Università Degli Studi Di Padova Department of Geosciences
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Head Office: Università degli Studi di Padova Department of Geosciences ___________________________________________________________________ Ph.D. COURSE IN: EARTH SCIENCES XXX SERIES DETERIORATION OF CARBONATE ROCKS AND VULNERABILITY OF CULTURAL HERITAGE IN A CHANGING CLIMATE Coordinator: Prof. Fabrizio Nestola Supervisor: Prof. Claudio Mazzoli Co-Supervisor: Prof. Matteo Massironi Ph.D. student : Silvia Salvini To Laura, gone too soon, never forgotten SUMMARY……………………………………………………………. Introduction………………………………………………………………………. 6 Part 1 A petrographic characterization of the carbonate rocks used for the monumental built heritage in northeastern Italy...................................................................... 9 1. Introduction . The stone materials . 2.1. Vicenza stone . 2.2. Istria stone. 2.3. Chiampo stone. 2.4. Red Verona marble . 2.5. Asiago stone . 2.6. Botticino marble . 2.7. White Carrara marble. 2. Analytical methods 3. Results. 4.1. OM observation and grain size estimation . 4.2. EBSD . 4.3. XRF and XRPD analyses . 4.4. Porosity analyses 4. Conclusions References Part 2 Assessing porosity of different carbonate rocks using multiple techniques… 35 1. Introduction 2. Materials and methods . 2.1. Sample materials . 2.2. Analytical techniques 2.2.1. Digital Image Analysis (DIA) of SEM – BSE images 2.2.2. Computerized X-Ray micro-Tomography (micro-CT) 2.2.3. Mercury Intrusion Porosimetry (MIP) 3. Results and discussion . 3.1. 2D- DIA (Digital Image Analysis) of 200x SEM – BSE images . 3.2. 2D and 3D DIA of micro – CT scans . 3.3. Mercury Intrusion Porosimetry . 3.5. Comparing techniques: cumulative curves reconstruction 4. Conclusions References 3 Part 3 Deterioration of headstones from the CWGC cemeteries in the Mediterranean area ……………………………………………………………………………….. 61 1. Introduction . 1.1. Influence of climate in stone decay processes . 1.2. Measuring stone recession 2. Locations . 2.1. Choice of sites. Why CWGC cemeteries? . 2.2. Italy 2.2.1. Padua 2.2.2. Bordighera (IM) 2.2.3. Savona 2.2.4. Dueville (VI) 2.2.5. Asiago Plateau (VI) 2.2.6. Tezze (TV) 2.2.7. Giavera del Montello (TV) 2.2.8. Cremona 2.2.9. Arquata Scrivia (AL) 2.2.10. Castiglione dei Pepoli (BO) 2.2.11. Bologna 2.2.12. Rome . 2.3. Greece 2.3.1. Athens 2.3.2. Thessaloniki 2.3.3. Souda Bay (Crete) 3. Materials and Methods . 3.1. Materials . 3.2. Methods . 3.3. A major issue: gravestone dating 4. Results . 4.1. Recession data . 4.2. Data elaboration 4.2.1. Influence of climate 4.2.2. Influence of orientation 4.2.3. Influence of exposition time 4.2.4. Influence of the rock type 4.2.5. A note on standard deviation error 5. Conclusions References Part 4 Accelerated ageing test of carbonate rocks and their assessment of their recession rates……………………………………………………………………………….. 89 1. Introduction . 1.1. Chemistry of rain affecting carbonate stone decay . 1.2. Pollutants 4 . 1.3. Damage functions and equations for the recession of carbonate rocks . 1.4. Simulation of rainwater and utilization of climate chambers . 1.5. Recession rates estimations 2. Materials and Methods . 2.1. Materials . 2.2. Laboratory analyses . 2.3. The preparation of the samples for the accelerated ageing tests . 2.4. The waters . 2.5. The climatic chamber . 2.6. The control tests 3. Results . 3.1. Laboratory analyses . 3.2. Sample recession based on weight measurements . 3.3. Sample recession based on micro-photogrammetry . 3.4. Sample recession based on confocal laser microscope 4. Discussion 5. Conclusion References Technical Note Photogrammetry as a tool for evaluating stone decay………………..…. ……..121 1. Introduction 2. On situ SfM microphotogrammetry 2.1. Materials 2.2. Methods 2.3. Results 3. Ultra close range microphotogrammetry 3.1. Materials 3.2. Methods 3.3. Results 4. Conclusion References Conclusions…………………………………………………………… 132 Bibliography…………………………………………………………. 134 Acknowledgements…………………………………………………... 151 5 Introduction The definition of cultural heritage is wide and it includes tangible artifacts (monuments, works of art, buildings, books, artifacts, …) and intangible culture (traditions, folklore, languages…) as well as natural heritage (significant landscape, biodiversity, …). The conservation of cultural heritage is our connection with the past and a moral duty for future generations. The conclusive remarks of the Bruntland Report (1987) stated the birth of the concept of sustainable development1 and now it is assessed that maintenance planning is the most sustainable conservation strategy for our cultural heritage. Nowadays, our cultural heritage is endangered because it is made of materials more or less prone to decay. Rock is a more durable