamentous fungi in technical microbiology. Progress in Industrial Microbiology. Elsevier, Amsterdam. Gomez-Bolea A., Arifio X., Balzarotti R., Saiz-Jimenez C., 1999. Surface treatment of stones: conseguences on lichenic colonisation. Microbiology and Conservation of Microbes and Art (ICMC '99), Proc. of the International Conference. Firenze. 233-237. Nugari M. P., 1999. Interference of antimicrobial agents on stone. Microbiology and Conservation of Microbes and Art (ICMC '99), Proc. of the International Conference. Firenze. 211-214 Pietrini A.M., Ricci S., Bartolini M., 1999. Long-Term evaluation of biocide efficacy on algal growth. Microbiology and Conservation of Microbes and Art (ICMC '99), Proc. of the International Conference. Firenze. 238-245. Urzi, C., Realini M., 1998. Colour changes of Noto's calcareous sandstone as related to its colonisation by microorganisms. International Biodeterioration and Biodegradation, 42, 45-54. Urzi C., De Leo F., Salamone, P. Rapid survey of marble colonisation using the adhesive tape stripes. Eurocare-Euromarble EU 49, Proc. of the 10th Workshop, Stocholm, Sweden, In press.
Acknowledgements This study was supported by the financial contribution of European community through the EC projects ENV4-CT98- 0707 and Murst 60%. We also like to thank Mr. William Fenton for his kind revision of the English text.
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Theme 4 Laboratory methods and techniques
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INSTRUMENTAL CHEMICAL ANALYSIS OF THE MORE COMMON MARBLES HISTORICALLY USED FOR DECORATIVE PURPOSES OR TO CREATE WORKS OF ART L. Campanella, E. Gregori, R. Grossi, M. Tomassetti* Dipartimento di Chimica, Universitb. di Roma "La Sapienza" G. Bandini Soprintendenza Archeologica di Roma, Museo Nazionale Romano
Abstract The aim of the work is to make concise records, several prototypes of which are illustrated in the present note, of a series of experimental data obtained using instrumental chemical methods applied to the more common marbles historically used to create artistic artefacts. This chemical information, accompanied by relevant mineralogical data, should speed up or at least facilitate the identification of the type of marble used to create many marble artistic finds about which little is still known. Keywords: marbles, chemical instrumental analysis, mineralogycal data. 1. Introduction We are currently carrying out basic chemical research on the most common types of marble historically used both for decorative purposes and to make marble statues. Numerous studies and researches of different kinds have already been carried out on several of the more common types of marble [L. Lazzarini, 1980; D. Cordischi,1983; K.J. Matthews,1997], mostly of a mineralogical nature [M. Pieri, 1966]. Nevertheless we consider that a collection of data obtained using modem instrumental chemical methods can provide a valid tool to be used for different purposes, above all to identify accurately and rapidly the type of marble used to create a number of works of art as yet inadequately studied. Furthermore, a knowledge of the chemical characteristics of the various types of marble is particularly important for conservation purposes and a correct identification of the type of marble through its chemical characteristics frequently makes it possible to determine the place of origin and to confirm and supplement the historiographic data which often already exist in the case of many marble works of art. 2. Results In pratice, the study under way, focused on marbles such as Paros, Pentelic, Aphyon, Lasa, Ephesus, several Carrara varieties, etc., entails systematic analysis carried out using inductively coupled plasma (ICP), X-ray diffractometry and thermoanalysis (TG, DTG and DTA) techniques. The chemical data thus obtained were further supplemented and completed by mineralogical and stratigraphic data obtained via optical microscopy. For each type of marble investigated all the data collected have been gathered in recapitulatory records of which examples are shown in the following for two Greek marbles Pentelic and Paros, and Italian marble, Carrara-Altissimo, and a Turkish marble, white Aphrodisias.
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
2.1 Pentelie Marble
Provenance:Greece Colour: white Mineralogical-petrographic analysis under optical microscope. Structure: polygonal granuloblastic homeoblastic with prevalent straight line contact among grains. Texture: isotropic. Identifiable minerals: calcite granules containing very rare, probably dolomite, rhombohedrons. Mineral size: varies from 0.6 mm to about 0.2 mm; the most common size is about 0.4 mm. Instrumental chemical analysis.
fig. 1 fig. 2 fig. 1 TG and DTG curves of Pentelic marble. Heating rate 10~ min-l; air stream: 100 cm 3 min-1. fig.2 DTA curve of Pentelic marble. Heating rate 10~ min -1 ; air stream: 100 cm3min -l
Thermogravimetric data 9 First step mass loss % T oC 283 9.3 403 557
Second step mass loss % T oc 557 40.5 716 850
residue % at 900~ 49.6
Plasma Emission (ICP) data; values in 9pm Ca
K
Mg
A1
309754
340
314
552
Si
Fe
Sr
Mn
Zn
54
58
14
-
Xra ~ ffraction data 3.85 3.03 2.49 2.09 dhkl (12) (100) (14) (18) and intensity ( ) Calcite found in literature (*) CaCO 3 dhk 1 found 3.86 3.03 2.50 2.09 experimentally in the sample (*) Mineral Powder Diffraction File - Data Book-1976
Pb
Cr
Cu
0.06
1.93
1.91
1.87
1.62
1.60
1.52
(5)
(17)
(17)
(4)
(8)
(5)
1.93
1.91
1.87
1.62
1.60
1.52
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2.2 Paros Marble
Provenance: Greece Colour : white with yellowish lamellae Mineralogical-petrographic analysis under optical microscope. Structure: polygonal crystalloblastic; contact among granules ranges from irregular to straight line Texture: isotropic. Identifiable minerals: calcite granules including occasional, probably dolomite, rhombohedrons, rare white muscovite mica, minute opaque mineral granulations. Mineral size: varies from 1 mm to about 0.05 mm; the common size is about 0.5 mm. NB: a thin irregular vein of tiny opaque reddish brown coloured granules runs through the stone.
Instrumental chemical analysis.
fig. 3
fig. 4
fig.3 TG and DTG of Paros marble. Heating rate 10~ min -1 ; air stream: 100 cm3min -I fig.4 DTA curve of Paros marble. Heating rate 10~ min -1 ; air stream: 100 cm3min -1
Thermogravimetric data First step mass loss % 1.8
T ~C 322 448 536
Second step mass loss % T oC 536 716 43.1 850
residue % at 900 ~ 53.2
Plasma Emission (ICP) data; values in p ~m Ca
K
Mg
A1
Si
Fe
Sr
Mn
Zn
364014
1368
1307
789
-
660
122
15
5
Pb
Cr
Cu
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Xray d~ffraction data
Calcite CaCO 3
dhkl and intensity ( ) found in literature (*) dhkl found experimentally in the sample
3.85
3.03
2.49
2.09
1.93
1.91
1.87
1.62
1.60
1.52
(12)
(100)
(14)
(18)
(5)
(17)
(17)
(4)
(8)
(5)
2.50
2.09
1.93
1.91
1.87
1 . , 6 2 1.60
1.52
3.85
3.03
2.3 White Aphrodisias Marble Provenance: Turkey Colour : white Mineralogical-petrographic analysis under optical microscope. Structure: highly heteroblastic and crystalloblastic. Texture: foliate schistose. Identifiable minerals: coarse levels composed of faintly bismarck coloured calcite granules with irregular contact among granules and little quartz; the fine grained levels are composed of elongated orientated carbonate crystals (the greatest of calcite and the smallest of dolomite) with irregular contacts among granules, little quartz, of elongated and orientated crystals and small quantities of orientated white mica. Mineral size: varies from 1 mm to about 0.025 mm. The rock is composed of alternate coarse grained (about one millimetre) and very fine grained (0.025 mm) layers.
Instrumental chemical analysis.
f
l
._
100.._.. =-.<
/!
D
ROd .....
o21
/
60-
\
i
I
\~
=
"k__~ ..
40
_.
= ,
O
.
]
_
', . :}
Ternperat.ure
1~
j . 20@
.i~ ')
fig. 5
.
. -~90
w
80',) Ten,F.~r =.t'-r e ( ~ SO~.~
"-
i !000
fig. 6
fig.5 TG and DTG of Aphr0disias white marble. Heating rate 10~ min -l ; air stream: 100 cm3min-I fig.6 DTA curve of Aphrodisias white marble. Heating rate 10 ~ C min -1 ; air stream: 100 cm3min-l
Thermogravimetric data First step mass loss % 5.3
T oC 293 404 584
Second step mass loss % T oC 584 40.1 733 850
residue % at 900 ~ 51.0
547
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Plasma Emission (ICP) data; values in
)m 9
Ca
K
Mg
A1
Si
Fe
164279
24678
21328
424
-
689
Xra diffraction data dhkl and intensity ( ) Calcite found in literature (*) CaCO 3 dhk 1 found experimentally in the sample
CaMg(C03)
2
Mn
Zn
Pb
71
3
1
Cr
Cu
3.85
3.03
2.84
2.28
1.91
1.87
1.62
1.60
1.52
1.47
(12)
(100)
(3)
(18)
(17)
(17)
(4)
(8)
(5)
(2)
3.84
3.03
2.50
2.28
1.91
1.87
1.62
1.60
1.52
1.47
dhkl and intensity ( ) found in literature (*) dhk 1 found experimentally in the sample
Dolomite
Sr
3.69
2.89
2.67
2.54
2.40
2.19
2.01
1.80
1.78
(5)
(100)
(10)
(10)
(10)
(30)
(15)
(20)
(30)
2.67
2.54
2.40
2.19
1.80
1.78
3.69
2.88
2.01
2.4 Altissimo Marble (Falcucci) Provenance: Italy Colour : white Mineralogical-petrographic analysis under optical microscope. Structure: polygonal homeoblastic crystallographic; contact among granules mostly regular. Texture: isotropic Identifiable minerals: calcite granules including possible irregular dolomite rhombohedrons. Mineral size: homogeneous, average 0.1 mm. Instrumental chemical analysis. 9
]. . . . . . . . . . . . . .
t"\
~ ! AT
+"
i
~'
I
i
I I
a~
~
9
~
-
.
.
.
.
Temperature
fig. 7
.
9
('C)
.... ,
9 0
200
400
608 ,~00 Tc m,r..er,_: ~.;.,r e ,"" C)
100('
fig. 8
fig.7 TG and DTG of Altissimo marble. Heating rate 10~ min "1 ; air stream: 100 cm3min-l fig.8 DTA curve of Altissimo marble. Heating rate 10~ min -1 ; air stream: 100 cmamin -!
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Thermogravimetric data First step mass loss % T oC
Second step mass loss % T oC 535 713 43.7 850
residue % at 900 ~ 56.0
Plasma Emission (ICP) data; values in ~pm Ca
K
Mg
A1
Si
Fe
Sr
Mn
350668
5397
5254
596
-
78
104
7
Xray d! 9action data dhkl and intensity ( ) Calcite found in literature (*) CaCO 3 dhk 1 found experimentally in the sample
Zn
Pb
Cr
Cu
3.85
3.03
2.49
2.09
1.93
1.91
1.87
1.62
1.60
1.52
(12)
(100)
(14)
(18)
(5)
(17)
(17)
(4)
(8)
(5)
3.86
3.03
2.50
2.09
1.92
1.91
1.87
1.62
1.60
1.52
dhkl and intensity ( ) Dolomite found in literature (*) CaMg(CO3) 2 dhk 1 found experimentally in the sample
3.69
2.89
2.67
2.54
2.40
2.19
2.01
1.80
1.78
(5)
(100)
(10)
(10)
(10)
(30)
(15)
(20)
(30)
2.89
.
1.80
1.78
.
.
.
.
3. Tests on archaeological marbles As further proof of the usefulness of our present work we used the systematic data gathered so far to successfully identify several marble samples used as decorative lining in ancient imperial age Roman buildings. The same chemical and mineralogical tests were performed also on these specimens and similar recapitulatory records made. The results for marble specimens from a temple capital and from a marble architectonic find from a 1-2 cent. A.D. building are illustrated in the following. 3.1 Marble specimen from a temple capital.
Provenance:unknown Colour : white Mineralogical-petrographic analys& under optical microscope. Structure: polygonal granuloblastic with frequent triple joints; contact among granules mostly regular and straight line. Texture: isotropic.
9th I n t e r n a t i o n a l Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
549
Identifiable minerals: calcite granules including probably dolomite rhombohedrons. Mineral size: varies from 1 m m to about 0.1 mm; the most common size is about 0.6 mm.
Instrumental chemical analysis.
A I~-
.,_.,
J
60:
40
,
0
,
\
I
i\t
loC
0 ' &o .... 4~0 " 6~0 ' ~,0 " l~o" zz'~ " z400
,
200
Temperature ('C)
Temperature (*C)
fig. 9
fig. 10
fig.9 TG and DTG of specimen from a temple capital. Heating rate 10~ min -I ; air stream: 100 cm3min -1 fig.10 DTA curve of specimen from a temple capital .Heating rate 10~ min -1 ;air stream: 100 cm3min -1
Thermogravimetric data First step mass loss %
T oC 301 370 539
7.8
Second step mass loss % T~ 539 40.2 707 850
residue % at 900 ~ 49.9
Plasma Emission (ICP) data; values in pm Ca
K
Mg
AI
Si
Fe
Sr
Mn
Zn
Pb
320987
1971
1524
487
8
69
104
35
-
1
Cr
Cu
Xray d ~action data
Calcite CaCO 3
dhkl and intensity ( ) found in literature (*) dhkl found experimentally in the sample
3.2
3.85 3.03 2.49 2.09 1.93 1.91 (12) (100) (14) (18) (5) (17)
3.83
Architectonic element find
Provenance" unknown Colour" white
3.03
2.50
2.08
1.93
1.91
1.87 (17)
1.87
1.62
1.60
1.52
(4)
(8)
(5)
1.,62
1.60
1.52
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Mineralogical-petrographic analysis under optical microscope. Structure: comparatively non evolved heteroblastic crystalloblastic; contact among granules irregular. Texture: isotropic Identifiable minerals: calcite granules including rare, probably dolomite, rhombohedrons. Mineral size: varies from 1.6 mm to about 0.1mm; the most common size is about 0.8 mm.
Instrumental chemical analysis. _
Y
I .-z ~o
.....
I
"-~
]
!i
I
80
i oc
"--'---N__F--~
3
40} Ter,-,pereture
fig. 11
(~
Temperate/re
(*C)
fig. 12
fig. 11 TG and DTG of specimen from architectonic element find. Heating rate 10~ min-l; air stream: 100 cm3min -1 fig.12 DTA curve of specimen from architectonic element find.Heating rate 10~ min -l ; air stream: 100 cm3min -1
Thermogravimetric data Second step mass loss % T oC 563 729 2.8 42.8 850 Plasma Emission (ICP) data; values in ppm First step mass loss %
T oC 335 431 563
Ca
K
Mg
A1
Si
Fe
Sr
Mn
313507
3654
2767
527
4
36
115
1
residue % at 900 ~ 54.6
Zn
Pb
Cr
Cu
Xray diffraction data
Calcite CaCO 3
dhkl and intensity ( ) found in literature (*) dhk 1 found experimentally in the sample
2.84
2.28
1.91
1.87
1.62
1.60
1.52
1.47
(12) (100) (3)
(18)
(17)
(17)
(4)
(8)
(5)
(2)
2.27
1.91
1.87
1.62
1.60
1.52
1.47
3.85
3.84
3.03
3.02
2.49
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
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4. Conclusions On the basis of a comparison of the data, particularly the thermoanalytical and mineralogical data, the first of the two archaeological finds may reasonably be classified as Pentelic marble, while the second, on the basis of the thermoanalytical and diffractometric tests, may be classified as Paros marble. However, the results of the still incomplete mineralogical investigation cast several doubts over the classification of the second find. We are currently examining other significant marble specimens taken from statues for which permission has recently been granted. 5. Acknowledgements The authors wish to thank the Archaeological Superintendency of Rome for making available several marble samples of archaeological interest. 6. References Article reference: L. Lazzarini, G. Moschini, B.M. Stievano, 1980. A contribution to the identification of italian, greek and anatolian marbles through a petrological study and the evaluation of Ca/Sr ratio. Archaeometry, 22, 173-183. D. Cordischi, D. Monna, A.L. Segre, 1983. ESR analysis of marble sample from mediterranean quarries of archaeologic interest. Archaeometry, 25, p.p. 68-76. K.J. Matthews, 1997. The establishment of a data base of neutron activation analyses of white marble. Archaeometry, 39, 321-332. Book reference: M. Pieri, 1966. Marmologia. Dizionario di marmi e graniti italiani ed esteri. Hoepli, Milano.
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553
PRESENCE OF D,L AMINO ACIDS IN OXALATE PATINAS ON A STONE MONUMENT Antonella Casoli*, Sara Negri Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universit/t degli Studi,Parma, Italy Gerardo Palla Dipartimento di Chimica Organica e Industriale, Universit~ degli Studi, Parma, Italy
Abstract The proteinaceous material in calcium oxalate patinas, collected from the stone surfaces of the Baptistery in Parma (Italy), was analysed in order to look at the racemisation level of the amino acids. This study was carried out by means of gas chromatography-mass spectrometry, after acid treatment and derivatization procedures. The amino acids were resolved as N-trifluoroacetyl-O-2-propyl-esters by using chiral capillary columns (ChirasilL-Val). The high racemisation levels - detected for several specific amino acids in all the samples examined - indicate that microbial flora contribute to the formation and modification of the organic material which mineralization leads to the oxalate patinas on the monument stones.
Key words: Oxalate patina, D/L amino acids, Stone monument 1. Introduction Calcium oxalate patinas over a variety of substrates (including calcareous and notcalcareous stone) have been described from different locations throughout the world [1,2]. These patinas form homogeneous and extensive layers, often variously coloured in yellow, brown or red. The interest in the origin of the calcium oxalate films has led to the formulation of some hypothesis, that are still being discussed. An hypothesis is that of treatments, carried out by the application of organic materials on the surfaces of artifacts or buildings for protective and/or aesthetic purposes, may be the cause of the formation of calcium oxalate [3]. In a previous paper, we analysed the oxalate patinas collected from the stone external surfaces of the Baptistery in Parma (Italy), with the aim of researching the organic material eventually present [4]. We selected samples, previously analysed by means of optical microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy [5], that included calcium oxalate (mostly in the dihydrate form: wedellite). The analysis was carried out by means of gas chromatography-mass spectrometry (GC/MS) and revealed the presence of proteinaceous and lipidic material in all of the selected samples. It has been pointed out that the chromatographic profiles of the samples mostly correspond with those obtained by the egg proteins analysis. Moreover, in some samples the presence of a lipidic content was observed, which could be attributed to drying oil. These results could assert the hypothesis according to which calcium oxalate originates as a secondary product of past treatments carried out by applying organic materials for protective and/ or aesthetic purposes.
* Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
In this paper, we report the investigation on a selection of the samples previously analysed by GC/MS, with the aim to look at the racemisation level of the amino acids present in the organic material. The study was carried out by means of GC/MS, using chiral capillary columns. Four oxalate patina samples were taken into consideration, collected from the sides of Baptistery at different heights and exposures: one of them were taken from the lower external band (sample B4), and three from the loggia on the first floor (B20, B22, B24). 2. Experimental Methods 5-10 mg of samples were dissolved in 2 ml of 6N HC1, and hydrolysed for 5 h at 100~ During hydrolysis, proteins are transformed into amino acids. Hydrolysed samples were spiked with 10 l.tg of D,L norleucine (10 ~l of a 1 g/1 solution), and 1 ~tg of D,L norvaline (10 ktl of a 0.1 g/1 solution) per 1 mg of weighted sample and were evaporated to dryness. The residue was dissolved in 3 mL of 2N HC1 in 2-propanol, and kept at 90~ for 1 h. After evaporation of the solvent, the residue was dissolved in 2 mL of dichloromethane and treated with 0.2 mL of trifluoroacetic anhydride at 60~ for 1 h. After evaporation of the solvent, the residue was recovered in 0.2 mL of dichloromethane, and used for GC/MS injection. The analysis of amino acid derivatives was carried out by means of a HP-5890 Series II gas chromatograph coupled to an HP-5971A mass selective detector (HewlettPackard, Palo Alto, CA, USA). Chromatographic separations were achieved by a ChirasilL-Val (25 m x 0.25 mm i.d. x 0.12~tm f.t.) fused-silica column (Chrompack Italia, Milan) according to the following temperature program: initial temperature 60~ for 3 min, then increased at 4~ up to180~ The injector was kept at 280~ while helium gas flow was approximately of 0.66 mL/min. The injection ( 1laL) was splitless (30 s). MS conditions were as follows: interface temperature 280~ ion source temperature ca 159~ electron impact 70 eV. The mass spectrometer was operated "scan mode" (at 1.8 scan/s in the range of m/z 40-450) to recognize the amino acid derivatives from their mass spectra and "SIM mode" (Selected Ion Monitoring) to measure with care the corresponding D/L ratios. When using the SIM mode, the following target ions were selected: m/z 140 for alanine (Ala), m/z 168 for norvaline (Nval), m/z 182 for leucine (Leu) and norleucine (Nleu), m/z 126 for glycine (Gly), m/z 166 for proline (Pro), m/z 164 for hydroxyproline (Hpro), m/z 184 for aspartic acid (Asp), m/z 198 for glutamic acid (Glu), m/z 91 for phenylalanine (Phe). 3. Results and Discussion All the four oxalate patina samples collected from the stone surfaces of the Baptistery showed the presence of D,L amino acids. Figure 1 shows a selected ion chromatogram of sample B24. One can observe that several amino acids show their D isomer. The levels of racemisation of the amino acids (D/L* 100) from the oxalate patina samples are reported in Table 1.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
555
Abor~da~re.:e
9000
L-Leu
L-Asp
L-Pro
Gly
L-Glu
D-A,,;g l
L-Phq
L'Ala 1 D-Leu '
9
~ - ,
u
,
, ,
9
~
, ,
!
,
t 14.00
10.00
,
,
9
,
18.00
~
.
.
.
.
~ 22.00
,
,
,
,~
,
~ n~n
Figure 1. A selected ion chromatogram of sample B24. Table 1. Levels of racemisation (D/L*100) of the amino acids from the oxalate patina samples of the Baptistery in Parma.
Sample B4
....
Aia
Leu
16
3
' 2 8
B20
12
8
B22
7
n'd
B24
.......
20
2
Pro
5
2
Asp
Glu
Phe
6
9
n.d.
1i
5
5 ......
2
8
2
4
12
9
n.d. - not detected One can observe that the level of racemisation of amino acids of these samples presents a wide variabilty. It is note that racemisation of the L-amino acid isomers to a mixture of D and L isomers is usually used for dating proteinaceous materials [6,7]. In particular, fossils like as bones, teeth, shells, snails - [8] and other proteinaceous materials were dated evaluating the aspartic acid racemization [9]. Observing Table 1, one could expect only the increase of the amount of D-aspartic acid, as it is known that it racemises faster than other amino acids [6]. On the contrary, in all the samples, alanine presents the highest D/L value, that can not simply be due by ageing, but also by other agents, as microbial growth on the stone. One could consider that bacteria present by nature some specific D-amino acids, as D-alanine, D-aspartic acid and D-glutamic acid that are constituents of the bacterial cell walls [10]. Moreover, it is known that D-alanine is recognized as a molecular marker of microbial activity in milk, in fruit juices and other food [11 ]. Taking into account these
556
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
considerations it is to believe that reasonable that micro-organisms contributed in the formation of the oxalate patinas of the Baptistery in Parma. In fact, microbial activity could be responsible or co-responsible of the accumulation of the organic material leading to oxalate and could also modify the composition of lipids and proteins previously applied on the stone surfaces for aesthetic or protective purposes.
4. Conclusions From the GC/MS analysis of the four samples of the oxalate patinas collected from the stone external surfaces of the Baptistery in Parma (Italy), the levels of racemisation of the amino acids were determined. In particular, it was noted that alanine presents the highest D/L value. This indicates that ageing is not responsible - or not only - of the determined values. It is possible to think that micro-organisms were present in the patinas of the Baptistery in Parma, and that the microbial activity could have had a role on the formation of the oxalate patina, by influencing the accumulation of the organic material or modifying the pre-existent residues of lipids and proteins. In the light of these first results, it is reasonable to plan a study devoted to the evalutation of D/L amino acid ratio on a wide series of oxalate patina samples in order to understand these unaspected values. Acknowledgments This work was supported by the National Research Council (CNR) of Italy, as part of the "Progetto Finalizzato Beni Culturali". 5. References Various Authors (1989) In: Proceedings of the International Symposium "The oxalate film: origin and significance in the conservation of works of art" Milan Various Authors (1996) In: Proceedings of the II International Symposium "The oxalate films in the conservation of works of art" Milan Lazzarini L, Salvadori O (1989) Stud Conserv 34: 20-26. Casoli A, Palla G, Pignagnoli F (1997) In: Proceedings of the IVth International Symposium "Conservation of Monuments in the Mediterranean" Rhodes: 141-151 Casoli A, Mangia A (1991 ) Annali di Chimica 81" 107-117. Meyer, V R (1992) Chemtech, 22 (7), 412-417. Csapb J, Csapb-Kiss Zs, Csapb J Jr (1998) Trends in analytical chemistry 17 (3): 140148. Shimoyama A, Muraoka, S, Krampitz, G, Harada, K (1989) Chemistry Letters 3: 505508. Maroudas A, Palla G, Gil-Av E (1992) Connective Tissue Research 28:161-169. Davies, JS (1977) Chem. Biochem. Amino Acids, Pept. Proteins 4:241-99. Bruckner H, Becker D, Lupke M (1993) Chirality 5:385-392.
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UNITE T E C H N O L O G I Q U E PORTABLE ET AUTONOME DE DIAGNOSTIC ANALYSE - INVESTIGATION DE CHOIX D'INTERVENTION AVEC VIDEO ASSISTANCE A DISTANCE ET BANQUE DE DONNEES Catalafini, Ing6nieur Paris, France.
R6sum6
Elle est compos6e d'un syst6me d'61aboration informatis6e du bilan technique (DIXI II) guidant l'analyse des besoins selon une programmation pr66tablie formant un triptyque : Bilan technique - Solution technique - Banque de donn6es. Cet examen sur le site prend en compte tous les crit6res relatifs aux 616ments/~ traiter, pour aboutir/~ l'6tablissement des pr6conisations de travaux/L ex6cuter. De plus, il y a possibilit6 de dissocier les phases Bilan technique et Solution technique, ce dernier volet pouvant ~tre trai't6 ult6rieurement. Le second 616ment est l'unit6 d'assistance au diagnostic par investigation non destructive (PERSPICIO). Cette technique permet sans aucune d6t6rioration d'assister soit le diagnostic, soit le contr61e des travaux avec prises de clich6s. De plus, cet 6quipement donne la possibilit6 de faire le traitement d'images, de les enregistrer et 6ventuellement de les transmettre. Le dernier volet (NEMATOS) est une base de donn6es. Elle permet d'assister le technicien de terrain dans l'6tablissement du diagnostic, d'aider a la communication et h la diffusion de l'information. Les divers 616ments de cet ensemble peuvent &re utilis6s sans probl6me de fagon isol6e, en duo ou en totale compl6mentarit6. De plus, chaque syst6me/t la possibilit6 de transmettre ses donn6es et pour PERSPICIO celle de recevoir tousles clich6s des banques de donn6es centrales. 1. DIXI II
II traite essentiellement de la Restauration et de la Protection des monuments et b~,timents du Patrimoine culturel et historique. La conception de DIXI H, d6veloppement de DIXI I (b~timent courant) a 6t6 r6alis6 sous la forme d'un double triptyque avec possibilit6 de dissociation des phases "Analyse" e t " Solution ". L'6tude de l'interaction entre l'image et le langage (composants essentiels de l'6quipemem cognitif humain) dans le processus des m6canismes mentaux a permis la concr6tisation informatique du passage de la prise d'informations (analyse in-situ), Faction (diagnostic) et a la d6eision (preconisation de travail, tout en pr6servant la biblioth6que que repr6sente le savoir-faire pratique et l'acquis ancien. La conception de D I ~ II est bas6 sur la convivialit6 du programme et de son processus d'analyse, la r6duction du " g a p " ce fameux temps de r6ponse et la fourniture dans un laps de temps des plus r6duits des 61ements recherches.
