Effects of wild-type and standard-strain bacteria immobilized in expanded perlite on the properties of self-healing concrete

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 × 10 8 , 3.0 × 10 8 , and 6.0 × 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 × 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.