Search Results (227)

Magnesium alloys that are low density and have a high specific strength are widely utilized as lightweight structural materials. Due to their hexagonal close-packed crystal structure, plastic deformation in magnesium alloys is strongly limited in dislocation slip and mainly accommodated by deformation twinning, which results in distinct mechanical anisotropy and tension–compression asymmetry. This paper, centered on mechanism competition and microstructure regulation, systematically reviews the recent progress in the compressive mechanical responses of magnesium alloys. Key results reveal the cooperative and competitive mechanisms between slip and twinning, the significant controlling effects of temperature and strain rate on deformation behavior, and the effective design strategies of gradient and heterogeneous structures that achieve superior strength–ductility synergy. This review provides essential theoretical support for the development and performance optimization of high-performance magnesium alloys. Full article

Against the background of the global “dual carbon” strategic goal, low-carbon upgrading of road engineering and efficient recycling of waste plastics have become critical approaches to relieve the shortage of natural aggregates and control plastic pollution. Most existing studies only focus on the optimization of single mechanical indicators, while lacking collaborative analysis of mechanical performances and carbon reduction benefits, meaning they cannot provide sufficient scientific support for the design of low-carbon and sustainable road materials. In this study, recycled plastic aggregate (PA) was used to partially replace natural coarse aggregate, and its influence on the mechanical characteristics of cement-stabilized macadam (CSM) was systematically investigated. Combined with life cycle assessment (LCA), the carbon emission reduction potential was quantitatively evaluated, aiming to improve the toughness of road base materials and promote low-carbon sustainable development. The results demonstrate that when the PA content increases from 0% to 20%, the mechanical strength of CSM gradually decreases, while the toughness presents a steady upward trend, and the maximum carbon emission reduction rate reaches 50.8%. The optimal toughness improvement of 28.39% is obtained at the PA content of 16%. This study clarifies the internal correlation between mechanical behaviors and low-carbon benefits of recycled plastic aggregate, provides reliable technical support for the high-value utilization of waste plastics and the optimization of sustainable road materials, and offers important references for the green and low-carbon transformation of transportation infrastructure. Full article

This study investigates the feasibility of incorporating high-volume municipal solid waste incineration (MSWI) fly ash into geopolymers, with a focus on its effects on mechanical performance and fragmentation behavior. A systematic experimental program was conducted in three stages. Geopolymer mixtures were first prepared with MSWI fly ash substitution rates ranging from 50% to 100% at seven distinct levels. Uniaxial compression tests were then performed to evaluate mechanical properties, followed by sieve analysis to examine fragment size distribution. The fractal dimension (D) was adopted to quantitatively characterize the degree of fragmentation. The results indicate that dry density, compressive strength, and elastic modulus all decrease progressively with increasing MSWI fly ash content. Specifically, as the fly ash content increased from 50% to 100% the compressive strength decreased from 9.57 MPa to 3.18 MPa. Notably, even at a 100% substitution rate, the compressive strength reached 3.18 MPa, which is 59% higher than the 2.0 MPa minimum requirement specified in the JTG/T F20-2015 standard. These findings demonstrate that MSWI fly ash can be effectively utilized at high replacement levels to produce sustainable geopolymers with satisfactory mechanical properties. This approach presents a viable strategy for recycling industrial solid waste into value-added construction materials. Full article

Using solid waste as supplementary cementitious materials (SCMs) is an effective strategy for promoting low-carbon construction development. However, single or binary systems often exhibit mismatched reaction kinetics, thereby limiting their performance at high cement replacement rates. This study focuses on a novel low-carbon concrete designed based on reaction sequence coordination, containing recycled brick powder (RBP), ground granulated blast-furnace slag (GGBS), and self-combusting coal gangue (SCCG). The effects of RBP, GGBS, and SCCG on the hydration process and microstructure of the novel low-carbon concrete with different replacement levels have been studied by testing compressive strength, workability, and durability and observing microstructural changes. The results showed that an optimized ternary composition with an RBP:GGBS:SCCG ratio of 4:3:1 achieves a cement replacement level of 30% while exhibiting a 28-day compressive strength of 38.26 MPa, representing a 14.2% increase compared with plain cement mortar. Microstructural analyses indicate that this enhanced performance results from a time-dependent reaction sequence, in which GGBS contributes predominantly at early ages by supplying calcium, whereas RBP and SCCG mainly participate through delayed pozzolanic reactions and pore refinement at later ages. Consequently, the optimized ternary mortar exhibits a water absorption of 11.12% and a 27.2% reduction in electrical flux. This study aims to provide practical strategies for enhancing the performance of low-carbon cementitious materials through a reaction sequence coordination design approach, thereby improving the utilization efficiency of solid waste in the production of low-carbon building materials. Full article

