Study on the evolution of wind-blown sand and gravel flow erosion resistance of aeolian sand concrete in cold regions and the coupling mechanism of freeze-thaw cycles: Laboratory tests and numerical simulation

Concrete structures in the wind-sand environments of the Gobi Desert, Northwest China, face severe damage from the combined effects of freeze-thaw (F-T) cycles and wind-blown sand and gravel flow. This region possesses abundant wind-deposited sand resources. Mitigating ecological degradation and other environmental issues can be achieved by using this sand to make aeolian sand concrete (ASC) instead of river sand. Consequently, this study comprehensively examined the erosion resistance and damage mechanisms of ASC by integrating laboratory experiments with numerical simulations. The simulated testing included a multi-factor, coupled environment with varying numbers of F-T cycles, different impact angles, flow velocities, gravel particles of various sizes, and replacement ratios of wind-deposited sand. The outcomes of the study suggest that the concrete erosion rate exhibits significant positive correlations with flow velocity and impact angle, decreases with increasing gravel particle size, and demonstrates an approximately exponential relationship with flow velocity. F-T cycles substantially aggravated erosion damage by inducing internal microcracking. After 300 F-T cycles, the mass loss rate of the ASC0 concrete group reached 4.8 %, which was 1.2, 1.37, and 1.5 times that of the ASC10, ASC30, and ASC50 groups, respectively. ASC exhibits optimal erosion resistance at a 30 % wind-deposited sand replacement ratio. Microstructural analysis indicates that small-sized gravels cause intensive shallow denudation, whereas large-sized gravels induce localized deep cratering and crack propagation. Furthermore, an enhanced Oka erosion model was developed, integrating a negative exponential function for wind-deposited sand admixture, a power function for particle size, and an exponential function for F-T damage. All of the R² values exceeded 0.90, comparing the results of the laboratory experiments with the numerical simulations. This indicates that the predictive accuracy of the Oka erosion model is relatively high. Numerical simulations further revealed that a pronounced flow field obstruction effect occurs at high impact angles, and the result is that the pressure is concentrated across the damaged surface, with the highest pressure peak occurring during vertical impact. These research results offer essential theoretical support for designing durable concrete structures and predicting their service life in cold regions exposed to wind-blown sand and gravel flow.