Microbially Induced Calcite Precipitation Research Articles

Single bacteria spore encapsulation through layer-by-layer self-assembly of poly(dimethyldiallyl ammonium chloride) and silica nanoparticles for self-healing concrete

Self-healing of cracks improves durability and reduces maintenance of concrete. Microbial induced calcite precipitation is a novel approach to engage self-healing in concrete, and bacteria spores are protected from direct contact with the surrounding cement matrix to maintain their viability. This study proposes a novel single bacteria spore capsule via layer-by-layer (LbL) self-assembly of poly(dimethyldiallyl ammonium chloride) and silica nanoparticles to enhance the consistency of healing as well as to minimize the negative impact on the mechanical properties of the resulting concrete. The resulting single bacteria spore capsule has a size of 1 μm and the inclusion of the capsules dose not compromise the compressive strength of the matrix. Cement paste incorporating the capsules shows complete closure of large crack of few hundred microns and complete recovery of transport property. Healing products are observed along the entire crack from the surface to the interior.

The hydro-mechanical characteristics and micro-structure of loess enhanced by microbially induced carbonate precipitation

Microbially induced calcite precipitation (MICP) is an emerging biological method for soil improvement which has been applied to several soil types. However, only very limited research is conducted on the effectiveness of MICP treatment on loess, especially its hydro-mechanical characteristics. A set of unconfined compression, disintegration and scanning electron microscopy tests under various conditions were performed to quantify the mechanical and water stability of MICP solidified loess, including the cement reagent concentration (CRC = 0.5, 0.75, 1.0, 1.5 M) and curing age (CA = 0, 7, 14, and 28 days). Results indicate that MICP is a promising method for improving the mechanical property and water stability of loess under the present scenario of sustainable development worldwide. The uniaxial compressive strength (UCS) of MICP treated loess under CRC of 1.0 M curing for 14 days can be increased by 260%. The observed maximum performance of disintegration ratio of MICP treated loess is reduced by 68% through the self-designed disintegration instrument. Considering different CRCs, the empirical equation of UCS and deformation modulus of MICP-treated loess is proposed by regression analysis. In addition, with the aid of the scanning electron microscope, it is found that: (i) the precipitated CaCO3 crystals bridge and bind the loess particles together which can effectively increase the shearing resistance of loess skeletons; (ii) the CaCO3 aggregates filling in the pores between the loess particles could prevent the water molecules from damaging the original loess structures, and effectively reduce the disintegration of loess.

Properties of a backfill material prepared by cementing coal gangue and fly ash through microbial-induced calcite precipitation

Microbes can induce the production of calcium carbonate deposits, which cement solid wastes such as coal gangue to form backfill materials. Filling such backfill materials in underground goafs can facilitate the disposal of solid wastes and control surface subsidence. In view of this, the idea of preparing a backfill material by cementing coal gangue and fly ash through microbial-induced calcite precipitation (MICP) induced by B. pasteurii was proposed and the preparation procedure and test methods of properties of the backfill material were introduced. Changes in the slump flow and bleeding rate of the backfill material under conditions of different bacterial concentration, urea concentration, and mass concentration were studied. Influences of factors including the bacterial concentration, urea concentration, mass concentration, curing time, and curing temperature on the compressive strength of the backfill material were estimated. Results show that as the bacterial concentration increases, the slump flow increases, the bleeding rate decreases, while the compressive strength of the backfill material increases. An increase in the urea concentration reduces the slump flow and bleeding rate of the backfill material while first increasing, then decreasing the compressive strength; excessive concentrations of urea suppress bacterial activities. An increase in the mass concentration decreases the slump flow and bleeding rate of the backfill material, while increasing the compressive strength. As the curing temperature is increased, the compressive strength of the backfill material first increases, then decreases and the temperature range of 30 ∼ 40℃ is more conducive to bacterial hydrolysis of the urea and chemical reactions in the coal gangue-fly ash slurry. The prolonged curing time can significantly improve the compressive strength of the backfill material. The research results provide a theoretical basis for the application of microbial-induced calcite precipitation (MICP) in backfilling mining of coal mines.