To investigate the mitigation of high-pressure CO₂-induced degradation of wellbore cement sheath in Carbon Capture, Utilization, and Storage–Enhanced Oil Recovery applications (CCUS-EOR), conventional Class G oil well cement and modified cement systems incorporating graphene, waterborne epoxy resin, and a composite of waterborne epoxy resin with graphene were formulated. This study presents the original comparative investigation on the long-term carbonation resistance of graphene-modified, waterborne-epoxy-modified, and their composite-modified oil well cements under 130 °C and 7 MPa CO₂ partial pressure, filling the research gap of unclear synergistic effects of the two modifiers in high-temperature CCUS environments. The specimens were subjected to simulated downhole conditions, and key properties, including compressive strength and permeability, were evaluated. The underlying mechanisms were elucidated through material characterization techniques such as X-ray diffraction, X-ray computed tomography, and scanning electron microscopy. Results indicated that the waterborne epoxy resin–modified cement system exhibited superior long-term carbonation resistance, achieving a 90 d compressive strength retention rate of 84%. The graphene-modified cement showed a 90 d compressive strength retention rate of 65%, while the waterborne epoxy–graphene composite system only retained 39.7% of its compressive strength at 90 d due to negative synergistic effects. The enhanced durability of the waterborne-epoxy-modified cement is attributed to the formation of a continuous polymeric film, which acts as a protective barrier against CO₂ penetration. This study provides valuable insights for the design of CO₂-resistant cement systems in CCUS-EOR environments. Full article

The recycling of waste clay bricks as raw materials for cement-based materials presents an effective solution to ecological pollution and resource shortages. Previous research has separately examined the effects of recycled brick fine aggregate and recycled brick powder on mortar or concrete, but few studies have investigated their combined use. This study aims to clarify the synergistic effect of recycled brick fine aggregate (RBA) and recycled brick powder (RBP) on mortar performance, quantify the influence of the RBP substitution rate on hydration characteristics and microstructural evolution, and determine the optimal mix proportion and curing system for fully recycled brick mortar. Mortar was prepared using 100% RBA and RBP at substitution rates of 0%, 10%, 20%, and 30%. The physical properties, mechanical performance, and durability of the mortar were evaluated, alongside an analysis of its microstructural morphology, mineral composition, and pore structure. The results indicate that adding an appropriate amount of RBP helped maintain the flowability of the mortar. As the RBP substitution rate increased, the mortar strength generally decreased in the early stages, but long-term curing (≥90 days) effectively mitigated this decline. The inclusion of RBP improved chloride ion permeability, with the 20% substitution rate achieving a favorable balance between compressive strength, fluidity, and durability without significantly affecting carbonation resistance. Microstructural analysis revealed that RBP regulated the morphology of hydration products and optimized the pore structure of the mortar, while the mineral composition of hydration products was similar to that of natural mortar. These findings provide a theoretical basis and technical support for the high-value utilization of construction and demolition waste in cement-based materials. Full article

Red mud (RM), a waste residue from alumina extraction, poses serious environmental impacts on water resources, land resources, and ecological systems due to its large production, high alkalinity, and low resource utilization. To enhance the overall utilization rate of RM solid-waste materials, this study focuses on RM, blast furnace slag (BFS), and fly ash (FA) cementitious materials as the research objects. Through mechanical tests and microstructural analysis, the optimal mix ratio of the ternary RM-based cementitious material is determined, and a systematic study of its microstructural evolution is conducted. Concurrently, fractal theory was used to quantify the microstructure of the material, revealing the evolution laws of the mechanical properties of ternary red-mud-based cementitious materials from a mesoscopic perspective. The results indicate that reducing the proportion of RM or slag alone to increase the FA content yields inferior modification effects compared to simultaneously reducing the proportions of both RM and BFS to increase FA content. Compared with the binary RM-based cementitious material made of RM and BFS, the 28-day compressive strength increases by approximately 25%, reaching 50 MPa. The incorporation of FA can reduce the volume of harmful pores in the cementitious matrix, providing ample reactive material for subsequent hydration reactions, promoting later hydration products, and improving the distribution of the internal pore structure. This leads to increases in both fractal dimensions, and a rational mix proportion can effectively improve the microstructure and mechanical properties of the ternary RM-based cementitious material. Full article

