Investigating freeze-proof durability of C25 shotcrete

• Physical and mechanical indexes tests were carried out firstly during freeze–thaw cycles.
• Characteristic parameters of bubbles in shotcrete were investigated.
• We evaluated the influence of an air-entraining agent on freeze-proof durability of shotcrete.

Currently, shotcrete was extensively used in civil engineering. In this study, the influence of an air-entraining agent on freeze-proof durability was investigated using C25 shotcrete via the laboratory tests of the mass loss, dynamic modulus of elasticity, ultrasonic wave velocity and cubic compressive strength. Then, characteristic parameters of bubbles in shotcrete were investigated in order to discover the inner structure of shotcrete. The test results showed the freeze-proof durability index of shotcrete with an air-entraining agent was more than 80% after 300 freeze–thaw cycles. Meanwhile, the freeze-proof durability of shotcrete mixed with the air-entraining agent was better than ordinary shotcrete.