Search Results (1,338)

Alkali-activated materials (AAMs) offer an eco-friendly alternative to traditional Portland cement, yet their rheological properties, particularly in concrete mixtures, remain largely underexplored. This study conducted rheological tests to investigate the flow properties and thixotropic behavior of alkali-activated slag (AAS) concrete with varying water-to-binder (w/b) ratios and silicate modulus (Ms). The thixotropy of AAS concrete was assessed using the thixotropic index, breakdown area, and variations in apparent viscosity under different shear rates, revealing correlations between thixotropic behaviors and rheological parameters. Mixtures with lower Ms and w/b ratios showed limited slump values and rapid structural build-up due to increased interparticle connections. As Ms increased, enhanced thixotropic behaviors were observed, attributed to the rapid formation of early hydration products. This led to a significant increase in peak torque values and a slight decrease in equilibrium torque values at various rotational speeds. In turn, AAS concrete with higher Ms demonstrated improved fluidity and workability retention after thixotropic build-up was erased. The results of this study provide valuable insights into the flow and thixotropic behaviors of fresh AAS concretes for practical applications. Full article

Limestone (LS) and stabilised secondary spruce chips (SCs) utilisation in wood–cement composites is still an unexplored area. Therefore, the main objective of the research presented here is the assessment of the long-term behaviour of cement-bonded particleboards (CBPs) modified by LS and SCs. Cement (CE) was replaced by 10% of LS, and spruce chips by 7% of SCs. The test specimens were stored in a laboratory and exterior environment (Middle Europe) for up to 2 years. The density, strength, and modulus of elasticity were evaluated after 28 days, and then in 6-month periods. The hygroscopicity was analysed separately. The mineralogical composition and microstructure were analysed due to possible LS participation during hydration. SC synergic behaviour in CBPs was also studied. After 2 years, the microstructure of the CBP was more compact, and denser. Strong carbonatation contributes to the improvement of CBP properties. The products of carbonatation were present in both the matrix and wood chips. The hydration of the matrix was almost finished. LS has a positive effect on the matrix microstructure development. LS acts both as an active component participating in the formation of the cement matrix structure and as an inert microfiller, synergic with hydration products. SCs have a positive effect on the hygroscopic behaviour of CBPs and slightly negative effect on the tensile strength. Full article

The application of nanocomposites based on polyacrylamide hydrogels as well as silica nanoparticles in various tasks related to the petroleum industry has been rapidly developing in the last 10–15 years. Analysis of the literature has shown that the introduction of nanoparticles into hydrogels significantly increases their structural and mechanical characteristics and improves their thermal stability. Nanocomposites based on hydrogels are used in different technological processes of oil production: for conformance control, water shutoff in production wells, and well killing with loss circulation control. In all these processes, hydrogels crosslinked with different crosslinkers are used, with the addition of different amounts of nanoparticles. The highest nanoparticle content, from 5 to 9 wt%, was observed in hydrogels for well killing. This is explained by the fact that the volumes of injection of block packs are counted only in tens of cubic meters, and for the sake of trouble-free workover, it is very important to preserve the structural and mechanical properties of block packs during the entire repair of the well. For water shutoff, the volumes of nanocomposite injection, depending on the well design, are from 50 to 150 m³. For conformance control, it is required to inject from one to several thousand cubic meters of hydrogel with nanoparticles. Naturally, for such operations, service companies try to select compositions with the minimum required nanoparticle content, which would ensure injection efficiency but at the same time would not lose economic attractiveness. The aim of the present work is to develop formulations of nanocomposites with increased structural and mechanical characteristics based on hydrogels made of partially hydrolyzed polyacrylamide crosslinked with resorcinol and paraform, with the addition of commercially available nanosilica, as well as to study their thermal degradation, which is necessary to predict the lifetime of gel shields in reservoir conditions. Hydrogels with additives of pyrogenic (HCSIL200, HCSIL300, RX380) and hydrated (white carbon black grades: ‘BS-50’, ‘BS-120 NU’, ‘BS-120 U’) nanosilica have been studied. The best samples in terms of their structural and mechanical properties have been established: nanocomposites with HCSIL200, HCSIL300, and BS-120 NU. The addition of hydrophilic nanosilica HCSIL200 in the amount of 0.4 wt% to a hydrogel consisting of partially hydrolyzed polyacrylamide (1%), resorcinol (0.04%), and paraform (0.09%) increased its elastic modulus by almost two times and its USS by almost three times. The thermal degradation of hydrogels was studied at 140 °C, and the experimental time was converted to the exposure time at 80 °C using Van’t Hoff’s rule. It was found that the nanocomposite with HCSIL200 retains its properties at a satisfactory level for 19 months. Filtration studies on water-saturated fractured reservoir models showed that the residual resistance factor and selectivity of the effect of nanocomposites with HCSIL200 on fractures are very high (226.4 and 91.6 for fracture with an opening of 0.05 cm and 11.0 for porous medium with a permeability of 332.3 mD). The selectivity of the isolating action on fractured intervals of the porous formation was noted. Full article

