Cementations bind sand/soil particles via physical and chemical interactions to form composite solids with macroscopic mechanical properties. While conventional cementation processes (e.g., silicate cement production, phosphate adhesive synthesis, and lime calcination) remain energy-intensive, bio-cementation based on ureolytic microbially induced carbonate precipitation (UMICP) has emerged as an environmentally sustainable alternative. This microbial-mediated approach demonstrates comparable engineering performance to traditional methods while significantly reducing carbon footprint, positioning it as a promising green technology for construction applications. Nevertheless, three critical challenges hinder its practical implementation: (1) suboptimal cementation efficiency, (2) uneven particle consolidation, and (3) ammonia byproduct emissions during ureolysis. To address these limitations, strategic intervention in the UMICP process through polymer integration has shown particular promise. This review systematically examines polymer-assisted UMICP (P-UMICP) technology, focusing on three key enhancement mechanisms: First, functional polymers boost microbial mineralization efficacy through multifunctional roles, namely microbial encapsulation for improved survivability, calcium carbonate nucleation site provision, and intercrystalline bonding via nanoscale mortar effects. Second, polymeric matrices enable homogeneous microbial distribution within cementitious media, facilitating uniform bio-consolidation throughout treated specimens. Third, selected polymer architectures demonstrate ammonium adsorption capabilities through ion-exchange mechanisms, effectively mitigating ammonia volatilization during urea hydrolysis. Current applications of P-UMICP span diverse engineering domains, including but not limited to crack repair, bio-brick fabrication, recycled brick aggregates utilization, soil stabilization, and coastal erosion protection. The synergistic combination of microbial cementation with polymeric materials overcomes the inherent limitations of pure UMICP systems and opens new possibilities for developing next-generation sustainable construction materials.

Bio-cement is a green and energy-saving building material, which has received wide attention in the field of ecological environment and geotechnical engineering in recent years. The aim of this study is to investigate the improvement effect of plant-based bio-cement (PBBC) in synergistic treatment of sand with organic materials, to highlight the effective use of tap water in PBBC, and to analyze the crack evolution pattern during the damage of specimens by using image processing techniques. The results showed that tap water can be used as a solvent for PBBC instead of deionized water. The characteristic trend of urease solutions prepared at different temperature environments was obvious, and the activity value of urease solution with low concentration is positively correlated with the ambient temperature, although the activity value is not high, it is not easy to inactivate. The incorporation of organic materials increased the peak stress up to 1809.30 kPa compared to the specimens modified only by PBBC. The damage of the specimens under uniaxial compression consisted of four stages: compaction, elastic deformation, pre-peak brittle damage and post-peak macroscopic damage. The corresponding crack evolution is the interpenetration of small-sized cracks into large-sized main cracks. The large-sized main cracks transform into penetration cracks before damage, and the small-sized cracks are distributed around the penetration cracks. The crack evolution parameters obtained by MATLAB processing are positively correlated with the strain.

Soil improvement is one of the most important issues in geotechnical engineering practice. The wide application of traditional improvement techniques (cement/chemical materials) are limited due to damage ecological environment and intensify carbon emissions. However, the use of microbially induced calcium carbonate precipitation (MICP) to obtain bio-cement is a novel technique with the potential to induce soil stability, providing a low-carbon, environment-friendly, and sustainable integrated solution for some geotechnical engineering problems in the environment. This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy. It systematically summarizes and overviews the mineralization mechanism, influencing factors, improved methods, engineering characteristics, and current field application status of the MICP. Additionally, it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement. This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand. Furthermore, we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future. The current review purports to provide insights for engineers and interdisciplinary researchers, and guidance for future engineering applications.

Background This study investigated the effect of B. Subtilis bacteria on the properties of cement mortar. This was done by using soil samples from Sharkia, Egypt, to isolate 48 bacterial strains, after which they were cultured using the Johnson method and various media. Bacteria were then added to the cement mortar in amounts of 5% and 10% by weight to evaluate their effect on the mechanical and chemical properties of the modified mortar. Results The study examined the compressive and flexural strength of the modified mortar over time, as well as its microscopic properties and chemical composition after 28 days. The results indicated that bacterial additions of 5% and 10% increased the compressive strength of the mortar after 28 and 56 days compared to the control. A 5% bacteria concentration resulted in significant improvements in strength, showing the best concentration for increasing mortar strength. The addition of 5% bacteria significantly enhanced the early flexure strength, while the 10% showed superior long-term strength after 56 days. Scanning electron microscopy (SEM) revealed high CaCO3 deposits in the bacterial samples, indicating microbial-induced calcite precipitation that filled the small cracks and increased strength. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of hydroxyl, carbonate, and silicate groups, with bacterial samples having a higher carbonate content, indicating an increase in calcium carbonate formation and microstructure. Conclusions The ideal bacterial concentration was 5% as it improved the compressive and flexural strength while also promoting a more flexible microstructure. This study supports the employment of microorganisms in the production of more durable and environmentally friendly building materials, enhancing the sustainability of building practices.

