Microstructure-based modelling of chloride diffusivity in non-saturated cement paste accounting for capillary and gel pores

Abstract

Accurate prediction of chloride diffusivity in non-saturated cement paste is crucial for durability design of concrete. This paper presents an integrated framework for modelling chloride diffusivity in non-saturated cement paste considering 3D microstructure, water-gas distribution in pore network and electrical double layer effect. Results indicate that the chloride diffusivity in C-S-H pore solution is dominantly influenced by surface electric potential regardless of water saturation level, porosity of C-S-H and chloride concentration of bulk solution. With the decrease of water saturation level, the relative chloride diffusivity in cement paste experiences sharp, slow and slight decrease stages, followed by a non-diffusive stage, corresponding to connected capillary water, combination of capillary water and saturated C-S-H network and non-saturated C-S-H network as the main diffusion channel, and pore depercolation. The relative chloride diffusivity in cement paste at a given water content decreases with increasing water-to-cement ratio. The simulation results show good agreement with experimental data.