Effect of initial curing on carbonation of lightweight concrete masonry units

The effect of initial curing on carbonation curing of lightweight concrete masonry units (CMUs) was examined. Initial curing was performed from 4 to 18 hours at a relative humidity (RH) of 50% and temperature of 25°C (77°F). Based on cement content, 4-hour carbonation curing allowed concretes to uptake 22 to 24% CO₂ with initial curing and 8.5% without initial curing, while prolonged 4-day carbonation recorded an uptake of 35%. Carbonated CMUs exhibited higher early strength but lower 28-day strength due to water loss by initial curing in comparison to hydrated and steam-cured references. A water-spray mechanism was thus devised to compensate the water loss and, ultimately, made the late strength of carbonated CMUs comparable to references. Carbonation curing can replace steam in CMU production to accelerate hydration, improve durability, and recycle cement kiln CO₂ in a beneficial manner.