Impact of glass aggregate particle size on CO2 curing effectiveness in suppressing alkali-silica reaction

The extensive application of glass aggregate (GA) in cementitious materials is limited due to the potential alkali-silica reaction (ASR). Although CO₂ curing has been demonstrated as an effective approach to mitigate ASR expansion, the potential pozzolanic reaction in smaller aggregates may change the effectiveness of CO₂ curing due to their competition with carbonation for portlandite and the change of microstructures. This study investigates the ASR expansion, compressive strength, and microstructure of mortars containing GA with different particle sizes (0.6–1.18 mm, 1.18–2.36 mm, 2.36–4.75 mm, and 0.15–4.75 mm) following CO₂ curing. Results showed that 3-day CO₂ curing suppressed 14-day ASR expansion of all mortars to below 0.01 %, indicating that the effectiveness of CO₂ curing was independent of GA particle size. However, microstructural analysis revealed that mortars with GA particles smaller than 1.18 mm exhibited enhanced formation of ASR gel with higher Ca/Si ratios due to the increased amount of surface sites for reaction. Meanwhile, a transfer of the ASR gel, which had formed in the cracks inside the GA, to the GA surface under CO₂ curing was observed. Furthermore, ASR gel formed on GA surface showed different characteristics from that formed inside GA cracks, as it not only prevented crack propagation but also improved mechanical properties by enhancing the interfacial transition zone.