Effect of aggregate on chloride diffusivity of cement-based composite materials

The effect of aggregate on the chloride diffusivity is mainly due to the presence of interfacial transition zone (ITZ). The experiments were carried out at various volume fractions and aggregate sizes. The effect of aggregate on the chloride binding capacity was analyzed by scanning electron microscopy equipped with energy dispersive X-ray detector. The results show that the addition of aggregate can improve the pore structure of cement-based materials and the chloride diffusion process. When the ITZ content increases with the grain size or the aggregates are sufficiently closely-spaced that the adjacent ITZ overlaps in space, the ITZ effect could be dominant among all the effects of the blocking aggregate and the tortuosity of matrix paste. As a result, the fluid and ions transport would be significantly enhanced. In addition, the binding capacity is greater at a high ITZ content.