Microstructural and mechanical effects of heating as an artificial weathering method for testing stone consolidants

The effectiveness of heating stone specimens to high temperature, to induce controllable microstructural, physical and mechanical alterations, was investigated. Three types of stones were considered: a highly porous limestone (LS1), a porous calcareous sandstone (SS1) and a siliceous sandstone with low porosity (SS2). Samples were artificially weathered by heating at 200 °C for 1 hour after water saturation; at 200 °C for 1 hour after water saturation and then at 400 °C for 1 hour; at 400 °C for 1 hour without prewetting. The heated samples exhibited an increase in porosity and water absorption, owing to the opening of new micro-cracks caused by the anisotropic thermal deformation of calcite crystals, the differential thermal deformation of different minerals and the presence of water in water-saturated samples. Correspondingly, LS1 and SS1 exhibited decreases in mechanical properties, which depend on the heating temperature and on the open porosity of the heated lithotype. SS2, on the contrary, exhibited an increase in compressive and tensile strength, attributed to the “hot melt effect” of some secondary clay minerals. All things considered, heating proved to be a fairly effective and reproducible method to obtain stone samples artificially weathered to different degrees, on which the effectiveness of new stone consolidants can be tested. Nonetheless, depending on the mineralogical characteristics of the studied lithotypes, the effects of heating may vary significantly, hence the suitability of this artificial weathering method should be preliminarily evaluated on each lithotype.