building material than wood and mud, so it has been used in anthropic structures since Palaeolithic age. Rock used by man as building material is called (ornamental or dimension) stone. Stones are subjected to deterioration due to exposure to pollution (emissions from industrial plants, air, vehicular and marine traffic, …), natural environment (rain, wind, frost, …), tourism, etc. In Italy, stone conservation is a relevant problem because the number of historical cities and towns and of archaeological remains over the entire national territory is extremely high. In the last decades many academic debates have been carried on about the most suitable and sustainable preservation practices necessary in order to maintain this huge amount of monuments and historical centers. In order to develop good conservation and maintenance plans we need to increase our knowledge about the decay of materials and realise reliable projections of future deterioration. Generally speaking, the historical buildings were built using the rock types locally available and easily workable, consequently the percentage of carbonate rocks (limestones, marbles) among the stone used in the cultural heritage is very high. The rate of carbonate rocks used in built heritage is about 90%2. Carbonate rocks were – and still are – preferred because of their aesthetic features, availability and workability, even if their chemical composition makes them more subjected to the environmental impact and prone to decay with respect to the silicate rocks. In geomorphology studies, degradation phenomena of rocks can be described in terms of change in their surface topography, material loss or surface recession. Different equations have been drafted over time for describing surface recession but the one by Lipfert (1989) is the most commonly used. This relation considers only a few key factors of decay and refers only to a specific period of time (i.e., year).3 + Loss/mrain = 18.8 + 0.016 [H ] + 0,18 (VdS * [SO2]+VdN * [HNO3])/R 1 From Brundtland Report (1987) “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs” 2 In Italy the use of silicate rocks is less diffuse than in other countries (e.g. Germany, Spain) but there are notable exceptions, such as the sandstones used in the cathedral of Piacenza and the Serena Stone in Florence (Rodolico 1963). 3 Some authors also tried to apply this equation to predict future limestone recession over long periods of time (Brimblecombe & Grossi, 2009; Sabbioni et al., 2010). 6 + where H is the hydrogen ion concentration, VdS and VdN are the deposition rates of SO2 and HNO3, respectively, [SO2] and [HNO3] are SO2 and HNO3 concentrations in the atmosphere, and R is the annual precipitation (the VdN*[HNO3] term is often omitted). The equation reported above completely disregards other environmental factors such as temperature and relative humidity which also have an important effect on deterioration, and textural features of the stone such as grain size and porosity. The main aim of this study was to understand the effect of petrographic and textural features on the deterioration of carbonate rocks under different environmental conditions. Results have been used to quantify the effect of such stone intrinsic properties on surface recession. To this aim, research has been organized in three main steps: 1. Selection of a set of carbonate rocks differing for their mineralogy and texture, and detailed characterization of their petrographic and textural features (Part 1 and 2); 2. Field survey for the measurement of total stone recession in headstones from different Commonwealth War Graves Commission (a.k.a. CWGC) cemeteries 3. Accelerated ageing tests under monitored environmental conditions on all the selected rocks in order to evaluate the effect of petrographic and textural features on recession rate (Part 4); Regarding the selection of materials, eleven carbonate rock types have been considered among those most frequently used in the built heritage of north-eastern Italy, including the Commonwealth War Graves Commission cemeteries: Vicenza Stone (Nanto and Costozza varieties), Istria Stone, Chiampo Stone (Porfirico and Ondagata varieties), Red and Brown Verona Stone, Pink and White Asiago Stone, Aurisina Stone, Botticino Stone. In addition, Carrara marble has also been selected. This was an important point, considering that most of the previous studies on the recession rate of carbonate rocks were mainly based on measurements performed on marbles, and often on Carrara marble (Meierding 1981, Reddy & Roberts 2005). The first issue was therefore to characterize all these rock types from a petrographic and textural point of view, using several routine laboratory analytical approaches. More specifically, the following techniques