Biochar-bacteria partnership based on microbially induced calcite precipitation improves Cd immobilization and soil function

Microbially induced calcite precipitation (MICP) technique utilizes ureolytic bacteria to decompose urea and generate carbonate ions for metal combination. MICP can remediate heavy metal (e.g., Cd) contaminated soils while maintaining or even improving soil functions, but its efficiency in agricultural soil practical application still needs to be enhanced. Here, we constructed a biochar-bacteria (2B) partnership in which biochar provides high nutrition and diverse sorption sites. Using the 2B system, Cd immobilization effectiveness and the underlying mechanism were examined along with the soil properties and soil functions. Results showed that compared to the single biochar and ureolytic bacteria systems, soil Cd mobility was reduced by 23.6% and 45.8% through co-precipitating with CaCO3 as otavite (CdCO3) in the 2B system, whereas soil fertility, bacterial diversity, and richness increased by 11.7–90.2%, 5.4–16.1%, and 6.8–54.7%, respectively. Moreover, the abundances of Proteobacteria and Firmicutes were enhanced in the 2B system. Notably, Sporosarcina and Bacillus (Firmicutes genus) that carry the ureC gene were boosted in the system, further implicating the microbiological mechanism in reducing Cd migration and its bioavailability in soil. Overall, the constructed 2B system was efficient in soil Cd immobilization by strengthening the ureolytic bacteria growth and their nutrient supply in the bacteria-rich soil ecosystem.

Potential Use of Microbially Induced Calcite Precipitation for the Biocementation of Mine Tailings

Mining activities offer clear economic benefits for mineral-rich countries. However, mining operations can produce several environmental impacts. Many of these are associated with generating and managing mining waste known as tailings, which are typically stored in surface facilities. Windblown dust emissions from tailing deposits can cause severe damage to local ecosystems and adverse health effects for the surrounding population. Microbially induced calcite precipitation (MICP) can be used for the superficial biocementation of tailings, thereby preventing such emissions. This research studied the capacity of MICP for the biocementation of tailings. The effect of applying different doses of biocementation reagents and two different methods for their application were evaluated. Results show that a relevant increase in surface strength can be achieved, especially if reagents are mechanically mixed with the tailings to induce a more homogeneous distribution of precipitates. Micrographical and mineralogical analysis by SEM, FTIR and XRD analysis showed the precipitation of calcium in the form of anorthite, calcite or vaterite. Overall results indicate that calcite precipitation can be induced in tailing by microorganisms with urease activity, providing a potential technique for the biocementation of this material.

Quality improvement techniques for recycled aggregates concrete incorporating fibers and Bacillus species bacteria – A review

Recycling demolition waste as an aggregate may be a crucial key to improving sustainability in concrete construction with universal increases in construction waste. Specific methodology is nevertheless warranted for its practical application in the reclaiming of concrete construction and demolition (C&D) waste. Countries like India generate 23 million tons of recycled aggregates (RA), which may double in the next year. Currently, the construction industry is facing the problems of diminishing natural resources and growing demolition waste. The use of old concrete as an aggregate source has proved to be an attractive alternative in concrete production to natural aggregates. A detailed review of the effects of bacteria from Bacillus species and fibers to improve some chosen physico-mechanical properties of recycled aggregate concrete (RAC) is presented in this paper. Different fibers used in RAC improved their propagation limits and also improved their strength properties to certain limits. On the other hand, microbially induced calcite precipitation (MICP) improved the microstructural properties of RAC. The approach implemented a review of literature sources addressing the techniques of quality assurance and their impact on RA properties, including practical and environmental viability, water absorption, and compressive strength.

A study on bacterial self-healing concrete encapsulated in lightweight expanded clay aggregates

Concrete is a widely used construction material susceptible to cracking due to internal and external stresses, affecting the long-term strength and durability of the structure. Self-healing concrete appears to be a promising solution to address this issue. For concrete, self-healing is naturally achievable to a certain extent by utilising unhydrated cement particles. However, to heal significant internal and external cracks over a long period, we need to develop new techniques to reach a practical level of self-healing. This study investigates autonomous self-healing concrete using Microbially Induced Calcite Precipitation (MICP). The concrete mix is created by incorporating Lightweight Expanded Clay Aggregate (LECA) encapsulated with Lysinibacillus sphaericus and Bacillus coagulans bacteria. Encapsulation is used to prolong the life of the bacteria and shield them from the highly alkaline environment of the concrete. A bacterial concrete mixture was made by replacing 20% coarse aggregate by volume with the bacteria-encapsulated LECA. The properties of self-healing concrete specimens were compared with conventional concrete specimens of grade M30. After curing, the cracked bacterial specimens underwent a 14-day wet and dry cycle to examine how well the bacteria healed the cracks. Then, the durability property was analysed based on water permeability and chloride penetration tests. The microstructure of concrete was examined using SEM and EDX analysis. Bacillus coagulans and Lysinibacillus sphaericus bacteria specimens showed favourable results compared to conventional concrete for hardened and durability tests performed. The two bacteria-encapsulated concrete also exhibited positive crack healing, and the macrocracks in the range of 0.1 to 0.5 mm were healed. A salt analysis confirmed the presence of Calcium Carbonate (CaCO3) in the healed portion of the concrete. Lysinibacillus sphaericus bacteria showed slightly better results than Bacillus coagulans, and both bacteria can be used for self-healing concrete applications.

