Impact resistance of PVA fiber-rubber particle modified concrete with spontaneously combusted coal gangue aggregate: response surface optimization and mechanisms

To improve the impact resistance of solid-waste-based concrete and to optimize the combined use of waste and reinforcing components, this study prepared concrete in which natural coarse aggregate was partially replaced by spontaneously combusted coal gangue (SCG) and modified with rubber particles (RP) and polyvinyl alcohol (PVA) fibers. A three-factor, three-level Box-Behnken response surface methodology (RSM) design was used, with PVA fiber content, RP replacement ratio, and SCG replacement ratio as variables. Cube compressive strength, splitting tensile strength, flexural strength, and final-crack impact number (N2) were measured, and sustainability and scanning electron microscopy analyses were used to interpret the mechanisms. PVA fibers markedly enhanced impact resistance, RP improved ductility and energy absorption but reduced strength at high contents, and increasing SCG replacement generally weakened mechanical properties. The RSM models showed high goodness of fit (R2 = 0.9779–0.9862), and the optimum mixture was 0.16% PVA fiber, 5% RP replacement, and 10% SCG replacement. The combined fiber-bridging and rubber-buffering mechanisms suppressed crack propagation, providing a feasible route for designing tougher and more sustainable solid-waste concrete.