The enzyme-induced calcium carbonate precipitation (EICP) method has been utilized for curing low-permeability clay by directly mixing the reaction solution with soil. The added reaction solution quantity is limited by the optimal water content, producing insufficient calcium carbonate. Herein, the high-activity urease and high-concentration cementation solution efficacy in treating dispersive soils was evaluated. Phase transitions and structural modifications in EICP-cured soils were investigated through oscillatory amplitude scanning. The soil gradation influence on the EICP treatment effectiveness was assessed. The fluidized EICP-cured soil cementation and rupture mechanisms were investigated by viscosity measurements, electron microscopy, and zeta potential evaluations. A 3 M cementation solution, coupled with 500g/L of soybean urease, significantly enhanced the soil shear resistance, increasing it by 339% to 1807%. The EICP-cured soil gradually transitioned from a fluid to a paste and eventually to a solid within 168 h. High-clay-particle-content soils exhibited pronounced increases in shear resistance after EICP treatment. Under dynamic loading, three shear crack types emerged in EICP-cured soils, emphasizing the importance of soybean protein viscosity and calcium carbonate crystal filling-bonding capability in enhancing soil structural stability. The fluid solidification effectiveness in treating fine-grained soils utilizing EICP was validated through erosion trenches in fluid-solidified check dams, validating its potential.

The modification of dispersive soils remains a prominent and challenging issue in the field of geotechnical engineering. Using lime, fly ash, and CaCl2 as benchmark materials, this study explores the potential of enzymeinduced calcite precipitation (EICP) technology to modify three kinds of dispersive soils. The modification effects of the four materials were systematically evaluated through crumb and pinhole tests. By linking the modification performance to curing time and material dosage, the study proposes a novel formula to compare the modification efficiency of the materials. To enhance practical applicability in engineering contexts, the study also investigates the impact of these materials on the mechanical properties of dispersive soils through unconfined compressive strength (UCS) tests. Furthermore, the modification mechanisms of the materials were compared using exchangeable sodium percentage (ESP) analysis, scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD). The results indicate that both EICP technology and lime exhibit superior modification effects, effectively enhancing the resistance to water erosion and the mechanical properties of dispersive soils. Compared to lime, EICP technology demonstrates higher modification efficiency and greater environmental sustainability. Notably, low-concentration EICP solutions can effectively modify all three kinds of dispersive soils tested in this study.

There is an increasing demand for innovative low-carbon alternatives to effectively improve soil properties to promote sustainability and achieve carbon neutrality. However, both the bio-carbonation of reactive magnesia cement (RMC) and enzymatically induced carbonate precipitation (EICP) had limitations, including inadequate strength and solidification inhomogeneity despite demonstrated effective for sand solidification. Therefore, the combination bio-carbonation of RMC and EICP was proposed to address their respective drawbacks. In addition to the combined treatment, other treatment methods (e.g., pure RMC hydration, bio-carbonation, and EICP) were also utilized to compare treatment effects under different treatment conditions (e.g., varying RMC contents, urea concentrations, and treatment cycles). Results showed that the combined treatment could effectively address the issue of insufficient precipitation resulting from low RMC concentrations or excessive CO2 levels, thereby both reducing the permeability of treated sand and enhancing its strength to improve the overall treatment efficacy. With one treatment cycle, the combined treated sample with 20 % RMC and 3 M urea concentration exhibited a higher strength, while the sample with 15 % RMC had better solidification effects after two treatment cycles. Compared to the bio-carbonation treatment, the combined treatment resulted in higher proportions of artinite, while obtaining lower proportions of nesquehonite, demonstrating an influence of calcium addition on the mineralogy of magnesium precipitates. The combined treatment can achieve both strength enhancement and homogenization of solidification as a low-carbon and highly efficient solidification method, showcasing significant application potential in geotechnical engineering and material engineering fields.

Sandy soils are prone to engineering issues due to their high permeability and low cohesion in the natural environment. Therefore, eco-friendly reinforcement techniques are required for projects such as subgrade filling and soft soil foundation reinforcement to enhance their performance. This study proposes a synergistic reinforcement method that combines Enzyme-Induced Calcium Carbonate Precipitation with Glutinous rice slurry (G-EICP). The macroscopic mechanical properties and pore structure evolution of reinforced sand were systematically investigated through triaxial permeability tests, unconfined compressive strength (UCS) tests, and microstructural characterization based on Scanning Electron Microscope (SEM) and Micro- Computed Tomography (CT) tests. The results indicate that when the glutinous rice slurry volume ratio (VG) reaches 10%, the UCS of G-EICP-reinforced soil peaks at 449.2 kPa. The permeability coefficient decreases significantly with increasing relative density (Dr), VG, confining pressure (sigma 3), and seepage pressure (p). Microstructural analysis reveals that glutinous rice slurry may promote calcium carbonate crystal growth, potentially by providing nucleation sites, establishing a dual mechanism of skeleton enhancement and pore-throat clogging. The increased incorporation of glutinous rice slurry reduces the number of connected pores, lowers the coordination number, and elevates tortuosity, thereby inducing marked enhancements in both the strength and permeability of the treated soil compared to plain soil.

