Exploring the synergistic and competitive mechanisms between early carbonation and pozzolanic reaction in green concrete incorporating GGBS: An optimal value for strength enhancement

Early carbonation is an effective approach to addressing the insufficient early-age strength of concrete blended with ground granulated blast furnace slag (GGBS). However, the synergistic and competitive mechanisms between early carbonation and the pozzolanic reaction of GGBS have not yet been fully elucidated. To this end, this study systematically investigated the effect of early carbonation curing on the strength development of concrete with different GGBS replacement ratios. The results showed that the 30% GGBS replacement ratio with early carbonation (Group G-30–2) exhibited a remarkable comprehensive advantage over the plain concrete group (Group G-0–1). Specifically, its 1-day and 90-day compressive strengths were 199.73% and 14.61% higher, respectively. Within this range, the CaCO₃ generated by early carbonation not only rapidly fills pores but also acts as stable nucleation sites for hydration products, thus ensuring the continuous progression of cement hydration and the GGBS pozzolanic reaction. The resulting C-S-H and C-A-S-H gels work synergistically with CaCO₃ to densify the matrix pore structure, thereby maintaining a high late-age strength. Conversely, excessively high GGBS replacement ratios (≥45%) exacerbate the alteration of the chemical environment induced by early carbonation, destabilizing the hydration products and GGBS, resulting in a coarsened pore structure. Furthermore, the net carbon emission of Group G-30–2 was reduced by 41% compared to that of Group G-0–1, while its unit strength cost was reduced by 15.8%. These findings provide a critical scientific basis and practical strategy for the design of cost-effective, low-carbon, high-performance GGBS-blended concrete. © 2026 Elsevier Ltd.