Early age carbonation curing for precast reinforced concretes

• Early age carbonation curing is developed for precast reinforced concrete.
• Carbonation curing forms carbonate-rich surface with higher electric resistivity.
• Carbonated concrete (pH > 12) is not more vulnerable to weathering carbonation.
• The process has shown environmental, technical and economical benefits.

Carbonation is considered detrimental to reinforced concrete. However if carbonation is performed at early age through curing, the process could be beneficial. This paper is to present a study on a unique process that is developed for early age carbonation curing of precast reinforced concrete to maximize the performance improvement and the carbon storage capacity. The process includes vibration casting, in-mold curing, off-mold preconditioning, carbonation curing and subsequent hydration. It was found that a carbon uptake of 16% based on the cement content could reduce concrete pH to 9.2 on the surface and maintain pH of 13.0 at core immediately after 12 h carbonation. The subsequent hydration was able to increase the pH on surface over 12.3 which was comparable to hydration reference. The carbonated concrete had shown more resistance to permeation by having a higher electrical resistivity on surface and was not more vulnerable to weathering carbonation. The off-mold preconditioning in open air caused no shrinkage cracking because of the controlled evaporation rate. The process makes concrete a sandwich structure with carbonate-rich surface which is responsible for strength gain, carbon storage and durability enhancement and is suitable for precast reinforced concrete production.