Induced Calcium Carbonate Research Articles

Application of microbially induced calcium carbonate precipitation (MICP) process in concrete self-healing and environmental restoration to facilitate carbon neutrality: a critical review.

Soil contamination, land desertification and concrete cracking can have significant adverse impacts on sustainable human economic and societal development. Cost-effective and environmentally friendly approaches are recommended to resolve these issues. Microbially induced carbonate precipitation (MICP) is an innovative, attractive and cost-effective in situ biotechnology with high potential for remediation of polluted or desertified soils/lands and cracked concrete and has attracted widespread attention in recent years. Accordingly, the principles of MICP technology and its applications in the remediation of heavy metal-contaminated and desertified soils and self-healing of concrete were reviewed in this study. The production of carbonate mineral precipitates during the MICP process can effectively reduce the mobility of heavy metals in soils, improve the cohesion of dispersed sands and realize self-healing of cracks in concrete. Moreover, CO2 can be fixed during MICP, which can facilitate carbon neutrality and contribute to global warming mitigation. Overall, MICP technology exhibits great promise in environmental restoration and construction engineering applications, despite some challenges remaining in its large-scale implementation, such as the substantial impacts of fluctuating environmental factors on microbial activity and MICP efficacy. Several methods, such as the use of natural materials or wastes as nutrient and calcium sources and isolation of bacterial strains with strong resistance to harsh environmental conditions, are employed to improve the remediation performance of MICP. However, more studies on the efficiency enhancement, mechanism exploration and field-scale applications of MICP are needed.

Micromorphology characterization of crystal calcium carbonate and exopolysaccharides quantification carbonatogenic bacterial LTP4-d isolated from historical painting of Maros-Pangkep karst area, Indonesia

Abstract. Zhafirah NA, Haedar N, Sentosa S, Gani F. 2024. Micromorphology characterization of crystal calcium carbonate and exopolysaccharides quantification carbonatogenic bacterial LTP4-d isolated from historical painting of Maros-Pangkep karst area, Indonesia. Biodiversitas 25: 2139-2147. Indonesia possesses the second-largest limestone/karst region globally, trailing only China. Among Indonesia’s limestone region, the Maros-Pangkep karst area in South Sulawesi stands out which obtained prehistoric rock art dating back at least 45.5 thousand years ago. However, over time, those paintings have begun to deteriorate due to many causes, one of which caused by overlayering of the deposition of calcium carbonate precipitates covering the surface of the paintings. This can occur due to the presence of microorganism with the ability to precipitate calcium carbonate on the surface of those paintings. Microorganism that have the ability to precipitate calcium carbonate are usually known as carbonatogenic bacteria or ureolytic bacteria. This study aimed to isolate the carbonatogenic bacteria and then assess how effectively it precipitates calcium carbonate, also to determine the production of EPS and characteristic micro-morfology of CaCO3 produced by carbonatogenic bacteria isolated from historical painting of Maros-Pangkep karst, Indonesia. Results showed that sixty bacterial isolates were successfully isolated from prehistoric paintings in Maros-Pangkep karst, which 24 isolates were confirmed as carbonatogenic bacteria. The highest amount of CaCO3 precipitate was recorded from LTP4-d isolates which able to precipitate 37.62±0.12 mgmL-1 calcium carbonate. The highest amounts of ammonia and EPS production were also from LTP4-d. The SEM results showed that CaCO3 precipitate from LTP4-d has a type of vaterite with element contents including C 0.32%; O 15.24%; Ca 84.53%. This study presents novel findings on the capability of carbonatogenic bacteria from prehistoric paintings in Maros-Pangkep karst to induce calcium carbonate precipitation which can be utilized as a reference for repairing and preserving prehistoric paintings found in the Maros-Pangkep karst area.

Comparison of calcium carbonate production by bacterial isolates from recycled aggregates.

