Mechanical performance and microstructural degradation of raw coal gangue aggregate concrete under chloride freeze–thaw exposure

Abstract This study investigated the influence of water freeze–thaw (WFT) and salt freeze–thaw (SFT) cycles on the mechanical performance and microstructure of concrete incorporating raw coal gangue aggregates (RCGA). Concrete specimens were prepared by replacing coarse natural aggregates (CNA) with RCGA at replacement ratios of 0%, 30%, 70%, and 100%. Freeze–thaw durability of specimens was evaluated in terms of surface deterioration, cubic compressive strength, mass loss, and relative dynamic elastic modulus (RDEM). In addition, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques were utilized to characterize the changes in microstructure and pore characteristics of specimens after different freeze–thaw cycles. The results revealed that increasing RCGA content significantly reduced compressive strength and freeze–thaw resistance. After 75 freeze–thaw cycles, concrete with 100% RCGA showed compressive strength losses of 29.79% after WFT and 54.21% after SFT, both greater than those of conventional concrete. Compared with WFT, SFT induced more pronounced deterioration, possibly due to the formation of chloride‐induced products in the interfacial transition zone (ITZ) and the growth of harmful pores. Furthermore, a freeze–thaw damage model for RCGA concrete was proposed based on the evolution of RDEM. These findings provide a reference for durability assessment of RCGA concrete in cold regions.