Microbial Induced Calcium Carbonate Precipitation (MICP), recognized as a low-carbon and environmentally sustainable consolidation technique, faces challenges related to inhomogeneous consolidation. To mitigate this issue, this study introduces activated carbon into uranium tailings. The porous structure and adsorption capacity of activated carbon enhance bacterial retention time, increase the solidification rate, and promote the growth and distribution of calcium carbonate, resulting in more uniform consolidation and improved mechanical properties of the tailings. Additionally, a novel independently developed grouting method significantly enhances the mechanical strength of the tailing sand samples. To perform a micro-scale analysis of the samples, distinct activated carbon-tailings DEM models are constructed based on varying activated carbon dosages. Physical experiments and parameter calibration are employed to investigate the micro-mechanical properties, such as velocity field and force chain distribution. Experimental and simulation results demonstrate that incorporating activated carbon increases the calcium carbonate production during the MICP process. As the activated carbon content increases, the peak stress of the tailings initially rises and then declines, reaching its maximum at 1.5 % activated carbon content. At 100 kPa confining pressure, the peak stress is 2976.91 kPa, 1.23-1.59 times that of samples without activated carbon and 6.08-7.86 times that of unconsolidated samples. Micro-scale motion analysis reveals that particle movement is predominantly axial at the ends and radial near the central axis. The initial direction of the primary force chains aligns with the loading direction. Following failure, some primary force chains dissipate, while new chains form, predominantly along the axial direction and secondarily in the horizontal direction. Compared with samples without activated carbon, those containing activated carbon exhibit more uniform force chain distribution, higher stress levels, and greater peak stress. This study offers a novel approach to enhance the stabilization and solidification efficiency of MICP and establishes a DEM model that provides valuable insights into the structural deformation and micro-mechanical characteristics of MICPcemented materials.

Numerous loess relic sites with cultural and historical values exist in the seasonally frozen ground region of Northwest China. Freeze-thaw action is an essential factor in inducing cracking and collapse of loess relic sites, and the creep behavior of loess also affects its long-term stability. Microbially induced calcium carbonate precipitation (MICP) technology has a promising application in earthen ruin reinforcement due to its environmental friendliness and good compatibility. To evaluate the feasibility of MICP technology for reinforcing loess relic sites in the seasonally frozen ground, triaxial compression tests, triaxial creep tests, and SEM tests were conducted on MICP modified loess after 0, 1, 3, 7, and 9 freeze-thaw cycles. Then, the changing laws of shear strength and creep properties of samples in the freeze-thaw conditions were analyzed. The results show that the MICP technology can enhance the mechanical properties and frost resistance of loess. The shear strength, cohesion, and long-term strength of MICP modified loess are enhanced by 27.8 %, 109 %, and 29.8 %, respectively, under 100 kPa confining pressure, and their reduction is smaller than that of the untreated loess after 9 freeze-thaw cycles; the internal friction angle fluctuates within 1 degrees. Finally, the reinforcement mechanism and freeze-thaw resistance mechanism of MICP technology were revealed. Microbially induced calcium carbonate can cement soil particles, fill interparticle pores, and inhibit the development of pores and cracks caused by freeze-thaw action. The results can provide a theoretical foundation and scientific basis for the long-term stability analysis of loess relic sites reinforced with MICP technology.

This study addresses the cracking issue of airport foundations in marine and coastal regions by proposing an unsaturated reinforcement method based on Microbially Induced Calcium Carbonate Precipitation (MICP) combined with coconut fibers. Composite sand columns incorporating coconut fiber and bioslurry were prepared, and the effects of fiber length and content on the mechanical properties of MICP-treated sand columns were investigated. Experimental results revealed that the addition of short fibers (1-5 mm) significantly improved the unconfined compressive strength and ductility of the MICP-treated sand columns. As the bioslurry content decreases in the sand columns, the enhancement effect of short fibers on the unconfined compressive strength becomes more pronounced, with fiber addition improving compressive strength by up to 98 %. However, the inclusion of medium fibers (5-10 mm) and long fibers (10-15 mm) negatively affected the mechanical properties of the sand columns. Microstructural analysis further confirmed the synergistic reinforcement effect of short fibers and calcium carbonate precipitation. Short fibers acted as bridges, forming additional contact points between sand particles, which facilitated calcium carbonate precipitation at critical contact points, thereby enhancing the overall stability and strength of the sand columns. This characteristic was more pronounced under unsaturated conditions. This study provides a feasible technical solution for the effective reinforcement of airport foundations and demonstrates potential in unsaturated reinforcement and improving the ductility of sandy soil foundations.

