Applying the Techniques on Materials II
Back-scattered Scanning Electron Microscopy (BSEM) has been used to identify weathering mechanisms occurring in two oolitic limestones from urban areas in London and Cambridge, United Kingdom. From a petrographical point of view, the two stones can be des
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Applying the Techniques on Materials II Nick Schiavon, Vasilios Melfos, Reiner Salzer, Renate Lunkwitz, K. Chrysafis, P. Spathis, D. Merachtsaki, K. Triantafyllidis, P. Giannakoudakis, P. Xidas, Giovanni Ettore Gigante, Stefano Ridolfi, R. Lahoz, L. A. Angurel, U. Brauch, L. C. Estepa and G. F. de la Fuente Leis
6.1 The Application of Back-Scattered Scanning Electron Microscopy to Unravel Building Stone Decay Mechanisms in Urban Environments Nick Schiavon Abstract Back-scattered Scanning Electron Microscopy (BSEM) has been used to identify weathering mechanisms occurring in two oolitic limestones from urban areas in London and Cambridge, United Kingdom. From a petrographical point of N. Schiavon (&) Evora Geophysics Centre and Hercules Laboratory for the Study and Conservation of Cultural Heritage, University of Evora, Largo Marqués do Marialva 8, 7000-809 Evora, Portugal e-mail: [email protected] V. Melfos Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece e-mail: [email protected] R. Salzer R. Lunkwitz Department of Chemistry, Dresden University of Technology, 01062 Dresden, Germany e-mail: [email protected] K. Chrysafis Department of Physics, School of Science, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece e-mail: [email protected] P. Spathis D. Merachtsaki K. Triantafyllidis P. Giannakoudakis P. Xidas School of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece e-mail: [email protected]
E. A. Varella (ed.), Conservation Science for the Cultural Heritage, Lecture Notes in Chemistry 79, DOI: 10.1007/978-3-642-30985-4_6, Springer-Verlag Berlin Heidelberg 2013
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view, the two stones can be described as oosparite and oomicrite, their main distinctive feature being the crystal size of the cement binding the limestone grains together. The sulphation mechanism, i.e. the replacement of calcium carbonate (calcite: CaCO3) by calcium sulphate dehydrate (gypsum: CaSO4 2H2O), at the surface and within the stone fabric is confirmed as the general decay process. Differences in macroporosity/permeability distribution in the two limestones lead to different weathering patterns. BSEM provides evidence that gypsum patinas still commonly found on limestone facades in polluted urban locations are advancing inside the diseased stone and that their removal is urgently needed to arrest the growth of the in-growing weathering front.
6.1.1 Introduction Rising levels of air pollution in modern urban agglomerates not only have deleterious effects on human health but may also be correlated with the onset of serious decay patterns on a variety of earth materials used in built heritage monuments. Stone is no exception. One of the most commonly used lithotypes is limestone, a high porosity sedimentary rock composed of a framework of grains (minerals, fossils and, as in the case illustrated in this chapter, ooids) bound together by a ‘‘ce
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