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.

Desertification is a global environmental issue that significantly threatens ecosystem stability and vegetation restoration in arid regions. This study proposes a multiple treatment strategy combining Artemisia sphaerocephala Krasch. gum (ASKG) with Enzyme-Induced Carbonate Precipitation (EICP) to enhance wind erosion control and seed germination. The effects of this approach were evaluated through field experiments. The results showed that single EICP treatment improved soil water retention and surface strength. However, high-concentration EICP treatment (>= 0.2 mol/L Cementation Solution, CS) induced salt stress, which suppressed plant survival. In contrast, when low-concentration EICP (0.1 mol/L CS) was combined with ASKG, a stable crust formed, improving surface strength and crust thickness, while preventing damage to the crust during early plant growth. The addition of 1.0 g/L ASKG reduced wind erosion depth by 67%, increased average moisture content to 7.4%, and promoted better seed germination, showing strong ecological compatibility and long-term stability. Furthermore, the second EICP treatment optimized the soil pore structure by adding CaCO3 precipitates, which increased average moisture content to 10.6% and increased surface strength by 114.5%. Microstructural analysis revealed that ASKG formed film or mesh structure around CaCO3 crystals, enhancing soil wind erosion resistance and water retention. Overall, the findings suggest that the multiple treatment strategy of EICP combined with ASKG successfully overcomes the ecological limitations of traditional high-concentration EICP, providing a sustainable solution for wind erosion control and vegetation restoration in desert areas.

Microbially induced calcium carbonate precipitation (MICP) is an emerging ecofriendly microbial engineering technique that utilizes urease-producing microorganisms to enhance the mechanical properties of soils. Sporosarcina pasteurii (S. pasteurii) stands out among these microorganisms as an efficient urease producer. However, field trials often lead to less-than-optimal experimental outcomes due to the presence of native soil microbes. To evaluate the impact of indigenous microorganisms on the effectiveness of MICP at the site, bacteria isolated from natural soil, classified of on-site low-ureolysis and high-ureolysis bacteria (OSLUB and OSHUB, respectively), were combined with S. pasteurii to conduct MICP experiments both in microfluidic chips and sand columns. Analysis covered the bacterial population, urease activity, pH changes, calcium carbonate crystal count and volume, as well as the unconfined compressive strength (UCS) of reinforced samples. Experimental results revealed that combining OSLUB with S. pasteurii led to a reduction in bacterial activity of 74% to 84% by 120 h, resulting in an approximately 60% decrease in the chemical conversion rate and the UCS of MICP-treated soils was 60% lower than the S. pasteurii. However, when OSHUB is mixed with S. pasteurii, although there is a reduction in bacterial activity by 49% to 54% by the 120-h mark, the decrease remains less pronounced than the activity decrease observed in S. pasteurii alone, which is 64%. Consequently, the rates of calcium carbonate chemical conversion were enhanced by 9% to 45%, and the UCS of the reinforced sand columns showed a slight improvement relative to the control group. This research highlights the distinct impacts of OSLUB and OSHUB on the efficiency of MICP on location. The main difference between OSLUB and OSHUB lies in their respective effects on pH levels following mixing. OSLUB tends to decrease the pH level gradually in the combined bacterial environment, while OSHUB, in contrast, increases the pH level over time in the same setting. The maintenance of both high bacterial activity and high precipitation rates is crucially dependent on pH levels, highlighting the importance of these findings for enhancing MICP efficiency in field applications. Strategies that either diminish the presence of OSLUB while augmenting that of OSHUB, or that sustain a relatively high pH level, could be valuable. These avenues promise significant improvements and merit further investigation in future studies.

Microbial-induced calcium carbonate precipitation (MICP) has attracted much attention as a promising technology for soil improvement in the infrastructures of marine engineering. This paper introduces a novel numerical sample preparation technique for MICP-treated sand, with particular attention paid to the distribution patterns of calcium carbonate, including contact cementing, bridging, and grain coating. The effect of calcium carbonate content (CCC) on the deformation and failure mechanism is studied at macroscopic and granular scales. The findings show that a small amount of calcium carbonate can quickly increase the strength of sand. The strength improvement and deformation control of MICP technology are better than those of traditional compaction treatment. As the calcium carbonate content increases, the mechanical coordination number of the sand also increases, indicating a more stable microstructure of the sand phase. In the contact bonding mode, initial failure occurs as shear failure between sand and calcium carbonate. In the bridge mode, initial failure manifests as shear failure between calcium carbonate particles. In the coating mode, initial failure occurs as tensile failure between sand and calcium carbonate. Calcium carbonate contributes to a reduction in both sliding and rolling movements among sand particles.

Expansive soil poses significant challenges for civil engineers, leading to structural damage, particularly in lightly loaded structures. This study employs an innovative and sustainable recipe to stabilize highly expansive soil using the MicrobialInduced Calcium Carbonate Precipitation (MICP) technique by substituting conventional ingredients with olive mill wastewater and hydrated lime. A series of laboratory tests were performed to evaluate the improvement in Atterberg's limits, Free Swell, Unconfined Compressive Strength (UCS), and pH, in addition to a series of qualitative measurements, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Microscopic Images, and bacteria growth rate. Different mellowing periods and different cementation concentrations were used. The proposed recipe results showed a 50% reduction in the soil's free swell value. The UCS of the treated soil using the proposed recipe was eight times that of the untreated soil and twice that of the soil treated with the traditional recipe. The SEM images showed flocculation and aggregation in the soil particles, with the voids becoming smaller and filled with calcium carbonate (CaCO3). The XRD results showed the formation of new CaCO3 particles. The optimized recipe demonstrated remarkable enhancement improvement and significant changes in soil physical properties and microstructure.

Microbial-induced calcium carbonate precipitation (MICP) is an emerging in situ grouting technology for sand ground improvement, slope stability, and subgrade reinforcement, featuring rapid implementation and low energy consumption. The precipitated calcium carbonate crystals can rapidly fill and cement sand particles so as to form a new soil structure that effectively reduces liquefaction sensitivity and dynamic damage. The centrifuge shake table test is an effective method for simulating liquefaction of sandy soil layers under shear wave excitation. Many studies have been conducted on this topic in recent years. However, the study on dynamic response, especially the liquefaction resistance of MICP-cemented sands by centrifuge shake table tests, is rare. In order to investigate the cementation effect of microbial treatment, centrifuge shake table tests were performed on two models, i.e., untreated and MICP cemented sand model. The test results indicated that, compared with untreated sand model, the liquefaction resistance of the MICP model was significantly improved in terms of acceleration response, shear stiffness, stress-strain relationship, and ground surface settlement. This study contributes to a better understanding of the mechanical law in the liquefaction process and enriches the engineering application of microbial grouting treatment of sand foundation prone to liquefaction.