Pores and Microanalysis of Microbe-Inspired Nano-CaCO3 Cementing Sand Columns

This paper introduced an innovative bioengineering method of consolidating incompact sand by urea hydrolysis producing calcite cementation under the inducement of reproductive urease microbe. The result of mercury intrusion porosimetry showed the pore volume fractions of sand columns cemented by microbe-inspired nano-CaCO3 on an accelerating reduction during the time of cementation, the process of which represented the bulk density of nano-CaCO3 cementing sand columns that reinforced themselves positively all the time. The white precipitate particles exhibited a uniformed distribution of about 15？μm size and of a hexahedral shape mostly under SEM. Based on the Scherrer equation, the crystallite size of the white precipitate was calculated for 18.5？nm. The diffraction pattern of the white precipitate under TEM was taken in alignment with the 52 inorganic crystal composed of three elements of Ca, C, and O in PCPDFWIN-2000 and the precipitate was identified as ID86-2334 calcite calcium carbonate. 1. Introduction Biomineralization is discovered and applied in geological material consolidation [1, 2]. With the application of this discovery to sand biocementation as the in situ microinspired calcite precipitation technique (MCP technique for abbreviation), a solution of urease-productive bacteria and urea was mixed and calcium chloride was first injected in sand and then in bacteria-producing urease dehydrates urea, shown in (1) and (2), and consequently calcium carbonate precipitates and fills in the spacing of sand, shown in (3) and (4): Microstructure analysis was made by the formulas of XRD, TEM, and SEM, combined with mercury intrusion porosimetry method to investigate the CaCO3 particles size distributions and locations. This paper focused on the characterization of nano-CaCO3 precipitate itself and its influence on sand-based material properties. 2. Materials and Methods 2.1. Microorganism and Growth Conditions Liquid culture media consisting of 3？g/L nutrient broth, 5？g/L peptone, and 2.4？g/L urea were adjusted to pH 7.0 and sterilized for 25？min at 121°C. 2？mL (OD600？nm？=？0.8). Bacillus pasteurii (isolated and preserved appropriately in our lab) were added into 100？mL culture medium and incubated at 30°C at 170？rpm for 24 hours in the shaker (XinZhi, China) [3]. 2.2. Microbe-Inspired Nano-CaCO3-Sand Cementation 15？g of sand in 200？μm diameter was added with appropriate vibrations into a plastic injection tube, 22？mm in diameter and 95？mm in length. Those tubes, filled with sand, were prepared for microbe-inspired CaCO3 cementation [4]. This endeavor