Experimental and theoretical study of fire resistance of steel slag powder concrete beams

Steel slag powder (SSP), used as a partial replacement for cement in concrete, contributes to resource conservation, environmental sustainability and carbon emission reduction. Despite these benefits, the fire performance of steel slag powder concrete (SSPC) remains underexplored, particularly its behavior during and after fire exposure. In this paper, the thermal response under fire and the structural response after fire of five SSPC beams made by replacing part of the cement with SSP were investigated. The results show that the thermal response of the concrete beams with 10 % SSP substitution rate is similar to that of pure concrete beams, but the thermal conductivity of concrete increases slightly with the increase of SSP substitution rate. After subjected to 1 h ISO 834 fire, the stiffness and ultimate load capacity of beams with 20 % SSP substitution rate decreased by 27 % and 8 %, respectively, while the ductility remained unchanged and the energy dissipation capacity increased by about 10 %. Compared with pure concrete beams, the addition of SSP has a slight adverse effect on the ductility, stiffness in elastic stage and crack width in damage stage of the beams after fire, but it has almost no effect on the stiffness in cracking stage, cutline stiffness, residual carrying capacity and deflection, and it even improves the energy dissipation capacity and resistance to the initial cracks. In addition, a theoretical model of the residual carrying capacity of SSPC beams after fire was established, and the accuracy of the model was verified by test results. This study provides a theoretical basis for the fire-resistant design and post-fire performance evaluation of SSPC beams.