Modeling of Effective Diffusion Coefficient of Substances in Concrete Considering Spatial Properties of Composite Materials

Abstract

This research is conducted to develop a model to predict the effective diffusion coefficients of substances (D_e) in concrete considering the spatial properties of composite materials. In this model, concrete is assumed to be composed of cement paste, an interfacial transition zone and aggregate, and the spatial properties of each material are considered with random arrangement of each material. D_e in concrete is calculated based on the calculation results for the cement paste and interfacial transition zone. The proposed model can appropriately evaluate D_e in concrete in previous research. The influence of the spatial properties of each composite material on the dispersion of D_e is analytically investigated. The influence of cement particle arrangement is larger than that of fine and coarse aggregate, and the lower W/C, the greater that influence. Moreover, the influence of the interfacial transition zone on chloride ion diffusivity in concrete is also analyzed. This influence was found to be quite large, so that the interfacial transition zone should be taken into account for simulating diffusion in cementitious materials. In this model, the pore structure of cement paste is very simplified. Thus, it is necessary to examine the correspondence of the modeled pore structure and the actual pore structure.