Healing cement mortar by immobilization of bacteria in biochar: An integrated approach of self-healing and carbon sequestration

Self-healing of cracks in concrete by bacterial carbonate precipitation is an effective mechanism to ensure better serviceability of civil infrastructure. This study explores biochar, derived from wood waste, as carrier for carbonate precipitating bacteria spores in cement mortar to seal cracks, and recover strength and permeability of healed samples. Superabsorbent polymer (SAP) and polypropylene microfibers (PP) were added to ensure moisture availability to bacteria and control crack propagation during damage of mortar. Samples were damaged by pre-loading to different levels - 50% and 70% of peak strength at 14-day. Experimental results show that biochar immobilized spores combined with SAP and PP precipitate copious amount of calcium carbonate, which completely sealed cracks up to 700 μm. This mix also showed highest recovery of impermeability and strength under both levels of preloading. Improvement in strength by 38% and reduction in water penetration and absorption by 65% and 70% was observed by immobilization of spores in biochar, compared to directly added spores. From comparison between samples, it was found that inclusion of PP fiber contributed to recovery of strength and impermeability, while SAP ensured higher precipitation of bacterial induced carbonate precipitation. The study suggests that spores immobilized in biochar has potential to offer excellent self-healing in cement composites. Using biochar is also a carbon sequestration strategy because of high volume of stable carbon stored in biochar particles during pyrolysis. Therefore, the proposed material combination would offer carbon storage in buildings, while also promoting waste recycling.