Alite calcium sulfoaluminate (ACSA) cement is an innovative and environmentally friendly cement compared to ordinary Portland cement (OPC). The synthesis and hydration of ACSA clinkers doped with gradient sulfur were investigated. The clinker compositions and hydrated pastes were characterized by X-ray diffraction (XRD), isothermal calorimetry, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) to analyze its mineral contents, hydration products, heat release, pore structure, and microstructure. The compressive strength and linear expansion of ACSA mortars were tested for their mechanical properties. Results showed that clinkers doped with 2 wt.% MgO can offset the hurdle that SO₃ caused to the formation of C₃S (tricalcium silicate). Clinkers with varying ratios of C₃S and C₄A₃$ (calcium sulfoaluminate) were obtained, achieving 58–70% C₃S and 2.0–5.6% C₄A₃$ in ACSA through adjusting the KH (lime saturation factor) values and SO₃ dosage. ACSA cement showed better early mechanical properties. The 0.93 KH value with 3% SO₃ dosage in the raw meal, which contains 63.9% C₃S and 2.98% C₄A₃$ in the clinker, reached an optimal compressive strength level at 1d (26.35 MPa) and at 3d (39.41 MPa), marking 30.45% and 18.70% increases compared to PII 52.5. The excellent early strength of ACSA cement may offer promising applications t increasing the incorporation of supplementary cementitious materials, thereby reduce pollution and carbon emissions. Full article

Rotor shafts are the most heavily loaded and accident-prone parts of powerful turbine generators, which are cooled using hydrogen. To eliminate damage sustained during operations, repair work was carried out, including the removal of defective parts, surfacing, and turning. This study tested the machinability of the rotor shaft using prototypes made from 38KhN3MFA steel. A section of the shaft was degraded due to prolonged operation (250 thousand hours), and compared to the central part, a decrease in the average grain size from 21.57 μm to 12.72 μm and an increase in the amount of hydrogen absorbed during operation from 2.27 to 7.54 ppm were observed. With the frequency of dry turning increasing from 200 to 315 RPM, the chips changed their form from mostly rectangular with linear dimensions of 10 to 20 mm to large spiral rings with a diameter of 15 to 20 mm and a length of more than 50 mm. Cracks of 1 to 4 mm in length were found in most chip particles at both rotational speeds. Increasing the rotational speed from 200 to 315 and up to 500 RPM led to the formation of an oxide film on the surface of the specimens, as evidenced by the appearance of oxygen during local analyses of the elemental content on the chip surface. The saturation of specimens by hydrogen gas led to the formation of finer chips compared to the non-hydrated material, and the roughness of the machined surface increased at hydrogen contents of 6 and 8 ppm. In both dry and coolant cutting operations, surface roughness reflects the degradation of the rotor shaft or experimental prototypes due to hydrogenation, which can be used to diagnose the condition of the rotor after long-term operation. Full article

This study developed a sustainable low-carbon cementitious material using calcium carbide residue (CCR) as an alkali activator, combined with ground granulated blast furnace slag (GGBS) and fly ash (FA) to form a composite. The objective was to optimize the CCR dosage and the GGBS-to-FA ratio to enhance the unconfined compressive strength (UCS) of the composite, providing a viable alternative to traditional Portland cement while promoting solid waste recycling. Experiments were conducted with a water-to-binder ratio of 0.55, using six GGBS-to-FA ratios (0:10, 2:8, 4:6, 6:4, 8:2, and 10:0) and CCR contents ranging from 2% to 12%. Results indicated optimal performance at a GGBS-to-FA ratio of 8:2 and an 8% CCR dosage, achieving a peak UCS of 18.04 MPa at 28 days, with 79.88% of this strength reached within just 3 days. pH testing showed that with 8% CCR, pH gradually decreased over the curing period but increased with higher GGBS content, indicating enhanced reactivity. Microstructural analyses (XRD and SEM-EDS) confirmed the formation of hydration products like C-(A)-S-H, significantly improving density and strength. This study shows CCR’s potential as an effective and environmentally friendly activator, advancing low-carbon building materials and resource recycling in construction. Full article

