Cementation Solution Research Articles

The use of waste glass in concrete production as a partial replacement of cement

The reuse and recycling of waste are considered the only way to reduce their generation. However, the application of waste in the construction industry is still at the research stage, providing an opportunity for the implementation of new technologies and the resolution of environmental aspects in this direction. This enables the creation of new eco-friendly building materials. The article discusses research in the field of using solid household waste in construction. It also explores the impact of particle size and the percentage of cement replacement with waste glass on the properties of the cementitious solution. The relevance of scientific research in this article lies in the possibility of using waste glass in concrete to improve the durability and sustainability of building structures. The use of glass waste as a pozzolanic material or as a partial replacement of cement can contribute to reducing CO2 emissions into the atmosphere, which is an important step in reducing the impact of construction on the environment. The results of this work can contribute to the development of a more sustainable and environmentally friendly construction industry

Anti-seepage reinforcement property and pollution control effect of bio-cemented fracture zone in electrolytic manganese residue dump

The heavy metal (HM) pollutants in electrolytic manganese residue (EMR) can easily diffuse through the seepage channel of the dump under the leaching action of rainfall. Particularly, the fracture zone, as one of the widely distributed seepage channels in the manganese residue dump (MRD), poses a greater threat to the ecological environment due to its weak mechanical properties, strong ductility, and numerous fractures. In this study, the microbially induced calcium carbonate precipitation (MICP) method was used for anti-seepage reinforcement of the fracture zone in an MRD to be constructed. The optimal conditions for the anti-seepage reinforcement of the fracture zone using the MICP method were proposed, and the control effect of the bio-cemented fracture zone on the major HM pollutant in the leachate of EMR was illustrated. Results showed that after grouting at a rate of 3 mL/min for 12 cycles with a grouting slurry of high urease activity (9 mM urea/min) and high cementation solution concentration (1.5 mol/L), the permeability coefficient of the fracture zone decreased from 10−4 to 10−5, and the unconfined compressive strength was approximately 5.58 times that of uncemented. Furthermore, the cubic calcite crystal clusters with high purity, good stability, dense arrangement, and high cementation properties were generated using the optimal conditions, and the pores were transformed from long columnar to spherical pores. Additionally, the Mn2+ concentration in the effluent from the fracture zone at the stabilization stage was only 663 mg/L, significantly lower than that of the leachate of EMR, and the risk of leaching changed from very high risk to low risk. The research outcomes can provide guidance and reference for laboratory model testing and in-situ testing of bio-cemented fracture zone, and it is expected to provide the theoretical and technological support for green and economic anti-seepage reinforcement of the fracture zone.

Microbial induce carbonate precipitation derive bio-concrete formation: A sustainable solution for carbon sequestration and eco-friendly construction.

The microbial-induced calcium carbonate precipitation (MICP) technique has high potential in the development of bio-concrete, enhancing the strength, durability, and self-healing properties of construction materials. In this review work, we have explored the crucial role of microorganisms in carbon sequestration, microbial methods in CaCO3 synthesis, and the application of bio-concrete formation, based on the SCOPUS database from 2010 to 2024. The production of construction materials consumes a significant amount of energy, which can emit high amounts of carbon dioxide (CO2) into the atmosphere. As a sustainable solution, researchers are working to introduce novel construction biomaterials through MICP, which play a key role in CO2 sequestration to address this issue. Herein, microorganisms (bacteria) can utilize CO2 through multiple absorption processes, converting it into value-added compounds or inducing CaCO3 precipitation. For example, specific bacteria like Bacillus cereus, Bacillus sphaericus, Bacillus pasteurii, Bacillus subtilis, and Bacillus megatherium are known for their capability to thrive in alkaline conditions and play a key role in bio-concrete formation. Furthermore, it has been highlighted that the bio-concrete ability to sequester CO2 through the carbonation process, emphasizes the roles of urease activity and carbonic anhydrase (CA) in bio-concrete. Overall, this paper provides a complete synopsis of recent research on the formation of bio-concrete through MICP and the various elements influencing the technique, including cementation solution, temperature, injection, pH, and bacteria. This suggests that emerging trends in bio-concrete utilization could significantly reduce CO2 emissions while enhancing the strength of non-reinforced concrete.