The new technology of microbially induced calcium carbonate precipitation (MICP) has been applied in construction materials as a strategy to enhance their properties. In pursuit of solutions that are more localized and tailored to the study's target, this work focused on isolating and selecting bacteria capable of producing CaCO3 for posterior application in concrete aggregates. First, eleven bacterial isolates were obtained from aggregates and identified as genera Bacillus, Lysinibacillus, Exiguobacterium, and Micrococcus. Then, the strains were compared based on the quantity and nature of calcium carbonate they produced using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. Bacillus sp. dominated the cultured isolates and, along with Lysinibacillus sp., exhibited the highest CaCO3 conversion (up to 80%). On the other hand, Exiguobacterium and Micrococcus genera showed the poor ability to MICP (21.3 and 20.3%, respectively). Calcite and vaterite were the dominant carbonate polymorphs, with varying proportions. Concrete aggregates have proven to be a source of microorganisms capable of producing stable calcium carbonates with a high conversion rate. This indicates the feasibility of using microorganisms derived from local sources for application in construction materials as a sustainable way to enhance their characteristics.

Influence of precast microbial reinforcement on lateral responses of monopiles

Microbially Induced Calcium Carbonate Precipitation (MICP) provides an environmentally friendly solution for reinforcing large diameter monopiles for offshore wind turbines (OWTs). This study presents an investigation into the lateral responses of monopiles with precast microbial reinforcement using a low-pH one-phase method. Both static and cyclic loading tests were carried out. The results of static loading tests show that the failure mode of the bio-reinforced monopile was an overall overturn failure. The lateral bearing capacity was increased by 50% and the bending moment was reduced by about 25% with the bio-reinforcement. Further investigation was conducted on the secant stiffness, damping ratio, and accumulated deformation of the bio-reinforced monopile under various cyclic loadings. With the bio-reinforcement, the accumulated deformation under one-way cyclic loading can be reduced by 30%–60%. The influences of cyclic loading parameters and loading sequence on pile stiffness were clarified. The growth ratio of pile stiffness due to bio-reinforcement under one-way loading was between 1.65 and 2.82, and decreased with increasing load amplitude. The ratio was smaller under two-way loading. Three competing factors on pile stiffness were identified: cyclic compaction of the unreinforced sandy soil, weakening of the bio-reinforced soil and soil subsidence around the bio-reinforced soil.

Experimental Study on Enhancing the Mechanical Properties of Sandy Soil by Combining Microbial Mineralization Technology with Silty Soil.

Currently, coastal sandy soils face issues such as insufficient foundation strength, which has become one of the crucial factors constraining urban development. Geotechnical engineering, as a traditional discipline, breaks down disciplinary barriers, promotes interdisciplinary integration, and realizes the green ecological and low-carbon development of geotechnical engineering, which is highly important. Based on the "dual carbon" concept advocating a green and environmentally friendly lifestyle, Bacillus spores were utilized to induce calcium carbonate precipitation technology (MICP) to solidify coastal sandy soils, leveraging the rough-surface and low-permeability characteristics of silty soil. The mechanical-strength variations in the samples were explored through experiments, such as calcium carbonate generation rate tests, non-consolidated undrained triaxial shear tests, and scanning electron microscopy (SEM) experiments, to investigate the MICP solidification mechanism. The results indicate that by incorporating silty soil into sandy soil for MICP solidification, the calcium carbonate generation rates of the samples were significantly increased. With the increase in the silty-soil content, the enhancement range was 0.58-3.62%, with the maximum calcium carbonate generation rate occurring at a 5% content level. As the silty-soil content gradually increased from 1% to 5%, the peak deviator stress increased by 4.2-43.2%, enhancing the sample shear strength. Furthermore, the relationship between the internal-friction angle, cohesion, and shear strength further validates the enhancement of the shear strength. Silty soil plays roles in adsorption and physical filling during the MICP solidification process, reducing the inter-particle pores in sandy soil, increasing the compactness, providing adsorption sites, and enhancing the calcium carbonate generation rate, thereby improving the shear strength. The research findings can provide guidance for reinforcing poor coastal sandy-soil foundations in various regions.

β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24 h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions.

