Search Results (58)

Microbially induced carbonate precipitation (MICP) is the precipitation of CaCO₃ crystals, induced by microbial metabolic activities such as ureolysis. Various applications of MICP have been proposed as innovative biocementation techniques. This study aimed to verify the feasibility of ureolysis-driven MICP applications in deep-subsurface environments (e.g., enhanced oil recovery and geological carbon sequestration). To this end, we screened sludge collected from a high-temperature anaerobic digester for facultatively anaerobic thermophilic bacteria possessing ureolytic activity. Then, we examined the ureolysis-driven MICP using a representative isolate, Bacillus haynesii strain SK1, under aerobic, anoxic, and strict anaerobic conditions at 30 °C, 40 °C, and 50 °C. All cultures showed ureolysis and the formation of insoluble precipitates. Fourier transform infrared spectroscopy analysis revealed precipitates comprising CaCO₃ at 30 °C, 40 °C, and 50 °C under aerobic conditions but only at 50 °C under anoxic and strict anaerobic conditions, suggesting efficient MICP at 50 °C. Interestingly, an X-ray diffraction analysis indicated that calcium carbonate crystals that were produced under aerobic conditions were in the form of calcite, while those that were produced under anoxic and strict anaerobic conditions at 50 °C were mostly in the form of vaterite. Thus, we demonstrated ureolysis-driven MICP under high-temperature and O₂-depletion conditions, suggesting the potential of MICP applications in deep-subsurface environments. Full article

Traditional soil stabilization methods, including cement and chemical grouting, are energy-intensive and environmentally harmful. Microbial-induced carbonate precipitation (MICP) technology offers a sustainable alternative by utilizing microorganisms to precipitate calcium carbonate, binding soil particles to improve mechanical properties. However, the application of MICP technology in soil stabilization still faces certain challenges. First, the mineralization efficiency of microorganisms needs to be improved to optimize the uniformity and stability of carbonate precipitation, thereby enhancing the effectiveness of soil stabilization. Second, MICP-treated soil generally exhibits high fracture brittleness, which may limit its practical engineering applications. Therefore, improving microbial mineralization efficiency and enhancing the ductility and overall integrity of stabilized soil remain key issues that need to be addressed for the broader application of MICP technology. This study addresses these challenges by optimizing microbial culture conditions and incorporating polyethylene fiber reinforcement. The experiments utilized sandy soil and polyethylene fibers, with Bacillus pasteurii as the microbial strain. The overall experimental process included microbial cultivation, specimen solidification, and performance testing. Optimization experiments for microbial culture conditions indicated that the optimal urea concentration was 0.5 mol/L and the optimal pH was 9, significantly enhancing microbial growth and urease activity, thereby improving calcium carbonate production efficiency. Specimens with different fiber contents (0% to 1%) were prepared using a stepwise intermittent grouting technique to form cylindrical samples. Performance test results indicated that at a fiber content of 0.6%, the unconfined compressive strength (UCS) increased by 80%, while at a fiber content of 0.4%, the permeability coefficient reached its minimum value (5.83 × 10⁻⁵ cm/s). Furthermore, microscopic analyses, including X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), revealed the synergistic effect between calcite precipitation and fiber reinforcement. The combined use of MICP and fiber reinforcement presents an eco-friendly and efficient strategy for soil stabilization, with significant potential for geotechnical engineering applications. Full article

