Effect of Interfacial Transition Zone on the Carbonation of Cement-Based Materials

This study dealt with an analysis of the effects of the interfacial transition zone (ITZ) on the carbonation of cement-based material. To this end, a series of experiments dealing with paste and the mortar-gallet interface carbonation were designed and conducted. Experimental results showed that the carbonation depth in the ITZ was several times greater than that in the cement matrix resulting in the emergence of an interfacial effect zone (IEZ). Backscattered electron (BSE) analysis and nanoindentation tests were also conducted on the material to examine the microstructure of the ITZ before and after carbonation and to explore the mechanisms of the ITZ effects. After carbonation, the thickness of the ITZ decreased from 50–60 μm to 20–30 μm, but its porosity was still greater than the porosity of the cement matrix. Therefore, after carbonation, the ITZ was still a weak zone so that the diffusion rate of CO2 in the ITZ was higher than in the cement matrix.