Enhancing the Strength and Durability of Soil Using Sugarcane Molasses as Broth Medium in the Microbial-Induced Calcite Precipitation (MICP) Technique

Microbial-induced calcite precipitation (MICP) is a promising, sustainable, and environmentally friendly ground improvement technique. This study examined the effectiveness of molasses (MS) as a broth medium compared to nutrient broth (NB). Sporosarcina pasteurii was used in a 0.5 M cementation solution with pore volumes (PV) of 0.50, 0.75, and 1 PV in biotreatment cycles of 9 and 18 days. Mechanical properties of biotreated samples were assessed through unconfined compressive strength (UCS) and split tensile strength (STS) tests, while calcite content, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to interpret biocementation. NB-treated samples exhibited significantly higher strength and calcite content than MS-treated samples. The durability of biotreated samples under 6, 12, and 18 freeze-thaw (FT) cycles revealed that the FT cyclic process affects the mechanical and physical characteristics of biotreated samples. Samples treated with higher PV and for a longer duration exhibited higher strength and durability. The mass losses in NB and MS samples were 7–14.5% and 15–32%, respectively, after 18 FT cycles. Overall, NB samples exhibit higher strength and durability than MS samples. While MS proved less effective as a broth medium compared to NB for the MICP process, its cost-effectiveness and abundant availability make it a promising choice for the MICP process.

Mitigating rainfall induced soil erosion through bio-approach: From laboratory test to field trail

Extreme rainfall events exacerbated by global warming can pose great threats to soil stability, causing severe soil erosion and triggering various disasters, such as landslide, debris flow, and land degradation. This study explores the efficacy and critical influence factors of a bio-approach utilizing microbially induced calcite precipitation (MICP) for soil erosion control by conducting a series of laboratory tests. The field trial was also performed to explore the long-term effectiveness of MICP treatment on soil slope under natural rainfall. The laboratory tests results indicate that the peak penetration strength increased 4.43 times, and the soil slaking index and soil loss during rainfall decreased by up to 65.7 % and 92.6 % after MICP treatment. The optimal concentration of cementation solution was found to be 1.0 M. Both the one-phase and two-phase MICP methods proved effective in enhancing soil erosion resistance. However, the two-phase MICP method demonstrated a more pronounced impact on surface soil improvement, while the one-phase MICP method achieved a more uniform treatment effect. The 11-months field erosion trials validated the remarkbale durability of MICP treatment in controlling soil erosion. Additionally, more cycles of MICP treatment further enhanced the soil erosion resistance to rainfall. The bonding and filling effect of MICP-produced CaCO3 precipitates played a crucial role in the improvement of soil water stability and mechnical strength, thereby significantly mitigating soil erosion caused by raindrop and surface runoff during natural rainfall. This study provides valuable suggestions for the pratical application of MICP approch on soil erosion control against increasing extreme rainfall, which is also expected to offer a controllable and sustainable soil improvement solution under the climate change.

Optimization of Strength Factors in Microbial Solidification of Uranium Tailings Using Response Surface Methodology

Once the uranium tailings dam collapses, it will cause great harm to the surrounding ecological environment and people’s safety. This study experimentally investigates microbial grouting reinforcement of uranium tailings to advance microbial reinforcement technology and facilitate its large-scale engineering applications. The study simulated original environmental conditions and used tap water to prepare the culture medium and cement without sterilization or pH adjustment. The response surface method was employed to optimize parameters affecting the immobilization of uranium tailings, and the results were verified. The mechanical strength of the immobilized uranium tailings was determined through unconfined compression tests, while their microstructures were analyzed using X-ray diffraction, scanning electron microscopy and computed tomography. The findings indicate that the response surface method optimizes test parameters accurately, with the concentration of the cementation solution and the grouting amount being two main factors influencing the compressive strength of the solidified uranium tailings. Without pH adjustment, sterilization, or slurry modification using tap water, the bacteria−cementation ratio was set at 1, the concentration of the cementation solution was 1.3 mol/L, and the grouting volume was 70 mL. Notably, the strength of the uranium tailings increased 27-fold after seven rounds of grouting compared to the water-only group, and 6-fold compared to the cementation solution-only group. This study contributes to reducing the complexity associated with the application of microbial grouting technology in soil stabilization and provides valuable references for other engineering practices.

