Effect of early CO₂ curing on the chloride induced steel bars corrosion in cement mortars

Abstract

Early CO₂ curing acting as a new curing technique is an effective way to cut down on carbon footprint in cement industry. It also improves the strength development and long-term durability of concrete without reinforcement. Given the fact that reinforcement concrete is most widely used in construction and building fields, the carbon sequestration potential will be enhanced remarkably if this curing technology can be used in reinforced concrete. However, the impacts of early CO₂ curing on the corrosion behavior of steels, which is the major concern for reinforced concrete exposure to chloride, is unclear yet. In this work, the permeability of chloride, threshold chloride value and corrosion behaviors of steels in cement mortar were determined to comprehensively study the effect of early CO₂ curing on the chloride induced corrosion of steels. Early CO₂ curing lowers the chloride ions permeability of mortars, in particular for the mortars with 28 day curing ages. Steels take longer time to form stable passive films in early CO₂-cured mortar than in conventional moist-cured ones. Early CO₂ curing reduces the chloride threshold concentration of mortar, in particular for the mortars that the whole cross section is carbonated, the reduction reaches ∼50%. However, it exerts few effects on corrosion induction phase of steel rebar. Moreover, early CO₂ curing decreases the corrosion rate of steel bars in corrosion propagation phase and thus the overall corrosion rate of steels during the whole testing process due to slower chloride ingress rate. Thus, early CO₂ curing can act as an alternative curing technique in the production of pre-cast reinforced concrete exposed to chloride.

Keywords:

• Early CO₂ curing
• chloride transport
• reinforcement corrosion
• threshold chloride value
• passive film

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors appreciate the financial support of Natural Science Foundation of China (Project Nos. 50978093 and 52078204), Natural Science Foundation of Hunan Province (No. 2024JJ5333) and Outstanding Youth Project of Department of Education of Hunan Province (No. 22B0443).