* Author to whom correspondence should be addressed.
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1.1 - Volet I
I1 fournit/t l'utilisateur, sous la forme d'un programme "arborescent" les donnres qui lui permettent de drfinir : 9la localisation de l'ouvrage (pays, rrgion, ville). les caractrristiques de celui-ci (fonction, style, date de construction). les rrponses fournies aux postes "fonction et style" commandent l'accrs et l'utilisation automatique du voeabulaire architectural adapt6/L l'rdifice analysr. Exemple d'une rrcapitulation d'rcran : France ILE DE F R A N C E - SEINE SAINT DENIS LARCHANT EGLISE abbatiale GOTHIQUE X I I e - XIVe sircle 1 . 2 - Volet 2
C'est la phase analytique (constat d'rtat) traitre in-situ, qui permet d'effectuer la "drtermination des besoins" Cet 616ment vital est la base de toute daboration de travail; le eheminement guid6 de cette analyse prend en compte tous les facteurs necessaires b. la prise de decision. L'analyse detaillre de la pathologic des matrriaux aneiens ( e x . le torehis, le pisr, les chaux anciennes) nrcessite une dichotomie poussre. Celle-ci permet par son arborescenee de dissocier les diverses causes de drsordre, cette forme de dissrcation permet d'rviter les omissions. L'origine reelle peut dans certains cas &re occultee par d'autres causes qui prrsentent des symptrmes analogues. L'rtude cognitive des divers drments qui interviennent dans le processus d'rtablissement du diagnostic (rrponse/t la question compatible - incompatible) a drbouch6 sur une forme d'audit qualit6 qui est la base de la mise au point de la trilogie DIXI II PERSPICIO - NEMATOS. 1.21 Phase 1 - liste des ~l~ments n~cessaires /t r identification et personnalisation de ! 'ouvrage :
(1) titre, sous-titre, composant avec possibilit6 d'affinage dans la prrcision par drveloppements successifs (2) analyse du site (compris altitude et classement de la rrgion) (3) climatologie (orientation, ensoleillement, pluie, vent, gel) (4) qualit6 du milieu ambiant (temprrature, PH de l'eau de pluie, prrsence et drsignation de gaz et/ou acides) Exemple de rrcapitulation de donnres sur reran 9 - RESTAURATION - ZONE URBAINE & RURALE . Bhtiment bas- Faible circulation . Zone forestiere - cuvette boisre 9Altitude de < 400 m - zone" 1a " 9Orientation sud-est 9Ensoleillement est
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Pluie battante ponctuellement avec zone de ruissellement PH normal Vent sud-est avec r6gime de turbulence partiel Temp6rature < -5 ~ / +25 o > 9Humidit6 moyenne de l'air 75% Gel faible ou mod6re ponctuellement
1 . 2 2 - P h a s e 2 9d~finition de I ' o u v r a g e ou de l'~l~ment consid~r~
(5) (6) (7) (8)
position fonction conception (appareillage, pose, parement) travaux de restauration d6j/t effectu6s (type, envergure, pr6sence de mat6riau de substitution, ...) N.B. - M6mes possibilites d'affinage qu'au poste 1 de la phase 1. Exemple de contr61e sur un 6 c r a n - VERTICALE A GEOMETRIE VARIABLE . ELEMENTS MIXTES Plans Sculptures Statues aecol6es ou dissoci6es de la paroi El6ments cisel6s - PORTEUSE Massive constitu6e d'un seul mat6riau El6vation avec zones de rejaillissement Scellement - mortier bfitard Appareillage regl6 de longueur & hauteur Restauration ant6rieure " n6ant.
1.23 - P h a s e 3 : caract~ristiques du c o m p o s a n t en o e u v r e
(9) composant de construction Exemple de l'6cran de contr61e : - S O C L E - SOUBASSEMENTS - B A N D E A U X - ASSISES DE REJAILLISSEMENT L I N T E A U X - APPUIS Calcaire : origine CHATEAU LANDON* - LACUSTRE COMPACT Grisfitre a grain fin et serr6 Porosite contr616e 17,45 % - ELEVATION et ASSISES D ' E L E V A T I O N SOUS SAILLIES* Calcaire : origine SOUPPES - LACUSTRE COMPACT Grisfitre/t grain fin et serr6 Porosit6 contrfl6e 18,30 %
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* Pour acc6s/L la "M6moire Sp6ciale" frapper MS-P + Nom du mat6riau N.B. - La "m6moire sp6ciale "permet de conna/tre les caract6ristiques du mat6riau d'origine et 6ventuellement d6terminer la pierre 6quivalente y compris sa conformit6 avec les classements et r6glements regissant la localisation de mise en oeuvre. (10) caraet6ristiques physiques (11) identification des propri6t6s (12) facteurs d' alt6ration (13) identification de 1'aspect de surface (14) identification du firfi de surface N.B. - Poss~ilit6 d'attinage dans la pr6cision par d6veloppements successifs. Exemple d'un r6capitulatif des 616ments choisis : - DETER/ORATIONS ET ALTERATIONS NATURELLES Encrassement naturel Pr6sence de eryptogames (lichens - mousses) par zones ponctueUes 9Erosion diffus6 avec - D61avage avec siUons - Perte de mat6dau 9Exfoliation Poudroiement - Gypsification tr6s ponctuelle - D6sagr6gation pouss6e en profondeur Corrosion biologique avec formation de micro-organismes - FACTEUR D'ALTERATION - ABSENCE TOTALE D'ENTRETIEN ET PROTECTION - INTEMPER/ES - DETERIORATIONS A CAUSES ANTHROPIQUES Eclats Perte de mat6riau Incendies (tr6s ancien)
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Trait6 par l'6quipe dirigeant l'op6ration de restauration, il comporte les postes suivants : (15) processus envisag6 (*) (16) identification de l'aspect de surface (17) identification du fmi de surface (18) luminance 6ventuelle (19) travaux annexes necessaires (autres corps d'6tat) (*) une grille d'analyse par cas. En pratique, le technicien est guid6 par le "menu d6roulant de r6f6rences" 6quipant son "laptop ", qui lui sugg6re, au fur et/l mesure, les questions auxquelles il doit r6pondre. I1 examine le support et/ou le subjeetile, visualise ehronologiquement sur l'6cran de son portable les donn6es, trouve la concordance tem~ologique a ce qu'il a eonstat6, "' seroole" la ligne choisie et passe/L la rubrique suivante. Cette proc6dure est effectu6e rubrique apr6s rubrique, eas par cas. Le programme pilotant l'analyse pr6voit : toute possibilit6s de revisualisation, correction, effacement, reconduetion des divers 616ments saisis ; les contr61es de coh6rence, 61iminant ainsi les erreurs les plus communes.
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En fin de traitement d'analyse, la totalit6 des criteres choisis apparait pour v6rification et validation avant envoi des donn6es ou impression. La fiche de preconisation sortira sur l'imprimante laser sous la forme suivante : en clair et suivants les codes correspondants : les titres, sous-titres et eventuellement d6tail, les caract6ristiques retenues et les travaux a ex6cuter (Pr6paratoires et Finition). N.B. - II faut rappeler que les responsables de l'op6ration "Restauration" (au sens large du terme) ont pour prendre lear d6cision la possibilit6 d'~tre aid6s par les documents techniques fournis par l'unit6 d'investigation (PERSPICIO) au cours de la phase "' Diagnostic "(volet 2 - phase 2 et 3). -
2. PERSPICIO La vision est pour l'homme le moyen privil6gie d'examen et de comprehension des ph6nom6nes de toutes sortes (la vid6o endoseopie en est une des formes les plus 6voluees). Cette technique permet de s'affranchir d'un certain nombre d'imp6ratifs et probl6mes : 9Non d6t6rioration des 616ments contr616s ; Non annulation de preuves par manipulations diverses afin d'acceder /t la zone souhait6e. De plus, le programme informatique permet de proc6der aux diverses analyses n6cessaires au diagnostic, notamment les mesures 9 des 6missions de SO 2 / SO 3 / NO x ; du ph des pluies, de la corrosion chimique ; de la corrosion biologique ; la drtermination de la nature des constituants ; l'absorption d'eau ; la prnrtration maximale d'agent de conservation ; 9la rrduction de l'absorption d'eau aprrs traitement. Elle permet l'acc~s visuel pur les contrrles/t l'intrrieur de matrriaux ou 61ements quelconques afro de vrrifier : la pr6sence des constituants annonc,rs, lear 6paisseur et la position ; la liaison ou l'adhrrence 6ventueUe entre les divers composants, la profondeur de l'altrration ou du drsordre ; . l'homogrnrit6 du matrriau, 9la crte de pe'nrtration des produits de traitement utilisrs (consolidant, hydrofuge, ...) ; la tenue darts le temps ; . le contrrle et la localisation d'armatures quelconques (section et profondeur)/t l'aide du Ferroscan (liaison par interface standart pour transmission des donnres sur PC). Cette aide pour l'rtablissement du diagnostic Cvirce maitresse de la pathologie) peat ~tre utilisre de deux faf,o n s en ind6pendance totale ou en liaison avec DIXI II et la "banque de donnres" dans le cadre de l'assistance et du contrrle. L'observation peat ~tre effectuee de plusieurs manirres 9 visualisation classique par l'endoscope lui-m~me avec possibilit6 de prise de vue /l l'aide d'un appareil photo 24 x 36 raccorde sur l'endoscope ; . par visualisation sur ecran video avec enregistrement des cliches souhaitrs sur disque optique et possibilit6 de developpement immrdiat des images sur "video-copy ". Pour effectuer ces investigations, le matrriel offre les possibilitrs suivantes : prises de rue haute definition couleurs (rue grnrrale, gros plan, ...) ;
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contr61e d'6paisseur ; clich6s macro (< ou = xl 0) ; traitement d'images y compris impression de texte frapp6 ou manuscrit en "fausse couleur suivant nomenclature (avec possibilite d'intervention sur cliche de base par impressions diverses sur 6cran tactile ou par l'interm6diaire du clavier) : - classification et rep&age des mat6riaux mis en oeuvre (carte lithologique) ; reperage des zones d'etats superficiels des materiaux 9 coloration des d6fauts ; - colorim6trie en "fausse couleur" ; - lithologie, - reperage des zone par mode d'intervention ; nomenclature des d6ments architecturaux ; -schemas de rep~rages ; grossissement d'images ; agrandissement d'une zone d6termin6e du clieh6 avec annonce automatique du coefficient utilis6 (ex. : x 10) ; examen eomparatif d'images ; cliches divers (eolorim6trie avant et apr~s test de traitement...) ; archivage des documents sans alteration des donn6es, cliches constats de l'6tat existant, inventaire des travaux/t envisager, donn6es des diverses phases de traitement, avance des travaux, ..., - possibilit~s de ventilation en fiehier (historique des travaux, guide technique, ete .... ). Transmission td6phonique (r6seau commute, numerique ou sp6cialis6) ou par satellite des donn6es. Cette operation est realisee sans perte de qualit8 des cliches (procede de compression d'images HD - mode JPEG.2 ou 6quivalent - et protoeole ~mission r&~eption" (avee reprise 6ventuelle automatique jusqu'/l r6ception 100/100). Transcodage automatique des donnees en Pal ou NTSC selon le r6eepteur. Cette derni&e possibilit~ permet d'entrer en liaison avec une banque de donn6es (NEMATOS) soit pour la faire evoluer, soit pour y puiser des renseignements (protocole d'acees eontr61~). Cet ~quipement permet d'une part au technieien de ehantier de b~6fieier, si n&,essaire, en permanence de l'assistance technique de son central technologique (ou d'une banque de donn~s) et d'autre part r~duire le "temps de r6ponse" et le cofit. ""
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3. N E M A T O S II est bas6 sur le principe comme "le meilleur moyen d'exciter la m6moire est de frapper la v u e " (Cic6ron) et poss6de trois fonctions : 9l'assistance technique ; la formation professionnelle ; l'information (banque de donn6es) Le pfincipe de base est la simplicit6 d'accks Apr6s armonce du code d'entr6e, recherche du clich6/~ l'aide des 616ments de la codification DIXI II : codes eomplets du support ou du subjectile et du d6faut, la photographie apparait imm6diatement. En cas de doute en ce qui conceme le d6sordre, r annonce des deux (2) ehiffres de gauche du code fait apparaitre/l l'6cran la nomenclature des rues disponibles, apr6s le choix du cas qui convient et et scroolant"/L l'aide du curseur d'6cran le clich6 demand6 appara/t ""
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La classification des documents est 6tablie avec plusieurs entrees par: mat6riau, alt6ration ou d6sordre, technique de remise en 6tat, monument. D'autres possibilit6s d'aec6s peuvent &re etudi6es en fonction des besoins. Les donnees n6cessaires /l l'identification du document se presentent de la fa~on suivante: en surimpression /L la base du clich6 la codification complete; sur simple " s c r o o l " l'image r6duite appara/t avec en regard la traduction totale du code, ce qui annule tous problemes de transcription et d'interpretation, la base de donnees m6moris6e 6tant au depart traduite dans la langue du pays. L'evolution de la banque documentaire est simple, compte tenu du cha/nage pr6vu avec le syst6rne "DIXI I I " et la technique "PERSPICIO ". Toute demande 6mise, d6clenche l'intervention d'investigation non destructive, provoque en aval la mise en memoire des nouveaux renseignements, dans la mesure 06 leur utilit6 g6n6rale est admise. Le principe fonctionne dans tous les cas d'intervention "diagnostic ou contr61e"
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LARGE SCALE EXPERIMENTAL FACILITIES AT ENEA FOR SEISMIC TESTS ON STRUCTURAL ELEMENTS OF THE HISTORICAL/MONUMENTAL CULTURAL HERITAGE G. De Canio ENEA CR Casaccia, V. AnguiUarese,301 00060 S.M. di Galeria - Roma- Italy
Abstract
The two experimental campaigns shown in this paper are representative of the shake table test activities at ENEA for the seismic protection of the historical-monumental structures. The scope of these experiments is the study of innovative systems for the seismic isolation and retrofitting of the civil, industrial, and historical buildings, together with the seismic tests of sub-structures and scaled mock-ups to evaluate the isolation/dissipation parameters of the anti seismic devices, and the identification of the failure modes of the typical structural elements of the various architectonic styles to define the proper restoration techniques. Keywords: Vibrations, Seismic tests, Shake Table, Modal Analysis. 1. Introduction
The scientific community involved in the geophysical sciences always points the importance of preventive interventions to mitigate the devastating effects of strong earthquakes. The technological complexity and the interconnections between different sectors of the modem society ( strategic centers, power plants, surgery rooms, etc...) needs a new approach to the seismic problem: to cohabit with earthquakes. That is, the structures must be safe and efficient during the seismic events. This is also important for the historical-monumental buildings. For many of them, representing inestimable cultural richness of the whole humankind, is imperative the preservation against the damages due to natural or technological events (aging, floods, fire, earthquakes...) to handle safe to the future generations. The restoration interventions of monuments shouldn't be simply peaches to repair the damages, they must also reduce the risk of damaging when events occur. Furthermore, the choice of materials and techniques for restorations must take into account the general principles of Compatibility and Reversibility of the Venice Charter. This necessitate studies for the knowledge of the original materials, their physical and chemical evolution in time, and the static and dynamic characterization of the whole monument together with its structural parts for the reduction of the seismic risk. Only the knowledge of the real damaging mechanisms of the structural elements allows to define the proper restoration and retrofitting intervention to increase the structure global performance under seismic loads. These are highly specialized operations, requiring the contribution of different scientific disciplines for the in-situ and laboratory tests on material samples and structural pans, with the support of large and well equipped laboratories.
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2. Two examples of Seismic test campaigns
The main experimental facilities for seismic tests at the ENEA C.R. Casaccia laboratories consist of two high performance six-degree-of-freedom shake tables ( see the appendix A) for three axial seismic tests of large specimens representative of structural elements of the historical/monumental cultural heritage. The shaking table tests can simulate the real stress fields in the structures during the dynamic loads induced by wind, traffic and earthquakes. The shake table experiments of full scale structural elements takes into account the intrinsic non-linear effects in the real structures, inducing the real distribution of the stresses and the real mechanism of cracking. Large experimental facilities are need to apply the required amount of earthquake energy at the base of specimens representative of the structural elements ( waiting many tons) of the historical structure. 2.1 Test on a Roman Arch
The first example of research activity carried out for historical structures is the test campaign on a full scale mock-up of a Roman Arch ( see the Fig. 1).
Fig. 1. Mock-up of the Roman Arch and selected measurement points The confrontation of it's structural responses during the earthquakes before and after the repairing interventions gave the required information to the effectiveness of the restoration technique. The test campaign was performed in collaboration with the University of Napoli and the "Sovrintendenza Alle Belle Arti di Caserta" SBAAS. The masonry arch is a characteristic element of a Cultural Heritage Structure, with almost identical behaviors since from Roman time. The tests verified that the collapse mechanism may occur by buckling of the voussoir and plastic hinge formation due to the tensile stresses. The verification of the real mechanism of cracking for the specific mock-up allowed to prepare the optimal consolidating intervention. The increased performance of the arch during the seismic tests after the consolidation showed its benefits. The figs. 2a and 2b show the numerical simulation of the mechanism responsible of the keystone plastic hinge formation due to the out-of-phase oscillation of the abutment walls.
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Fig.2: Plastic hinge formation mechanism at the keystone The fig. 3 shows the reference time history (W-E component of the Sturno, Italy-1980 earthquake ) applied at the base of the arch by the shake table. The time history have been scaled up t o - 1 2 d B to perform the test sequence of 0.1 g step. Fig.3:Calitri,1980
earthquake.
E-W
component
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Fig. 3: E-W component of the Calitri earthquake, Italy 1980: base table acceleration- tests T1A, T1B and T1C (chn 6 data record). A random characterization have performed before and after each seismic test to look at the frequency contents of the response spectra, indicative of the crack formation. Three groups of experiments, using two Roman Arches full scale mock-ups ( Arch N~ and Arch N~ have been performed. The first two groups - group A and group B - were relative to the Arch N~ with 14.1 KN overweight in the original ( group A) and consolidated ( group B) configurations. The group C tests were relative to the Arch N~ consolidated with concrete injections. The tables 1 and 2 summarize the test sequences A, B, C. The test identification rules are: test CR1 A = Test N ~ 1 - Random Characterization - Test Group A test CS 1 A - Test N ~ 1 - Shock Characterization -Test Group A test T1 A - Test N~ - Seismic test - Test Group A
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Table 1 "test Test name CR1 A CS1 A T1A T2 A T3 A
CR1 B CS 1 B T1 B T2 B T3 B T4 B T5 B T6 B T7 B T7B,..T16B
sequence for the Time History Random Half sine W-E Sturno " "
Random Half Sine W-E Sturno " " " " " "
Table 2: test sequence for the Test Name Time history CR1 C Random CS 1 C Half Sine T1C,..T20C W-E Sturno
Roman Arch N ~ 1 with 14.1 KN overweight. Max g ARCH N ~ 1 Random Characterization test 0.01 0.1 Shock impulse 0.087 0.174 Cracks at the keystone, at the 0.261 springing and at the base of the abutment walls. Consolidate the arch and continue to the group B tests 0.01 Random Characterization test 0.1 Shock Characterization test 0.087 0.174 0.261 0.348 0.435 0.522 0.609 Formation of large fractures 0.69...1.4 Test sequence until collapse Roman Arch Max g 0.01 0.1 0.087...1.9
N ~ 2. ARCH N ~ 2 Random Characterization test Shock Characterization test Test sequence until collapse
The figs 4, 5, 6 represent the top wall (chn 16) and keystone (chn 18) accelerations recorded during the tests T1A, T1B and TIC ; the fig 7 shows the chnl8 (keystone) Frequency Response Spectra measured during the tests T1A, T1B (Arch N ~ 1 ) and T1C (Arch N ~ 2 ). The max peak accelerations and amplification factors are summarized in the tab.3. Table 3 9Max acceleration values reached at the Top Wall and Keystone. Test Name Max g Top wall Peak Keystone Peak T1A 0.087 0.31 0.11 T1B " 0.32 0.12 TIC " 0.32 0.14 Test Name Csl A Cs 1 B Csl C
Max g 0.1g " "
FRF 10. 8.8 8.6
Freq Hz 4.5 3.2 11.5
FRF 6. 5.3 5.1
Freq Hz 4.5 3.2 11.5
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Fig.4: Test TIA, Chn16= top wall, Chn 18= keystone
Fig.5: Test TIB, Chn16= top wall, Chn 18= keystone
Fig.6: Test TIC, Chn16= top wall. Chn 18= kevstone
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Fig. 7a: Frequency Response Function
Fig, 7b: Frequency Response Function Reference= chn6 (Base), Response= chn18 (keystone)
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The following sequence shows the plastic hinge formation at the keystone and the collapse mechanism of the Arch N ~ 2 during the group C tests.
Fig. 12 9Collapse III^
Fig. 13" Collapse IV ^
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Fig. 14: Collapse V ^
Fig. 15: Collapse VI A
2.2 Test campaign of a mock-up representative of a Church "timber" During the period March-July 1999 two test campaigns on a couple of structural elements of masonry walls up to 4.5m high have been performed ( see the figs. 16 17 ) . The experiment was performed within the Environment project ISTECH ( proj. N ~ ENV4CT95-0106).
Fig.16 : Construction of the Twin walls with conventional and SMA devices
Fig. 17 : FEM model of the twin walls showing the stress fields at the base and at the attachment of the conventional and SMA devices
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The twin walls were representative of a "timber" anchored at the church facade. The usual consolidation technique for a timber consists to anchor at the church facade using steel bars. During an earthquake event, such a timber is subjected to overstresses at the bar insertions, where often fractures occur. In this experiment the two walls were anchored at the steel frame structure ( see the figs. 16 and 17) simulating the church body with conventional and Shape Memory Alloy (SMA) devices respectively. To compare the performance of the SMA and the conventional devices, the two structures were tested together on the shake table, with the same seismic input at the base. The scope of the test campaign was to verify the reduction of overstresses in the timber anchored with SMA devices, due to the allowed small oscillations of the timber dissipating seismic energy. The following signals have recorded during the tests: Tab. 4: Sensor locations and identification rules L1,. .... ,L6 LVDT Displacements at the locations 1,...,6 of the wall with conventional devices (left wall) LS 1...... ,LS6 LVDT Displacements at the locations 1,...,6 of the wall with SMA devices (right wall) C7, C8, CS7,CS8 Load cells at the locations 7, 8 of the wall with conventional and SMA devices respectively. The figs 18-19 show their position on the two walls.
Fig. 18 Front view
Fig 19 rear view
The left wall was anchored to the steel support structure by SMA devices, the right wall was anchored with conventional devices. The load cells CsT,Cs8 and C7,C8 measured the
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
dynamic loads, and the LVDT's Ls7,Ls8 and L7,L8 measured the horizontal displacements. The SMA devices were made by FIP Industriale S.p.A. ,Padova, Italy. The fig. 20 show the details of the attachment points.
Fig. 20: Attachment of the SMA devices at the wall. As a first step of the experimental campaign, a modal analysis test using the impact hammer method was performed to evaluate the modal frequencies, damping and residuals. In this experiment a " one-impact / two-measurement points" test configuration was used for two reasons: i. To hammer at the top of the wall in order to minimize the impact energy requested for the excitation of the lower vibration modes of the structure. ii. To distribute the energy uniformly, using the concrete reinforcement on the top of the wall as impact zone. The response signals at the two-measurement points A2, A4 and AS2,AS4 were used for the FRF analysis: FRF-44 = Acc-A4/Force-4 FRF-24 = Acc-A2/Force-4 Tab.7 Time history analysis of the wall A : FRF-44 Location Sensor Peak RMS 1st Freq Point $4 AS4 .0206 g .00173 2.5 Hz Point $4 Force 330N Tab. 8 Time histor) Location Sensor Point $2 AS2 Point $4 Force
isis of the wall A : FRF-24 Peak RMS 1st Freq .6 g .092 2.5 Hz 495N -
2 nd Freq
% damp
18.75Hz
.0186
2 nd Freq
% damp
18.75 Hz
.0145
Log. Decr .117
Log. Decr .0914
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The following parameters were evaluated during the Modal Analysis tests: the first 3 peaks of the FRF Inertance Iik between the point i and the point k (eq. 1), the modal constant rAik of the r th mode (eq. 2) and the resonance amplification factor rQik of the r th mode (eq. 3) Iik = Acc.i/Forcek (1) rAik = l likl • 2~r / 0~r
(2)
rQik = 2~/mr
(3)
The modal damping ~r was evaluated using t h e - 3 d B method at the resonance frequency fr = 2n0~r. The tables 7-8 show the principal modes detected and the modal constants" Tab. 7 FRF-44 fr
I44
~r
rA44
rQ44
2.5 Hz 6.375 Hz 18.7 Hz
.498E-3 .288E-3 .888E-3
.0375 .098 .0083
.374E-4 .564E-4 .148E-4
13.3 5.1 60.
fr
I24
2.5 Hz 18.7 Hz
.885E-2 .443E-1
~r .0375 .0083
rA24 .663E-3 .738E-3
rQ24 13.3 60.
1st Mode 2 nd Mode 3 nd Mode Tab.8 FRF-24 1st Mode 2 i nd Mode
The two main flexural modes occurs at 2.5 and 18.7 Hz. The cross and point FRF agree with the frequency, damping and Q-factors values. The resonance at 6.3 Hz is evident only in FRF-44 due to the higher energy at the top of the wall where is positioned the accelerometer AS4. The second series of experiments were the seismic tests using a modified EC8-BGS synthetic time history, with uniform frequency contents of the response spectrum in the range of 0.5-15 H z . Tab.9 Test sequences and test identification rules: Test name Table acc. g Wall anchored using SMA devices BN0 +0.09/-0.06 ok BN 1 +0.17/-0.18 ok BN3 +0.36/-0.41 ok BN4att +0.51/-0.58 ok BN4 +0.56/-0.65 ok BN5att BN5
+0.68/-0.72 +0.77/-0.83
Wall anchored using conventional devices" ok ok ok ok Fracture in the wall in proximity of the flanges. ok Fracture in the midle ( fig. 21) Remove the upper corbel (see fig 22) ok wall destroyed ( figs. 23,24,25)
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
Fig. 21: Walls ready to be tested
Fig. 23 : Test BN5
fig. 22 : Corbel fracture
Fig. 24: test BN5
The Fractures in the wall anchored with conventional devices during the test BN5 are evident in the figs 23 and 24. A more extensive experimental campaign is proposed by ENEA for the verification of the restoration techniques ( conventional and innovative) for the different type of structural elements representative of the different architectural styles. The knowledge of these mechanisms allow to define the more appropriate consolidation technique for the structural elements of the monuments representative of the various historical periods. The following table shows a partial list of some typical structural elements with a short description of the principal mode of failure and the conventional consolidation strategies:
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Table 9: Damage mechanism of typical structural elements Structural element Typical damage mechanism
577
Type of intervention
1. Columns
Overturning, Rocking motion
Collars, long. strips
2. Arches
Buckling, splitting at the plastic hinges
3. Vaults and Domes
Outward pushing of the supporting piers, splitting at the connecting arches, drop of crowns, radial cracking due to the span
4. Walls and piers
Separation of blocks, Original weak mortar, sliding of the bed joints for out of plane loads, cracks at the base of timbers, hamming of the roof beams Cracks due to bending and/or shear loads
Steel cables, epoxy injection, metallic nets Steel cables for the span containment, metallic nets, prestressed tendons. Re-j ointing, rebonding, new key blocks, grouting injection, anchorage Reinforcement, load redistribution
6. Buttresses
4. Conclusions The 6DOF Seismic tables at the ENEA Casaccia laboratories are one of the biggest high performance technological facilities in Europe for the seismic tests. They are at the service of the Scientific Community, the Universities and the industries for the research programs which increase the knowledge for the prevention of the damaging effects of the earthquakes on civil, industrial and historical-monumental structures.