Elucidating deposition process of calcium carbonate and mechanical properties of precipitation via molecular dynamics simulation

Brittle cracking is a critical issue affecting the load bearing capacity and service life of concrete. Microbially induced calcium carbonate precipitation can heal concrete cracks, but the relation between its microscopic morphology and macroscopic mechanical properties remains poorly understood. This study employs molecular dynamics simulations to investigate the deposition processes of calcite and aragonite unit cells on calcium carbonate substrates. The deposition process of a single unit cell can be divided into two stages: collision rebound and adsorption. The deposited unit cells combine to form amorphous calcium carbonate. Local disordering of substrate upper-surface caused by unit cell collision reduces the tensile strength of the substrates, while the ductility of amorphous precipitations enhances its failure strain. The deposition velocity significantly impacts the mechanical properties of the precipitations. At higher temperature, greater molecular mobility enhances cohesive strength within the precipitations. Aqueous environments can weaken the collisional impacts of deposited unit cells on the substrate. Matching the substrate and deposited unit cell types facilitates ordered structures and strengthens precipitations. This work deepens the understanding of deposition process of calcium carbonate on the substrate and the mechanical properties of precipitations.

Influence of bacterial biomineralization conditions on the microstructural characteristics of cement mortar

Bacterial concrete is considered an effective self-healing material due to its capacity to repair damages such as cracks autonomously throughout microbially induced calcium carbonate precipitation (MICP). This study aimed to evaluate the direct incorporation of bacteria into mortar within the framework of concrete damage repairing technol-ogy. Sporosarcina pasteurii, a bacterium capable of surviving in alkaline conditions and inducing biomineralization by precipitating calcium carbonate, was selected for this purpose. Cement mortars with and without bacteria were prepared, and these samples were cured in different solutions to examine bacterial reactivity: a media solution for bacterial growth and calcium carbonate precipitation, a urea solution for calcium carbonate precipitation, and normal water. Mechanical properties and microstructural characteristics were investigated using various approaches. The out-comes revealed that the calcium carbonate precipitated by bacteria in cement mortar exhibited varying phases, such as calcite and vaterite, depending on the specific curing solutions employed. Particularly, the presence of properly precipitated calcium carbonate was found to significantly enhance the durability and mechanical properties of the cement mortar.

AN EXPERIMENTAL STUDY ON STABILIZING COHESIVE SOIL USING MICROBIALLY INDUCED CALCIUM CARBONATE PRECIPITATION

Bio-cementation is an environmentally friendly procedure grounded on microbial induced carbonate precipitation mechanism, occurring in environments abundant in calcium. In the effort to bolster soil stability, traditional urea is combined with bacteria to enhance the mechanical properties of soil. The research delves into the microbial mechanisms involved in microbially induced calcite precipitation, highlighting the role of urease-producing bacteria in facilitating calcium carbonate precipitation within the soil structure. This also entails pivotal laboratory and field experiments, evaluating the efficacy of microbially induced calcium carbonate in improving soil engineering characteristics, such as strength, permeability, and durability. Furthermore, this process can be employed across various soil types, offering adaptability in geotechnical applications. Additionally, we investigate the environmental consequences and sustainability aspects by underscoring its potential as an eco-friendly substitute for soil enhancement. Nonetheless, challenges such as optimizing bacterial activity, regulating the precipitation process, and ensuring even distribution of calcium carbonate within the soil necessitate further exploration. Based on the envisioned review, it contributes to the comprehension of MICP as a promising method for soil stabilization, providing insights for researchers, practitioners, and policymakers keen on sustainable and inventive approaches to geotechnical engineering. Key Words: Bio-geotechnical engineering, soil stabilization, Microbially induced calcium carbonate Precipitation, Soil improvement.

