Search Results (9,744)

In this study, a water-based epoxy curing agent was prepared using polyamines (mixed amines), and epoxy coatings were formulated by blending this with a polyurethane-toughened water-based epoxy curing agent in specific proportions. By testing the tensile properties of the water-based epoxy coatings, the curing agent ratio was adjusted and the curing process optimised. A layer of water-based epoxy coating was applied to both the rebar electrodes and the rebar surfaces. Through electrochemical testing, coating thickness measurement, and coating continuity testing, the effects of filler type, particle size, and content on coating performance were investigated. On this basis, steel bars coated with a water-based epoxy coating containing 0.3% graphene–polyaniline composite nanomaterials were used as the control group, whilst a water-based epoxy coating incorporating a silane solution served as the primer. Based on the results of the preliminary screening, a water-based epoxy coating containing 1% silane coupling agent and 10% zinc phosphate was selected as the intermediate coat, whilst a water-based epoxy coating containing fly ash microspheres and polystyrene microspheres was selected as the top coat. Through cold bending tests and tensile strain tests on the coated reinforcing bars, the study investigated the effects of zinc phosphate, fly ash microspheres, and polystyrene microspheres on the cold bending performance and deformation combination performance of the water-based epoxy-coated reinforcing bars. By optimising the curing process, the tensile strength of the coating reached 40.11 MPa, with an elongation at break of 19.94%; the corrosion resistance of the zinc phosphate composite coating (corrosion current density: 0.00589 μA/cm²) was comparable to that of the 0.3% graphene/polyaniline coating; and the fly ash microsphere top coat significantly improved the deformation compatibility between the reinforcing bars and the coating. The high-performance, cost-competitive water-based epoxy coating system developed in this study offers a new technical approach to the durability protection of reinforced concrete structures in marine environments. Full article

This study presents a comparative investigation of the microstructure, phase composition, microhardness, tribological behavior, and corrosion resistance of heterogeneous coatings deposited on St3 steel by twin-wire electric arc spraying (TWEAS). Three wire combinations were examined: ER309LSi + Steel 70, Sv-08G2S + Steel 70, and 30KhGSA + ER309LSi. The coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), Vickers microhardness testing, ball-on-disc tribological measurements, and potentiodynamic polarization in 3.5 wt.% NaCl solution. All coatings exhibited a characteristic lamellar structure with a thickness of 340–360 μm and hardness values significantly higher than those of the steel substrate. The 30KhGSA + ER309LSi coating demonstrated the highest cross-sectional microhardness (532 ± 13 HV) and the lowest specific wear rate (0.411 × 10⁻⁴ mm³/(N·m)), which was more than five times lower than that of the substrate. The enhanced wear resistance was associated with the formation of the Cr₇C₃ and Cr₂₃C₆ carbide phases, as identified by XRD. The Sv-08G2S + Steel 70 coating exhibited the lowest corrosion rate among the investigated coatings due to its more homogeneous ferritic structure and reduced electrochemical contrast between lamellae. The results demonstrate that the phase composition and distribution of alloying elements play a decisive role in determining the functional properties of heterogeneous TWEAS coatings. Full article

This review synthesizes findings from more than 100 journal articles, reports, and design standards on the design, simulation, and testing of steel beam-to-column connections, with emphasis on semi-rigid bolted extended end-plate (EEP) joints. The core objective of this study is to highlight the critical importance of accurately capturing this semi-rigid behavior, given the significant implications of improper modeling for the global response, safety, and design reliability of steel frames. While connections are often idealized as fully rigid or pinned, EEP connections typically exhibit a semi-rigid response governed by nonlinear moment–rotation (M–θ) behavior. The reviewed literature is organized around: (i) mechanical response and key failure mechanisms (end-plate yielding, bolt fracture, and prying action); (ii) analytical and numerical prediction methods, including component-based models and finite-element approaches capable of representing contact, bolt pretension, and cyclic degradation; and (iii) system-level implications for steel frames. Approaches used in major standards (AISC and Eurocode 3) for classifying connection stiffness and strength are compared, and experimental programs are summarized to identify the dominant parameters controlling resistance, ductility, and failure mode. Translating these component-level findings to the structural-system level, the review highlights how appropriately detailed semi-rigid EEP connections can enable moment redistribution, reduce member demands, and support stable inelastic deformation under seismic actions. Key research gaps include three-dimensional and multiaxial loading, impact and other high-rate actions, and the performance of alternative materials such as stainless steel. Full article

