In order to assess the durability of concrete structures, it is essential to investigate the ionic diffusivity under unsaturated conditions. Simulation of the ioinc diffusivity in unsaturated cement-based materials is big challenge due to the complicated microstructures and the difficulties in modelling of multi-phase fluid flow in cement-based materials. In this study, the 3D microstructure of cement paste is obtained from X-ray μCT with a high resolution. In the simulation, the Shan-Chen multi-phase lattice Boltzmann model is modified to simulate the equilibrium distribution of water and gas in the obtained 3D microstructure at various degree of water saturation. A lattice Boltzmann diffusion model is applied to simulate the ionic diffusion and determine the ionic diffusivity based on Fick’s law. It was found that the ionic diffusivity shows a strong dependence on the degree of water saturation. The simulated results fit very well with the experimental data obtained from literature.
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