Influence of humidity conditions on the performance of CO2-cured LC3

In the pursuit of low-carbon cement technologies, both limestone calcined clay cement (LC 3 ) and CO₂ curing have shown great promise for reducing emissions in the construction industry. This study investigates the synergistic effects of CO₂ curing and ambient humidity on the mechanical performance and microstructure of LC 3 . Cylindrical LC 3 specimens were prepared using a low water-to-binder ratio and compaction molding, followed by 3-hour CO₂ curing under different relative humidity conditions (50 %, 70 %, and 95 %) and subsequent conventional curing. The results reveal that CO₂ curing significantly enhances the strength and densification of LC 3 . At an optimal cement replacement level of 30 %, compressive strength at 28 days increased by up to 18.8 % under high-humidity carbonation (95 %) compared to non-carbonated reference samples. At 90 days, the strength reached 87.3 MPa. High humidity during carbonation facilitated the formation of calcium carbonate and C-S-H gels, leading to a denser microstructure with reduced porosity and crack formation. These findings demonstrate that combining LC 3 with humidity-optimized CO₂ curing offers a robust pathway toward high-performance, low-carbon cementitious materials, with clear implications for sustainable construction practices.