To address the global challenges of waste valorization and climate change mitigation, alkali-activated slag (AAS) is used as a sustainable alternative binder to produce low-carbon concrete. However, the low hydraulic reactivity and slow early-age strength development of AAS limit its practical use in marine civil engineering. This research examined the impact of synergy between carbonation curing and marine exposure on the mechanical properties and durability of AAS pastes. The findings indicated a synergistic enhancement and resistance to chloride-ion erosion in carbonated AAS pastes, with a 24-hour carbonated specimen achieving a strength of 42 MPa compared to the 6-hour specimen (12.7 MPa) after 28 days of corrosion. This was attributed to the combined effects of carbonation and chloride-ion penetration, which not only reduced porosity, free chloride ions, and pH but also refined the pore structure. The reduced porosity facilitated the progressive development of calcite in the paste matrix, thereby encapsulating non-carbonated particles within the densified matrix, enhancing the stability of CS-H gels and promoting the formation of Friedel's salt. Overall, carbonated AAS pastes exhibited stable CO2 sequestration capacity, remarkable stability, and corrosion resistance in marine environments, indicating that they are well-suited for marine civil engineering applications.
