Multiscale characterization of limestone used on monuments of cultural heritage
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Multiscale characterization of limestone used on monuments of cultural heritage Mandana Saheb1, Jean-Didier Mertz2, Estel Colas2, Olivier Rozenbaum3, Anne Chabas1, Anne Michelin1, Aurélie Verney-Carron1, Jean-Pierre Sizun4 1 LISA, UMR CNRS 7583, Université Paris-Est Créteil and Université Paris-Diderot, 61 avenue du Général de Gaulle, 94010 Créteil Cedex France 2 LRMH, USR 3224, 29 rue de Paris, 77420 Champs-sur-Marne, France 3 ISTO, UMR 7327, 1A rue de la Férollerie, 45100 Orléans, France 4 LCE, UMR 6249, 16 route de Gray, 25030 Besançon, France ABSTRACT In the context of the preservation of the cultural heritage, it is important to understand the alteration mechanisms of the materials constituting historical monuments and architecture. Limestone especially is widely used in many French monuments exposed to an urban aggressive atmosphere affecting their durability. To better understand the alteration mechanisms, the first step is to characterize at different scales the stone material properties. In one hand, the pore network that drives the fluids transfer inside the materials was characterized. And on the other hand, the alteration layer formed on several decades aged materials was studied. Results on this fine-scale characterization are discussed. INTRODUCTION The preservation of the built heritage constitutes an environmental, economic, and cultural challenge. In France 52% of the stone buildings are made out of limestone, so that their preservation is of primary and immediate importance. The climate plays a role on the natural ageing of the building constructions. Moreover atmospheric pollution directly affects the evolution of the materials due to the chemical reactions induced by dry and wet deposition and their alteration kinetics. For over 200 years, the increased production of energy has caused high atmospheric emissions in the form of gases (SO2, CO2, NOx) and particulate matter. The gases cause an acidic deposit that could accelerate the materials dissolution and/or the formation of crusts. The particulate matter blackening the surface of the materials often increases the water sorption mechanism or catalyzes the sulphation reaction. The present work belongs to an ongoing study aiming at understanding the alteration processes on limestone exposed to an urban polluted area. The first step is the characterization of the relevant parameters of the stones that could influence the further alteration processes and/or evolve with the alteration. Thus, the pore network needs to be characterized because it allows the water transfer (that is the main alteration factor) inside the materials and because it can be modified by dissolution, pressure solution or crystallization processes. The alteration zones need to also be characterized by a multiscale approach (macro- to micrometric) as they play a significant role in the further alteration (changes of the kinetics) and in order to evaluate their evolution, physical pathways and chemical mechanisms as a function of time. To this purpose, non-destructive methods are f
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