Performance degradation mechanisms of highly hydrated concrete subjected to simulated ambient temperature cycling: From quasi-static to impact compression

Under long-term thermal cycling, the beneficial effect of pore filling from ongoing hydration competes with the detrimental effect of thermal damage in concrete. Previous studies have suggested that 50 ℃ and 120 cycles represent the threshold at which these opposing effects reach equilibrium. However, the influence of thermal cycles on the compressive behavior beyond this threshold remains poorly understood. Moreover, it is uncertain whether the hydration observed under thermal cycling is thermally induced or merely a continuation of normal hydration. To address these questions, this study investigates C40 concrete at a curing age of 1080 days, by which time hydration had become nearly stagnant and strength had largely stabilized. The results demonstrate that both the quasi-static and impact compression of highly hydrated concrete declines with increasing thermal cycling temperature (25–80 ℃) and number of cycles (0−270). The concrete maintains a stable phase composition throughout thermal cycling. Instead, thermal cycling induces internal dehydration and microstructural reorganization, generating pores and microcracks that are responsible for the degradation of compressive behavior. These findings provide experimental evidence and theoretical guidance for improving the service performance of concrete structures subjected to combined ambient temperature cycles and impact loads during their service life.