Prediction of chloride diffusion coefficients using multi-phase models

Chloride-induced reinforcing steel corrosion is a worldwide problem. In order to design durable concrete structures, one has to understand the diffusion mechanism of chlorides in concrete. Unfortunately, most of the experimental data obtained from laboratory studies are for chloride diffusion in cement paste. Thus, it is important to discuss and examine the difference between chloride diffusion in cement paste and in concrete. This paper presents a theoretical study on chloride diffusion in concrete. By treating the concrete as a composite consisting of aggregates, interfacial transition zones and cement paste, a combined series and parallel multi-phase transport model was developed. The model explains how the shape of aggregates affects the chloride diffusion in concrete. Using the model, the effects of aggregates and corresponding interfacial transition zones on chloride diffusion in concrete and mortar were examined. Comparisons of the model with other models published in the literature and with experimental and numerical data are also provided.