Engineered Production of Biochar as Concrete Additives and Its Role in Carbon-Negative Cementitious Composites

Abstract

This study explores how biochar with different physicochemical properties affects its performance in cementitious composites and therefore can help to formulate carbon-negative cementitious composites. Eight types of biochar were produced using three methods: (I) air exposure for varying durations, (II) adding K₂SiO₃ during pyrolysis and exposing to air for different durations, and (III) incorporating NaOH at different dosages during pyrolysis. These functionalized biochar samples were added at 30% by weight of the binder, containing slag cement and Ordinary Portland Cement (OPC). Biochar exposed to air for 12 weeks captured more atmospheric CO₂, which accelerated cement hydration and improved compressive strength, achieving 26 MPa after 28 days of sealed curing. The inclusion of K₂SiO₃ or NaOH additives during the pyrolysis process enhanced the performance of biochar as concrete additives. Specifically, K₂SiO₃ improved the performance by achieving a 33 MPa compressive strength, 44% higher than the biochar produced without any additives. The addition of NaOH significantly improved workability and cement hydration by acting as an activator. The addition of 0.5% NaOH to biochar was found to be the optimum dosage, providing a 27% higher compressive strength (29 MPa) compared to the air-exposed biochar batch. The life cycle assessment revealed that all biochar batches had negative carbon footprints, reducing global warming potential by 117%−133% compared to the control (mortar batch without biochar).

Citation

Ahmed, Nishad; Tahsin, Adhora; Ashraf, Warda; Yan, Qiangu; Cai, Zhiyong. 2025. Engineered Production of Biochar as Concrete Additives and Its Role in Carbon-Negative Cementitious Composites. ACS Sustainable Resource Management. 2(12): 2402-2415. https://doi.org/10.1021/acssusresmgt.5c00158.