Experimental Investigation on Flexural Behavior of Desert Sand Concrete Beams Subjected to Freeze–Thaw Cycles

To mitigate the shortage of natural river sand in northwest desert regions, utilize local desert sand resources, and address structural performance under harsh winter conditions, this study investigates the flexural behavior of freeze-thaw conditioned desert sand concrete beams (DSCBs) through rapid freeze-thaw and flexural testing. The investigated variables included desert sand replacement ratios (0%, 20%, 40%, 60%) and freeze-thaw cycles (0, 25, 50, 75). Failure modes, load-concrete strain curves, load-deflection relationships, and load-longitudinal reinforcement strain were analyzed. The results indicate that the crack development and failure modes of DSCBs are similar to those of normal concrete beams, and the plane-section assumption remains valid after freeze-thaw cycles. After 75 freeze-thaw cycles, specimens with the same replacement ratio exhibited the poorest mechanical properties-compared to unfrozen specimens, the ultimate capacity decreased by up to 17.5%, reinforcement strain increased by up to 31.9%, and failure deflection decreased by up to 62.0%. Under all freeze-thaw conditions, the 20% replacement ratio yielded the best performance, with ultimate capacity up to 5.3% higher, reinforcement strain up to 18.2% lower, and failure deflection up to 37.5% higher than those of ordinary concrete beams. Finally, correction factors for desert sand replacement ratio and freeze-thaw cycles were introduced to establish predictive equations for cracking moment and ultimate flexural capacity. The predictions are in good agreement with experimental results, providing a theoretical basis for engineering applications.