摘要:
A series of cyclic triaxial tests were conducted on marine soft clay deposits to establish and validate a predictive model for cumulative plastic strain. Additionally, a numerical model of particle flow code in cyclic triaxial tests was developed. The effects of confining pressure, moisture content, and dynamic stress ratio on the dynamic properties of marine soft clay were examined, considering factors such as volume deformation and microscopic failure patterns. The results indicated that both the predictive model and numerical model showed strong consistency with the experimental data. The plastic strain of marine soft clay was influenced by moisture content, stress ratio, and confining pressure in a consistent manner, with moisture content being the primary factor. A predictive model for the cumulative plastic strain of marine soft clay was successfully established, allowing for the evaluation of dynamic properties from the perspective of cumulative plastic strain. During the loading process in the numerical model, microcracks within the soil structure gradually compacted, and the main displacement of the specimen extended from the vertical center axis to the sides, ultimately resulting in shear damage.
摘要:
Nowadays, geopolymer coatings have been studied a lot due to their green and sustainable properties, and they have a great potential to partially replace traditional coatings in terms of corrosion resistance and economy. In this study, metakaolin-based geopolymer coating was used as the control group, and anticorrosive coatings were prepared by adding different dosages (2–8 wt%) of ZnO fillers to study the effect of ZnO on physical properties and anticorrosion properties of metakaolin-based geopolymer anticorrosive coatings. The results showed that when the mass fraction of the zinc oxide was 8%, it had the optimum effect on physical performance. The water absorption was 12.4%, and the toughness was 3 mm. In addition, the anticorrosive properties of the coating were studied by sodium chloride (NaCl) solution immersion test, wet–dry cyclic test, salt spray test, and electrochemical test. In sodium chloride (NaCl) solution immersion, wet–dry cycle, and salt spray test, a reduction of 43.8%, 50.6%, and 74.2% in corrosion area ratio, respectively, were achieved with a coating of 8% ZnO filled as compared with pure geopolymer coatings. The results indicated that the addition of ZnO enhanced the anticorrosion performance of the coating. The macroscopic test results were verified by SEM. This study lays a foundation for the subsequent research and performance improvement of metakaolin-based geopolymer anticorrosive coatings.
摘要:
Phase change energy storage technology using phase change materials (PCMs) is a viable solution to effectively address the heat dissipation problems of electronic devices. Herein, we proposed to prepare a modified PCM using CH3COONa center dot 3H(2)O (SAT) as main PCM, 9 wt% DL-Alanine (DL) as temperature modifier, and 2 wt% Na2HPO4 center dot 12H(2)O as nucleating agent. Calculations using density functional theory method confirmed that the adjustment of DL on phase change temperature of SAT was originated from the hydrogen bond between them. Then, the modified PCM was loaded into 14 wt% expanded graphite (EG) to obtain a composite PCM with a suitable phase change temperature of 52.9 degrees C, phase change enthalpy of 227.4 J/g as well as supercooling degree of 6.6 degrees C, and the thermal conductivity of the composite PCM was as high as 11.52 W.m(-1).K-1. SEM and pore structure analyses showed that the modified PCM was successfully loaded into the pore structure of EG, and their combination was verified by XRD and FT-IR as a physical interaction. After 200 heating-cooling cycles, the phase change temperature and enthalpy of the composite PCM was basically unchanged along with consistent crystal structure and chemical composition, showing an excellent thermal reliability. A comparative analysis applied in a testing system showed that with loading of the composite PCM temperature control module, the critical time of the electronic chip was extended by 4670 s and the thermal equilibrium temperature was decreased by 20.4 degrees C, presenting a good thermal management performance. Therefore, the prepared composite PCM had great potential for application in thermal management of electronic devices.
