Change on shear strength of concrete fully immersed in sulfate solutions

Sulfate-caused deterioration on concrete is principally evaluated by measuring the variation of uniaxial compressive strength and longitudinal expansion at different exposure ages. The evolution of concrete shear strength and its components over exposure period in such a sulfate-rich environment is overlooked. This study aims to characterize the time-dependent evolution of concrete shear strength and its components and to identify the possible microscopic deterioration mechanisms corresponding to these macroscopic properties changes under sulfate-exposure conditions. For this study, direct shear tests on concrete specimens subjected to different sulfate-exposure periods were conducted, where the effects of three water-to-binder ratios (w/b of 0.38, 0.45 and 0.52) and four sulfate-exposure periods (0, 3, 6 and 9 months) were considered. Results indicate that the shear strength and its components of concrete specimens under direct shearing are significantly influenced by external sulfate attack (ESA). For example, shear dilation of concrete specimens under direct shearing diminishes over sulfate-exposure period. However, friction component has a slight increase at the early exposure period in sulfate solutions, followed by a rapid drop at the later exposure period. In addition, the failure criterion of concrete specimens is found to be transformed from the bi-linear Mohr-Coulomb (M-C) before exposure to the linear M-C criterion after exposure in sulfate solutions.