Search Results (359)

The development of low-carbon binders from industrial solid wastes can reduce Portland cement use and support sustainable construction. However, the combined roles of alkalinity supply, sulfate reaction, and reactive silica supplementation in ground granulated blast furnace slag (GGBS)–calcium carbide slag (CCS)–desulfurized gypsum (DG)–silica fume (SF) binders remain unclear. A Box–Behnken design was used to evaluate the 3 d and 28 d mechanical properties, and response surface methodology (RSM) was subsequently applied to optimize CCS, DG, and SF contents based on the 28 d flexural and compressive strengths. Hydration and microstructure were characterized by isothermal calorimetry, XRD, TG–DTG, and SEM–EDS. Within the investigated ranges, DG exhibited the strongest quadratic effect on both 28 d strength responses, while CCS showed a pronounced effect on compressive strength and SF exhibited significant dosage-dependent effects. The optimized mixture contained 16.1% CCS, 9.7% DG, 9.5% SF, and 64.7% GGBS, achieving experimentally validated 28 d flexural and compressive strengths of 10.2 and 35.9 MPa, respectively. CCS promoted GGBS dissolution, DG facilitated ettringite formation, and SF enhanced C-(A)-S-H formation and pore filling. Their coordinated action produced a denser gel–crystal framework, providing guidance for the design of multi-solid-waste binders for low-carbon construction applications. Full article

The mantle of bivalves plays a fundamental role in shell formation and maintenance through biomineralization. Experiments performed on mantle–shell preparations using different experimental techniques revealed the presence of phosphorus (P)-containing compounds in the shell as the first mineral phase formed at the growing edge of the periostracum in the freshwater bivalve Limnoperna fortunei. The low P concentration in the shells suggests that phosphate is restricted to the growth regions and occurs at concentrations too low to be detected by techniques such as X-ray diffraction (XRD). Nevertheless, a crystal morphology closely resembling that of hydroxyapatite (HAp) was identified at the shell growth front, and a Ca/P ratio of 1.67, consistent with HAp, was determined in two of these regions. Fourier transform infrared (FTIR) spectroscopy also revealed the principal and most intense absorption band of the phosphate group (PO₄³⁻) at 1024 cm⁻¹. Enzymes such as carbonic anhydrase (CA), or proteins with equivalent functions, are likely involved in phosphate dissolution and the subsequent precipitation of calcium carbonate. In addition, the occurrence of calcium phosphate was confirmed in the shells of the marine bivalve Perna perna. Phosphate dissolution and carbonate precipitation during biomineralization suggest two important evolutionary advantages: first, the release and availability of phosphate, an essential nutrient for energy production and other metabolic functions; and second, the formation of a calcium carbonate shell, a structure indispensable for the protection, mechanical support, and survival of mollusks. Full article

Concrete is fundamentally susceptible to cracking, which creates pathways for aggressive agents, accelerating reinforcement corrosion and reducing service life. Traditional repair methods are ineffective for micro-cracks and generate volatile compounds. Microbially induced calcium carbonate precipitation (MICP) offers a sustainable bio-based alternative that catalyses in situ calcium carbonate (CaCO₃) precipitation within cracks, sealing pathways. This study compares two MICP repair systems consisting of Sporosarcina pasteurii (SP, ureolytic) and Bacillus mucilaginosus (BM, non-ureolytic), utilising a dual-viscosity-modifying-agent (VMA) system comprising Welan Gum and Attagel 50 (WA). The repair treatments were applied externally on cracked concrete specimens across crack widths of 0.10–0.80 mm for 16 days. Crack repair effectiveness was evaluated through splitting tensile strength, capillary water absorption, rapid chloride migration (RCM), and X-ray diffraction (XRD). SP + WA exhibited high performance trends compared with BM + WA, achieving tensile strength retention of 59.57–68.95% vs. 56.68–67.15%, capillary water absorption recovery ranges of 58.36–64.81% vs. 51.71–58.02%, chloride resistance recoveries of 63.7–82.1% vs. 50.5–60.0%, and D_RCM recoveries of 57.35–77.68% vs. 46.04–61.00% relative to intact controls. Durability recovery efficiency decreased with increasing crack width. XRD confirmed calcite as the sole CaCO₃ polymorph in both systems, with sharper peaks in SP + WA indicating differences in calcite crystal characteristics, while BM + WA produced broader peaks similar to a nanocrystalline CaCO₃ structure. These findings demonstrate that the dual-VMA-assisted MICP approach potentially improves mechanical and durability properties in cracked concrete, with ureolytic SP demonstrating better repair performance trends. Full article

