Effect of bacteria on the self-healing ability of concrete containing zeolite

Recent years have seen increasing interest in the use of bacteria to induce self-healing properties in concrete. In this study, the effect of Bacillus subtilis, Bacillus megaterium, and Sporosarcina pasteurii on the self-healing, durability, and strength properties of concrete containing zeolite was investigated. Four different concentrations of these bacteria were tested to determine the optimal concentration of each strain. Bacillus subtilis was isolated from alfalfa stems and leaves and Bacillus megaterium and Sporosarcina pasteurii were acquired as lyophilized ampoules and cultured in the laboratory. For zeolite-containing specimens, the mix design was modified to replace 20wt% of cement with zeolite. Four series of destructive and non-destructive tests including ultrasonic pulse velocity (UPV), impermeability, water absorption, and compressive strength tests were conducted on the specimens at different ages. To determine the effect of bacteria on the self-healing property, 3-day-old specimens were put under a load equal to 30% of the fracture load so that they would develop cracks and then imaged by a scanning electron microscope (SEM) and an optical microscope to examine the progress of self-healing. An energy-dispersive X-ray spectroscopy (EDS) analysis was also performed to identify the constituting elements of the specimens. The optimal concentration of each type of bacteria for maximum self-healing was determined from experimental results. The results showed that the best bacterial concentration for producing calcite and filling cracks and voids in concrete is 2.8 x 108 for Bacillus subtilis and 105 for Bacillus megaterium and Sporosarcina pasteurii. Using these concentrations resulted in enhanced compressive strength, lower permeability, lower water absorption, and improved UPV. The introduction of bacteria to the mix design decreased the concrete's water absorption by 15% in the absence of zeolite and by 30% in the presence of zeolite.