This study investigates the development of high-strength biofiber cement boards with enhanced thermal insulation properties by utilizing recycled biofibers derived from cement packaging bags, combined with a water-based adhesive to enhance the curing efficiency of Portland cement through a cementation–curing process. This approach reduces waste from cement packaging and other biofiber residues through recycling, thereby promoting environmental sustainability. Moreover, it does not require the use of additional chemicals for the disposal or treatment of fiber waste, nor does it require the incineration of biofiber waste. Recycled biofiber from cement bags, composed primarily of cellulose (60 wt%), lignin (15 wt%), and hemicellulose (10 wt%), serves as a reinforcing phase, while the cement and adhesive mixture functions as a strong binding matrix. The fabrication of composite materials using undamaged cement bag fibers preserves fiber integrity and enables a well-ordered one-dimensional (1D) fiber alignment, which promotes more effective reinforcement than two-dimensional (2D) or three-dimensional (3D) orientations, in accordance with the rule of mixtures. In addition, the incorporation of a water-based PVAc adhesive accelerates the curing rate of the cement phase, promoting the formation of a strong interconnected network structure, and facilitates a more complete curing process. The physical, mechanical, chemical, and thermal properties of the biofiber cement boards were evaluated in accordance with relevant industrial standards, including TISI 878:2023, BS 874, ASTM C1185, ASTM D570, ASTM C518, ISO 8301, and JIS A1412. The results indicate that an optimal cement mortar to water-based adhesive ratio of 1:2, combined with an increased number of biofiber sheet layers, significantly enhances material performance, particularly in Formulas (7)–(9). Among these, Formula (9) exhibits the lowest water absorption (0.0835 ± 0.0102%), the highest tensile strength (19.489 ± 0.670 MPa), the highest flexural strength (20.867 ± 2.505 MPa), the highest Young’s modulus (5735.068 ± 387.032 MPa), and low thermal conductivity (0.152 W/m.K). The resulting boards demonstrate strong bonding ability, enhanced resistance to fire, moisture, and weathering, and a longer service life compared to lower cement-to-adhesive ratios (1:1 and 1:0). These findings demonstrate the potential of recycled biofiber composites, combined with water-based adhesives, as sustainable alternative materials for thermal insulation and structural applications, including ceilings and walls in building construction. Full article

To achieve the large-scale, high-value utilization of vanadium–titanium slag (VTS) in the metallurgical industry, this study replaces blast furnace slag (BFS) with VTS to construct a quaternary all-solid-waste cementitious system composed of VTS, BFS, steel slag (SS), and desulfurization gypsum (DG). It systematically investigates the effects of VTS content (0–60%) on the mechanical properties, leaching toxicity, and hydration heat behavior of the system. XRD, TG–DSC, and SEM–EDS techniques are employed to explore the influence of VTS on hydration behavior and microstructural evolution. The results show that when VTS replaces 30% of the BFS (A3, VTS:BFS:SS:DG = 3:3:3:1), the 28-day compressive strength reaches 31.33 MPa. The leaching concentrations of heavy metals in all specimens are far below the standards for drinking water quality. Hydration heat analysis reveals that the incorporation of VTS advances the acceleration period of hydration. The A3 specimen maintains a relatively high heat release rate in the middle and later stages (after 72 h), and its cumulative heat release is significantly higher than that of the system without VTS, revealing the “slow hydration” mechanism of VTS at later stages. The [SiO₄]–[AlO₄] bonds in VTS undergo a depolymerization–repolymerization process. In addition, an appropriate amount of VTS promotes the deposition of hydration products such as ettringite (AFt), C–S–H, and C–A–S–H gels through micro-filling effects and heterogeneous nucleation, thereby improving the microstructure of the system. However, excessive VTS (≥45%) significantly inhibits the hydration reaction and reduces gel formation due to the decrease in highly reactive BFS components and the increased TiO₂ content. This study provides new insights into the resource utilization of VTS in multi-solid-waste cementitious materials. In addition, VTS-based cementitious materials are suitable for practical scenarios with low early strength requirements, such as goaf backfilling. Therefore, future studies should further investigate the long-term sulfate resistance and carbonation resistance of these materials under real application conditions. Full article