Background: Calcium phosphate cements (CPCs) are excellent biomaterials for peri-implant bone regeneration but suffer from slow resorption. This study evaluated whether adding carbonate salts improves the in situ porosity and resorption rate of customized CPCs. Methods: The control group comprised α-tricalcium phosphate (α-TCP) and phosphoserine (3:1 weight-to-weight ratio). The test group incorporated 3 wt.% anhydrous sodium carbonate (Na₂CO₃) into the powder. Both were hydrated with water at a liquid-to-powder ratio of 300 μL:1 g. Characterization included micro-computed tomography (μCT), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR), removal torque tests, compression modulus tests, and hardness tests. Results: μCT and SEM confirmed higher porosity and uniform crystal plates in the test group compared to the dense control group. FTIR-ATR spectra showed a distinct CO₂ peak at 2349 cm⁻¹ for the test group, confirming gas entrapment. Mechanically, the control group significantly outperformed the test group in removal torque (71.58 ± 5.56 N/cm vs. 41.37 ± 4.54 N/cm) and compression modulus (1248.01 ± 278.21 MPa vs. 195.42 ± 29.55 MPa). Hardness tests showed increased brittleness in the test group (15.31 ± 1.63 vs. 2.01 ± 1.58). Conclusions: Incorporating Na₂CO₃ successfully induced in situ porosity via gas release but significantly compromised mechanical strength. Further optimization is required to balance porosity and mechanical integrity. Full article

To address the environmental hazards caused by massive bauxite red mud stockpiles, phase-change unburned bricks have been developed. The slump flow and initial setting time of fresh mortar were tested, while the flexural strength, compressive strength, splitting tensile strength and rebound hardness of hardened mortar specimens were measured. The synergistic influence of stearic acid on mechanical strengths, rebound hardness and thermal conductivity was revealed, and the corresponding indoor simulation tests were performed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ultra-depth-of-field microscope cross-section scanning were adopted to interpret the intrinsic microstructure and inner mechanism. Results indicate that slump flow, initial setting time and all mechanical indices follow cubic functional relationships with red mud mass ratio. Specimens incorporating 20 wt.% red mud achieve the optimal mechanical strength, rebound hardness and thermal conductivity, with the maximum growth rates of up to 32.7%, 18.7% and 27.0%, respectively. Appropriately, straw fibers improve the mechanical properties and rebound hardness yet reduce thermal conductivity. In simulated thermal cabin tests, wall temperature continuously rises under heating and declines after heat termination; red mud and straw fibers jointly slow the heating-up rate and post-heating cooling rate. Samples with 5 wt.% red mud possess the densest hydration matrix. Red mud promotes the generation of ettringite (AFt), calcium carbonate and dolomite crystals, and elevates the content of dicalcium silicate (C₂S) within the binder system. This study provides a reference for fabricating functional wall materials using industrial solid waste (red mud) and agricultural solid waste (straw fibers). Full article

Microbially induced calcium carbonate precipitation (MICP) is a promising biotechnology for environmental remediation; however, the high cost of conventional chemical-grade calcium sources limits its large-scale scalability. This study evaluated the feasibility of utilizing an aqueous extract of natural attapulgite clay as a sustainable, low-cost calcium source for MICP-mediated arsenic (As) immobilization in both aqueous and soil systems. Among the tested minerals, Baiyin attapulgite (group B) exhibited the highest calcium content (62,808.94 mg kg⁻¹) and minimal toxic metal impurities, providing a favorable chemical matrix for biomineralization. At an optimal solid-to-liquid ratio of 1:10, Lysinibacillus fusiformis LF and Enterococcus LZU-1 successfully induced calcite precipitation driven by the attapulgite extract. In batch aqueous remediation experiments (20 days), the attapulgite extract significantly enhanced As removal efficiency compared to the controls; As removal rates peaked at 66.4% for strain LZU-1 (with LZ1 extract) and 65.8% for strain LF (with group B extract), drastically outperforming the standard CaCl₂ groups (31.2–37.3%) and blank controls (21.8–24.5%). Concurrently, soil incubation experiments (30 days) demonstrated that the combined application of attapulgite and MICP bacteria reduced the highly bioavailable exchangeable As fraction from 0.115 to approximately 0.03 mg kg⁻¹, while effectively driving its transformation into more stable carbonate-bound and organic-bound fractions without causing secondary soil salinization. Morphological and mechanistic analyses revealed that, compared to the well-defined euhedral crystals in the CaCl₂ control, the precipitates mediated by the clay extract exhibited distinctly irregular, defect-rich rhombohedral structures. This structural disruption was governed by the natural matrix effect of attapulgite, which simultaneously supplied dissolved Ca²⁺ and provided an abundance of fine clay fragments, calcite micro-grains, and associated amorphous Fe/Al/Mn-bearing phases. These constituents acted as physical scaffolding and heterogeneous nucleation sites that became embedded in the growing CaCO₃ lattice, driving the formation of highly reactive, defect-rich clay-calcite-arsenic composite precipitates that efficiently encapsulated arsenate. Mantel analysis further revealed that the remediation efficiency was significantly correlated with key environmental variables including Ni, V, Ca. These findings highlight the dual-system potential of natural attapulgite as an inexpensive, eco-friendly calcium alternative for sustainable MICP-based remediation of As-contaminated water and agricultural soils. Full article

