Abstract
Chloride induced steel corrosion is the greatest problem for the durability of reinforced concrete structures exposed to marine environment. A cause of chloride induced steel corrosion is fundamentally due to diffusion of chloride ion into concrete, which is greatly affected by the alkali ions in the pores. When alkali ion concentration increased in the pore, Si in C-S-H was substituted by Al. So-called C-A-S-H is produced by Al substitution. However the prediction model of diffusion of chloride ion is not still established when the alkali concentration is varied. Therefore, experiments were carried out using specimens with different alkali contents. It was confirmed experimentally that the alkali ions influenced the diffusion of chloride ion and then enhanced our previous model integrated with phase equilibrium model, surface complex model and multi-component diffusion model considering that C-A-S-H changed adsorption ability of chloride and also varied the equilibrium constant in surface complexation reaction. Moreover, it was considered that the C-A-S-H formation influenced tortuosity of diffusion of chloride ions because slag cement paste included C-A-S-H had different tortuosity from OPC paste constituted of C-S-H. Refined model with modifying equilibrium constant in surface complexation reaction and tortuosity could predict preciously the experimental data. Therefore it is concluded that diffusion of chloride into hardened cement paste was influenced by C-A-S-H. This required the more detailed study on the effect of Al substation for Si in C-S-H on the diffusion of chloride to accurately predict the chloride ingress into concrete.