5. acknowledgment Many thanks to A. Baratta, G. Bongiovanni, P. Clemente, D. Rinaldis for the arches campaign, and A. Bonci, M.G. Castellano , M. Forni, M. Indirli, A Martelli for the ISTECH campaign. Particular acknowledge to the staff of the ENEA INN-TEC-DIN laboratories for their contribution to the test activity : M. Baldini, A. Cenciarelli, F. Di Biagio, M. Guglielmucci, A. Picca, B. Rapone, S. Spadoni, A. Terrusi. APPENDIX Characteristic of the ENEA Shaking table: System 1 4m x 4m Table size 6 DOF Degree of Freedom Frequency range 0-50 Hz Acceleration 3g peak 0.5 m/s (0-peak) Velocit7 Displacement 0.25 m (0-peak) mass and G.C. height 10 ton mass for rigid specimen lm c.g height
System 2 2m x 2m 6 DOF 0-100 Hz 5g peak 1 m/s (0-peak) 0.30 m (0- peak 1 ton mass 1 m c.g.height
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EVALUATION OF STONE PORE SIZE DISTRIBUTION BY MEANS OF NMR. Marcella Alesiani, Silvia Capuani, Francesca Curzi, Laura Mancini, Bruno Maraviglia* Department of Physics, University of Rome "La Sapienza", and INFN, P.le A.Moro 2, 00185 Rome
Abstract.
NMR is a very useful technique that exploits magnetic properties of atomic nuclei with spin quantum number different from zero when they are in an external magnetic field. By studying the time length needed for the spin system magnetization to reach the equilibrium value after a selected perturbation, we obtain plenty information on the energy exchanges between the system and its surroundings. Therefore, by means of NMR we can study the interactions between the pore walls and the hydrogen nuclei of water molecules trapped in the stone porous structure, aiming to determine the chemical-physical properties of the porous matrix. We will present the results of a relaxation data elaboration designed with the goal of non-destructively determining the pore size distribution function in samples of carbonated stones. Our technique consists in the comparison of the experimental relaxation data with the data obtained from a simulated porous system. By the minimization of the differences between the functions describing the systems' magnetization relaxation we obtain the stone most probable pore size distribution. Recently, moreover, it has been demonstrated that by means of the MSE (Multiples Spin Echo) sequence it is possible to obtain very detailed information on the porous system examined. This technique has been employed particularly on bone samples to evaluate the trabecular bone dimensions. One of the possible developments of this research line could be the employ of this sequence to study the stone porosity. Key words: pore size distribution, porosity, NMR. 1 Introduction.
Determination of porous matrix properties in natural porous stones is a very important goal in the Cultural Heritage conservation field. Porous structure of a natural stone depends on its genesis and on its particular history (natural and artificial processes happening in time) and strongly determines employing characteristics and durability of the material itself. Most of the studies on porous structure, in the Cultural Heritage conservation field, concerns building materials as natural stones, bricks, concrete, mortar and ceramic materials. This choice is based both on the high utilization and on the greater alterability depending on their outdoor exposure. Besides the original porous matrix characteristics, natural aging and artificial conservative treatments strongly modify the original porous structure and reduce durability. It's therefore clear that porous structure study is basically important and extremely useful for the alteration phenomena comprehension, mostly when it is conducted in parallel with the study of other material properties. * Author's to whom correspondence should be addressed.
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
In this paper we present the results of the application of the NMR technique to non destructively determine pore size distribution function on samples of Carrara marble, Candoglia marble and travertine. 2 Materials and methods.
In this study quarry samples of three material categories, two marbles and one limestone, have been compared with samples treated with three different agents, usually employed in the Cultural Heritage conservation field: 9 a consolidating, adhesive and binding agent (commercial label: Paraloid B72 (m) composed by a meta- acrylate and ethyl- acrylate copolymer; 9 an hydrophobic protective and pre- consolidating agent (commercial label" Fluorophase(m), composed by a fluorinated copolymer of vinylidene and esaphluoropropene; 9 a hydrophobic protective no- film agent (commercial label: Hidrophase(R)), composed by alchyl, alcoxy silanic chains. Since nuclear magnetic resonance is a technique that exploits magnetic properties of nuclei with spin quantum number different from zero in an external magnetic field, we employed water as a contrast agent to visualize the porous structures of lapideous materials. Samples, whose dimensions were 5x5x2 cm 3, absorbed water by capillarity from filter paper as suggested by the Normal Recommendations 80/15. Experimental results here reported, were obtained by using the tomographicspectroscopic system Bruker Biospec BMT 70/15 composed by a superconducting magnet generating a 7.05T static magnet field and by a number of electronic components controlled by an Aspect 3000 computer with an Adakos operative system. The elaboration of the longitudinal magnetization decay curve to obtain the best fitting pore size distribution function has been separately performed on a PC Pentium II with a proper designed program running under Mathematica (R). Although the original idea has were proposed and employed by Packer and Davies [S. Davies, K. J. Packer, D. R. Roberts, & F. O. Zelaya, 1991; S. Davies & K.J. Packer, 1989; S. Davies, M. Z. Kalam, K.J. Packer & F.O.Zelaya, 1989] in the Fortran POREFIT program, the exigency of evaluating porous structures with dimensional scales very small (shorter then micrometer) requested a more detailed analysis of the technique, which produced the results reported in this paper. 3 Theory. One of the most frequently observed experimental effects of the interaction between rock and a fluid confined within its porous structure is the shortening of nuclear magnetization relaxation times which jointly appears with a multi- exponential magnetization decay. To explain such experimental evidence, at the end of 70'es Brownstein and Tarr [K. R. Brownstein, C. E. Tarr, 1976] developed a general model, exclusively depending on the volume properties of the fluid. They adopted the classical approach to the magnetization diffusion by Bloch and Torrey, in which m(r,t) is defined as a magnetization density fulfilling the following differential equations: D V 2 m = Om Ot
0)
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
581 (2)
(D x nVm + Pm)s = 0
The former concerning the pore volume, while the latter is a bonding condition at the pore surface considering the superficial relaxation effect p. D is the fluid self diffusion coefficient. Relaxation of the magnetization M(t) is therefore:
M(t) = m(r,t)V
(3)
with the starting condition:
m(r,O) = M(0____~)
(4)
V
The general solution is a sum of geometry dependent normal modes. These modes, dependent on m too, assume the following form: t
M(t) = Mo ~ i, e ro
(5)
/7
here In and T, are determined by the molecular self diffusion coefficient D and the m mean value at the surface. We assume that relaxation time of a fluid confined in a pore is determined by the volume and surface fluid relaxation, by the presence of paramagnetic impurities acting as relaxation sinks, and by the diffusion inside the pore. The most interesting feature of these normal modes is their dependence on pore dimensions. General solution for the longitudinal magnetization equation can therefore be expressed as the following: t
M_ (t) = M 0 (1 - 2)--' I/Te r, )
(6)
7l
With the Brownstein and Tarr model, it is possible to analytically calculate relaxation results in cylindrical, planar and spherical pores. 4. Model and results.
Regarding symmetry considerations, we concentrated on spherical pores with radius 'a' for whose intensities and temporal constants Ii and Tli are given [P. T. Callaghan, 1991 ]. We furthermore assumed connections between pores so small to allow considering independent pores. Assuming that P(a) is a theoretical pore size distribution function, signal from pores whose radius ranges from 'a ~ to 'a+da' is proportional to the volume:
47ro2P(a)da
(7)
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
By integrating on all possible 'a' values, we obtain, for the magnetization, the expression: t
I4~2P(a)~I,(a)e ro-(a~da M(t)=M o 1 - 2
(8)
N
With the normalization factor
N= I47cP(a)da
(9)
It is actually evident the possibility of obtaining an estimate of P(a) from the analysis of experimental data concerning the longitudinal magnetization decay. P(a) is different from zero only for positive values of the radius 'a'. We assume that is given as a sum of two lognormal distributions, whose parameters are iteratively varied to calculate a theoretical magnetization value to be compared with the experimental one, with the aim of minimize the difference between the experimental and the theoretical value of the magnetization. Limiting the sum to two factors mainly means that we argue from the experimental decay curves that water is trapped in pores of two mean dimensions in the sample examined. The results are reported in the following tables (tab.l, tab.2, tab.3), where ai and si indicate the dimension mean value and the standard deviation of pores containing water molecules, whose relaxation provides the experimental NMR signal.
Table (1), mean values and standard deviations of pore size distribution function in Carrara marble. Sample al (m) sl(m) a2 (m) s2(m) Quarry Hidrophase Fluophase Paraloid
9.54x 10 .9 6.60x 10 .8 5.08x 10 .9 1.86x 10 .7
9.16x 10 -16 1.29x 10 14 4.20x 10 16 5.08x 10 14
1.13x 10 .5 1.07x 10 .5 1.13 x 10 .5 9.23x 10 .5
5.86x 10 -11 5.18x 1fill 5.91 x 10 -)1 9.63x 10 16
Table (2), mean values and standard deviations of pore size distribution function in Candoglia marble. Sample al (m) sl(m) a2 (m) s2(m) Quarry Hidrophase Fluorophase Paraloid
1.05x10 -1~ 4.25x 10 1~ 1.39x10 1~ 2.77x10 -1~
2.29x10 -18 1.52x 10 -17 3.50x10 18 8.62x10 -18
1.24x10 -5 1.20x 10 .5 1.22x10 5 1.21x10 -5
7.02x10 -11 6.60x 10 11 6.86x10 -11 6.70x10 -11
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Table (3), mean values and standard deviations of pore size distribution function in travertine. Sample al (m) sl(m) a2 (m) sz(m) Quarry Hidrophase Fluorophase Paraloid
1.25x 10 -7 1.00x 10 -7 1.00x 10 .7 1.82x 10-7
4.25x 10"14 3.45x 10-14 3.25x 1014 8.69x 10 14
9.61 x 10-6 9.43x 10 -6 9.60x 10 .6 8.81 x 10 -5
4.41 x 10 11 4.34x 10 -11 4.44x 10 -ll 3.86x 10 -ll
We also report some plots (Fig.l, Fig. 2) of the pore size distribution function. For each material we plotted the pore size distribution function for the quarry and the treated samples. Since the curves have different scale factor, we report for each material two plots representing pores with dimensions of the order of micrometers and nanometers.
ai[m] Fig. 1. Pore size distribution in travertine samples. On abscissa we report the radius value expressed in meters. The quarry sample is represented by (a), (b) Hydrophase, (c) Fluorophase and (d) Paraloid treated samples respectively. The application of treating agents causes a substantial variation both on dimensions and on the ratio of small to large pores.
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Fig. 2. Pore size distribution in travertine samples. On abscissa we report the radius value expressed in meters. The quarry sample is represented by (a), (b) Hydrophase, (c) Fluorophase and (d) Paraloid treated samples respectively. 5 Conclusions.
Although the order of magnitude of these data fits the one of the mercury porosimeter, we want to underline the great difference between the two techniques: while the former is more properly sensible to the pores containing water, the latter describes the porous structure geometry. Moreover, the NMR data based analysis is totally non-destructive and is representative of the critical regions where water can be dangerous; data from other techniques, also if more complete and detailed regarding the total open porosity, do not allow establishing a correlation between the material properties and the real degrading mechanisms. This original characteristic of the method here proposed allows a more useful analysis of the material conservation degree and a pointed conservative treatment. Preliminary results, based on the application of non linear NMR methods, have demonstrated in our laboratory a strong sensitivity to pore size distribution, specially in the large scale side. Other measurements are being taken in these days and a deeper theoretical analysis is currently under development. All these results will be part of our report. 6 References.
S. Davies, K. J. Packer, Pore- size distributions from nuclear magnetic resonance spin- lattice relaxation measurements of fluid-saturated porous solids.I. Theory and simulation. J. Appl. Phys., 67, 3163 (1990) S. Davies, K. J. Packer, D. R. Roberts, F. O. Zelaya, Pore- size distributions from NMR spin-lattice relaxation data. Mag. Res. Imag., 9, 681 (1990)
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 S. Davies, M. Z. Kalam, K.J. Packer & F.O.Zelaya, Pore-size distributions from nuclear magnetic resonance spin- lattice relaxation measurements of fluid- saturated porous solids. II. Applications to reservoir core samples. J. Appl. Phys ,67, 3171 (1989) K. R. Brownstein, C. E. Tarr, Letter: relaxation time versus water content: linear or non linear ? Science, 194, (4261) 213 (1976) P. T. Callaghan, 'Principles of Nuclear Magnetic Resonance Microscopy' Clarendon Press, Oxford (1991)
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NEW RESULTS IN THE APPLICATION OF INNOVATIVE EXPERIMENTAL TECHNIQUES FOR INVESTIGATION OF STONE DECAY'S PROCESSES
Rodorico Giorgi and Piero Baglioni* Department of Chemistry and Consortium CSGI, University of Florence, via Gino Capponi, 9 50121, Florence. Marcella Alesiani, Silvia Capuani, Laura Mancini, Bruno Maraviglia Department of Physics and INFN, University of Rome "La Sapienza", Piazzale A.Moro, 51 00185, Rome, Italy.
Abstract
Water penetration whitin the stone porous structure is one of the main reasons of the stone deterioration and superficial degradation. Nuclear Magnetic Resonance Imaging (NMR Imaging) allows obtaining high-resolution images of water contained inside the porous sample without damaging it. NMR Imaging is also the only one technique able to provide in a non-destructive way precise descriptions of the water penetration and distribution in porous stones. We present high-resolution images obtained with a detailed study conducted by NMR Imaging on samples of marble and travertine. For each of these materials we compared samples both from quarry and treated with commercial products usually employed for the consolidation and the protection of degraded stones. The study has been performed on 5x5• cm 3 samples that absorbed water by capillary pressure from filter paper. Natural absorption conditions following standard laboratory methods for imbibition by capillary pressure were used in this study, instead of examining vacuumed samples. The stones under investigation, composed of calcium carbonate (over 99%), consist of a structured porous matrix characterized by small pores in which water is strongly trapped as shown by the considerable amount of water retained and heterogeneously distributed as revealed by NMR Imaging. Furthermore, in this paper we present the preliminary results obtained by scanning electron microscopy with an EDX system for the study of decay's mechanisms. The mapping of 'element probe' by SEM-EDX system for microanalysis provides information on the distribution of organic resins in the first layers of porous structures. Such information was, so far, unavailable. Keywords: NMR-imaging, stones, porosity, tomography, water-distribution, polymeric resin, SEM-EDX.
1. Introduction
The water amount within plaster or porous stone is the most powerful origin of decay of the historical and artistical materials. In fact, the environmental relative humidity is the parameter involved in most of the degradation processes in the porous matrix (Mora P. 1984; Honeyborne D.B., 1990). Then it is very important to study the dynamics of processes involving water, because this is crucial to understand the best operative choices in restoration. Even if many papers present remarkable studies on degradation effects due to * Author's to whom correspondence should be addressed
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
water content in porous matrix, so far very few studies have dealt with the decay mechanism. In fact, there is no general model to describe the time evolution of porosimetric characteristic, under the common environmental conditions. The performance and the durability of materials are strictly related to their porosimetric properties. These parameters are fundamental because all system's properties are related to them. We can get information on the pore size distribution function, total porosity, and surface area by various porosimetric techniques, that unfortunately are usually destructive. The existing procedures have brought to a deep knowledge of decay processes, but the results have not been set in the framework of a complete pore coalescence theory. The processes of ageing originate variations in the values of porosimetric parameters (Rossi-Doria P. 1976; Hatsagorian Z., 1985); moreover the application of restoration products, in particular of organic nature, seems to be at the origin of further degradation processes. The products used for consolidation and protection of stones belong to various chemical classes, but usually we deal with organic polymeric resins, that may originate some physico-chemical incompatibility with the inorganic substrate. In particular, in the 60's they have been widely used and nowadays we can observe the effect of degradation of organic resins, on top of the common decay processes of stones. A more complete investigation of porosimetric characteristic of stone is then necessary, and in particular a deep study of the activity of polymeric resins into porous matrix. The full understanding of decay's processes is possible only by developing new experimental techniques. In this review, we give a contribution on the study of the dynamics of decay's processes by the application of innovative methodologies. We present our preliminary results obtained by NMR tomography (Imaging method) that allows us to obtain information about the porous structure of stone, and by Scanning Electron Microscopy with EDX (Energy Dispersive X-rays) system for microanalysis. We have applied the last one for the 'mapping' of the polymeric resins as a function of Cartesian co-ordinates, by checking the proper 'element probe'. We must underline that the NMR technique is absolutely nondestructive; as a matter of that we simply used water as contrast agent. The latter is destructive, and it is necessary to remove samples of 1-2 mm 3. 2. Theoretical principles NMR by the Imaging method (De Luca F. 1982) is a very useful technique that exploits nuclear spins in an external magnetic field. When a system of protons is placed in an external magnetic field, the sum of all protons' spin magnetic moments gives rise to a macroscopic magnetisation vector. The magnetisation vector revolves (or evolves) around the axis of the external field. By means of short resonant radio-frequency pulses it is possible to rotate the magnetisation vector until it forms pre-established angle(s) with the static field direction. The measure of the length of time, needed for the magnetisation to reach the equilibrium value, provides information on: (i) dynamical properties of the proton-system (by the spin-spin relaxation time called T2) and (ii) the energy exchange between the spin system and the confining structure (by the spin-lattice relaxation time and spin-spin relaxation time called T~). Our attention is focused on the water molecules, specifically, the hydrogen nuclei contained within it. Each hydrogen nucleus consists of a proton with a stated spin value. This allows us to get info on: (i) the relaxation times of hydrogen nuclei of water molecules absorbed by capillarity in the porous materials; (ii) the pore size distribution of the samples; (iii) the high-resolution images of water distribution in the volume sample. Water molecules in the thin liquid layer in contact with the pore walls exhibit a slow dynamic corresponding to short relaxation times. The bulk molecules lying in the centre of the pore space are free to
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
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diffuse and exhibit longer spin-spin relaxation times. The analysis of the spin-spin relaxation times distribution provides information on the distribution of the pores volume. Moreover, when a proton system is confined in a porous heterogeneous structure, the proton's magnetisation reaches the equilibrium value with different time constants. These time factors are related to the surface dimensions of the pores with which the system exchanges energy. In small pores the interactions with the pore surface causes a rapid energy exchange, which results in a short spin-lattice relaxation time. In bigger pores slower energy exchange generates longer spin-lattice relaxation times. The analysis of the spin-lattice relaxation times-distribution provides information on the number of small and large pores containing the proton system. In a Scanning Electron Microscope (SEM) the image is formed in a cathode ray tube synchronised with an electron probe as it scans the surface of an object. The resulting signals are secondary electrons, backscattered electrons, characteristic X-rays, Auger electrons, and photons of various energies. Interpreting scanning electron micrographs is different from interpreting images formed directly by bending light or electron rays from object to image. The SEM indirectly constructs a pattern or map that can be interpreted as an image of the object. When a n electron beam impinges on a solid, X ray photons may be emitted by core scattering, manifested as a continuous background of X rays and innershell ionization, which yields the characteristic spectrum of X rays. We can detect the signal of an 'element probe' from the analysis of the energy emission, in such way we get an elementary microanalysis of the surface. Furthermore, we can obtain by means of a proper software the mapping of the 'element probe', along with the different directions in the space, in this way we can build the distribution map of the element (Rochow T.G., 1994).
3. Experimental section In our study we have selected some carbonated materials as Carrara marble, Candoglia marble, travertine. The stones are characterised by a calcium carbonate (calcite) content over 99% and without heavy metals impurities. These stones come from quarry. All the surfaces were treated by commercial products usually used for consolidation and protection of degraded materials. The application was executed by brush. The applied products were: Phluorophase, Hydrophase, and Paraloid B72. The first one is a fluorinated copolymer of vinylidene and esaphluoropropene, made by | used as hydro-repellent protective. The second one is a protective constituted by alchyl-alcoxy silanic chains, made by | The last is a consolidating agent (made by Rhom & Haas) constituted by a copolymer of ethyl-acrylate and meta-acrylate. The stone samples were treated in the same way. According to the commonly employed procedures, we have applied the following amount of consolidating agent: 2.58 mg/cm 2 of Paraloid B72, 0.50 mg/cm 2 of 2 Phluorophase, 0.09 mg/cm of Hydrophase. After 3 month we carried out our measurements. The NMR experimental results were performed by the spectroscopic and tomographic system: Bruker Biospec BMT 70/15 in which a super-conductive horizontal magnet generates a static field of 7.05 Tesla, in a cylindrical region, 20 cm in length and 15 cm in diameter. An Aspect 3000 computer, with Adakos operative system controls the electronic components. The NMR experiments require that all samples absorbed water by capillarity up to saturation, from filter paper. The samples were put in contact with water reservoir for 12 hours. The selected materials have very low values of total porosity (Candoglia marble:
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2.4%; Carrara marble: 3.2%; travertine: 5.5%). The water amount adsorbed by pression capillary is 0.07% in water/sample (w/w) for Candoglia marble; 0.09% for Carrara Marble; and 0.4% for travertine. The study has been performed on 5xSx2 c m 3 samples and the medium weight of the samples were 126g for Candoglia marble, 137g for Carrara marble and 120g for travertine. The software created for the elaboration of magnetic parameter data, in order to obtain information on the pore size distribution, is based on the Brownstein-Tarr model of magnetisation diffusion inside a porous matrix (Brownstein K.R., 1979; Davies S., 1990) The basic idea considers that the connections among pores are small. In this assumption the magnetisation signal measured is proportional to the water volume contained in each pore. Based on the results of the spin-lattice relaxation data, we are able to determine the parameters of the pore size distribution-function. Assuming that the pore sizes are distributed according to the sum of lognormal function we can calculate a theoretical magnetisation value. The comparison between the theoretical magnetisation value and the experimental magnetisation data produces the size distribution of the pores. This is one of the few non-destructive techniques capable of providing porosimetric data. The use of magnetic field gradients, for the spatial localisation, provides a detailed map of the proton density, which means the map of the water molecules contained in the samples. The NMRimaging allows obtaining high-resolution tomographic images of porous materials by analysis of spin density of the nuclei of hydrogen in the water molecule (contrast agent). The high-resolution images are obtained by the acquisition of spin-echo signal with spinwarp method for the reconstruction of the image (Kumar A., 1975). The NMR-imaging allows us to check directly the dynamic of the processes of decay in not invasive way. Moreover, the magnetic parameters (i.e. the relaxation times) give information about the molecular distribution of water inside the pores and about molecular interactions with the substrate. The mapping of the treated surfaces and the analysis of surface morphology were carried out by a Scanning Electron Microscope Jeol-JSM 5600 with the graphitization system Jeol Jee 4B and an energy-dispersive spectrometer for microanalysis. The measure was performed at 25 kV and at 300 magnification. The experimental technique has a limitation: we can't detect element lighter than fluorine. By SEM-EDX we can obtain mapping of fluorinated polymeric resins as Phluorophase ('element probe': fluorine) and polysiloxanic resins as Hydrophase ('element probe': silicon). We performed SEM analysis on samples cut along a plane, perpendicularly to the surface. So we can observe the inner cavities of the porous matrix along different directions of penetration of the polymeric resins.
4. Results and discussion In this section we illustrate some remarkable results obtained by NMR in order to emphasise the potentiality of the method, which is absolutely non-destructive. By imaging we can check the pore filled by water and can gain information about interactions between pore surfaces and contrast agent (Baglioni P., to be submitted). SEM analysis allows us to obtain original output about the distribution of polymeric resins within the porous structure. Through the innovative methodologies we checked the dynamics of penetration process and the effects of degradation process on polymeric resins. 4.1 High resolution images We have collected high-resolution images by NMR-imaging method on all the samples investigated. Here we report only some results. In figure 1 we show the comparisons
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between the untreated sample of Candoglia marble and the sample treated by Phluorophase. In the comparison between different samples the NMR-I provides information on the relative water content. This allows to establish the efficacy of a treatment and to define the proper application technique. The materials examined were from quarry and they are characterised by low values of total porosity. In fact, the water amount of water adsorbed by capillarity is very low (from 0.07% up to 0.4% in weight variation). Nevertheless we obtained high-resolution images. The picture gives a qualitative information on the system properties, by studying the density spin function that we get by Fourier anti-transform of the magnetisation signal function. The comparison between the obtained data with the SANS experiments (Small Angle Neutron Scattering) performed on stone materials, allow us to obtain the length correlation function and to apply the Debye model in order to describe the pore coalescence of porous matrix, which is considered to be a bi-continuous system (Safran S.A. 1985; Berk N.F., 1987)
Figure 1: In the lower section of picture is the sample of Candoglia marble, in its native state, taken from the quarry, while in the upper section is the sample treated with Phluorophase. The treated surface is turned toward the centre of picture. The black colour identifies the areas with the highest water content (the lowest is identified by white colour). In this figure the colours are reversed by scannering. In the PC's monitor they're exchanged. 4.2 pore size distribution The experimental results show that the interaction between fluid and stone lowers the proton relaxation times. Moreover the protons' magnetisation exhibits a multi-exponential decay, that could be explained by the presence of pores of different dimension in the natural samples. The analysis of the longitudinal magnetisation decay shows the presence of at least two different spin-lattice relaxation time values. This means that we can separate the pores in two different average populations. We measured the magnetic parameters in every sample and we also collected the pore size distributions of samples from quarry and of samples treated by Hydrophase, Phluorophase, and Paraloid b-72. It is also collected the pore size distribution in samples vacuumed prior to water filling. In figure 2, we show the comparison among untreated travertine and treated by Paraloid B72 sample. The theoretical distribution employed is the sum of two lognormal functions. The plot denotes the pore sizes distribution of pores with radius of the order of micrometers. In this range of dimensions the effects due to the treatment process are particularly meaningful and can be easily detected from the analysis of the relaxation time.
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a.u. paraloid B72
0
2
4
6
8
micron
0
2
4
6
8
micron
Figure 2: In the x-axis are the pore dimensions (micron). In the left hand the sample of travertine treated by Paraloid B72, on the right hand the sample untreated and vacuumed prior water filling.
4.3 The Mapping of 'element probe' by SEM with EDX system In this brief report we summarise the results obtained in our laboratories, with the SEMEDX system. We underline that no experimental technique gives direct information on the depth penetration and distribution in the porous matrix of restoration materials; in particular there is no data concerning the activity of polymeric resins entrapped in stone.
Figure 3: The 'mapping' of fluorine atoms by SEM with EDX system in function of the depth penetration. The top of the picture corresponds to treated surface. The product applied is the protective called Phluorophase|
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The direct observation of the picture (see figure 3), referring to Phluorophase treated samples, clearly shows that the depth penetration is very low for marbles (10-20 let) and also for travertine (max 50-60 l.t). The results obtained for Hydrophase are less clear, probably because the silicon amount to be detected was too low. The products for stone protection have a localised action. Nevertheless the studied samples come from quarry, and surfaces are not degraded. The treatment originates a homogeneous film that covers the surface: this ensures the unwettability of the surfaces. It is interesting to investigate their activities on degraded surfaces; in that case the depth penetration of resins should be increased. The applied methodology gives the possibility to check the efficacy of restoration treatment over every kind of surfaces.
5. Conclusions
The results presented in this paper refer to the first application of SEM-EDX and NMR Imaging techniques to the Cultural Heritage conservation. These methods lead to a direct evaluation check of some properties in the porous matrix: in particular the spatial water distribution within the stone, and the penetration extent of organic resins applied for stone consolidation and protection. The mapping of the 'element probe' by SEM-EDX system provides a totally original information on the distribution of organic resins in the first layers of porous structure. Such data would be otherwise unavailable. NMR imaging offers a great potentiality in the analysis of the decay processes and its time evolution and degradation of the Cultural Heritage. This is a very powerful experimental technique for the study of porous structures. Moreover, NMR tomography is one of the few non-destructive techniques for porosimetric data.
6. Acknowledgements Financial supports from CNR 'Progetto Finalizzato Beni Culturali 1996-2000', from MURST ex-60%, and from the University Consortium CSGI, are gratefully acknowledged.
