Search Results (182)

The cement industry, a major contributor to global CO₂ emissions, urgently requires sustainable solutions that maintain or enhance material performance. This study investigates the efficacy of Microbially Induced Calcite Precipitation (MICP) as a partial cement replacement strategy by incorporating two distinct microorganisms, the bacterium Bacillus subtilis (B1) and the fungus Aspergillus fumigatus (B2), into cement mortar. The experimental design involved a significant 30% reduction in total cement content compared to the control mix, with each microorganism added at a dosage of 5% by cement weight. Flexural performance was assessed via three-point bending tests at 7, 28, and 56 days. Microstructural and chemical analyses were conducted using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) to elucidate the underlying mechanisms. The results demonstrate that the incorporation of both microorganisms effectively compensated for the reduced cement content, with the A. fumigatus mix (B2) showing a marked enhancement in flexural behavior, achieving a 4.3% increase over the full-cement control mix at 56 days. This superior flexural performance is attributed to its hyphal scaffolding and crack-bridging effect, which contributes to improved toughness. XRD and XRF analyses confirmed the formation of additional biogenic calcium carbonate (CaCO₃) and provided qualitative insights into matrix densification. This study validates the use of A. fumigatus via the MICP technique as a structurally efficient and eco-friendly pathway to produce high-performance mortars with enhanced flexural properties and a substantially reduced carbon footprint, offering a critical alternative for sustainable cementitious materials. Full article

This study investigates the mechanical properties, moisture stability, and environmental safety of microbial-induced carbonate precipitation (MICP)-treated phosphogypsum (PG)-based mixtures (MPGT) for road base utilization. Optimal cementation solution concentrations and bacterial-to-cementation solution ratios were determined via unconfined compressive strength (UCS), California bearing ratio (CBR), and splitting tensile strength tests. Durability was compared with untreated mixtures, and enhancement mechanisms were analyzed using XRD, SEM, and FTIR. Additionally, toxicity leaching tests evaluated environmental safety. Results indicated optimal parameters of 2.0 mol/L cementation solution and a 2:1 bacterial/cementation solution ratio for maximum mechanical strength. Under these conditions, MPGT durability significantly improved compared to untreated mixtures. Mechanism analysis revealed that MICP-generated calcium carbonate coats PG particles and fills voids, enhancing strength and durability. Furthermore, F⁻ and PO₄³⁻ leaching concentrations were significantly reduced. In summary, MICP improves the mechanical performance, durability, and environmental safety of PG-based mixtures, promoting PG recycling in road engineering. Full article

To facilitate the large-scale recycling of phosphogypsum (PG) as a construction material and mitigate the environmental safety concerns associated with its stockpiling or discharge, this study proposes an innovative approach. The method employs modified (acid-treated) basalt fibers (MBF) synergistically combined with microbially induced carbonate precipitation (MICP) technology for PG solidification. This synergistic MBF–MICP treatment not only enhances the strength and further improves the toughness of the solidified PG but also effectively immobilizes heavy metals within the PG matrix. Bacterial attachment tests conducted on fibers subjected to various pretreatment conditions revealed that the maximum bacterial adhesion occurred on fibers treated with a 1 mol/L acid concentration for 2 h at 40 °C. However, MICP mineralization experiments performed on these pretreated fibers determined the optimal pretreatment conditions for mineralization efficiency to be an acid concentration of 0.93 mol/L, a treatment duration of 0.96 h, and a temperature of 30 °C. Unconfined compressive strength (UCS) tests and calcium carbonate content measurements identified the optimal reinforcement parameters for MBF–MICP-solidified PG as a fiber length of 9 mm and a fiber dosage of 0.4%. Furthermore, comparative analysis demonstrated that the UCS and toughness of MBF–MICP-solidified PG were superior to those of bio-cemented PG specimens treated with unmodified fibers or without any fiber reinforcement. It was found by scanning electron microscopy that there was an obvious phosphogypsum particle-fiber-calcium carbonate precipitation interface in the sample, and the fiber had a bridging effect. Finally, heavy metal leaching tests conducted on the solidified PG confirmed that the leached heavy metal concentrations were below the detection limit, complying with national discharge standards. Full article

