Investigating the damage mechanism of concrete in Alpine Gobi under the combined action of freeze-thaw cycles and wind-blown sand and gravel

Freeze-thaw cycles and wind-blown sand and gravel (WBS/G) have severely degraded the concrete piers along the Golmud-Korla Railway, which substantially compromises their structural integrity. To address this challenge, this study employs the airflow sand injection technique to determine the anti-erosion characteristics of concrete undergoing freeze-thaw cycles, with a focus on its resistance to WBS/G. An increased number of freeze-thaw cycles reduces the compactness of the aggregate and reduces the strength of the mortar on the concrete surface. This leads to the breakdown of the cement coating. Simultaneously, internal degradation of the void structure exacerbates the increase in void ratio, prolonging the accelerated damage stage during the erosion process induced by WBS/G. Consequently, the overall damage to the concrete breaks more severely. Following 200 freeze-thaw cycles, the level of erosion of the concrete rises by 19.9-49.2 mg/cm² compared to unfrozen concrete. At lower freeze-thaw cycle counts, the erosion rate caused by small-sized gravel is higher. However, at high freeze-thaw cycle counts, the mortar and coarse aggregate are not as firmly bonded as they could be, leading to a significant increase in erosion caused by large-sized gravel. This is attributed to the larger erosion range and higher kinetic energy of large-sized gravel, which exacerbates damage during WBS/G exposure. Concrete's rate of erosion and compressive strength exhibit a strong negative linear correlation prior to and following freeze-thaw cycles, with the coefficient of determination (R²) exceeding 0.80. This study builds upon the classical Bitter theoretical model by incorporating the compressive strength factor, particle size function, and freeze-thaw damage factor. The goal is to develop a WBS/G erosion resistance model for concrete undergoing freeze-thaw cycles. This model serves as a scientific design framework for durability and maintenance of concrete constructions in cold climates of Northwest China, offering insights into erosion mechanisms and practical guidance for mitigating freeze-thaw-induced degradation.