This study investigated the potential for efficient and resourceful utilization of phosphogypsum (PG) through the preparation of a High-volume Phosphogypsum Cement Stabilized Road Base (HPG-CSSB). The investigation analyzed the unconfined compressive strength (UCS), water stability, strength formation mechanism, microstructure, and pollutant curing mechanism of HPG-CSSB by laser diffraction methods (LD), X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma-mass spectrometry (ICP-MS). The optimal mix ratio of HPG-CSSB was 4% cement, 1% CA2, 35% PG, and 60% graded crushed stone. The UCS reached 6.6 MPa, 9.3 MPa, and 11.3 MPa at 7, 28, and 60 d, respectively. The alkaline curing agent stimulated cement activity and accelerated the release of Ca²⁺ and SO₄²⁻ from the PG. This formed many C-S-H gels and ettringite (AFt). The curing agent converted Ca²⁺ to C-(A)-S-H gels due to high volcanic ash activity. The diverse hydration products strengthened HPG-CSSB. The HPG-CSSB exhibits favorable water stability, demonstrating a mere 7.6% reduction in strength following 28 d of immersion. The C-S-H gel and AFt generated in the system can carry out ion exchange and adsorption precipitation with F⁻ and PO₄³⁻ in PG, achieving the curing effect of toxic and hazardous substances. HPG-CSSB meets the Class A standard for integrated wastewater discharge. Full article

Using solid waste-based materials, such as recycled building aggregate (RCA), preparing 3D-printed materials can reduce costs but increase the water–cement ratio of the printed material, which reduces its mechanical performance. In order to solve the problem of mechanical properties decline caused by an increase in the w/c ratio, this experiment found that adding calcined salt mud (CSM) to the printing materials and changing the water-to-cement ratio from 0.37 to 0.4 CSM can ensure that the compressive strength of the printing materials remains basically unchanged. Moreover, through TG, SEM, and other microscopic data, it can be seen that calcium hydroxide in CSM can not only participate in the synergistic reaction of ethylene/vinyl acetate copolymer (EVA) and dust ash (DA), produce more NaOH, and promote the hydration of granulated blast furnace slag (GBFS) but also promote the formation of ettringite together with SO₄²⁻ in solution, optimizing pore size distribution. Full article

Chloride binding technology can effectively reduce the content of free chloride ions in seawater (used for cementitious materials), thereby extending the service life of seawater concrete structures. Currently, affordable and highly dispersed nanomaterials that can enhance the chloride binding capability of seawater cement are finite. This paper presents the first experimental study on N-doped graphene quantum dots (NGQDs), an innovative carbon nanomaterial with low price and high dispersibility, to strengthen the mechanical and chloride binding capabilities of seawater cement. Concretely, NGQDs are prepared through the hydrothermal process. The morphology and structure of NGQDs are measured by TEM, AFM, FTIR, and XPS. And the strengths and chloride binding performance of different specimens are analyzed by compressive/flexural strength tests and chloride adsorption equilibrium tests. The phase compositions of various specimens are analyzed by XRD, TGA/DTG, and SEM. The consequences indicate that the unique structure of the prepared NGQDs endows them with excellent water solubility and dispersibility. Notably, the introduction of NGQDs enhances the mechanical performance of seawater cement and 0.05 wt.% NGQDs have the greatest improvement effect. The compressive and flexural strengths of seawater cement containing 0.05 wt.% NGQDs increase by 8.21% and 25.77% after 28 d curing, respectively. Additionally, the seawater cement containing 0.2 wt.% NGQDs have the best chloride binding capability and are 41.08% higher than the blank group. More importantly, the chloride binding mechanism is that NGQDs accelerate seawater cement hydration, resulting in an increased formation of hydrated calcium silicate (C–S–H) and Friedel’s salt (Fs), thereby strengthening the physisorption and chemical combination of chloride. This study highlights an inexpensive and highly dispersible nanomaterial to heighten the stability of seawater concrete structures, opening up a new path for the better utilization of seawater resources. Full article