7. References Baglioni P., Giorgi R., Alesiani M., Capuani S., Mancini L., Maraviglia B.. Application of Nuclear Magnetic Resonance Tomography in the study of porous materials, Studies in Conservation [to be submitted] Berk N.F., 1987. Scattering properties of a model bicontinuous structure with a well defined length scale, Physical review letters, 58, 2718-2721. Brownstein K.R., Tarr C.E., 1979. Importance of cassical diffusion in NMR studies of water in biological cells, Physical review A, 19, 2446-2453. Davies S., Packer K.J., 1990.
Pore-size distributions from nuclear magnetic
resonance spin-lattice relaxation measurements of fluid-saturated porous solids, Journal of Applied Physic, 67, 3163-3170.
594
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 De Luca F., De Simone B.C., Maraviglia B., 1982. Tomografia NMR, Le Scienze,
166, 36-47. Mora P., Mora L., Philippot L., 1984. Conservation of Wall Paintings, Butterworths Ed., 166-207. Hatsagorian Z., 1985. Principes experimentaux et theoriques pour l'evaluation de durabilit~ de la pierre, Actes du V e Congres International sur l'alt6ration et la conservation de la pierre, Lausanne, 195-202. Honeyborne D.B., 1990. Weathering and decay of masonry, Conservation of building & decorative stone, Butterworth-Heinemann Ed., 153-177. Kumar A., Welti D., Ernst R.R., 1975. NMR Fourier zeugmatography, Journal of magnetic resonance, 18, 69-83. Rochow T.G., Tucker P.A., 1994. Scanning Electron Microscopy and compositional analysis, Introduction to microscopy by means of light, electrons, x-rays or acoustic, Plenum Press Ed.,297-327. Rossi-Doria P., Tabasso M., 1976. Proceedings of International Symposium on the Conservation of Stone I, Bologna, Manaresi Edizioni. 749. Safran S.A., Webman I., Grest G.S., 1985. Physical Review A, 32, 506.
595 FRACTAL
GEOMETRY
DESCRIPTION
OF
THE
PERMEABILITY
OF
A
NATURAL FISSURED R O C K A. F. Miguel* Department of Physics, University ofEvora, Rua R. Ramalho 59, 7000-671 Evora, Portugal Rui Rosa Department of Physics, University of Evora, Rua R. Ramalho 59, 7000-671 Evora, Portugal Department of Physics, IST, Av. Rovisco Pais, 1049-001 Lisbon, Portugal Ana Maria Silva Department of Physics, University ofEvora, Rua R. Ramalho 59, 7000-671 Evora, Portugal
Abstract
Fractal geometry has become a widely accepted description tool to model the capillary fissure network in rocks. The fractal theory is applied to model the permeability and porosity of a natural fissured rock. The fissured structure is treated as having three fractal dimensions: the fissure breadth, the fissure length and the fissure depth. In a first attempt the permeability model predictions are found to agree satisfactory well with data presented in literature. Keywords: fissures, fractal, permeability, porosity
1. Introduction
The fluid flow properties of a fissured rock are determined by its fissure network. The rock permeability is a complex function of fissures characteristics and dimensions. From the theoretical point of view the rock fissure is seen as a network of narrow slits with constant breadth (Bear, 1977). The rock permeability is determined from the slit equation, and using Darcy's law, as a function of porosity and an average fissure breadth. These approaches are simple but only able to represent very particular fissures network configurations (Bear, 1977). Due to this limitation, the permeability is often obtained in the laboratory, from one of two techniques: a) radial flow method (Raven and Gale, 1985) and the linear flow method (Timmer et al, 1980). In both methods fluid is injected in the sample, and the permeability is determined from the fluid flow and the pressure drop though the sample, based on the Darcy equation. The injection pressure of fluid induces rock deformation, and consequently, permeability determinations increase with injection pressure. Furthermore, the pressure drop over the fissure area is not uniform, so results are affected by heterogeneities in void geometry (Cook et al., 1990). Fissure networks have been described with success using fractals. The findings in numerous research studies (Katz and Thompson, 1985; Barton and Hsieh, 1989; R. Rosa, 1993) suggest that fractal methods could be potent scaling tools. The aim of this study is to present a coherent modelling of permeability of natural fissured rocks. This is achieved within the framework of fractal theory. The permeability is related with capillary fissure structure by three fractal dimensions: the fissure breadth, the fissure depth, and the fissure *Author's to whom correspondence should be addressed
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length. For a sample of granite, both fractal dimensions are obtained from the data presented by van Meurs (1995). Experimentally-determined permeability agrees fairly well with the prediction obtained with the model developed.
2. Theoretical considerations
Consider a material containing narrow capillary fissures. A fissure is a slit-shaped aperture bounded by two parallel planes. These planes are considered impervious. A steady and a fully developed laminar flow through the fissures are assumed. 2.1 Fluid flow through a fissure
For a steady and a fully developed laminar flow, the momentum equation is the Poisson equation dP/dx=~t(02u/0y2)=constant
(1)
where P is the pressure, ~t the dynamic viscosity and u the fluid velocity. Integrating the equation (1) subject to no-slip boundary conditions, the fluid flow, Q (m3/s), through a fissure of constant width or breadth b, length w and depth L, is Q=-b3w(12~t) -~ (AWL)
(2)
2.2 Model for a rock composed by N fissures
Consider a cubic material sample of size Lo, whose cross-section contains N fissures whose characteristic dimension drops inside the infinitesimal interval between b and b+db. The material exhibits tortuous fissures paths of various sizes, along the material length and depth, whose tortuosity depends on the fissure breadth: the greater the fissure breadth, the smaller is the fissure length and depth per cross-section area, and the vice-versa. The fluid flow, Q, through the material is obtained integrating equation (2) over the range of whole fissures breadth, between bminto b ..... leading to Q=-J b3 w(b) (12~t)-' (AWL(b)) dN
(3)
On the other hand, the material porosity is defined as the volume of the saturating fluid divided by the total volume occupied by the sample, being expressed as e=Lo-3I b w(b) L(b) dN
(4)
2.3 Fractal model for a rock composed by fissures
Assuming the natural rock fissures forming a fractal structure, the cumulative fissure breadth distribution, inside the infinitesimal interval b to b+db, follows the power law (Mandelbrot, 1983) N(B>b)=( b/b .... )-D where D is the fissure breadth fractal dimension.
(5)
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According to equation (5) the number of fissures, within an infinitesimal interval, is given by dN= -D(b/b . . . . )-D-'d(b/b . . . . )
(6)
Consider that the fissures size, along both the material depth and length, also exhibits fractal behaviour with respect to the fissure breadth. Then, the measure of this fractal structure can be related to the length scale b, through a scaling dimensionless relationship, for a given cube dimension Lo, of the form (Mandelbrot, 1983; Feder, 1988) L(b)=OtLo(Lo/b)n-1
(7)
w(b)=13Lo(Lo/b)'~
(8)
and
where 1"1and 03 represent the fissure depth and length fractal dimensions (1 <(rl,co)<2); ot and 13represent factors accounting for the difference of influence of the fissures' connectivity on a plane parallel to the fluid flow and on a plane normal to the fluid flow, respectively. Higher fissures' network density on a plane normal to the fluid flow necessarily brings about a higher fluid flow. But a higher fissures' density and resulting connectivity on a plane parallel to the fluid flow does not result to the same extent into an increase of the fluid flow. Consequently, ~< [3
(9)
By inserting equations (5) to (8) into (3), and integrating the resulting equation, we obtain Q=(D/12~t)-l[3~-lb .... 3(b .... /L0)n-~~(3+q_co-D)-lAp[1-xvmin. v(h/t~ . . . . )3+rl-0~-D] ..
(10)
In the study of fluid flow in a material containing micro and meso fissures only, the basic relationship is Darcy's law. The material permeability, K, can be obtained relating equation (10) with Darcy's law, thereby resulting K=(b . . . . 2/12) ~0~ -1
D
l+rl-c0
(bmax/L0)
-1
3+q-03-D
(3+q-o~-D) [l-(bmin/bmax)
]
(11)
As to the material porosity it can be obtained by inserting equations (5) to (8) into (4), and integrating the resulting equation, the conclusion being 13=~[~D(3-II-(_o-D) -1 (b .... /Lo)3-n-c~[ 1 -(bmin/b .... ) 3-n-co-D]
(12)
which, solving for the ratio between bmi n and b . . . . reads as /L "n+o-3 l/(3-rl-co-D) (bmJb .... )={1-(c~13D)-le(3-rl-co-D) (b . . . . . ) }
(13)
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such that q+co+D<3 must hold for physical acceptability. Thus, the porosity is always a positive quantity. When bmax>>> bmin, the ratio between bminand bmax approaches zero, and consequently, the porosity approaches its maximum (Feder, 1988). As a consequence (bmax/Lo) can be written, in term of the fractal dimensions, as (bmax/Lo)= [(ctl3O)-~(3 _q _c0_O)] 1/(3-q-m)
(14)
After substitution of equation (13) into (11), and elimination of (bmax/Lo) by means of equation (14), one finally obtains the permeability of the rock sample. That final result may be simplified taking b . . . . > > > bmi n equal to zero, in which case one has K=(D/12) 13c~-1(3+q-c0-D)-I [(al3D)~ (3-q-m-D)](~+n-o)/(3-n-o)b . . . . 2
(15)
Equation (15) is the key relation is this study. The material permeability, K, is related to some characteristic dimension of the fissures (b .... ) -determined by the sample size-, to the fractal dimensions (D, q, co) and to the fissures' connectivity factors (or, [3).
3. Methodology for the determination of permeability parameters In order to use the equation (15), the parameters b . . . . . ( Z , [3, D, m and q must be known. The parameters bmax, ct, [~, D, co and q can be obtained though the analysis of structural image of the material. The fractal dimensions, D, is evaluated by image analysis of the cross-section of the sample structure on a plane normal to the fluid flow direction. Two methodologies are available in the literature (Mandelbrot, 1983; Feder, 1988; Barton and Hsieh, 1989) in order to analyse the structure of material, producing both similar results. However, the "box-counting method" is preferred due to lower computer time consuming. This methodology consists in the discretization of the sample section in boxes of a certain size b, and counting the number N(b) of such boxes on the sample section that cover the fissure network. The procedure is repeated for different box sizes (mesh sizes) and the results are represented in a logarithmic graphic. The spatial fissure distribution is considered having a unique fractal dimension if the resulting plot is described by a straightline slope. The line slope is the fractal dimension of the material understudy. As to the fissure parameters (q,a) and (c0,[~), they can be obtained based on the structural image of a cross section of the material sample parallel and normal to the fluid flow direction, respectively. The methodology used in this case is the "box-counting method" once again, but with larger mesh sizes.
4. Determination of bmax,D, q, o~, ~ and [3 The parameters b ..... D, q, co, ~ and [3 were determined for a sample of granite (3 cm 3, porosity 1.3%), based on experiments conducted by van Meurs (1995). The results presented concerned to the fractal analysis of the fissure network in the granite sample were obtained based on the "box-counting method". It study was focused in obtaining the cumulative fissure population in plane normal to flow direction, and the fractal dimension
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of the perimeter of the fissures in the cross-section of the sample parallel to the flow direction (figs. 1 and 2).
Figure 1: The cumulative fissure breadth distribution N(b) versus the fissure ratio b/bmaX The lines that best fits the plots in figs. 1 and 2 were straight lines. The data can be fitted with equations 5 and 7, which demonstrate the existence of fractal dimensions. The line slops D and rl determined by the figures 1 and 2 were 0.56 (slope -0.56) and 1.12 (slope 2.12), respectively. The factor ot determined by figure 2 was 1.02. According to van Meurs (1995), the sample of granite studied was isotropic. This allow us to presume that the fractal dimensions co and rl might be equal. The maximum fissure breadth, bmax, was also measured by van Meurs (1995), through the analysis of the structural image of the rock sample. The value obtained was 0.09 mm. 5. Model validity The permeability of the granite sample was measured by van Meurs (1995), based on a linear flow method. The value obtained was 6.12x10 -1~ m 2. This value can be compared with an estimate obtained with the approach developed in the present study, if the fractal information obtained in section 4 is introduced in the model. There is no available information in literature about the factor I~, but it is assumed that the factor 13 will be about twice ~, in which case, the predicted permeability is 3.21x10 11 m 2.
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10 Slope:0.12 R2=0.99 3" 100
1000
10000
Lo/b Figure 2: L(b)/Lo versus Lo/b 6. Final Remarks
In this paper the permeability of a fissured rock is described within the framework of fractal theory. In formulating the present approach, some simplifications have been assumed: the fissures are considered slit-shaped apertures bounded by parallel planes and the flow is considered to be a steady and a fully developed laminar flow. Experimental data obtained for the purpose of testing our approach is found for one granite sample only. Further experimental data is required to obtain a larger number of tests and validate our model.
7. References
Barton C., Hsieh P., 1989. Physical and hydrologic-flow properties of fractures. 28th International Geological Congress Field Trip Guidebook T385, Washington DC, American Geophysical Union. 16-46. Bear J., 1972. Dynamics of fluids in porous media. American Elsevier Environmental Sciences Series, New York. Cook A., Myer L., Cook N., Doyle F., 1990. The effect of tortuosity on flow through a natural fracture. Rock mechanics contributions and challenges. Proceedings of the 31st U.S. Symposium on Rock Mechanics, edited by A. Balkema. 371-378 Katz A., Thompson A., 1985. Fractal sandstone pores: implications for conductivity and pore formation. Physical Review Letters, 54, 1325-1328 Mandelbrot B., 1982. The fractal geometry of nature. W. H. Freeman and Co., San Francisco van Meurs W., 1995. Experimental characterisation of some soils and rocks. Report 00456GW/95, IMA-DLO, Wageningen, 97 pp. (in Dutch) Raven K., Gale J., 1985. Water flow in natural rock fracture as a function of stress and sample size. Int. J. Rock Mech. Mining and Geomechanics Abst, 22, 251-261 Rosa R., 1993. Transport and mechanical properties of granitic rock as influenced by geometry of its fissures and crack network. Proceedings of International Symposium on Safety and Environmental Issues in Rock Engineering, Lisbon, edited by Balkema. 10051010 Timmer D., Bonner B., Heard H., Duba A., 1980. Effect of pressure and stress on water transport in intact and fractured gabbro and granite. J. Geophysical Research, 82, 70597071
601
MICROSTRUCTURAL CHANGES CONSOLIDATION TREATMENTS: TRANSPORT
IN GRANITIC ROCKS THEIR EFFECTS ON
DUE TO MOISTURE
Maria J. Mosquera* Departamento de Quimica-Fisica, Universidad de Cfidiz, SPAIN Teresa Rivas, Beatriz Prieto and Benita Silva Departamento de Edafoloxia, Universidad de Santiago de Compostela, SPAIN
Abstract The modifications induced by two silicic consolidants in the pore structure of three granitic rocks used in monumental construction are studied. The effect of microstructural changes on moisture transport is also evaluated. The pore structure of the rocks was investigated using mercury intrusion porosimetry (MIP) and porosity accessible to water analyses. Additionally, the permeability of the rocks, which is one of the main moisture transport mechanisms, was evaluated. As results, both treatments reduced the porosity accessible to water, while the evolution of MIP porosity was different according to granite type and consolidant applied. In some specimens, a surprising increase of porosity after the consolidation was observed; suggesting that the stress generated inside the rocks pores during the process of consolidants drying could cause cracking. With reference to the discrepancy of porosity values for both analytical procedures, the MIP results are more reliability since they correspond exclusively to surface regions of the rock where, due to the poor penetration of consolidant, the microstructural changes were observed. Finally, both consolidation treatments modify the water transport properties of the rocks. It was possible to establish a direct relationship between permeability coefficient and the pore structure parameters determined by MIP (porosity and pore size). Keywords: granites, consolidation treatments, ethylsilicates, MIP, permeability, water transport.
1. Introduction Consolidation treatments are commonly used in the conservation and restoration of stone buildings and monuments in order to strengthen the stone and increase its resistance to further deterioration (Silva et al., 1997 and 1999). Since moisture movement through the stone pore network is believed to be the primary transport mechanism in damage processes, the evaluation of changes in the pore structure of the rocks therefore assumes special importance. In fact, the larger pores provide routes for transport and the smaller pores lead to high surface area adsorption and reaction sites. In the case of granitic rocks consisting of a well interconnected fissure system (Mosquera et al., 1999), the evaluation of these changes in microstructure plays a decisive role in the correct selection of consolidation treatments. *Author to whom the correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
However, the few studies found in the literature (Moropoulou et al., 1997), (Rossi Manaresi et al., 1995) are exclusively dedicated to sedimentary rocks. Thus, the objective of this paper is to evaluate the effect of two silicic consolidants: Tegovakon (TG) and Consolidant OH (COH), on the pore structure of three granitic rocks widely used in historic construction in NorthWest Spain. Additionally, measurements of water vapour permeability, one of main mechanisms of water transport, were used to evaluate the effect of consolidation on transport properties, and to establish a relationship between this transport and the microstructural changes associated with consolidation application.
2. Materials and Experimental procedure 2.1. Granitic rocks The following granites were selected for this study: 9 Roan, used as construction material in Santiago de Compostela, is medium-to-fine grained two-mica migmatitic granite with flow structure, xenoliths and no apparent mineral orientation. 9 Axeitos, used in the construction of an important megalithic monument, is a slightly pinkish coarse-grained post-Hercynian granite, with an allotriomorphic to subidiomorphic heterogranular texture and no apparent mineral orientation. 9 Baleante, used in the construction of new buildings in Santiago de Compostela, is a leucogranite rich in muscovite and comprises medium to coarse grains. Its shows a fairly mineral orientation. 2.2. Consolidation treatment Two ethyl-esters of silicic acid were applied as consolidants: Tegovakon V R (Goldschmidt), which is a mixture of a low-molecular-weight ethyl silicate and an polymethylsiloxane, and Consolidant OH (Silicem-Wacker), which is a low-molecularweight ethyl silicate. The test specimens (six 5 cm-cubes for each granite and consolidant) were totally immersed in each of consolidants for 24 hours. The samples were then removed from the product and the amount of product absorbed (uptake of product) was determined. Samples were then left for a period of 30 days at ambient temperature to allow polymerisation to take place. The amount of polymerised material was determined by the weight gain of the samples. Both the amount of product absorbed and the amount of dry material were expressed in g/m 2 2.3. Characterisation methods The following tests were carried out before and after the treatment: 9 Porosity accessible to water of six 5 cm-cubic samples of each type of granite was determined following the RILEM procedure (1980). 9 Microstructural analysis of the pore space of the rocks were determined by means of Mercury Intrusion Porosimetry (M.I.P). The M.I.P. measurements were carried out with low pressure (up to 400kpa) and high pressure (max. 400 Mpa) Pascal Porosimeter (Fision Instruments). Three specimens of each type of granite, with an
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average size of 2 c m 3, w e r e pre-treated by washing in an ultrasonic bath, dried at 60~ and then analysed. Permeability to water vapour coefficient was determined for six 5 cm-cubic samples of each type of granite following the ICR-CNR standard (1985) modified by Ferreira (1993).
3. Results and discussion 3.1. Consolidant absorption Table 1 shows the values of absorption of product and amount of dry polymer after the application of the two consolidants. The amount of polymerised material in the rock was higher for Baleante treated with Consolidant-OH (94 g/m2) and Roan after the two treatments (74 and 76 g/m2). The others specimens, Axeitos, after the two treatments, and Baleante treated with Tegovakon showed similar lower values (around 40 g/m2). The uptake of both consolidants was highest in Baleante and lowest in Axeitos. However, taking into consideration the ratio uptake/dry polymer, the amount of dry polymer remaining in the rock was highest in the Axeitos granite. It might mean that the polymerisation reaction was, at least initially, more efficient in this granite. In all granites, the ratio uptake/dry polymer was lower for Tegovakon than for Consolidant OH, suggesting that the polymerisation process was more efficient after the treatment with Tegovakon.
Table 1: Uptake of consolidant (g/m 2) (U), amount of dry polymer in the rock (g/m2) (DP) and ratio between these parameters (U/DP) after the treatment with the two consolidants. Tegovakon Consolidant OH Granite U DP U/DP U DP U/DP Roan 156 76 2.05 158 74 2.13 Baleante 189 41 2.19 211 94 2.24 Axeitos 75 41 1.82 79 42 1.88 3.2. Microstructure changes Table 2 shows the porosity accessible to water values and porosity obtained by MIP, for each type of granite selected, before and after the consolidation application. In the case of untreated specimens, the MIP porosity data were close to those obtained by RILEM, indicating the reliability of these results. The pore size distribution (fig.l) obtained by MIP was clearly bimodal for the three granites, with the proportion of macro-fissures in Axeitos being significantly higher (90% of total porosity) than in the others (about 40%).
Table 2: Values of Porosity accesible to water and total porosity obtained by MIP, expressed in volume (%) for each granite, before and after the two consolidation application. Accessible to water MIP Granite Untreated Tegovakon C-OH Untreated Tegovakon C-OH Roan 2.11 1.65 1.59 2.10 2.58 3.14 Baleante 2.78 2.34 2.20 2.80 2.40 3.52 Axeitos 1.94 1.68 1.80 1.50 0.80 1.59
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The porosity values of treated specimens showed differences according to the test procedure (tab. 2): the porosity accessible to water was reduced after the application of both treatments, while the evolution of MIP porosity was different according to the type of granite and consolidant applied. In fact, for Roan granite both consolidants caused a surprising increase of porosity, which was higher after Consolidant-OH application. In the case of Baleante granite, Tegovakon treatment decreased the porosity, while ConsolidantOH increased it. For Axeitos granite, the porosity was reduced after Tegovakon consolidation and with Consolidant-OH it remained practically constant. This discrepancy in porosity values between the RILEM and MIP procedures was related to the poor penetration of the two consolidants into the rocks, which only produced microstructural changes in the rock surface region. The MIP data are more reliable because this corresponds more precisely to the surface region where the consolidant penetrates and thus microstructural changes can be observed. RILEM porosity values are measures of porous volume of the whole specimen.
The surprising increase of porosity in the surface region of some rocks after consolidation treatment could be caused by cracking inside the granite pores as a consequence of a considerable increase of tensile stress within the consolidant during its drying process. In fact, these observations are consistent with the theory of drying stresses of Conservare OH, developed by Scherer and Wheeler (1997). Comparing the results obtained for the three granite rocks, two conclusions may be drawn:
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9 The increase of porosity after the treatment could be related to the amount of dry material in the rock after the polymerisation reaction. In fact, Roan treated with TG and COH and Baleante treated with COH, with the highest amount of dry polymer, showed porosity increases after the two treatments. Axeitos treated with COH remained constant and Baleante and Axeitos treated with TG, which showed the lowest amount of dry polymer, showed decreased porosity values. 9 Since the porosity increase could be originated by cracking of rocks pore due to the high stress developed during the drying of the consolidant inside the pores, in granites with lower pore size more cracking could occur. In fact, in Axeitos, with the largest size fissure (40 ~tm) the porosity is not increased, while Roan and Baleante (10 and 20 ~tm, respectively) show increases in porosity. The maximum fissure sizes were determined in an earlier paper (Mosquera et al., 1999)
With reference to the pore size distribution changes after the treatment, the following results were observed: for Roan granite treated with Tegovakon, the proportion of lowest pores (below to 0.1 ktm) was increased, while after Consolidant-OH application macrofissure proportion was slightly increased. For Baleante granite, the distribution was practically constant after the two treatments. For Axeitos, a slight decrease of pore size was observed after the application of two consolidants. Comparing the evolution of pore size distribution in each one of granites, an increase of pores below 0.1 9m is noticed after the Tegovakon application for the three cases. 3.3. W a t e r v a p o u r p e r m e a b i l i t y
The two consolidation treatments modify the permeability coefficients of the three granites studied (Table 3). It should be noted that two different permeability values for each untreated granite are given in Table 3, since specimens with different orientation were used in each case. The existence of a strong anisotropy in water transport properties of these granites is well known and explains the different values obtained. Comparing the three rocks studied: permeability of Roan is decreased after Tegovakon application, while Consolidant-OH increases its permeability. In Baleante granite, an increase of permeability is observed after Consolidant-OH treatment. Finally, the permeability coefficient of Axeitos is decreased after the application of the both consolidants. T a b l e 3: Vapour water permeability, expressed in Kg.m"h"Pa-' for the granites studied, before and after the application of the consolidants. Untreated
Tegovakon
Untreated
Consolidant-OH
Roan
2.70.10 .9
1.49.10 .9
2.92.10 .9
Baleante Axeitos
1.81.10 -9
1.72.10 -9
1.48" 10 -9
3.91.10 -9 2.18.10 .9 1.14.10 -9
1.47-10 .9
From the results obtained, it is not possible to establish any relationship between porosity accessible to water and permeability coefficient. Obviously, the reduction of RILEM porosity after the two treatments suggested a decrease of permeability in all the specimens. However, the permeability changes observed after the treatments could be explained from the MIP porosity values. In fact, in specimens for which an increase of porosity is observed after the
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consolidation (Roan and Baleante treated with consolidant-OH), the permeability presents a significant increase. In Axeitos, where the porosity is decreased (TG) or remains constant (COH), a decrease of permeability is observed. The only discrepancy between permeability and MIP porosity is observed for Roan treated with Tegovakon where the consolidant application produces a slight increase of porosity, while the permeability is reduced. The reason for this discrepancy is that the pore size distribution of the rocks also influences the coefficient transport for permeability. Since bottlenecks obstruct the transport, Meng (1994) has suggested that permeability values decrease in direct proportion to pore radius. Then, the increase of proportion of lowest pore size after the Tegovakon treatmem in Roan granite could produce the decrease of its permeability coefficient. 4. Conclusions
The small amount of consolidant absorbed in all the cases suggests a poor penetration of product, limited to the surface region of the rocks. Therefore, the porosity data obtained by MIP (where only surface region is considered) are more reliable than those obtained by the Rilem procedure. In fact the evolution of water vapour permeability can be explained according to the MIP results, while this is not possible by means of the porosity accessible to water. In some specimens the consolidant application gives rise to a surprising increase of porosity, which could be related to the drying process of the consolidant causing cracking in the rock pore. The consolidant selected and the pore size distribution of the rocks can be considered key parameters in microstructural changes observed after consolidation application. In fact, the results presented are preliminary data from a study still in progress, which could permit the correct selection of consolidants according to these parameters. The effect of the quantity of dry polymer in the porosity of specimens is also demonstrated. Finally, it should be noted that the consolidation treatments studied modify the water transport in the rocks, according to the evolution of porosity and pore size distribution of the rock after the treatment. These modifications should be evaluated before choosing a consolidation treatment, due to its importance in the alteration process. 5. References Ferreira, A.P., 1993. Conservacao de pedras graniticas. Estudo da accao de hidr6fugos. Dissertaccao para a obtencao do grau de mestre en construccao. Itto. Superior T6cnico, Universidade T6cnica de Lisboa. Istituto Centrale del Restauro-Commisione Normal (I.C.R.-C.N.R.), 1985. Alterazioni dei materiali lapidei e trattamenti conservativi. Proposte per l'unificazione dei metodi Sperimentali di studio e di controlo. Permeabilit~t al vapor d'acqua. Doc. Normal 21/85. Meng, B., 1994. Calculation of moisture transport coefficients on the basis of relevant pore structure parameters. Materials and Structures, 27, 125-134. Mosquera, M.J., Rivas, T., Prieto, B. and Silva, B., 1999. Capillary rise in granitic rocks: Interpretation of kinetics on the basis of pore structure. Journal of Colloid and Interface Science (In press). Moropoulou, A., Tisiourva T., Biscontin, G., Bakolas, A., Michaidilis, P., Zendri, E., 1997. Evaluation of consolidation treatments of porous stones-Application on the Medieval city of Rhodes. The conservation of monuments in the Mediterranean, Proc. of 4~' International Symposium, Rhodes, Technical chamber of Greece ed. Vol. 3,239-256.
