Experimental investigation on fire spalling behaviour of concrete: effect of biaxial compressive loading and cement type

Fire spalling of concrete can seriously jeopardise the integrity of the entire structure due to the reduction of the cross-sectional area of the structural elements, which lead to direct exposure of reinforcing bars to flames. In the literature, it is shown that the occurrence of fire spalling is influenced by various parameters, the external compressive load being one of them, which role is not well known in detail. Within this context, an extensive experimental campaign has been conducted to investigate the interaction between pore pressure and thermo-mechanical stresses in triggering spalling. Mid-size concrete slabs (800 x 800 x 100 mm3) were exposed to ISO 834-1 fire curve at the bottom face, while an external membrane biaxial compressive stress was applied before heating parallel to the heated face of the slab. The experimental results have clearly shown that the loaded specimens are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Spalling behaviour of B40-II (12% of calcareous filler and 3% of slag) and B40-III (43% of slag) appear similar.