In France 52% of the historical monuments are made out of limestone; the preservation of this material is therefore an economic, scientific and cultural challenge. In urban area, limestones used in the façade of the buildings are exposed to a polluted environment and their degradation is already well documented. Several alteration processes are expected to occur such as phases precipitation and dissolution. In such environment, the most common alteration secondary phase is gypsum (CaSO4, 2H2O) formed from the reaction between calcareous stones, environmental water and sulfuric acid from the atmosphere.
Whatever the alteration process, water as rainfall (wet deposition) or as vapor state (dry deposition) is the alteration agent, so that it is the main parameter to focus on .Thus in order to better understand the stone/water interaction and to propose solutions for preserving the built cultural heritage, we developed an original methodology based on water isotopic tracers (D and 18O). Deuterium was used to localize water penetration front in the material, while 18O enabled to determine secondary phase reaction sites, mainly composed of gypsum.
Pristine samples from quarry and samples from Parisian monuments were selected to compare different alteration stages. Firstly, their main chemical and physical properties linked to the alteration were studied based on a multiscale characterization.(Saheb et al., 2015). Then, samples were altered in laboratory by realistic and controlled conditions of dry deposition during 2 months using isotopically labeled water. The reaction zones were analyzed by nano-SIMS. This experimentation enabled determining that water entirely penetrated in samples from quarry and from monuments, what highlights that the alteration layer does not seem to have a protection effect. In surface or deeper inside the sample, 18O enrichment highlights preferential reaction sites, localized in micro-cracks inside the gypsum zones and along grains of calcite (Figures 1 and 2).
This innovative methodology is a first step to understand the alteration mechanism formation on limestone used in the façade of the buildings. Understanding the mechanisms and especially the role of the alteration layer will contribute to improve the knowledge of stone chemical alteration processes to develop appropriate conservation strategies for the buildings.
M. Saheb, J.D. Mertz, E. Colas, O. Rozenbaum, A. Chabas, A. Michelin, A. Verney-Carron, J.P. Sizun, Multiscale characterization of limestone used on monuments of cultural heritage, MRS Proceedings (2014), p. 1656.
To cite this abstract:Adam Drici, Mandana Saheb, Jean-Didier Mertz, Aurélie Verney-Carron, Loryelle Sessegolo, Laurent Remusat, Adriana Gonzalez-Cano; Alteration mechanisms of limestone used in built cultural heritage : use of isotoping labelling to determine the water penetration and reaction sitesIn France 52% of the historical monuments are made out of limestone; the preservation of this material is. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/alteration-mechanisms-of-limestone-used-in-built-cultural-heritage-use-of-isotoping-labelling-to-determine-the-water-penetration-and-reaction-sitesin-france-52-of-the-historical-monuments-are-made-o/. Accessed: May 26, 2020
EMC Abstracts - https://emc-proceedings.com/abstract/alteration-mechanisms-of-limestone-used-in-built-cultural-heritage-use-of-isotoping-labelling-to-determine-the-water-penetration-and-reaction-sitesin-france-52-of-the-historical-monuments-are-made-o/