To investigate the strength evolution of concrete structures operating in long-term service in humid environments while facing threats such as earthquakes, explosions, and impacts, this study utilized a Hopkinson pressure bar (SHPB) and an MTS testing system to conduct experiments on concrete with four different moisture contents (relative saturation of 0%, 50%, 80%, and 100%) across a strain rate range of approximately 10⁻⁵ to 2 × 10² s⁻¹. Based on these results, a relationship equation was established describing how the strength factor of wet concrete varies with strain rate. The study identified sensitive and non-sensitive regions for the strain rate effect in wet concrete. As the water content increases, the threshold for the sensitive region decreases. Specifically, the inflection strain rate for dried concrete is approximately 32 s⁻¹, whereas for saturated concrete, it drops below 5 s⁻¹. A functional equation describing the variation in the strain rate sensitivity coefficient with water content was derived, showing that the strain rate effect on strength becomes more pronounced as water content increases. The rate-wet coupling effect on concrete compressive strength was analyzed, and zones dominated by the strain rate strengthening effect and the water-weakening effect were identified. The mechanism of strength variation in wet concrete across different strain rate ranges was investigated. The analysis indicates that free water participates in the action processes of each mechanism from low to high strain rates. As the strain rate increases, the mechanisms of pore water interaction and thermal activation undergo a transition. At higher strain rates, the significant increase in the dynamic strength of wet concrete results from the combined and coupled effects of the material’s “true strain rate effect” and the stress wave effect in wet concrete, which are driven by the mutual coupling of pore water, thermal activation, and viscous drag mechanisms. This paper aims to provide a reference for the in-depth understanding of the strength evolution and control of hydraulic concrete structures. Full article

This research investigates novel polymeric composite materials made from recycled polyolefin and waste plant biomass (poplar seeds and vegetable peels), which have potential applications in the relatively unexplored field of electrical insulation. For composites made from poplar seeds with low density polyethylene matrix, the structure appears more uniform, even with increased biomass content, in contrast to those utilizing high density polyethylene matrix, which displays notable heterogeneous areas where the polymer appears separated from the fibrous network at higher biomass levels. Concerning the composites of vegetable peels with high density polyethylene matrix, the fragments of vegetable peels are clearly recognizable, and their bond to the polymer matrix appears weaker. When incorporating vegetable peels into the polypropylene matrix, it results in a better distribution of the vegetable peel fragments within the polymer matrix, as well as enhanced structural homogeneity. Overall, the incorporation of biomass reduces the Shore hardness measurement for every polymer matrix. Regarding tear resistance, the inclusion of biomass reduces the values only for low density polyethylene with poplar seeds. For both high density polyethylene and polypropylene, regardless of the biomass type, the property seems to enhance marginally with the addition of biomass. The primary advantage of utilizing these composites is that their water absorption rate is at least twice as low as that of transformer board, while still offering a similar capacity for absorbing transformer oil. All composite types exceeded the minimum required threshold of 70 °C for service exposure, and adhered to insulation class A, similar to cellulose-based insulations. The addition of cellulose to polyolefin composites appears to slightly improve their breakdown strength. The conductivity for this type of composite is at least three times lower than that of cellulose insulation materials, rendering them beneficial for applications in electrical engineering as potential substitutes for cellulose-based materials in multiple electrical insulation uses, e.g., for insulating low voltage electrical machines, as well as serving as a substitute for pressboard in transformers. Additionally, their thermoplastic properties offer enhanced processing versatility, opening up new opportunities for electrical engineering technology, especially with regard to electrical insulation recyclability in the context of a circular economy. Full article

To address the low utilization rate of straw and environmental pollution caused by traditional processing methods, this study developed a novel composite material based on straw for manufacturing outdoor furniture. Designed to achieve high-value recycling of agricultural waste and enhance the durability and sustainability of outdoor materials, the straw is treated with alkali and processed using an MDI curing system, with the addition of ZnO to enhance functional properties. Characterization of material properties was performed using contact angle measurements, UV-visible spectroscopy, and mechanical testing. The results indicate that a water contact angle of 93.51° was achieved for the composite material at a ZnO content of 6 wt.%, demonstrating excellent hydrophobicity. The introduction of ZnO reduced light absorption, indicating that the material exhibits superior stability in interior and exterior environments. The synergistic interaction between ZnO and straw fibers, along with the resulting active free radicals (·OH), endows this material with hydrophobic and UV-resistant properties. This composite material combines excellent mechanical strength with environmental friendliness, offering broad prospects in the field of sustainable outdoor furniture manufacturing. Full article

