Multiple-phase enzyme-induced carbonate precipitation (EICP) method for soil improvement

doi:10.1016/j.enggeo.2021.106374

Engineering Geology

Volume 294, 5 December 2021, 106374

https://doi.org/10.1016/j.enggeo.2021.106374 Get rights and content

Highlights

•
Soybean crude urease was employed to catalyze CaCO₃ precipitation via EICP.
•
A multiple-phase EICP method was proposed for soil improvement.
•
The proposed method could significantly improve utilization efficiency of urease.
•
A relatively uniform CaCO₃ precipitation was obtained in EICP-treated sand.
•
The UCS of EICP-treated sand exceeded 10 MPa with a CaCO₃ content of ~20%.

Abstract

Enzyme-induced carbonate precipitation (EICP) is a potential method to improve the mechanical properties of granular soil. The one-phase premixed percolation method using purified urease enzyme is widely adopted for in-situ EICP treatment currently, but it is expensive and uses a relatively large amount of urease. This paper proposes a multiple-phase method consisting of a percolation of premixed soybean crude urease and cementation solution followed by several percolations of cementation solution in one cycle of biocementation. The utilizing rate of urease was increased by at least four times for the production of precipitated carbonate compared with the one-phase method. The proposed method also weakened the clogging of carbonate precipitation, thus bringing out a relatively uniform EICP treatment. After four cycles of biocementation (each cycle included five applications of cementation solution), the unconfined compressive strength of EICP-treated ASTM C778-graded sand exceeded 10 MPa with a CaCO₃ content of ~20%.

Introduction

Biocementation is an innovative soil improvement method for geotechnical applications such as ground improvement (DeJong et al., 2010; Cardoso et al., 2020), slope protection (Salifu et al., 2016; Liu et al., 2020), erosion mitigation (Hamdan and Kavazanjian, 2016; Meng et al., 2021), and seepage control (Jiang and Soga, 2017; Wu et al., 2019). In the most investigated biocementation technique, including microbially induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP), urease catalyzes the hydrolysis of urea and thus results in the production of carbonate ion and the rise of pH. Precipitation of CaCO₃ occurs in soil when soluble calcium sources are provided. The biocatalyzed CaCO₃ crystals can improve the shear strength and stiffness of soil by interparticle binding and pore filling (Almajed et al., 2018). In contrast to the MICP method, the EICP method uses free urease to catalyze the hydrolysis of urea. Thus, it is free from issues related to bio-safety and controlling microbial growth (activity) in soils (Khodadadi et al., 2017). Besides, the relatively small size of free urease enzyme, compared to bacterial cells, facilitates its transport in soil pores (Almajed et al., 2018).

Adsorption of free urease is weaker than that of live bacteria to the soil particle. In the commonly used single-phase method for in-situ EICP treatment, a mixture of purified urease and cementation solution is injected into the soil matrix throughout the biocementation process (Almajed et al., 2018; Nafisi et al., 2019; Cui et al., 2021). However, the widely adopted EICP treatment method appears to have several drawbacks. Firstly, as reported by Almajed et al. (2018), commercial purified urease is the most expensive component of the EICP solution, which is the main challenge of the large-scale application of EICP at this stage. Secondly, as urease is added into the EICP solution throughout EICP treatment, the enzyme is used inefficiently, which further enhances the cost of biocementation. At last, the mixing may cause intensive precipitation of CaCO₃ at the injection point after a few cycles of treatment, leading to a severe clogging and the nonuniformity of CaCO₃ during the biocementation treatment. The bio-clogging may impede the further progress of EICP treatment, and a lack of uniformity can result in lower UCS levels (Cheng et al., 2019; Hoang et al., 2020). Therefore, it is urgent to find an inexpensive urease resource and seek for an advanced method in terms of making efficient use of urease and improving the uniformity of CaCO₃ precipitation.

In this paper, a multiple-phase method using soybean crude urease as an alternative to purified urease enzyme was proposed to improve the utilization efficiency of urease and the uniformity of CaCO₃ precipitation in EICP treatment. The method included a percolation of premixed soybean crude urease and cementation solution followed by several percolations of cementation solution in one cycle of biocementation. The properties of the EICP treated samples after various cycles of biocementation were tested with regard to chemical conversion efficiency, CaCO₃ distribution, unconfined compressive strength (UCS), secant modulus (E50), permeability, and microstructure. This paper also provided a comparative study of the multiple-phase EICP method and the commonly used one-phase EICP method focusing on the soil engineering properties.

