Biochar-improved cement composites for carbon sequestration

The carbonation curing technology of cement-based materials is a potential carbon capture and storage method; however, it is important to address the serious concerns it raises. During carbonation curing, strength loss and shrinkage often occur to concrete due to excessive carbonation exposure. The carbonation degree is relatively low and uneven due to the difficulty of inward CO2 diffusion in concrete. This study investigates the effects of adding biochar derived from corn straw at different pyrolysis temperatures to cement mortars. Dosages ranging from 1% to 5% were used to address the issues mentioned above. The results suggest that the loss in strength and increase in water permeability of cement mortar caused by excessive carbonation curing can be compensated by the incorporation of biochar. Furthermore, the corporation of biochar into cement mortar was found to promote early-age hydration and improve pore structure. At 3 days, the carbonation degree of biochar added specimens is comparable to that of plain ones, but at 28 days, the internal carbonation degree is significantly higher. In addition, measurements of total CO2 uptake in cement mortar and life cycle assessment results demonstrate that the use of biochar has a positive environmental impact on carbonation-cured cement mortars.