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To investigate potential implications of microbial activity on sand bioconsolidation and subsurface environments, two ureolytic strains, Sporosarcina pasteurii and Bacillus subtilis were tested for the production of calcium carbonate (CaCO3). Laboratory experiments with monoculture S. pasteurii (column 1) and coculture S. pasteurii-B. subtilis (column 2) were conducted to determine urea and calcium chloride reactivity and volumetric carbonate formation. Both columns were able to consolidate sand, whereas, column 1 induced greater CaCO3 precipitation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed two columns with different mineralogy with calcite, and vaterite formation. Column 1 showed rhombohedral and trigonal crystals morphology, whereas column 2 developed the prismatic calcite and the spherulite vaterite crystals might be due to the differences of the micro-environment caused by the urease expression of these bacterial species. These results indicate the possibility of using those crystals to cement loose sand whereas, highlighted the importance of combining these techniques to understand the geomicrobiology found in the subsurface environments.

This report describes a novel way to generate a highly effective hydrophobic cement surface via a carbonation route using sodium stearate. Carbonation reaction was carried out at different temperatures to investigate the hydrophobicity and morphology of the calcium carbonate formed with this process. With increasing temperatures, the particles changed from irregular shapes to more uniform rod-like structures and then aggregated to form a plate-like formation. The contact angle against water was found to increase with increasing temperature; after 90 °C there was no further increase. The maximum contact angle of 129° was obtained at the temperature of 60 °C. It was also found that carbonation increased the micro hardness of the cement material. The micro hardness was found to be dependent on the morphology of the CaCO3 particles. The rod like structures which caused increased mineral filler produced a material with enhanced strength. The 13C cross polarization magic-angle spinning NMR spectra gave plausible explanation of the interaction of organic-inorganic moieties.