To address the challenges of winter pavement icing and the disposal of organic waste, this study developed a sustained-release deicing filler utilizing biochar derived from spent coffee grounds (SCGs). The material was synthesized through high-temperature carbonization, followed by physical adsorption of chloride salts and surface hydrophobic modification to control release rates. The study made asphalt mixtures and replaced normal mineral filler with the SCG material by volume at ratios of 0%, 50%, 75%, and 100% to test road and deicing performance. Wheel-tracking tests showed that the additive improved high-temperature stability and dynamic stability went up by 27.04% at the 75% replacement level. Salt dissolving created voids and slightly lowered water stability at high dosages, but all performance numbers still met the current engineering rules. Rutting slab tests at −5 °C showed the 100% replacement mix cut snow coverage to 11.43% in 60 min and proved it works for deicing. Pull-out tests measure the bond strength between ice and pavement at −5 °C, −7 °C, and −9 °C. The SCG deicing material weakens ice sticking and the bond strength for the 100% group at −5 °C was 0.35 kN, which is about 57.8% lower than the control asphalt. The bond strength of the deicing mix at −9 °C was still lower than the normal mix at −5 °C. This big drop in stickiness means the pavement stops ice from packing hard and makes mechanical removal easier. This study shows that the prepared deicing materials exhibit excellent sustained-release performance and snow-melting efficiency while ensuring satisfactory road performance. SCG deicing materials can effectively reduce snow accumulation on road surfaces in winter, lower the difficulty of ice-layer removal, and realize the sustainable utilization of SCGs. Full article

Active support systems are being increasingly applied in the control of large deformation in soft rock tunnels, and exploring the bearing characteristics of prestressed anchor bolts is of great engineering value for improving the long-term stability of tunnel structures. To address the problems of insufficient quantitative characterization of the bearing performance of prestressed anchor bolt support in soft rock tunnels and the difficulty of small-scale model tests in revealing the synergistic bearing law of support and surrounding rock, this study took a 350 km/h double-line high-speed railway tunnel as the prototype and established a large-scale tunnel structure model test system to conduct comparative tests under three working conditions: unsupported, ordinary bolt support, and prestressed anchor bolt support. By monitoring the tunnel failure process and mechanical response of the support structure throughout the test, the failure modes, bearing capacity, deformation characteristics, and axial force distribution of anchor bolts of tunnels under different support forms were systematically analyzed to quantitatively reveal the active support mechanism and bearing strengthening effect of prestressed anchor bolts. The results show that the design bearing capacity of the tunnel model with prestressed anchor bolt support is increased by 127.3% and 31.6% compared with that of the unsupported and ordinary bolt support models, and the ultimate bearing capacity is increased by 120.0% and 43.5%, respectively. Its secant stiffness in the initial loading stage reaches 80.0 kPa/mm, which is five times that of the ordinary bolt support and can effectively restrain the early plastic deformation of the surrounding rock. When the design bearing capacity is reached, the tensile stress of prestressed anchor bolts accounts for 40.2~69.8% of the ultimate tensile strength, with a more uniform axial force distribution and a much higher utilization rate of material mechanical properties than ordinary anchor bolts, which can fully mobilize the bearing potential of deep rock mass and realize the synergistic bearing of support and surrounding rock. This study accurately quantifies the bearing strengthening law of prestressed anchor bolts on tunnel support systems and clarifies the core mechanism of their active support. The research results provide important experimental basis and theoretical reference for the optimal design and engineering application of prestressed anchor bolts in soft rock tunnel engineering. Full article

Ferronickel slag, as a major solid waste in the stainless-steel industry, poses a serious threat to the environment due to its large-scale production and low utilization rate. In this study, magnesium oxide in the ferronickel slag was leached out and converted into high-purity magnesium sulfate, while the leach residue was utilized for cement clinker production. During the complete utilization of ferronickel slag, the Mg leaching efficiency reached 90.75% and was significantly enhanced by reducing the particle size of the ferronickel slag with H₂SO₄ solution as the sole solvent. High-purity magnesium sulfate with a purity of 99.92% was prepared from the leachate through a multi-step process involving primary crystallization, purification, and secondary crystallization. The leach residue, accounting for 68.20% of the original mass, was primarily composed of 79.4 wt% SiO₂ and less than 6.1 wt% MgO and is used as a key raw material in the production of Portland cement. Sintering temperature significantly influenced the structure and properties of the resulting cement. Both the Portland clinker and cement were successfully produced at sintering temperatures of 1400 °C and 1450 °C when the leach residue was used as a primary raw material, with well-developed cementitious phases of calcium silicate and aluminate formed during calcination. The setting time, soundness, and compressive and flexural strengths of the hardened C1400 and C1450 mortars met the requirements specified in relevant standards. Through this integrated process, the overall utilization rate of the ferronickel slag reached 100%. Based on a preliminary estimate, full utilization of the annual ferronickel slag production in China could substitute at least 19.5 million tons of magnesite and 15.0 million tons of silica and reduce CO₂ emissions by 10.3 million tons. Full article