Experimental Analysis of Chloride Penetration into Concrete Subjected to Drying–Wetting Cycles

To clarify the mechanism of chloride penetration into concrete subjected to drying–wetting cycles, two kinds of concrete, ordinary portland cement concrete and fly ash (FA) concrete, were tested in a cyclic NaCl solution to show the influence of mix proportion, period ratio of drying to wetting, and exposure time. Based on the experimental profiles of free chloride concentration obtained after 30 and 60 weeks, it was found that the depth of convection zone varied from 6 to 15 mm and increased in duration when the air-drying period in one cycle was prolonged or the exposure time increased. Through a regression analysis of chloride profiles located in the inner part of the concrete beyond the advection zone, it was verified that diffusion was the dominant mechanism of chloride transport and could be well fitted with the proposed modified diffusion model taking into account the influence of convection depth. Finally, the time-dependent chloride diffusion coefficient DCl was calculated on the basis of the apparent chloride diffusion coefficient Dapp and the obtained time exponent m. The effect of FA content on DCl was also examined.