Improving the spatial control of soil biocementation using indigenous microorganisms: Column experiments and reactive transport modeling

Microbially-Induced Calcite Precipitation (MICP), or biocementation, is a biomediated soil improvement process that uses microbial ureolytic activity to enable the precipitation of CaCO3 on soil particle surfaces and contacts. As the technology advances towards practical adoption, approaches that can modulate the spatial uniformity of biocementation and maximize treatment extent will be critical towards reducing implementation costs and impacts. In this study, treatment strategies capable of enriching indigenous ureolytic microorganisms at controlled ureolytic activities and the effects of these techniques on resulting spatial distributions of MICP were explored using centimeter- and meter-scale soil column experiments and reactive transport simulations. In column experiments, differences in treatment solution supplied yeast extract concentrations were shown to reliably control the enrichment of indigenous ureolytic microorganisms and achieve a wide range of ureolytic activities. Reactive transport simulations further demonstrated that reductions in stimulated ureolytic rates could enable more uniform improvement and increases in the extent of improvement with reduced sensitivity to changes in solution injection velocities. A reaction-to-injection duration ratio (RTIDR) parameter was proposed and captured the collective impacts of changes in injection rates and ureolytic reaction rates on reactive transport conditions thereby unifying outcomes from both simulations and experiments. A nonuniformity area (NA) parameter was also introduced to quantitatively characterize differences in biocementation uniformity independent of length scale and CaCO3 magnitudes. Results from this study collectively demonstrate the utility of changes in stimulated ureolytic activities towards controlling the spatial uniformity and extent of biocementation over meter-scale distances.

Optimization of biocementation responses by artificial neural network and random forest in comparison to response surface methodology.

In this article, the optimization of the specific urease activity (SUA) and the calcium carbonate (CaCO3) using microbially induced calcite precipitation (MICP) was compared to optimization using three algorithms based on machine learning: random forest regressor, artificial neural networks (ANNs), and multivariate linear regression. This study applied the techniques in two existing response surface method (RSM) experiments involving MICP technique. Random forest-based models and artificial neural network-based models were submitted through the optimization of hyperparameters via cross-validation technique and grid search, to select the best-optimized model. For this study, the random forest-based algorithm is aimed at having the best performance of 0.9381 and 0.9463 in comparison to the original r2 of 0.9021 and 0.8530, respectively. This study is aimed at exploring the capability of using machine learning-based models in small datasets for the purpose of optimization of experimental variables in MICP technique and the meaningfulness of the models by their specificities in the small experimental datasets applied to experimental designs. This study is aimed at exploring the capability of using machine learning-based models in small datasets for experimental variable optimization in MICP technique. The use of these techniques can create prerogatives to scale and mitigate costs in future experiments associated to the field.

Investigation of the effect of microbial-induced calcite precipitation treatment on bio-cemented calcareous sands using discrete element method

Owing to the bio-geological origin, calcareous sands are characterized by irregular particle shapes and abundant internal pores. These weak soil structures undergo extensive particle breakage under specific stress conditions. In recent years, microbial-induced calcite precipitation (MICP), a green soil treatment technique, has been widely utilized to improve the mechanical properties of calcareous sands. The treatment effect of MICP on calcareous sands and the underlying mechanism are still relatively unclear owing to the complex microstructures of the sands. This study investigated the micromechanism of MICP treatment on calcareous sands via the discrete element method (DEM). First, a group of calcareous sand particles were individually treated via a proposed MICP process. Single-particle crushing tests were conducted on the MICP-treated calcareous particles and a control group of untreated calcareous particles. The experimental results were further used to verify and calibrate the DEM models and parameters. The DEM model of MICP-treated calcareous particles was established via a novel modeling technique using the commercial PFC3D platform, which considered the inter-particle bridging and intra-particle pore filling effects by MICP treatment. Through this method, a series of MICP-treated calcareous sand samples subjected to uniaxial compression were simulated. The effects of calcite content and its spatial non-uniformity on the compression behaviors of the bio-cemented calcareous sand samples were studied. The micromechanics in terms of crack propagation and distribution as obtained from DEM were investigated to elucidate the mechanism of the MICP treatment of calcareous sands.

