Multiscale numerical-analytical modelling of oxygen diffusivity in partially saturated concrete: Role of interfacial transition zone

This study presents a multiscale model to simulate oxygen diffusivity in partially saturated concrete accounting for multiscale nature of concrete and water-gas distribution in its pore structure. At microscale, 3 D microstructure of cement paste ITZ is simulated, based on which the water-gas equilibrium distribution in capillary pore structure and oxygen diffusivity at different degrees of water saturation (DWSs) are mimicked using lattice Boltzmann models. Afterwards, a (n + 1)-phase model based on effective media theory is used to predict oxygen diffusivity in non-saturated concrete at mesoscale. Results indicate that the evolution of oxygen diffusivity with the increasing DWS follows an initial drop, a plateau, a slight decrease and a sharp decrease, which correspond to the decreasing gas-filled gel pores, depercolation of gas-filled gel pores, and decreasing gas-filled capillary pores until their depercolation. The role of ITZ in oxygen diffusion in non-saturated concrete becomes more remarkable with the increasing DWS.