Microfluidic chips for microbially induced calcium carbonate precipitation: Advantages, challenges, and insights

Microbially induced calcium carbonate precipitation (MICP) has garnered significant attention as a biomineralization process with diverse applications spanning from construction to environmental remediation. To propel MICP research and deepen our comprehension of MICP mechanisms, microfluidic chips have emerged as potent tools offering precise control over environmental parameters and real-time observations. Herein, we explore the benefits and challenges associated with employing microfluidic chips as a platform for investigating MICP. The advantages of microfluidic chips lie in their capacity to create controlled microenvironments conducive to emulating specific conditions crucial for MICP. The high-throughput nature of these devices accelerates experimentation by facilitating simultaneous testing of various microbial strains and nutrient compositions. Throughout the MICP process, observations were made on the behaviors of both bacterial cells and CaCO3 cementation. The inherent reduction in reagent consumption offered by microfluidics is both cost-effective and environmentally friendly. However, scaling up from microscale findings to practical applications necessitates careful consideration. Fully replicating the three-dimensional complexity and heterogeneous structures of the soil matrix, which influence microbial behavior, mineral distribution, and overall precipitation dynamics, using microfluidic chips remains challenging. Additionally, certain environmental complexities, including macroscopic soil components such as organic matter and various particle types, which significantly affect microbial activities and mineral precipitation patterns, may be difficult to replicate in microfluidic setups. However, microfluidic chips stand as invaluable tools for advancing MICP research. By addressing the advantages and disadvantages outlined here, researchers can harness the capabilities of microfluidic systems to unravel the intricacies of MICP, ultimately bridging the gap between fundamental understanding and real-world applications.

Influence of biochar in the calcite precipitation of sandy soil using sporosarcina ureae

The microbially induced calcium carbonate precipitation (MICP) technology is an emerging novel and sustainable technique for soil stabilization and remediation. MICP, a microorganism-mediated biomineralization process, has attracted interest for its potential to enhance soil characteristics. The inclusion of biochar, a carbon-rich substance formed by biomass pyrolysis, adds another degree of intricacy to this process. The study highlights the impact of the combination of biochar and MICP together, using a bacterium, Sporosarcina ureae, on soil improvement. This blend of MICP and biochar improved the soil in terms of its geotechnical properties and also enabled the sequestering of carbon safely. It was observed that addition of 4% biochar significantly increased the soil's shear strength parameters (c and φ) as well as its stiffness after 21 treatment cycles. This improvement was because the calcium carbonate precipitate, which acts as a crucial binding agent, increased significantly due to microbial action in the soil-biochar mixture compared to the pure soil sample. The excess carbonate precipitation on account of biochar addition was verified through SEM-EDAX analysis where the images showed noteworthy carbonate precipitation on the surface of particles and increment in the calcium mass at the same treatment cycles when compared with untreated sand. The collaboration between MICP and biochar effectively increased the carbon sequestration within the sand sample. It was observed that at 21 cycles of treatment, the carbon storage within the sand sample increased by almost 3 times at 4% biochar compared to sand without any biochar. The statistical analysis further affirmed that strength depends on both biochar and the number of treatment cycles, whereas carbon sequestration potential is primarily influenced by the biochar content alone. This strategy, as a sustainable and environmentally friendly approach, has the potential to reform soil improvement practices and contribute to both soil strength enhancement and climate change mitigation, supporting the maintenance of ecological balance.

The Application of Microbially Induced Calcium Carbonate Precipitation (MICP) Technology in Building Materials and its Contribution to Waste Resource Utilization

Abstract: In many countries around the world, waste generation has become an increasingly pressing issue, particularly in urban areas experiencing rapid population growth and industrialization. The volume of waste produced by human activities continues to rise, posing significant challenges to the environment, economy, and public health. Improper waste management can lead to air and water pollution, soil degradation, and the spread of diseases. Additionally, waste generation consumes substantial natural resources and energy, exacerbating resource depletion and contributing to greenhouse gas emissions.To address these challenges, sustainable waste management practices are essential to reduce waste generation and promote resource recovery and recycling. In this context, the development of innovative technologies, such as Microbially Induced Calcium Carbonate Precipitation (MICP) in building materials, offers an effective means of converting waste into valuable and sustainable applications. MICP is an environmentally friendly biogeochemical technique that employs microorganisms and chemical agents in biological processes to produce carbonate minerals, providing an energy-efficient, cost-effective, and sustainable solution to environmental and engineering challenges.Recent research indicates that waste streams can substitute for several MICP chemical components in microbial and cementitious agent growth media. MICP technology has been found not only to be effective in handling hazardous waste streams but also to be a cost-effective and sustainable solution applicable to various waste media. This comprehensive review aims to provide insights into the environmental advantages and engineering applications of MICP technology, with a particular focus on the potential contributions of waste streams. It also offers guidance for researchers on identifying and overcoming challenges associated with using waste streams for MICP technology applications.

