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Laminar gypsum crust on lede stone: microspatial characterization and laboratory acid weathering

By Tim De Kock, Jeroen Van Stappen, Gilles Fronteau, Marijn Boone, Wesley De Boever, Fabrice Dagrain, Geert Silversmit, Laszlo Vincze and Veerle Cnudde

Abstract

Gypsum crusts are typical decay forms on limestone in polluted urban environments. Their origin and relation to the stone facies have been thoroughly investigated in the past three decades. Here, we present the combined use of novel techniques for a microspatial structural, chemical and mechanical characterization of a laminar black gypsum crust on a sandy limestone. These techniques include i.a. X-ray computed microtomography, Xray Fluorescence micromapping, permeability mapping and the scratch test. They reveal the typical architecture of a laminar gypsum crust, with an outer opaque layer, a subsurface gypsum crystallization layer and a deeper cracked zone passing irregularly into the sound stone. Gypsum crystallization is mostly restricted to an irregular outer zone with an average thickness of 500 mu m, while cracks are found deeper within the rock. These cracks decrease the rock strength to more than 27.5 mm below the surface. Because of their surface parallel orientation and thickness of textrangle10-100 mu m, they create the potential for surface scaling. This is shown by a laboratory acid test where the crack network extensively developed due to further exposure to an SO2 environment. The use of novel techniques opens potential for the study of different decay forms and can be used for stone diagnosis with regards to conservation studies

Topics: Gypsum crust, X-ray computed microtomography, Drilling restistance, Scratch test
Year: 2017
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Provided by: NARCIS
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