Modeling the fire response of reactive powder concrete beams with due consideration to explosive spalling

Reactive powder concrete (RPC) is susceptible to fire-induced spalling because of its dense microstructure and lower permeability compared with normal-strength concrete and high-strength concrete, which may compromise the structural integrity and load-carrying capacity of RPC members significantly. A macroscopic finite-element model was therefore extended to track the fire behavior of RPC beams, especially fire-induced spalling. New sorption isotherms were used to identify the mass of liquid water in RPC at elevated temperatures. Furthermore, an improved spalling criterion was proposed, based on the biaxial strength theory of RPC, to judge if the spalling occurs in RPC members. Additionally, the effect of the improved and previous spalling criteria (based on the uniaxial strength theory) on the fire performance prediction of RPC beams was studied. It was found that the improved spalling criterion can provide more-accurate spalling and fire performance prediction for RPC beams since it considers the effect of both the stresses induced by pore pressure, thermal gradients and applied load and the change in concrete strength caused by the spatial stress superposition.