Analysis of unconfined compressive strength and environmental impact of MICP-treated lead-zinc tailings sand instead of sand as embankment material

Tailings can be used as embankment materials instead of sand. However, they contain large amounts of heavy metal pollutants, which can lead to groundwater pollution. In this study, (lead-zinc) Pb-Zn tailings with five particle sizes and Sporosarcina pasteurii were used as test materials. Combined with the unconfined compressive strength (UCS) and leaching of heavy metal pollutants from Pb-Zn tailings, the feasibility of applying microbial induced carbonate precipitation (MICP)-treated Pb-Zn tailings to embankment materials was analysed from the perspective of strength and environmental performance. The results showed that the UCS and carbonate content of the specimens made of Pb-Zn tailings treated using MICP decreased with a decrease in the number of Pb-Zn tailing particles. The pH value of the leaching solution after MICP treatment of Pb-Zn tailings sand was stable at 7.83–8.03, and the fixation rate of metal ions was 90.28 %–100 %. FTIR, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy tests showed that after the Pb-Zn tailings with particle sizes less than 100 mesh were treated using MICP, the number of carbonate crystals, crystal uniformity, and crystal overlap on the surface of the sample were considerably higher than those of the tailings with particle sizes greater than 250 mesh. The compressive strength and environmental performance of Pb-Zn tailings with particle sizes less than 100 mesh treated using MICP are good, and they are more suitable for embankment materials.

Removal of cadmium through biomineralization using halophilic and ureolytic bacteria under saline conditions

Heavy metal pollution poses an immense challenge to humanity owing to its severe toxic effects on living beings. This study investigates the bioremediation potential of the urease-hydrolyzing and halophilic bacterium Bacillus paramycoides- MSR1 to reduce the toxicity of cadmium (Cd) in the environment under salt stress through microbially induced calcium carbonate precipitation (MICCP). The enzymatic activity of urease and calcium carbonate (CaCO3) precipitation was studied under different concentrations of salt stress (0%, 3.5%, 5%, 7.5%, 10%, 15%) and maximum urease activity of 735.7 U/ml was recorded at 5% salt stress. The urease activity and CaCO3 precipitation decreased with increasing Cd toxicity (0, 10, 20, 30, 40, 50, and 60 μM). The maximum concentration of Cd endured by bacteria was determined by IC50 value and the minimum inhibitory concentration of Cd was recorded as 9.86 μM under 5% stress. Atomic absorption spectroscopy results revealed that Cd removal was as high as 90.3% under 5% salt stress. Microstructural analysis through FE-SEM revealed the surface topography of carbonate crystals as rhombohedral, whereas EDS confirmed the presence of CaCO3 and Cd in the bio-precipitates. These results suggest that MICCP is a potential, environmentally safe, low-cost technique and an excellent alternative to conventional heavy metal removal strategies from the environment.

Microbially mediated rock fine fracture mineralization sealing: Evolution of flow channels and the resulting transmissivity reduction

The sealing of fine aperture fractures in geological repositories is an important consideration for long-term sealing integrity. Common grouting materials have some disadvantages, such as low sealing efficiency, environmental pollution, etc. Microbially induced calcium carbonate precipitation (MICP) has been proposed as a potential solution for sealing fine fractures. In this paper, the microbially mediated fine fracture mineralization sealing process was investigated by using a designed visual test device. The flow channel evolution and fracture transmissivity reduction during the sealing process were systematically monitored and analysed. Based on the experimental results, a sealing pattern of microbially mediated rock fracture mineralization was proposed. In addition, the influence of biomineralized floc particles formed by different bacterial concentrations on the critical sealing threshold of fracture was discussed. The results show that the sealing pattern can be divided into four stages: (a) flow channel formation; (b) preferred channel blocking; (c) finer channel blocking; (d) filtration zone formation. The four sealing stages correspond to different fracture transmissivity reduction trends, and the majority of transmissivity reduction occurs in stage III. However, the transmissivity decreases rapidly only after the preferred channels are blocked, which indicates that the critical threshold of sealing fracture is reached. The critical sealing threshold is mainly attributed to two factors: biomineralized floc particle size and fracture aperture. Larger floc particles and finer aperture are more likely to reach the critical sealing threshold, improving the sealing efficiency of fractures. It is crucial to further study the interaction between the biomineralized floc particle sizes and the fracture aperture at the critical sealing threshold to optimize the application of MICP-grouting in rock fine fractures.

