Carbonation Curing of Concretes in a Flexible Enclosure under Ambient Pressure

Abstract

Early-age carbonation curing of concrete is considered an alternative curing method that efficiently utilizes carbon dioxide to improve the performance of concrete and reduce carbon emission. Carbonation curing is commonly implemented in a pressure chamber at high pressure. The application is therefore limited only to special products such as concrete masonry units. To promote wider applications of the technology for general precast concrete with any shapes and sizes, an ambient pressure carbonation system in a flexible enclosure is needed. This paper presents a study on developing a new carbonation curing system at a curing pressure of 1.4 kPa (0.014 bar), which is considered as ambient pressure. The system includes a flexible enclosure made from a plastic sheet with a pressure-resistant zipper that can accommodate any shape and size of precast concrete products and can be made either in a factory or on a job site. Compared to the traditional high-pressure carbonation at 0.5 MPa (5 bars), which generates 12% CO2 uptake, carbonation in the ambient-pressure system at 1.4 kPa (0.014 bar), can achieve a carbon dioxide uptake of 11% with a comparable strength at both the early and late ages. Besides, the ambient pressure carbonation has shown less pH reduction and smaller carbonation depth than high pressure, which would have the advantage of protecting the reinforcing steel in concrete from carbonation-induced corrosion. Furthermore, ambient pressure carbonation-cured concretes were found to have higher compressive strength, higher surface electrical resistivity, lower porosity, and faster ultrasonic pulse velocity than normal hydration concretes at both the early and late hydration stage. Microstructure analysis indicated that carbonates were intermingled with C─ S─ H, contributing to the strength gain and performance improvement of concretes subject to ambient pressure carbonation curing.