Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model

The knowledge of the relationship between porosity and transport properties of concrete is a point of major importance to run properly the models coupling chemistry, transport and mechanics in order to simulate the engineered barrier degradations in the context of the nuclear waste deep repository. The present work proposes a simplified composite model aiming at linking microstructure and effective diffusivity of cement pastes. The proposed analytical method allows the estimation of the evolution of effective diffusivity of such materials submitted to porosity opening or plugging, at the scale of the Representative Elementary Volume (REV). The method is then applied to Ordinary Portland Cement (OPC) pastes. The porosity–diffusion evolutions determined from the composite model for various OPC pastes are implemented into simplified chemo-transport simulations aiming at describing the leaching of cementitious materials. Using these evolutions, OPC paste leaching simulations are in good agreement with the available experimental data, indicating a good reliability of the simplified composite model.