Development of Foam Concrete toward High Strength and CO₂ Sequestration

Excessive CO2 emissions present major environmental challenges. This study developed carbonation-enhanced high-strength foam concrete (HSFC) to maximize the CO2 sequestration and utilization. HSFC was produced by incorporating a fine and stable foam into a designed dense paste matrix, followed by carbonation enhancement. Micro and macro tests revealed that HSFC achieved a notable CO2 uptake capacity of up to 12.6 wt % (∼90 kg of CO2 per m3 of concrete). In the low water-to-binder (W/B) ratio system, carbonation curing consumed calcium hydroxide, calcium silicate hydrate (CSH) gel, and unhydrated cement, producing substantial amounts of calcium carbonates (CCs) in three forms: amorphous, calcite (predominant), and aragonite (at higher carbonation levels). Notably, the carbonation process slightly increased the matrix microhardness by filling micropores and reducing porosity by 19.8%. The generation of CCs on foam pore walls refined the pore size, further enhancing HSFC compressive strength to nearly double that of conventional foam concrete at a similar density. Carbonation curing also improved durability, reducing water absorption and increasing electrical resistance. Finally, strategies for fabricating high-performance HSFC with significant environmental benefits were proposed, contributing to sustainable construction practices.