The effect of carbonation on chloride redistribution and corrosion of steel reinforcement

Desalinated sea sand concrete (DSSC) is increasingly used to mitigate the shortage of natural river sand. However, one major concern lies in the corrosion risks of steel reinforcement embedded in DSSC under combined chloride and carbon dioxide attacks. To understand the corrosion mechanism, the corrosion process of steel reinforcement embedded in the cement paste containing chloride ions (Cl⁻) was monitored by electrochemical measurements, during which pH, Cl⁻ profile and corrosion products were examined simultaneously. Raman spectroscopy was employed to evaluate the carbonation depth in microscale. Tests results showed that corrosion was initiated before the carbonation front reached the steel reinforcement. Interestingly, it was the carbonation-induced Cl⁻ redistribution rather than the decrease of pH that dominated the corrosion initiation. Before the carbonation front, a Cl⁻ accumulation zone was identified, and the corrosion mechanism was revealed. This study shall advance the understanding of the corrosion of steel reinforcement in DSSC for durability design of reinforced concrete structures.