Time dependent models of apparent diffusion coefficient and surface chloride for chloride transport in fly ash concrete

This paper presents a Fick-based chloride transport model, which is mathematically consistent with time dependent apparent diffusion coefficient and surface chloride for fly ash concrete. In the paper, the inconsistency in a simple close-formed solution used to predict chloride penetration through fly ash concrete in a previous study of other researchers is pointed out. The inconsistency can be seen by comparing chloride profiles calculated by the simple close-formed solution to those calculated by a finite difference program. The inconsistency is caused by the use of simplified diffusion coefficient and mathematically incompatible surface chloride models. To avoid the inconsistency, a chloride transport model is developed in this study. In developing the model, regression analysis to fit coefficients of the developed model is compared to the regression analysis results obtained from the experiment of the researchers. In the experiment of the researchers, the effect of water to binder ratio and the amount of fly ash replacement in concrete is considered. Furthermore, the chloride transport calculated from the developed model is validated by comparing to other experimental results. Finally, the sensitivity analysis of the model coefficients and some remarks on the developed model are presented.