Investigation of self-healing properties in concrete with Bacillus licheniformis isolated from agricultural soil

Abstract

One of the best methods to enhance the strength and durability of concrete and repair the cracks is to use a self-healing mechanism, based on bacterial-induced calcite precipitation. The main goal of this study includes the isolation and identification of wild-type calcium carbonate precipitation bacteria compatible with concrete from agricultural soil as a bacterial self-healing agent. These bacteria were recognized as Bacillus licheniformis by molecular identification.The bacteria were immobilized inside lightweight expanded clay aggregate (LECA) to be protected bacteria against harsh concrete conditions. Five different bacterial concentrations (104, 105, 106, 107, and 108 cells/ml) were studied in the mixtures to evaluate the optimum concentration of bacteria.The mechanical properties and durability were tested to estimate the effectiveness of bacteria on the performance of concrete specimens at 7, 28, and 90 days. Furthermore, the physicochemical properties of precipitated calcium carbonate were characterized using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD).Test results showed that in the specimen containing 107 cells/ml Bacillus licheniformis, the compressive and tensile strength was 21% and 32% more than ordinary concrete, respectively. Also, the maximum decrease in water and chloride ion permeability was 45% and 55%, respectively. These results suggest that the wild-type strain can survive in the cement matrix and by producing calcium carbonate deposits, it has the potential to improve the mechanical properties and durability.