This study was conducted to determine the optimal mineralization enhancement period for recycled aggregates, and to elucidate the mechanisms underlying the mineralization enhancement of recycled aggregates and the self-healing of concrete cracks. Microbial-induced calcium carbonate precipitation enables the self-healing of concrete cracks: microbial carriers can effectively increase the survival rate of microorganisms within the concrete matrix, thereby enhancing the self-healing performance of the concrete. However, current carriers suffer from poor mechanical properties, poor compatibility with cement-based materials, and high costs. This study proposed a crack-self-healing concrete based on a mixed culture of microorganisms immobilized in recycled aggregate, and investigated the effects of the time of recycled aggregate incorporation on the concrete’s compressive strength and self-healing performance. The results showed that the optimal adsorption and incubation times for the recycled aggregates were 15 min and 9 days, respectively. Following mineralization and reinforcement, the water absorption and crushing index of the recycled aggregates was 11.4% and 20.4%, respectively. Moreover, the precipitates at the concrete cracks were in the form of regular cubes and clusters, and the crystals were calcite and aragonite. Small amounts of phosphorus were detected, originating from extracellular polymers produced by microbial metabolism, indicating that the organic matrix was involved in the crystal nucleation and growth processes. The compressive strength of the concrete increased by 35%. After repair and curing, the crack healing rate of the concrete reinforced with microorganisms immobilized on the recycled aggregates reached 70%. Full article

Calcite habit engineering offers a route to transform CO₂ mineralization from bulk sequestration into value-added nanomaterial production. Here, we demonstrate that additive chemistry and seeding strategy can serve as separable, recipe-level levers for directing calcite habit formation within a unified CaO/Ca(OH)₂ gas–liquid carbonation platform. This strategy highlights how solution-mediated habit control can bridge fundamental calcite crystallization mechanisms with scalable CO₂ utilization and value-added carbonate nanomaterial production. Sodium glutamate yielded ~100 nm rhombohedral nanoparticles, staged MgSO₄/ZnSO₄ dosing produced whisker-like crystalline nanorods with aspect ratios of 4–7, and two-step seeded carbonation with NH₄Cl generated fusiform spindle subunits that assembled into hierarchical rosette architectures. X-ray diffraction confirmed calcite as the only crystalline calcium carbonate phase detected under the present measurement conditions, with no detectable aragonite or vaterite reflections. SEM/TEM revealed distinct primary-subunit architectures, including internal striations in spindle particles indicative of oriented attachment. Thermogravimetry, N₂ physisorption, and EDS further distinguished the products and showed that Mg/Zn/S modifiers in the whisker route are retained predominantly at crystal surfaces rather than incorporated into the calcite lattice. These results define calcite habit control through two independent levers: additive-driven facet selectivity and kinetic decoupling of nucleation from growth/assembly. The platform links scalable synthesis, CO₂ utilization, and functional carbonate design. Full article

The extreme environment characterized by repeated freeze–thaw cycles poses a severe challenge to the stability and durability of loess in engineering applications. This study systematically investigates the improvement of Weinan loess using a plant-based bio-cement (BC) combined with fly ash (FA) under extreme freeze–thaw environments. Through unconfined compressive strength tests, permeability tests, calcium carbonate content measurements, and microscopic analyses (SEM and XRD), the mechanical properties, microstructural evolution, and crack development characteristics of the improved loess were comprehensively evaluated. The results demonstrate that BC-FA modification significantly enhances the mechanical strength and impermeability of loess. The unconfined compressive strength of the 7% FA-amended specimen increased by 201.6% compared to untreated loess, while the permeability coefficient decreased by 61.58%. Freeze–thaw-induced deterioration predominantly occurred within the first five cycles, with a maximum peak strength reduction of 33.29%, after which the soil structure gradually stabilized beyond ten cycles. Microscopic observations revealed that biomineralized calcium carbonate crystals (calcite, aragonite, and vaterite) filled pores and bridged soil particles, forming a continuous cementation network. Furthermore, a novel Crack Identification Method Based on Multi-Feature Mechanical Responses (CIMBMFMR) was proposed, which establishes a quantitative mapping between mechanical degradation, micro-damage, and crack evolution, offering superior accuracy and physical interpretability over traditional image-based techniques. The BC-FA system exhibits notable low-carbon and eco-friendly advantages, providing a promising green solution for loess reinforcement in seasonally frozen regions. Full article

