Self-Healing Assessment and Biresponse Optimization of Hybrid Fiber–Reinforced Bioconcrete

This study quantified the crack healing efficiency of hybrid fiber (polypropylene and glass fibers)-based bacterial concrete. Bacillus subtilis and Bacillus megaterium, supplemented with calcium lactate and yeast extract, were added to the concrete as a healing agents. In addition to the effectiveness of self-healing, the influence of three healing agent concentrations–105, 107, and 109 cells/mL—on the mechanical and durability properties of hybrid fiber concrete (HFC), was investigated. A significant enhancement of mechanical properties was observed due to the incorporation of self-healing agents in concrete, largely for bacterial concentrations of 105 and 107 cells/mL. Healing efficiency of the precracked specimens was determined using ultrasonic pulse velocity tests, digital image processing, and recovery of compressive strength after a 28-day healing period. The experimental results indicate that the use of HFC incorporating 107 cells/mL of Bacillus subtilis and HFC incorporating 107 cells/mL of Bacillus megaterium led to the maximum global crack closure ratio and the highest possible recovery of compressive strength. Field-emission scanning electron microscopy and X-ray diffraction suggested that the healing products contained a substantial quantity of calcium carbonate (CaCO3), thus confirming the microbially induced calcite precipitation. Lastly, the response surface methodology was used to develop models for the determination of compressive strength and global crack closure ratio. These models were optimized to account for various bacterial concentrations and healing periods.