Wellbore instability caused by hydration during the development of shale gas reservoirs poses significant challenges to drilling engineering. In this study, a novel and environmentally friendly shale inhibitor, TIL-NH₂, was synthesized via free radical polymerization using 1-vinylimidazole and N-(2-bromoethyl)-1,3-propanediamine dihydrobromide as the main raw materials. The molecular structure of TIL-NH₂ was characterized by infrared spectroscopy and nuclear magnetic resonance. Incorporating imidazole cations and amino bifunctional groups, TIL-NH₂ exhibits excellent inhibitory performance and environmental friendliness. Its performance was systematically evaluated through linear swelling tests, shale cuttings rolling recovery tests, permeability recovery experiments, and dynamic adsorption analyses. The results indicate the following: (1) At a concentration of 1.2 wt%, TIL-NH₂ reduced the linear swelling height of shale by 65.69%, significantly outperforming traditional inhibitors like KCl and NW-1. (2) Under conditions of 140 °C, the cuttings rolling recovery rate of TIL-NH₂ reached 88.12%, demonstrating excellent high-temperature resistance. (3) Permeability recovery experiments showed that at a concentration of 2.0 wt%, TIL-NH₂ achieved a permeability recovery rate of 90.58%, effectively mitigating formation damage. (4) Dynamic adsorption experiments indicated that at a concentration of 2.5 wt%, the adsorption capacity tended toward saturation, reaching 26.00 mg/g, demonstrating stable adsorption capability. Additionally, environmental friendliness evaluations revealed that TIL-NH₂ has a degradation rate exceeding 90% within 28 days, and its acute toxicity is significantly lower than that of traditional inhibitors like KCl (the LC₅₀ of TIL-NH₂ is 1080.3 mg/L, whereas KCl is only 385.4 mg/L). This research provides a high-efficiency and environmentally friendly new inhibitor for green drilling fluid systems in horizontal shale gas wells, offering important references for technological advancements in unconventional energy development. Full article

Background: Diabetes is a growing global health crisis that requires effective therapeutic strategies to optimize treatment outcomes. This study aims to address this challenge by developing and characterizing extended-release polymeric matrix tablets containing metformin hydrochloride (M-HCl), a first-line treatment for type 2 diabetes, and honokiol (HNK), a bioactive compound with potential therapeutic benefits. The objective is to enhance glycemic control and overall therapeutic outcomes through an innovative dual-drug delivery system. Methods: The tablets were formulated using hydrophilic polymers, such as Carbopol^® 71G NF and Noveon^® AA-1. The release kinetics of M-HCl and HNK were investigated through advanced mathematical models, including fractal and multifractal dynamics, to capture the non-linear and time-dependent release processes. Traditional kinetic models (zero-order, first-order, Higuchi equations) were also evaluated for comparison. In vitro dissolution studies were conducted to determine the release profiles of the active ingredients under varying polymer concentrations. Results: The study revealed distinct release profiles for the two active ingredients. M-HCl exhibited a rapid release phase, with 80% of the drug released within 4–7 h depending on polymer concentration. In contrast, HNK demonstrated a slower release profile, achieving 80% release after 9–10 h, indicating a greater sensitivity to polymer concentration. At shorter intervals, drug release followed classical kinetic models, while multifractal dynamics dominated at longer intervals. Higher polymer concentrations resulted in slower drug release rates due to the formation of a gel-like structure upon hydration, which hindered drug diffusion. The mechanical properties and stability of the matrix tablets confirmed their suitability for extended-release applications. Mathematical modeling validated the experimental findings and provided insights into the structural and time-dependent factors influencing drug release. Conclusions: This study successfully developed dual-drug extended-release matrix tablets containing metformin hydrochloride and honokiol, highlighting the potential of hydrophilic polymers to regulate drug release. The findings emphasize the utility of advanced mathematical models for predicting release kinetics and underscore the potential of these formulations to improve patient compliance and therapeutic outcomes in diabetes management. Full article

Nano metakaolin (NMK) has attracted considerable interest for its potential to improve the durability of cementitious materials. However, the effect of NMK on the splitting tensile performance of concrete has not been systematically investigated. This study investigates the splitting tensile performance of NMK concrete and analyzes its failure behavior under splitting load. Different NMK dosages (0%, 1%, 3%, 5%, and 7%) were considered, and splitting tensile tests were conducted. The crack propagation process, crack width, and crack growth rate on the surface of NMK concrete during the splitting tensile test are analyzed using the Digital Image Correlation (DIC) method. The mechanisms by which NMK affects the splitting tensile performance of concrete were examined using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and Thermogravimetric Analysis (TG). The results indicate that the incorporation of NMK enhances the splitting tensile performance of concrete. Concrete with 5% NMK addition exhibited the highest splitting tensile strength, with an increase of 17.4% compared to ordinary concrete. NMK improved the cracking resistance and overall integrity under splitting tensile load. With 5% NMK addition, the surface crack length, width, and main crack propagation rate of the concrete decreased by 4.5%, 35.3%, and 29.6%, respectively. NMK contributed to a denser internal structure of the concrete, promoted the formation of C-S-H gel, and increased the degree of cement hydration. Moreover, a lower thickness and Ca/Si ratio of interfacial transition zone (ITZ) were observed in NMK concrete. The ITZ thickness and Ca/Si ratio of concrete with 5% NMK were reduced by 64.4% and 85.4%, respectively, compared to ordinary concrete. In summary, the influence mechanism of NMK addition on the splitting tensile strength and failure behavior of concrete is explored in this study, providing experimental data to support the application of NMK concrete in practical engineering. Full article

