Tufa, a loose and porous calcium carbonate deposit, is vulnerable to weathering, which can heighten the risk of geological hazards. This study investigated the potential of microbial-induced calcite precipitation (MICP) to stabilize weathered tufa by isolating urease-producing bacteria from Jiuzhaigou, Sichuan Province. Two strains with the highest urease activity, identified as Stenotrophomonas sp. (U1) and Lysinibacillus boronitolerans (U2), were selected for mixed cultures (Mc). The physiological characteristics and calcification capacity of the strains (U1, U2, and Mc), along with the mechanical properties of treated tufa columns (SCU-1, SCU-2, and SCM), were analyzed. The findings revealed that these strains effectively induced the formation of CaCO3. Mc demonstrated strong growth dynamics (OD600 = 3.9 +/- 0.1) and urease activity (865 +/- 17 U/ml), leading to enhanced CaCO3 production. Furthermore, MICP significantly improved the compressive and shear strength of the weathered tufa, with the SCM sample showing superior results compared to SCU-1 and SCU-2. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed that Mc produced a greater quantity of CaCO3 in the crystalline form of calcite. Overall, the results indicate that MICP represents a promising environmental protection technology that can effectively enhance the engineering properties of weathered tufa.

In this article, the mechanical properties and frost resistance of soil solidification rock (SSR) recycled coarse aggregate concrete (RCAC) prepared by using SSR as a total replacement for ordinary silicate cement were investigated, based on which bio-mineralisation was used to improve the properties of recycled aggregate (RCA) in SSR RCAC as a means of improving the performance of SSR RCAC. The results showed that the mineralisation modification by Bacillus pasteurii enhanced the apparent density of RCA by 3.5%, reduced the water absorption by 20.4% and decreased the crushing value by 17.6%. SSR RCAC prepared using mineralised RCA increased its compressive and flexural strengths by 91.2% and 33.3%, respectively, at the age of 28 days, and maintained 93.5% relative dynamic elastic modulus after 225FTCs, with a 100% enhancement in frost durability factor compared with the untreated group. Although the slow early hydration of SSR resulted in low initial concrete strength, the combination of biomineralisation enhanced the early compressive strength growth by about 140%. It increased the post-freeze-thaw compressive strength residual to 67%. The SSR RCAC proposed in this study provides a solution with both environmental benefits and engineering applicability for infrastructure such as roads and bridges in seasonal permafrost regions.

Microbial induced carbonate precipitation (MICP) is gaining recognition for enhancing the mechanical properties of construction materials. This study aims to explore the potential of using phosphogypsum (PG), a solid waste mainly composed of CaSO42H(2)O, as both a sufficient calcium source for MICP based bio-cement and an aggregate for mine backfill applications. First, the interaction between MICP bacteria and the PG was assessed by monitoring pH, electrical conductivity, and Ca2 + and SO42- levels. Results indicated that bacteria maintained robust urease activity in the PG environment, leading to CO32- production. These ions, combined with the Ca2+ naturally present in PG to form CaCO3 precipitation, which acted as a binding agent for PG backfill. Further testing of the bio-cemented PG backfill showed excellent fluidity which is suitable for efficient pipeline transportation in underground mining. After a 7-day curing period, the backfill exhibited an unconfined compressive strength (UCS) of 947 kPa, meeting the standards for mining backfill applications. Additionally, the environmental impact of the bio-cemented PG backfill was notable. Unlike traditional cement-based backfills with high pH levels (>11), the leachate from the bio-cemented PG backfill maintained a neutral pH (7.16), highlighting its eco-friendly nature. This positions the bio-cemented PG backfill as a sustainable solution for the construction and mining industries.

