A three-phase model for predicting the effective chloride migration coefficient of ITZ in cement-based materials

Specimens (water/cement ratio of 0.35) with various volume fractions (0, 0.1, 0.2, 0.3, 0.4 and 0.5) of fine aggregates were cast and tested to investigate the behaviour of the interfacial transition zone in mortar and the effect of the interfacial transition zone on the chloride migration coefficient. The double-inclusion method and Mori-Tanaka theory were used to predict the migration coefficient of three-phase composite materials, which are cement paste, interfacial transition zone and fine aggregate. There are two stages to calculate the overall migration coefficient of mortar. The first stage, the equivalent migration coefficient of fine aggregate and the interfacial transition zone, was calculated by Hori and Nemat-Nasser's double-inclusion model. The second stage, the equivalent migration coefficient, was used to calculate the overall migration coefficient of the mortar composite by Mori-Tanaka theory. A comparison was conducted between the theoretical and experimental data in this study. The results indicated that the migration coefficient of the interfacial transition zone is 1.5 to 10 times the migration coefficient of cement paste when an interfacial transition zone thickness of 20 to 30 mu m is assumed.