Search Results (1,866)

In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce_0.8Gd_0.2O_1.9, Sc_0.1Ce_0.01Zr_0.89O_1.95, and Sc_0.09Yb_0.01Zr_0.9O_1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH₃ in argon, 10% H₂ in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce_0.8Gd_0.2O_1.9 material is a mixed ionic–electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH₃ gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc_0.09Yb_0.01Zr_0.9O_1.95, showing a high, reversible reaction with hydrogen. Full article

In societies worldwide, there is significant pressure on the construction industry to employ waste/recycled materials instead of natural-sourced materials to develop infrastructures to mitigate negative environmental consequences. This study investigated the feasibility of using waste pumice powder as a binder in place of granular blast-furnace slag to manufacture geopolymer concrete. Three sets of GC mixes were developed with three ratios of alkaline activator/binder (A/B) of 0.45, 0.5, and 0.55. Eight GC mixes were prepared for each set, with eight replacement ratios of GGBFS with WPP (0%, 30%, 50%, 60%, 70%, 80%, 90%, and 100%). The influence of WPP addition as a substitute source of aluminosilicate precursors on the fresh (workability and setting time), mechanical (compressive strength and flexural strength), physical characteristics (density and water absorption), and microstructure morphology of WPP/slag-based geopolymers were studied. A linear correlation between UPV and compressive strength was found. The results revealed that setting times and workability are affected by the A/B ratio and content of WPP. WPP reduces the workability and increases setting time (both initial and final). There was a drop in compressive and flexural strengths as the percentage of WPP in the GC increased. The maximum compressive (60 MPa) and flexural strength (4.96 MPa) at an A/B ratio of 0.45 for a 100% slag content mix were obtained. However, a GC mix containing 50% WPP and 50% slag with a compressive strength of 28 MPa after 28 days of curing at ambient temperature was achieved, which is acceptable for structural applications. Full article

In order to study the axial compression performance of steel pipe concrete short columns filled with steel slag micronized ultra-high-performance concrete (UHPC), this paper designs 27 steel pipe UHPC short columns for axial compression test and compares and analyzes the axial compression performance of the specimens in terms of the damage mode, the deformation curve, and the coefficient of strength enhancement, which is aimed at investigating the differences in the actual load-bearing performance of steel pipe UHPC short columns through changes in the aspect ratio, concrete type, and steel content rate, and so on. The purpose of this paper is to compare and analyze the axial compressive performance of the specimens in terms of damage mode and strength enhancement factor in order to investigate the difference in the actual bearing capacity performance of steel pipe UHPC short columns through the changes in length-to-diameter ratio, concrete type, and steel content. The test results show that the axial compressive performance of steel slag powder steel pipe UHPC short columns is greatly affected by the L/D ratio and steel content; the specimen bearing capacity increases with the increase in the wall thickness of the steel pipe and decreases slightly with the increase in the L/D ratio, and the steel fibers can effectively improve the deformation of the concrete so as to enhance the composite effect with the steel pipe; the contribution of the core UHPC to improve the value of bearing capacity accounts for a higher percentage when UHPC with 1% steel fiber dosage and 20% coarse aggregate dosage gave the best uplift with no change in the type of steel pipe. In this paper, the axial compression test bearing capacity results of steel slag micro powder steel pipe UHPC short column are compared with the calculated bearing capacity results of domestic and international specifications and analyzed from the perspectives of perimeter compression strength, steel fiber mixing of core concrete, and the relevant parameter design suggestions for high-strength steel pipe concrete specimens are put forward. Full article

In today’s era of rapid infrastructure development, ensuring the durability and environmental sustainability of soil subgrades in road construction remains a critical concern. With recent advancements in non-traditional soil stabilizing binders, including environmentally friendly industrial waste materials such as fly ash and slag, there is growing recognition of the potential for limestone powder (LSP), a low-carbon alternative soil stabilizing material, to replace traditional calcium-based additives like ordinary Portland cement (OPC) and lime. However, the full extent of LSP’s efficacy in soil treatment has yet to be fully explored. Therefore, this paper investigates the partial substitution of cement with LSP for stabilizing sulfate-bearing saline sandy soil and assesses its impact on the treated soil samples’ mechanical properties and durability parameters. For this purpose, five stabilized mixes, including a control mix (no stabilizer), were designed, wherein LSP partially replaced 8% of the OPC at 25%, 50%, and 75% substitution levels. A series of laboratory tests were conducted to track the changes in the geochemical properties and the mineralogical compositions and evaluate the stabilized soil samples’ improved mechanical performance and durability parameters. The experimental results show that adding LSP to the cement-treated sulfate-bearing saline soil improved the soil’s mechanical properties and enhanced the soil’s durability parameters. Specifically, it decreased the soil plasticity, improved the soil strength parameters, enhanced the soil stability, and reduced the volumetric swelling and soil moisture susceptibility. In addition to its technical advantages, using LSP, an industrial byproduct, in soil stabilization offers environmental and economic benefits, highlighting its potential as a sustainable solution in engineering practices. Full article

