MODELLING OF CHLORIDE TRANSPORT IN CONCRETE

Abstract

Chloride-induced corrosion of reinforcing steel has been recognized as the primary factor in degrading the durability of reinforced concrete structures exposed to chloride-rich environments. This research aims to investigate the underlying mechanisms of ionic transport behaviors in both natural and recycled aggregate concrete and to develop accurate and reliable prediction models to estimate the chloride transport processes during diffusion and migration tests. Based on the understanding of ionic diffusion, electromigration, polarization, and physicochemical reactions, several numerical and analytical models for chloride penetration in heterogenous concrete are proposed. Firstly, Poisson, Laplace, and current conservation models are developed based on Gauss’s law and current conservation law to investigate the interaction of different ionic species in concrete. The differences and application scope of the three models are discussed based on the obtained numerical results. A five-phase numerical model and a two-step analytical model are proposed to characterize the heterogeneous properties of concrete with both natural and recycled aggregates and to investigate the influence of each phase on concrete resistance to chloride ingress. Polarization-induced potential drop between outside electrodes and concrete surfaces during migration tests and its influences on inner ionic transport are investigated using a multi-species and overpotential model. A sequential non-iterative algorithm (SNIA) is introduced to connect the outside polarization and inner ionic transport. Physical and chemical reactions between free ions in pore solution and cement hydrates and their influences on chloride penetration are investigated by using a reactive mass transport model and a non-equilibrium binding model. This thesis has contributed to an improved understanding of the mechanisms of chloride penetration in heterogeneous concrete and provided recommendations for modelling the durability performance of concrete structures in terms of chlorides attack.