Mesoscale Simulation of Steel Slag Fine Aggregate Concrete Using a Cohesive Zone Model: Influence of Microparameters on Uniaxial Compressive Behavior

Steel slag fine aggregate (SSFA) concrete is a composite material comprising cement mortar, SSFA, coarse aggregate, and an interfacial transition zone (ITZ). To simulate the SSFA concrete’s uniaxial compression performance on the mesoscale this study applied Python in conjunction with the Monte Carlo simulation method to develop a two-dimensional random aggregate generation and placement program with built-in cohesive elements, characterizing the ITZ and the crack development process. The model’s reliability was validated by comparing mesoscale simulation predictions with macroscopic uniaxial compression test results. On this basis, a two-dimensional mesoscale numerical model of SSFA accurately reflecting aggregate shape, mesh size, and steel slag replacement ratio was established. It was used to analyze the effects of mortar strength, ITZ strength, and steel slag particle size on the damage evolution and stress–strain relationship of fine steel slag aggregate concrete were analyzed. Results indicate that the concrete compressive strength rises significantly with increasing steel slag content, accompanied by increasing crack paths and a characteristic X-shaped shear failure pattern. Increasing mortar strength can effectively enhance the compressive strength of steel slag fine aggregate concrete. The compressive strength of steel slag fine aggregate concrete is less affected by ITZ strength, but as steel slag particles are dispersed in the mortar, they strongly influence the crack propagation in concrete cracks and, thus, ITZ parameter settings cannot be neglected. Increasing the SSFA particle size enhances concrete compressive strength and vice versa, making SSFA concrete with too fine SSFA particles prone to multiple microcracking and less strong than ordinary concrete. In particular, the SSFA particle size range from 2.37 to 3.56 mm yielded the optimal SSFA cement compression strength. This research provides a solid theoretical foundation for steel slag utilization, enhancing the resource efficiency of waste steel slag.