The microbial-induced calcite precipitation (MICP) technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils. However, the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions. Furthermore, the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented. Moreover, the effect of wetting-drying (WD) cycles on the cyclic characteristics of MICP-treated sand is not readily available, which may contribute to the limited adoption of MICP treatment in field applications. In this study, strain-controlled consolidated undrained (CU) cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains: Sporosarcina pasteurii and Bacillus subtilis. The treatment durations of 7 d and 14 d were considered, with an interval of 12 h between treatments. The cyclic characteristics, such as the shear modulus and damping ratio, of the MICP-treated sand with the different bacterial strains have been estimated and compared. Furthermore, the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5-15 cycles and aging of samples up to three months. The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand, considering the influence of different bacterial strains, treatment duration, and WD cycles. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This study investigates the efficacy of microbial-induced carbonate precipitation (MICP) on the mechanical properties of poorly graded sand through a set of laboratory experiments. Unconfined compressive strength (UCS), ultrasonic pulse velocity, scanning electron microscopy, and calcium carbonate assessments were conducted to evaluate the influence of MICP under varying cementation concentrations, cementation ratios, and injection cycles. To this end, treated samples underwent 3, 14, and 21 injection cycles with cementation ratios ranging from 10 to 90% and molarities of 0.25, 0.5, 0.75, and 1 mol/L. Optimally stabilized samples were then subjected to 2, 4, 6, 8, 10, and 12 freeze-thaw cycles to evaluate their thermal durability. Correlation relationships were also developed to predict the compressive strength and stiffness of MICP-treated sand. Results demonstrated that MICP treatment effectively enhanced the UCS and stiffness by forming interlocking zones between the sand particles. Accordingly, the maximum UCS, secant stiffness, and constrained modulus were achieved at 14.98% calcite content using Sporosarcina pasteurii bacteria accompanied by a 50% cementation ratio and molarity of 0.75 mol/L over 21 injection cycles. Also, optimally stabilized specimens exhibited 70% and 90% retention in USC and stiffness after 12 freeze-thaw cycles, confirming their sustainability under harsh thermal conditions.

Microbially Induced Calcite Precipitation (MICP) is an eco-friendly method for improving sandy soils, relying on micro-organisms that require nitrogen and essential nutrients to induce carbonate mineral precipitation. Given the substantial annual generation of chicken manure (CM) and the associated challenges in its disposal resulting in environmental pollution, the nutrient-rich composted form of this waste material is proposed in this study as a supplementary additive (along with more costly industrial reagents, e.g., urea) to provide the necessary carbon and nitrogen for the MICP process. To this end, different CM contents (5 %, 10 %, and 15 %) along with various concentrations of cementation solution (1 M, 1.5 M, and 2 M) are employed in multiple improvement cycles to augment the efficiency of the MICP technique. Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), and Water Absorption (WA) tests are performed to assess the mechanical properties of the samples before and after exposure to freeze-thaw (F-T) cycles, while SEM, XRD, and FTIR analyses are carried out to delineate the formation of calcite within the porous structure of MICP-CM-treated sands. The findings suggest that an optimum percentage of CM (10 %) in the MICP process not only contributes to environmental conservation but also significantly enhances all the mechanical properties of bio-cemented sandy soils due to markedly improved bonding within their porous fabric. The results also show that although prolonged exposure to consecutive F-T cycles causes a reduction in strength and stiffness of enhanced MICP-treated soils, the mechanical properties of such geo-composites still remain within an acceptable range for optimal CM-enhanced biocemented mixtures, significantly superior to those of MICP-treated sands.

