Time-Dependent and Stress-Dependent Chloride Diffusivity of Concrete Subjected to Sustained Compressive Loading: Fid-Bau Portal

Time-Dependent and Stress-Dependent Chloride Diffusivity of Concrete Subjected to Sustained Compressive Loading

Wang, Hai-Long / Dai, Jian-Guo / Sun, Xiao-Yan / Zhang, Xiao-Long

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 $0.7 f_{c}$ ) 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 $D_{a}$ of the concrete, and the surface chloride content $C_{s}$ . It was found that the $D_{a}$ and $C_{s}$ values are both time and stress dependent and that these two dependencies have complex interactions. The value of $D_{a}$ decreases with time due to the hydration of the cement matrix, whereas the value of $C_{s}$ increases over time. The effects of compressive stress on the values of $D_{a}$ and $C_{s}$ strongly depend upon the applied stress level, which has a threshold value at approximately 30% of the ultimate compressive strength. Below this threshold, the value $C_{s}$ remains constant; after this threshold, $C_{s}$ increases linearly as the applied stress increases. Below the threshold, the value of $D_{a}$ decreases marginally as the stress level increases. However, above the threshold, $D_{a}$ increases 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 $D_{a}$ and $C_{s}$ on the exposure time and stress level. The validity of these models is evaluated through comparisons with test results.