Abstract: To enhance the utilization of recycled aggregate concrete (RAC) in high-altitude and cold regions of northern China, we investigated three anti-freezing performance indicators, namely, mass loss rate (MLR), relative dynamic elastic modulus (RDEM), and compressive strength loss rate (CSLR) of RAC reinforced with single and combined basalt fiber (BF) and polyvinyl alcohol fiber (PVAF). Scanning electron microscopy (SEM) was employed to analyze the meso-mechanical behavior of the mixed-fiber recycled concrete following 200 freeze-thaw cycles. Subsequently, the optimal mixed fiber content was determined using the response surface method. Findings indicate that fiber additives enhance the frost resistance of recycled concrete, with the combined fiber exhibiting superior performance compared to single fiber. Both BF and PVAF are intricately interwoven within the specimen's network, synergistically reinforcing the structure while mitigating crack formation. Optimization analysis reveals that the optimal volume content of PVAF and BF is 0.170% and 0.246%, respectively, yielding the highest frost resistance in recycled concrete. These results offer valuable insights for the design of basalt-polyvinyl alcohol fiber content in recycled concrete applications.

Key words: recycled concrete, mixed fiber, optimized fiber content, freeze-thaw cycle, response surface method