Experimental and simulation study of calcium carbonate non-uniform distribution characteristics of bio-cemented sand

The innovative technology of microbially induced calcium carbonate precipitation (MICP) soil modification is widely used in soil reinforcement, soil remediation, environmental remediation and other fields, and has gradually become a hot research direction. Recent research is more focused on the overall physical and mechanical characteristics of the uniform reinforced specimen. There is limited research on the distribution characteristics of calcium carbonate along the seepage path during the reinforcement process. However, the distribution characteristics of calcium carbonate play a significant role in the physical and mechanical characteristics of the solid, especially in the large-scale MICP reinforcement process. In this study, based on the microbial mineralization reaction tests of different concentrations of cement solution at the laboratory sample scale, the calcium carbonate distribution on the surface of the sample at the microscale SEM observation and the CT scanning reconstruction of the micro pore structure characteristics of the microbial reinforced soil, we discussed the characteristics of the non-uniform reduction of calcium carbonate distribution and porosity in the process of microbial consolidation. Based on the Kozeny-Carman equation, the conceptual model of effective porosity was introduced, and the time relationship between porosity and calcium carbonate precipitation was considered to establish a bio-chemical-seepage multi-physics field coupling model. The precipitation of calcium carbonate in the axial direction of the model sample exhibits an uneven feature of more at the top and less at the bottom, and the distribution characteristics of porosity also show an uneven feature of more at the top and less at the bottom.

Behaviour and mechanism of cadmium immobilization in contaminated soil by calcium carbide residue-enhanced MICP

A novel technique that couples microbially induced calcite precipitation (MICP) and calcium carbide residue (CCR) is proposed for immobilizing Cd2+ in contaminated soil. The properties and mechanism of CCR-enhanced MICP were investigated through a series of experimental analyses considering factors such as heavy metal concentration, curing time, and the effect of Ca2+. The unconfined compressive strength (UCS) increased with increasing curing time and reached a maximum value at 28 d, and the leaching concentration of Cd2+ decreased and tended to level off with increasing curing time. The addition of CCR enhanced the immobilization performance of Cd2+ through the MICP method, resulting in UCSs that were 3.8–4.2 times those of samples without CCR and leaching concentrations of Cd2+ that were 38.9–69.2% lower at a curing time of 28 d. The addition of Ca2+ to cementation solutions further improved the immobilization effectiveness, resulting in the UCSs of the samples increasing by 18.7–49.8% and the leaching concentrations of Cd2+ decreasing by 11–40% CaCO3 and its hydration products can immobilize Cd2+ through coprecipitation, reducing its toxicity by converting weak acid-extractable cadmium into residual cadmium. Consequently, Sporosarcina pasteurii combined with CCR improved the UCS of the treated contaminated soil and greatly decreased cadmium migration.

Improving the quality of well reinforcement in the representation of the Umid-Babek field

High-quality drilling of gas and gas-condensate deposits on the world shelf, including in the Caspian Sea part of Azerbaijan, is of great national economic importance. For many years by the most advanced achievements, the wells were achieved to be drilled to the project depth, and the required amount of gas and condensate were successfully produced. Azerbaijan’s achievements in this field were realized at such a high pace that currently Azerbaijan has managed to export its natural resources to the European market. In our modern times, the penetration of drilling to greater depths and the occurrence of a number of complications have brought to the fore the application of the most advanced innovative approaches in well drilling technology and strengthening as well. One of the prospective fields mentioned is the ‘‘Umid-Babek’’ structure. Currently, the drilling operations are carried out on a very large scale and the most advanced technologies of the world drilling experience are applied in the mentioned field. Well reinforcement is one of the most difficult and responsible stages of well construction. It is no coincidence that due to high-quality reinforcement of the well, favorable conditions for the effective operation of the field are created. The most advanced technologies for the qualitative strengthening of casings are also applied in the ‘‘Umid-Babek’’ field. As a result of the researches, it was determined that if the well wall stability violation, absorption of drilling fluid and occasional manifestations are observed during drilling, the presence of more serious and effective complications is observed after the protective belt is lowered. First of all, injecting the required amount of cement solution behind the casing lowered into the well, making sure that this solution completely covers the annular space, and finally, the formation of qualitative cement is one of the actual problems. In the presented article, some directions of technological solutions related to the strengthening of wells in the ‘‘Umid-Babek’’ structure were presented.