This paper presents the development of a novel eddy current array (ECA) system for real-time, layer-by-layer quality control in powder bed fusion (PBF) additive manufacturing. The system is integrated into the recoater of a PBF machine to provide spatially resolved electrical conductivity imaging of the manufactured part. The system features an array of 40 inductive sensors spaced at 1 mm pitch and is capable of performing a full array readout every 0.192 mm at 100 mm/s recoater speed. Array scalability was achieved through the careful selection of the electromagnetic configuration, miniaturized and seamlessly integrated sensor elements, and the use of advanced mixed signal processing techniques. Experimental validation was performed on stainless steel 316L parts, successfully detecting metallic structures and confirming system performance in both laboratory and real-time PBF environments. The prototype achieved a signal-to-noise ratio (SNR) of 26.5 dB, discriminating metal from air and thus demonstrating its potential for improving PBF part design, process optimization, and defect detection. Full article

This study investigated the enhancement of the mechanical and acoustic properties of polyurea (PU) composites by incorporating iron microparticles (Fe). The Fe/PU composites were prepared using a mixing process, where iron microparticles were evenly distributed within the polyurea matrix via mechanical stirring. The primary purpose of this study was to explore how varying volumes of iron microparticles influence the viscoelastic properties and acoustic performance of the composites, with a particular focus on applications in underwater acoustic stealth technology. Dynamic mechanical analysis was conducted to study the effect of the iron powder volume fraction on the mechanical properties of the composites, i.e., on the temperature-dependent storage moduli (E′), loss moduli (E″) and loss factor (tanδ). The intrinsic properties of the components and the nature of the interface between the phases determined the dynamic mechanical properties of the composite. It was found that the storage and loss moduli of the composite both increased as the iron volume fraction increased, which indicates that the incorporation of iron powder in a polyurea matrix appreciably induces reinforcing effects. Moreover, the tanδ curve of the Fe/PU composite generally had broader widths of the tanδ peak than those of pure polyurea, which showed better damping behavior. The height of the damping peaks depended on the iron powder content, and the glass transition temperature (measured as the temperature at the maximum value of the tanδ) shifted toward higher temperatures as the iron volume fraction increased. Also, the compression stress–strain curves of the composites obtained by a universal testing machine indicated that the addition of iron powder improved the compressive strength and the energy storage capacity of the composite. In addition, the acoustic absorption coefficient was found to increase with the addition of iron powder, and the increase in sample thickness was found to be the effective in improving low-frequency sound absorption. Full article

Synthetic graphite of complex fractional composition was mixed with phenolic resin as a binder and pore-forming component. The mixtures were pressed and subsequently heat-treated to obtain porous matrices. The structural transformations of phenolic resin by heating up to 900 °C in oxygen and inert gas media were studied and the patterns of amorphization of fixed carbon formed on the walls of the pore system during carbonization were investigated. We found regularities in the changes in matrix volume density in the function of the open porosity and the average pore diameter. It is shown that, in order to obtain graphitized carbon matrices with a density of 1 g/cm³ and an open porosity of at least 50%, it is necessary to introduce no more than 20% of phenolic resin into the molding powder with an equal content of 60, 100 and 250 μm graphite fractions. This allows for high intensity and completeness of bulk silicon infiltration. Full article

