Impact of heat exposure (fire damage) on the properties of sandstone

The present study was conducted in support of damage examination as part of the reconstruction efforts currently undertaken on the Charles Rennie Mackintosh - Glasgow School of Art after the building suffered severe fire damage in 2014. In this study, compared to most of similar nature, attention was paid to the minimisation of the effects caused by the apparent heterogeneity within sandstone (even when sourced from the same quarry) to understand the consequences of heat for the structural stability of the building. Mechanical property values related to mechanical strength such as compressive strength, ultrasound pulse velocity (UPV) and surface hardness, as well as petrophysical properties (bulk density, water sorptivity and porosity) were measured on sandstone specimens burnt at temperatures of 300°C, 450°C, 600°C, 750°C and 900°C. In conjunction with investigations of mineralogical and textural changes, a correlation was attempted between attributes that were analysed/determined non-destructively with the mechanical strength and structural damage level, to allow for a better on-site judgement on the degree of damage. The results showed that even minor mineralogical and textural variation within the stone specimens of a test series lead to very significant differences in the observable effects after burning. Nonetheless it became clear that the performance of the burnt stone specimens started to deteriorate significantly beyond temperatures of 450°C. As expected, from a material science’s point of view, a discrepancy between UPV, compressive strength results and Leeb rebound values (surface hardness) was observed. Evaluating the mechanical performance of materials, such as sandstone, based on surface hardness may be misleading if one is unaware of the physics behind the testing technique and the materials to be tested.