Al-Cu-Fe quasicrystalline coatings were deposited on AISI 321 stainless steel substrates by high-velocity oxy-fuel (HVOF) spraying at oxygen pressures of 3.0, 3.5, and 4.0 bar. The influence of oxygen pressure on the phase composition, microstructure, porosity, corrosion behavior, thermal stability, and microhardness of the coatings was investigated using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), ImageJ porosity analysis, electrochemical corrosion testing in 3.5 wt.% NaCl solution, simultaneous thermal analysis (TGA/DSC), and microhardness measurements. XRD analysis revealed the formation of quasicrystalline-related intermetallic phases together with Al, Fe₃Al₁₃, FeAl, Fe₃O₄, CuFe₂O₄, Cu₂O, and CuO phases. The coating deposited at 3.5 bar exhibited the lowest porosity (5.37%), the most homogeneous microstructure, and the largest residual coating thickness after corrosion testing. SEM and EDS analyses indicated that corrosion preferentially initiated at pores, splat boundaries, and phase interfaces, while the coating produced at 3.5 bar demonstrated the most stable surface condition after exposure to a 3.5 wt.% NaCl solution. Thermal analysis showed that all coatings remained stable up to 900 °C. Sample (a) exhibited the lowest mass loss and the highest thermal stability, whereas sample (b) demonstrated the most favorable combination of structural integrity, phase ordering, coating density, corrosion-related performance, and thermal stability. Microhardness values of the coatings ranged from 754 to 778 HV, significantly exceeding that of the AISI 321 substrate. The results demonstrate that oxygen pressure is a critical parameter controlling the microstructure and functional properties of HVOF-sprayed Al-Cu-Fe coatings, with 3.5 bar providing the most balanced set of properties. Full article

Amid China’s transition from rapid urbanization to high-quality development, quantifying urban building metabolism is crucial for building resilient resource management systems. However, current research predominantly focuses on eastern cities, largely overlooking non-residential buildings. Here, we apply dynamic material flow analysis (dMFA) to quantify the material stocks of residential and non-residential buildings in two major economic hubs in western China, Xi’an and Chengdu. The stock patterns from 1950 to 2050 and the underlying drivers are further clarified. Model projections suggest that material stocks in both cities will peak around 2040, reaching 2.2 billion tons in Chengdu and 1.08 billion tons in Xi’an, under the intensive scenario. Chengdu reaches stock saturation 2 to 3 years earlier than Xi’an, and the total stocks are approximately twice those of Xi’an. Reinforced concrete and steel structures dominate future building development and increase the accumulation of cement and steel. Sand and gravel still account for the majority of building materials. Demand for new construction materials shows a pronounced double-peak pattern, occurring in 2016 and 2026. Construction waste is projected to rise sharply by mid-century; scenario analysis indicates that an 80% material recovery rate has the potential to largely offset new material demand. Sensitivity analysis identifies building lifetime extension and construction technology improvement as the strategies with the greatest potential for mitigating future waste generation. This study expands the scope of urban building material metabolism research and provides a scientific basis for low-carbon urban planning and construction waste management in China. Full article

The steel industry is currently grappling with the dual environmental challenges of massive steel slag accumulation and carbon emissions. To address the limitations of traditional carbonation processes—namely slow reaction kinetics and insufficient mechanical properties—this study proposes a novel rapid carbonation enhancement method coupling microwave thermal field intensification, silicon carbide (SiC) physical absorption, and potassium silicate chemical activation. The effects of microwave heating parameters on the performance of carbonated steel slag blocks were systematically investigated. The results indicate a significant synergistic effect between the microwave thermal effect and the alkali-activated system. Under the conditions of a 0.14 liquid-to-solid ratio and microwave heating at 90 °C for 45 min, the compressive strength reached a peak of 48.82 MPa (a 44.7% increase over the conventional treatment group). Microstructural characterization revealed the reinforcement mechanism: the introduction of SiC and potassium silicate solution (K₂SiO₃) under microwave heating promotes a denser distribution of carbonation products. Synchronized with alkali activation, this effect promotes the in-situ growth of dense calcite crystals within a gel network, thereby significantly optimizing the pore structure (e.g., reducing the average pore size to 43 nm), and enhancing strength through synergistic effects. This research is subject to further energy and life-cycle assessments, and this approach holds potential for CO₂ mineralization and the recycling of steel slag. Full article

