• Geomechanics and Engineering
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• v.32 no.1
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• pp.85-96
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• 2023

Microbially induced carbonate precipitation (MICP) is extensively discussed as a promising topic for ground stabilization. The practical effect of stabilizing the expansive soil is presented in this paper with a logical process from the bacterial activity to the treatment technology. Temperature, pH, shaking frequency, and inoculation amount are discussed to evaluate the bacterial activity. The physic-mechanic properties are also evaluated to discuss the effect of the MICP process on expansive soil. Results indicate that the MICP method achieves the mitigation of expansion. The treated soil has a low proportion of fine particles (< 5 ㎛), the plasticity index significantly decreases, and strength values improve much. MICP process has a significant cementation effect on the soil matrix. Moreover, the infiltration model test presents the coating effect on the topsoil. According to the relation between the CaCO₃ content and the treatment effect, the topsoil has better treatment than the deeper soil.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.95-108
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• 2023

Soft soil ground is a crucial factor limiting the development of the construction of transportation infrastructure in coastal areas. Soft soil is characterized by low strength, low permeability and high compressibility. However, the ordinary treatment method uses Portland cement to solidify the soft soil, which has low early strength and requires a long curing time. Microbially induced carbonate precipitation (MICP) is an emerging method to address geo-environmental problems associated with geotechnical materials. In this study, a method of bio-cementitious mortars consisting of MICP and cement was proposed to stabilize the soft soil. A series of laboratory tests were conducted on MICP-treated and cement-MICP-treated (C-MICP-treated) soft soils to improve mechanical properties. Microscale observations were also undertaken to reveal the underlying mechanism of cement-soil treated by MICP. The results showed that cohesion and internal friction angles of MICP-treated soft soil were greater than those of remolded soft soil. The UCS, elastic modulus and toughness of C-MICP-treated soft soil with high moisture content (50%, 60%, 70%, 80%) were improved compared to traditional cement-soil. A remarkable difference was observed that the MICP process mainly played a role in the early curing stage (i.e., within 14 days) while cement hydration continued during the whole process. Micro-characterization revealed that the calcium carbonate filling the pores enhanced the soft soil.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.429-438
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• 2019

Microbially induced carbonate precipitation (MICP) is an innovative soil improvement approach utilizing metabolic activity of microbes to hydrolyze urea. In this paper, the shear response and the erodibility of MICP-treated sand under axial compression and submerged impinging jet were evaluated at a low confining stress range. Loose, poorly graded silica sand was used in testing. Specimens were cemented at low confining stresses until target shear wave velocities were achieved. Results indicated that the erodibility parameters of cemented specimens showed an increase in the critical shear stress by up to three orders of magnitude, while the erodibility coefficient decreased by up to four orders of magnitude. Such a trend was observed to be dependent on the level of cementation. The treated sand showed dilative behavior while the untreated sands showed contractive behavior. The shear modulus as a function of strain level, based on monitored shear wave velocity, indicated mineral debonding may commence at 0.05% axial strain. The peak strength was enhanced in terms of emerging cohesion parameter based on utilizing the Mohr-Coulomb failure criteria.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.421-427
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• 2019

Coastal erosion is becoming a significant problem in Greece, Bangladesh, and globally. For the prevention and minimization of damage from coastal erosion, combinations of various structures have been used conventionally. However, most of these methods are expensive. Therefore, creating artificial beachrock using local ureolytic bacteria and the MICP (Microbially Induced Carbonate Precipitation) method can be an alternative for coastal erosion protection, as it is a sustainable and eco-friendly biological ground improvement technique. Most research on MICP has been confined to land ureolytic bacteria and limited attention has been paid to coastal ureolytic bacteria for the measurement of urease activity. Subsequently, their various environmental effects have not been investigated. Therefore, for the successful application of MICP to coastal erosion protection, the type of bacteria, bacterial cell concentration, reaction temperature, cell culture duration, carbonate precipitation trend, pH of the media that controls the activity of the urease enzyme, etc., are evaluated. In this study, the effects of temperature, pH, and culture duration, as well as the trend in carbonate precipitation of coastal ureolytic bacteria isolated from two coastal regions in Greece and Bangladesh, were evaluated. The results showed that urease activity of coastal ureolytic bacteria species relies on some environmental parameters that are very important for successful sand solidification. In future, we aim to apply these findings towards the creation of artificial beachrock in combination with a geotextile tube for coastal erosion protection in Mediterranean countries, Bangladesh, and globally, for bio-mediated soil improvement.

• Journal of Microbiology and Biotechnology
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• v.22 no.2
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• pp.244-247
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• 2012

To remediate lead (Pb)-contaminated soils, it is proposed that microbially induced calcite precipitation (MICP) would provide the best alternative to other remediation technologies. In this study, Pb bioremediation in soils was investigated using the calcite-precipitating bacterium Kocuria flava. Results indicate that the Pb is primarily associated with the carbonate fraction in bioremediated soil samples. The bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated. This research provides insight into the geochemistry occurring in the MICP-based Pb-remediated soils, which will help in remediation decisions.

