Differences between Time-Dependent Instantaneous and Apparent Chloride Diffusion Coefficients of Concrete in Tidal Environment

Abstract

Time-dependent chloride diffusivity can reflect the chloride transport in concrete, which is greatly affected by different factors such as material composition and environment condition. In this paper, three tests with eight kinds of concrete in different exposure environments (two natural tidal environments and one artificial simulated environment) were designed, and the profile of free chloride concentration at different depths and exposure times were obtained. The apparent and instantaneous chloride diffusion coefficients were determined, and their time-dependent properties were analyzed. The differences between apparent and instantaneous chloride diffusion coefficients were discussed, and the corresponding influencing factors were analyzed. Results show that under the similar climate environments, water salinity is the main factor affecting the age reduction factors of apparent and instantaneous chloride diffusion coefficients of ordinary concrete, i.e., age reduction factors increase with water salinity. Besides, the artificial simulated environment with characteristics of high temperature and high humidity has a significant effect on the age reduction factor of the instantaneous chloride diffusion coefficient. Moreover, the difference between apparent and instantaneous chloride diffusion coefficients of ordinary concrete decreases gradually with the increasing water-cement (w/c) ratio and the addition of silica fume (SF), but increases when adding fly ash (FA) and basalt fiber (BF) into concrete. Temperature is the most important factor affecting the difference between apparent and instantaneous chloride diffusion coefficients, but the effect of exposure time is not significant.