Carbon sequestration in MgO: Application for co-encapsulating bacteria and nutrients for self-healing concrete

Portland cement (PC)-based composites are prone to cracking due to the inherent brittleness of cementitious materials, and their maintenance is labor-intensive, costly, and results in significant carbon emissions. To address these issues, this study focused on utilizing the CO₂ sequestration capability of MgO to fabricate bacteria-based capsules for self-healing concrete. Overall, the feasibility of co-encapsulating bacteria and nutrients in carbonated reactive MgO cement (RMC) capsule was investigated. The developed capsule presented to be a core-shell structure with 6.1 % CO₂ sequestered in the form of nesquehonite. PC pastes with the capsules showed 10 % enhancement on 28-day compressive strength and demonstrated superior autonomous healing of large cracks and recovery of transport properties. After encapsulation, the concentration of viable bacteria remained high and stable in the capsule. By incorporating capsules into PC pastes and subjecting cracked specimens to 50 wet/dry conditioning cycles (each cycle comprising one day submerged in water and one day of air-drying), the capsules enabled complete healing of cracks under 350 µm and over 90 % healing for cracks between 350 and 500 µm. Simultaneously, water permeability decreased by 89.3 %, and ultrasonic pulse velocity (UPV) indicated a crack internal recovery of 97 %.