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 SO 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.

Selectional removal of the harmful gypsum weathering layer on the calcareous stone heritages

“…After sulphation treatment, the surface of the sample becomes coarse and porous (Fig. 2b), which is similar with the natural gypsum weathering layer [18] . The surface composition of the marble sample is also converted from calcium carbonate (calcite, d = 3.86, 2.29 and 2.09 Å) to gypsum (calcium sulfate dihydrate, d = 7.70, 4.31, 3.08, 2.88 and 2.69 Å) (Fig.…”

Rock Features and Alteration of Stone Materials Used for the Built Environment: A Review of Recent Publications on Ageing Tests

“…The action of pollutants was found to exploit finer crystals (higher specific surface) in limestones [14]. On the other hand, in heating tests of magmatic rocks, the presence of minerals with coarser size and different coefficients of thermal expansion corresponded to worse results [48].…”

Effect of Thermal and Freeze-thaw Stress on the Mechanical Properties of Porous Limestone

“…The stone is similar to the porous limestone of the Loire valley, France [3,4]. Highly porous limestones are especially susceptible to weathering; gypsum crusts are formed on their surface as a result of air pollution -stone interaction [5,6,7]. Others studies suggest that limestone is not only sensitive to water but also salt weathering can significantly damage its structure [8,9].…”