Damage mechanisms of pumice concrete under wind-sand erosion and freeze-thaw cycles

This study investigates the durability evolution of pumice concrete with three different strength grades, using natural pumice from Inner Mongolia, China, as the coarse aggregate. A self-developed wind-sand flow erosion apparatus and a rapid freeze-thaw cycling system were employed to examine the coupled effects of wind-sand erosion and freeze-thaw cycles on the concrete in cold regions. The durability was characterized by measuring the mass loss rate, relative dynamic elastic modulus, and pore structure using Nuclear Magnetic Resonance (NMR). The multi-factor coupled deterioration mechanism was systematically revealed. The results indicate that the combined impact of wind-sand erosion and freeze-thaw cycles causes more severe damage compared to individual factors. Wind-sand erosion acts as a "catalyst", damaging the surface cement mortar layer and accelerating freeze-thaw degradation. For instance, in the LC20 test group, the mass loss rate of the freeze-thaw group was 4.34%, whereas the wind erosion and freeze-thaw coupling group exhibited a 6.60% mass loss. After five freeze-thaw cycles, the relative dynamic elastic modulus of the freeze-thaw group dropped below 60% of its initial value. In contrast, the wind-sand erosion and freeze-thaw coupling group experienced a similar reduction after just three freeze-thaw cycles. The relative dynamic elastic modulus is more sensitive than the mass loss rate in reflecting concrete deterioration. NMR analysis reveals that higher water-cement ratios result in an increase in harmful large pores within the concrete, while free fluid saturation serves as a potential indicator for assessing pumice concrete durability. For critical structures in northern frigid wind-sand regions, implementing wind-sand protection measures is essential for effectively extending their service life.