Chloride transport in concrete under sustained flexural loading

Chloride transport in structural concrete has been found to be both stress- and time-dependent. Several models have been developed to take into account the time dependency of the chloride diffusivity of concrete. However, less is understood about the stress dependency and the interaction between the two dependencies. Experiments were conducted to investigate chloride transport in concrete subjected to different tensile stress levels and different periods of wet–dry cycling exposure (56, 112, 168 and 224 d). Two key parameters were investigated – surface chloride content (C_s) and the apparent chloride diffusion coefficient (D_a). It was found that regardless of the tensile stress level, the values of D_a and C_s respectively decreased and increased with time due to the continuous hydration of cement and the periodic surface wetting with chloride solution. However, both the decreasing and increasing rates were found to be dependent on the tensile stress levels. Both D_a and C_s increased with the tensile stress level due to the opening of pores and the development of microcracks in concrete. Practical models were developed to reflect the above time and stress dependency of D_a and C_s, as well as their interactions. The models were validated through comparisons of the experimental and predicted chloride profiles of all the tested specimens.