Studies on Sustainable Concrete Incorporating Carbonated Aggregates Developed from Industrial Waste

The utilization of carbonated aggregates developed from industrial waste has attracted attention in the construction industry to reduce CO2 emissions. This study examines the production of carbonated aggregates from industrial waste such as Class F fly ash (FA) and calcium carbide sludge (CCS) through water curing and autoclave methods. The findings revealed that a mix comprising 70% FA and 30% CCS, when carbonated for 12 h, achieved a maximum single aggregate strength of 2.2 MPa in autoclave carbonated aggregates, which is comparable to the strength obtained after 56 days of water curing in nonautoclave carbonated aggregates. The resulting aggregates are lightweight aggregates having a bulk density of 820−860 kg/m3 and water absorption of approximately 23%. Thermogravimetric analysis revealed that autoclave carbonated (AC) aggregates and water-cured carbonated (C) aggregates have CO2 uptakes of 11.6% and 13.3%, respectively. Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) analyses showed the formation of C-A-S-H gel in noncarbonated aggregates, which convert to silica gel and calcium carbonate upon carbonation. The AC aggregates were incorporated into concrete at various replacement levels (25%, 50%, 75%, and 100%), with 100% replacement resulting in an 18.3% reduction in concrete density while maintaining a compressive strength above 30 MPa. Further, this study investigates the reduction in CO2 emissions with the utilization of AC aggregate.