Biocementation Of Sand Research Articles

Bio-cementation of sand using enzyme-induced calcite precipitation: Mechanical behavior and microstructural analysis

The enzyme-induced calcite precipitation (EICP) has recently gained popularity as a ground improvement technique. Bio-cementation via EICP increases the strength, stiffness, and soil liquefaction resistance by clogging the voids and binding the soil particles with calcium carbonate. The objectives of the study involve assessing the mechanical behavior of the EICP-treated sand by performing monotonic consolidated drained triaxial and undrained cyclic triaxial tests. This study adopted a one-phase EICP cementation solution consisting of 1 M Urea, 0.67 M Calcium chloride dihydrate, and 3 g/l urease enzyme. The monotonic triaxial tests on pure sand and EICP-treated sand with 3,7, and 14 curing days were carried out at 50, 100, and 200 kPa confining pressures, respectively. A noticeable effective cohesion was observed for EICP-treated sand for all curing durations. Undrained cyclic triaxial tests on the EICP-treated specimens with 7 days of curing were performed at an effective confining pressure of 100 kPa. As expected, the number of cycles to liquefaction was higher in the EICP-treated specimen compared to pure sand due to the cementation effect. Finally, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) mapping confirmed the enhanced liquefaction resistance in EICP-treated sand due to calcium carbonate precipitation, leading to particle-to-particle interlocking. Additionally, X-ray Diffraction (XRD) analysis revealed the presence of calcite crystals resulting from the EICP treatment.

Effect of precipitation pattern of enzyme-induced calcite on compressive strength of sand

The biocementation of sand through calcite precipitation is a promising approach that has been investigated for nearly 10 years as an attempt to find practical solutions to ground improvement challenges due to sustainability considerations. This study aims to evaluate the effect of the precipitation pattern on the unconfined compressive strength (UCS) of sand treated through the enzyme-induced calcite precipitation (EICP) technique. The microscale characteristics of calcium carbonate (CaCO3) (spatial distribution, shape, size and amount) under three different precipitation conditions (EICP, skim-milk-added EICP and EICP on calcite-nanoparticle-coated medium) were investigated through microfluidic chip experiments. The outcomes of these observations were linked to the UCS of sands treated under each of these conditions through column tests. The densely packed, homogeneous and small-sized rhombohedral crystals promoted by the nanoparticle-coated condition led to lower UCS values (maximum of 0.15 MPa at 5% calcium carbonate content). In contrast, sparsely distributed, less uniform and large-sized spherical crystals yielded higher values (maximum of 1.4 MPa at 3.9% calcium carbonate content). The precipitation pattern of calcium carbonate was found to influence significantly the UCS of EICP-treated sand.

Simplified biogeochemical numerical model to predict pore fluid chemistry and calcite precipitation during biocementation of soil

Microbially induced calcite precipitation (MICP) technique has gained attention recently as a novel method to enhance the engineering properties of soils, especially sandy soils. However, the applicability of this method to field scale is challenging and requires understanding of the factors affecting MICP process under variable subsurface conditions. This study presents a laboratory investigation and numerical predictive model to assess pore-water chemistry and calcite precipitation during the biocementation process. Laboratory experiments were conducted to assess the microbial treatment of Narmada sand in plastic tubes using three bacterial strains and two cementation media concentrations. Calcite precipitation via ureolysis as a result of biogeochemical reactions was measured. The effects of pH and electrical conductivity (EC) on the rate of urea hydrolysis and calcite precipitation were assessed. The presence of calcite crystals was analyzed using scanning electron microscopy (SEM). The SEM images confirmed the formation of calcite at the surface and between the sand particles. A simplified numerical model was developed to estimate the rate of urea hydrolysis and their effects on the biocementation of sand. Three stages of MICP process were identified: bacterial ureolysis, dynamic equilibrium between liquid-gas interface and oversaturation of ions, and calcite precipitation. The variations of pH and EC at these three stages were modeled. The predicted pH, EC, and calcite precipitation based on the simplified model were found to be in close agreement with the experimental results. The numerical model can be used to assess and optimize the system variables for effective MICP field applications.

Insights into the Current Trends in the Utilization of Bacteria for Microbially Induced Calcium Carbonate Precipitation.