Concrete curing is a critical factor influencing its mechanical properties and durability. Traditional curing methods, such as water curing and plastic film curing, have significant limitations, including high water consumption and environmental pollution. This study introduces Microbial Induced Carbonate Precipitation (MICP) as an innovative, environmentally friendly curing method for ready-mixed concrete, addressing the urgent need for sustainable construction practices. The feasibility of MICP surface curing is investigated through comprehensive mechanical and durability tests, coupled with microscopic analyses to understand the underlying mechanisms. The results demonstrate that MICP curing substantially enhances concrete performance. Compared to traditional water curing, the samples cured using MICP have increased compressive strength and splitting tensile strength by up to 31.69% and 24.66%, respectively. Additionally, MICP surface curing significantly reduced capillary water absorption, electric flux, and chloride ion migration coefficient by 12.83%, 15.50%, and 17.36%, respectively. It is found that the optimal concentration of Ca2+ in the MICP solution initially improves concrete performance, which then diminishes at higher concentrations due to bacterial activity inhibition. Spraying the MICP solution at appropriate intervals and increasing the number of treatments further improved concrete properties by ensuring a more extensive and dense deposition of CaCO3. Microscopic analyses, including XRD, TG, and SEM-EDS, revealed that MICP surface curing leads to the formation of vaterite and calcite, which densely cover and fill microscopic cracks and pores, ensuring adequate hydration and simultaneously enhancing the concrete's mechanical and durability properties. This study concludes that MICP surface curing provides superior performance than traditional methods and offers a more sustainable and environmentally friendly curing method.

This study aimed to enhance the efficiency of microbial-induced carbonate precipitation (MICP) for reinforcing sandy soil by inspiring natural processes involving microbial-induced carbon cycling and carbonation. The experiment focused on enhancing MICP curing of sandy soil using carbonic anhydrase (CA), which significantly increases the reaction rate of CO2 hydration (10(8) times faster) and facilitates the rapid hydration of CO2 (produced by urease (UA) decomposition of urea) to form a substantial amount of carbonate. The effect of carbonic anhydrase on MICP-reinforced sandy soil and its underlying mechanism were systematically examined through a combination of macroscopic physical and mechanical tests and microfabrication tests. The results showed that: (1) CA significantly increases the production of cement during the microbial consolidation of sandy soils, and the optimum dose of carbonic anhydrase producing bacteria is reached at about 4%, which increases the production of cement by 105.3%, compared with conventional MICP. (2) The incorporation of CA improves the compressive strength and resistance of the cured body. In the range 0.25-4.00%, the unconfined compressive strength of the solidified soil sample increases with the increase of the CA bacteria content. The strength of the cured soil sample reaches 1.915 MPa when the content is 4%, which is 8.54 times the strength of the conventional MICP cured sample. (3) CA does not change the product of the MICP process, it is still calcite, but after adding CA, the grain size of the calcite is larger, the shape of the hexahedron is more standardised, and the mechanical properties are improved. (4) In the process of MICP, urease and CA co-precipitate calcium carbonate-cured sandy soil. CA can significantly accelerate the rate of urea-generated CO2 hydrate and form HCO3- and CO32-, providing more favourable conditions for mineralisation.

Microbial induced carbonate precipitation (MICP) has the potential to have less hazardous impacts on the environment compared with traditional reinforcement technologies. In this paper, the mechanical property and cementing mechanism of MICP-treated mortar (MTM) are studied, and the double-layer rigid soaking mold is invented to prepare high-strength MTM samples. The effects of the cementation solution concentration (CSC), the concentration ratio of urea to calcium chloride (CRUC), aggregate particle size, and soaking time on the mechanical properties of MTM are researched. The results show that the strength of the MTM sample increases first and then decreases with the increase of CSC. The mean UCS of MTM samples reaches the peak of 8.19 MPa when the CSC is 1.5 M. The strength performance of MTM samples is relatively better when the CRUC is 1. For MTM samples with graded particle size, the sample with the particle size of 0.4-0.8 mm has the highest strength of 5.03 MPa. For MTM samples with full particle size, the mean UCS increases from 1.18 to 12.88 MPa with the increase of the maximum particle size from 0.2 to 2 mm. The MTM sample with full particle size has a higher strength when the maximum particle size is larger than 0.8 mm. The strength of MTM samples increases within 9 days over the soaking time and then tends to be stable at the later stage. The calcium carbonate mineral in the MTM sample is mainly calcite and a small amount of vaterite, and the strength of MTM is positively correlated with its CaCO3 content. The CaCO3 content of the sample shows a high surrounding and low middle distribution.