The Impact of Calcium Chloride in Cementation Solution on Microbial Induced Calcite Precipitation: A Systematic Review

This review aims to quantify the impact of calcium chloride in cementation solutions on Microbial Induced Calcite Precipitation (MICP). Specific soil strength properties, such as the Unconfined Compressive Strength (UCS) test, permeability (k) and calcium carbonate content of the soil, form the basis of quantifying the test results. Relevant articles from various online databases such as Scopus, Science Direct, ProQuest Dissertations and Theses Global (PQDT), Mendeley and Google Scholar are obtained with search strings of suitable keywords. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) were used to screen and select related articles based on exclusion and inclusion characteristics. This review shows a positive correlation between calcium concentrations and soil strength properties, where higher concentrations of calcium solutions induce stronger bonding between soil particles due to better calcite precipitation. However, we also note a reversed correlation when the concentration of calcium solutions is higher than 1 M. This review also verifies that the MICP process enhances soil strength using optimum calcium chloride concentration to avoid soil brittleness. This result benefits other fields, such as agricultural and soil engineering.

Experimental Study on Cemented Tailings Backfill Based on Microbially Induced Calcite Precipitation

The backfill mining method is an effective method to control ground pressure and prevent surface subsidence in the process of underground resources exploitation. Tailings backfill not only relieves the pressure of tailings reservoir but also protects the environment. However, traditional Portland cement as the cementing material results in groundwater pollution. In addition, the production process of Portland cement consumes a significant amount of mineral resources and causes air pollution. Therefore, a cementation method for tailings based on microbially induced calcite precipitation (MICP) is proposed in this paper. Tailings cementation by the MICP technology with facultative anaerobic bacteria (Castellaniella denitrificans) can overcome the problems of MICP technology based on urea hydrolysis of aerobic bacteria (Sporosarcina pasteurii), which cannot be applied in anoxic or anaerobic environment. In addition, in view of the small amount and poor uniformity of calcium carbonate precipitation in the specimens cemented by facultative anaerobic bacteria alone, a mixture of facultative anaerobic bacteria and aerobic bacteria was adopted for tailings cementation in this study. The results showed that, with increasing Castellaniella denitrificans concentration, the cementation effect improved. The tailings sand was cemented into a compact specimen when the OD600 of the bacterial solution was one and the uniaxial compressive strength could reach 987.93 kPa. Compared to cementation induced by a single strain, the amount of calcite precipitation induced by the mixed bacteria increased from 2.54% to 3.59%, the uniaxial compressive strength was enhanced by 29.9%, and the shear strength increased by 24.4%. This study indicates that MICP technology with facultative anaerobic bacteria has great potential in tailings cementation, and it can provide a solution to replace cement as the cementing material for tailings.

Experimental Study on the Mechanical Behaviors of Aeolian Sand Treated by Microbially Induced Calcite Precipitation (MICP) and Basalt Fiber Reinforcement (BFR).

Aeolian sand flow is a major cause of land desertification, and it is prone to developing into a dust storm coupled with strong wind and thermal instability. The microbially induced calcite precipitation (MICP) technique can significantly improve the strength and integrity of sandy soils, whereas it easily leads to brittle destruction. To effectively inhibit land desertification, a method coupled with MICP and basalt fiberreinforcement (BFR) was put forward to enhance the strength and toughness of aeolian sand. Based on a permeability test and an unconfined compressive strength (UCS) test, the effects of initial dry density (ρd), fiber length (FL), and fiber content (FC) on the characteristics of permeability, strength, and CaCO3 production were analyzed, and the consolidation mechanism of the MICP-BFR method was explored. The experiments indicated that the permeability coefficient of aeolian sand increased first, then decreased, and subsequently increased with the increase in FC, whereas it exhibited a tendency to decrease first and then increase with the increase in FL. The UCS increased with the increase in the initial dry density, while it increased first and then decreased with the increase in FL and FC. Furthermore, the UCS increased linearly with the increase in CaCO3 generation, and the maximum correlation coefficient reached 0.852. The CaCO3 crystals played the roles of providing bonding, filling, and anchoring effects, and the spatial mesh structure formed by the fibers acted as a bridge effect to enhance the strength and brittle damage of aeolian sand. The findings could supply a guideline for sand solidification in desert areas.