The impact of Microbially Induced Calcite Precipitation (MICP) on sand internal erosion resistance: A microfluidic study

Fine particle internal erosion involves the detachment, transport, and deposition of fine particles within soil, significantly impacting agriculture, engineering, and environmental protection. Microbially induced calcite precipitation (MICP) has proven to be an effective method for controlling internal erosion. To optimize MICP protocols for effective erosion control, understanding the microscopic mechanisms by which MICP reduces fine particle erosion is essential but remains unclear. In this study, microfluidic chip experiments were conducted to observe the characteristics of calcium carbonate crystals and fine particles before and after MICP reinforcement and erosion. Through quantitative analysis of the calcium carbonate produced by MICP and eroded fine particles, the effects of bacterial density, concentration of cementation solution, and flow rate on the efficiency of MICP in resisting soil internal erosion were investigated. In addition, three primary mechanisms by which MICP reduces fine particle erosion were identified. Firstly, in situ sand stabilization occurs when calcium carbonate generated by MICP bonds and encapsulates fine particles, forming larger particles that remain stable under erosive flow conditions. Secondly, regional sand stabilization is achieved as MICP-produced calcium carbonate crystals narrow or block the flow channels, preventing extensive migration of fine particles. Lastly, adjacent particle stabilization is facilitated by calcium carbonate crystals, which remain stable during water flow erosion and alter the erosion flow lines, creating zones adjacent to the crystals where fine particle movement is minimized. These findings provide a deeper understanding of the role of MICP in erosion control and can inform the development of more effective erosion mitigation strategies.

Soil Water Characteristics Curves (SWCC) of Residual Soils Stabilized using Emerging and Novel Bioinspired Technique

The development of unsaturated soil mechanics stemmed from the inadequacies of classical soil mechanics in addressing the partial pore spaces found in real-world soil systems. However, assessing soil parameters under partial saturation is resource-intensive. To streamline this, the Soil-Water Characteristic Curve (SWCC) theory was introduced. Widely applied across geotechnical engineering, water resources, and agriculture, SWCC predicts parameters of unsaturated soil systems. In geotechnical engineering, SWCC is vital for designing systems near the Earth's surface, like slopes, clay liners and foundations. Furthermore, most of conventional soil improvement techniques pose a lot of environmental concerns. thus, emergence of green construction materials widely known as bio mediated and bioinspired soil improvement techniques like Enzymatic induced calcite precipitation (EICP). EICP, an emerging eco-friendly as it employs use of simply chemical compound that reduces carbon footprints, bioinspired technique as it mimics natural forming process, was applied to stabilize tropical soil for SWCC determination. SWCC parameters were derived by subjecting EICP-treated soils at varying concentration of cementation solutions (0 – 1.00 M) using pressure plate method. Results revealed that saturated water content θs, retention water content θr, and air entry value Ψa increased with higher cementation solution concentration. The values of θs, θr, and Ψa improved from of 0.663, 0.23405, and 3.4832 at 0 concentration of cementation solution to 0.701, 0.22864, and 7.7086, respectively upon treatment with 1.00 M cementation solution. Finally, it has been demonstrated EICP is capable of improving the SWCC parameters of residual soil, thus the EICP technique can be exploited in stabilization of residual for construction of compacted clay liner.

Use of rise husks to improve the efficiency of MICP-based soil improvement technique

Biogrouting has been identified as the best alternative approach for the conventional cement and chemical grouts. Among the various types of biogrouting techniques, microbial induced carbonate precipitation (MICP) has been recently recognized as a promising pathway for producing biogrout material, hence densifying the weak soils. In MICP, calcium carbonate (CaCO3) biocement is produced through biochemical reactions induced by the urease enzyme. The efficiency and productivity of MICP can be further improved by introducing various additives, including fibers, organic polymers, powders, waste materials, etc. In this research, rice husk was sustainably incorporated into the MICP process, and (i) the effect of the rice husk content, (ii) the concentration of the cementation solution and (iii) the treatment time on the unconfined compressive strength (UCS) of the sandy soil were investigated at the laboratory-scale. Cementation solutions with higher concentrations exhibited a higher UCS values than solutions with lower concentrations. Interestingly, the content of rice husk had a marked influence on the UCS, and the optimum rice husk content was 15%. Compared to that of the control sample (0% rice husk), a threefold greater UCS was obtained for 15% of the rice husk content sample. The outcomes further suggested that longer treatment with lower concentration of cementation solution was the best combination for achieving effective cementation within the sand matrix. Rice husk acted as the template for CaCO3 crystals to nucleate while promoting the efficient formation of CaCO3, indicating that the rice husk is an excellent additive to improve the efficiency of the MICP biocementation in a sustainable way.