Section snippets

Soybean crude urease (SCU)

Soybean, a urease-abundant species of legume, was used to prepare crude urease in this study. The soybean crude urease was extracted simply by mixing powdered soybeans and tap water. The extraction process was divided into three steps: (1) Grinding and soaking, (2) salting-out of excess protein, and (3) liquid-solid separation. In step (1), the soybean was ground into powdered soybeans with a shredding machine, and 60-mesh sieved powdered soybeans were soaked in tap water at room temperature

Factors affecting chemical conversion efficiency of EICP in one cycle of biocementation

The effect of powdered soybeans concentration (enzyme activity of SCU) and percolation time (x in MPM x-y) on chemical conversion efficiencies of EICP in one cycle of biocementation was evaluated to determine the preferred treatment strategy. Fig. 1 shows the enzyme activity of SCU extracted using different concentrations of powdered soybeans and its effect on conversion efficiencies of EICP in the sand treated by a single premixed percolation (i.e., without following percolation of CS, MPM

Conclusions

The proposed multiple-phase method included a percolation of premixed SCU and CS followed by four percolations of CS in one cycle of biocementation. Considering the current price of soybeans, the material cost of the SCU with a powdered soybeans concentration of 80 g/L was much lower than that of the frequently-used purified urease. In addition, the utilizing rate of urease was increased by at least four times for CaCO₃ production compared with the one-phase method. Furthermore, the proposed

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The work described herein was supported by the National Natural Science Foundation of China under grant No. 51978244 and 51979088. The authors are grateful for this support. Any opinions, findings, and conclusions or recommendations expressed in this article are the authors only, and do not reflect the view of the National Natural Science Foundation of China.

