Abstract
Microbial-induced calcium carbonate precipitation (MICP) is a new soil remediation technology, which can improve the physical and mechanical properties of soil by transporting bacterial solution and cementation solution to loose soil and precipitating calcium carbonate precipitation between soil particles through microbial mineralization. Based on this technique, the effects of different fine particle content and pore ratio on the physical and chemical properties of silt after reinforcement were studied. The content of calcium carbonate, the ability of silt to fixed bacteria, unconfined compressive strength (UCS), permeability coefficient and microstructure of the samples were determined. The results showed the following: In the process of calcium carbonate precipitation induced by microorganisms, more than 50% bacterial suspension remained on the surface of silt particles and their pores. The higher the bacterial fixation rate of silt, the more CaCO3 was generated during the solidification process. The bacterial fixation rate and CaCO3 content both decreased with the increase in the pore ratio and increased with the increase in the fine particle content. XRD and SEM images show that the calcium carbonate is mainly composed of spherical vaterite and acicular cluster aragonite. There is an obvious correlation between unconfined compressive strength and CaCO3 content of silt. When CaCO3 content accumulates to a certain extent, its strength will be significantly improved. The unconfined compressive strength of silt A with pore ratio of 0.75 and fine particle content of 75% is 2.22 MPa when the single injection amount of cementing fluid is 300 mL. The permeability coefficient of cured silt can be reduced by 1 to 4 orders of magnitude compared with that of untreated silt. In particular, the permeability of MICP-treated silt A is almost impermeable.
Highlights
Introduction iationsMicrobial-induced calcite precipitation (MICP) is a bacteria-induced bio-mineralization process, which has been paid close attention to civil, infrastructure and environmental engineering [1–3]
In this paper, based on calcium carbonate precipitation induced by microorganisms
Andbeen so improved to the varying degrees.properties and microstructure of the strengthened silt samon, show that macroscopic ples been improved to varying degrees
Summary
Urease-active strain Sporosarcina pasteurii (CGMCC 1.3687) was used, provided by the China General Microbiological Culture Collection. It is an aerobic bacterium with a diameter of 2 μm to 3 μm. Optical density was measured using a spectrophotometer at a length of 600 nm (OD600 ), and urease activity was measured immediately after sampling at 25 ◦ C by the conductivity method [18]. Under aerobic batch conditions at 32 ◦ C, bacteria were cultivated in a medium containing 5 g/L soy peptone, 3 g/L beef extract, 0.02 g/L NiCl2 , and 20 g/L CO(NH2 ) , at a pH of 8, to late exponential phase with OD600 of 3 ± 0.5 and urease activity of 18 ± 2 mM urea/min
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