The ITZ microstructure, thickness and porosity in blended cementitious composite: Effects of curing age, water to binder ratio and aggregate content

Due to its higher porosity, the interfacial transition zone (ITZ) in cementitious composite is often considered as a weak phase, compared to aggregate and bulk paste. In this paper, we present some results of a study on the ITZ including microstructure, thickness and porosity for the case of a ternary blended cementitious system, i.e., Portland cement, blast furnace slag and limestone filler. In particular, based on the backscattered electron image analysis and the HYMOSTRUC model, the ITZ microstructure, thickness and porosity are investigated in an elaborative way. The effects of casting factors such as curing age, water to binder (w/b) ratio and aggregate content are discussed, and two new formulas are proposed to fit the ITZ thickness and porosity. Results indicate that curing age influences both the ITZ thickness and porosity, while w/b ratio and aggregate content only influence the ITZ porosity.