Microbial-induced carbonate precipitation technology allows concrete to detect and diagnose cracks autonomously. However, the concrete’s compact structure and alkaline environment necessitate the adoption of a proper carrier material to safeguard microorganisms. In this study, various bacterial strains, including Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium, were immobilized in lightweight expanded clay aggregates (LECA) to investigate their effect on the self-healing performance, mechanical strength, and freeze–thaw durability. Self-healing concrete specimens were prepared using immobilized LECA, directly added bacterial spores, polyvinyl acetate (PVA) fibers, and air-entraining admixture (AEA). The pre-cracked prisms were monitored for 224 days to assess self-healing efficiency through ultrasonic pulse velocity (UPV) and surface crack analysis methods. A compressive strength restoration test was conducted by pre-loading the cube specimens with 60% of the failure load and re-testing them after 28 days for strength regain. Additionally, X-ray diffraction and scanning electron microscopy (SEM) were conducted to analyze the precipitate material. The findings revealed that self-healing efficiency improved with the biomineralization activity over the healing period demonstrated by the bacterial strains. Compression and flexural strengths decreased for the bacterial specimens attributed to porous LECA. However, restoration in compression strength and freeze–thaw durability significantly improved for the bacterial mixes compared to control and reference mixes. XRD and SEM analyses confirmed the formation of calcite as a self-healing precipitate. Overall, results indicated the superior performance of Bacillus megaterium followed by Bacillus sphaericus and Bacillus subtilis. The findings of the current study provide important insights for the construction industry, showcasing the potential of bacteria to mitigate the degradation of concrete structures and advocating for a sustainable solution that reduces reliance on manual repairs, especially in inaccessible areas of the structures. Full article

Soil erosion is a serious environmental problem that leads to land degradation and ecological imbalance, thereby eliciting extensive and profound worldwide concern. Biological soil crusts (biocrusts) play a crucial role in soil stabilization; however, the underlying microbial enzymatic mechanisms remain poorly understood. The present study aimed to characterize carbonatogenic bacteria and investigate the role of their carbonic anhydrase-induced carbonate crystals in promoting soil shear strength within biocrusts. The results demonstrated a significant increase in the activity of carbonic anhydrase during biocrust formation and development (p < 0.05). A total of 35 strains exhibiting carbonic anhydrase activity were isolated from biocrusts, belonging to Actinomycetota, Bacillota, Pseudomonadota and Cyanobacteriota. The subsequent investigation revealed a positive correlation between the carbonic anhydrase activities of the strains and the shear strength during sand consolidation. Specifically, strain SCSIO19859, a type of cyanophyta, exhibited the highest carbonic anhydrase activity, of 1.50 U/mL. It produced 0.70 g/day of calcium carbonate and demonstrated a shear strength that was 6.09 times greater than that of the control group after sand consolidation for seven days of incubation under optimal conditions. X-ray diffraction and scanning electron microscope analysis revealed that SCSIO19859 produced calcite and vaterite carbonates, which significantly increased the shear strength of the sand grains (p < 0.05). This study provides evidence for the ecological function of biocrusts in promoting soil erosion resistance from the perspective of carbonatogenic bacteria-derived carbonic anhydrase. The functional strains with carbonic anhydrase obtained from this study have significant potential applications in enhancing soil erosion resistance. Full article

Rough surfaces known as stylolites are common geological features that are developed by pressure solution, especially in carbonate rocks, where they are used as strain markers and as stress gauges. As applications are developing in various geological settings, questions arise regarding the uncertainties associated with quantitative estimates of paleostress using stylolite roughness. This contribution reports for the first time a measurement of the temperature at which pressure solution was active by applying clumped isotopes thermometry to calcite cement found in jogs linking the tips of the stylolites. This authigenic calcite formed as a redistribution of the surrounding dissolved material by the same dissolution processes that formed the extensive stylolite network. We compare the depth derived from these temperatures to the depth calculated from the vertical stress inversion of a bedding parallel stylolite population documented on a slab of the Calcare Massiccio formation (early Jurassic) formerly collected in the Umbria-Marches Arcuate Ridge (Northern Apennines, Italy). We further validate the coevality between the jog development and the pressure solution by simulating the stress field around the stylolite tip. Calcite clumped isotopes constrain crystallization to temperatures between 35 and 40 °C from a common fluid with a δ¹⁸O signature around −1.3‰ SMOW. Additional δ¹⁸O isotopes on numerous jogs allows the range of precipitation temperature to be extended to from 25 to 53 °C, corresponding to a depth range of 650 to 1900 m. This may be directly compared to the results of stylolite roughness inversion for stress, which predict a range of vertical stress from 14 to 46 MPa, corresponding to depths from 400 to 2000 m. The overall correlation between these two independent depth estimates suggests that sedimentary stylolites can reliably be used as a depth gauge, independently of the thermal gradient. Beyond the method validation, our study also reveals some mechanisms of pressure solution and the associated p,T conditions favouring their development in carbonates. Full article

