Effect of chlorides on the deterioration of mechanical properties and microstructural evolution of cement-based materials subjected to sulphate attack

Long-term service of specimens with different water-cement ratios (0.45, 0.5, and 0.55) and different slag dosages (0, 20%, and 50%) in sole sulphate and composite chloride-sulphate solutions was carried out to comparatively study the effects of sole sulphate ion and chloride-sulphate ions coupling on the macro-mechanical properties and microstructure of the specimens. The results show that the strength of the materials exposed to individual sulphate, compound chloride-sulphate solutions basically show a first increasing and then decreasing trend with exposure time. Moreover, under dynamic competitive interaction, the strength of specimens under combined attack changes more slowly compared with sole sulphate attack. The mitigation of specimen mechanical properties and microstructural deterioration by competitive interaction under compound chloride-sulphate solution decreases as the water-to-cement ratio increases. Increasing the slag dosage leads to an increase in the duration of the mitigation of strength deterioration by the competitive interaction. In addition, a time-varying model of the corrosion resistance coefficient was developed, which can provide a reference for the optimal design of the mechanical properties of concrete for long-term service in the marine environment.