Microbial carbonates are globally known petroleum reservoirs. However, the complex interplay between deposition and diagenesis significantly influences the pore network distribution in these microbial carbonate reservoirs. The present study aims to discuss diagenetic alterations in the Jurassic microbial carbonate successions from foreland basins in the NW Himalayas. Geological field observations, petrographic analysis, scanning electron microscopy, and isotopic analysis were applied to highlight the role of diagenesis in reservoir characterization of shallow marine carbonates. The results indicate that dolomitization, dissolution, and fracturing during the early to late phase of diagenesis enhanced the reservoir pore network. However, cementation, micritization, and mechanical compaction considerably reduced the reservoir pore distribution. Furthermore, fractures and stylolites that developed perpendicular to bedding planes indicate the role of convergent tectonics in developing the fracture network that allowed fluid migration and improved the pore spaces in microbial carbonate reservoirs. Isotopic data revealed shallow-burial diagenesis with marine and meteoric influx that provides avenues for the movement of fluids. These fluids are associated with microbial activity in carbonate rocks along the faults and fractures that were developed because of compressional tectonics, evident from the perpendicular fracture network. This study recommends the integration of deposition and diagenesis to refine the pore network distribution and characterization of carbonate reservoirs around the globe. Full article

This study presents an innovative approach by combining magnetized water (MW) with Bacillus megaterium to improve the sustainability of concrete under various curing conditions. These enhancements contribute directly to reduced cement use and improved durability, both essential factors in sustainable construction. An experimental program with 27 distinct mixes analyzed variables such as the type of water (tap water/TW and two magnetization sequences/MW1 and MW2), bacterial dosage (0%, 2.5%, and 5% relative to cement weight), and curing methods (traditional water curing/C1, thermal shock/C2, freeze–thaw/C3). The primary discovery is a synergistic relationship between MW and bacteria: the MW1 treatment (1.5 T followed by 0.9 T) paired with a 2.5% bacterial dosage significantly improved the mechanical and self-healing properties of the concrete. This combination led to significant improvements in workability and compressive strength, achieving an increase of as much as 46.5% compared to the control. There was also an impressive recovery of strength in pre-cracked specimens, particularly under thermal shock curing (C2), where some healed cubes exceeded the strength of the uncracked ones. On the other hand, a 5% bacterial dosage was less effective, often resulting in reduced returns due to variations in microstructure. SEM and XRD analyses confirmed a more compact matrix and increased calcite precipitation with 2.5% bacteria, illustrating the combined effects of microbial activity and microwave treatment for sustainable concrete. Full article

Aeolian sand in arid mining regions is highly susceptible to wind erosion, posing serious threats to ecological stability and surface engineering safety. To enhance its resistance, this study applied the microbially induced carbonate precipitation (MICP) technique and conducted wind tunnel experiments combined with SEM and XRD analyses to examine the effects of cementing solution type and concentration, bacteria-to-cementation-solution ratio (B/C ratio), and spraying volume on the wind erosion behavior of MICP-treated aeolian sand. Results show that the cementing solution type and concentration jointly control erosion resistance. The MgO-based system exhibited the best performance at a B/C ratio of 1:2, reducing erosion loss by 47.2% compared with the CaCl₂ system, while a 1.0 mol/L concentration further decreased loss by 97.4% relative to 0.5 mol/L. Increasing the spraying volume from 0.6 to 1.2 L/m² reduced erosion loss by 70–99%, and a moderate B/C ratio (1:2) ensured balanced microbial activity and uniform CaCO₃ deposition. Microstructural observations confirmed that MICP strengthened the sand through CaCO₃ crystal attachment, pore filling, and interparticle bridging, forming a dense surface crust with enhanced integrity. From a symmetry perspective, the microbially induced mineralization process promotes a more symmetric and spatially uniform distribution of carbonate precipitates at particle contacts and within pore networks. This symmetry-enhanced microstructural organization plays a key role in improving the macroscopic stability and wind erosion resistance of aeolian sand. Overall, MICP improved wind erosion resistance through a coupled biological induction–chemical precipitation–structural reconstruction mechanism, providing a sustainable approach for eco-friendly sand stabilization and wind erosion control in arid mining regions. Full article

