Self-healing investigation on engineered cementitious composites incorporating Bacillus subtilis immobilized in silica gel

Engineered Cementitious Composites (ECC) has emerged as a remarkable class of construction materials distinguished by its superior ductility compared to traditional concrete. In addition, ECC possesses a self-healing capability that contributes to sustainability goals by facilitating autogenous healing of cracks. This healing mechanism is primarily effective for narrow cracks and faces limitations on the healing of wider ones. To further enhance the self-healing performance of ECC, a novel approach is introduced in this study by incorporating Bacillus subtilis immobilized in silica gel (BS+SG) into ECC mixtures. In this paper, the influence of BS+SG content ranging from 5% to 15% on the self-healing behavior of ECC was experimentally investigated. Specifically, the morphology of healed cracks and the recovery of tensile strength were examined. The result revealed significant enhancements in both crack-healing percentage and the recovery of tensile strength. Notably, ECC with 5% to 15% BS+SG exhibited remarkable increases in crack-healing percentage, ranging from 53.5% to 82.3% after 28 days of healing compared to 30.2% for ECC without BS+SG. In addition, water absorption and pulse velocity were also determined to assess the internal healing performance. The results confirmed that the incorporation of BS+SG enhanced the self-healing capability of ECC, as evidenced by improvements in water tightness and the regain ratio of pulse velocity.