The American Concrete Institute (ACI) has released a paper which presented a study on chloride-induced corrosion in reinforced concrete subjected to carbonation curing.
ACI says carbonisation curing has demonstrated potential if improving concrete performance while facilitating carbon dioxide utilisation. However, reinforcement corrosion behaviour in carbonation-cured concrete has not been documented.
The paper, carbon dioxide utilization; carbonation curing; concrete durability; corrosion; pore structure, explains that a special carbonisation process was developed for precast non-presented applications.
ACI says: “Performance of carbonation curing was evaluated by concrete compressive strength, pH value, and carbon dioxide uptake, while corrosion resistance of the carbonation-cured concrete was assessed by reinforcing bar mass loss and concrete chloride content.”
To understand the mechanism, concrete and cement paste were further characterised using mercury intrusion porosimetry, absorption, and electrical resistivity tests. Micromorphology was assessed by scanning electron microscopy.
“It was found that apart from rapid early-age strength gain, carbonation curing could significantly reduce chloride permeation in concrete concerning both total and free chloride contents. It was attributed to the reduced pore size and pore volume by calcium carbonate precipitation.”
Through subsequent 28-day hydration, the carbonation-cured concrete displayed a pH over 12.0 at the surface of steel reinforcing bars and a micromorphology similar to the non-carbonated reference.
“The direct corrosion tests showed that the corrosion-induced mass loss of steel reinforcing bar was lessened by 50% in concrete subjected to carbonation curing,” ACI concludes.
This paper was written by Duo Zhang and Yixin Shao.
