Meso-analysis method for the compressive strength of steel fiber-reinforced recycled aggregate concrete: a six-phase numerical model

This study investigates the impact of steel fibers on enhancing the mechanical properties of recycled aggregate concrete (RAC) at the mesoscale. A six-phase convex polygonal mesoscale model of steel fiber-reinforced recycled aggregate concrete (SF-RAC) was developed using a self-compiled program, incorporating steel fibers, aggregates, old mortar, new mortar, old interfacial transition zone (ITZ), and new ITZ. A mesoscale numerical analysis model was further proposed by developing FEM software to evaluate the compressive strength of SF-RAC, considering the bond-slip behavior between steel fibers and concrete through defined bond and damage parameters. The proposed numerical model was validated by comparison with experimental results. The influence of steel fiber length and diameter on the compressive strength of SF-RAC was explored based on meso-numerical method. The findings indicate that, at a fixed steel fiber content: (1) the larger diameters of steel fibers reduce the enhancement effect on SF-RAC, specifically, a 47.62% reduction in the lifting effect was observed when using steel fibers with a diameter of 0.5 mm, compared to those with a diameter of 0.2 mm; (2) the compressive strength exhibits a trend of initial decrease, followed by an increase, and then, a subsequent decrease as steel fiber length increases. These results provide a theoretical foundation for the engineering application and technical promotion of RAC.