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-tiles are a biobased alternative to conventional tiles that utilise a promising technology called microbially induced calcium carbonate (CaCO3) precipitation (MICP). This technology has low energy requirements and also sequesters carbon. Bio-tiles have been made in previous work using a submersion method, however, the process required additives such as 0.3 M magnesium chloride to achieve bio-tiles that meet international standards. The current study aimed to improve the bio-tile strength properties with CaCO3 crystal seeding and a pumping method instead of the use of magnesium that also increases ionic strength. With this technique, cementation solution containing the required calcium and urea for the MICP reaction was pumped through a sealed mould in a series of programmed treatments. The highest concentration of ureolytic Sporosarcina pasteurii with an effective urease activity of 40 mmol NH4-N/L center dot min was found to be most beneficial to the breaking strength of the bio-tiles, as were the shortest retention times of 1 h between treatments. Seeding with CaCO3 crystals offered significant benefit to the MICP process. Pre-seeding of the geotextiles was explored and the mass of seeds initially present on the geotextiles was found to have a direct improvement on the breaking strength of 21-82 %, increasing with seed loading. The highest CaCO3 seed loading tested of 0.072 g seeds/cm2 geotextile resulted in bio-tiles with a breaking strength of 940 +/- 92 N and a modulus of rupture of 16.4 +/- 1.7 N/mm2, meeting international targets for

Contemporary reinforced concrete structures suffer from the drawback of developing micro-cracks during their service due to causes related to shrinkage and fatigue. This may compromise their technical and functional serviceability due to the possible reduction in durability which may lead to a decrease in load carrying capacity of the structure. In recent years, experimental studies on biomineralization or biocementation have shown a potential to address this issue. Biocementation is the process in which microorganisms induce the production of calcium carbonate which can improve self-healing capabilities by filling the micro-cracks and pores in the structures, similar to the traditional lime-based materials. The most used pathway of biocementation is urea hydrolysis, which is brought about by the urease enzyme secreted by ureolytic bacteria. Although there have been numerous laboratory-scale studies that have yielded positive results, the widespread adoption of this technology in practical applications is still hindered by a range of constraints. The information about the solutions to resolve these limitations is fragmented and dispersed throughout the literature. This review aims to compile state-of-the-art knowledge in one place. This article provides a detailed assessment of the challenges in the application of biocementation and suggests strategies to overcome the obstacles that hinder its use in construction projects.

In bio-calcification, microbes precipitate calcium carbonate (CaCO3), forming versatile solid substances that promotes eco-friendly materials and reduce carbon emissions. Marine bacteria can generate bio-cements to strengthen dikes and combat coastal erosion. However, the role of marine bacteria in generating bio-cements for enhancing coastal structures and combating erosion is not fully understood. This study investigates the potential of CaCO3 precipitating bacteria isolated from methane hydrate-bearing marine sediments. Five calcifying marine bacteria were isolated using Christensen's urea agar from marine sediments collected from Gawadar coastal, Pakistan. Bacterial strains induced CaCO3 precipitation producing urease enzymes. Strains were identified as Pseudomonas putida, Bacillus altitudinis, Vibrio sp., Bacillus sp., and Vibrio plantisponsor. Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and X-ray diffraction were applied for the identification and differentiation of calcite and vaterite precipitates. The growth of isolates and precipitation potential were observed optimum at 5% NaCl and pH 9.5-11. Bacillus altitudinis (ST4SD3) and Bacillus sp. (ST4SD1) produced more soluble Ca2+ (8532.53 mg/l and 7581.98 mg/l) as compare to other isolates at higher pH 10 and pH 11, favorable for CaCO3 precipitation. It is concluded that marine ureolytic bacteria possess significant potential for bio-cementation, which can stabilize methane hydrate-bearing sediments, improve soil properties, protect coastal regions from erosion, and crucial in the methane cycle, a greenhouse gas. We recommend further exploration of such bacteria's applications in marine construction and sediment stabilization to enhance the robustness and longevity of coastal infrastructures. Furthermore, such bacteria could also be beneficial in extracting gas from unconsolidated methane hydrates containing sediments.