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Reunion Internationale des Laboratoires d'Essais et de Recherche sur les Materiaux et les Constructions (R.I.L.E.M.). Comission 25 PEM. Protection et Erosion des Monuments, 1980. Essaid recommand6s pour mesurer l'alteration des pierres et 6valuer l'efficacit6 des m6thodes de traitement. Materiaux et construction, 13, 75. Test n ~ I.l.: Porosit6 accesible/t l'eau. Rossi Manaresi, R., Rattazzi, A., Toniolo, L., 1995. Long term effectiveness of treatments of sandstone. Methods of evaluating products for the conservation of porous building materials in monuments. Pre-prints of International colloquium, Rome, 225-244. Scherer, G.W. and Wheeler, G.E., 1997. Stress development drying of Conservare OH R. The conservation of monuments in the Mediterranean, Proc. of 4 th International Symposium, Rhodes, Technical chamber of Greece ed. Vol. 3, 355-362. Silva, B., Rivas, T., Prieto, B., 1997. Evaluation of the efficacy of the treatment of granitic rocks with two silicic consolidants. The conservation of monuments in the Mediterranean, Proc. of 4 th International Symposium, Rhodes, Technical chamber of Greece ed. Vol. 3,375-383. Silva, B.; Rivas, T.; Prieto, B., 1999, Tratamientos de consolidacidn e hidrofugacidn aplicados en sustratos graniticos hfimedos y contaminados por sales. Materiales de Construccidn (In press).
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609
THE USE OF SOUND VELOCITY DETERMINATION FOR THE NONDESTRUCTIVE ESTIMATION OF PHYSICAL AND MICROBIAL WEATHERING OF LIMESTONES AND DOLOMITES
Sophia Papida School of Biological Sciences, University of Portsmouth, UK William Murphy School of Earth, Environmental and Physical Sciences, University of Portsmouth, UK Eric May* School of Biological Sciences, University of Portsmouth, UK
Abstract
Two limestones from Crete, Greece and Mansfield dolomite from the UK were tested experimentally for their resistance against physical and microbial attack. XRD and SEM were used for the assessment of their mineralogy, original structure and weathering patterns. Stone discs subjected to physical, microbial and combined physical/microbial weathering simulation cycles were treated with distilled water, NaCl and NaESO4 solutions, alone or in combination with mixed microbial populations (MMP). Measurements of weight change, mechanical alteration and viable bacterial counts were augmented by the non-destructive technique of sound velocity transmission. Both longitudinal (Up) and shear (Us) waves velocities were mostly stable or slightly accelerated in the case of distilled water and NaCl treatments, but with the NaESO4 weathering regime, involving expansion due to hydration and dehydration, they decreased. However, a marked decrease was found whenever MMP were present. These observations suggest a possible contribution of microorganisms to physically induced deterioration of stone. Correlation of Up and Us to weight, other mechanical properties and bacterial counts highlighted the importance of surface hardness in predicting mechanical behaviour. Furthermore, the evidence suggests that porosity size might influence the type of stone attack and a possible contribution of sulphur bacteria to deterioration. Sound transmission velocity proved to be an effective diagnostic technique to assess the mechanical state of building stones. Keywords: stone, biodeterioration, microbial weathering, sound velocity transmission, nondestructive techniques 1. Introduction
The integrity and preservation state of stones in buildings and monuments has been assessed by measuring compressional (P) and shear (S) acoustic wave velocities (Christaras, 1991a; 1991c; 1993; Simon et aL, 1994; Villegas S~nchez et aL, 1996). Other workers have used this technique for test specimens (Murphy et aL, 1996; Simon and Snethlage, 1996) and natural crops (Christaras, 1991b) with good results. Success has been shown to depend on several properties of stone controlling its homogeneity, such as density, porosity and water saturation (Simon, 1998). Any reduction of the velocity would indicate discontinuities *Author to whom correspondenceshouldbe addressed
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
and obstacles for the propagation of ultrasonic waves (Fassina et aL, 1993). The main advantage is its non-destructive character (Rodriguez-Navarro et al., 1994; Montoto et al., 1994; K6hler, 1996). This paper describes the application of a sound velocity technique for non-destructive assessment of building stone during a series of experiments to monitor physical and biological deterioration. Statistical correlation of the ultrasonic velocities to weight change was used to assess the potential of the method for describing the preservation state of stones or for prediction of weathering behaviour. In addition, ultrasonic velocities were related to other stone properties such as porosity, dry density and surface hardness to evaluate their importance for weathering processes.
2. Materials and Methods
Three stone types were examined: a dolomite from Mansfield, UK (MD), a soft limestone from Psathas, East Crete, Greece (PL) and a limestone from Stavros, West Crete, Greece (SL). Mineralogy was assessed by X-ray diffraction (XRD). The velocities of compressional (P-) and shear (S-) were determined according to Rummei and Van Heerden (1981). Both P- and S- wave velocities were calculated from the measured travel time and the distance between transducers, according to the following equations: P- wave velocity Up = d x tp-1 (1) S- wave velocity
Us = d x ts-1
(2)
where t was the time required to travel the distance d. Original dry density and porosity of stone discs were assessed as suggested by Franklin et al. (1981) and Ross and Butlin (1989). Porosity was measured using water saturation and caliper techniques. Surface hardness was estimated by determining the rebound of the material, using a Shore model C-2 scleroscope (Bamford et aL, 1981; Atkinson, 1985). Viable counts of heterotrophic bacteria including halotolerant, acidophilic and mesophilic sulphur types originally occurring on and in stone structures were assessed by the methods of Lewis (1987). Wave velocities, dry weight and properties indicative of change in the stone discs were determined after every 20 cycles. Changes in microbial populations were estimated by count procedures on each sampling occasion. Physical weathering was simulated by a regime that involved 100 consecutive 24-hour thermal cycles using the following weathering agents: a) distilled water, b) 0.5 M NaC1 and c) 0.5 M Na2SO4. The microbial weathering involved exposure to mixed microbial populations (MMP), followed by 100 24-hour thermal cycles and this was combined with a), b) or c) above in the case of the combined physical/microbial weathering. The discs were subjected to sequential temperature/time combinations of 30~ hours, 8~ hours and 21 ~ hours.
3. Results
XRD allowed a qualitative determination of the three stones only. The light brown dolostone from Mansfield (MD) mainly consisted of dolomite, quartz and calcite in that order of abundance. Cerussite and the clay minerals Illite trioctahedral, Mont-chlorite reg and Montmorillonite were also identified in smaller quantities. In the white sott limestone from Psathas (PL), calcite and aragonite were the dominant minerals with quartz present in
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
611
smaller amounts, followed by a number of oxides/hydroxides (Akaganeite, Goethite, SrManganese oxide, Rutile) and halides/sulphates (Halite, Antarcticite, Lithium Fluorite, Mirabilite, Anglesite). The porous limestone from Stavros (SL) was composed mainly of calcite, with smaller quantities of quartz and dolomite. Lithium fluorite and gypsum were also identified in trace amounts (fig. 1).
|
i ..............................................................................................................................................................................
i r"
l
S ta vros limes ton e
i
~
[
Psathas limestone
Mansfield dolomite Il
L..........................................................................................................................................
.
.
,- ~ ~ ~
j
....
,, ~ ~ ~. ~ ~ ~ ~" 6
Ang le [o 2 e]
Figure 1" X-Ray diffractometry of stones investigated MD was the most dense and least porous stone with the highest surface hardness probably due to the high quartz content. PL was the softest stone and supported the largest natural populations of heterotrophic, acidophilic-sulphur and halotolerant bacteria. SL had the lowest density and the highest porosity. High porosity did not adversely affect the surface hardness of a stone or have a retarding effect on the shear wave velocity and did not imply greater colonisation by bacteria (tab. 1).
Table 1" Stone properties PROPERTY Dry density (~/cm 3) Porosity (%) Surface hardness Up (m/s) Us (m/s) Heterotrophic bacteria (cfu/g) Acidophilic sulphur bacteria (cfu/g) Mesophilic sulphur bacteria (cfu/g) Halotolerant bacteria-0.09M NaCI (cfu/g) Halotolerant bacteria-0.86M NaCI (cfu/g)
MANSFIELD DOLOMITE MD 2.01 17.1 17 2667 1000
PSATHAS LIMESTONE PL
1200
4000
C h a n g e s in s t o n e p r o p e r t i e s u n d e r d i f f e r e n t w e a t h e r i n g
1.77
21.4 4 3125 1111 2000 1200
STAVROS LIMESTONE SL 1.55 24.3 5 2714 2111 1600
1000 400
regimes
The three stones, namely Mansfield dolomite (MY)), Psathas limestone (PL) and Stavros limestone (SL) were subjected to a series of experiments to determine the impact of salts alone and in combination with mixed microbial populations on the structural integrity of the
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stones. The results are presented in table 2. Comparisons were made between the physical properties and the performance in tests using sound velocity determinations. Table 2: Final stone properties change (%) under weathering regimes PROPERTY
. MMP
MANSFIELD D O L O M I T E MD : Weight Up Us Dry density Porosity r Surface hardness PSATHAS L I M E S T O N E PL Weight Up Us 9 Dry density Porosity Surface hardness STAVROS L I M E S T O N E SL Weight Up Us 9 Dry density Porosity Surface hardness
. -6.0 -31.7 20.2 0.6 10.6 -58.8
. 0.1 .-47.0 -22.9 . 3 19.1 75
.
. . .
. . .
Na2SO4
j i .
-3.1 11.6 76.3 -4.1 5.8 -70.6
-6.6 . -32.4 -17.0 . 4.7 . 7.0 -58.8
1.2 11.6 79.7 . 1.1 . -2.3 -58.8
0.1 -14.3 53.4 1.6 21.0 0
-7.7 -46.5 -23.0 5.7 24.0 25
. 4.5 .-17.1 42.5 . 5.2 -21.6 -62.5
.
.
M]VIP/ ! I
i
. .
[
WEATHERING REGIMES MMP/ NaCI MMP/ dH20 NaCl
dHzO
NaESO4
j -5.1 -41.7 -20.1 8.5 -23.8 -47.1
. . .
2.8 9.5 92.9 3.0 -26.5 -88.2
-13.6 -43.2 -17.5 -2.6 . -33.8 i -94.1 i
3.0 -51.5 -47.2 11.4 -23.6 25
-5.8 -33.7 -32.0 6 - 11.2 -100
. -31.1 .-73.0 -63.7 . 20.3 6.8 -100
1.7 -37.9 -65.2 3.0 -2.5 -20
9.9 14.0 -28.0 -6.2 -7.1 -80
. -9.8 . -39.1 -64.0 . -0.7 32.1 -80
. . .
r . -3.1 . -38.0 -66.3 . -1.0 38.9 -60
. . .
-0.9 -5.1 - 17.8 -7.3 22.2 -40
.
-0.6 9 -42.0
-60.0 -3.6 25.7 -40
. .
2.8 9.9 - 18.0 . -1.2 9 100
. .
Weight change
Weathering assessed by weight change clearly demonstrated the potential o f particular treatment regimes, especially the combined ones. Final weight changes and changes in Up and Us (%) o f stones are given in table 2. MMP/Na2SO4 caused high material loss o f all stones, followed by MMP/dH20 for MD and PL and MMP for SL. PL was the most prone to deterioration by MMP/dH20 or Na2SO4. with or without MMP, but MD showed weight loss by all treatments involving MMP. The porous SL was subject to the minor weight variations. In most treatments, salts applied alone caused only weight uptake except for Na2SO4 applied on PL. Weight loss was always accompanied by decreases in Up and Us. In most cases the increase in Up and Us accompanying weight uptake was indicative o f filling o f pores and internal voids by salts. Up and Us were most often strongly correlated to weight change, but inconsistencies did occur. It was clear that measurement o f both o f these factors was necessary when they were
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613
correlated with weight and other changes in stone properties, as well as bacterial counts. In practice, weight and Up and Us were most often positively correlated (tab. 3). Table 3" Correlation factors for weight to Up and Us
Control dH20 NaCl Na2SO4 MMP MMP/dH20 MMP/NaC1 MMP/Na2SO4
Mansfield dolomite Up US 0.831
0.675
-0.163 0.185 0.124 -0.068 -0.573 -0.173 0.627
-0.161 0.775 0.555 0.433 0.642 -0.291 0.276
Psathas limestone Up US -0.020 0.220 0.277 -0.675 -0.524 0.705
Stavros limestone Up US 0.482 0.503 0.429 0.091 0.579
-0.001
0.704
0.760
-0.109 0.411 -0.533 0.821
0.303 -0.047 0.455 0.546
0.222 -0.775 0.874 -0.456 0.576
-0.921 0.733 0.702
-0.165
0.302
Dry density The final dry density of PL was increased in all treatments, but this was always greater when MMP were involved. A similar effect was observed with MD so that dry density was increased more when the water and NaCl treatments were coupled with MMP. With the more porous SL, dry density usually decreased except with MMP/NaC1 that caused an increase and MMP involvement was associated with a smaller reduction in dry density. The destructive impact of an increase in dry density on the mechanical state of MD due to MMP was indicated by its negative correlation to Up. The occasional decrease in dry density with MD and SL did not significantly affect mechanical structure. In fact, increases in dry density of the low porosity stones by water in the presence of MMP caused a reduction in sound velocity. Na2SO4 increased the dry density of MD and PL, and reduced that of SL but these changes did not affect their structure. However in combination with MMP, it substantially increased the dry density of PL and had an equally damaging effect on its mechanical strength. Porosity
The final porosity of MD and PL was increased by treatment with both water and MMP separately but more dramatically when they were coupled. In addition, both salts caused a decrease but the effect was greater for MD when MMP were present. When coupled with MMP, NaCl reduced the porosity of PL but Na2SO4 eventually increased it. The initial high porosity of SL was further increased by water and MMP amplified the effect. NaC1 increased porosity, particular in combination with MMP, while Na2SO4 decreased porosity but increased it in combination with MMP. Mechanical degradation, indicated by reduction in wave velocity, was variable and dependent on the stone and its treatment. Positive correlations were found for the two limestones treated with water, the dolomite treated with salts/MMP and PL treated with MMP/NaC1. The correlation was negative for all stones treated with NaC1 and the limestones treated with MMP with or without water and SL treated with MMP/dH20. When coupled with MMP, NaCl further reduced the pore size of all stones causing a dramatic reduction in sound velocity. A negative correlation of sound velocity with porosity for limestones treated with Na2SO4 suggested an initial strengthening of stone structure due possibly to blockage of pores by salt crystals, but this is followed by mechanical breakdown
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and a decrease in sound velocity due possibly to expansion by salt deposition. No clear correlation between porosity and sound velocity were shown with the MMP/Na2SO4 treatment despite the deteriogenic action of the salt which fills newly formed cracks and voids due to its highly expanding nature. Surface hardness The surface hardness of all stones was reduced in all treatments and particularly those involving NaESO4, with or without MMP. An exceptional increase of the original surface hardness of PL was found with MMP, MMP/dH20 and MMP/NaC1 and also with SL under NaC1 treatments. NaESO4 uptake caused both a reduction of sound velocity and the surface hardness of PL, but for SL a reduction in the surface hardness was accompanied by a rise in Up for the stone. However, when NaESO4 was coupled to MMP, the surface hardness reduction was accompanied by a reduction in sound velocity. Sulphur bacteria There was a particularly strong series of positive correlations between the numbers of sulphur bacteria and the waves velocities, i.e. the mechanical state of stones (tab. 4). Higher numbers were found to occur on mechanically stronger stones, and this is contrary to previous in situ examinations by other workers (Milde et al., 1983; Lewis, 1987).
Table 4: Correlations between either aciduric (ATM) or non-aciduric (NATM) sulphur bacteria and sound velocity determinants, Up~Us
MD MMP MMP/dH20
MMP/NaCI MMP/Na2SO4
PL MMP MMP/dH20
MMP/NaC1 ~'I]ViP/Na2 SO4
SL MMP MMP/dH20
MMP/NaC1 MMP/Na2SO4
ATM 0.610 0.621 0.836 0.708 ATM 0.725 0.423 0.6 0.759 ATM 0.521 0.334 0.450 0.429
P-wave (Up) NATM 0.568 0.667 0.632 0.623 NATM 0.743 0.479 0.6 0.561 NATM 0.509 0.285 0.452 0.434
ATM 0.6 0.818 0.43 0.976 ATM 0.841 0.631 0.7 0.813 ATM 0.37 0.316 0.402 0.466
S-wave (Us) NATM 0.568 0.811 -0.309 0.495 NATM 0.809 0.623 0.699 0.567 NATM 0.471 0.361 0.402 0.306
4. Discussion The potential of MMP to deteriorate stone alone, or in combination with physical agents, could quickly be assessed via sound velocity measurements. The use of changes in original weight, dry density, porosity, or surface hardness proved less reliable as an index of deterioration. The decrease of Up and Us provided a non-destructive method to assess the mechanical behaviour of stones, in the absence of any weight change, or the weathering effects of the stone treatments. Regardless of final mass variations, treatment with dH20,
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
615
NaCI and Na2SO4 did not significantly affect the mechanical state of stones under the conditions of the experiment, evidenced by the variable behaviour of wave velocities. On the contrary, the contribution of microorganisms to the mechanical deterioration of stone was clearly demonstrated by the decreases in Up and Us. The positive correlation of weight with Up and Us reflected pore completion, resulting in weight gain and stone homogeneity. Further salt accumulation and action of MMP promoted a change in the coefficient of expansion/contraction, mechanical rupture, occasional weight loss and a decrease in wave velocity. Moreover, growth of MMP in biofilm slimes might provide appropriate conditions for salts to remain hydrated for long periods and thus prolong their disruptive effect on stone structure. The impact of NaC1 varied according to the porosity of the stone tested. Using sound velocity, a negative correlation to porosity with all stones and positive correlation to dry density with porous SL indicated the initial consolidating impact of salt by completing pores and internal voids. These effects were greater in the presence of MMP with all stones. The highly expanding Na2SO4 increased the dry density of the low porosity stones and decreased the porosity and surface hardness of all stone types. The completion of pores in the limestones by this salt might temporarily strengthen them, but its destructive potential is indicated by the weight loss with PL and reductions in surface hardness for all stones. Mechanical breakdown measured by sound velocity was due to the high uptake of NaESO4 by stones, reflected by pore reduction, dry density increase and surface hardness decreases of low porosity stones. When NaESO4 was combined with MMP, the large reductions in surface hardness and wave velocity were accompanied by unpredictable, large variations of density and pores, indicated by the very high material loss of all stones. During the first 20 cycles, all stones except PL exhibited increased transmission of sound velocity through limestone, indicating the initial consolidating effect of salts and MMP on structure, but this was followed by a decrease indicating mechanical ruptures. Occasionally between the 80th-100th cycles, some increases in velocity were observed, implying further consolidation on sound stone when debris had been removed. The negative correlation between sound velocity and porosity with NaC1 treatment (and perhaps with MMP) showed that the structure of all stones could be strengthened mechanically by completing internal voids and pores. The final increase of porosity of SL indicated that the consolidating effect of NaCl may be temporary. Na2SO4 strengthened the most porous stone, allowing this highly expanding salt to complete its voids without causing any mechanical disruption of its structure. The deteriorating potential of sulphur bacteria is achieved mostly by chemical means and requires further investigation. They are chemolithotrophic microorganisms living upon reduced inorganic sulphur compounds, usually found in urban and industrial areas. They form H2SO4 and seriously attack calcite-containing stones (Ehrich and Bock, 1996). Sulphate salts formed may also affect stone mechanically (Petushkova and Lyalikova, 1993). This form of biodeterioration can be of economic importance (Pochon and Jaton, 1967; Milde et al., 1983; Sand and Bock, 1988; Fernandez, 1995). PL was the most vulnerable stone and this was revealed by the sound velocity transmission technique. It was also the softest stone and this might have been an indication of its predisposition to weathering. The most porous stone (SL) was subject to the lowest weight variations but high porosity was not related to low surface hardness or mechanical strength.
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Acknowledgements This project was partly funded by the A. S. Onassis Public Benefit Foundation. We are greatly thankful to Mr G. Long (sound transmission velocity), Mr D. Weights (XRD) and Mr B. Loveridge (SEM), all from the School of Earth, Environmental and Physical Sciences, University of Portsmouth. References Atkinson RH. 1985. Five hardness tests for rock characterisation. In Hudson JA. (Ed) Comprehensive Rock Engineering, Principles, practice and projects, vol. 3. Rock Testing and Site Characterisation. Pergamon Press; 105-17. Bamford WE, Van Duyse H, Nieble C, Rummel F, Broch E, Franklin JA, Atkinson RH, Tarkoy PJ, Deere DU. 1981. Suggested methods for determining hardness and abrasiveness of rocks. Suggested methods for determining sound velocity. In Brown ET (Ed) Rock characterisation testing and monitoring ISRM Suggested Methods. Published for the Commission on Testing Methods International Society for Rock Mechanics by Pergamon Press; 95-103. Christaras B. 1991a. Durability of building stones and weathering of antiquities in Creta/Greece. Bulletin of International Association of Engineering Geology 44:17-25. Christaras B. 1991b. M6thode d'6valuation de l'alteration et modification des propri6t6s m6echaniques des granites en Grace du Nord. Bulletin of International Association of Engineering Geology 43:21-26. Christaras B. 1991c. Old bridges in Epirus, Greece. Hardness test using a thin section lapping mashine. In Decrouez D, Chamay J, Zezza F (Eds) Proceedings of the 2 nd International Symposium on the Conservation of Monuments in the Mediterranean Basin. Ville de Gen~ve; pp 453-462. Christaras B. 1993. Anisotropy effects on the physico-mechanical behaviour of stones: application using ultrasonic techniques. In Stone Materials in Monuments: Diagnosis and Conservation. Community of Mediterranean Universities - C.U.M. University School of Monument Conservation, 2 nd c o u r s e . Heraclion, Crete, 24-30.5.1993; pp 114-8. Ehrich S, Bock E. 1996. Biogenic sulphuric acid corrosion. Test procedure for cement bound materials. In 10th International Biodeterioration and Biodegradation Symposium. Hamburg, 15-18.9.1996. The Biodeterioration Society - Universit~t Hamburg. DECHEMA Monographs, vol. 133; pp 193-8. Fassina V, Rossetti M, Fumo G, Zezza F, Macri F. 1993. The marble decay of Pilastri Acritani and problems of conservation. In Thiel M-J (Ed) Conservation of Stone and Other Materials, Proceedings of the International RILEM/UNESCO Congress, Paris 29.61.7.1993, pp 75-82. Fernandez MGM, Mustin C, De Donato P, Barres O, Marion P, Berthelin J. 1995. Occurences at mineral-bacteria interface during oxidation of arsenopyrite by Thiobacillus ferrooxidans. Biotechnology and Bioengineering 46: 13-21. Franklin JA, Vogler UW, Szlavin J, Edmond JM, Bieniawski ZT. 1981. Suggested methods for determining water content, porosity, density, absorption and related properties and swelling and slake durability index properties. In Brown ET (Ed.) Rock characterisation testing and monitoring ISRM Suggested Methods. Published for the Commission on Testing Methods International Society for Rock Mechanics by Pergamon Press; 71-94.
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K6hler W. 1996. Investigations on the increase in the rate of weathering of Carrara marble in Central Europe. In Riederer J (Ed) Proceedings of 8th International Congress on Deterioration and Conservation of Stone, vol. 1.30.9-10.4.1996, Berlin; p 167-73. Lewis FJ. 1987. Investigations of bacteria on building stone and their role in stone decay. PhD thesis. University of Portsmouth, UK. Milde K, Sand W, Wolff W, Bock E. 1983. Thiobacilli of the corroded concrete walls of the Hamburg sewer system. Journal of General Microbiology 129: 1327-33. Montoto M, Valde6n L, C6tte, Calleja L, Corral N, L6pez T, S~,achez B, Esbert RM. 1994. Non-destructive characterization of the state of deterioration of Megaliths by ultrasonic tomography: a petrophysical interpretation. In Fassina V, Ott H, Zezza F (Eds) Proceedings of the 3d International Symposium on The Conservation of Monuments in the Mediterranean Basin. Venezia 1994; 3-9. Murphy W, Smith JD, Inkpen RIJ. 1996. Errors associated with determining P and S acoustic wave velocities for stone weathering studies. In Processes of Urban Stone Decay. Proceedings of SWAPNET'95 Stone Weathering and Atmospheric Pollution Network Conference, Belfast, 19-20.5.1995.228-44. Petushkova J, Lyalikova N. 1993. The microbial deterioration of historical buildings and mural painting. In Garg KL, Garg N, Mukerji KG. (Eds) Recent Advances in Biodeterioration and Biodegradation, vol. 1. pp 145-71. Pochon J, Jaton C. 1967. The role of microbiological agencies in the deterioration of stone. Chemistry and Industry, 23.9.1967: 1587-9. Rodriguez-Navarro C, Sebastian-Pardo E, Zezza U. 1994. Petrophysical-mechanical parameters for decay evaluation of building stones. A case study: Jaen Cathedral (Andalusia, Spain). In Fassina V, Ott H, Zezza F (Eds) Proceedings of the 3d International Symposium on The Conservation of Monuments in the Mediterranean Basin. Venezia 1994. 595-603. Ross KD, Butlin RN. 1989. Durability tests for building stone. Building Research Establishment Report, Department of the Environment. Rummel F, Van Heerden WL. 1985. Suggested methods for determining sound velocity. In Rock Characterisation Testing and Monitoring. ISRM Suggested Methods. Pergamon Press. 105-10. Sand W, Bock E. 1988. Simulation of biogenic sulphuric acid corrosion of concrete importance of hydrogen sulphide, thiosulphate and methyl mercaptane. In LHG Morton (Eds) Biodeterioration of Constructional Materials, Biodeterioration Society, pp 29-36. Simon S. 1998. Ultrasonic analyses. Project HERMES ENV4-CT98-0704. http ://iaclab. iceht, forth, gr/lab/hermes/ultrason, htm. Simon S, Snethlage R. 1996. Marble weathering in Europe - Results of the EUROCAREEUROMARBLE exposure programme 1992-1994. In Riederer J (ed) Proceedings of 8th International Congress on Deterioration and Conservation of Stone, Berlin, 159-66. Simon S, Verg6s-Belmin V, Blanc A, Snethlage R. 1994. The marble columns in the cloister of the Primatial church St. Trophime in Aries, France. Ultrasonic velocity measurements as a tool for anamnesis and diagnosis. In Fassina V, Ott H, Zezza F (Eds) Proceedings of the 3d International Symposium on The Conservation of Monuments in the Mediterranean Basin. Venezia 1994; p 11-7. Villegas S~achez R, Martin Garcia L, Vale Parapar JF, Bello L6pez MA, Alcalde Moreno M. 1996. Characterization and conservation of the stone used in the Cathedral of Almeria (Spain). In Riederer J (ed.) Proceedings of 8th International Congress on Deterioration and Conservation of Stone, Berlin 30.9-10.4.1996; 89-99.
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ANALYTICAL TECHNIQUES FOR CHARACTERIZING POLYCHROMATED COATINGS ON QUARTZITE SAMPLES FROM A PREHISTORICAL CAVE. A. Carmelo Prieto*, Juan Jimenez. Fisica de la Materia Condensada, Cristalografia y Mineralogia, Universidad de Valladolid. 47005 Valladolid, Spain. Begofia P6rez, Luis Leal. Centro de Tecnologia L/tser. Parque Tecnoldgico de Boecillo. 47151 Boecillo, Valladolid, Spain.
Abstract Different analytical techniques have been employed in the mineralogical, morphological and physico-chemical characterization of a quartzite sample extracted in the vicinity of an archaeological site. The main objective of this work has been the identification of pigments deposited on the sample surface with the aim of determining if they have an anthropological origin. The interaction between the pigment layer and an infrared radiation from a Nd:YAG laser has been studied. Keywords: microRaman spectroscopy, LIBS, cathodoluminescence, identification of pigments and stone substrates, archaeological prospecting.
1. Introduction One of the most relevant aspects in cave paintings conservation is the accurate determination of the nature and origin of the pigments used in its polychromy. Several analytical techniques permit to determine wether the presence of pigments is due to natural or human causes. This is important in order to define prospecting studies and conservation methodologies for cave paintings heritage.
