Microbial‐Induced Carbonate Precipitation for Strengthening Soft Clay

Abstract

Currently, calcite produced in sediments by microbial-induced carbonate precipitation (MICP) is mainly used as a strengthening binder in sand because sands are porous and have good permeability. Conventional wisdom does not consider MICP to be suitable for use in soft clay because of the clay particles’ small size and its minimal porosity. Because of the clay’s high water content and complex chemical composition, very little research has been done and not much is known about the use of MICP in soft clay for strength enhancement. For this paper, soft clay specimens were prepared by mixing a solution containing Sporosarcina pasteurii bacteria, solutions with different concentrations of nutrient salts, and soft clay. Unconfined compressive strength tests were carried out on these specimens after they had cured for 28 days in a moisture-controlled environment. These laboratory tests were used to study the chemical reactions, the clay’s strength, and other influencing factors. The results are as follows: (1) directly mixing a S. pasteurii solution, nutrient salts, and soft clay considerably improves the uniformity of the spatial distribution of the bacteria and the nutrients in the soft clay. Directly mixing these constituents promotes the formation of calcium carbonate and greatly simplifies soft clay sample preparation. (2) It is feasible to use MICP to increase the strength of soft clay. Compared to control specimens cured under the same conditions but without introduced nutrients and bacteria solution, the unconfined compressive strength of MICP-treated specimens can be increased by as much as 2.42 times to an unconfined compressive strength of 43.31 kPa. The water content in MICP-treated specimens was significantly reduced by the MICP reactions and in one case decreased from 40% to 30.73%. (3) The strength enhancement of microbially solidified soft clay is the result of two processes: urea hydration catalyzed by enzymes consumes water in the clay and the bacterially precipitated calcite forms in the sediment’s pores. (4) The micro-organism-produced calcite in the soft clay increases the calcite abundance from 0% to as much as 3.5%. (5) The MICP-treated strength of soft clay varies with the concentration of the nutrients provided. For the experimental conditions used for this paper, the optimum concentration of the CaCl2·2H2O and CH4N2O nutrients is 0.5 mol/L.

Use of Microbially Induced Calcite Precipitation for Soil Improvement in Compacted Clays

“…Furthermore, the samples that contained CaCO 3 according to XRD coincided with samples that had higher strength modulus and q u values from physical property tests. Therefore, we can relate MICP's ability to improve clay strength to the formation of CaCO 3 [57].…”

Improvement and Soil Consistency of Sand–Clay Mixtures Treated with Enzymatic-Induced Carbonate Precipitation

“…The EDS test was not conducted in this study; however, previous studies have used the EDS test to confirm the CaCO 3 produced in MICP-solidified clay soils [ 40 , 41 , 42 ]. SEM testing can be used to evaluate the treatment effect from a microscopic perspective.…”

Application of Nature-Based Nanotechnology for Enhancing Biocementation in Clay by Microbially Induced Calcium Carbonate Precipitation

“…The UCS values in the three clay soil samples (which were modified by MICP treatment) surged by 177% and 278%, respectively [9]. In another study, the application of the MICP method in modifying clayey soils was investigated [28]. A 2.42-fold increase in UCS was observed.…”