Lime stabilization is a sustainable technique due to its use of local materials, increased durability, reduced maintenance, and improved resistance to water action. This paper examines the impact of lime stabilization on the mechanical, microscopic, and mineralogical properties of a tropical soil. Two types of lime, calcitic and dolomitic, were tested at 3% and 5% by weight. Compressive, indirect tensile and flexural test results and statistical analysis revealed that calcitic lime mixtures had higher strength and stiffness, whereas dolomitic lime mixtures exhibited greater deformability with higher tensile strain at break. Scanning electron microscopy indicated that the soil’s porous matrix closed within 7 days for both lime types due to flocculation, with increased matrix interlocking over time. The calcitic lime mixture developed a more closed matrix compared to the dolomitic lime, which showed weaker cementing. X-ray diffraction analysis indicated higher consumption of clay minerals and a notable reduction in calcium hydroxide peaks in the lime-treated soils. The study concludes that calcitic lime provides better pavement performance for stabilizing the soil, enhancing its engineering properties while also being sustainable by reducing the need for raw material extraction and improving resilience to climate-related issues such as floods. Full article

The brittleness index, as the most important parameter for brittleness evaluation, directly affects the compressibility of unconventional reservoirs. Currently, there is no unified calculation method for the brittleness index. This article uses a three-axis rock mechanics servo testing system to test the rock mechanics parameters of shale oil reservoirs in Block Y of the Ordos Basin and uses an X’Pert PRO X-ray diffractometer to test the rock mineral composition. The average volume fraction of quartz minerals, feldspar, and clay minerals in 36 samples of Block Y was tested to be 22.6%, 51.6%, and 18%, respectively. Calcite, dolomite, and pyrite are only present in a few samples. When the confining pressure is 30 MPa, the elastic modulus of the Chang 7 shale in this block is 14.72–34.58 GPa, with an average value of 23.77 GPa; The Poisson’s ratio ranges from 0.106 to 0.288, with an average of 0.182; The differential stress ranges from 100.8 to 260.1 MPa, with an average of 164.36 MPa; The peak strain ranges from 0.57 to 1.21, with an average of 0.91. This article compares several mainstream brittle index evaluation methods and identifies the most suitable brittle index evaluation method for Block Y. Using the Jarvie mineral composition method to calculate the brittleness index 1 (MBI), the average value of 36 experimental results is 0.5393. Using the Rickman normalized Young’s modulus and Poisson’s ratio average value to calculate the brittleness index 2 (EBI), the average value of 36 experimental results is 0.5204. Based on the stress-strain curve and energy method, a model for brittleness index 3 (DBI) is established, and the average value of 36 experimental results is 0.5306. The trend of the brittleness index calculated by the three methods is consistent, indicating the feasibility of the newly established brittleness evaluation method. From the perspectives of mineral composition, rock mechanics parameters, and energy, establishing a brittleness evaluation method for shale oil reservoirs and studying its evaluation method is of great significance for sweet spot prediction in reservoir engineering, providing theoretical support for the selection of fractured intervals in the Chang 7 shale oil reservoir in Block Y of the Ordos Basin. Full article

Microbial mineralization of calcium–magnesium carbonate has been a hot research topic in the fields of geomicrobiology and engineering geology in the past decades. However, the formation and phase transition mechanism of calcium–magnesium carbonate polymorphs at different Mg/Ca ratios still need to be explored. In this study, microbial induced carbonate mineralization experiments were carried out for 50 days in culture medium with Mg/Ca molar ratios of 0, 1.5, and 3 under the action of Curvibacter sp. HJ-1. The roles of bacteria and the Mg/Ca ratio on the mineral formation and phase transition were investigated. Experimental results show that (1) strain HJ-1 could induce vaterite, aragonite, and magnesium calcite formation in culture media with different Mg/Ca molar ratios. The increased stability of the metastable phase suggests that bacterial extracellular secretions and Mg²⁺ ions inhibit the carbonate phase-transition process. (2) The morphology of bacteriological carbonate minerals and the formation mechanism of spherical minerals were different in Mg-free and Mg-containing media. (3) The increased Mg/Ca ratio in the culture medium has an influence on the formation and transformation of calcium–magnesium carbonate by controlling the metabolism of Curvibacter sp. HJ-1 and the activity of bacterial secretion. Full article

