Prediction of the Effective Diffusion Coefficient of Chloride Ions in Cement-Based Composite Materials

A multiscale model is established for effective diffusion coefficient of chloride ions in cement-based composite materials. The model takes into account the relationship between the diffusivity and microstructure of cement-based materials, where the microstructure includes the interfacial transition zone (ITZ) between the aggregate particles and the bulk cement pastes, and the microstructure of the bulk cement paste itself. In addition, the model also includes the parameters such as water-to-cement ratio, hydration degree of cement, the thickness of ITZ, the volume fraction, and gradation of aggregate. A model for predicting the porosity distribution in ITZ is proposed based on the cement-particle distribution and modified Powers model, and then effective chloride diffusivities of ITZ can be estimated. Thus, the effective diffusion coefficient is predicted by n-layered inclusion theory in which mortar and concrete is considered as four-phase materials consisting of matrix phase, aggregate, ITZ, and their homogenization phase at a mesoscopic level. To validate the proposed model, the diffusion coefficient of chloride ions by the steady-state migration test is measured on a series of mortar and concrete and compared with the calculated data. The results show that the model prediction agrees quite well with the available test results. DOI: 10.1061/(ASCE)MT.1943-5533.0000477. (C) 2012 American Society of Civil Engineers.