To explore potential strategies for improving the applicability of cyanidin-3-O-glucoside (C3G) and to avoid the health risks associated with the in vivo accumulation of aluminum by intake of traditional aluminum-based lake pigments, food-grade CaCO₃ was used as a matrix to prepare two types of edible lake pigments, namely C3G-CaCO₃ and MA-CaCO₃, via coprecipitation method using purified cyanidin-3-O-glucoside (C3G) and non-purified mulberry anthocyanins (MA). The effect of pH on adsorption was systematically investigated, and various characterization methods were used to analyze the physicochemical properties and formation mechanism of lake pigments. The results showed that pH 9.5 was the optimal condition for CaCO₃ to adsorb MA. The introduction of C3G altered the particle size, surface charge, and other characteristics of CaCO₃ without changing its calcite crystal form. The adsorption of MA and C3G on the CaCO₃ surface was multilayer physical adsorption, dominated by the Freundlich model. The isothermal adsorption results showed that CaCO₃ exhibited a higher adsorption capacity for C3G than for MA at equivalent equilibrium concentrations, demonstrating C3G’s superior binding affinity. C3G primarily binds to calcium carbonate through surface adsorption, with possible partial diffusion of molecules into the matrix, without forming new chemical bonds, and slightly regulated the thermal stability of CaCO₃. This study successfully constructed a lake pigment system based on CaCO₃, systematically elucidated its adsorption behavior and structural characteristics toward anthocyanins, and provided a material foundation for the further application of this type of carrier in the food sector. Full article

Loess has a metastable microstructure and high water sensitivity. When exposed to water, it undergoes rapid structural damage and disintegration, posing significant risks to the stability and durability of geotechnical structures such as foundations and slopes. Unconfined compressive strength (UCS) tests, direct shear tests, uniaxial tensile strength tests, and slake durability tests were conducted to evaluate the treatment performance. Optical microscopy and SEM were used to characterize the changes in microstructure to explain the potential reinforcement mechanism. The results show that microbial-induced carbonate precipitation (MICP) treatment leads to substantial improvement. Compared with untreated loess, the UCS, cohesion, internal friction angle, and uniaxial tensile strength increased by 370%, 663%, 43.7%, and 480%, respectively. Empirical refinements to the Mohr-Coulomb criterion were established to relate the measured UCS and uniaxial tensile strength to their theoretical values predicted from cohesion and friction angle. Both correlation models achieved R² > 0.82, quantifying the additional structural strength contributed by bio-cementation. At the same time, the treatment significantly improved water stability, and the slaking index was reduced from 100% to less than 20%. Microstructural analysis shows that precipitated calcium carbonate crystals bond soil particles at contact points and fill inter-particle pores, constructing a bonding framework, which enhances the mechanical strength and water stability of the soil mass. These research results further illustrate the potential of MICP in enhancing the performance of loess in engineering projects. Full article

Phosphogypsum (PG) was used as a calcium source for preparing calcium carbonate (CaCO₃) through NH₄Cl leaching followed by high-pressure carbonation. The effects of NH₄Cl concentration, liquid-to-solid mass ratio, temperature, and leaching time on Ca²⁺ extraction were investigated, and the effects of CO₂ pressure, carbonation time, and NH₃·H₂O dosage on Ca²⁺ conversion were evaluated. The optimal conditions were an NH₄Cl concentration of 1.5 mol/L, a liquid-to-solid mass ratio of 60:1, a leaching temperature of 25 °C, a leaching time of 60 min, a CO₂ pressure of 1 MPa, a carbonation time of 10 min, and 12 vol% NH₃·H₂O addition. Under these conditions, the Ca²⁺ leaching rate and conversion rate reached 81.25% and 97.36%, respectively. The product obtained without organic additives was mainly spherical vaterite with partial particle agglomeration. Based on the optimized process, aspartic acid, glutamic acid, ethanol, and glycerol were introduced to regulate CaCO₃ crystallization. Appropriate additive dosages further improved Ca²⁺ conversion, promoted calcite as the dominant polymorph, and produced well-dispersed spherical CaCO₃ particles. Among the tested additives, glutamic acid and glycerol showed the strongest effects on crystal morphology regulation. Full article

