Influence of the C-S-H amount on [Cl-]/[OH-] ratio of simulated concrete SPS and the corrosion susceptibility of steel

Abstract

Two kinds of simulated concrete pore solutions (SPSs) were treated with different amounts of synthetic calcium silicate hydrate (C-S-H). The variation of the [Cl-]/[OH-] ratio in SPS was measured and the corrosion susceptibility of carbon steel in the SPS was investigated with potentiodynamic polarization, EIS and weight lose tests. The experimental results showed that for the SPS at pH 12.5, as the amount of C-S-H increases, the [Cl-]/[OH-] ratio increases thereby causing an increase in the corrosion susceptibility of the steel. While for the SPS at pH 9.7, with increasing C-S-H amount, the drop amplitudes of both [Cl-]/[OH-] ratio and steel corrosion rate first decrease and then increase, and a 3% C-S-H addition shows the best inhibition effect. XPS results demonstrate that after C-S-H treating in pH 12.5 SPS the [Fe3+]/[Fe2+] ratio in the film on steel surface is reduced while in pH 9.7 SPS the [Fe3+]/[Fe2+] ratio is increased. The different effects of the C-S-H amount on the two SPSs and the steel corrosion behavior result from the influences of C-S-H on the SPS pH, which is related to the composition of the SPS.