Wet-grinding carbonation of concrete slurry waste under low-concentration CO₂ for preparing low-carbon foam concrete

Mineral carbonation of industrial by-products is a promising strategy for carbon capture and storage, contributing to carbon emission reduction in the construction industry. Previous studies have mainly focused on carbonation under high CO₂ concentration above 99% to maximize carbon storage, whereas efficient carbonation under low CO₂ concentration is more meaningful for practical engineering applications. In this study, high-moisture concrete slurry waste (CSW) was carbonated by wet-grinding carbonation under 25% CO₂ concentration. The changes in CSW properties were characterized by pH, conductivity, XRD, TG, and SEM-EDS. Moreover, carbonated CSW with different carbonation degrees was incorporated into foam concrete to evaluate its effects on compressive strength, hydration behavior, hydration products, and microstructure. The results showed that the CO₂ uptake and carbonation degree reached 21.0% and 57.2%, respectively, after 60 min of carbonation. Incorporating 10% and 20% CSW carbonated for 15 min significantly accelerated early hydration kinetics, and the 1-day compressive strength increased by more than two times compared with samples containing uncarbonated CSW. This enhancement was attributed to the heterogeneous nucleation effect of ultrafine CaCO₃ and the pozzolanic reactivity of silica gel, although later-age strength decreased. In contrast, deeper carbonation reduced CSW reactivity and weakened foam concrete strength. Furthermore, carbonated CSW reduced CO₂ emissions by 32.5%, demonstrating its environmental benefits and potential for sustainable foam concrete production.