摘要:
本文利用醋酸乙烯酯-乙烯共聚乳液(EVA)、丙烯酸酯乳液(PAE)分别对装配式水泥基套筒灌浆料进行改性,制备了2种聚合物乳液改性套筒灌浆料。研究了聚合物乳液对套筒灌浆料流动度、抗压强度、吸水率、膨胀率、耐久性、拉伸性能和微观结构的影响,并进行了成本核算。结果表明:掺入聚合物乳液能显著改善灌浆料的流动度、抗压强度、吸水率、抗硫酸盐侵蚀和抗冻融侵蚀性能,而且PAE改性的套筒灌浆料的综合性能优于EVA改性;PAE改性能增强灌浆料整体内聚力和密实度,使得灌浆料的膨胀率基本无负面影响且无泌水现象,同时可以增强灌浆料接头的拉伸性能、抗拉强度以及黏结强度。当PAE掺量在0.3%~1.0%(质量分数)时,PAE改性灌浆料性能均满足相应国家标准要求,且制备成本较低。 In this study, two kinds of polymer emulsion-modified sleeve grouting materials were prepared with vinyl acetate-ethylene copolymerization emulsion (EVA) and acrylate emulsion (PAE), respectively. The effects of polymer emulsion on the fluidity, compressive strength, water absorption, expansion rate, durability, tensile property and microstructure of the sleeve grouting material were investigated and its cost accounting was executed. The results show that polymer emulsion can significantly improve the fluidity, compressive strength, water absorption, sulfate resistance and freeze thaw resistance of grouting materials, and the comprehensive properties of PAE modified sleeve grouting materials are better than EVA modified ones. PAE modification enhances the overall cohesion and density of grouting material, ensuring that the expansion rate of the grouting material has little negative impact and no bleeding phenomenon. At the same time, it can enhance the tensile performance, tensile strength, and bonding strength of grouting material joint. When the PAE content is between 0.3% and 1.0% (mass fraction), the performance of PAE modified grouting material meets the corresponding national standard requirements, and the preparation cost is relatively low.
摘要:
The influence of polymer emulsion, pigment filler, and dispersant on the corrosion resistance of polymer cement-based composite anti-corrosion coatings were investigated in this study. Adhesion loss rate tests and electrochemical tests were conducted on samples. The research results show that optimal corrosion resistance can be achieved with a 45 wt% dosage of emulsion, a 6 wt% dosage of pigment filler, and a 0.30 wt% dosage of dispersant. The bonding properties of bare steel bars, epoxy-coated steel bars, and polymer cement-based composite anti-corrosion coated steel bars with grout were compared. The results show that the polymer cement-based composite anti-corrosion coating can enhance the bonding properties of the samples. Furthermore, the microscopic analysis was conducted on the samples. The results demonstrate that the appropriate addition of emulsion can fill internal pores of the coating, tightly bonding hydration products with unhydrated cement particles. Moreover, incorporating a suitable dosage of functional additives enhances the stability of the coating system and leads to a denser microstructure.
摘要:
Hot stamping (or press hardening) is a new technology that is widely used in the production of advanced high-strength steel parts for automotive applications. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), and accelerated corrosion tests (the neutral salt spray test and periodic immersion test) were conducted on press-hardened samples produced from uncoated (cold-rolled and cold strip production (CSP) hot-rolled) and Al-Si-coated press-hardened steels to elucidate their distinct anti-corrosion mechanisms. The cross-sectional micromorphology and element distribution of three types of press-hardened steels after a neutral salt spray test were observed using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The corrosion resistance of Al-Si-coated press-hardened steel was found to be significantly diminished following the hot stamping process due to the presence of microcracks and elevated iron content in the coating subsequent to austenitizing heat treatment. On the other hand, the corrosion resistance of uncoated press-hardened sheets produced from cold-rolled and CSP hot-rolled press-hardened steel was found to be proximal due to their nearly identical composition and microstructure (fully martensite) after the hot stamping process. Considering the high efficiency and energy-saving properties of hot-rolled press-hardened steel, it holds the potential to replace cold-rolled and even aluminum-silicon-coated press-hardened steel in automobile manufacturing.
