Utilization of cement–pozzolana–carbide slag binder and carbonation curing in concrete: A step towards carbon-neutrality

Early carbonation curing is an effective approach to mitigate the environmental impacts of concrete. This is particularly valid when coupled with other strategies, such as substituting cement with alternative low-carbon materials. Nevertheless, little attention has been paid to understanding the behavior of ternary blended cementitious concrete subjected to early carbonation curing. The main objective of this research is to assess the carbon storage potential, performance, and microstructure of carbonation-cured concrete incorporating volcanic ash (VA) and carbide slag (CS). The mixture design of experiments was utilized to evaluate and optimize the concrete mix design containing 60%–100% cement, 0%–40% VA, and 0%–40% CS and subjected to three carbonation schemes. The analysis revealed that setting the pre-curing and carbonation for 20 and 4 h, respectively, rendered the highest carbon uptake when incorporating up to 5% VA and up to 40% CS. The optimum 28-day compressive strength was achieved when the pre-curing and carbonation intervals were 4 and 20 h, respectively, with a binder incorporating up to 35% VA with no more than 5% CS. The microstructural analysis of the optimum mixes highlighted advanced calcite formation in mixes designed for maximum carbon uptake and 1-day strength. Meanwhile, the mixes designed for maximum 28-day performance underlined the coexistence of hydration and carbonation reaction products. The findings demonstrated that carbonation curing and the chemical composition of the ternary blended binder system influenced the properties and microstructure of carbonation-cured concrete.