title: Laminar gypsum crust on lede stone: Microspatial characterization and laboratory acid weathering.
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, X-ray 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 500µm, while cracks are found deeper within the rock. These cracks decrease the rock strength to more than 27.5mm below the surface. Because of their surface parallel orientation and thickness of >10-100µm, 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 SO2environment. 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.
authors.affiliation: PProGRess/UGCT - Department of Geology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium; Inspect BVBA, Technologiepark 3, 9052 Ghent-Zwijnaarde, Belgium. Electronic address: tim.dekock@ugent.be.
authors.forename: Tim
authors.initials: T
authors.lastname: De Kock
authors.affiliation: PProGRess/UGCT - Department of Geology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Van Stappen
authors.affiliation: GEGENAA (EA3795), Université de Reims Champagne-Ardenne (URCA), 2 Esplanade Roland Garros, 51100 Reims, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Fronteau
authors.affiliation: PProGRess/UGCT - Department of Geology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium.
authors.forename: Marijn
authors.initials: M
authors.lastname: Boone
authors.affiliation: PProGRess/UGCT - Department of Geology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium; Inspect BVBA, Technologiepark 3, 9052 Ghent-Zwijnaarde, Belgium.
authors.forename: Wesley
authors.initials: W
authors.lastname: De Boever
authors.affiliation: Stone Assistance sprl, Spin-Off of University of Mons, Clos des Botteresses 4, 4317 Viemme, Belgium.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Dagrain
authors.affiliation: XMI - Department of Analytical Chemistry, Ghent University, Krijgslaan 281/S12, 9000 Ghent, Belgium.
authors.forename: Geert
authors.initials: G
authors.lastname: Silversmit
authors.affiliation: XMI - Department of Analytical Chemistry, Ghent University, Krijgslaan 281/S12, 9000 Ghent, Belgium.
authors.forename: Laszlo
authors.initials: L
authors.lastname: Vincze
authors.affiliation: PProGRess/UGCT - Department of Geology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium.
authors.forename: Veerle
authors.initials: V
authors.lastname: Cnudde
keywords: Drilling resistance; Gypsum crust; Scratch test; X-ray computed microtomography; X-ray fluorescence mapping