The Effect of Bacteria-to-Calcium Ratio on Microbial-Induced Carbonate Precipitation (MICP) under Different Sequences of Calcium-Source Introduction.

To explore the effects of the introduction order of calcium sources and the bacteria-to-calcium ratio on the microbially induced calcium carbonate precipitation (MICP) product CaCO3 and to achieve the regulation of CaCO3 crystal morphology, the mineralisation products of MICP were compared after combining bacteria and calcium at ratios of 1/9, 2/9, 3/9, 4/9, 5/9, and 6/9. A bacterial solution was combined with a urea solution in two calcium addition modes: calcium-first and calcium-later modes. Finally, under the calcium-first addition method, the output of high-purity vaterite-type CaCO3 was achieved at bacteria-to-calcium ratios of 2/9 and 3/9; under the calcium-later addition method, the output of calcite-type CaCO3 could be stabilised, and the change in the bacteria-to-calcium ratio did not have much effect on its crystalline shape.

Influence of pore property and alkalinity on the bio-deposition treatment efficiency of recycled aggregates

Microbial induced calcium carbonate precipitation (MICP) technology has been successfully used to enhance the properties of recycled concrete aggregates. However, the complex source and varied physical and chemical properties of recycled aggregates may have influence on the modification efficiency since microbes are often sensitive to the surroundings. In this study, two representative types of recycled aggregates, recycled concrete aggregates (RCA) and recycled brick aggregates (RBA), were subjected to two kinds of MICP treatments, basic MICP treatment and sodium alginate (SA) aided MICP treatment. The absorption and desorption of bacteria in/on aggregates during MICP treatments were quantified. The physical and chemical properties of aggregates after the bio-treatments were tested, and the influence of alkalinity and pore structure of aggregates under various MICP treatment methods on treatment efficiency were detailed investigated. Results indicated that, when the aggregates were subjected to the basic MICP treatment, the treatment efficiency was more remarkable in RBA, because of its high porosity and moderate pH (around 8–9), which facilitated the absorption of bacteria in/on aggregates and urease activity respectively. While under SA-aided MICP treatment, the influence of pore structure and alkalinity of aggregates on the treatment efficiency was not significant compared with that under the basic MICP treatment, especially the mass of CaCO3 on the aggregates. The biogenic CaCO3 generated by SA-aided MICP treatment not only plugged micropores, but also distributed all over the entire surface of the aggregates, resulting in a sufficient repair of microcracks. Meanwhile, the surface repair may reduce the influence of pore structure and pH of aggregates on the precipitation process, thereby reducing the impact of varied physical and chemical properties of aggregates on the treatment efficiency, which was conducive to the widely unified application of SA-aided MICP treatment in the modification of recycled aggregate based on construction solid waste.

A Numerical Bio-Geotechnical Model of Pressure-Responsive Microbially Induced Calcium Carbonate Precipitation

The employment of Microbially Induced Calcium Carbonate Precipitation (MICP) is of increasing interest as a technique for environmentally sustainable soil stabilisation. Recent advancements in synthetic biology have allowed for the conception of a pressure-responsive MICP process, wherein bacteria are engineered to sense environmental loads, thereby offering the potential to stabilise specific soil regions selectively. In this study, a 2D smart bio-geotechnical model is proposed based on a pressure-responsive MICP system. Experimentally obtained pressure-responsive genes and hypothetical genes with different pressure responses were applied in the model and two soil profiles were evaluated. The resulting model bridges scales from gene expression within bacteria cells to geotechnical simulations. The results show that both strata and gene expression–pressure relationships have a significant influence on the distribution pattern of calcium carbonate precipitation within the soil matrix. Among the evaluated experimental genes, Gene A demonstrates the best performance in both of the two soil profiles due to the effective stabilisation in the centre area beneath the load, while Genes B and C are more effective in reinforcing peripheral regions. Furthermore, when the hypothetical genes are utilised, there is an increasing stabilisation area with a decreased threshold value. The results show that the technique can be used for soil reinforcement in specific areas.

