<p>The effectiveness of air-entraining agents in enhancing the frost resistance of concrete is significantly reduced under low-pressure conditions, such as those found in plateau and alpine regions, leading to severe freeze–thaw damage. To address this challenge, this study investigates the use of rubber powder as a compensatory material for air-entraining agents, introducing “solid pores” to replace traditional air voids. The combined effect of rubber powder and nano-silica was evaluated through macroscopic performance tests and microstructural analyses, focusing on the evolution of pore structure parameters and frost resistance during freeze–thaw cycles. The results show that rubber powder increases the air content and optimizes the pore structure, with “solid pores” accounting for an increasing proportion of total air content as the dosage rises. The addition of nano-silica further refines the pore size distribution by reducing the proportion of larger pores and stabilizing the bubble spacing coefficient. Concrete incorporating both rubber powder and nano-silica exhibits significantly improved frost resistance, with only a slight reduction in compressive strength compared to ordinary concrete. These findings demonstrate that the synergistic use of rubber powder and nano-silica effectively compensates for the diminished performance of air-entraining agents under low-pressure conditions, offering a practical approach to enhancing the freeze–thaw durability of concrete in cold, high-altitude environments.</p>