Characterization of failure modes and mechanical behavior of micro-fiber-reinforced recycled aggregate concrete under Hopkinson pressure bar and in-situ CT techniques

This study systematically investigates the dynamic mechanical behavior and failure modes of micro-fiberreinforced recycled aggregate concrete (MF-RAC) under varying strain rate conditions using a split Hopkinson pressure bar (SHPB) system. The effects of fiber volume fractions (0 %, 1.0 %, 1.5 %, 2.0 %, and 2.5 %) on the stress-strain relationships were analyzed, revealing that fiber reinforcement significantly enhances crack resistance, toughness, and ductility, shifting the failure mode from brittle splitting to ductile shearing. At high strain rates, a 2.0 % fiber volume fraction increased peak stress, peak strain, and ultimate strain by approximately 13.7 %, 7.2 %, and 23.4 %, respectively, demonstrating substantial improvements in dynamic deformation capacity. Fiber influence factor models (Eqs. (5)-(13)) and a dynamic increase factor (DIF) model (Eqs. (18)-(26)) were developed to predict the mechanical response of MF-RAC under dynamic loading, achieving average prediction errors of 7.05-12.21 %. The findings provide theoretical and experimental insights for optimizing MFRAC in seismic and impact-resistant engineering applications, contributing to the advancement of sustainable construction materials.