Performance enhancement of alkali-activated slag via in situ CO2 mineralization

Alkali-activated slag (AAS) binders activated solely by sodium hydroxide often exhibit poor performance, requiring additional sodium silicate, which increases both cost and environmental impact. To overcome these limitations, in this study, a novel CO 2 -assisted activation (CAA) strategy, integrating CO 2 mineralization with mechanical activation, is proposed to enhance the performance of AAS binders. Reaction kinetic modeling revealed that the slightly lower reaction order observed in the CAA-treated AAS system, reflects a suppression of diffusion-controlled hydration, which in turn prolonged the nucleation-growth stage and enabled a uniform hydration pathway. Structural analysis suggests enhanced silicate polymerization in CAA-treated AAS samples, as evidenced by increased Q 2 (1Al) content, mean chain length, and polymerization degree from 29 Si NMR. These gel-level refinements resulted in a denser and more cohesive matrix, contributing to improved mechanical performance. Specifically, the optimized system exhibited a 68.0 % increase in 1-day compressive strength and a 45.6 % enhancement at 28 days, along with reduced porosity and higher micromechanical stiffness. The synergy between CO 2 and the mechanical activation in CAA process suggests that CO 2 acts as a field-enhancing agent, modifying the physicochemical environment and promoting nucleation processes. Overall, this work demonstrates that CAA offers a dual-function strategy—both chemical and environmental—for designing high-performance, low-carbon AAS systems.