摘要:
To investigate crack propagation and the coalescence mechanism of a rock bridge under unloading condition induced by intensive excavation of rock mass, the direct shear test with unloading normal stress and corresponding particle flow code (PFC) simulation were conducted on the sandstone specimen containing a parallel fissure pair considering different fissure inclinations (varied from 0 degrees to 90 degrees) and initial shear stresses (varied from 4 to 7 MPa). Three failure patterns (i.e., shear failure, tensile failure, and tensile-shear mixed failure) are identified as experimental and numerical results. The failure pattern transforms in the order of a shear, tensile, and tensile-shear mixed failure pattern as the fissure inclination increases. Three displacement field types are summarized and correspond to different failure patterns. Comparing the shear strength, cracking process, and microscopic displacement field in the direct shear test with unloading normal stress and the conventional direct shear test, normal unloading weakens the shear strength of the specimen under the selected stress conditions (initial normal stress is 20 MPa, initial shear stress ranges from 4 to 7 MPa). Rebound deformation in the process of unloading promotes the high proportion of tensile cracks for the tested fissure inclinations.
摘要:
Geophones are typically arranged along the dam axis when seismic wave methods are used to detect latent hazards. Due to the complexity of the potential hazards and physical parameters inside the dam, the detection results may be inaccurate based on the seismic data in a single direction. The incorporation of seismic data perpendicular to the dam axis will effectively improve the detection accuracy. Mastering the propagation characteristics of seismic waves perpendicular to the earth-rock dam axis are necessitated for seismic data processing and interpretation yet remain a research gap, and the kinematic characteristics of various wave fields are underexplored. Here, an adaptive free boundary treatment scheme at the dam crest and slope is proposed based on the structural features of actual earth-rock dams, and the corresponding difference mode is provided. The full-wavefield simulation of seismic waves perpendicular to the dam axis is achieved using a finite-difference method with a spatial sixth-order and temporal second-order staggered grid. The kinematic characteristics of seismic wave propagation within the dam are elaborated. The layout of geophones perpendicular to the dam axis allows for recording the direct longitudinal wave and direct shear wave penetrating the dam, and surface wave reflection occurs at the crest corners and bottom corners. Influenced by the dam's slope structure, the path lengths of the reflected body waves vary irregularly depending on the locations of receiver points on the dam slope, resulting in irregular travel-time curves in seismic records.
摘要:
Enzyme-induced carbonate precipitation (EICP) is a promising technique for soil reinforcement. To select a suitable calcium source and a suitable solution amount for aeolian sand stabilization using EICP, specimens treated with different solution amounts (1.5, 2, 2.5, 3, and 3.5L/m(2)). Surface strength, crust thickness, calcium carbonate content (CCC) and water vapor adsorption tests were performed to evaluate the effect of two calcium sources (calcium acetate and calcium chloride) on aeolian sand solidification. The plant suitability of solidified sand was investigated by the sea buckthorn growth test. The suitable calcium source was then used for the laboratory wind tunnel test and the field test to examine the erosion resistance of solidified sand. The results demonstrated that Ca(CH(3)COO)(2)-treated specimens exhibited higher strength than CaCl(2)-treated specimens at the same EICP solution amount, and the water vapor equilibrium adsorption mass of Ca(CH(3)COO)(2)-treated specimens was less, indicating that Ca(CH(3)COO)(2)-solidified sand was more effective and had better long-term stability. In addition, plants grown in Ca(CH(3)COO)(2)-treated sand had greater seedling emergence percentage and higher average height, which indicated that calcium acetate is a more suitable calcium source for EICP treatment. Furthermore, the surface strength and crust thickness of solidified sand increased with increasing the solution amount. For sand treated with 3L/m(2) of solution, the excessive strength and thickness of the crust made plants growth difficult, and the performance of sand treated with more than 2L/m(2) of solution significantly improved. Thus, the solution amount of 2-3L/m(2) is suggested for engineering applications. The sand solidified using EICP in the field could effectively mitigate wind erosion and facilitate the growth of native plants. Therefore, EICP can be combined with vegetative method to achieve long-term wind erosion control in the future.