Carbon-based electrodes have recently been most widely used in P-MFC due to their desirable properties such as biocompatibility, chemical stability, affordable price, corrosion resistance, and ease of regeneration. In general, carbon-based electrodes, particularly graphite, are produced using a complex process based on petroleum derivatives at very high temperatures. This study aims to produce electrodes from bio-pitch and charcoal powder as an alternative to graphite electrodes. The carbons used to manufacture the electrodes were obtained by the carbonisation of Robinia pseudoacacia and Azadirachta indica wood. These carbons were pulverised, sieved to 50 µm, and used as the raw materials for electrode manufacturing. The binder used was bio-pitch derived from coconut shells as the raw materials. The density and coking value of the bio-pitch revealed its potential as a good alternative to coal-tar pitch for electrode manufacturing. The electrodes were made by mixing 66.50% of each carbon powder and 33.50% of bio-pitch. The resulting mixture was moulded into a cylindrical tube 8 mm in diameter and 80 mm in length. The raw electrodes obtained were subjected to heat treatment at 800 °C or 1000 °C in an inert medium. The electrical resistivity obtained by the four-point method showed that N1000 has an electrical resistivity at least five times lower than all the electrodes developed and two times higher than that of G. Fourier-transform infrared spectroscopy (FTIR) was used to determine the compositional features of the samples and their surface roughness was characterised by atomic force microscopy (AFM). Charge transfer was determined by electrical impedance spectroscopy (EIS). The FTIR of the electrodes showed that N1000 has a spectrum that is more similar to that of G compared to the others. The EIS showed the high ionic mobility of the ions and therefore that N1000 has a higher charge transfer compared to G and the others. AFM analysis revealed that N1000 had the highest surface roughness in this study. Full article

Since rare earth oxides and hard ceramic particles improve coating quality, a novel Al₂O₃@Y₂O₃ core–shell structure was prepared. Then, Ni60A coatings with different amounts (2~6 wt.%) of Al₂O₃@Y₂O₃ core–shell structures were prepared using laser cladding technology on an H13 steel surface. To demonstrate the unique effect of the core–shell structure on the performance of the coatings, a set of controlled experiments was also conducted with different proportions of Al₂O₃-Y₂O₃ mechanically mixed powders. The effect of Al₂O₃@Y₂O₃ addition on the phase composition, element distribution, microstructure, wear, and corrosion resistance of the coatings was characterized and tested thoroughly. By comparing the forming quality, hardness, wear, and corrosion resistance of the different coatings, 2 wt.% was confirmed as the optimal concentration of Al₂O₃@Y₂O₃, and its corresponding friction coefficient was about 0.44. The wear rate was approximately 4.15 × 10⁻³ mm³·(N·m)⁻¹, the self-corrosion potential was around −0.3659 V, and the self-corrosion current density was about 1.248 × 10⁻⁶ A·cm⁻². Full article

Fully utilizing solid waste as supplementary cementitious materials (SCMs) while ensuring the mechanical properties of cement-based materials is one of the pathways for carbon reduction in the cement industry. Understanding the effects of the two solid wastes-limestone powder (LP) and rice husk ash (RHA) on the mechanical properties of cement-based materials is of great significance for their application in concrete. This study investigates the impact of LP and RHA on the strength of cement mortar at various ages and the microhardness of hardened cement paste. The results suggest that two materials have a certain synergistic effect on the mechanical properties of the cementitious materials. The addition of RHA effectively addresses the issues of slow strength development, insufficient late-stage strength of the cementitious material, and the low strength blended with a large amount of LP, while a suitable amount of LP can promote the strength increase in the cement-RHA system. Based on the comprehensive analysis of compressive strength and microhardness, the optimal solution for achieving high mechanical properties in composite cementitious materials is to use 10% each of LP and RHA, resulting in a 9.5% increase in 28 d strength compared to a pure cement system. The higher the content of LP, the greater the increase caused by 10% RHA in compressive strength of the composite system, which makes the strength growth rate of cementitious material mixed with 10% LP at 3–56 d 62.1%. When the LP content is 20% and 30%, the addition of 10% RHA increases the 28 d strength by 44.8% and 38.8%, respectively, with strength growth rates reaching 109.8% and 151.1% at 3–56 d. Full article

This study proposes a new dense membrane for selectively separating CO₂ and O₂ at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce_0.9Zr_0.05Y_0.05O_2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO₂/N₂ and O₂/N₂ permselectivity and a high permeation flux under different CO₂ concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO₂ valorization via the oxy-CO₂ reforming of methane, wherein both CO₂ and O₂ permeated gases were effectively utilized to produce hydrogen-rich syngas (H₂ + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver. Full article

