Waste-Derived Alternatives for Sustainable Cement Replacement in Concrete

The construction industry’s dependence on Portland cement greatly contributes to global CO₂ emissions, highlighting the need for low-carbon alternatives. This research partially replaces cement with materials such as recycled concrete fines (WC), ground glass (GG), sugarcane bagasse ash (SCBA), and coffee husk biochar (CHB) produced via microwave-assisted pyrolysis (MAP). Comprehensive physicochemical, mechanical, microstructural, and thermal analyses and life cycle and techno-economic assessments were carried out in this research. SCBA and GG increased compressive strength by up to 64% and 46%, respectively, compared with the control specimen at 7 days, while CHB enhanced internal curing due to its high porosity. Life-cycle analysis revealed CHB concretes emitted as little as 0.005–59 kg CO₂/m³, significantly lower than conventional mixes. Techno-economic analysis highlighted GG as the most cost-effective alternative, while MAP-enabled CHB demonstrated commercial viability. The results substantiate a circular economy model by integrating waste feedstocks in concrete production and a scalable pathway to decarbonise concrete through sustainable waste utilisation.