Fire-exposed stones in constructions: Residual strength, performance loss and damage mode shift due to mineralogical transformation and micro-cracking

The heritage restoration and the design of modern stone masonry structures bear in mind the material response to fire, the residual strength and post-fire resilience. In this attempt, the decomposition of fire-exposed natural and engineered stones and their mineralogical transformations are reported. The fire-induced petrographic change is further correlated to rise in shrinkage and porosity, and loss of mechanical properties, such as strength, toughness and stiffness. Stones of different nature (limestone, sandstone, quartzite, polymer/quartz-based engineered stone) are selected to trigger various thermal degradation mechanisms. Also, the stones were sorted considering their sustainability profile since all stones, except the artificial ones, were collected from local quarries and linked to the regional heritage and architecture. An integrated inspection methodology is designed that implements non-destructive monitoring on mechanical tests. A novel proof-loading concept is introduced at which the residual performance is assessed exclusively based on ultrasound pulse velocity (UPV) and early acoustic emission (AE) data. The damage mechanisms that dominate fracture and the shift of failure from strong brittle to weak pseudo-ductile with an early transition from crack initiation to propagation are determined based on AE features analysis.