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.

To explore the shear behavior and evolutionary pattern of desert sand concrete beams (DSCBs) subjected to freeze–thaw cycles, 16 DSCBs were subjected to rapid freeze–thaw cycling and shear tests, with desert sand replacement ratios (0%, 20%, 40%, and 60%) and numbers of freeze–thaw cycles (0, 25, 50, and 75) considered as the main variables. The failure mode, diagonal crack development, diagonal cracking load, shear capacity, and load–stirrup strain curves of DSCBs were tested and analyzed. The results indicate that all specimens exhibited typical shear-compression failure. The diagonal crack development pattern of DSCBs was similar to that of ordinary concrete beams, whereas freeze–thaw cycles accelerated the initiation and propagation of cracks. Freeze–thaw cycling significantly reduced both the diagonal cracking load and shear capacity. After being exposed to 75 cycles of freezing and thawing, the ultimate shear capacity of test pieces with desert sand replacement proportions of 0%, 20%, 40%, and 60% decreased by 15.6%, 12.9%, 13.9%, and 13.8%, respectively, while the corresponding stirrup strains increased by 47.2%, 34.1%, 37.1%, and 53.7%, respectively. An appropriate desert sand replacement ratio can improve the shear performance of concrete beams. Among all specimens, the beam with a 20% replacement ratio exhibited the best overall mechanical performance, achieving a maximum increase of 6.0% in shear capacity and a maximum reduction of 26.8% in stirrup strain compared with conventional concrete beams. Finally, by introducing modification coefficients related to the desert sand replacement ratio as well as the freeze–thaw cycling times, predictive equations for the diagonal cracking load and shear capacity of DSCBs under freeze–thaw conditions were established. The numerical predictions achieve a high consistency with measured data.