Bio-mediated ground improvement techniques, including Microbial Induced Calcite Precipitation (MICP) and Enzyme Induced Calcite Precipitation (EICP) treatment methods, are extensively being employed nowadays in a variety of construction projects as newly emerging sustainable and environmentally-friendly approaches to enhance the mechanical properties and durability characteristics of earthen composites. The intrinsic brittleness of MICP- and EICP-treated soils, however, considerably limits their applications in practical geotechnical engineering. Fiber reinforcement has been widely acknowledged as an efficient solution to overcome such challenges and augment the ductility of biologically stabilized soils. Accordingly, there is growing attention to integrating natural and synthetic fibers into bio-based composites, opening up exciting possibilities for improved performance and versatility in different civil engineering applications. This review aims to examine the current state of research on utilizing fiber additives to enhance the effectiveness of MICP and EICP treatment methods in an attempt to provide an in-depth insight into the effects of fiber type, content, and length as well as the underlying mechanisms of fiber interactions within the porous structure of such treated soils. The applications of fiberreinforced bio-cemented soils, their limitations, and the major challenges encountered in practice, as well as the potential areas of interest for future research and the key factors to be considered when selecting suitable fiber for optimal soil treatment using MICP/EICP, are all critically elaborated and discussed. By synthesizing the current research findings, the study provides engineers with a valuable resource to guide the development and optimization of fiber-reinforced MICP and EICP techniques for effective soil improvement and stabilization. Based on the findings of all relevant studies in the literature, a comprehensive cost-performance-balance analysis is conducted aiming to serve as a useful guideline for researchers and practitioners interested in applying fibers in various construction projects or other related applications where either MICP or EICP technique is being utilized as the main soil stabilization approach.

Municipal solid waste incineration bottom ash (MSWIBA) emerges as a potential alternative to natural aggregates due to its similar mineral composition and engineering properties as embanking fillings. However, the instability and environmental pollution risks of MSWIBA limit its large-scale application. This study proposes to employ Enzyme Induced Carbonate Precipitation (EICP) technology to enhance the mechanical properties of MSWIBA and reduce its environmental impact. Initial analyses focused on the basic physicochemical properties and morphological changes of MSWIBA before and after modification. Then the modified MSWIBA exhibited improvements in shear resistance, resilient modulus, and permanent deformation behavior. It was also found that existing resilient modulus and permanent deformation predicting models for soils are applicable to EICPmodified MSWIBA. The column leaching tests were conducted on samples subjected and not subjected to freeze-thaw and dry-wet cycles. The results revealed the modified MSWIBA released reduced heavy metal concentrations in both water and acid leaches. These findings establish a solid theoretical foundation for employing EICP-modified MSWIBA as an embankment fill material, highlighting the potential for wider adoption of this eco-friendly alternative in road constructions.

Enzyme-induced carbonate precipitation (EICP) is an appealing bio-cementation technology for soil improvement in geotechnical engineering. This study investigated the bio-reinforcement efficacy of sword bean crude urease (SWCU)-mediated EICP and the enhancement effect of various additives on it. A set of sand column specimens with different bio-cementation levels were prepared. Magnesium chloride, sucrose, xanthan gum, sisal fiber, calcite seeds, and skim milk powder were adopted for comparison. Bio-reinforcement efficacy was evaluated by mechanical properties. SWCU possessed a similar to 127% higher specific activity than entry-level commercial urease while saving over 2000 times the enzyme cost. All specimens treated with SWCU-mediated EICP presented excellent moldability and uniformity for one-time treatment. UCS increased exponentially with bio-cementation level due to the uniformly growing CaCO3 content and crystal size. UCS of similar to 1.8 MPa was achieved in a single treatment using 60 g/L SWCU and 3.0 M urea-CaCl2. SWCU exhibited a superior bio-reinforcement efficiency over soybean crude urease, commercial urease, and bacterial urease, since higher soil strength was achieved at lower CaCO3 content. Magnesium chloride showed the most significant enhancement effect, implying an extensive application prospect of SWCU-mediated EICP in seawater environments. The absence of wet strength, markedly elevated dry strength, and notably higher stiffness and hardness at low stress (load) phase indicated that xanthan gum would be more suitable for windbreak and sand fixation in arid/semi-arid environments. Sisal fiber could also effectively improve soil mechanical properties; however, the labor and time costs caused by its premixing with soil should be considered additionally in practical applications.

