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.