Recently, the biostimulation has received attention due to its sustained mineralization, environmental adaptability and lower cost. In the current study, a series of isotropic consolidated undrained triaxial shear (CU) tests were performed on biocemented soil treated through biostimulation approach to examine the effect of cementation levels on the undrained shear behaviors. The test results demonstrate that the biocementation generated by the biostimulation approach can improve the shear behaviors remarkably, with the observed changes in stress-strain relationship, pore water pressure, stress path, stiffness development, and strength parameters. The variations of the strength parameters, i.e., effective cohesion and effective critical state friction angle, with increasing cementation treatment cycles can be well fitted by an exponential function and a linear function, respectively, while the variation of the effective peak-state friction angle is relatively small. The increased shear strength, stiffness, effective cohesion, and strain softening phenomenon of biocemented soils are related to the densification, increased particle surface roughness, and raised interparticle bonding caused by biostimulation approach. The liquefaction index decreases with the increase in cementation treatment cycles, especially at lower initial mean effective stress (100 and 200 kPa), indicating that the biostimulation approach may be a viable method for anti-liquefaction of soil.

This study introduces a novel method for stabilising expansive subgrade soils by integrating microbially induced calcite precipitation (MICP) process with a synergistic combination of waste sugarcane bagasse and recycled polyester fibres. This innovative approach aims to enhance strength properties and reduce volume susceptibility. The study demonstrates increases in Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and California Bearing Ratio (CBR), while substantially decreasing linear shrinkage, swell strains and pressures, indicating improved soil stability. The study also investigates the microstructural and chemical transformations through SEM-EDS, FTIR, and DSC-TGA, further corroborated by 16S metagenomic sequencing to understand microbial dynamics. Optimal stabilisation results were obtained with 0.5% fibre content and a four-day mellowing period, enhancing soil structure and durability by calcite precipitation and leveraging the combined benefits of natural and synthetic fibres. These fibres strengthen the soil structure and facilitate calcite nucleation, ensuring lasting stability, particularly valuable for stabilising expansive subgrade soils.

Microbial-induced calcite precipitation (MICP) is an eco-friendly soil stabilization technology widely applied to the solidification of aeolian sand. To further enhance the effectiveness of MICP in cementing aeolian sand, this study introduced wheat straw powder (WSP) as a reinforcing material and conducted experimental research on WSP-enhanced microbial cemented aeolian sand. By combining macroscopic physical and mechanical tests with discrete element method (DEM) simulations, this study systematically investigated the mechanisms by which WSP enhances microbial cementation and the mesoscopic failure characteristics of the material. The results indicated that adding WSP significantly increased the calcium carbonate content, resulting in uniform calcite deposition and encapsulation of sand particles. This enhancement increased the compressive strength and deformation resistance of the cemented sand columns, with a notable increase in strain at failure. DEM simulations further revealed that as the calcium carbonate content increased, macroscopic cracks within the sand columns evolved from single to multiple pathways, eventually penetrating the entire sand column along the loading direction. The internal bonding failure process could be divided into compaction, expansion, and rapid growth stages. Additionally, the uniformity of particle bonding in WSP-reinforced sand columns significantly impacted their macroscopic mechanical behavior, with uneven interparticle bonding likely inducing microcrack accumulation, leading to severe fracture patterns. These findings provide valuable insights for optimizing microbial cementation techniques for aeolian sand.

The disposal of tailings in a safe and environmentally friendly manner has always been a challenging issue. The microbially induced carbonate precipitation (MICP) technique is used to stabilise tailings sands. MICP is an innovative soil stabilisation technology. However, its field application in tailings sands is limited due to the poor adaptability of non-native urease-producing bacteria (UPB) in different natural environments. In this study, the ultraviolet (UV) mutagenesis technology was used to improve the performance of indigenous UPB, sourced from a hot and humid area of China. Mechanical property tests and microscopic inspections were conducted to assess the feasibility and the effectiveness of the technology. The roles played by the UV-induced UPB in the processes of nucleation and crystal growth were revealed by scanning electron microscopy imaging. The impacts of elements contained in the tailings sands on the morphology of calcium carbonate crystals were studied with Raman spectroscopy and energy-dispersive X-ray spectroscopy. The precipitation pattern of calcium carbonate and the strength enhancement mechanism of bio-cemented tailings were analysed in detail. The stabilisation method of tailings sands described in this paper provides a new cost-effective approach to mitigating the environmental issues and safety risks associated with the storage of tailings.

