The effects of two different bacteria species on the strength, durability, and microstructure of self-healing concrete were compared. A new wild-type calcifying strain, extracted from agricultural soil of Gilan province, Iran, was used to prepare bacterial concrete. This strain was identified as Bacillus licheniformis. The self-healing capacity of this bacteria was evaluated at three different cell concentrations (1.5 x 10(8), 3.0 x 10(8), and 6.0 x 10(8 )cells/ml), and its performance was compared with a standard strain of Sporosarcina pasteurii, which was prepared from the Iranian culture collection. Expanded perlite aggregate was used as a carrier. The mechanical properties and durability of mixtures at 7, 28, and 90 days were tested. The microstructure of some mixtures was also analyzed using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction. The results indicated that the strength and permeability of the concrete were improved with the addition of bacteria. The mixture with 6 x 10(8 )cells/ml B. licheniformis showed, respectively, 22% and 38% increases in compressive and tensile strength at 28 days. The FESEM and EDS results showed that the precipitation of calcite in concrete containing wild-type B. licheniformis was higher than that of the concrete containing S. pasteurii.

This research aims to isolate and identify calcite-precipitating bacteria and investigate whether they can be used in concrete to enhance its mechanical qualities and self-healing capabilities. Microbial-induced precipitation of calcium carbonate is a new technique for making cement concrete stronger. The present study aims to compare cement concrete's compressive and split-tensile strengths to those of conventional concrete to examine the possible use of alkaliphilic bacteria to improve its qualities and ability to self-repair hairline cracks in concrete. Through conducting experiments on concrete samples at ages 7, 28, and 56 days, to which the isolated bacteria were added and characterized at the molecular level using the AccuPrep Genomic DNA Extraction kit, amplified, and subjected to agar gel electrophoresis, the sequences were obtained and compared with those in the GenBank database using the BLAST tool in the NCBI-GenBank database. Using PCR and scanning electron microscopy, it was confirmed that the isolated alkaline bacteria had a 99.69% identity rate. The bacteria Alkalibacterium iburiense were used at different concentrations of 105and 108. Additionally, 2% of recycled coarse aggregate and 10% & 20% was used. It was found that the concrete properties were improved. It was determined that the optimum improvement in mechanical properties was with the addition of bacteria at a concentration of 108 and a total recycled aggregate ratio of 10% after 56 days. The compressive, tensile, and flexural strengths increased by 25.75%, 17.27%, and 19.4%, respectively.