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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 drying-wetting cycles on pore characteristics and mechanical properties of enzyme-induced carbonate precipitation-reinforced sea sand
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Enzyme-induced carbonate precipitation (EICP) is an emanating, eco-friendly and potentially sound technique that has presented promise in various geotechnical applications. However, the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting (D-W) cycles is under-explored yet. This study investigates the evolution of mechanical behavior and pore characteristics of EICP-treated sea sand subjected to D-W cycles. The uniaxial compressive strength (UCS) tests, synchrotron radiation micro-computed tomography (micro-CT), and three-dimensional (3D) reconstruction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles. The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis (GRA). Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles. The proportion of mesopores gradually decreases whereas the proportion of macropores increases due to the exfoliated calcium carbonate with increasing number of D-W cycles. The microstructure in EICP-reinforced sea sand was gradually disintegrated, resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched. The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100–1000 μm under the action of D-W cycles. Overall, the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.
Experimental study on the reinforcement mechanism and wave thumping resistance of EICP reinforced sand slopes
2023, Biogeotechnics
Sand slope is an important part of coastal zone and islands, which is severely affected by wave erosion and causes problems such as degradation of coastal zone and reduction of island area. Enzyme-induced calcium carbonate precipitation (EICP) technology is a new reinforcement technology with environmental friendly and excellent effect, which has been widely studied in the field of geotechnical engineering in recent years. In this research, we focus on the coastal or reef sand slopes in marine environments. The EICP reinforcement of representative sand slope units and large scale flume wave thumping experimental study are conducted indoors. By analyzing the physical and mechanical properties, erosion resistance, and microstructure of EICP-reinforced sand slopes, the mechanism of EICP reinforced sand slopes is revealed, the feasibility of EICP reinforced sand slopes is confirmed, and a feasible solution for EICP reinforced sand slopes is finally obtained. Results show that: (1) EICP reinforcement effectively enhances the surface strength and erosion resistance of sand slopes. Higher calcium carbonate content in the sand slopes corresponds to greater surface strength and improved erosion resistance. When the calcium carbonate content is similar, using low-concentration reinforcement twice is more advantageous than using high-concentration reinforcement once due to its superior uniformity. (2) The intensity of waves, the angle of the sand slope, and the severity of erosion damage are interrelated. Higher wave intensity, steeper sand slope angles, and more serious erosion damage require stronger reinforcement measures. (3) Scanning Electron Microscope (SEM) image analysis reveals that the reinforcing effect of sand slopes primarily depends on the amount of calcium carbonate crystals cemented between sand particles. A higher content of calcium carbonate crystals leads to better erosion resistance in the sand slope.
Desiccation cracking remediation through enzyme induced calcite precipitation in fine-grained soils under wetting drying cycles
2023, Biogeotechnics
The effects of desiccation cracking in clay soils on geotechnical constructions are substantial. This study investigates the viability of utilizing Enzyme-induced calcite precipitation (EICP), a bio inspired approach, as a potential solution for addressing desiccation cracking in fine-grain soils. For the EICP technique, crude soybean extract is employed for the purpose of urea hydrolysis. Multiple fluid samples, including a control sample, a cementation solution containing 1 M urea, 0.675 M CaCl₂, and 4 g/L milk, along with various concentrations of enzyme solutions (3–80 g/L), were tested for the study. To evaluate the surface cracking patterns, the method involved constant monitoring and photo recording using a high-resolution camera aided by image processing software. The results showed that fine-grain soils improved from increased calcite precipitation and decreased desiccation cracking intensity when the EICP method was used. Cementation and enzyme solution with low concentrations (3 g/L and 10 g/L) had similar effects on crack remediation, suggesting a modest influence. In contrast to the sample treated with water, the crack network remained unaltered in this case. CaCO₃ precipitation within the void area kept the crack network in place even as the void thickness decreased at increasing enzyme concentrations (30 g/L, 50 g/L, and 80 g/L). Wetting and drying cycles were found to decrease the crack ratio, crack width, and crack length in the EICP-treated sample, particularly under higher concentrations of urease enzyme. Lower enzyme concentrations of 3 g/L and 10 g/L have minimal impact on crack remediation but effectively inhibit new crack formation. Furthermore, higher enzyme concentrations result in calcium carbonate precipitates, forming a soil crust and increasing surface roughness. The study aims to enhance understanding of the EICP methodology and to provide novel perspectives on potential uses for soil enhancement.
Effect of freeze–thaw cycling on mechanical properties of Na-montmorillonite modified EICP-treated silty sand
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Enzyme induced carbonate precipitation (EICP) has been developed as a new soil improvement technology. In this study, Na-montmorillonite (Na-Mt) was introduced into traditional EICP to improve the curing efficiency. In order to examine the applicability of the proposed method in seasonal frozen soil area, the mechanical properties of Na-Mt modified EICP treated soil subjected to freeze-thaw (FT) cycling were analyzed. The effects of different number and temperature ranges of FT cycles on the stress-strain curve, unconfined compressive strength (UCS), secant modulus, and strain corresponding to peak stress of silty sand were studied by UCS test. Then, the porosity and microstructure of silty sand under different FT cycling numbers and FT temperature ranges was measured by scanning electron microscope. When not subjected to FT cycling, Na-Mt modified EICP can reduce the apparent porosity of silty sand, and increase UCS and secant modulus by 4.9 and 3.1 times respectively compared with untreated soil; the increase in FT cycling numbers and FT temperature ranges generally reduces the soil particle size, increases the porosity and decreases the UCS; the silty sand solidified by Na-Mt modified EICP still has the most compact structure, the smallest porosity, the highest strength and the best toughness and stiffness compared with other methods even after FT cycling in extreme environment. Na-Mt can effectively fill the newly formed pores in EICP treated soil during FT cycling, thereby offsetting part of the pore changes. Na-Mt modified EICP is suitable for soil reinforcement in seasonal frozen soil area.
The physical and mechanical properties of recycled aggregates strengthened by enzyme induced carbonate precipitation
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Enzyme induced carbonate precipitation (EICP) which applied to improve the quality of recycled aggregates (RA) is a novel technology in the field of civil engineering. The urease was extracted from soybean, and the factors including soybean powder concentration, temperature and pH value on urease activity were investigated. Then the EICP reaction kinetics was carried out to obtain the most suitable reaction environment. A spraying method instead of soaking method for modifying RA was proposed, and the physical and mechanical properties of RA were evaluated by water absorption, hardness, apparent density and crushing index. The results show that the optimum pH value of soybean urease is 8.0, the concentration of soybean power is 40 g/L, and the urease activity increases with temperature in the range of 10–50 °C. Spraying method was better than soaking method in water absorption reduction rate of RA with different particle sizes. When the concentration of the chemical solution is 0.5 mol/L, the improvement in the water absorption characteristics of the RA is most significant. And the modified RA have also undergone substantial improvements in terms of hardness and apparent density. On the 7-day of modification, the crushing index of the RA reaches the peak. Through microscopic observation, the pore volume of the modified RA is significantly reduced, and the content of CaCO₃ is significantly increased, and the main crystalline form of CaCO₃ are calcite and vaterite.

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Technical noteMultiple-phase enzyme-induced carbonate precipitation (EICP) method for soil improvement

Highlights

Abstract

Introduction

Section snippets

Soybean crude urease (SCU)

Factors affecting chemical conversion efficiency of EICP in one cycle of biocementation

Conclusions

Declaration of Competing Interest

Acknowledgments

Eng. Geol.

Ecol. Eng.

Eng. Geol.

Geoderma

Soils Found.

Eng. Geol.

Eng. Geol.

Soils Found.

Baseline investigation on enzyme-induced calcium carbonate precipitation

J. Geotech. Geoenviron. Eng.

Enzyme induced biocementated sand with high strength at low carbonate content

Sci. Rep.

Standard Test Method for Unconfined Compressive Strength of Cohesive Soil

Influence of key environmental conditions on microbially induced cementation for soil stabilization

J. Geotech. Geoenviron.

Soil bio-cementation using a new one-phase low-pH injection method

Acta Geotech.

Technical note
Multiple-phase enzyme-induced carbonate precipitation (EICP) method for soil improvement