Damage and Energy Evolution at the Sandstone–Concrete Interface Under Freeze–Thaw Action

Purpose: To investigate the mechanical-damage behavior and energy-evolution characteristics of the sandstone–concrete interface when subjected to freeze–thaw cycles. Method: Uniaxial compression tests were conducted on sandstone–concrete-composite specimens subjected to 0, 10, and 20 freeze–thaw cycles. The effects of interface angle and roughness were considered, and the stress–strain behavior, elastic modulus, failure modes, and energy-evolution characteristics were systematically analyzed. Results: Freeze–thaw cycles significantly reduce the strength and stiffness of the sandstone–concrete interface and intensify the differences in its mechanical performance. Increasing interface roughness enhances mechanical interlocking and delays damage development; however, damage continues to accumulate with repeated freeze–thaw cycles. Conclusions: Freeze–thaw cycling is a key factor governing the degradation of sandstone–concrete interface performance, while interface angle and roughness exert significant influences on the damage-evolution process.