Enzyme-induced carbonate precipitation (EICP) has emerged as an environment-friendly solution for soil improvement. As a composite material, it is challenging to determine the micromechanical properties of EICP-reinforced sand using common macromechanical tests. In this work, a systematic study was conducted to determine the micromechanical properties of EICP-reinforced sand. The development of the micromechanical properties obtained from indentations along the route of sand particle-CaCO3-sand particle was examined. The width of the interfacial transition zone (ITZ) in EICP-reinforced sand was investigated. The effect of the reaction environment on ductility (i.e., the ratio of elastic modulus over hardness) of CaCO3 was investigated. The experimental results have identified that the width of ITZ in EICP-reinforced sand ranges from 0 to 180 mu m, which is significantly influenced by the crystal crystallinity or crystal morphology of CaCO3. The presence of porous media (i.e., sand particles) leads to the decrease in impurity content in the crystal formation environment, resulting in the lower ductility of CaCO3 accordingly. The mean value of fracture toughness of CaCO3 precipitation was identified to be the lowest one among sand particles, CaCO3 precipitation, and sand particles-CaCO3 interface. The lowest fracture toughness of CaCO3 indicating the failure of biocementation is derived from the CaCO3-CaCO3 breakage.

To enhance the improvement effect of Enzyme-Induced Carbonate Precipitation (EICP) technology more effectively, an abundant renewable resource-lignin-was introduced as an additive during the EICP modification process of silty clay. The mechanical properties of the improved soil specimens were analyzed from a macroscopic point of view by using unconsolidated undrained (UU) triaxial tests and unconfined compressive strength (UCS) tests to determine the optimal lignin content and curing time. The micro-mechanism of the improved soil specimens was elucidated from the microscopic point of view by combining scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The experimental results showed that lignin synergized with EICP could effectively improve the mechanical properties of the soil, and the mechanical properties of the co-consolidated soil specimens were better than those of the single consolidated and untreated soil specimens as a whole. The single EICP-consolidated soil specimen had undergone brittle damage; lignin could enhance the toughness of the soil and weaken its brittle characteristics. With the increase of lignin content, the mechanical indicators of co-consolidated soil specimens showed the trend of increasing and then decreasing, and reached the optimum at 0.75%. Moreover, the addition of lignin significantly increased the cohesive force, while the friction angle was less affected. With extended curing time, the mechanical indicators of the co-consolidated soil specimens increased overall, and tended to stabilize after 7 days of curing, hence selecting 7 days as the optimal curing time. From the microscopic point of view, lignin provides nucleation sites for the calcium carbonate precipitates generated by EICP, and the joint action of the two can fill the soil pores and cement the soil particles, thereby improving the overall strength of the soil. The results of the study can provide a theoretical basis and practical reference for the construction of foundation projects in silty clay areas.

Biocementation is an emerging field within geotechnical engineering that focuses on harnessing microbiological activity to enhance the mechanical properties and behavior of rocks. It often relies on microbial-induced carbonate precipitation (MICP) or enzyme-induced carbonate precipitation (EICP) which utilizes biomineralization by promoting the generation of calcium carbonate (CaCO3) within the pores of geomaterials (rock and soil). However, there is still a lack of knowledge about the effect of porosity and bedding on biocementation in rocks from a mechanistic view. This experimental study investigated the impact of porosity and bedding orientations on the mechanical response of rocks due to biocementations, using two distinct biocementation strategies (MICP and EICP) and characteristically low porosity but interbedded rocks (shale) and more porous but non-bedded (dolostone) rocks. We first conducted biocementation treatments (MICP and EICP) of rock samples over a distinct period and temperature. Subsequently, the rock strength (uniaxial compressive strength, UCS) was measured. Finally, we analyzed the preand post-treatment changes in the rock samples to better understand the effect of MICP and EICP biocementations on the mechanical response of the rock samples. The results indicate that biocementations in dolostones can improve the rock mechanical integrity (EICP: +58% UCS; MICP: +25% UCS). In shales, biocementations can either slightly improve (EICP: +1% UCS) or weaken the rock mechanical integrity (MICP: -39% UCS). Further, results suggest that the major controlling mechanisms of biogeomechanical alterations due to MICP and EICP in rocks can be attributed to the inherent porosity, biocementation type, and bedding orientations, and in few cases the mechanisms can be swelling, osmotic suction, or pore pressurization. The findings in this study provide novel insights into the mechanical responses of rocks due to MICP and EICP biocementations.