Mechanical and multiscale analysis of bamboo fiber reinforced fully recycled coarse aggregate concrete

This study investigates the reinforcing mechanism of bamboo fiber (BFR) in fully recycled coarse aggregate concrete through a multiscale experimental framework of macroscopic mechanical properties, macro/meso-scale damage evolution, and microstructural morphology. Five BFR volume fractions from 0% to 1.2% were designed while keeping other parameters constant. At the macroscopic level, mechanical tests show that BFR addition enhances compressive strength by up to 44.0% at 0.9% dosage, splitting tensile strength by up to 24.51% at 0.6% dosage, and flexural strength by up to 27.56% at 0.6% dosage. At the macro/meso-scale, ultrasonic pulse velocity (UPV) testing confirms that all specimens fall within the good quality range, and digital image correlation tracking demonstrates that fiber incorporation extends the stable crack propagation period by 40–60%. At the microscale, scanning electron microscopy reveals that appropriate fiber content forms a three-dimensional network within the matrix, bridging microcracks and inducing crack deflection. Based on these multiscale results, predictive models incorporating both UPV and fiber content are proposed with R² values from 0.84 to 0.95. This study establishes an integrated understanding of how fiber dosage affects mechanical response through crack evolution and microstructural reinforcement, providing fundamental data for the application of this material system in structural components.