Abstract: Microstructure phase features in interfacial transition zone of concrete are important for concrete's macroscopic properties. Methods of representing CH crystal, pore and C-S-H gel and evolution law are always research hotspots. In this article, we summarized the representation methods for the main phases in interfacial transition zone of concrete and their advantages and disadvantages.We also recommend to employ SAXS in association with MIP method for studying the pore structure at microscopic and mesoscopic scales for the interface, XRD method for the orientation of CH in the interface region,FTIR for qualitative analysis on interface C-S-H gel and NMR for quantitative analysis on interface C-S-H gel. Results show that decreasing of water to binder ratio, increasing of curing age, blending of active admixture, good permeability and large size of aggregate all lead to the decreasing of porosity and CH orientation index in the interface. Moreover, the content of interface C-S-H gel increases with the growth of curing age and the blending of active admixtures.

Key words: interfacial transition zone, microstructure, pore, CH crystal, C-S-H gel