Abstract
Cracking in concrete compromises durability and service life by enabling water and aggressive agents to penetrate, leading to accelerated deterioration. This study addresses this problem by investigating the self-healing potential of microbial-induced calcium carbonate precipitation (MICP) as a sustainable approach to enhance concrete performance. The objective is to compare the mechanical, durability, and self-healing behavior of concrete incorporating Bacillus subtilis , Bacillus sphaericus , Escherichia coli , and a novel hybrid combination of Bacillus and E. coli . Five concrete mixes were prepared, each containing 5% bacterial suspension (10 5 cells/ml) and 0.5% urea by cement weight, with a control mix for comparison. Compressive, tensile, and flexural strengths were measured at 7, 28, 56, and 90 days; water absorption, permeability, and scanning electron microscopy (SEM) were used to assess durability and microstructure. Statistical analysis (ANOVA, p < 0.05) confirmed significant improvements over the control. At 90 days, the hybrid mix achieved the highest gains in compressive strength (+ 19.57%), split tensile strength (+ 28.89%), and flexural strength (+ 23.45%), while reducing water absorption by 27% and permeability by 13% compared to the best-performing single-strain mix. SEM analysis revealed extensive crack sealing with dense calcite deposition. Compared to polymer-based self-healing methods reported in literature, the bacterial systems demonstrated comparable crack closure with potentially lower environmental impact. Further research should include life-cycle and cost–benefit assessments, as well as long-term performance evaluation under environmental stressors such as freeze–thaw cycles, salinity, and temperature fluctuations.