During the works of cleaning and consolidation of cave paintings in Benquerencia de la Serena (Badajoz, Spain), some natural pigments were discovered on the quartzite wall of the shelter. The interest of the conservators was to analyse these pigments, which were extracted from the wall by rubbing its damp surface. This work reports on the morphological, mineralogical and physico-chemical characterization of samples from previously cited archaeological site. Morphological aspects were studied by optical stereomicroscopy, Nomarski microscopy (OM) and scanning electron microscopy (SEM). These analyses have been completed by means of a microcolourimetric study on different regions of the sample. Sample characterization was carried out using powder X-Ray diffractometry (XRD), microRaman spectroscopy and infrared spectroscopy (IR). A study to determine the main components of the sample has been done on the surface by means of energy dispersive X-ray fluorescence analysis (SEM+EDX). Physico-chemical characterization and depth of pigmentation and chromaticity in the stone sample has been achieved by Laser Induced Breakdown Spectroscopy (LIBS), cathodoluminescence (CL) and Raman microprobe of stratigraphic profiles.
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All these non-destructive techniques present a high spatial resolution and enable analyses with an spatial resolution better than 1 gm.
2. Experimental Methods Samples under study did not require any previous preparation. Analyses were carried out on the external surface (covered by the pigment) and also on the interface pigment/quartz. A stereomicroscope (Nikon SZM-U zoom 1:10) and a microscope (Olimpus BH2) equipped with Nomarski differential interface contrast objectives were employed for the optical microscopy observation. Both microscopes are fitted with a digital system which enables the capture of images for later treatment. Chromatic parameters have been determined by using two colourimeters from Dr. Lange (LZM 076 "microcolor") and Minolta (CR 200). SEM microphotographs were obtained using a scanning electron microscope JEOL JSM820 equipped with an energy dispersive X-ray (EDX) analyser (LINK QX-2000). XRD patterns were obtained on a Phillips PW 1729 instrument with a graphite monochromator for selecting the CuKc~ radiation. IR spectra from samples prepared in KBr (1%) pellets were recorded on a Mattson Cygnus-100 FTIR spectrometer in the 4000-400 cm-1 spectral range. Micro-Raman spectra were recorded with a DILOR X-Y Raman spectrometer attached to a metallographic microscope. The excitation was done with either 488.0 or 514.5 nm lines of an Ar laser focused by the microscope objective which also collects the scattered light. The Raman signal spectrally resolved with the spectrograph was detected with a liquid nitrogen cooled CCD. The Raman spectra were obtained in backscattering with the laser beam perpendicular to the sample plane. Raman spectra were measured at different positions of the processed surfaces. Stratigraphic studies have been performed following analytical microRaman profiles for transversal and perpendicular sections of the painting samples. The diameter of the laser beam at the focal plane is diffraction limited according to the Rayleigh criterion (D=l.22k/NA); where ~, is the laser wavelength and NA is the numerical aperture of the objective. In our standard experimental conditions the lateral resolution was around 1 gm. +
Cathodoluminescence is based upon the study of a the light emitted by the crystal under the action of electronic bombardment [1] [2], Cathodoluminescence (CL) microscopy and spectroscopy in a scanning electron microscope (SEM) are particularly suitable techniques for high spatial resolution (lam) and high sensitivity (ppm) detection of defect centers in materials [3]. The migration and electrodiffusion of particular luminiscent centers may be imaged with high spatial resolution using monochromatic CL microscopy, following the identification of the mechanisms producing the emission bands in the CL spectrum. CL microanalysis complements the defect structure information available from other spectroscopic techniques. The observed changes in the quartz stratigraphy are correlated to the changes observed in the CL micrographs. Therefore, CL microanalysis gives insight into the microscopic processes contributing to the changes in the profile stratigraphy. The CL experiments were performed in a JEOL JSM-820 SEM equipped with an Oxford mono CL2 cathodoluminescence imaging and spectral analysis system. CL spectra were collected as a function of wavelength ~. (nm). The CL was excited using a continuous stationary electron beam at normal incidence and measured using a retractable parabolic mirror collector.
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The LIBS technique is based on the spectroscopic analysis of the emission from the intense plasma generated when a pulsed laser beam is focused onto a sample surface. In recent years, many works describing several analytical applications of this technique have been published [4]. For instance, LIBS has been shown to be very useful in the analysis of elemental composition of metal alloys, identification of metallic constituents and impurities on the surface of inorganic minerals, trace analysis of metal ions on aqueous solutions and so on. LIBS measurements were carried out in the Foundation for Research and Technology Hellas (F.O.R.T.H., Crete, Greece). A Q-switched Nd:YAG Spectron laser (~,=1064 nm, 300 mJ per pulse, 10 ns pulse duration) was used in the coating removal. A quartz fiber was used to guide the emitted light from the plasma to the detection system, consisting of a spectrograph (PTI Model 01-001 AD) equipped with two interchangeable gratings and an optical multichannel analyser (EG&G PAR OMA III 1420 UV) with an intensified photodiode array detector.
3. Results and Discussion
The sample morphological study shows that the rock presents a high homogeneity and a superficial red tonality. On the red-coloured region we can appreciate some dispersed dark spots. Figure 1 reveals the presence of cavities without pigmentation and with quartz crystals surfacing in its interior. Small formation of lichens have been appreciated in circular arrangement. The study of the surface stratigraphy by means of optical microscopy (OM-Nomarski) and scanning electron microscopy (SEM) shows the presence of only one pigment layer of variable thickness (100 gm average) in all the samples analysed. Colourimetric measured the CIELAB chromatic coordinates (L*: [0 Black; +100 white], a*: [-60 green; +60 red], b*: [-60 yellow; +60 blue]) on the different areas presenting chromatic and tone differences. Chromatic data are shown on Table I. Following the parameter a*, it is noticeable its Figure 1: Aspect of the pigmented high value (a*=25) in the red coloured areas, surface of the analysed sample decreasing in greyish areas (a*=l 5). Lower values are obtained in black pigmented areas (a*=2.5). Dark zones do not show lower values for L* (luminosity) due to the presence of small cavities with small quartz crystals in their surface. The values of L* in quartz substrate (uncovered by pigments) and in red pigmented region show small variations. Table I Colourimetric anal, rsis Zone L* a* b* Substrate without pigment 27,9 9,1 4,7 Red intense 33 25 12,3 Red and grey 20,6 25,9 5,4 Red, grey and quartz 27,8 2,5 -0,6
Zone Grey Grey-black Black Black and quartz holes
L* 27,1 25,6 19,8 27,4
a* b* 16,9 3,8 14,5 1,3 12,6-1,3 11,6 0,1
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The mineralogical phases forming these natural pigments on quartzite have been determined by powder X-ray diffractometry, indicating that the painted surfaces are basically constituted of kaolinite and hematite (Marsred). Table II show the experimental reflections assigned to the three mineralogical species found. It is noticeable the major presence of reflections attributed to hematite (He) and quartz (Qz), with minor reflections attributed to kaolinite (Ka). Table II. XRD results dhk, I/Io (hkl) He. 7,0813 5,2 4,2560 29,8 3,6928 13,1 (012) 3,5829 20,4 3,3496 100,0 2,9318 15,2 2,7010 66,8 (104) 2,5236 62,3 (110) 2,4523 33,9 2,3435 20,1 2,2821 37,4 2,2385 33,9 2,2083 30,4 (113) 2,1318 30,4 1,9777 28,7 (221) m
(hkl) Q
(hkl) Ka (001) (100) (020) (021) (002) (101) (111) (112) (022) (13 1) (110) (13 1) (20 2) (102) (111) (13 2) u
(200) (02 3) (201)
dhkl 1,8892 1,8425 1,8238 1,8193 1,6957 1,6741 1,6017 1,5414 1,4906 1,487 1,4586 1,4550 1,3829 1,3761 1,3711
(hkl) I/Io (hkl) (hid) He Q Ka 12,8 (203)(132)(004) 40,5 (024) (133) 86,5 (112) 86,5 (024) 46,7 (116) _(24 1) 36,0 (116)(202) (240)(204) 16,6 (210) (2 4 2)(043__) 64,0 (211) (134)(313) 40,5 (060)(33 1) 40,5 (214) (lOO) 45,7 (113) 43,3 (300) 50,5 (212) 79,9 (203) 74,7 (301) m
Both FTIR and microRaman spectra confirmed the presence of kaolinite and hematite. Table III show the vibration modes from FTIR spectra of the external pigmented layer in the region 450-4000 cm~. Spectra obtained are easily correlated with typical spectrum from hydroxy kaolinite. Table III: FTIR data for mineralogical phases Wn. Assignment (Ka: Kaolinite, (cml) He: Hematite, Qz: Quartz) 466 6 (Si-O) and p~ Eu (He) 536 E~ v (Si-O-A1) (Ka); Eu (He) 690 A~ v(Si-O-Si) (Ka) 739 Libration OH (Ka) 777 Libration OH (Si Si O'"OH) (Ka) 794 Libration OH(Si A10"-'OH) (Ka) 912 8 (M-OH) (Ka) 1010 E1 vl(Si-0-Al) (Ka) 1032 E1 vl(Si-0-Si) (Ka) 1093 11 ~t1 (SiO)(Qz) 1425 Carbonate (trace) 1
of red ~igment Wn. Assignment (Ka: Kaolinite, (cm"1) He Hematite, Qz: Quartz) 1547 Librat. OH...O(SiA1) (Qz) 1639 cg(SiSiO...OH) (Qz) 1658 0(SiA10...OH) (Qz) 2850 Combination bands (Ka) 2920 Combination bands (Ka) 2956 Combination bands (Ka) 3408 v (OH...O(SiA1) (Qz) 3614 v(In OH) (Ka) 3633 v3(Ou OHs) (Ka) 3658 v2(Ou OHs) (Ka) 3691 ~/I(OUOHs) (Ka)
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Stretch bands of hydroxyl groups have been identified, as is common in octahedric silicates with Si(A1) substitutions in tetrahedric position [5]. The four infrared bands are assigned as follows: the three high frequency vibrations (labeled Vl, v2, v3) are due to the three inner surface hydroxyl groups (OuOHs). The band at 3614 cm -1 is due to the inner hydroxyl (InOH) [6]. Presence of perpendicular (Si-O) vibrations at 1093 cm -1 and in-plane Si-O-Si stretching vibrations at 1032 cm -1 (Si-O-Si), 1010 cm -1 (Si-O-A1) and 912 cm -1 (N-O-H), confirm the presence of kaolinite in the surface pigmentation. Two characteristic bands of hematite (He) at 466 cm 1 and 536 cm -1 (attributed to 02. displacements p 1 and a, respectively) with symmetry Eu [7] do also appear. The last band can be overlapped by Si-O-A1 bending vibrations of dioctahedric minerals. Presence of quartz with substitutional Si(A1) is evident by a high absorption band at 3408 cm 1 corresponding to OH stretching vibration of Si(A1)OH and two bands at 1639 cm 1 and 1658 cm 1 corresponding to the water bending vibration. MicroRaman measurements on the pigment surface (Figure 2) and on the rock substrate (Figures 3 and 4) have been done. MicroRaman spectra corresponding to red pigmented areas show a wide fluorescence band with a maximum around 3400 cm 1. Figure 2 shows a typical hematite spectrum in the spectral region 120-900 cm ~, without fluorescence effects. Bands at 222 (m), 242 (w) and 289 (w) cm 1 are assigned to e 3+ displacements with species of symmetry A lg and Eg, respectively. Modes of O z- displacements P2 -1
-1
(Eg) at 292(s) cm , Pl (Eg) at 405(s) cm , -1
and a (Eg) at 603 (w) cm are also present. The spectrum shows some complex bands at 850-940 cm 1 and 1100 cm 1 which might be attributed to librations Fe A1 Si (OH) of dioctahedric silicates present in the hematite pigmentation. This hypothesis is confirmed by the stretching bands of hydroxyl groups at 3550-3600 cm 1. Figure 2: Typical microRaman spectrum of hematite in the 120-900 cm ~ region.
Figure 3 Raman spectra of a-quartz in the 120-900 cm 1 and 700-1400 cm -~ Stone substrate shows a typical Raman spectrum of a-quartz at room temperature [8]. Figure 3 the complete spectrum in the region 150-1400 cm 1. A1, E(LO+TO), E(TO) and E(LO) modes are Raman active [9]. A1 modes appear at 205, 355, 465 and 1082 cm 1,
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E(LO+TO) modes appear at 264, 696 and 1161 cm~. E(TO) and E(LO) modes appear at 393, 450, 795 and 1065 cm1 and at 406, 509, 807 and 1236 cm-1, respectively. Weak bands, as in the pigmented surface, appear at 840, 900 and 917 cm-1, attributed to librations of the cations replacing Si in tetrahedric positions linked to surface hydroxyl groups, as it happens in dioctahedric materials (hydroxy kaolinite). Two components appear at 13001320 cm1 which are rather probably associated with the presence of graphite [10]. This material can arise from the thermal treatment applied to the pigment to achieve the desired chromatic appearance. The microprobe analysis (SEM+EDX) reveals a major presence ofFe, Si and A1, a minor amount of Ca and K and eventually C1, S, Ti and Pb. EDX spectra have been obtained on the pigmented surface with different colourimetric parameters. Elemental analyses and relative distribution of concentrations agree with chemical composition of mineralogical components obtained by means of DRX, FTIR and microRaman analyses. SEM+EDX spectra of intense red pigment show majority presence of Fe, Si and A1 and minority presence of P, C1 and K. Black pigmented regions present a major presence of Fe, Si and A1 and traces of P, C1 and K. Fe/Si (A1) relative proportion is higher in Fe for dark areas than for red areas. This is due to a decrease in the relative concentration of kaolinite in black regions. SEM+EDX analysis of rock cavities covered with quartz crystals show a high concentration of Si and a low concentration of Fe. The stratigraphic profile analysed and the microRaman spectra obtained from the substrate, interface and external pigmented layer is shown in Figure 4. The evolution of the Raman parameters along the scan line has been analysed in the region 150-900 cm~. In this region, it is noticeable the high intensity of A1 mode for quartz at 205, 355 and 465 cm a.
Figure 4: microRaman spectra of stratigraphic profile. E(LO+TO) modes at 264 cm-1 appear with lower intensity. E(TO) and E(LO) modes appear at 393 and 406 cm1, respectively. The spectrum obtained at a depth of 180 [am (Figure 4a) remains nearly unchanged almost to the chromatic interface at 105 [am of the external surface (Figure 4b). On the other hand, the spectrum at 95 [am from the surface do not show the bands of the quartz. Spectra recorded at 95 gm, 50 [am and 5 ~tm from the external surface (Figures 4c, 4d and 4e) present bands at 222 cm1 (Alg), 242 cm1 (Eg), 292 cml -1
(p2 Eg) and a high intensity peak at 404 cm (p 1 Eg), characteristics of the hematite. Figure
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4 shows also a reference spectrum of hematite (marsred), [ 11 ] which confirms the results explained above. CL images are shown in Figure 5a. The CL image is correlated to the one obtained by SEM and shown in Figure 5b. Cathodoluminescence spectra (Figure 5c) have been obtained following the stratigraphic profile of the samples. Two main luminescence centres are usually reported in quartz: intrinsic and impurity-associated defects [12]. There are several types of intrinsic defects of which the most common is the E l' centre (electron at oxygen vacancy in the polyhedral SiO4). Other intrinsic defects are oxygen vacancy, interstitial 2-
oxygen (O centre) and oxygen associated trapped-hole centres called peroxy centre for dry quartz and NBOHC (non-bonding oxygen hole centre) for wet quartz [ 13]. Main impurities in quartz are iron (Fe), titanium (Ti), aluminium (A1) and alkaline metals.
Figure 5: a) CL image, b) SEM micrograph, c) CL spectra The typical CL spectrum of crystalline quartz shows two wide bands centred at 430 nm (2.75 eV, blue emission) and 629 nm (1.93 eV, orange-red emission) respectively. The blue emission band is associated with a radiation recombination of an E 1' centre, while the red emission band is associated with NBOHC defect [14-16]. The spectra obtained in our samples were compared with the one obtained on a natural quartz crystal (rose quartz with impurities from the natural deposit of Puente Mocha-Perefia (Salamanca, Spain) with a red tonality due to a small concentration of iron impurities (Fe 3+) used as reference. The CL was more intense in the quartz region underneath the pigment (Figure 5a) while CL intensity decreases for inner parts in the quartz substrate. This suggest
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that iron originally in the pigment in-diffuses the quartz substrate. CL spectra (Figure 5c) reveal a dominant contribution of the 629 nm band, which suggests once again that iron is incorporated. The spectrum obtained in a point far from the coloured surface of the sample (Figure 5c3) shows a high resemblance with the reference spectrum. Regions with low CL luminosity near the interface quartz-pigment show a spectrum slightly different from the reference one. It is noticeable a slight splitting in the red band which could be attributed to the existence of impurities associated to centres [Fe3+-M+] where M + can be an alkaline metal [14] (Figure 5c2). In regions with high luminosity CL and close to the interface quartz-pigment (Figure 5c 1), it is found a more important contribution of the red band (629 nm) with a shoulder in the low energy side. This could be due to the fact that a desorption produced by the incorporation of Fe 3+ from the pigment to the quartz substrate is taking place in the vicinity of the region measured [14]. Total CL spectrum (Figure 5c) can confirm that hypothesis since it presents an incipient peak centred at 725 nm (1.70-1.80 eV) due to the presence of Fe 3+ in tetrahedric positions replacing Si4+ or AI3+ previously introduced in the crystalline structure. LIB S measurements were done after consecutive laser impacts on different areas resolved by the colourimetric study. The intensity of all the identified bands decreases with the number of pulses applied confirming the non existence of a multi-layer structure. The intensity of the emission bands associated with iron decrases with the number of laser pulses applied on the same area. Four different areas have been identified (black, brown, reddish and white). Spectra from black and brown areas are very similar, with high intensity peaks attributed to Fe (indicating presence of pigments) and Si (due to the quartz from the substrate). Concentration of Fe in reddish and white regions is significantly lower, revealing the major contribution of the quartz substrate.
4. Conclusions
In this work a complete study of the natural pigments deposited on the surface of a quartzite sample from an important archaeological prospecting has been carried out. Morphologic observation using optical stereomicroscopy (OM) shows only one pigment layer less than 100 ~tm thick. Mineralogical phases forming pigments have been determined by XRD, FTIR and microRaman spectroscopy indicating the presence of kaolinite hydroxyls and hematite. Microprobe analyses by SEM+EDX reveal that Fe, Si and A1 .are the major chemical constituents of the pigments. Minor amounts of Ca and K (and eventually C1, S and Ti) have been detected. The stratigraphic and physico-chemical study have been obtained on cross sections with high spatial resolution. Only mineralogical phases corresponding to pigment and quartz have been detected which confirms the absence of different layers on the surface. Typical spectra of metamorphic quartz showing two bands at 430 nm and 629 nm due to oxygen vacancies associated with cationic impurities were obtained from cathodoluminescence analysis. These detected bands are more intense beneath the pigment surface, which suggest the migration of Fe 3§ ions from the pigment layer to crystalline quartz. A natural quartz crystal with rose tones due to small intercrystalline concentrations of iron was used as a reference material.
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LIBS spectra were recorded after consecutive laser impacts on the same zone of the sample surface. The intensities of all the identified emission bands decreased with the number of pulses applied showing the non-existence of a multi-layer structure. In summary, analytical techniques with a high spatial resolution have been proven to be unique tools to analyse the interaction between pigments and the quartz substrate. These techniques provide significant advantages, particularly respecting a reduction in time analyses, sensitivity, specificity, spatial resolution and immunity to interference even when a very small amount of specimens is required for the extraction of information.
Acknowledgements The authors wish to thank R. Casasus and A. Barr6n (Consejeria de Cultura y Patrimonio, Junta de Extremadura, M6rida, Spain), for their collaboration and kindly supply of samples. Also, we are indebted with Dr. V. Zafiropulos from Foundation for Research and Technology Hellas (FORTH, Crete, Greece), for the facilities given during the LIBS experiments. Dr. M. P. Avella is acknowledged for his help with cathodoluminescence analyses. References [ 1] Marshall D.J., 1988. Cathodoluminiscence of geological materials. Academic Division of Unwin Hyman Ltd, London, UK. [2] Yacobi B.G. and Holt D.B., 1990. Cathodoluminiscence microscopy of inorganic solids. Plenum Press, New York. [3] Remond G., Cesbron F., Chapoulie R., Ohnenstetter D., Roques-carmes C., and Schvoerer M.,1992. Cathodoluminiscence applied to microcharacterization of mineral materials: A present status in experimentation and interpretation, Scanning Microscopy International, 6 (1) 23-68. [4] Maravelaki P.V., Zafiropulos V., Vilikoglou V., Kalaitzaki M., Fotakis C., 1997. Laser-Induced breakdown spectroscopy as a diagnostic technique for the laser cleaning of marble, Spectrochimica Acta Part B52, 41-53. [5] Frost R.L., 1997. The structure of the kaolinite Clay Minerals - An FT-Raman Study. Clay Minerals, 32, 73-85. [6] Johansson U., Frost R. L., Forsling W., Kloprogge J.T., 1998. Raman Spectroscopy of the Kaolinite Hydroxyls at 77K, Applied Spectroscopy, 52(10), 1277-1282. [7] Farmer V.C., 1974. The anhydrous oxide minerals: in The Infrared Spectra Minerals, V.C. Farmer, ed., Miner. Soc. Monograph 4, London, 185-189. [8] Castex J. and Madon M., 1995. Test of the Vibrational Modelling for the)~-Type Transitions: Application to the ct-15 Quartz Transition. Phys. Chem. Minerals 22, 1-10. [9] Scott J.F., Porto S.P.S., 1967. Longitudinal and Transverse Optical Lattice Vibrations in Quartz, Physical Review, 161 (3), 903-910. [ 10] Lespade P., Marchand A., Couzi M., Cruege F., 1984. Caracterisation de materiaux carbones par microspectrometrie Raman, Carbon 22, 375-385. [11] Bell I.M., Clark R.J.H. and Gibbs P.J., 1998. Raman spectroscopic Library of natural and synthetic pigments, http://calcium.chem.ucl.ac.uk/webstuff/resources/raman
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[12] Stevens KalceffM.A., Phillips M.R., Moon R., 1996. Electron irradiation-induced changes in the surface topography of silicon dioxide. J. Appl. Phys. 80 (8), 4308-4314. [ 13] Stevens Kalceff M.A., Phillips M.R., 1995. Cathodoluminescence microcharacterization of the defect structure of quartz. Physical Review B, 52 (5), 3122-3134. [ 14] Picouet P., Ramseyer K., Pradell T., 1998. Evolution of cathodoluminescence from fired low carbonate bricks (CACO3_<0.4%)in Zi-Annual for the brick and tile, structural ceramics and clay pipe industries, Ed. Kokot C. Bauverlag BMBH, Wiesbaden und Berlin. [ 15] Picouet P., Maggetti M., Piponnier D., Schvoerer M., 1999. Cathodoluminescence spectroscopy of quartz grains as a tool for ceramic provenance. Journal of Archaeological Science, 26, 943-949. [16] Picouet P. 1999, Cathodoluminescence spectroscopy and the orientation of a hydrothermal quartz crystal. Bull. Swiss Society of Mineralogy and Petrography. (in press)
629 STONE D R Y I N G SURFACE AREA
:
AN APPROACH OF THE EFFECTIVE EVAPORATING
B6n6dicte Toumier *, Daniel Jeannette, Christine Destrigneville Centre de g~ochimie de la surface, Strasbourg, France
Abstract
In this experimental study of drying stones, we compare evaporation kinetics between - reference : free water cupels, - 8 cm long and 4 cm in diameter cylindrical rock cores. Cupels filled with water and saturated samples are drying in a closed box where relative humidity is controled by salts. The samples were cored in Fontainebleau sandstone (11.5% of porosity) and in Lourdines micrite (26.5 % of porosity). During the first drying stage of samples we can observe that : - fluxes calculated with respect to the macroscopic surface areas of the rock samples are higher than fluxes calculated for the references, - for a given sample, fluxes obtained after a partial saturation are higher than fluxes obtained after total saturation. Different factors contribute to over-estimate the effective evaporating surface area with respect to the macroscopic surface area. We present here the evaluation of the effective evaporating surface area of cupels containing free water, using formulas of the Wilhelmy method. Results allow us to relate water loss with cupels evaporating surface area, and with this relation we calculate the rock samples effective evaporating surface areas. This kind of approach can be used to evaluate alterations or the influence of treating products on the evaporating surface. Keywords : drying, porous material, Fontainebleau sandstone.
stone,
effective
evaporating surface area,
1. I n t r o d u c t i o n
Alteration shapes and intensity depend on the position of salt crystallisations themselves depending on evaporation kinetics of the solutions circulating through the porous stones. The understanding of mechanisms controlling the rock drying allows us to explain degradation shapes. This study is an extention of the previous one done by Hammecker (1993). In his study, he estimated the external parameters importance and the influence of rock capillary properties on drying kinetics. We have studied more precisely the evaporation of water from Fontainebleau sandstone and Lourdines micrite saturated cores. The petrophysical properties of these rocks are relatively different and well known. But in this paper we will develop essentially the results obtained with the sandstone. In the case of both rocks some cores have been several times totally or partially saturated. Then they are dried with temperature and relative controlled constant humidity. The aim of these experiments is to compare drying kinetics of both rocks and to test the initial saturation effect upon those kinetics. * Author to whom correspondence should be addressed.
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2. Experimentation 2.2 The materials
Figure 1. Photographs of colored thin sections " a. Fontainebleau sandstone, b. Lourdines mierite. The red resine represents the free porosity accessible by capillarity whereas the blue resine represents the trapped porosity. Scale = 100 lam. The Fontainebleau sandstone (fig. l a) is formed of 98 % quartz grains of about 300 lam in diameter. Its porosity is very low (= 11.5 %) and its specific surface determined by krypton adsorption is about 0.02 m2/g. The free accessible volume of voids by water during a capillary absorption under atmospheric conditions (free porosity, materialized by the red resine fig. 1) corresponds only to 5 % of the bulk volume of voids. This free porosity is located in the thin intergranular voids (<1 lam) and on the periphery of the maeropores (about 100 lam in diameter). Determined by mercury porosimetry, the radius of the pore threshold corresponds to the larger eonnexions giving access to the majority of the porous volume. The value of the sandstone radius threshold is equal to 10 lam. The low value of free porosity can be explained by the big difference between the pore diameters and their access dimensions (Dulien 1979, Bousquir, 1979). The Lourdines micrite (fig. l b) containing 98 % calcite is composed of micritic intraelasts cemented by scattered sparitie calcite. Its bulk porosity is 26.5%. Most of this porous volume is located in the microporous intraclasts (<1 lam). The radius of the pore threshold given by mercury porosimetry is 0.1 lam. The maeropores (of about 15-30 lam in diameter) are rare. In this rock, porosity is more homogeneous than in the Fontainebleau sandstone : pore thresholds and pores themselves are of the same dimensions. These homogeneous porosity structures justify the more efficient capillary absorption and the lower trapped porosity : as the porosity is more homogeneous the connectivity is better and then the free porosity is higher (about 23 %). The specific surface is small, equal to 1 m2/g, but higher than the sandstone one. The petrophysieal properties of both rocks are summarized in table 1.