The construction industry is characterised by high raw materials consumption and large waste generation. Upcycling waste construction materials offers an opportunity to reduce embodied carbon emissions while creating community assets. This paper examines how integrated design supports the effective reuse of waste materials from a modular building factory through the design of a community garden pavilion. Using Whole Lifecycle Assessment, the carbon impacts of three scenarios were evaluated. Case 1, the baseline scenario, represented the traditional temporary accommodation system using new materials with a hybrid steel–timber structure. Case 2 adopts new materials for the timber frame structure, combined with reused wooden pallets for the envelope. Case 3 represents an upcycling scenario where structural and envelope materials are reused from the modular building factory’s waste streams. Results show that the whole-life carbon emissions were 15,892.32 kgCO₂e for Case 1, 4293.25 kgCO₂e for Case 2, and 3044.99 kgCO₂e for Case 3, representing reductions of 73% and 81%, respectively, compared with the baseline. The findings demonstrate that integrated design and industrial material reuse can significantly reduce embodied carbon across a building’s life cycle. Recommendations for applying modular factory waste in community-led urban projects are provided. Full article

This study focused on burn-through leakage at girth welds of mechanically lined pipe (MLP) during field service. Field failure analysis, experimental tests, and numerical simulation were combined to investigate the process parameters of seal welding and multi-pass girth butt welding. Macroscopic metallography and energy dispersive spectroscopy (EDS) of failed specimens showed that excessive welding heat input (high current) caused severe expansion of the heat-affected zone (HAZ) and significant element dilution. The results indicated that the HAZ width of the solid-wire girth weld increased markedly from 1.312 mm to 2.247 mm under high-current conditions. Meanwhile, the Fe mass fraction in the root pass sharply increased to 33.66%, while key corrosion-resistant elements such as Cr and Ni were greatly reduced, which directly led to local pitting corrosion and perforation leakage. In addition, a moving heat source model was established in Abaqus 2024 to simulate the multi-pass welding process. The results showed that strong stress concentration developed at the groove root and the interface between the backing steel pipe and corrosion-resistant liner during repeated thermal cycles. The maximum von Mises stress reached 686.56 MPa during the second butt welding pass. After final cooling, the residual hoop tensile stress and axial tensile stress at the center of the inner surface reached 500–550 MPa and 480–510 MPa, respectively. By correlating microscopic compositional evolution with the macroscopic residual stress field, this study revealed the weld failure mechanism of MLP joints. The proposed finite element method can also be used as an efficient tool to predict the effects of welding speed, current, and voltage on residual stress, providing guidance for field welding procedure optimization and pipeline structural integrity assessment. Full article

High-temperature structural components are susceptible to creep deformation, which can ultimately lead to failure. In this work, an AI-based framework was developed capable of predicting the creep time of 316 austenitic stainless steel. Here, creep time refers to both the time to reach specific strain levels and the time to rupture. However, the scope of the present work is limited to rupture-time prediction, while the application of the framework to strain-level prediction will be reported in future work. The dataset consisted of creep strain curves from four heats, including both rupture and non-rupture curves. Random Forest (RF), Gradient Boosting (GB), Extreme Gradient Boosting (XGB), Support Vector Regressor (SVR), Gaussian Process Regressor (GPR), and Neural Network (NN) were employed. The effects of square-root and cube-root transformations on data distribution and model learning behaviour were analysed using model learning curves. An Optuna (version 4.3.0)-based hyperparameter tuning strategy was employed. The cube-root transformation improved the learning performance of SVR, GPR, and NN, whereas RF, GB, and XGB remained unaffected. Learning curves revealed mild overfitting for RF, GB, and XGB, and very minimal overfitting for SVR, GPR, and NN. NN achieved the best predictive performance (${\mathrm{R}}^2=0.92,\mathrm{R}\mathrm{M}\mathrm{S}\mathrm{E}=0.195$, deviation factor of 1.57). The findings demonstrated that the combined useof creep strain curves, data transformation, learning curve guided model selection, and rigorous hyperparameter tuning can improve the prediction accuracy under a limited dataset. Full article