Shale gas extraction is underway in the Karoo Basin. Previous oil and gas explorers abandoned several wells, and the abandonment statuses of these wells are unknown. Critically, improperly abandoned wells can provide a pathway for the leakage of stray gas into shallow aquifers and degrade water quality. To understand the abandonment integrity risk posed by these wells, a qualitative risk model was developed to assess the likelihood of well-barrier failure leading to a potential leak. The potential leak paths identified include zones with cement losses during grouting, casing corrosion, cement channels, failure to case and cement risk zones, uncased and uncemented sources, uncemented annuli, and unplugged wells. To confirm whether these wells are leaking, geochemical tracing of stray gas was integrated. Eleven of the fifty samples collected had dissolved hydrocarbon gas concentrations that were high enough to use isotopic analysis to determine the source. The results revealed microbial gas via fermentation and carbon dioxide reduction, thermogenic gas, and geothermal gas, as evidenced by larger δ¹³C₁ values and isotopic reversals associated with dolerite intrusions. The thermogenic-type gas detected in legacy abandoned wells and <1 km water boreholes adjacent to these wells serves as evidence that the downhole plugs did not maintain their integrity or were improperly plugged, whereas the thermogenic gas detected in >1 km water boreholes indicates leakage contamination due to natural fracture pathways. The presence of thermogenic gas in legacy wells and in groundwater boreholes <1 km from legacy wells implies that shale gas extraction using hydraulic fracturing cannot be supported in these situations. However, using safety buffer zones greater than 1 km from the legacy wells for shale gas drilling could be supported. Full article

Sewer corrosion driven by sulfur metabolism threatens infrastructure durability. Current study examined the effect of conductive lining materials on microbial communities and sulfide control under simulated sewer conditions. Three lab-scale reactors (3.5 L total volume, 2.1 L working volume) were prepared with amorphous carbon (SAN-EARTH) and magnetite-black (MTB) linings, while a Portland cement reactor with no coating served as the control. Each reactor was operated for 120 days at room temperature and fed with artificial wastewater. The working volume consisted of 1.4 L of synthetic wastewater mixed with 0.7 L of sewage sludge used as the inoculum source. Sulfate, sulfide, hydrogen sulfide, nitrogen species, pH, and organic carbon were monitored, and microbial dynamics were analyzed via 16S rRNA sequencing and functional annotation. SAN-EARTH and MTB reactors completely suppressed sulfide and hydrogen sulfide, while Portland cement showed the highest accumulation. Both conductive linings maintained alkaline conditions (pH 9.0–10.5), favoring sulfide oxidation. Microbial analysis revealed enrichment of sulfur-oxidizing bacteria (Thiobacillus sp.) and electroactive taxa (Geobacter sp.), alongside syntrophic interactions involving Aminobacterium and Jeotgalibaca. These findings indicate that conductive lining materials reshape microbial communities and sulfur metabolism, offering a promising strategy to mitigate sulfide-driven sewer corrosion. Full article

In order to address the poor volume stability and low reactivity of steel slag powder (SS) as a supplementary cementitious material (SCM), this study investigates a microbial-assisted carbonation method for its enhancement. Using untreated SS as a control, we compared the performance and microstructure of carbonated steel slag powder (CSS) and bio-mineralized steel slag powder (BSS). Results indicate that, compared to CSS, BSS exhibits a more significant reduction in the content of f-CaO and f-MgO (from 6.25% and 3.19% to 0.8% and 1.36%, respectively) and a greater improvement in 7-day and 28-day activity indices (from 59% and 72% to 78% and 87%), leading to markedly enhanced volume stability and reactivity. Calculations show that each ton of BSS can sequester 114.2 kg of CO₂, and it achieves a cement replacement ratio exceeding 30%. The utilization of BSS as an SCM not only addresses the inherent technical challenges of steel slag powder but also creates dual environmental benefits through emission reduction and active carbon sequestration, demonstrating significant potential for advancing the low-carbon transition in the construction materials industry. Full article