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Table 1 9 Principal petrophysical properties of Fontainebleau sandstone and Lourdines micrite Fontainebleau sandstone Lourdines micrite 11.5 26.5 Bulk porosity (%) 5.5 Free porosity (%) 23 10 Mercury radius threshold (lam) 0.1 Specific surface (m2/g) 0.02 1 2.3 Experimental procedure The results exposed hereafter were obtained with 8 cm high and 4 cm in diameter cylindrical cores. The core dimensions correspond to a representative rock volume and a height small enough to avoid the gravity effects on hydric transfers (Mertz, 1989). Samples are totally or partially saturated with water. Total saturation is obtained under vacuum whereas partial saturation is carried out with a capillary absorption under atmospheric conditions. This kind of partial saturation is like natural saturation. The saturated samples are wrapped in a Teflon sheath to limit evaporation from the upper surface. Cores and cylindrical cupels (5.5 cm in diameter) dry simultaneously in closed boxes in which brines control the relative humidity. The relative humidity is maintained at 33% or 75% with repectively MgCI2,6H20 or NaCI. The temperature is fixed at 24~ 2.4 Results presentation
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Figure 2. Typical experimental curve of rock drying showing the three classical phases. Saturation = percentage of porosity filled with water, dW/S = water loss per macroscopic surface area unit To present drying experiments results we ploted curves representing the water loss versus time 9samples and cupels are weighed at regular periods of time. To compare water loss between different rocks in one hand and on the other hand between references and rock samples, all fluxes are calculated with respect to macroscopic evaporating surface areas (=
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7rr2). So we can .compare water loss per time unit and surface unit for different objects drying in the same conditions. In cupels, if a constant water level is maintained, water loss is linear versus time. So in a graph dW/S = f(t), where dW is the weight or water loss, S the macroscopic evaporating surface area ( - xr 2) and t the time, we can define the flux r = dW/St correponding to the slope of the straight line. When a porous media is drying, we usualy to distinguish 3 phases (cf. fig. 2). During the first stage (phase I), the water loss is high and constant as long as the evaporating surface keeps wet. During phase II the evaporating surface is dry and water loss small and not constant. Finally, during the last stage (phase III), the tiny water loss is relatively constant. We can define several representative values on these curves " for the first drying stage we have the slope,
References and sample fluxes calculated with respect to the macroscopic surface areas (cf. fig. 3, table 2) allow two observations"
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Figure 3 : Curves showing the water loss of a 8 cm high Fontainebleau sandstone sample (Ft4a3). Drying is carried out at 33% relative humidity after total saturation (bit) and partial saturation (Nc). To compare samples and reference fluxes we have ploted a cupel water loss obtained in exactly the same conditions. References fluxes are always smaller than the sandstone samples fluxes whatever the initial saturation and relative humidity. This observation is true for the Fontainebleau sandstone and most of the other rocks.
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With the experimental conditions described in 2.3, for a given relative humidity and a given sample, the flux measured after partial saturation by capillary absorption is always higher than the flux measured after total saturation. We can make the same observation for the Lourdines micrite. Table 2 : Mean values and errors of measured fluxes during the first drying stage on Fontainebleau sandstone cores. All samples are 8 cm high. We report the measured fluxes of 5.5 cm in diameter cupels. 9 Nc 9flux measured atter capillairy imbibition, 9 N t flux measured after total absorption. t FIux (g/cm2.h) Relative humidity = 33% Relative humidity = 75% O Nc 010118 + 0.0006 0.0036 + 0.0002 9 Nt 0.0083 ~: 0.0007 0.0030 + 0.O001 Reference . . . . . 0.0047 4- 0.0002 .... O.0015 + 0.000 i . . . . .
4. Interpretations The first observation about reference comparison to porous samples rate of evaporation is well known. In particular Jouany (1981) stated that the greater the porosity of the samples, the higher the ratio samples evaporation flux versus free water surface evaporation flux. She calculated the mineral surface area on samples evaporating surface, that is to say she took the surface roughnesses into account. She has shown that the greater the developped surface, the higher the rate of evaporation is. In agreement with this argument we can think that if the calculated flux for a cupel free water surface is smaller than the calculated flux for a sample macroscopic surface area it is because the effective evaporating surface area is higher than the macroscopic surface area. Also the higher the sample porosity and the higher its specific surface, the greater its effective surface area. In our experiments, the difference between the evaporation fluxes of Fontainebleau sandstone and Lourdines micrite verify this hypothesis : Lourdines micrite is caracterised by a specific surface of 1 m2/g and a porosity of 26.5% whereas the Fontainebleau sandstone is caracterised by a specific surface of 0.02 m2/g and a porosity of 11.5%. Whatever the relative humidity and the initial saturation, the Lourdines micrite fluxes are always higher than the Fontainebleau sandstone fluxes. The second observation concerns the first drying stage for which one admits that the flux is constant because of constant external evaporating conditions. Those external conditions are supposed to be balanced by capillary tranfer which maintain the surface wet. The second phase would be due to a capillary transfers diminution. And these tranfers would be higher than the potentiel evaporating flux fixed by the external conditions as long as the saturation is greater than the critical saturation (Sc, fig. 2). If the flux depends only on external factors, for a given sample and given experimental conditions we should always observe the same flux as long as the initial saturation is higher than Sc. This is not true : for the studied cores (fig. 3, table 3), after partial saturation the flux is systematically higher than the flux obtained after total saturation. If we reason in term of effective evaporating surface, we can explain this observation : after a total saturation, big broken open pores at the surface of cores are filled with water but not after "natural" saturation by capillary absorption. On the contrary after this kind of partial saturation only the smallest pores are filled with water at the surface. With total saturation
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the effective evaporating surface is smoother than with a partial saturation for which the most of the roughnesses at the sample surface is responsible of the increase of the effective evaporating surface. 5. An effective surface area approach Atter previous observations, it stands to reason that the effective evaporating surface area is not the macroscopic evaporating surface area. We propose an approach allowing to calculate the effective evaporating surface area.
Table 3 : Evaporating surface areas (in cm2) calculated for four sandstone from the experimental water loss measured at 33 or atter total (Nt) or partial (No) saturations. For comparison, the surface area is equal to 22• that is to say 12,6 cm2 Surface areas (cm2) 7s*/o Nc Nt Ft4a3 28.18 22.1 Ft4a6 Ft4b3 25.75 23.3 ' Ft4a4 .
.
.
.
.
samples of Fontainebleau 75% relative humidities, macroscopic evaporating 33% Nc 42.6 45.6
Nt 31.6 29.4
This calculation is based on the next hypothesis : during the first drying stage of a porous medium, for a given relative humidity, only the effective evaporating surface area is responsible for the value of the water loss per unit time. So, if the relation (dW/t)Rn = f(t) is known, for a porous medium drying at a relative humidity RH, we can deduce the value of the effective evaporating surface area from the experimental measures of the flux. To establish this relation we have made drying experiments with glass pipes of different diameters. During these experiments we determined values of water loss per unit time versus the evaporating surface areas. As the water in the cupels forms a meniscus, the effective evaporating surface area is higher than the macroscopic one rcr2. So, first we have calculated the effective evaporating surface area of the pipes taking into account the meniscus curvature. To do this we have used Wilhelmy method formulas mentioned by Goodrich (1961) and Joanny (1985). We have reported experimental values of water loss per unit time and calculated values of effective evaporating surface areas in a graph (dW/t)= fit). From this we have deduced the next relations : (dW/t)75% = -0.00155 Sw - 0.00278
(1)
(dW/t)33% = -0.00324 Sw - 0.00514
(2)
With these relations, we have estimated the sample rocks effective evaporating surface areas responsible for water loss during the first drying stage at 33 and 75 % relative humidities. Results are shown in table 3. After these results, the Fontainebleau sandstone effective evaporating surface area is 1.8 to 3.5 times higher than its macroscopic surface. Then we can see that after a capillary absorption the effective evaporating surface area is 1.18 to 1.45 times higher than after total saturation.
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Conclusion
In our approach of the evaporation first phase we have considered that : - all participating water to evaporation has the same thermodynamic properties wherever located on a free water surface or in the over-lapping of the mineral surfaces ; - for same external conditions, the evaporating flux is only controlled by the effective evaporating surface area, that is to say surface capillary supply is always in excess and has no limiting part in evaporation. Our experimental study shows that : - a rock sample effective evaporating surface area is higher than its macroscopic surface area and with greater reason than its porous surface area submitted to evaporation ; - the effective evaporating surface area is a developped surface of the macroscopic one, so rock porosity structures have a direct effect on the evaporation flux ; - the flux of evaporation is influenced by the initial saturation rate : depending on whether superficial large pores are filled with water (total saturation) or just overlapped with water (partial saturation) the effective evaporating surface area changes. These observations have applications in evaluation of damaged and treated stones evaporating surfaces. - Every kind of weathering contributes to modify stone surfaces. These modifications involve a constant evolution of the effective evaporating surface area and so constant evolution of the weathering mechanisms. It is the case of salt precipitations in voids at stone surface or for crusts over lapping which modify permeabilities (Thomachot, 2000). - All consolidation or protection treatments modify stones superficial properties and particularly porosity structures. Consequently effective evaporating surfaces are changed and weathering mechanisms are changed too. It is the case for indurated surfaces which break because of salt crystallisations in depth. The experimental approach we exposed in this paper would permit the evaluation of treatment modification surfaces without new damages.
References
Bousqui6 P., 1979. Texture et porosit6 de roches caleaires. Thesis, University Pierre et Marie Curie, Paris VI, 163 p. Dullien F. A. L., 1979. Porous M e d i a - Fluid Transport and Pore Structure. Academic Press, New York, 396 p. Goodrich F. C., 1961. The mathematical theory of capillarity. Proc. Roy. Soc. London, A, 260, 481-489. Hammecker C., 1993. Importance des transferts d'eau dans la degradation des pierres en oeuvre. Thesis, University Louis Pasteur, Strasbourg I, 254 p. Joanny J.-F., 1985. Le mouillage- quelques problemes statiques et dynamiques. Thesis, University Pierre et Marie Curie, Paris VI, 260 p. Jouany C., 1981. Transferts d'eau par 6vaporation dans les milieux argileux. Thesis, University Paul Sabatier, Toulouse, 96 p. Mertz J.-D., 1989. Structures de porosit6 et proprirtrs de transport dans les gres. Thesis, University Louis Pasteur, Strasbourg I, 174 p. Thomachot C., 2000. Petrophysical properties modifications of Strasbourg's Cathedral sandstone by black crusts, 9th international congress on deterioration and conservation of stone, Venice, Italia.
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637 FRACTAL MODELLING OF PARTICULATE DEVELOPMENT OF BLACK CRUSTS ON STONE.
DEPOSITION
IN
THE
John Watt Middlesex University, London, UK Stephen Massey Building Research Establishment,Watford, UK Michaela Kendall Imperial College of Science, Technology and Medicine, London, UK.
Abstract The manner in which the structure and porosity of particle agglomerates develop is known to affect the physical properties of materials and may also control the growth rate crusts formed on stone. The paper describes a study to examine the growth and structure of the agglomerates using computer modelling and microscopic examination of developing crusts. Fractal analysis is ideally suited to describe irregular surfaces such as those encountered in particulate deposition and the agglomerates formed. The build up of particulates is studied using a computer model where a particle migrates towards an agglomeration of particles and sticks at the point of contact. After preliminary descriptions of the concepts involved, the models and the basic results arising from the fractal dimension measurements are presented. The results are discussed with reference to crusts studied and photographed at St Paul's Cathedral in London. Keywords: Black Crusts, Fractals, Diffusion Limited Aggregation, Soiling, 1. Introduction Soiling is a visual nuisance resulting from the darkening of exposed surfaces by deposition of atmospheric particles. In the urban environment anthropogenie activities have the dominant role in the soiling of external surfaces, with black carbon aerosols produced by the incomplete combustion of carbonaceous fuels being the principal cause for the increasing of soiling rates (Hamilton, R. S. And Mansfield, T. A., 1991). The rate of soiling is dependent on a variety of factors such as atmospheric aerosol concentration, aerosol size distribution, aerosol eolour (a function of composition), the roughness of the deposition surface, aspect of the surface (vertical, horizontal, etc.), efficiency of re-suspension and removal mechanisms by wind and washing out by rainfall, etc. A number of theoretical and experimental programmes have been undertaken to estimate a soiling rate, which would allow prediction of blackening from knowledge of ambient pollutant concentrations. These models of soiling relate to processes which take place on flat, non-reactive surfaces where the reflectance of the surface is related to the reflectance of the deposited particles and the fraction of the surface covered by particles (Haynie, F. H.,1986; Lanting, R. W.,1986). One model also considers the depth of cover (Lanting, R. W.'1986). Soiling models are an attempt to derive a damage function for the process, which would provide a basis for estimating costs. It should perhaps be noted that, although the study of the effects of air pollution can often be divided into decay and soiling, there is in practice no real boundary between the two
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effects. One area where stone damage and soiling overlap considerably is the formation of black crusts, which often develop in urban stone structures in areas protected from rainfall, especially on limestone and sandstone buildings. Attempts have been made to calculate damage functions for the erosion of buildings (Lipfert, F. W.,1989) but these do not include the effects of spalling black crusts as they are based on calculation of steady-state loss mechanisms for various materials and erosion regimes. The processes modelled here relate to deposition processes that occur without the build-up of gypsum or precede it. 1.1 Fractals Fractal analysis has received considerable attention since the concept was first outlined by Mandelbrot in the late 1970s (Kaye, B. H.,1999;Mandelbrot, B.,1983). It offers a convenient framework for the description of complex morphologies and other dynamic parameters (Colbeck, I and Nyeki, S.,1992). The basic property of fractal objects is that they obey the scaling relationship: Number of features oc resolution of measurements D Where D is the fractal dimension of the object. This dimension is therefore a concept that may be used to describe the roughness of irregular or self-similar shapes (XIE, Y. et.al.,1994). Self-similar means that any part of the object looks the same as any other part (or the whole object). As a structure is examined with increasing magnification, more and more detail becomes apparent and the apparent length increases. The fractal dimension, however, does not change with magnification and so can be used to describe the roughness. A number of techniques to measure fractal dimension have been developed. In each case, the ffactal dimension is evaluated by plotting the magnitude of the various perimeter estimates against the resolution, ;~, after both have been normalised. The data are plotted on log-log paper and the slope of the line generated is thus an estimate of the fractional addendum to the topographical dimension represented as fractal dimension (Kaye, B. H.,1993). 2. Modelling. Research into the characteristics of processes which grow by accumulation show that these can be modelled by diffusion limited aggregation (DLA), (Kaye, B. H.,1989). DLA accumulation occurs where a particle migrates, by diffusion, towards an agglomeration of particles and sticks to the agglomeration at the point of contact. In this manner the agglomeration gradually grows in size. Diffusion Limited Agglomeration models have traditionally been implemented in several different ways. Initial simple models operate at pixel resolution where each particle is modelled by a single pixel. The path taken by a particle released well away from the agglomerate is described by series of random steps taken one pixel at a time. When the particle hits the agglomerate it sticks at that location and another particle is launched toward the agglomerate. More complex models use agglomerates of particles (cluster-cluster models). For this preliminary research two different models have been implemented - pixel agglomeration and disk aggregation.
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In this paper the fractal dimension is calculated by using the height correlation, or structure function, which is mathematically defined as : C(N,s)=<
2(h~+~-h~ >
(1) where
hx = height at x hx.s = height at distance x+s N = Number of data points <> = Average taken for all data points
This calculates the average height difference between data points that are at a distance s apart along a profile across a surface. The length of s is varied to give the change in resolution required to make the ffactal measurement. The average value is determined using all the data points along a profile. A double logarithmic plot of C(N,s) against length s gives a straight line the slope of which is equal to the ffactal dimension (Massey, S. W.,1993). The ffactal dimension provides information about the roughness and structure of the surface profile. Basically the higher the ffactal dimension the rougher the surface.
2.1 Pixel agglomeration technique Models using individual pixels as particles have been used to demonstrate the build up of stable two-dimensional profiles. The pixel agglomeration is the same as the simple DLA models - each particle is modelled by one pixel. In this initial simple model particles are added to the surface at the point of intersection of a straight linear trajectory inclined at a fixed angle to the horizontal, rather than being allowed to move randomly. The point of intersection is varied by adding a random set of constant displacements to the fixed angle trajectories. This may model larger particles, with the possibility of adding deposition of small features by deposition in later version. A profile is considered stable when it has a constant fractal dimension. Profiles stabilise after approximately 150,000 particles have been placed across a base width of 1000 pixels. The variance in the fractal dimension was determined from the variation in the fractal dimension of the profile between 150,000 particles and 660,000 particles. Shorter runs using a base width of 500 pixels, which were less computer intensive, were used to determine the variation due to randomness in the agglomeration technique. On the basis of these measurements it can be seen that the incident angle of the incoming particle determines the value of the fractal dimension of the resultant surface; both sets of data are presented in Figure 1. Both sources of variation have a similar magnitude of error. The lower values for the fractal dimension for the long run profiles is due to the increase in the length of the profile.
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Figure 1 Incident angle of pixel trajectory against fractal dimension of resulting surface With the pixel agglomeration technique the pre-defined system of rules governing impact is simple and limits the movement of the simulation particle after impact. This typically results in very jagged profiles (Figure 2).
Figure 2 Typical surface profile for pixel agglomeration
2.2 Disk aggregation technique As a step toward a more general model the particle dynamics at impact have been modelled using a disk aggregation model that uses a group of pixels to model each particle. In the research to date, the particles are circular disks of a fixed radius. The intention behind using a group of pixels is to provide a facility for varying the size of the particle and also incorporating irregular shaped particles in the simulations. In the case discussed here, the
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disks stick at the point of impact. Other simulations where subsequent movement is permitted were undertaken to simulate gravitational settling of large particles on horizontal surfaces but these are less relevant to the soiling problem. Figure 3 shows the agglomeration for sticky disks. The number of particles is much smaller than the pixel based model to dearly show the structure.
Figure 3 Agglomeration of Disks Using the Disk Aggregation Model with Sticking The model works on the basis of particles moving down a linear trajectory inclined at a fixed angle to the horizontal. Adding a random set of constant displacements to the fixed angle trajectories varies the point of intersection with the agglomerate. Figure 3 shows a simulation for particles arriving at 90 degrees to the surface. As with the pixel version the fractal dimension was seen to increase as the number of disks in the agglomerate increased from zero and then stabilise after some 500 disks had been incorporated. Figure 4 shows that there is no dependence on the angle of incidence. 0.8
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3. Discussion
A common feature of all the agglomerate surface profiles is that the range over which fractal behaviour extends is several orders of magnitude greater than the individual pixel size or disk size. This suggests that measurements at a length scale other than the size of the individual particle on fractal profiles can provide useful information which may ease the analysis of surfaces created from sub-micron sized particles. The pixel model gives a very pronounced series of almost triangular shaped waves. The behaviour of these as particles are added is very similar to the sand tipples on beaches and fiver estuaries - they move along maintaining a constant profile. Certainly any such behaviour on the surface of a building would be readily identifiable and given the dependence of the fractal dimension on deposition angle, measurement of the fractal dimension should provide information on the average deposition angle. Such an angular dependence results from the growth of the agglomerate away from the surface being described by a non-linear growth equation (Barabasi, A. L. and Stanley H. E., 1995). Barasabi & Stanley consider models for growth which are similar to the pixel model described above and suggest that variations in the deposition models available can be described in terms of three scaling exponents a, b and z referring to surface roughness, saturation width and cross over time to saturation. The dependence of the height variance C(N,s) on s described above is one example of a scaling relationship where the exponent is the fractal dimension. The scaling exponent related to the surface roughness, defined as the root mean square (rms) fluctuation in the height by Barasabi and Stanley, can easily be demonstrated to be related to the fractal dimension. These authors also observe in their experiments that the rms fluctuation of the height stabilises at a constant value after a certain number of particles have been added and that the stabilised value and the number of panicles added to reach this value both depend on the length of the profile analysed, which is also observed in the models used here (Figure 1). Some points along the profile are shielded from incoming disks by adjacent high points, which grow in preference to the low points. The degree of shielding depends on the height of the protruding high point and the size of the incoming particle. Small fluctuations affect smaller panicles far more than large particles. In addition the length of the profile has an effect, such that areas of accelerated growth seed at different spatial resolutions depending on the angle of incidence. This is evident from the periodic profiles generated by the pixel model. Which of the two models is best suited for analysing panicle agglomerates cannot be determined without further experimentation. On purely physical grounds the disk models is more appealing since it is constructed from elements of a specific shape and mimics the growth patterns observed in some crusts. 3.1 Physical implications
The aim in developing these preliminary models is to begin to move to a situation where useful general points can be inferred about the behaviour of different crusts as they develop, together with the implications for removal. As the models develop it should be possible to consider: - the actual strength of the agglomerate & the bond to the substrate or agglomerate interlayers, which is of relevance to cleaning the surface. - the rate at which the substrate is obscured, which will depend on the rate at which the agglomerates spread out from the initial seed points, - the surface roughness which affects optical scattering of light & therefore the perception of discoloration,
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- effect of roughness on the boundary layer dynamics at the surface which may lead to local fluctuations in the deposition rate. These in turn may lead to self-regulating or accentuated growth. Preliminary investigations of the first and second of these have been undertaken to give an indication of the data which might be obtained from the disk agglomeration models. 3.1.1 Soiling curves Calculation of a soiling curve is a simple matter of recording the amount of surface that is obscured by the particle agglomerate. A perpendicular viewing angle was selected in order to keep the illustration simple. Obviously the degree of obscuration depends on the angle from which the surface is viewed. Figure 5 shows a summary of the soiling data for all the different incident angles used to generate the agglomerates. The X-axis, or time axis, is simply the total number of particles added to the agglomerate. It can be seen that angles between 45 and 90 degrees soil at roughly the same rate. Whilst the very low angles on incidence soil at a slightly lower rate. Interestingly all of the curves converge to a constant initial soiling rate irrespective of the angle of incidence.
Figure 5
Soiling Curve for the various Generated Agglomerates.
In order to get a better feel for the time duration involved in soiling it is possible to make an estimate of the equivalent time to deposit a number of particles. As an example, we can take a particle size of 0.2 lam and assume that there are about 15000 particles per cm 3. These particles will have a deposition velocity of 0.02 mm/s (Hollander and Pohlmann,1991). This gives a deposition rate of 30 partieles/cm2/s. Each of these will occupy a square of approximately 1/~/30/rn, which is clearly initially a rather sparse cover. Simulation profiles of 640 pixels were undertaken. With a disc size of three pixels per particle, a 0.2ktm particle size means this represents a length of 43 lam. Based on area ratios, the probability of randomly hitting a strip 43 x 0.2 m within a given centimetre square (the simulation represents a single slice though the surface equivalent to the width of one particle) with a deposition rate of 30 particles/em2/s is 2.6 x 10 "6. Therefore, 1/2.6 x 10-6 or 4 x 105 particles are required within the centimetre square to register one hit on the 43 x 0.2 ktm sample (simulation) strip; that is to say 4 x 10" seconds (111 hours or 4.6 days) elapse per additional
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9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
particle added to the simulation. Thus, for the 600 particles required on average during the simulation runs to cover the strip, the true elapse time is about seven years, which is not an unreasonable estimate for the rate of soiling of buildings (Newby, P. T., Mansfield, T. A., and Hamilton, R. S.,1991). The calculated example uses a single particle size and an assumption of particle numbers based on estimates from published data but the true potential of the method will be realised once the models have been refined to examine particles of different sizes and to reflect true size distributions for urban aerosols of different locations and ageing characteristics.
3.1.2 Strength ofthe agglomerate Each of the disks witmn the agglomerate is held, above and below their position, by a number of contact points. Assuming there is no other contribution from cementation processes the strength of these contact points will govern the strength of the agglomerate. Whilst the low incident angle simulations present somewhat unrealistic structures, the high incident angle simulations are more realistically compact. The data show that there is an increase in the number of contacts for the more compact, high incident angle agglomerates. Calculations from the soiling curve simulations show the agglomerate reaches maximum strength after three years. This would suggest that early and frequent cleaning is easier than cleaning after a longer time has elapsed. 3.2 Comparison with actual crusts The disc aggregation model produced characteristic "fronds" of particle protrusions, which can be observed in fine crusts on stone surfaces of the cathedral balustrade. As the stone has eroded to expose more resistant elements, which protrude from the surface, the increased surface roughness has led to enhanced particle deposition on these protrusions. The "fine frond" crusts found in such positions are a specific type of crust located at St Paul's. These crusts are not the most frequently found, but they do dominate on relatively protected, vertical stone surfaces with fossiliferous protrusions. Figure 6 shows two such surfaces (shown horizontally for ease) with the fine crusts dearly visible. These crusts are visible at sizes ranging between c. l mm to 10mm and are assumed to have formed relatively recently since there are clear signs of cleaning on the underlying stone surface.
Figure 6 Close-ups of Black Crust Developments.
9th International Congresson Deterioration and Conservationof Stone, Venice 19-24June 2000
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Figure 7 SEM Micrographs of Structures in Newly Developed Crust. Figure 7 shows the growth stems or "fronds" found in the dominant crust type at St Paul's which is found in well-protected areas e.g. under the balustrade lip. The stems range in size, but typically measured 200 lam comprising a matrix of gypsum crystals and deposited particulate matter. The particle pictured on the right, is typical of particles within the fine fraction of the urban aerosol and is presumed to originate from diesel vehicles. This particle is made up of entangled single chains of carbon spherules measuring approximately 35 nm in diameter and these ultrafine spherules stick together to form micron-sized agglomerates. 4. Conclusions
Aggregation models provide a controlled way to examine the dynamics of particle growth and, of the two simulations discussed here, disk models provide a more intuitive representation of agglomeration than pixel models. Potentially useful information concerning the internal structure of the agglomerate can be gained from measurements taken from a surface profile. In the case presented, the strength of the agglomerate increases with time, implying early cleaning is easier than delayed cleaning. As the models develop, it is hoped that realistic soiling curves can be constructed. 5.