State-of-the-Art Review of Utilization of Microbial-Induced Calcite Precipitation for Improving Moisture-Dependent Properties of Unsaturated Soils

Unsaturated soil is a form of natural soil whose pores are filled by air and water. Different from saturated soil, the microstructure of unsaturated soil consists of three phases, namely, the solid phase (soil particle), vapor phase, and liquid phase. Due to the matric suction of soil pores, the hydraulic and mechanical behaviors of unsaturated soils present a significant dependence on the moisture condition, which usually results in a series of unpredictable risks, including foundation settlement, landslide, and dam collapse. Microbial-induced calcite precipitation (MICP) is a novel and environmentally friendly technology that can improve the water stability of unsaturated soft or expansive soils. This paper reviews the microscopic mechanisms of MICP and its effect on the mechanical properties of unsaturated soils. The MICP process is mainly affected by the concentration of calcium ions and urea, apart from the concentration of bacteria. The moisture-dependent properties were comparatively analyzed through mechanical models and influence factors on the experimental data among various unsaturated soils. It suggests that the variations in resilient modulus and permanent deformation are strongly related to the extent of MICP applied on unsaturated soils. Finally, the problems in the MICP application, environmental challenges, and further research directions are suggested.

Effects of Al2O3, SiO2 nanoparticles, and g-c3n4 nanosheets on biocement production from agricultural wastes

Environmental issues are brought up concerning the production of Portland cement. As a result, biocement serves as a reliable substitute for Portland cement in green construction projects. This study created a brand-new technique to create high-quality biocement from agricultural wastes. The technique is based on nanomaterials that improve and accelerate the "Microbially Induced Calcite Precipitation (MICP)" process, which improves the quality of the biocement produced. The mixture was further mixed with the addition of 5 mg/l of graphitic carbon nitride nanosheets (g-C3N4 NSs), alumina nanoparticles (Al2O3 NPs), or silica nanoparticles (SiO2 NPs). The cement: sand ratio was 1:3, the ash: cement ratio was 1:9, and water: cement ratio was 1:2. Cubes molds were prepared, and then cast and compacted. Subsequent de-molding, all specimens were cured in nutrient broth-urea (NBU) media until testing at 28 days. The medium was replenished at an interval of 7 days. The results show that the addition of 5 mg/l of g-C3N4 NSs with corncob ash delivered the highest “Compressive Strength” and the highest “Flexural Strength” of biocement mortar cubes of 18 and 7.6 megapascal (MPa), respectively; and an acceptable “Water Absorption” (5.42%) compared to all other treatments. This treatment delivered a “Compressive Strength”, “Flexural Strength”, and “Water Absorption” reduction of 1.67, 1.26, and 1.21 times the control (standard Portland cement). It was concluded that adding 5 mg/l of g-C3N4 NSs to the cementitious mixture enhances its properties, where the resulting biocement is a promising substitute for conventional Portland cement. Adding nanomaterials to cement reduces its permeability to ions, increasing its strength and durability. The use of these nanomaterials can enhance the performance of concrete infrastructures. The use of nanoparticles is an effective solution to reduce the environmental impact associated with concrete production.

Bio-Assisted Improvement of Shear Strength and Compressibility of Gold Tailings

Safe storage of mine tailings has challenged engineers as shown by numerous historical tailings dam failures. While the storing of tailings behind tailings dams is the most practical containment solution, poor mechanical characteristics (low strength and high compressibility) of these waste materials raises serious concerns regarding the stability of tailings dams. In this study, the microbially-induced calcite precipitation (MICP) technique is used to treat gold tailings. Accordingly, tailings were enriched with Sporosarcina pasteurii and flushed with different concentrations of cementation solution to find the CaCl2 amount that produces the highest shear strength in studied tailings. Their shear strength and compressibility were measured in direct shear and one-dimensional oedometer tests and compared with those of the untreated tailings. Results showed that the 50 mM CaCl2 cementation solution proved the most effective treatment solution with respect to MICP, reducing compressibility of tailings by about 300% when loaded up to 800 kPa and improving shear strength by 140%. X-Ray Diffraction (XRD) analysis and Scanning Electron Microscope (SEM) images of treated samples further illustrated the effects of MICP on the composition and structure of the tailings specimens.

