Enhancing self-healing concrete performance through optimized bacterial spore encapsulation using response surface methodology

This study presents the optimization of alginate-encapsulated bacterial spores (AEBS) for self-healing concrete. Bacillus sphaericus LMG 22257 spores were encapsulated in alginate microcapsules using ionotropic gelation, followed by freeze-drying. Response surface methodology was employed to determine the optimal conditions for bacterial spore microencapsulation, considering alginate concentration, calcium chloride concentration, and spore inoculum. The resulting AEBS were characterized in terms of encapsulation yield, capsule hardness, and swelling capacity. Statistical analysis revealed the significance and validity of the model. In addition, colorimetric urea analysis showed that AEBS decomposed urea more effectively than non-encapsulated bacterial spores. The self-healing performance was assessed via image processing and microstructural analysis. The mortar specimens treated with AEBS exhibited a complete crack-healing ratio (100 %) within 14 days, with the formation of CaCO 3 confirmed as the healing product. These findings indicate that AEBS prepared under optimal conditions have a strong potential for crack repair in concrete structures. • Optimal alginate–CaCl 2 –spore ratio determined using response surface methodology. • Optimized AEBSs achieved desirable yield, hardness, and swelling for crack healing. • Regression models confirmed strong predictive accuracy for AEBS traits. • Mortar cracks with optimized AEBSs completely healed within 14 days. • Optimized microcapsules demonstrate the potential for biological concrete repair.