Lattice Boltzmann modelling of ionic diffusivity in non-saturated limestone blended cement paste

The accurate prediction of ionic diffusivity in non-saturated limestone blended cement paste is essential for the durability design of blended cementitious materials. This paper presents an integrated framework for simulating the ionic diffusivity in limestone blended cement paste considering its 3D microstructure, water saturation level, and distribution of water and gas phases in the pore network. The 3D microstructure of hydrating blended cement paste with various limestone powder (LP) contents and water-to-binder (w/b) ratios was simulated using the voxel-based CEMHYD3D model, based on which a lattice Boltzmann model with in-house codes was employed to simulate the solid-fluid interaction and ionic diffusivity in cement paste. Results indicate that the relative ionic diffusivity in blended cement paste is strongly dependent on the water saturation level, the evolution of which consists of the sharp drop, slow decrease, slight decrease and depercolation periods. For blended cement paste with 10% LP and w/b ratio of 0.5 at 28 d, the change in decrease rate occurs at the critical water saturation levels of 69%, 34% and 7%, respectively. With the increase of w/b ratio and LP content, the relative ionic diffusivity decreases due to the increasing volume fraction and connectivity of capillary pores. However, the relative ionic diffusivity at degrees of saturation above 70% only undergoes a slight decrease from 0.24 to 0.17 with the increasing LP content from 0% to 20%, which can be ascribed to the low reactivity of LP that cannot much modify the pore structure.