Damage constitutive modeling of microfiber‐reinforced recycled aggregate concrete under cyclic loads

This study conducts a multiscale investigation on microfiber‐reinforced recycled aggregate concrete (MF‐RAC) under cyclic loading using in situ four‐dimensional (4D) computed tomography (CT) to characterize real‐time microstructural evolution. Incorporation of 2.0% steel microfibers significantly enhances residual strength (by 66.2%) and reduces permanent strain accumulation (by 54.1%) compared to plain RAC. 4D CT imaging directly visualizes fiber‐bridging, crack deflection, and inhibition of microcrack coalescence, elucidating the key mechanisms governing damage resistance in MF‐RAC. A novel multiphase constitutive model is proposed, accurately capturing the nonlinear hysteretic response and elastic‐plastic transition under cyclic loading. Additionally, a damage evolution model quantitatively correlates stiffness degradation with real‐time internal crack propagation, validated via image‐based damage indices. These findings advance understanding of microstructure–property relationships in recycled aggregate composites and provide a scientific basis for designing durable, sustainable, and high‐performance concrete infrastructure.