Microbially mediated calcium carbonate precipitation on normal and lightweight concrete

This study investigates the characteristics of microbiological precipitation of calcium carbonate on normal and lightweight concrete by two types of bacteria, Sporosarcina pasteurii and Bacillus sphaericus. Concrete specimens were treated by pure water, a cell-free medium, and medium with cells; and a macrographic study of the distribution of calcium carbonate precipitation on the concrete specimens was carried out using a conventional digital camera to investigate the effects of the addition of bacteria. As a micrographic study, scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) spectra were used to observe the shapes and distributions of the calcium carbonate crystals at a microscale level. The X-ray diffraction (XRD) analysis was carried out to characterize the crystalline phases of the calcium carbonate crystals formed in liquid medium with and without cells. In addition, a capillary water absorption test of the concrete specimens was conducted to evaluate the effects of microbiological precipitation of calcium carbonate on the properties of moisture transport, which may affect the durability of the concrete. It was found that B. sphaericus precipitated denser calcium carbonate crystals than S. pasteurii. Moreover, the concrete specimens treated by the medium with B. sphaericus showed the lowest weight increases per unit area.