Abstract <p>This study investigates the impact of a CO₂-rich environment on the aluminosilicate gel in alkali-activated fly ash (AAAFA) using NMR spectroscopy. After 24 h of curing at 80°C, the AAAFA samples were exposed to a 10% ambient CO₂ concentration. Highly reactive elements such as Na and Al fully reacted within the initial hours and remained unaffected by carbonation under high CO₂ levels. However, Si, which reacts more slowly, exhibited distinct behaviour. Monomeric silicates rapidly polymerized despite the carbonated sample showing a lower overall reaction extent. This indicates the formation of a binding gel phase due to intense CO₂ exposure, leading to an increased gel content in the carbonated sample. These findings enhance the understanding of aluminosilicate gel chemistry and behavior under elevated CO₂ concentrations, providing insights into the long-term performance of alkali-activated materials in carbon-rich environments.</p>