Biochar-augmented carbon-negative concrete

Biochar is a waste-derived carbon-based material that can sequester carbon. This study proposed a revolutionary design of carbon-negative concrete with a large volume of biochar incorporation and elaborated the roles of biochar in the cement hydration and microstructure development of biochar-augmented concrete. The total CO₂ emissions and economic values of biochar-augmented concrete were, for the first time, quantified by conducting life cycle assessment and cost-benefit analysis. Biochar as aggregate in concrete promoted the cement hydration process, facilitating the formation of calcium-silicate-hydrate (C-S-H) gel and enhancing the polymerization degree of C-S-H gel via internal curing. The incorporation of supplementary cementitious materials (SCMs) in the binder further enhanced the mechanical strength of biochar-augmented concrete via time-dependent pozzolanic reaction. The life cycle assessment confirmed that the biochar incorporation significantly reduced CO₂ emissions, and most importantly, the combined use of biochar and SCMs successfully achieved carbon-negative concrete production. Preliminary cost and benefit analysis illustrated that the biochar-augmented concrete could yield satisfactory overall economic profits. Considering the mechanical performance, resource availability, negative CO₂ emissions, and economic profits, the 30BC-MK (with biochar as aggregate and metakaolin as a binder representing 30 wt% and 9 wt%, respectively) was the most promising mixture, which could sequester 59 kg CO₂ tonne^-1 and potentially generate the overall profit of 35.4 USD m⁻³. In summary, our novel design of biochar-augmented concrete can open up a new field of biochar application that produces technically feasible and financially profitable carbon-negative construction materials.