• Geomechanics and Engineering
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• v.33 no.2
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• pp.133-140
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• 2023

Soil erosion can cause scouring and failures of underwater structures, therefore, various soil improvement techniques are used to increase the soil erosion resistance. The microbially induced calcium carbonate precipitation (MICP) method is proposed to increase the erosion resistance, however, there are only limited experimental and numerical studies on the use of MICP treatment for improvement of surface erosion resistance. Therefore, this study investigates the improvement in surface erosion resistance of sands by MICP through laboratory experiments and numerical modeling. The surface erosion behaviors of coarse sands with various calcium carbonate contents were first investigated via the erosion function apparatus (EFA). The test results showed that MICP treatment increased the overall erosion resistance, and the contribution of the precipitated calcium carbonate to the erosion resistance and critical shear stress was quantified in relation to the calcium carbonate contents. Further, these surface erosion processes occurring in the EFA test were simulated through the coupled computational fluid dynamics (CFD) and discrete element method (DEM) with the cohesion bonding model to reflect the mineral precipitation effect. The simulation results were compared with the experimental results, and the developed CFD-DEM model with the cohesion bonding model well predicted the critical shear stress of MICP-treated sand. This work demonstrates that the MICP treatment is effective in improving soil erosion resistance, and the coupled CFD-DEM with a bonding model is a useful and promising tool to analyze the soil erosion behavior for MICP-treated sand at a particle scale.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.465-473
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• 2019

Biocementation due to the microbially induced calcium carbonate precipitation (MICP) process is a potential technique that can be used for soil improvement. However, the effect of biocementation may be affected by many factors, including nutrient concentration, bacterial strains, injection strategy, temperature, pH, and soil type. This study investigates mainly the effect of chemical concentration on the formation of calcium carbonate (e.g., quantity, size, and crystalline structure) and unconfined compressive strength (UCS) using different treatment time and chemical concentration in the biotreatment. Two chemical concentrations (0.5 and 1.0 M) and three different treatment times (2, 4, and 8 cycles) were studied. The effect of chemical concentrations on the treatment was also examined by making the total amount of chemicals injected to be the same, but using different times of treatment and chemical concentrations (8 cycles for 0.50 M and 4 cycles for 1.00 M). The UCS and CCC were measured and scanning electron microscopy (SEM) analysis was carried out. The SEM images revealed that the sizes of calcium carbonate crystals increased with an increase in chemical concentrations. The UCS values resulting from the treatments using low concentration were slightly greater than those from the treatments using high concentration, given the CCC to be more or less the same. This trend can be attributed to the size of the precipitated crystals, in which the cementation efficiency increases as the crystal size decreases, for a given CCC. Furthermore, in the high concentration treatment, two mineral types of calcium carbonate were precipitated, namely, calcite and amorphous calcium carbonate (ACC). As the crystal shape and morphology of ACC differ from those of calcite, the bonding provided by ACC can be weaker than that provided by calcite. As a result, the conditions of calcium carbonate were affected by test key factors and eventually, contributed to the UCS values.

• Geomechanics and Engineering
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• v.29 no.1
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• pp.79-90
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• 2022

Soybean-urease induced carbonate precipitation (EICP), as an alternative to microbially induced carbonate precipitation (MICP), was employed for soil improvement. Meanwhile, soluble calcium produced from industrial waste carbide slag powder (CSP) via the acid dissolution method was used for the EICP process. The ratio of CSP to the acetic acid solution was optimized to obtain a desirable calcium concentration with an appropriate pH. The calcium solution was then used for the sand columns test, and the engineering properties of the EICP-treated sand, including unconfined compressive strength, permeability, and calcium carbonate content, were evaluated. Results showed that the properties of the biocemented sand using the CSP derived calcium solution were comparable to those using the reagent grade CaCl₂. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed that spherical vaterite crystals were mainly formed when the CSP-derived calcium solution was used. In contrast, spherical calcite crystals were primarily formed as the reagent grade CaCl₂ was used. This study highlighted that it was effective and sustainable to use soluble calcium produced from CSP for the EICP process.

• Journal of the Korean Geosynthetics Society
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• v.22 no.2
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• pp.13-21
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• 2023

Mean sea level has recently been rising due to global warming causing coastal erosion. As Korea is peninsula, the land loss due to coastal erosion is critical. An approach in this study is cementing the coastal area using bacteria, which is called microbially induced carbonate precipitation (MICP). This study tried to see how fresh water and sea water work with MICP as a solvent. Ureolytic activity during the MICP reaction was measured with deionized and sea water. A soil column was prepared to evaluate the strength of MICP-treated sand. Sands were treated by MICP with surface percolation method. As the treatmen t style was different with other conventional methods, several methods were proposed to properly evaluate the MICP-treated sand surface. A micro-scale evaluation was performed to assess the mineral structure treated by different solvents. As results, sea water rendered the ureolytic reaction slower. A needle penetrometer worked well to evaluate the MICP-treated sand surface. This study confirmed the utilization of sea water is feasible as the solvent of MICP.

• Journal of Microbiology and Biotechnology
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• v.31 no.9
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• pp.1311-1322
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• 2021

Microbially induced calcium carbonate precipitation (MICP) has recently become an intelligent and environmentally friendly method for repairing cracks in concrete. To improve on this ability of microbial materials concrete repair, we applied random mutagenesis and optimization of mineralization conditions to improve the quantity and crystal form of microbially precipitated calcium carbonate. Sporosarcina pasteurii ATCC 11859 was used as the starting strain to obtain the mutant with high urease activity by atmospheric and room temperature plasma (ARTP) mutagenesis. Next, we investigated the optimal biomineralization conditions and precipitation crystal form using Plackett-Burman experimental design and response surface methodology (RSM). Biomineralization with 0.73 mol/l calcium chloride, 45 g/l urea, reaction temperature of 45℃, and reaction time of 22 h, significantly increased the amount of precipitated calcium carbonate, which was deposited in the form of calcite crystals. Finally, the repair of concrete using the optimized biomineralization process was evaluated. A comparison of water absorption and adhesion of concrete specimens before and after repairs showed that concrete cracks and surface defects could be efficiently repaired. This study provides a new method to engineer biocementing material for concrete repair.