Study on the Flexural Strength of Glass Fiber Reinforced M20 Grade Self-Compacting Bacterial Concrete

Aim: The goal of this research is to determine the effect of glass fibre on the flexural strength of M20 grade self-healing concrete utilising a unique approach called microbial induced calcite precipitation.. Materials and methods: For data collection, two groups of 18 samples each were produced. The first group is formed without the presence of glass fibre, whereas the second group is formed with the presence of glass fibre. Bacillus subtilis bacteria were cultured in the bioinformatics laboratory using a strain obtained from Hi media laboratories. Results: SPSS statistical software was used to analyse the data. The mean flexural strength of bacterial concrete without fibre was 7.944 N/ mm2, while Glass fibre reinforced concrete had a mean flexural strength of 8.666 N/mm2. The events had a significance of 0.00 (p<0.05). Conclusion: The flexural strength of glass fibre reinforced M20 grade self-healing concrete was higher than that of conventional M20 grade self-healing concrete prepared utilising a unique process of microbial induced calcite precipitation. The strength of Glass fibre reinforced M20 grade self-healing concrete increased by 9 percent.

Study on the tensile strength of plastic fiber reinforced M20 grade self-compacting bacterial concrete using a novel microbial technique Microbial induced calcite precipitation

Aim: The objective of this study is to quantify the influence of plastic fiber on the tensile strength of self-compacting concrete using a novel microbial technique Microbial induced calcite precipitation. Materials and Methods: There are 2 groups taken for the study and a total of 18 samples were prepared per group with Gpower (80%). Group-1 refers to the conventional self-healing concrete and group-2 refers to the plastic fiber reinforced self-compacting. concrete. The number of samples was calculated using clinical software by adopting the values from previously published research papers. The independent sample T-test has been carried out using SPSS software version 21 which shows a clear increment in the tensile strength of the fiber reinforced self-compacting concrete. Result: Tensile strength of plastic fiber reinforced self-compacting concrete increased by 3.73% when compared with the normal self-compacting concrete. The standard deviation of the tensile strength of plastic reinforced bacterial concrete was 0.28965. A significant difference between the two groups was observed with a p-value of 0.010 (p<0.05) Conclusion: From this experimental study it is concluded that the plastic fiber reinforced M20 grade self-healing concrete has greater tensile strength than the normal self-compacting concrete.

Self-repairing of shrinkage crack in mortar containing microencapsulated bacterial spores

The purpose of this research work was to evaluate the efficacy of microbially induced calcite precipitation (MICP) method in shrinkage crack repairing. Portland cement was combined with sand, bacterial spores, water, and nutrients to prepare self-healing composites. The microencapsulated bacterial spores were employed as an additive substance at ratios of 0%, 0.5%, and 1% by weight of cement. Specimens were kept in a climate-controlled room after casting to induce shrinkage crack. Crystalline phases formed in the specimen were identified using the X-ray diffraction (XRD) technique. The scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) method was used to investigate the morphology of precipitated calcite (CaCO3) crystals. Additionally, the specimen's permeability and compressive strength were also determined. When the bacterial spores were added to produce MICP procedure, the results demonstrated that it was successful in healing the shrinkage cracking. Within three days, the specimen with 1% spores could completely seal the shrinkage crack. According to the XRD patterns, the CaCO3 crystals appeared to promote the production of the calcite phase. Based on SEM/EDS investigation, the MICP process leads to concentrations of calcite crystal in certain regions, especially at the top surface of the crack. The 28-day compressive strength, on the other hand, decreased, owing to the addition of nutrients.

A discrete element simulation considering calcite crystal shape to investigate the mechanical behaviors of bio-cemented sands

Microbial-induced calcite precipitation (MICP) is an effective way to stabilize soils, but the microscopic mechanism is unclear. Discrete element method (DEM) models of the mechanical behaviors of bio-cemented sands offer a way to understand this process. This paper used DEM simulations considering calcite crystal shape to understand the microscopic behavior of MICP-cemented sands. Simulation results showed that macrocracks caused by biaxial tests are mainly caused by shear failure. Decreasing calcite content increases the number of high-amplitude acoustic emissions events. The magnitude of the contact force becomes more homogenous with increased calcite. Sand particles initially sustain the load, then calcite particles contribute more to the strong contact force chain. The calcite concentration also affects the magnitude and direction of anisotropy. The proposed DEM model demonstrates its potential to analyze the underlying mechanisms of MICP process.