The main aim of this investigation is to determine the influence of *Bacillus* species on the crack healing ability and flexural strength of concrete. In this regard, four *Bacillus* species, such as *Bacillus halodurans* (BH), *Bacillus cereus* (BC), *Bacillus licheniformis* (BL), and *Bacillus subtilis* (BS), and two bacterial cell concentrations are selected (viz., 108 and 109 cells/ml of water), and the concrete specimens are cracked with a 65% stress level concentration.
To identify the crack healing ability of selected *Bacillus* species, three different curing conditions are adopted: calcium lactate, water, and ambient curing conditions. The ultrasonic pulse velocity test (UPV) has been conducted to identify the crack healing ability of the selected *Bacillus* species.
From the results, calcium lactate-based cured concrete specimens showed better UPV values and crack healing ability, whereas *Bacillus halodurans* (BH) effectively filled the crack with calcite precipitation, which is the reason for 90% of crack healing ability and the high flexural strength recovery compared to other selected *Bacillus* species. There is not much difference observed between the bacteria with cell concentrations of 109 and 108; however, 109 has a higher healing ability and recovers flexural strength.