Single-Particle Crushing Test of Coated Calcareous Sand Based on MICP

Calcareous sand is a crucial construction material for island and reef development and reinforcing it using Microbially Induced Calcite Precipitation (MICP) technology is a promising new method. This study employed 3D scanning technology to assess changes in the particle size and morphology of MICP-treated, coated calcareous sand particles. Single-particle crushing tests were conducted to analyze their crushing strength, crushing energy, crushing modes, and fragment fractal dimensions. The results indicated that MICP treatment significantly increased particle size, surface area, and volume, while reducing flatness. At a cementation solution concentration of 1 mol/L, both crushing strength and crushing energy were optimized. The coated particles exhibited three crushing modes: explosive crushing, mixed crushing, and splitting crushing. Thicker coatings led to a tendency for particles to break into larger fragments through the mixed and splitting crushing modes. Fractal analysis revealed that coating thickness directly affects the local crushing characteristics of the particles.

Evaluation of wind erosion resistance of EICP solidified desert sand based on response surface methodology

Wind erosion is the primary cause of land desertification in arid and semi-arid regions. Enzyme-induced carbonate precipitation (EICP) will produce a solid coating on the surface of desert sand that inhibits wind erosion. Three critical variables for EICP treatment, including enzyme-cementation ratio A, cementation solution concentration B, and spraying volume of reaction solution C, were evaluated with three wind erosion-resistance indexes (surface strength, calcium carbonate content, and solidified layer thickness) of desert sand, and further optimized with the response surface methodology (RSM). The mass loss of the EICP-treated desert sand was studied by wind tunnel tests with wind speeds of 8–14 m/s and erosion times of 0–30 min. Material composition and microstructure of the EICP precipitates were investigated with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Results indicate that the three wind erosion-resistance indexes tend to rise with greater A and B values followed by a decline while monotonically increasing with C but the increments decrease when C>5 L/m2. The optimal solidification effect was reached when A=1.082:1, B=1.282 mol/L and C=8.70 L/m2, which corresponds to a maximum wind speed of 14 m/s for solidified desert sand. Large amounts of calcite crystals were produced in the EICP-treated sand and filled soil pores. The particle contacts transform from point contact to surface contact and the enhanced particle bonding induces a more compact soil skeleton. The above experiment evidence corresponds to increased surface strength and wind erosion resistance. The results of this study will provide an experimental foundation for the application of EICP technology to enhance wind erosion resistance of desert sands.

Current and potential materials for the low-carbon cement production: Life cycle assessment perspective

Given the carbon-intensive nature of cement production, conducting a comprehensive environmental evaluation using life cycle assessment (LCA) modeling is paramount to achieving eco-friendly cement standards. This study meticulously compiles and evaluates LCA findings from diverse analyses of current and potential supplementary cementitious materials (SCMs) within the blended cement sector. It underscores the impact of the functional unit (FU) within the LCA approach, supply chain considerations, and technical and regulatory factors on the sustainability of blended cement mixtures. Most of LCAs studied herein show that integrating SCMs into the cement matrix typically reduces land use, energy consumption, and greenhouse gas (GHG) emissions, thereby lowering the global warming potential (GWP) of ordinary portland cement (OPC) samples from 831 to 980 kg of CO2-eq to 768-481 kg of CO2-eq per ton of cement. However, in some instances, environmental indicators like abiotic depletion potential-elements (ADP-E) and human toxicity potential (HTP) rise due to increased mining, electricity, and transportation demand for SCMs. Regarding the environmental potential of alkali-activated cementitious materials and low-carbon clinker formulations, we found that limitations arise in fully replacing OPC due to global raw material availability constraints, rendering them economically unfavorable and impeding their widespread adoption. Among the SCMs examined in this study, clays, which are more widely available compared to industrially sourced materials like fly ash, slag, and silica fume, exhibited a more favorable environmental profile when evaluated using a mass-based FU. Incorporating compressive strength into the FU resulted in greater environmental benefits from high-strength blendedcement composites. However, this approach might lead to inaccurate results because higher strength does not always correspond to a lower environmental impact. Thus, establishing a FU that accurately reflects the environmental impact of blended cement and its composites (e.g., concrete and mortar) is crucial. Despite the potential of various pozzolanic materials to reduce clinker content in cement mixtures, their wide utilization remains restricted due to the absence of widescale market-based initiatives, green procurement strategies, and effective policy measures, which hampers their industrial and public acceptance. Consequently, governmental support is essential for developing and integrating sustainable cement solutions.

