A new model for investigating the formation of interfacial transition zone in cement-based materials

The interfacial transition zone (ITZ), located between aggregate and cement paste, has the features of high porosity, low unhydrated cement content, and enrichment of calcium hydroxide crystals (CH) and is often regarded as the weak link in cement-based materials. The present study is devoted to investigating the influence of multiple mechanisms or factors on ITZ formation, including the wall effect, ion transport, and aggregate features. A new modelling system is proposed to assess the interactions between these mechanisms or factors. The time-spatial distribution of hydration products and pores is studied by considering the reaction-diffusion-crystallization process of a non-uniformly distributed cement. Based on the developed model, the effects of individual mechanisms and their interactions on ITZ formation were clarified. The results indicated that the wall effect would determine the spatial distribution of cement and most hydration products due to the repulsion of aggregates on cement particles. The ion transport would influence the time evolution and redistribution of hydration products, which couples with the role of the wall effect. It was also found that aggregate features, including spacing and surface roughness, can affect the distribution of cement and the heterogeneity of cement-based materials, which works synergistically with the wall effect.