Carbon sequestration in aggregate and concrete by encapsulated biochar and carbonation: Experiment and simulation

Biochar is emerging as a novel method for carbon sequestration in concrete to reduce its carbon footprint, however, the high volume incorporation of biochar would unavoidably deteriorate the concrete performance due to biochar's drawbacks in high water absorption and low strength. Facing this conflict, a novel biochar-enabled core-shell aggregate (BCSA) developed by encapsulating biochar with cementitious materials was proposed for firstly overcoming biochar's drawbacks and then utilizing in concrete for carbon sequestration. The results showed that the optimal BCSA performance achieved a loose bulk density of 857 kg/m³, a crushing strength of 8.05 MPa, and a strength efficiency of 9393 Pa m³/kg. These properties were better than commercial sintered aggregate, indicating the advantages of the core-shell design technology in developing artificial aggregate. The BCSA-based concrete attained a density of 1778 kg/m³ and a compressive strength of 35.8 MPa, which maintained concrete with structural performance and realized high biochar usage of 92.8 kg/m³. Comparatively, the utilization of biochar showed greater promising in carbon sequestration than carbonation curing. Direct carbonation curing the fresh BCSA attained higher carbonation degree and CO₂ uptake than firstly sealing and then carbonation curing, which can be explained by its higher moisture pore walls, which helped both CO₂ migration and adsorption as indicated by the molecular dynamics simulation. In sum, BCSA and BCSA-based concrete respectively realized total 250.4 kg/t and 247.1 kg/m³ CO₂ sequestration, which indicates a great carbon storage potential and puts a new way of using biochar for producing aggregate and concrete with promising engineering application potentials.