Dual Role of Biochar in Low-Carbon Cement Composites: Performance Enhancement and Carbon Sequestration

The cement and concrete industry contributes approximately 8% of global CO2 emissions, creating a need for cementitious materials that can both reduce emissions and store carbon. This study demonstrates that biochar can be incorporated at unprecedented levels of up to 20% by mass of cement while maintaining or improving compressive strength, overcoming limitations previously associated with high biochar dosages. Three biochar types derived from distillers’ grain, corn stover, and wood waste were evaluated. The results revealed a bimodal strength response, with optimum performance at low dosages (1–2.5%) and high dosages (~15%). Low biochar contents enhanced strength through nucleation effects, while higher contents improved performance by reducing the effective water-to-cement ratio, providing internal curing, and contributing pozzolanic reactivity. Furthermore, low-dosage biochar enabled 10–20% cement reduction while recovering up to 26% of the associated strength loss. Life-cycle and economic assessments indicated that the environmental and economic benefits were strongly scenario-dependent, with CO2 emission reductions of 32–66% and cost savings of up to 17% under favorable biochar-cost and carbon credit assumptions. These findings demonstrate a practical pathway for producing lower-carbon, carbon-storing cementitious composites without compromising mechanical performance.