Time-dependent and stress-dependent chloride diffusivity of concrete subjected to sustained compressive loading

This paper studies the chloride diffusivity of concrete subjected to long-term exposure in a simulated marine environment with sustained compressive loading for up to 224 days. A series of concrete prisms were loaded under five different compressive stress levels (0, 0.2, 0.3, 0.5, and 0.7fc) and were subjected to different numbers (4, 8, 12, and 16) of wet/dry seawater exposure cycles. At the end of each exposure period, the concrete specimens were analyzed to determine their chloride penetration profile, the apparent chloride diffusion coefficient Daof the concrete, and the surface chloride content Cs. It was found that the Daand Csvalues are both time and stress dependent and that these two dependencies have complex interactions. The value of Dadecreases with time due to the hydration of the cement matrix, whereas the value of Csincreases over time. The effects of compressive stress on the values of Daand Csstrongly depend upon the applied stress level, which has a threshold value at approximately 30% of the ultimate compressive strength. Below this threshold, the value Csremains constant; after this threshold, Csincreases linearly as the applied stress increases. Below the threshold, the value of Dadecreases marginally as the stress level increases. However, above the threshold, Daincreases rapidly with the stress level as a result of microcracking. Through regression of the chloride penetration profiles, empirical models are proposed to quantify the dependence of Daand Cson the exposure time and stress level. The validity of these models is evaluated through comparisons with test results.