Mechanical performance and freeze-thaw durability of RAC Reinforced with silica fume and basalt fibers

Abstract This study investigates the synergistic effects of highly active silica fume (SF) and short-cut basalt fibers BF on the mechanical and durability performance of recycled concrete subjected to freeze–thaw cycles. Recycled concrete mixtures were prepared with varying SF contents (0, 5%, 10%, and 15%) and basalt fiber dosages (0, 0.5%, 1.0%, and 1.5%). Compressive and flexural strength tests, together with durability evaluations after 50, 100, and 150 freeze–thaw cycles, were conducted to assess performance evolution. In addition, a response surface methodology (RSM)-based multivariate regression model was developed for performance prediction. The results indicated that appropriate incorporation of SF and BF significantly refined the interfacial transition zone, improved matrix densification, and enhanced crack resistance, thereby increasing compressive and flexural strength and optimizing failure modes. Specifically, at 10% SF and 1.0% basalt fiber, compressive and flexural strengths reached maximum values of 53.7 MPa and 6.09 MPa, respectively. Freeze–thaw tests further revealed that this combination achieved the best strength retention and structural integrity after 150 cycles. The RSM model exhibited high fitting accuracy and predictive reliability, with the optimal mix predicted at 10.51% SF and 0.96% basalt fiber, which closely matched the experimental results. Overall, the synergistic incorporation of SF and BF markedly enhanced the mechanical and frost resistance properties of recycled concrete, while promoting the sustainable utilization of industrial by-products and contributing to low-carbon construction practices.