通讯机构:
[Yu, P ] H;Huazhong Univ Sci & Technol, Sch Civil & Hydraul Engn, Wuhan 430074, Hubei, Peoples R China.
关键词:
Asphalt mixture;Interfacial transition zone;Acid and alkaline water environments;Water stability;Microscopic erosion mechanism
摘要:
Acidity and alkalinity of water environments have been proven to influence the water stability of asphalt mixture. However, the relevant influencing mechanism still remains unclear. To fulfill this research gap, this study conducted a series of microscopic tests, aiming at unveiling the microscopic erosion mechanism of the water environment on the water stability of asphalt mixture for better moisture stability achieved. Specifically, the asphalt-aggregate interfacial transition zone (ITZ) samples were prepared by combining #70 asphalt with limestone and granite, respectively, which were then immersed in water solutions at 3 different pH levels (pH = 3.0, 7.0, and 11.0) for 7 days. The chemical composition and microstructure of the asphalt film on the surface of the ITZ samples pre and post-treatment were scrutinized using the Fourier Transform Infrared Spectroscopy (FTIR) and the Atomic Force Microscope (AFM), while the development of microcracks at the asphalt-aggregate interface were identified and traced utilizing the Scanning Electron Microscope (SEM). The test results indicate that after treatment with acidic and alkaline aqueous solutions, the asphalt film 's surface is enriched with polar components such as asphaltenes, resins, and aromatic fractions. The migration of these polar components to the surface of the asphalt film reduces the adhesion between asphalt-aggregate, leading to the formation of microcracks at the asphalt-aggregate interface. The most severe crack development occurs in alkaline water environment, followed by acidic water environment. It is interestingly noted that the adhesion at the asphalt-granite interface is improved under the acidic environment. This improvement may be attributed to the covalent nature of silica, which hinders the adsorption of ions from acidic solution into the asphalt film. This hindrance effectively prevents water intrusion at the asphalt-aggregate interface, thereby reducing the adhesion loss. These findings can help elucidate the mechanism of water damage in asphalt pavement exposed to real -world conditions and enhance its water stability with effective countermeasures proposed.
作者机构:
[Ma, Haoqin; Li, Guodong; Li, Changlong; Liu, Tianle; Huang, Xiege; Duan, Bo; Zhai, Pengcheng] Wuhan Univ Technol, Hubei Key Lab Theory & Applicat Adv Mat Mech, Wuhan 430070, Peoples R China.;[Li, Jialiang] Wuhan Polytech Univ, Sch Civil Engn & Architecture, Wuhan 430023, Peoples R China.;[Li, Guodong; Zhai, Pengcheng] Wuhan Univ Technol, State Key Lab Adv Technol Mat Synth & Proc, Wuhan 430070, Peoples R China.
通讯机构:
[Li, GD ; Duan, B] W;Wuhan Univ Technol, Hubei Key Lab Theory & Applicat Adv Mat Mech, Wuhan 430070, Peoples R China.;Wuhan Univ Technol, State Key Lab Adv Technol Mat Synth & Proc, Wuhan 430070, Peoples R China.
摘要:
Band convergence is considered to be a strategy with clear benefits for thermoelectric performance, generally favoring the co-optimization of conductivity and Seebeck coefficients, and the conventional means include elemental filling to regulate the band. However, the influence of the most electronegative fluorine on the CoSb3 band remains unclear. We carry out density-functional-theory calculations and show that the valence band maximum gradually shifts downward with the increase of fluorine filling, lastly the valence band maximum converges to the highly degenerated secondary valence bands in fluorine-filled skutterudites. The effective degeneracy near the secondary valence band promotes more valleys to participate in electric transport, leading to a carrier mobility of more than the threefold and nearly twofold effective mass for F0.1Co4Sb12 compared to Co4Sb12. This work provides a new and promising route to boost the thermoelectric properties of p-type skutterudites.
