Transforming recycled construction waste fines into carbon sink material via accelerated mechanochemical carbonation: A novel approach to CO2 sequestration

The increasing demand for sustainability in construction has driven research into alternative CO 2 sequestration and mineral utilization strategies. The present study investigates the innovative solvent-free mechanochemical carbonation (MCC) of various recycled construction waste fines, including construction and demolition waste (CDW), concrete waste (CW), and excavation waste (EW), to enhance carbonation efficiency and CO 2 sequestration. The effect of MCC time on direct mineral carbonation was systematically assessed, and its performance was evaluated based on the calcium carbonate (CC) content. MCC activation reduced crystallite size and promoted depolymerization of the silica chain structure of CDW, CW, and EW, enhancing its carbonation reactivity. Fourier-transform infrared spectroscopy (FTIR) analysis detected significant shifts in peaks corresponding to carbonate and silicate groups, confirming the chemical transformations associated with carbonation. The thermogravimetric analysis (TGA) results indicated the formation of calcite, with maximum CO 2 uptake occurring within one hour of MCC. Prolonged MCC (2h and 4 h) resulted in the formation of metastable and amorphous calcium carbonates. Results indicated that MCC effectively enhances the carbonation of EW, demonstrating the highest carbonation degree of 87.96% after one hour of milling. The carbonation degree of CDW and CW reached 40.11% and 21.47%, respectively, within the same duration. The CO 2 uptake was 12.55 wt% for 1 h MCC-treated EW, highlighting the potential of the MCC to achieve rapid and efficient carbonation. The performance surpassed the results of conventional wet carbonation, which typically requires around 3 hours to achieve a similar outcome. • Carbonation of recycled construction waste fines by the mechanochemical method. • Mechanochemical activation improves the carbonation capacity of excavation waste. • Sequestered CO 2 (12.55 wt%, 87.96 %) with excavation waste. • Correlated carbonation efficiency with the duration of mechanochemical process. • CO 2 uptake by construction waste can offset the carbon footprint.