Researchers have explored various materials and methods to improve the strength and stabilization of peat soil for construction. Deep peat soil's significant compressibility, low bearing capacity, and high creep potential present major challenges in geotechnical engineering. In this paper, the unconfined compression strength (UCS) and oedometer testing were conducted to determine peat strength and compressibility behavior after being stabilized with a bio-cement called vege-grout, derived from fermented vegetable waste. Soil stabilized with 5 %, 10 %, 15%, 20%, and 25% vege grout was cured for up to 8 weeks before undergoing UCS testing. The finding showed that, in between 4 and 6 weeks of the curing period, the UCS of the peat stabilized with vege-grout exhibiting substantial mechanical strength at all vege-grout inclusion levels. The results showed optimum strength improvements, with a 449 % increase in UCS at 15 % vege-grout after 8 weeks. At the optimal percentage, vege grout's cementitious properties bind peat particles, densify the matrix, and enhance soil strength and load-bearing capacity. The coefficient of consolidation (Cv) also improved, reducing settlement from 23.34 +/- 7.8 m2/year to 7.13 +/- 3.5 m2 per year over increasing effective stress. The significant improvement in strength and compressibility of peat after treatment with 15 % vege grout demonstrates the effectiveness of vege grout as a peat stabilizer and highlights its potential as an alternative to chemical stabilizers for foundation applications.

In the present study, the undrained cyclic behaviour of biotreated sands using microbial and enzyme-induced carbonate precipitation was investigated for a wide range of initial void ratio after consolidation (e0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$e_{0}$$\end{document}), initial effective normal stress (sigma N0 '\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma{\prime }_{{{\text{N}}_{0} }}$$\end{document}) and calcium carbonate content (CC) under direct simple shear (DSS) testing conditions. The critical state soil mechanics framework for untreated sand was first established using a series of drained and undrained (constant volume) tests, which served as a benchmark for evaluating the undrained cyclic liquefaction behaviour of untreated and biotreated sands. The results indicated that the modified initial state parameter (psi m0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\psi_{{{\text{m}}_{{0}} }}$$\end{document}) in DSS condition showed a good correlation with instability states and phase transformation under monotonic shearing. In undrained cyclic DSS loading condition, samples displayed cyclic mobility indicated by an abrupt accumulation of large strain or sigma N0 '\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma{\prime }_{{N_{0} }}$$\end{document} transiently reaching zero or a sudden build-up of excess pore water pressure. The linkage between static and cyclic liquefaction was established for untreated and biotreated sand specimens based on the equivalence of characteristic soil states. The number of cycles before liquefaction (NL) for the biotreated sand specimens was mainly controlled by the cyclic stress ratio, e0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$e_{0}$$\end{document}, sigma N0 '\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma{\prime }_{{{\text{N}}_{{0}} }}$$\end{document} and CC. For a similar initial state prior to undrained cyclic loading, the biotreated specimens required a larger NL compared to the untreated sand. The cyclic resistance ratio at NL = 15 (CRR15) increased with decreasing psi m0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\psi_{{{\text{m}}_{{0}} }}$$\end{document} for the untreated sand, while the CRR15 for biotreated sand increased with increasing CC and decreasing sigma N0 '\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma{\prime }_{{N_{0} }}$$\end{document}.

Landslides are one of the most catastrophic natural disasters. These calamities that are often caused by heavy rainfall, rapid snowmelt, and human activities may cause significant damage to people and property in the affected regions. The risk of landslides can be eliminated by investigating the probable cause of failure in the specific slopes and then mitigating them with an appropriate stabilization technique. Even though the available methods of mitigating landslides are highly effective, they may need to be more sustainable in nature. In recent years, microbially induced calcite precipitation (MICP) has proved to be a sustainable measure for improving the stability of slopes and preventing landslides. However, the efficacy of this method, considering various circumstances, such as soil type, slope geometry, the effective area of cementation, the effect of long-term exposure to climatic conditions, is a matter of debate among various researchers. In the present study, the potential of MICP to stabilize a homogeneous slope has been investigated numerically. Various parametric studies depending on the slope geometry and the effective areas of cementation were carried out to assess the efficacy of MICP in mitigating landslides in the chosen homogeneous slope. Preliminary analysis results indicate that MICP can effectively reduce landslides even with significant variations in soil type and slope geometry. However, certain constraints must be appropriately identified and addressed while designing such slopes. Based on these extensive numerical investigations, design charts can also be provided to determine the suitable range of parameters for slope geometry and effective area of cementation for designing an adequate bio-cemented slope in mitigating landslides.