Microbial-induced calcite precipitation (MICP) and enzyme-induced calcite precipitation (EICP) have emerged as research hotspots in recent years at the intersection of geotechnical engineering, environmental engineering, and materials engineering. Compared with traditional grouting reinforcement and repair methods, these methods exhibit greater environmental benignity, higher calcium carbonate precipitation yield, and more significant improvement in mechanical properties of repaired materials. The urease activity in the urease-based MICP and EICP techniques lies at the core of rock fracture repair, soil reinforcement, and concrete crack remediation. This paper presents a systematic review of urease-based MICP and EICP repair technologies, focusing on repair principles, environmental influencing factors, research methods, and application approaches, including microbial cultivation, enzyme activity determination, preparation of cementing solutions, selection of carriers, injection methods, and repair cycles. It also compares the advantages and disadvantages of MICP and EICP. This review clarifies the intrinsic similarities and differences between the two technologies in mineralization mechanism, crystal characteristics and engineering applicability, and constructs a complete technical system of urease-based biomineralization. Additionally, this paper discusses current macroscopic and microscopic evaluation methods for biomineralization repair effects, synthesizes existing mineralization repair systems, and assesses the challenges of self-healing biomaterials, including long-term microbial durability, repair strength stability, and the overall cost of widespread application. It includes long-term microbial durability, repair strength stability, enzyme activity retention, and the overall cost of widespread application, which are key issues to be solved for engineering implementation. The aim of this study is to provide a theoretical and practical reference for the theoretical improvement and engineering application of EICP and MICP technologies. Full article

Enzyme-Induced Carbonate Precipitation (EICP) represents a sustainable advancement in geotechnical engineering for stabilizing fine-grained soils (e.g., silt). Utilizing plant-derived urease (~12 nm) to catalyze urea hydrolysis, this technique generates calcium carbonate (CaCO₃) for soil reinforcement. Unlike Microbially Induced Carbonate Precipitation (MICP), EICP overcomes microbial size constraints (0.5–3 µm) by penetrating soil micropores, enabling uniform cementation. Its innovative single-phase low-pH method achieves >98% calcium conversion efficiency, yielding 6.41 MPa unconfined compressive strength (UCS) in sand—a 92.97% improvement over MICP. EICP demonstrates versatility: enhancing soil strength (up to 650% for silt), erosion resistance (wind erosion modulus increased ~20-fold), anti-seepage performance (permeability reduced from 10⁻⁶ to <10⁻⁹ cm/s), and heavy metal immobilization (>99%). However, challenges include unstable crystal morphologies (e.g., excessive vaterite), urease stability/cost constraints, and environmental concerns related to NH₃ emissions from urea hydrolysis. The manuscript acknowledges these emissions’ impacts and introduces mitigation strategies: ammonia capture technologies, optimized dosing protocols, and exploration of alternative N-sources. Long-term durability data under complex field conditions remain insufficient. Ongoing research addresses these gaps through nucleating agents (dried skim milk, biochar), enzyme immobilization, process optimization, and byproduct treatment. As a low-carbon technology with targeted mitigation measures, EICP advances environmentally conscious soil stabilization practices. This study presents a comparative narrative analysis of EICP’s performance and challenges, integrating laboratory findings and field applications. Full article

Nanoscale precipitated calcium carbonate (NPCC) is a versatile functional material whose performance is highly governed by particle size, morphology, and dispersion state. Conventional synthesis methods often rely on complex additives or multi-step processing, thereby impeding scalability and precise morphological regulation. Herein, we present a simple and additive-free route for the tunable synthesis of NPCC via the direct reaction of an aqueous Na₂CO₃ solution with a Ca(OH)₂ suspension under ambient conditions. A systematic investigation was conducted to elucidate the influence of key synthetic parameters—namely, reactant concentration, temperature, injection rate, stirring speed, and aging duration—on the resultant particle characteristics. Under optimal conditions, cubic NPCC with a mean particle size of approximately 90 nm, distinct crystalline features, and good dispersion was successfully obtained. Furthermore, integrated analysis employing time-resolved pH and conductivity monitoring, electron microscopy, and diffraction techniques revealed a growth trajectory distinct from the classical crystallization pathway of CaCO₃. This observed behavior suggests a mechanistic association with non-classical crystallization. These findings not only furnish a practical and environmentally benign strategy for the production of high-quality NPCC but also offer fundamental insights into the crystallization mechanisms of calcium carbonate, with broader implications for the rational design of advanced inorganic nanomaterials. Full article