In this study, low-alloy structural steels with different La and Ce contents were prepared via vacuum smelting and controlled rolling and controlled cooling technologies, and their microstructures were characterized. The influence of La and Ce on the corrosion resistance of low-alloy steels was compared through indoor cyclic-immersion accelerated tests simulating tropical marine atmospheres. The corrosion mechanism of low-alloy steels with different La and Ce contents in simulated tropical marine atmospheres was investigated using electrochemical measurements and corrosion product analysis. The results show that La and Ce improve the uniform corrosion resistance of low-alloy steels. With increasing La/Ce content, the corrosion current density decreased from 1.8936 × 10⁻⁶ A cm⁻² for 0LaCe to 1.29 × 10⁻⁶ A cm⁻² for 0.3LaCe, corresponding to a reduction of approximately 31.9%. This is attributed to the fact that La/Ce addition promotes rust layer stabilization and densification, as suggested by the evolution of major rust phases and the presence of La/Ce-related oxidized species. Meanwhile, alloying with La and Ce improves the cracking of the rust layer, reduces the number of pores, and stabilizes the rust layer structure. Full article

The growing demand for sustainable construction materials has led to significant advancements in ultra-high-performance concrete (UHPC), with a particular focus on geopolymer-based systems as an alternative to conventional cementitious binders. This review explores the latest developments in sustainable Ultra-High-Performance Geopolymer Concrete (UHPGPC) by analysing key material composition, mechanical, durability and microstructural properties. The incorporation of ground granulated blast furnace slag (GGBFS), silica fume (SF), and fly ash (FA) has demonstrated notable improvements in compressive strength, durability, and workability. Additionally, the use of activators such as sodium silicate and sodium hydroxide optimizes geopolymerization, resulting in a denser microstructure and enhanced mechanical performance. This review highlights the critical role of fibre reinforcement in UHPGPC, where steel fibres (SFs) and hybrid fibres significantly enhance compressive and tensile strength, as well as crack resistance. The inclusion of waste materials such as rice husk ash and recycled glass promotes sustainability by reducing CO₂ emissions while maintaining structural integrity. However, higher waste-glass content may adversely affect bonding due to its smooth surface texture. The findings highlight the potential of UHPGC as a high-performance, eco-friendly alternative to traditional cement-based UHPC. By integrating industrial by-products and alternative activation techniques, UHPGPC can contribute significantly to the global shift towards sustainable and low-carbon construction materials. Full article

Micro-structured SAE H13 tool steel inserts for polymer injection molding require accurate replication of sub-millimeter features while retaining adequate densification and heat-treatment response. This study compared two powder-based routes on the same hemispherical insert containing pyramidal features of approximately 0.145 mm base width: hot embossing (HE) of water-atomized SAE H13 powder (supplier d50 = 5.7 µm, irregular morphology) compounded with a commercial M1 binder, and material extrusion (MEX) of a commercial gas-atomized SAE H13 filament processed on a Markforged Metal X. Rheological screening selected a 57:43 vol% powder-to-binder ratio for the in-house HE feedstock, and DSC/TGA measurements defined two-step debinding windows. The best HE conditions were 220 °C, 8 MPa, and 45 min for the in-house mixture, and 210 °C, 8 MPa, and 30 min for the granulated commercial filament; the latter showed a 0.15% linear deviation from the silicone replica diameter among the best-rated samples. Under the tested commercial MEX configuration, the pyramidal features were not resolved because the 0.40 mm deposition line width exceeded the target feature base width, causing the slicer to omit the sub-line-width geometry. The defect populations differed qualitatively: HE specimens showed porosity and local cracking associated with powder morphology and pressureless sintering, whereas MEX specimens showed build-direction-aligned inter-raster voids associated with the toolpath. Microhardness and tensile data are therefore interpreted as process-history-specific results rather than as a direct route ranking, because sintering conditions were not uniform across all specimens. The study defines an experimentally bound process-selection limit for SAE H13 micro-tooling: HE remains preferable for sub-nozzle surface features, whereas MEX remains attractive for macro-scale geometric freedom, if resolution, densification, and post-sintering consolidation are addressed. Full article