Preparation of an environment-friendly microbial limestone dust suppressant and its dust suppression mechanism.

The development of an efficient and environmentally friendly dust suppressant is crucial to address the issue of dust pollution in limestone mines. Leveraging the synergistic microbial-induced calcium carbonate precipitation (MICP) technology involving NaHCO3 and dodecyl glucoside (APG), the optimal ratio of the dust suppressant was determined through single-factor and response surface tests. The dust suppression efficacy and mechanisms were analyzed through performance testing and microscopic imaging techniques, indicating that the optimal ratio of the new microbial dust suppressant was 20% mineralized bacteria cultured for 72h, 0.647molL-1 cementing solution, 3.142% NaHCO3, and 0.149% APG. Under these conditions, the yield of calcium carbonate increased by 24.89% as compared to when no NaHCO3 was added. The dust suppressant demonstrated excellent wind, moisture, and rain resistance, as well as curing ability. More calcite was formed in the dust samples after treatment, and the stable form of the dust suppressant contributed to consolidating the limestone dust into a cohesive mass. These findings indicate that the synergistic effect of NaHCO3 and APG significantly enhanced the dust suppression capabilities of the designed microbial dust suppressant.

Enhancing biocementation performance in low permeability clayey soil through sand column strategy

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeability-clayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.

Seeding improves the strength of bio-tiles grown with microbially induced calcium carbonate precipitation

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·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 extruded tiles with 6–10 % water absorption. When a seed loading of 0.021 g/cm2 was used instead, bio-tiles meeting targets for tiles with a water absorption of >10 % were produced at 628 ± 18 N and 10.5 ± 1.1 N/mm2.

Mechanical and Microstructural Behavior of Sand Treated by Filamentous Fungus Mycelium Mediated Calcite Precipitation

ABSTRACT Fungus Mycelium mediated Calcite Precipitation (FMCP) is a novel bio-inspired method for enhancing the mechanical and microstructural properties of sand. This study investigates the potential of Aspergillus Niger fungus mycelium to induce calcite precipitation in sand, thereby improving its unconfined compressive strength (UCS) and permeability. The experimental approach involves mixing sand with Aspergillus Niger and subsequently injecting a cementation solution containing urea and CaCl in an equimolar 1:1 ratio at 24-hour intervals. The effect of different treatment durations (7, 14, 21, and 28 days) on the UCS of the samples is examined. Our findings demonstrate that the highest average UCS of 3.93 MPa was achieved after 28 days using FMCP, corresponding to an average calcium carbonate content of 15.19%. Additionally, permeability of FMCP treated sand decreased to 99.54% compared to untreated sand. The Scanning electron microscopy identified the presence of fungus mycelia and calcium carbonate crystals that bind the sand grains together resembling fibrous structure. The Energy-Dispersive X-ray Spectroscopy analysis confirmed the presence of calcium carbonate crystals associated with the sand grains and fungal mycelium. These findings contribute valuable insights into the feasibility of FMCP as a sustainable approach to soil improvement, with implications for geotechnical and construction applications.

Effects of urease and cementing solution concentrations on micro-scale enzymatic mineralisation characteristics

Enzymatically induced carbonate precipitation holds significant promise in geotechnical engineering. The concentrations of urease enzyme and cementing solution play vital roles in precipitation behaviours under distinct injection strategies. In situ microscale experiments, conducted in S-shaped microchips, were aimed at exploring precipitation distribution characteristics and micro-clogging effects due to biological precipitation. In the one-phase continuous injection methods, elevated urease concentrations correlated with increased amorphous calcium carbonate formation and more heterogeneous distributions. Conversely, lower cementing solution concentrations produced larger, fewer crystals and more uniform distributions. Higher urease improved efficiency but increased cost, while lower cementing solution concentrations displayed efficient performance. Permeability reduction exhibited a power-law relationship with the precipitation area fraction. In the two-phase staged injection method, elevated urease concentrations fostered more regularly shaped crystals. Higher calcium ion concentrations could inhibit ureolysis rate, reducing precipitates. Higher urease concentrations proved beneficial in improving efficiencies. Permeability exhibited a marginal decrease initially, followed by a significant decline as the precipitation area fraction increased. The results offer microscale insights into concentration effects, aiding the understanding of upscaling mechanisms and numerical simulations.