Freeze–thaw resistance, service life prediction, and damage mechanism of coal gangue concrete modified with nano-SiO₂ and basalt fiber

The relatively poor freeze–thaw durability of coal gangue concrete limits its application in cold regions. Therefore, this study investigated the combined modification effect of nano-SiO₂ (NS) and basalt fiber (BF). Rapid freeze–thaw tests were conducted, and the deterioration behavior was evaluated using the mass loss rate, relative dynamic elastic modulus (RDEM), and compressive strength. Surface damage observations and scanning electron microscopy (SEM) were used to examine the modification mechanism. In addition, a service life prediction model was established based on the Wiener degradation process, with RDEM damage used as the degradation indicator. A two-dimensional mesoscopic heterogeneous model was further developed for the optimal mixture to analyze the uniaxial compressive response and mesoscopic damage evolution after freeze–thaw damage. The results indicate that the combined incorporation of NS and BF markedly improved the freeze–thaw resistance of coal gangue concrete, effectively suppressing surface mortar spalling and aggregate exposure, slowing the decline in RDEM, and improving compressive-strength retention. The reliability evolution curves of all mixtures exhibited a typical three-stage nonlinear degradation pattern, with marked differences in the stage-specific degradation rates among the mixtures. Under the present test conditions, the mixture containing 1% NS by mass of cement and 0.1% BF by volume exhibited the best overall freeze–thaw resistance and the longest predicted equivalent service life among the investigated mixtures under pure-water freeze–thaw conditions. The mesoscopic simulation further revealed the evolution of freeze–thaw damage, which initiated at pore edges and in the interfacial transition zone, progressively propagated and coalesced under compressive loading, and ultimately induced the formation of dominant cracks, thereby clarifying the intrinsic relationship between macroscopic performance deterioration and mesoscopic damage accumulation.