Fly ash–cement composite backfill slurry, prepared by partially replacing cement with fly ash, has been demonstrated to effectively reduce the mine backfill costs and carbon emissions associated with cement production. However, the use of fly ash often results in insufficient early and medium-term strength of the backfill material. To address the demand for high medium-term strength in backfill materials under continuous mining and backfilling conditions, this study developed a silica fume–fly ash–cement composite backfill slurry. The effects of varying silica fume contents on the slurry’s flowability, uniaxial compressive strength, microstructure, and pore characteristics were systematically investigated. The results showed that increasing the silica fume content significantly reduced the slurry’s flowability. However, at a silica fume content of 5%, the slurry achieved optimal medium-term strength, with a 14-day uniaxial compressive strength of 3.98 MPa, representing a 25% improvement compared to the control group. A microstructural analysis revealed that a moderate silica fume content promoted the formation of calcium silicate hydrate gel, filled micropores, and optimized the pore structure, thereby enhancing the overall strength and durability of the material. Conversely, an excessive silica fume content above 5% led to a marked decrease in both flowability and strength. Based on a comprehensive evaluation of silica fume’s effects on the flowability, strength, and microstructure, the optimal silica fume content was determined to be 5%. This study provides a theoretical basis and practical guidance for improving the efficiency of continuous mining and backfilling operations, and for designing high-performance backfill materials suitable for continuous mining and filling conditions. Full article

By volume, cement concrete is one of the most widely used construction materials in the world. This requires a significant amount of Portland cement, and the cement industry, in turn, causes a significant amount of CO₂ emissions. Therefore, the development of concrete with a reduced cement content is becoming an urgent problem for countries with a significant level of production and consumption of concrete. Therefore, the purpose of this article is to critically investigate the possibility of using inert granite dust in combination with highly active silica fume in reactive powder concrete. The main physical and mechanical properties, such as the compressive strength at different curing ages and the water absorption, were studied using mathematical planning of experiments. The consistency and microstructure of the reactive powder concrete modified with granite dust in combination with silica fume were also analyzed. Mathematical models of the main properties of this concrete are presented and analyzed, and the graphical dependencies of the influence of composition factors are constructed. A more significant factor that affects the compressive strength at all curing ages is the silica fume content, increases in which to 50 kg/m³ lead to a 25–40% increase in strength at 1 day of age, depending on the granite dust content. In turn, an increase in the amount of granite dust from 0 kg/m³ to 100 kg/m³ in the absence of silica is followed by an increase in strength of 8–10%. After 3 days of curing, the effect of granite dust becomes more significant. Increases in the 28-day strength of 25%, 46% and 56% were obtained at a content of 50 kg/m³ of silica fume and 0 kg/m³, 100 kg/m³ and 200 kg/m³ of granite dust in concrete, respectively. It is shown that the effect of inert granite dust is more significant in combination with silica fume at its maximum content in the range of variation. The pozzolanic reaction between highly active silica and Ca(OH)₂ stimulates the formation of hydrate phases in the space between the grains and causes the microstructure of the cement matrix to compact. In this case, the granite dust particles act as crystallization centers. Full article

Bio-sulfur (BS), extracted from landfill bio-gas via microbial methods, was examined herein as a potential cement replacement material. The study developed five modified BS variants through limestone incorporation processes (sulfur-to-limestone ratios of 1:0.5, 1:1, 1:1.5, 1:3, and 1:5). The study revealed that modified BS with higher limestone ratios demonstrates significant workability and strength reductions of over 50% with increased content, leading to the adoption of a sulfur-to-limestone ratio of 1:1. The concrete specimens exhibited compressive strength improvements of up to 12% with increased BS content, while the UPV showed proportional increases with increased BS content that remained independent of the water/binder (W/B) ratio. Statistical analysis confirmed significance with p-values below 0.05. XRD analysis identified initial cement hydrate peaks at 3 d that evolved into distinct Mg-S hydrate and Ca-Al-S hydrate formations in the BS-containing specimens by 28 d. Full article