Sensor-based time-dependent formation factor in prediction of chloride ingress in mortar

Characterisation of chloride ingress rate is crucial for service life predictions in reinforced concrete. In this study, the time-dependent chloride diffusion coefficient (D-Cl(t)) was determined using real-time non-destructive embedded sensors. First, the time-dependent formation factor was established based on continuous electrical conductivity data from the sensors, which provided D-Cl(t) by the Nernst-Einstein equation. Twelve mortar mixtures were included that varied in water/cementitious materials ratio (w/c) and supplementary cementitious material (SCM) content. A numerical model of chloride diffusion using the established D-Cl(t) was developed by solving Fick's second law of diffusion using the finite-difference method. The model's predictions agreed well with experimental chloride profiles available in the literature. The results of chloride ingress simulation for all tested mixtures clearly showed the effect of reducing the w/c and using more SCM on slowing the rate of chloride ingress. Furthermore, the developed D-Cl(t) relations were used to establish a diffusion decay coefficient (m(diff)) for all tested mixtures, leading to the development of empirical formulations for D-Cl(t) and m(diff) as a function of w/c and SCM content. The results of this study demonstrate the potential of the implemented non-destructive technique in efficient assessment of transport properties of mortar related to chloride ingress.