Optimization of Bacterial Self-healing Concrete Using Bacillus licheniformis with Micro Silica and Fly Ash Aggregates

This research investigates the application of bacterial self-healing materials for resilient concrete using a cement matrix. It focuses on incorporating Bacillus licheniformis (B. licheniformis), a gram-positive microorganism, to repair structural and non-structural cracks at the nano-scale. The study addresses the challenge of microbial sustainability in concrete mixtures by employing an efficient immobilization technique using iron oxide nanoparticles. These nanoparticles were characterized using XRD and FTIR techniques. The effects of immobilized B. licheniformis on the concrete's strength and healing mechanisms were analyzed by measuring compressive and split tensile strengths per ASTM standards. Fly ash aggregates partially replaced coarse aggregates in varying proportions, with the mix containing 25% fly ash substitution demonstrating a 50% increase in compressive strength and complete healing of wider cracks. Furthermore, the optimization of fly ash, micro silica, and bacteria content in cement mortar was conducted using Response Surface Methodology (RSM). The RSM-based models were validated through ANOVA and found significant for all parameters (p < 0.05), with no significant lack of fit. The optimal mix achieved a 30% substitution of fly ash and micro silica at normal temperature, yielding compressive strengths of 23.22 MPa at 7 days and 28.72 MPa at 28 days and split tensile strengths of 1.68 MPa and 2.53 MPa, respectively. The findings highlight the potential of bacterial concrete in achieving self-healing and strength recovery, with a desirability factor of 1 confirming the precision of the optimization results. This study underscores the synergy between bacterial activity, pozzolanic materials, and statistical optimization techniques in enhancing the performance of concrete.