The impact of forced early-age carbonation on the hydration of cementitious materials

CO2 curing has emerged as a promising method for carbon sequestration in cementitious materials. However, the complex interactions during CO2 curing and the impact on the maturation pathways of cement during hydration remain a significant research gap. This paper introduces significant innovations in the study of CO2 curing cement using (bi)-carbonate additives in both OPC and C3S systems to address a critical challenge in measuring the heat release during CO2 curing due to instrumental limitations-specifically, the difficulty of simultaneously introducing CO2 gas into the system and measuring the reaction heat in real-time. The findings reveal that earlystage addition of HCO3- /CO32- leads to varied calcium carbonate polymorphs and a distinctive C-S-H/CaCO3 composite with a clustered morphology. This configuration offers additional sites for further hydration/ carbonation, leading to a more complete and rapid development of the products. Moreover, the research utilizes in-situ TGA to uncover a novel three-phase competitive reaction process-comprising induction, acceleration, and deceleration phases-between hydration and carbonation, with the availability of Ca2+ ions being a critical factor. Finally, the study also reveals a preferential formation of Type II and III carbonates, offering insights into optimizing CO2 curing for improved cementitious material performance. This dynamic perspective provides new insights into the interplay between these two processes, offering a more comprehensive understanding of the effects of forced early-age carbonation on cement hydration.