In this investigation, coral sand is presented as a sustainable substitute for conventional river and machine-manufactured sand. This study comprehensively investigated the macro-scale strength, deformation, and permeability characteristics of coral sand, alongside analyzing the mechanical behavior, deformation, and permeability under various conditions and in relation to distinct particle characteristics. It revealed that coral sand primarily consists of biotite and high-Mg calcite, featuring abundant internal pore space. Its compressive properties resemble clayey soils, displaying minimal unloading rebound and predominant plastic deformation during compression. In direct shear tests, the stress–strain relationship follows an approximate hyperbola, with no pronounced strain softening. Describing particle fragmentation in the process proves challenging, making indicators like internal friction angle less applicable in engineering. Triaxial tests indicate a rapid initial bias stress increase, followed by a gradual decrease post-stress peak, suggesting a strain softening phenomenon. As surrounding pressure rises, the axial strain needed to reach peak strength also increases. The permeability coefficient of coral sand correlates linearly with pore ratio increase, represented by 10e. The complex interaction of multiple factors influences the strength, deformation, and permeability of coral sand blown fill mixes, with specimen porosity having the greatest impact. The design and construction of high-weight foundation elements in coral sand blown fill projects should consider porosity effects. Full article

The Badami Caves are a significant example of ancient Indian rock-cut architecture, dating back to the 6th century. These caves are situated in the Malaprabha River valley and are part of the candidate UNESCO World Heritage Site known as the “Evolution of Temple Architecture—Aihole-Badami-Pattadakal”, which is considered to be the cradle of temple architecture in India. Our study aimed to investigate the diversity, distribution, and biodeterioration phenomena of the fungal communities present on the cave surfaces. The study also conducted a comprehensive analysis of fungal biodeterioration on the cave carvings. Utilizing specialized techniques, the dissolution of calcite, alterations in pH levels, and biomineralization capabilities of isolated fungal strains were monitored. Additionally, this study analyzed fungal acid production using high-performance liquid chromatography (HPLC). Our findings revealed that the major genera of fungi found on the cave surfaces included Acremonium, Curvularia, Cladosporium, Penicillium, and Aspergillus. These isolated fungi were observed to produce acids, leading to the dissolution of calcium carbonate and subsequent decrease in pH values. Notably, the dominant genus responsible for acid production and the promotion of biomineralization was Aspergillus. These discoveries provide valuable insight into the ecology and functions of fungi inhabiting stone surfaces, contributing to our understanding of how to preserve and protect sculptures from biodeterioration. Full article

Microbial-induced calcite precipitation (MICP) is an innovative technology in civil engineering. However, the high cost of components and the fragility of the treated soil limit its wide use. One of the possible solutions is organic waste incorporation at different stages of the technology. In the present study, we consider the use of spent brewer’s yeast (BSY) to produce bacterial inoculates and wastepaper, flax shives and sawdust as reinforcing additives into the soil. We showed that the replacement of expensive components of LB medium by BSY extract increased biomass growth characteristics of Bacillus subtilis K51, B. cereus 4b and Micrococcus luteus 6 strains by 1.4, 1.5 and 1.8 times, respectively, while for B. subtilis 168, they were comparable to LB medium. The urease activities of all strains were not reduced compared to the control. Among the three kinds of cellulose-containing waste, wastepaper incorporation into MICP-treated soil samples led to an increase in compressive strength by 2.1 times and precipitated calcite percentage by almost 1.5 times compared to a sample without additives. Thus, we showed the potential for soil stabilization through MICP using organic waste. Full article