References
Barabasi, A. L. and Stanley H. E. 1995.Fractal Concepts in Surface Growth. Cambridge University Press. Colbeck, I And Nyeki, S.1992.Optical And Dynamical Investigations Of Fractal Clusters. Science Progress.76.149-166 Hamilton, R. S. And Mansfield, T. A. 1991.Airborne Particulate Elemental Carbon- Its Sources, Transport And Contribution To Dark Smoke And Soiling. Atmospheric Environment Part A-General Topics.25.715-723 Haynie, F. H, 1986. Theoretical Model of Soiling of Surfaces by Airborne Particles. 1985. Hollander, and Pohlmann. 1991. Measurement of the Influence of Direct Particle Motion on the Turbulent Particle Deposition Velocity by Means of a Laser Doppler Anemometer. Particle & Particle Systems Characterization.8.12-15 Kaye, B. H.1989.A Random Walk Through Fractal Dimensions. VCH Publishers.Weinheim
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9th InternationalCongresson Deteriorationand Conservationof Stone, Venice 19-24June 2000
Kaye, B. H.1993.Applied Fractal Geometry And The Fineparticle Specialist. 1. Rugged Boundaries And Rough Surfaces. Particle & Particle Systems Characterization. 10.99-110 Kaye, B. H. 1999. Measurement and Description of Particle Properties and Behavior in Powders and Other Disperse Systems. Particle & Particle Systems Characterization. 16.146Lanting, R. W.1986. Black Smoke and Soiling.1985. Lipfert, F. W.1989.Atmospheric Damage to Calcareous Stones: Comparison and Reconciliation of Recent Experimental Findings. Atmospheric Environment.23.2.415-429 Mandelbrot, B. 1983. The Fractal Geometry of Nature. W.H. Freeman and Company.San Francisco Massey, S. W.1993. Fractal Analysis of Stone Fabric.15-11-1993.1712-1719. Newby, P. T., Mansfield, T. A., And Hamilton, R. S.1991.Sources And EconomicImplications Of Building Soiling In Urban Areas. Science Of The Total Environment. 100.347-365 Xie, Y., Hopke, P. K., Casuccio, G., And Henderson, B.1994.Use Of Multiple Fractal Dimensions To Quantify Airborne Particle- Shape. Aerosol Science And Technology.20.161-168
647
CHARACTERIZATION AND PHYSICO-CHEMICAL ACTION OF CONDENSED WATER ON LIMESTONE SURFACES E. Zendri, G.Biscontin*, P.Kosmidis Dept. of Environmental Sciences, Ca' Foscari University, Venice (Italy) A.Bakolas Dept. of Chemical Engineering, National Technical University of Athens, Athens (Greece)
Abstract This is a proposal for a method for the study of the effects of condensation on limestone surfaces. The results of condensation's characterization in a lake environment indicates rather low pH values, in various eases lower than 6. The bicarbonate ion contents corresponds to the pH. The ion concentration regarded as representative of both condensation and its effect on stone surfaces was evaluated. The evaluation, at this stage in the research, consisted of observations of SEM and XPS analyses. Initial results indicate effects related to the direct action of acidic substances, particularly dissolved CO2, leading to the recrystallization of calcite into smaller crystals. Keywords: condensation, limestone, Venice 1. Introduction As is well known, the exposure of limestone used in traditional architecture to the outside environment leads to greater wear with respect to what is observed on stone of a different chemical nature (Charola, 1988). The effect of water in the form of condensation and of possible solutions formed to absorb species present in the air has not yet been established, either due to the lack of data regarding the composition of the condensation itself, or due to the difficulty of studying the condensation-evaporation process on actual surfaces. Once condensation is formed, it acts as a solvent for a series of gaseous substances present in the atmosphere (CO2, SO2, NOx, etc.) transporting substances present in aerosol form. The solutions that are thus formed possess a high concentration of "reactive" species for stony surfaces (Amoroso and Fassina 1983) (Hicks, 1981) (Camuffo et al. 1984). This essay presents a proposal for method for the study of the effect of condensation on limestone surfaces, based on the evaluation of some parameters characterizing the condensation itself and regarded as significant, and the simultaneous evaluation of chemical and physical transformations produced by condensation on stone. Still currently being carried out, the research particularly focuses on Venice's lagoon environment, as well as in the choice of the Istria stone as the specific stone studied, it being typically used in the city's historic buildings. The results exposed here relate to a period of approximately one year of condensation sampling. 2. Experimental part The Istria stone is a type of sedimentary reef limestone, essentially composed of CaCO3, with clay-based inclusions. The selected stone presents a cumulative volume of * Author to whom correspondence should be addressed.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000
approximately 10 mm3/g, with pores distributed in a radius of 70 and 200 A, and a density of 2.7 g/cm3. 2.1 Setup and development of the research method. 2.1.1 Chemical characterization of condensation As regards condensation collection, a normal dehumidifier was used as a condenser. Condensation was collected at the same time and place in which the condensationevaporation cycles were performed on stone samples, according to the method described below (part 2.1.2). First of all, the condensation's pH values were taken, which we believe to be a prime indicator of the condensation's reactivity with the stone. The amount of CO2 dissolved in the water, found under the form of COfH:O, in correspondence with the HCO3 and CO3form, was also associated with the pH value. The concentration of bicarbonate present in the condensation was determined via a potentiometer (Metodo Analitiei per le aeque, 1979). Following these observations, CI, SO4- and NO3" ions were examined via ionic chromatography (DIONEX 2010I.), Na § K § Mg ++, Ca ++ via spectrophotometry in atomic absorbency (Perkin Elmer 3030). These ionic species have been considered characteristics of the condensation because they are present in considerable amounts, as also determined by previous research (Zilio Grandi, 1991) (Maravelaki, 1989-90). 2.1.2 "Forced" condensation cycles on stone. The term "forced cycle" refers to the fact that the condensation is obtained by suitably cooling the surface of the samples to a temperature lower than that of dew. Indeed, by operating at normal outdoor temperature, condensation is formed only at relative humidity values close to those of saturation. For this reason it was decided to perform the exposures to the outside environment prior to cooling the samples to -10~ at which temperature no microstructural variations on the samples were detected. This way it is possible to obtain, on the one part, a significant amount of condensation on the stones' surface and on the other, also a longer-lasting condensation-evaporation cycle, thus increasing the possibility of interaction between condensation and the stone samples. Observing that the condensation process begins soon after the samples' exposure to the outside environment, it was measured how long the condensation lasted on the surface. This interval was defined as the duration of the only cycle, that is, the time span between the beginning of the samples' exposure, coinciding with the forming of the first traces of condensation on the surface, and the moment in which the condensation completely evaporates. In the case of the Istria stone, the cycle lasts approximately one hour, as shown in figure 1, with the maximum amount of condensation forming around 10 minutes after exposure to the outside environment. As regards the size of the exposed stone samples, it was considered more convenient to use samples that were not thick so that they could be more sensitive and easily show both the quantity of condensation gathered and possible weight variations after the cycle. 10 samples were used, with the average size of 50 x 25 x 5 mm, positioned horizontally on a special support. Along with the samples, two Teflon plates of the same size were exposed for particulate matter collection. After 50, 100, 200 and 300 cycles, the samples were taken at a constant weight in a stove at 105 ~ and then weighed to determine weight variations.
650
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24June 2000 Table 1" minimum, maximum and average pH values of the condensation collected. N ~ of measures 91
minimum pH 5,54
maximum pH 6,93
average pH 6,26
6.5
6.4 t 6.3 6.2
pH 6.1 6.0 5.9 5.8 5.7
I,~
!
I
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/I
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Figure 2: average monthly pH trend during the February 96-December 96 period During the February-June period the pH values were higher than in preceding months (July-December period). The lowest pH values were recorded in the month of September, generally less than 6. The frequency value percentages recorded during that same period, shown in figure 3, were interesting. It is important to note that 12% of the measurements indicated pH values between 5.5 and 5.8. Under these conditions it can be said that the condensation's acid attack deteriorates the stone samples, even if calcium earbonate's buffeting action probably limits the phenomenon to the material's top layers.
Figure 3: pH percentage distribution.
9th International Congresson Deteriorationand Conservationof Stone, Venice 19-24June 2000
649
30-
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'
3000
,0'
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Figure 1. Istria stone condensation-evaporation cycle. 2.2 Evaluation of the effects of condensation on exposed surfaces
Believing that at least at this point the condensation's effect is limited to the samples' surface, specific research techniques are proposed for the study of surfaces, particularly XPS (X-ray Photoelectron Spectroscopy) (VG ESCALAB MK II, which operates with MgKa monochromatic radiation). The technique, already used for the study of the alterations in stone exposed to rain, permits the gathering of important information on the phenomena under study (Maravelaki, 1992). Table 5 contains the atomic intensity of species regarded as the most significant of both the material and the condensation's effect, expressed in percentages, relating to sputtering time. The data thus obtained refers to the data average relating to two Istria stone samples aider 200 condensation-evaporation cycles. In the conditions under which the experiment was performed, 10 minutes of surface "sputtering" erodes around 10/~ of the material. The results are compared with the ones obtained with quarry samples. To analyze the state of the samples' surface and the morphological modifications ensuing from the condensation's effect, observations were made with the Electronic Scanning Microscope (SEM) on some stone samples after 200 condensation cycles. 3. Results and discussion 3.1 Chemical characterization of the condensation - The condensation's acidity
Acidity checks are important for an initial evaluation of the possible effects of condensation on carbonate species. Table 1 shows the minimum, maximum and average values found during the period of February-December 1996, while fig. 2 shows the monthly trend, expressed in terms of average values.
652
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
-Contents of the most important ions Figure 6 shows the monthly average trends of Na § K +, Mg +§ cations. 90 80 ~
~ N a +
60 50 40 30 20 10 0
:::k o
Figure 6: monthly average trends of Na § K § Mg++ cations. The Ca ++ ion trend, given its high concentration, is shown in figure 7, while figure 8 shows CI, SO4-and NO3-anion trends. All the concentrations are in txeq/l.
I.i .i
180 160 140 120 I00
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Fig.7: Ca++ion average monthly trend
+SO4=
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Fig. 8: CI',
804-
e
NO3" anion average monthly trend
I
9th I n t e r n a t i o n a l Congress on D e t e r i o r a t i o n and C o n s e r v a t i o n of Stone, Venice 19-24 June 2000
651
-HCO3- contents The HCO3 concentration was determined during the May-December '96 period and figure 4 shows the monthly trend, expressed in laeq/l, resulting from the average calculated from 10 measurements per month. Figure 5 also shows the HCO~" ion concentration trend with regard to the condensation's pH, which shows an increase in the two parameters, as is already known.
100 80 60 40 20
I
I
~
I
I
I
I
I
0
Fig.4: average monthly trend of riCO3 concentration (laeq/l). During the July-October period the HCO3 concentration was relatively constant and between 40 and 50 ~teq/l. In the month of December there was a sudden increase in concentration, probably due to the air's lower temperature. During May the concentration values were lower, not in correspondence with the condensation's pH, but probably due to special environmental conditions.
80
~
70
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60
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,50
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:30
.
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Fig. 5: HCO3" ion concentration trend relative to the condensation's pH.
9th International Congress on Deterioration and Conservationof Stone, Venice 19-24June 2000
653
A general increase in ionic concentrations was observed during the winter to spring transition, which tends to decrease again during the summer. A concentration peak was observed in July for all the ions, probably due to special weather conditions. In general the ion trends determined are similar, both for the cations and the anions, except in the case of the Ca ++ ion, present in quantities between 50 and 150 laeq/l. Potassium shows a concentration lower than 10 ~teq/1, and at different times of the year it was present only in traces. The amount of CI- and Na + is high, also due to sea aerosol. The Mg +§ ion is present at a rather constant concentration, around 12 ~teq/l, except for the month of May, when its trend approximately doubled. Sulfates are present in concentrations similar to those of chlorides, while nitrates recorded lower and relatively more constant values. It should be noted that the overall trends between anions and cations is not balanced. In various occasions the ammonia concentration was determined as rather significant. We therefore believe that this species could be included among the condensation's characterizing elements. 3.2 "Forced" condensation cycles on stone. -Weight variations Effective weight variations were obtained by comparing the differences among total weight variations and the particulate matter's contribution, evaluated through the two Teflon samples exposed with the stone samples. The stone's weight variation results after 50, 100, 200 and 300 evaporation-condensation cycles are listed in table 2.
Table 2: Istria stone sample weight variations. N ~ of cycles
AP %
50 100 200 300
0,004 0,004 0.005 0.005
Given the cycles' performance mode and the samples' horizontal position, the resulting signs of deterioration formed as a reaction between condensation and support remain on the stone, in addition to atmospheric particulate matter. Small weight variations, ranging around 0.005%, indicate that the condensation's effect on the stone was rather limited and difficult to evaluate via this parameter's reading. The soluble salt analysis, even at a preliminary stage and performed on some stone samples after 300 condensation-evaporation cycles, indicates the presence of significant amounts of Na +' and a lower concentration, but nevertheless quite elevated, of sulfate ion. These initial results seem consistent with what was found with the condensation analysis.
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
3.3 Evaluation of the condensation's effects on the exposed surfaces - X P S analysis on the samples
Tables 3 and 4 show the atomic percentages of the species considered most significant for the quarry stone (table 3) and for the stone samples exposed to 200 condensation cycles (table 4). The data refers to both the stone's surface as well as deep inside the stone (10
A/min).
Table 3: atomic T (min) 0 2 4
C 1s 33,6 23,2 20,3 8 15,1 12 . .!6,7
es of the s ~ecies considered most 0 Mg CI Ca 2p 2p ls ls 49,5 ' 0,2 0,1 12,4 0,1 15,9 55,6 0,6 0,1. 17,5.. 57,8 0,8 .60,4 0,5 0,2 21,0 60,0 1,0 0,2 20,5
si nificant for the c Si S Na 2p 2p Is 0 0,7 0 0 0,6 0 0,7 0 0 0 0,5 o 0 0,4 0
try stone
,
.
Tab.4: atomic percentage of the species considered most important for stones exposed to 200 condensation cycles T C (min) ls 0 37,3 2 29,1 4 .27,4 . 8 2.7,7 12 ,23,3
0 Mg ls ls '48,2 0,7 52,2 2,0 52,9 1,0 55,1 ~ 1,4 55,8 !,1
CI 2p 0,5 0,5 0,4 0,5 0,5
Ca si 2p 2p !0,6 ..... 2,1 14,0 , 2,2 ,14,7 2,4 16,2 2,2 '!6,5 2:2
s 2p 0,3 0,2 0 0 0,.
Na ls 0,1 0,4 0,4 0,7 0,6
Carbon's atomic percentages are higher in the stones exposed to condensationevaporation cycles with respect to the quarry stones, probably due to deposits of hydrocarbon substances and carbon particulate matter. On the average, calcium is present at a lower percentage to the theoretical percentage of calcium carbonate both in the quarry samples and the samples exposed to 200 condensationevaporation cycles. As regards the probable effect of the condensation on the carbon matrix, it was observed that the sulfur percentage detected was low and limited to the first 20 A in depth. Sodium shows a higher percentage, at least up to a depth of 120 A. The values found could be due to the higher solubility of the salts in which it is generally contained, and therefore there is a higher possibility of penetration into the material. Chloride is also present at a significant percentage up to a depth of 120 A. - S E M Observations
Photos 1 and 2, showing a quarry stone and a sample after it has undergone 200 condensation cycles, seem to indicate that the condensation apparently reduces the size of calcite crystals and causes them to separate (photo 2). The presence of smaller crystals could be a consequence of the recrystallization of sodium carbonate from sodium bicarbonate. During this phase there was no evidence of particulate matter deposits.
9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
Photo 1 Istria stone from a quarry (5000X)
Photo 2: Istria stone after 200 condensation cycles (5000X).
655
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9th International Congress on Deterioration and Conservation of Stone, Venice 19-24 June 2000
4. Conclusions The study identified some significant parameters for the study of condensation's effects on carbon surfaces, and has permitted the laying of a research procedure, which, despite needing some modifications, is effective in supplying useful indications on the processes being studied. The results obtained from the condensation analysis in the Venice area indicate that it contains significant amounts of HCOfions, while other ions generally included in the "polluting" category (SOz e NOx) are not present in particularly high concentrations. On the other hand, CI" and Na +, characteristics of sea aerosol, were detected. Determining the pH was very important, indicating the intensity of the interaction between condensation and stone. The pH values found are nevertheless below neutrality and in approximately 22% of the tests are lower than 6. Condensation's interaction with the Istria stone, still under study, indicates the probable effect on calcite with its recrystallization from bicarbonate, while the effect of other acid substances, particularly sulfuric acid, seems more limited, involving rather superficial layers of the material. It was nonetheless found that there was a higher penetration capacity by soluble species, affecting the material down to a considerable depth and that may cause the stone's physical deterioration. The study will proceed with some adjustments to the proposed system and with the examination of the behavior of limestone samples with different degrees of porosity. Acknowledgements: the authors thank the CNR- PF Beni Culturali for the financial support of the work. References Amoroso G. G., Fassina V., 1983. Stone decay and conservation. Atmospheric pollution, cleaning, consolidation and protection. Elsevier Ed. Camuffo, D., Dd Monte, M, Ongaro, A., 1984. The pH of the atmospheric precipitation in Venice, related to both dynamics of precipitation events and the weathering of monuments. Sci.Total Environ.,40, 125-139. Charola, A. E., 1988. Chemical-physical factors in stone deterioration. Durability of building materials,5, 185-616. Hicks, B. B., 1981. Wet and dry surface deposition of air pollutants and their modeling. National Academic conf. Conservation of historic stone buildings and monuments, Washington/D.C., II. Maravelaki, P. 1989-90. Effetto chimico delrambiente su superfici lapidee esposte ed indagini per il loro recupero. Tesi di dottorato di ricerca in scienze chimiche, IV ciclo, Universitb. di Venezia. Maravelaki P., Bertoncello R., Biscontin G., Battagliarin G., Zendri E., Tondello E., 1992. Investigation of the surface processes on exposed limestone. Mat. Res. Soc., 267, Mat. Res. Soc. Editor, 943-953. Metodi analitici per le acque, 1979. Carbonati e Bicarbonati. Istituto di Ricerche sulle Acque (IRSA), CNR. Zilio Grandi F., Szpyrkowicz, L, 1991. Air pollution monitoring network for the Venice region: preliminary results for the rain quality. Toxicological and environmental chemistry, 29, 281-296.
657
AUTHOR INDEX VOLUME 1 Aires-Barros L. Albertano P. Alesiani M. Alonso F. J. Altieri A. Alves C. A. S. Antonelli F Artioli D. Ausset P. Baglioni P. Bajare D. Bakolas A. Balzarotti R. Bardanis M. Bartolini M. Batchelder M. Bede E. A. Bellezza S. Bellezza T. Bennardo C. Berlucchi N. Birginie J. M. Biscontin G. Bistoni F. Borroni S. Boutin F Bromblet P. Bruno L. Bugini R. Cabello M. N. Calcaterra D. Calia A. Campanella L. Cappelletti P. Capuani S. Carmelo Prieto A. Casoli A. Catalafini J. Cavallucci F. Charola A. E. Colella A. Costa D. Curzi F. De Canio G. De Leo F.
79, 295 425 579, 587 323 433 225, 235 445 375 329, 339 587 3 647 531 255 453 283 303 425 483 13 13 171,313 13, 647 483 41 31 31, 69 425 41 507 59 49, 195 543 59 579, 587 619 553 557 89 155 59 235 579 565 531
Del Monte M. 329, 339 Delgado Rodrigues J. 235 Dessandier D. 69 Destrigneville C. 629 Dews S.J. 391 Diaz-Pache F. 323 Dionisio A. 295 Dornieden T. 461 Dunakin R . C . 109 Esbert R . M . 323 Figueiredo A. M . C . 79 Figueiredo M . O . 165, 235, 493 Folli L. 41 Forsyth G. 473 Fort Gonz/tles R. 125 Franzen C. 25 Fratini F.F. 89 Galletta M. 531 Garzonio C.A. 89 Gennaro, de', M. 59 Gennaro, de, R. 59 Ghedini N. 383 Ginanni Corradini R. 13 Giorgi R. 587 Giovagnoli A. 375 Giovannini P. 89 Giraldi M. 483 Gobbi G. 383 Gorbushina A . A . 461 Gouveia M . A . 235, 493 Gregori E. 543 Grossi C . M . 323 Grossi R. 543 Gustavson H. 119 Halls C. 283 Halsey D . P . 357, 391 Helmi F . M . 99 Heyrman J. 469 Hubbard C. 283 Ivone A. 375 Jeanette D. 265, 629 Jim6nez J. 619 Joksimovic S.M. 135 Jones M.S. 473
Kendall M. 637 Klemm W. 401 Kosmidis P. 647 Langella A. 59 Leal L. 619 Lefbvre R . A . 329, 339 Leite MagalhS, es S. 521 Lindborg U. 109 Lindqvist O. 349 Lindsay W. 283 L6fvendahl R. 119 Lonati G. 375 L6pez de Azcona M. C. 125 Lundberg B.A. 119 Macnaughton K. 357 Malaga-Starzeg K. 181,349 Mancini L. 579, 587 Manganelli del F~t C. 89 Maraviglia B. 579, 587 Marques J.M. 79 Massey S. 637 Matovic V.B. 135 Mattolin F. 13 Mauricio A.M. 79 May E. 609 Mecchi A . M . 49, 195 Meli P. 13 Mergaert J. 469 Mertz J-D. 69 Miguel A . F . 595 Milovanovic D . J . 135 Mingarro Martin F. 125 Mirwald P. 25 Mitchell D . J . 357, 391 Monte M. 453 Moroni B. 367 Mosquera M . J . 601 Murphy W. 609 Nasraoui M. 165, 235, 493 Negri S. 553 Nugari M . P . 375 Ordaz J. 323 Palla G. 553 Papida S. 609 Paradise T . R . 145
658 Paradossi G. Pasini P. Paterno M . C . Pavese A. P6rez B. Piervittori R. Pietrini A . M . Pinna D. Pitzurra L. Poli G. Prieto B. Prud~ncio M . I .
425 499 155 41 619 433 433 513 483 367 171, 601 165, 235, 493 Quarta G. 49 Ranalli G. 499 Rasolofosaon P. N . J . 215 Ricci S. 433 Riontino C. 383 Rivas T. 171, 601 Roccardi A. 433 Roda A. 499 RomS.o P. 493 Rosa R. 595 Rosato V . G . 507
Rowcliffe D . J . 109 Sabbioni C. 383 Sahlin T. 181,349 Salamone P. 531 Salvadori O. 513 Sbaraglia G. 483 Scherer G . W . 187 Schiavon N. 411 Schouenborg B. 181 Scudeler Baccelle L. 195 Searle D . E . 357, 391 Sequeira Braga M . A . 165, 225, 235, 521 Sheremeti-Kabashi F. 247 Siedel H. 401 Siegesmund S. 205, 215 Silva A . M . 595 Silva B. 171, 601 Silva T. 235, 493 Smith J.P. 391 Snethlage R. 247 S6zmen B. 275 Spera G. 483 Stigh J. 181
Svinka V. Swings J. Theoulakis P. Thi6bault S. Thomachot C. Tomassetti M. Bandini G. Topal T. Tournier B. Trancoso A. Traversa L. Trindade M. J. 165, 235, Tschegg E . K . Urzi C. 445, Valdeon L. Ventikou M. Waerenborgh J.C. Wakefield R . D . Watt J. Weiss T. 205, Zagari M. Zappia G. Zendri E.
3 469 255 339 265 543 275 629 225 507 493 205 531 323 283 235 473 637 215 445 383 647
659
A U T H O R INDEX V O L U M E 2 Abd E1-Hady M . M . 783 Aglietto M. 209, 215 Agostini S. 793 Aktfire Z. 801 Alberti S.A. 649 Alcalde Moreno M. 697 Alessandrini G.209, 853, 863 Almesberger D. 317 Altieri A. 225 Alvarez A. 641 Alvarez de Buergo Ballester M. 235, 881 Alvarez J.I. 873 Amadori M . L . 853, 863 Amorosi E. 679 Andersson T. 731 Antenucci D. 33 Antonelli F. 649 Arnold A. 749 Avdelidis N . P . 119 Baccaro M. L.P. 3 Bakolas A. 403 Ball J. 13, 179, 813 Balzi S. 3 Banier J. 33 Barbary P. 245 Barone G. 91 Begonha A. 593, 689 Belacchi S. 43 Bemporad E. 23 Berlucchi N. 23 Bernabe J.M. 715 Bianchini P. 569 Bidner T. 139 Blanco-Varela M . T . 435 Bocci A . M . 853, 863 Bonafede L. 187 Bonomi R. 23 Bossiroy D. 33 Botteghi C. 209 Boutin F. 197 Bradley S.M. 503 Brinker C.J. 541 Bryan P. 101 Burtet B. 623
Calvi G. Campisi T. Cancelliere S. Canegallo P. Carretero M.I. Casadio F. Casalicchio G. Cassar J. Castelvetro V. Chalupar I. Charola A . E . Chiantore O. Chiavarini M. Ciardelli F. Colombo C. Costa D. Crivellari F. Croveri P. D'Anselmo M. De Witte E. Del Chiaro L. Delgado Rodrigues
793 853, 863 649 63 715 739 721 251 209, 215 453 335 209, 215 263 209 215, 739 361 613, 623 263 829 361 3 J. 273, 361 Dell'Agli G. 379 Di Marco F. 679 Dingelstadt C. 33 Domas~owski W. 843 Dreesen R. 33 Ercolani G. 853, 863 Escalante M . R . 459 Espinosa-Gaitan J. 697 Fabbri B. 853, 863 Fabiani F. 569 Fassina V. 209, 603, 613, 623 Favaro M. 613, 623 F61ix C. 287, 633 Ferchiou N. 641 Fernandez-Caliani J.C. 715 Ferone C. 371,379 Ferrari P. 287 Ferreira Pinto A . P . 273 Figueiredo M . O . 641 Fiori C. 43, 721 Fitzner B. 53 Flatt R . J . 297
Fleming S.A. 541 Floc'h P. 307 Fort Gonzfiles R. 235 Fumo G. 623 Furlan V. 633 Galfin E. 715 Geometrante R. 317 Ghiossi S. 351 Giamello M. 569 Ginanni Corradini R. 23 Giovagnoli A. 63 Girardet F . J . 297 Giusti A . M . 671 Godin J. 73 Goins E.S. 541 Gonz/tles Lim6n T. 881 Graudums I. 889 Grossi C . M . 83 Guidetti V. 327 Heinrichs K. 53 Henau, de P. 661 Henriques F. M . A . 335 Hubrich K. 583 Hunt B.J. 83 Igaune S. 175 Ioannidou N. 819 Ioppolo S. 91 Ivone A. 63 Jornet A. 343 Karatasios I. 351 KaraveziroglouWeber M . K . 921 Khosrof S. 641 Koller M. 903 Koui M. 119 Krage L. 889 Kung A. 749 Kusch H . G . 583 Laing R . A . 179, 813 Lalli C. 671 Lambropoulos V . N . 351 Lanterna G. 387 Lanterna G. 671 Larbi J.A. 523 Lazzari M. 209
660 Lazzarini L. 649 Leavengood D. 513 Lee N . J . 503 Leirens I. 661 Leroux L. 197, 361 Levko L.V. 547 Lindner H. 145 Lobovikov-Katz A. 897 Lonati G. 225 L6pez de Azcona M. C. 235 Lorenzi G. 33 Lorusso S. 721 Lfisis R. 175 Macchiarola M. 43 Magris D. 623 Mairani A. 387, 561 Majolino D. 91 Malagodi M. 225 Mannuccia F. 649 Marabelli M. 63 Marino O. 379 Mark S. 245 Martin A. 873 Martin B. 101 Martinet G. 165, 307 Maryniak-Piaszczynski E. 477 Mascolo G. 379 Mascolo M . C . 371 Mason D. 101 Massey S. 361 Massidda L. 111 Matteini M. 387, 561,671 Matteoli U. 209 Mavrikakis S.P. 921 Maxovfi I. 395 Meloni P. 111 Mertz J . D . 165 Messori M. 561 M6ndez-Vivar J. 541 Migliardo P. 91 Mingarro Martin F. 235 Mirwald P. 139 Moggi G. 419 Montoya C. 873 Moroni B. 129 Moropoulou A. 119, 403 Moundoulas P. 403
Muscarfi A. Naccari A. 613, Naizot S Navarro I. Negrotti R. 853, Neri N. F. Neumeister K. Niculescu G. Nimmrichter J. 453, Nugari M. P. O'Connor J. Palomo A. Pansini M. Parodi V. Paschinger H. Pavlovskaya M. V. Pecoraro I. Pedemonte E. Pentrella R. Perego G. Pereira Da Silva T. Peruzzi R. 209, Pigo M. Pini R. 569, Piras M. G. Pithon M. Poli G. Poli T. Portieri R. Prasartset C. Prestileo F. Pretzschner C. Previde Massara E. Puertas F. Puterman M. Quaresima R. Queisser A. 287, Recheis A. Requena A. Richard H. Richter D. Richter I. Rizzi M. 387, Rizzo A. Rodriguez Blanco J. Rohatsch A. Rolland O. Romer A.
91 623 245 873 863 91 583 837 903 225 413 435 371 419 903 553 913 419 721 425 641 215 623 577 111 73 129 215 613 765 721 145 425 435 443 679 633 139 715 903 145 145 671 317 235 453 307 343
Rosignoli R. Ruedrich J. Salemi A. Salimbeni R. 569, Sanfilippo G. Sanna U. Santalucia F. Saxena K. Saxena V . K . Scala A. Scherer G . W . Scoccia G. Scott J. Scuto S. Sequeira Braga M . A . Sharma R . K . Siano S. 569, Sidraba I. Siedel H. Siegesmund S. Simon S. Simonetta M. Singer B. Skoulikidis T. Slavid I. Snethlage R. Sobott R. Spiazzi A. Stavrakakis E.J. Strotmann R. Suran P. Tcheremkhine V.I. Teles M. Tewari S.K. Theoulakis P. Thickett D. Thorez J. Tiano P. Tisato M. Toniolo L. 209, 215, Tonna G. Torpiano A. Torrens F. Twilley J. Tzamalis A. Uminski M. Valentini M. Valenza J.
679 145 707 577 707 111 649 467 467 569 459 679 813 387 689 467 577 889 583 145 165 419 361 155 533 361 583 613 921 477 317 485 593 467 493 503 33 361 23 739 251 251 641 513 493 327 759 459
661 Vallet J.M. 165 Van Hees R. P.J. 523 Vannucci S. 3 Vassilieva O.A. 775 Vassiliou P. 155 Vfizquez T. 435 Veiga J.P. 641 Vergbs Belmin V.73, 307, 361 Vicini S. 419 Villegas Sanchez R. 697
Vincenzi F. Vitale A. Vit~ia I. Vlad A . M . Volkova N . V . Volpe R. Von Haslingen B. Weiss N . R . Weiss T. Wendler E.
387 371,379 175 837 553 679 731 533 145 765
Wheeler G. 533 Wheeler G. 541 Wiedemann G. 583 Woyde M. 145 Yemelyanov D. N. 547, 553 Young M . E . 13, 179, 813 Zammit G. 251 Zannini P. 387, 561 Zbirnea I.M. 187 Zehnder K. 749
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