Weakening-strengthening evolution law of concrete flexural strength under sulfate attack

For plain concrete materials, the degradation of concrete by seawater is mainly reflected in the corrosion of sulfate ions. In this study, the variation in the flexural strength of concrete specimens with different water-cement ratios under different sulfate concentrations for 470 days is explored, and the effect of sulfate environment on the decay of flexural strength of concrete with corrosion time is experimentally examined. The results show that the evolution of flexural strength can be divided into three stages: strength attenuation stage, strength recovering stage and strength re-attenuation stage. According to the experimental results, the mechanism of strength attenuation, rebound and re-attenuation is established. Combining the chemical reaction rate equations of continued hydration, delayed growth of ettringite and growth of hydroxy-AFm, a new model for the flexural strength degradation of concrete under sulfate corrosion is proposed. Further, the influence of water-cement ratio and corrosive sulfate solution concentration on the flexural strength of concrete is analyzed. Since the ability of concrete to resist sulfate corrosion can be different for different corrosion systems, a unified method is proposed for evaluating the sulfate corrosion resistance of concrete.