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

CO 2 curing has emerged as a promising method for carbon sequestration in cementitious materials. However, the complex interactions during CO 2 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 CO 2 curing cement using (bi)-carbonate additives in both OPC and C 3 S systems to address a critical challenge in measuring the heat release during CO 2 curing due to instrumental limitations—specifically, the difficulty of simultaneously introducing CO 2 gas into the system and measuring the reaction heat in real-time. The findings reveal that early-stage addition of HCO 3 - /CO 3 2- leads to varied calcium carbonate polymorphs and a distinctive C-S-H/CaCO 3 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 Ca 2+ ions being a critical factor. Finally, the study also reveals a preferential formation of Type II and III carbonates, offering insights into optimizing CO 2 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. • Forced early-age carbonation was applied to both OPC and C 3 S systems. • Early-stage addition of HCO 3 - /CO 3 2- led to a distinctive C-S-H/CaCO 3 composite. • A three-phase competitive carbonation and hydration process was highlighted. • A preferential formation of Type II and III carbonates was noted in the study.