In response to the issues of increased brittleness and insufficient toughness in microbially solidified saline sandy soils in cold and arid plateau regions, this study investigated saline sandy soils and indigenous microorganisms from the Qaidam Basin, Qinghai. A dual-reinforcement method combining microbial-induced calcium carbonate precipitation (MICP) with alkali-modified reed fiber (ARF) was proposed to enhance both strength and ductility. The study explored the adsorption characteristics and solidification mechanisms of this approach. Key innovations include: (1) alkali modification significantly improved the interfacial bonding between reed fibers and sand particles, with pull-out tests indicating a 1.24-fold increase in adhesion strength; (2) an orthogonal experimental design identified optimal parameters—fiber length of 15 mm, fiber content of 0.5%, and cementation solution concentration of 3 mol/L—leading to the development of a synergistic “microbial cementation–fiber bridging” enhancement model. Experimental results showed that the proposed method increased the unconfined compressive strength (UCS) of the solidified soil to 2082.85 kPa, 2.99 times higher than that of traditional MICP-treated soil, while it significantly enhanced the ductility of the soil. This approach offers a mechanically robust and environmentally adaptive solution within the ambient temperature range of 0–35 °C for the ecological restoration of saline soils in high-altitude regions. Full article

Soil aggregate stability plays a central role in mediating slope erosion, a key ecological process in North China. This study aimed to investigate how aggregate structures (reflected by rainfall intensity and vegetation-type differences) influence the erosion process. Using wasteland as the control, we conducted artificial simulated rainfall experiments on soils covered by Quercus variabilis, Platycladus orientalis, and shrubs, with three rainfall intensity gradients. Key findings showed that Platycladus orientalis exhibited the strongest infiltration capacity and longest runoff initiation delay due to its high proportion of stable macroaggregates (>0.25 mm), while barren land readily formed surface crusts, leading to the fastest runoff. Increased rainfall intensity significantly exacerbated runoff and erosion. When the macroaggregate content exceeded 60%, sediment yield rates dropped sharply, with a significant negative exponential relationship between the mean weight diameter (MWD) and sediment yield; barren land (dominated by microaggregates) faced the highest erosion risk and fell into an erosion–fragmentation vicious cycle. Redundancy analysis revealed that microbial communities (e.g., Ascomycota) and fine roots were dominant erosion-controlling factors under heavy rainfall. Ultimately, the synergistic system of the macroaggregate architecture and root-microbial cementation enabled Platycladus orientalis and other tree stands to reduce soil erodibility via maintaining aggregate stability, whereas shrubs and barren land amplified rainfall intensity effects. barren landbarren landmm·h⁻¹ mm·h⁻¹ mm·h⁻¹ barren land. Full article

Well cementing is an important step in oil and gas development. It uses cement to seal the formation and the casing, preventing fluid leakage. However, when conducting offshore oil well cementing operations, deep-water formations are usually weakly consolidated soils, and it is difficult to form a good cementation between the cement and formation. Therefore, enhancing the strength of the formation is one of the effective measures. This study uses the microbial-induced carbonate precipitation technology to cement sandy formations containing clay minerals. The triaxial tests were conducted to evaluate the consolidation effectiveness in the presence of three clay minerals: montmorillonite, illite, and kaolinite. X-ray computed tomography was utilized to characterize microscopic pore parameters, while thermogravimetric analysis, X-ray diffraction, and surface potential measurements were applied to analyze the mechanisms of clay minerals affecting microbial consolidation. The results showed that microbial mineralization mainly affects the cohesion of the samples. The cohesion of the montmorillonite sample increased from 20 kPa to 65.4 kPa, an increase of up to 3.27 times. The other two samples (illite and kaolinite) had increases of only 0.33 times and 1.82 times. Although the strength of the montmorillonite sample increased the most, unexpected large pores appeared with a diameter of over 120 µm, accounting for 7.1%. This is mainly attributed to the mineral expansion property. The expansion of the minerals will trap more microorganisms in the sample, thereby generating more calcium carbonate. And it also reduced the gaps between sand particles, creating favorable conditions for the connection of calcium carbonate. Although the surface charge of the minerals also affects the attachment of microorganisms, all three minerals have negative charges and a difference of no more than 0.84 mV (pH = 9). Therefore, the expansion property of the minerals is the dominant factor affecting the mechanical and microstructure of the sample. Full article