Rutting is a significant form of pavement distress that arises from irreversible strains accumulating along wheel paths, directly impacting pavement safety. This research investigates the effectiveness of nanocarbon-coated micronized calcium carbonate powder as a modified filler to mitigate rutting, utilizing numerical methods via finite element software. The study specifically examines the addition of 5% by weight of this modified filler to the asphalt mix. To validate the numerical results, laboratory wheel-tracking tests were conducted on samples incorporating both conventional and modified fillers. The findings reveal that the modified calcium carbonate filler enhances the asphalt’s resistance to rutting, with the 5% inclusion demonstrating a marked improvement in durability and performance. The study also underscores the necessity of characterizing the elastic and visco-plastic properties of materials through rigorous testing methods, such as elastic modulus and dynamic creep tests, to better understand their behavior under load. Numerical analysis based on linear elastic conditions was prioritized over viscous conditions to effectively compare the results of these specialized materials. The strong correlation between the numerical simulations and laboratory results reinforces the effectiveness of finite element methods in predicting pavement behavior and optimizing asphalt mixtures. Full article

Recycled concrete incorporating additional super-absorbent polymer (SAP) and machine-made stone powder (MSP) was prepared using a two-factor, four-level orthogonal test. To enhance the frost resistance of recycled concrete and improve its mechanical properties, such as compressive and flexural strength, the prepared concrete underwent 200 freeze–thaw cycles. Before freeze–thaw cycles, the amount of SAP has a predominant influence on the mechanical properties of recycled concrete in comparison with MSP. After 200 cycles of freeze–thaw, the influence of MSP became more significant than that of SAP. Typically, the compressive strength and flexural strength exhibited a trend of initially increasing and then decreasing as the contents of SAP and MSP increased. The optimized recycled concrete was identified as S16M6, containing 0.16% SAP and 6% MSP, as demonstrated by the minimal strength loss after freeze–thaw cycles. This study also proposed a linear regression model for predicting the mechanical properties which offered valuable guidance for the engineering application of recycled concrete mixed with SAP under the freeze–thaw cycle environment. Full article

The usage of manufactured sand concrete is widespread in modern engineering, and it is important to study its performance to improve the overall engineering quality. This paper presents an experimental study on the working performance and durability of 12 groups of manufactured sand high-performance concrete (MSHPC) with varying mix ratios, in the context of the construction of the Dalian Bay undersea immersed tube tunnel. The study reveals that the stone powder content significantly affects the physical and mechanical properties, as well as the durability, of manufactured sand concrete. At an approximately 9% stone powder content, the concrete achieves the highest slump and best workability. However, excessive stone powder reduces early crack resistance. Furthermore, an optimal stone powder content (ranging from 5% to 13%) enhances the compressive strength, with the 28-day compressive strength reaching 60 MPa at a 13% stone powder content, while the effect on the splitting tensile strength is negligible. The stone powder content does not significantly impact impermeability and frost resistance, but at 7–9%, the RCM method shows the lowest chloride ion diffusion coefficient. Additionally, a lower water–binder ratio enhances resistance to chloride ion diffusion. High-performance RCM concrete with a 9% stone powder content was used in the construction of the Dalian Bay Cross-Harbor Tunnel, achieving 28-day and 56-day compressive strengths of C45 and C50, respectively, an impermeability grade of P14, a chloride ion diffusion coefficient of 1.9 × 10⁻¹² m²/s, and a frost durability index of 92%, meeting the project’s 100-year lifespan design requirements. Full article

This study presents an exhaustive exploration into the development and rigorous evaluation of nano-TiO₂-modified recycled aggregates (NT@RAs) as an environmentally sustainable substitute for natural aggregates in concrete applications. A methodical framework was devised for the synthesis and thorough characterization of NT@RAs, emphasizing the optimization of nano-TiO₂ loading onto the RA surface and within its intricate porous structure. The investigation encompassed three distinct types of recycled aggregates: recycled glass sands (RGSs), recycled clay brick sands (RCBSs), and recycled concrete sands (RCSs). Of particular interest, NT@RGS, with its properties of an inherently smooth surface texture and low water absorption, was found to exert a favorable influence on the rheological behavior of concrete, manifested in reduced yield stress, thereby underscoring the potential for fine-tuning mix designs to enhance workability. As the substitution levels of NT@RGS and NT@RCBS escalated, an initial decrement in compressive strength was discernible, which subsequently reversed to strength restoration at optimized substitution ratios. This phenomenon is attributed to the synergistic interplay among NT@RA components. Remarkably, NT@RA-incorporated concrete demonstrated unparalleled self-cleaning abilities, surpassing the performance of concrete with direct nano-TiO₂ powder incorporation. This comprehensive research contributes significantly to the advancement in sustainable, high-performance photocatalytic construction materials within the realm of concrete technology. It underscores the potential for enhancing not only the rheological and mechanical properties but also the environmental responsiveness of concrete through the innovative utilization of NT@RAs. Full article