Weathering Carbonation Behavior of Concrete Subject to Early-Age Carbonation Curing

Early-age carbonation for concrete curing has gained increasing attention due to the remarkably enhanced material performance and substantial CO2 storage capability. However, carbonation curing leads to reductions in concrete pH and may weaken concrete's ability to resist weathering carbonation-induced corrosion during service. This study examines the atmospheric weathering carbonation behavior of portland cement-based concretes after carbonation curing. Two types of concrete mixtures representing normal and high-strength concretes were cured with carbonation at two different durations of high-pressure CO2 exposure. Compressive strength and water absorption of concrete were measured upon the completion of carbonation curing and the 28-day subsequent moisture curing. An accelerated weathering carbonation test (AWCT) was consecutively performed for 12 weeks, and concrete carbonation depth, pH distribution, and compressive strength were measured. It was found that the coefficients of CO2 diffusion due to weathering carbonation were significantly reduced in concrete subject to carbonation curing. The ultimate carbonation depth was attributed to both carbonation curing and weathering carbonation. The normal strength concrete with a higher water-to-cement (w/c) ratio showed a larger ultimate carbonation depth because of the more intensive carbonation curing but was found to substantially slow down the rate of weathering carbonation. With sufficient rebar depth, reinforced concretes made with this mix design could potentially develop a more robust resistance to weathering carbonation-induced corrosion through carbonation curing. With a lower w/c ratio, high-strength concrete cured by carbonation appeared less vulnerable to weathering carbonation due to the lower intensity of carbonation curing and hence proved to be viable for this curing approach. On exposure to 12-week AWCT, concrete made with 0.4w/c ratio exhibited comparable carbonation depths and pH profiles regardless of curing methods. It is inferred that carbonation curing could potentially be applied to normal-strength reinforced concretes with large rebar depths or general high-strength concrete formulations without accentuating the risk of carbonation-induced corrosion.