Cracks in concrete are a persistent issue that compromises structural durability, increases maintenance costs, and poses environmental challenges. Self-healing concrete has emerged as a promising innovation to address these concerns by autonomously sealing cracks and restoring integrity. This review focuses on two primary healing mechanisms: autogenous healing and microbial-induced calcite precipitation (MICP), the latter involving the biomineralization activity of bacteria, such as Bacillus subtilis and Sporosarcina pasteurii (formerly known as B. pasteurii). This review explores the selection, survivability, and activity of these microbes within the alkaline concrete environment. Additionally, the review highlights the role of fiber-reinforced cementitious composites (FRCCs), including high-performance fiber-reinforced cement composites (HPFRCCs) and engineered cement composites (ECCs), in enhancing crack control and enabling more effective microbial healing. The hybridization of natural and synthetic fibers contributes to both improved mechanical properties and crack width regulation, key factors in facilitating bacterial calcite precipitation. This review synthesizes current findings on self-healing efficiency, fiber compatibility, and the scalability of bacterial healing in concrete. It also evaluates critical parameters, such as healing agent integration, long-term performance, and testing methodologies, including both destructive and non-destructive techniques. By identifying existing knowledge gaps and performance barriers, this review offers insights for advancing sustainable, fiber-assisted microbial self-healing concrete for resilient infrastructure applications. Full article

Cracks in concrete dam tunnels compromise structural safety, watertightness, and durability, while conventional repair materials such as epoxy and cement impose environmental burdens. This study investigates biomineralization methods, namely Microbially Induced Calcium Carbonate Precipitation (MICP) and Enzyme-Induced Carbonate Precipitation (EICP), for repairing fine cracks in a large hydropower dam tunnel. Laboratory tests and field applications were conducted by injecting urea–calcium solutions with Sporosarcina pasteurii for MICP and soybean-derived urease for EICP, applied twice daily over three days. Both techniques achieved effective sealing, with precipitation efficiencies of 93.75% for MICP and 84.17% for EICP. XRD analysis revealed that MICP produced a mixture of vaterite and calcite, reflecting biologically influenced crystallization, whereas EICP yielded predominantly calcite, the thermodynamically stable phase. SEM confirmed that MICP generated irregular layered clusters shaped by microbial activity, while EICP formed smoother spherical and more uniform deposits under enzyme-driven conditions. The results demonstrate that MICP provides higher efficiency and localized nucleation control, while EICP offers faster kinetics and more uniform deposition. Both methods present eco-friendly and field-applicable alternatives to conventional repair, combining technical performance with environmental sustainability for hydraulic infrastructure maintenance. Full article

Well integrity is paramount for the safe, environmentally responsible, and economically viable operation of wells throughout their lifecycle, encompassing conventional oil and gas production, unconventional resource extraction (e.g., shale gas and tight oil), and geological storage applications (CO₂, H₂, and natural gas). This review presents a comprehensive synthesis of well integrity challenges, failure mechanisms, monitoring technologies, and management strategies across these operational domains. Key integrity threats—including cement sheath degradation (chemical attack, debonding, cracking, microannuli), casing failures (corrosion, collapse, burst, buckling, fatigue, wear, and connection damage), sustained casing pressure (SCP), and wellhead leaks—are examined in detail. Unique challenges posed by hydraulic fracturing in unconventional wells and emerging risks in CO₂ and hydrogen storage, such as corrosion, carbonation, embrittlement, hydrogen-induced cracking (HIC), and microbial degradation, are also highlighted. The review further explores the evolution of integrity standards (NORSOK, API, ISO), the implementation of Well Integrity Management Systems (WIMS), and the integration of advanced monitoring technologies such as fiber optics, logging tools, and real-time pressure sensing. Particular emphasis is placed on the role of digital technologies—including artificial intelligence, machine learning, and digital twin systems—in enabling predictive maintenance, early failure detection, and lifecycle risk management. The novelty of this review lies in its integrated, cross-domain perspective and its emphasis on digital twin applications for continuous, adaptive well integrity surveillance. It identifies critical knowledge gaps in modeling, materials qualification, and data integration—especially in the context of long-term CO₂ and H₂ storage—and advocates for a proactive, digitally enabled approach to lifecycle well integrity. Full article