Coal and rock dynamic disasters such as rock burst and outburst seriously threaten the sustainable development of the coal mining industry, which are intimately correlated with the nonlinear dynamic response process of the deep coal and rock mass. This study conducts coal dynamic experiments under vibration load from room temperature to 60 °C by using the split Hopkinson bar (SHPB) with a temperature real-time control system and analyzes the variation in stress and strain and the energy dissipation characteristics of coal during the dynamic load process. The expression equation of dissipated energy of coal at different scales is established, and the judgment conditions of the macroscopic mechanical behavior of coal are analyzed theoretically. The stress curves show a multi-stress peak phenomenon when the coal samples are subjected to different temperatures and dynamic loads, and the coal’s dynamic stress and temperature show a polynomial fitting relationship at different stages. When the coal sample is subjected to temperature and dynamic load, the macroscopic changes in incident energy, reflected energy, and dissipated energy are consistent; that is, various energies gradually increase to a fixed value and tend to stabilize with the time of stress wave action. The transmission energy exhibits a rising trend in correlation with the duration of the dynamic load action, but the value is less than 0.1 J. The growth gradients of the different energies, in descending order, are: the growth gradient of incident energy, reflection energy, dissipation energy, and transmission energy. The energy inflection point appears at 60 °C. Based on the linear elastic fracture mechanics and damage mechanics theories, the expression for coal energy dissipation from the nanoscale to the microscale is established, and the relationship between energy dissipation and macroscopic mechanical behavior response of the coal samples is analyzed. The main physical components of the coal sample are calcite and kaolinite. Within the temperature range of 18–60 °C, the macroscopic failure form of the coal is horizontal tensile failure. The study results are introduced into dynamic disaster prevention and control and the surrounding rock system stability evaluation in deep mines. Full article

Microbially induced calcium carbonate precipitation (MICP) by the urease-producing bacteria has wide applications in the field of geology and environmental engineering. Compared to bacteria, fungi usually possess more tolerance to high salts and heavy metals, enabling MICP induced by the urease-producing fungi to be applied to harsh environments. In this study, the carbonate minerals, induced by the urease-producing fungi isolated from marine sediments, were investigated. One of the urease-producing fungi, designated as YPLJS-14, was identified with the high efficiency of precipitating calcium carbonate. The ITS sequence of YPLJS-14 revealed that it belongs to the genus of Cladosporium. The precipitates induced by this strain were characterized by XRD, SEM, TEM, SAED, and FTIR, respectively. The results show that the mineral phase of fungal precipitates is composed of calcite and vaterite. SEM, TEM, and SAED confirm that the minerals in rhombohedral morphology are calcite and the spherical minerals are vaterite. Thermogravimetric and derivative thermogravimetric (TG/DTG) analyses show that vaterite is a thermodynamically unstable mineral phase compared to calcite and easily decomposes at lower temperatures. These findings provide a foundation for understanding the mineralization mechanism of the urease-producing fungi and the potential applications in environmental engineering. Full article

Aeolian sand flow is identified as the main factor in the formation of sandstorms. However, conventional sand fixation methods cannot meet the current development requirements of environmental protection. In this paper, the method using Microbially Induced Calcite Precipitation (MICP) combined with basalt fiber reinforcement (BFR) was adopted to solidify the aeolian sand. Consolidated undrained triaxial shear tests were carried out to analyze the influence of fiber content, fiber length, confining pressure, and other factors on stress–strain characteristics, peak strength, brittleness index, and shear strength of aeolian sand. A shear strength model of aeolian sand solidification using MICP-BFR and considering the effect of fiber length and fiber content is established according to the test results. The results show that the peak strength of aeolian sand solidified by MICP-BFR is remarkably higher than that of aeolian sand solidified by MICP alone, and the peak strength rises with the increasing fiber length, fiber content, and confining pressure. The application of fiber can effectively reduce the brittleness index of aeolian sand solidified by MICP and improve the sample ductility. As fiber content and fiber length increase, the cohesion of solidified aeolian sand increases while the internal friction angle changes relatively little. In the limited range set by the test, the fiber length of 12 mm and the fiber content of 1.0% constitute the optimum reinforcement condition. The test results coincide with the model prediction results, indicating that the new model is fitting for predicting the shear strength of aeolian sand solidified by MICP-BFR. The research results provide an important reference value for guiding the practice of wind prevention and sand fixation in desert areas. Full article

Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H₂NCONH₂, C₆H₁₀CaO₆, CaCl₂, MgCl₂). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated. Full article