The objective of the current study is to explore the effect of biostimulation treatment methods on the mechanical properties and microstructure characteristics of biocemented soil. Biostimulated microbially induced carbonate precipitation (MICP) is an eco-friendly and economical soil reinforcement measure. It relies on the stimulation of the urease-producing bacteria (UPB) in situ for the MICP process. Different biostimulation treatment methods involve different oxygen availability, stimulation solution content and distribution, and number of biostimulation treatments. There may be differences in the effect of UPB stimulation and biocementation when different biostimulation treatment methods are used. In this study, four biostimulation treatment methods, i.e., unsaturated single biostimulation treatment (USBT), unsaturated multiple biostimulation treatments (UMBT), saturated single biostimulation treatment (SSBT) and saturated-unsaturated-combined single biostimulation treatment (CSBT), were used to stimulate native UPB in soil columns, and then, the same cementation treatment was applied to the soil columns. Subsequently, the mechanical behavior and microstructural properties of the biocemented soil were investigated. The results indicated that the saturated single biostimulation treatment was more conducive to stimulating native UPB to induce CaCO3 precipitation. Samples subjected to the saturated single biostimulation treatment exhibited higher CaCO3 precipitation content (CCP), dry density, unconfined compressive strength (UCS) and lower permeability within the same cementation treatment cycle (NC). However, UCS was not only determined by CCP, but was also regulated by CaCO3 spatial distribution and precipitation pattern. This study could help guide the selection of biostimulation treatment methods.

This study comprehensively investigates the literature on using bacteria to confer self-repair abilities on concrete and mortar. Although crack-healing is the main objective, calcite-precipitating bacteria affect concrete's durability and mechanical properties. This article reviews the research on bacteria-based self-healing concrete and its developments from 1984 to 2023. This systematic review was developed by adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. R studio and Vosviewer were used to perform bibliometric analysis and visualization of the 295 documents by 874 authors affiliated with 97 sources acquired from Scopus (NY). It is vital to emphasise that the document selection was carried out by two impartial reviewers to prevent any bias. In addition to repairing cracks in the material, the data indicate that applying various self-healing bacteria improves concrete's mechanical and durability properties. A meta-analysis evaluated the summary effect size of the most cited articles. It was concluded with the statistical evidence from the meta-analysis that bacteria incorporated concrete, which shows self-healing efficiency of 5.07 and 7.29 times than that of control concrete.

Microbial induced carbonate precipitation (MICP) is a promising method for improving the performance of geotechnical engineering materials. However, there has been limited research on the creep characteristics of expansive soil treated with MICP. Therefore, this study investigated the improvement of consolidation creep characteristics of expansive soils using the MICP method through one-dimensional consolidation creep tests. The microstructure of the treated soil was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate that the MICP method effectively enhances the resistance of expansive soil to creep deformation. Compared to untreated expansive soil, the creep deformation of the treated soil decreased by 3.85%, 22.62%, and 18.40% for cementation solution contents of 50 mL, 100 mL, and 150 mL, respectively. Additionally, the creep curve of the improved expansive soil exhibits significant nonlinear characteristics. The creep process of the improved expansive soil can be divided into three stages: instantaneous deformation, decay creep, and stable creep. SEM images and XRD patterns reveal that the calcium carbonate precipitates generated during the MICP process can wrap, cement, and fill the voids between soil particles, which is the fundamental reason why the MICP method improves the deformation resistance of expansive soil. On the basis of the creep test results, a fractional-order creep model for MICP-treated expansive soil was established. Compared to traditional integer-order creep model, the fractional creep model can more accurately describe the entire process of consolidation creep of expansive soil improved by MICP method. The findings of this study provide a theoretical basis for analyzing the deformation of MICP-treated expansive soil under long-term loads.