关键词:
Aminomethylphosphonic acid;Bacterial community;Glyphosate;Phosphorus cycle;Rice-crayfish system
摘要:
Glyphosate, a commonly used organophosphorus herbicide in rice-crayfish cropping regions, may alter regional phosphorus cycle processes while affecting the structure of microbial communities. However, the effects of glyphosate residues on rice-crayfish systems remain unclear. In this study, we assessed the spatial and temporal distribution characteristics of glyphosate and its primary degradation products, as well as the impact mechanisms of glyphosate on microbial communities and the phosphorus cycle in rice-crayfish systems such as paddy fields, breeding ditches and recharge rivers. The detection rates of glyphosate and aminomethylphosphonic acid (AMPA) were 100% in rice-crayfish systems. Concentrations of glyphosate in the water phase and soil/sediment were as high as 0.012μg/L and 7.480 μg/kg, respectively, and concentrations of AMPA were as high as 17.435μg/L and 13.200 μg/kg, respectively. Glyphosate concentrations were not affected by rainfall or sampling site, but concentrations of AMPA in the water phase of recharge rivers were affected by rainfall. The glyphosate concentration was significantly and positively correlated with RBG-16-58-14 abundance, and the AMPA concentration was significantly and positively correlated with Actinobacteria and Lysobacter abundance, and negatively correlated with Cyanobacteria abundance (P<0.05). The highest abundances of phoD, phnK, and ppx genes were found in all soils/sediments. Glyphosate concentration in soil/sediment was significantly and positively correlated with the abundance of phoD gene encoding an organophosphorus-degrading enzyme and ppx gene encoding poly inorganic phosphate (Pi) hydrolase (P<0.05). In addition, the glyphosate concentration was significantly and positively correlated with the Ca-bonded Pi content (P<0.05). This implies that glyphosate may promote the production of stable Pi in rice-crayfish systems by increasing the abundance of phoD and ppx genes. The results of this study reveal the impact mechanism of glyphosate on the phosphorus cycle in rice-crayfish systems and provide a basis for the risk assessment of glyphosate.
摘要:
<jats:p>In the practical operation of traditional landfills, compaction clay often experiences cracking, while the HDPE geomembrane may tear and bulge, resulting in a compromised performance of the landfill covering system. To address this issue, a capillary retarding covering material for landfill sites is proposed by utilizing municipal sludge and construction waste particles as substrates and incorporating a small quantity of calcium bentonite. The mechanical characteristics of the covering material were investigated using a standard consolidation test and a triaxial compression test. A permeability test and a soil water characteristic curve (SWCC) test were conducted to examine the permeability and capillary retarding effect of the covering material. Microscopic tests including SEM scanning, laser particle size analysis, and T2 NMR analysis were performed to investigate the connection mode, particle size composition, and pore structure characteristics of the covered particles. Based on the aforementioned research, the following conclusions can be drawn: The cohesion of the covering material ranged from 50 to 150 kPa, while the internal friction angle ranged from 24.23° to 31°. The cohesion was directly proportional to the content of construction waste, whereas the internal friction angle was inversely proportional to calcium bentonite content. The permeability coefficient ranged from 5.04 × 10−6 cm/s to 7.34 × 10−5 cm/s, indicating a certain level of impermeability. Both the sludge and the calcium bentonite contents jointly influenced the final permeability coefficient in a negative correlation manner, with a notable hydraulic hysteresis phenomenon observed. A higher content of construction waste leads to a more pronounced supporting force exerted by the formed skeleton structures within a load pressure range between 0 and 1600 kPa. When considering a mass ratio of municipal sludge: construction waste: calcium bentonite as 30:60:7, respectively, only a decrease in the pore ratio by approximately 13.20% was observed. This study provides valuable data support for designing and applying capillary retarding cover barrier systems in landfills.</jats:p>