High-entropy alloy (HEA) coatings exhibit enhanced chemical stability when doped with carbon, primarily due to the strong bonding between carbon and transition metals. Typical transition metals used in these coatings include Cr, Fe, Co, Ni, Cu, Ti, V, W, Nb, Ta, and Zr. Owing to their excellent chemical stability, HEA coatings are widely employed to protect component surfaces operating in highly corrosive environments. Against this backdrop, the present study investigates the effect of carbon doping introduced via methane gas flow during the physical vapor deposition of TiAlTaZrNb HEA coatings on corrosion resistance. The morphology and structure of the coatings were analyzed by field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Corrosion protection and coating resistance were assessed through potentiodynamic polarization and electrochemical impedance spectroscopy. While increasing the methane flow resulted in an approximately 34% reduction in coating thickness, the overall coating resistance increased by one order of magnitude, reaching a maximum at a methane flow rate of 9 sccm, corresponding to the carbon solubility limit. This improvement was evidenced by a decrease in the corrosion rate from 8.02 × 10⁻² mm y⁻¹ for the uncoated H13 steel to 8.00 × 10⁻⁴ mm y⁻¹ for the HEA-coated samples. However, at higher methane flow rates, carbon precipitation and the formation of parallel microcracks contributed to an increase in corrosion rate. Full article

This paper investigates the in-plane bending stiffness of light timber-framed (LTF) and light steel-framed (LSF) wall elements with different sheathing materials (fibre-plaster board (FPB) and oriented-strand board (OSB)), focusing on the influence of the fastener spacing (s) on the wall elements’ structural response. The analytical model accounts for bending, shear, and slip deformations in the sheathing-to-frame connection, while boundary conditions are assumed to be rigid in accordance with the Eurocode 5 standard. The results indicate a strong dependence of global stiffness on fastener spacing. Increasing the fastener spacing from 37.5 mm to 300 mm reduced the racking stiffness by approximately 42% in LTF–FPB walls and by 31% in LSF–FPB walls. The highest stiffness was obtained for LSF–FPB wall elements (6514 N/mm), while the lowest stiffness was observed for LTF–OSB elements (1236 N/mm). LSF wall elements generally exhibited stiffness values approximately two times higher than comparable LTF systems, although both framing systems showed similar trends with increasing fastener spacing. This study provides a solid basis for the design and optimization of lightweight wall systems and supports the development of efficient structural solutions in both timber and steel construction. Full article

The high energy consumption of conventional mixers equipped with active mixing elements necessitates the development of more efficient technologies for mixing bulk materials and feed mixtures. This study presents a gravity-driven mixing approach based on the rotation of an inclined cylindrical chamber, eliminating the need for active mixing elements. During chamber rotation, the mixture components move toward both end walls while simultaneously undergoing a circular motion along the inner cylindrical surface. This movement intensifies the mixing process and reduces energy consumption, thereby providing an energy-efficient gravity-based mixing approach that operates without active mixing elements. Laboratory experiments were conducted to determine the key physical and mechanical properties of the sapropel, organic fertilizer, and compound feed (formulation K-60-1). The measured values were as follows: velocity on an inclined steel surface, 0.65–1.21 m/s; coefficient of friction, 0.40–0.91; bulk density, 453–1166 kg/m³; and angle of repose, 36–39°. The experimental results confirmed the validity and adequacy of the developed analytical relationships. A structural and technological design of the gravity mixer was developed, and an experimental prototype was manufactured. Analytical relationships were obtained to determine the critical rotational speed of the chamber, particle movement velocity, and the power required for the mixing process. Under optimal operating conditions, the mixture uniformity reached 95.7% after 4 min of mixing. The mixer productivity was 0.95 t/h, while the specific energy consumption was 0.5 kWh/t, which is 2.5 times lower than that of conventional mixers equipped with active mixing elements. The obtained results confirm the feasibility and effectiveness of the proposed gravity-based mixing method for the preparation of feed and organomineral mixtures under the operating conditions of small-scale farms. Full article