Developing low-carbon high-strength core-shell aggregates using solid waste by cold-bonding techniques

Facing the challenges of natural aggregate sustainability and carbon neutrality, a novel low-carbon and high-strength core-shell aggregate (CSA) was developed in this study by cold-bonding with solid wastes. The developed CSA was characterized by crushing strength (CS), loose bulk density (LBD), water absorption (WA), and analyzed by hydration heat, pore properties, and then evaluated by carbon footprint assessment for comparing with the common artificial lightweight aggregates. The results showed that a water/binder ratio of 0.21 for the CSA production restricted the cement hydration, which provided a chance to reduce the cement usage by replacing it with GGBS and FA for low carbon purposes. Compared with FA, GGBS was more suitable for replacing cement in producing CSA because of its better micro-aggregate effect and secondary volcanic ash reaction for promoting hydration and optimizing pore structure. The pelletization CO2 emission (COE) for the CSA production only ranged from 4.2% to 11.9% of the total COE, which proved the green feature of cold-bonding in producing CSA. Replacing cement with 0–80% GGBS decreased the COE from 578.9 kg to 188.1 kg for 1 ton of CSA production. The CSA with 80% GGBS developed in this study attained CS of 7.68 MPa, LBD of 843 kg/m3, and WA of 17.8%, which showed much higher strength efficiency of 9110 Pa·m3/kg and much lower COE of 188.1 kgCO2 eq/t than the common artificial lightweight aggregates.