Nowadays, microbially induced calcium carbonate precipitation (MICP) has received great attention for its potential in construction and geotechnical applications. This technique has been used in biocementation of sand, consolidation of soil, production of self-healing concrete or mortar, and removal of heavy metal ions from water. The products of MICP often have enhanced strength, durability, and self-healing ability. Utilization of the MICP technique can also increase sustainability, especially in the construction industry where a huge portion of the materials used is not sustainable. The presence of bacteria is essential for MICP to occur. Bacteria promote the conversion of suitable compounds into carbonate ions, change the microenvironment to favor precipitation of calcium carbonate, and act as precipitation sites for calcium carbonate crystals. Many bacteria have been discovered and tested for MICP potential. This paper reviews the bacteria used for MICP in some of the most recent studies. Bacteria that can cause MICP include ureolytic bacteria, non-ureolytic bacteria, cyanobacteria, nitrate reducing bacteria, and sulfate reducing bacteria. The most studied bacterium for MICP over the years is Sporosarcina pasteurii. Other bacteria from Bacillus species are also frequently investigated. Several factors that affect MICP performance are bacterial strain, bacterial concentration, nutrient concentration, calcium source concentration, addition of other substances, and methods to distribute bacteria. Several suggestions for future studies such as CO2 sequestration through MICP, cost reduction by using plant or animal wastes as media, and genetic modification of bacteria to enhance MICP have been put forward.

Biocementation of sand by Sporosarcina pasteurii strain and technical-grade cementation reagents through surface percolation treatment method

The use of microbially induced carbonate precipitation (MICP) to produce biocementitious material for soil stabilization has emerged in recent decades as a sustainable alternative approach to conventional methods. However, the use of standard analytical-grade reagents for various MICP studies makes this technology very expensive and unsuitable for field-scale consideration. In this present study, the feasibility of using commercially available and inexpensive technical-grade reagents for the cultivation of ureolytic bacteria and enhancement of soil stabilization was investigated. Low-cost growth media prepared in deionized water and tap water were used to cultivate Sporosarcina pasteurii as a replacement to standard laboratory-grade media. Biocement treatment was carried out on sand columns using different concentrations (0.25–1.0 M) of technical-grade and analytical-grade cementation solutions via surface percolation method. After 92 h of treatment, the columns were cured for 3 weeks at room temperature (26 ± 2 °C) before analysing their respective surface strengths, CaCO3 content, pH of effluents and sand microscopic structures. The results indicated that the growth of bacteria in low-cost cultivation medium was similar to that observed in the standard cultivation medium. Surface strengths and CaCO3 contents of the consolidated samples were in the ranges of 11448.00 ± 69.00–4826.00 ± 00 kPa and 5.56 ± 1.15–33.24 ± 0.59%, respectively. Overall, the obtained results of the current study encourage future MICP studies to utilize commercially available technical-grade reagents for economical MICP field-scale trials.

Role of fungal-mediated mineralization in biocementation of sand and its improved compressive strength

The process of microbially induced calcite precipitation (MICP) is widely used recently in construction engineering in improving compressive strength, durability and self-healing of building materials and culture heritages. However, most of researches to date have concentrated on prokaryotic systems despite of associated limitation of urease-positive bacteria in biocementation. In the present study, we exploited the role of one urease-positive fungal strain Penicillium chrysogenum CS1 for the first time in biocementation of sand in column to produce sandstone of significant compressive strength. Further, the research provided understanding of the involved mechanisms and advantages of fungal-mediated production of calcite in cementing sand granules over same process using bacteria.

Optimization of calcium-based bioclogging and biocementation of sand

Bioclogging and biocementation can be used to improve the geotechnical properties of sand. These processes can be performed by adsorption of urease-producing bacterial cells on the sand grain surfaces, which is followed by crystallization of calcite produced from the calcium salt and urea solution due to bacterial hydrolysis of urea. In this paper, the effect of intact cell suspension of Bacillus sp. strain VS1, suspension of the washed bacterial cells, and culture liquid without bacterial cells on microbially induced calcite precipitation in sand was studied. The test results showed that adsorption/retention of urease activity on sand treated with washed cells of Bacillus sp. strain VS1 was 5–8 times higher than that treated with culture liquid. The unconfined compressive strength of sand treated with the suspension of washed cells was 1.7 times higher than that treated with culture liquid. This difference could be due to fast inactivation of urease by protease which was present in the culture liquid. The adsorption of bacterial cells on sand pretreated with calcium, aluminum, or ferric salts was 29–37 % higher as compared with that without pretreatment. The permeability of sand varied with the content of precipitated calcium. For bioclogging of sand, the content of precipitated calcium had to be 1.3 % (w/w) or higher. The shear strength of biotreated sand was also dependent on the content of precipitated calcium. To achieve an unconfined compressive strength of 1.5 MPa or higher, the content of precipitated calcium in the treated sand had to be 4.2 % (w/w) or higher. These data can be used as the reference values for geotechnical applications such as bioclogging for reducing the permeability of sand and biocementation for increasing the shear strength of soil.