Identification and extraction of cementation patterns in sand modified by MICP: New insights at the pore scale.

Microbially induced calcium carbonate precipitation (MICP) is an environmentally friendly technology that improves soil permeability resistance through biocementation. In this study, 2D microscopic analysis and 3D volume reconstruction were performed on river sand after 24 cycles of bio-treatment based on stacked images and computed tomography (CT) scanning data, respectively, to extract biocementation patterns between particles. Based on the mutual validation findings of the two techniques, three patterns in the biocemented sand were identified as G-C-G, G-C, and G-G. Specifically, 2D microscopic analysis showed that G-C-G featured multi-particle encapsulation and bridging, with a pore filling ratio of 81.2%; G-C was characterized by locally coated particle layers, with a pore filling ratio of 19.7%; and the G-G was marked by sporadic filling of interparticle pores, with a pore filling ratio of 11.7%. G-C-G had the best cementation effect and permeability resistance (effective sealing rate of 68.5%), whereas G-C (effective sealing rate of 2.4%) had a relatively minor contribution to pore-filling and flow sealing. 3D volume reconstruction showed that G-C-G had the highest pore filling rate, followed by G-G and G-C. The average filling ratios of area and volume for G-C-G were 83.979% and 77.257%, respectively; for G-G 20.360% and 23.600%; and for G-C 11.545% and 11.250%. The analysis of the representative element volume (REV) was conducted, and the feasibility and reliability of the micro-scale pattern extraction results were confirmed to guide the analysis of macro-scale characteristics. The exploration of the effectiveness of cementation patterns in fluid sealing provides valuable insights into effective biocementation at the pore scale of porous media, which may inspire future research.

The synergistic effect of microorganisms and multiple admixtures on improving the self-healing of cracks in biogenic mortar exposed to different marine environments

Existing research has inadequately addressed the synergistic effects of microorganisms and admixtures in promoting self-healing behavior and mechanisms of cracks in marine environments, including the atmospheric zone, tidal-splash zone, and submerged zone. This study primarily involved the incorporation of multiple admixtures and microorganisms into cement to prepare two types of biogenic mortars: Bacillus pasteurii-based mortar (BPM) and Bacillus subtilis-based mortar (BSM), with ordinary mortar (OM) serving as the control group. The mechanical properties, electrical flux, and pore structure of the mortars were investigated. Additionally, the self-healing behavior and mechanisms of cracks were studied under atmospheric, tidal-splash, and submerged conditions. The results indicate that with increasing curing age, the synergistic effect of admixtures and microorganisms continuously refined the pore structure of the specimens and enhanced their flexural strength, compressive strength, and resistance to chloride ion penetration. The atmospheric environment was found to be unfavorable for the self-healing of cracks in the specimens. However, in the submerged and tidal-splash zones, the combined action of microorganisms and admixtures led to more pronounced self-healing phenomena in the biogenic mortars compared to OM. Particularly, the self-healing effect of BSM cracks was more pronounced in the tidal-splash zone, with a 100% self-healing efficiency observed after 53 days. This was attributed to the ability of microorganisms in the tidal-splash zone to induce calcium carbonate precipitation on the surface of cracks in admixture-modified cementitious materials, thereby reducing the penetration of seawater, CO2, and O2 into the cracks, lowering the carbonation reaction of Ca(OH)2 crystals, and reducing the formation of brucite crystals inside the cracks, consequently enhancing the water permeability resistance of the specimens. These research findings hold significant engineering implications for improving the durability and service life of coastal self-healing concrete structures.