Determination of the chloride migration coefficient for interfacial transition zone in cement-based material with fly ash replacement

Because the properties of the interfacial transition zone (ITZ) are difficult to quantify, this study provides a method for measuring the chloride penetration depth of the ITZ and calculating the migration coefficient (the diffusivity of chlorides under an electric field) of the ITZ. To obtain a continuous ITZ, a mortar specimen was added with a rod-shaped aggregate (phi 19mm x 50 mm). The migration coefficient of the mortar specimen with fly ash replacement was determined through the rapid chloride migration test. The results indicated that the migration coefficient of the ITZ was 1.627-2.651 times that of the matrix for specimens with various water-to binder (w/b) ratios. Adding fly ash improved the ITZ; the degree of improvement of ITZ was up to the 2.5 times that of the matrix. On the basis of the relationship between the migration coefficient and w/b ratio, the w/b ratios of the matrix and ITZ were determined.