Plasma-functionalized graphene fiber reinforced sulphoaluminate cement-based grouting materials

Fiber-reinforced cement-based grouting materials have aroused intensive attention due to the promising applications in coal mining. However, how to enable a fiber-cement grouting material with high mechanical strength and stability, and meanwhile with favorable toughness and electrical conductivity, still remains challenging. Herein, a facile and effective strategy to solve the problem was proposed by developing a plasma-functionalized graphene fiber (PGF) with the combined feature of excellent flexibility, good dispersion, high surface roughness and tensile strength, via the wet spinning and oxygen plasma etching. Thanks to the uniform distribution and strong interfacial interaction of PGFs in the cement matrix, the resultant PGF-sulphoaluminate cement grouting materials with water-cement ratio of 0.8 and 0.3% PGF dosage delivered the compressive and flexural strengths of 18.6 and 3.7 MPa after curing for 7 days, respectively, 1.1 and 1.3 times higher than that of control samples, respectively. Meanwhile, resulted from the formation of a continuous and homogeneous conductive network consisting of PGFs in the cement matrix, the composite featured a significant improvement of electrical conductivity. This work has shed light on new strategies for fabricating fiber-reinforced cement-based grouting materials with high mechanical strength, toughness and electrical conductivity toward future uses.     

The role of electronic and ionic conduction in the electrical conductivity of carbon fiber reinforced cement

Electrical conduction in carbon fiber reinforced cement with a fiber volume fraction below the percolation threshold involves electrons and ions. The fiber affects both the electronic conduction and the ionic conduction. The ozone treatment of the fiber surface helps the ionic conduction. Latex as an admixture helps provide a relatively high ionic conductivity; silica fume as an admixture helps provide a relatively high electronic conductivity. In the dry state (the state of practical importance attained by room temperature drying), electronic conduction is more significant than ionic conduction. In the wet state (water saturated state), ionic conduction dominates. When silica fume is present with the fiber, the fractional electronic contribution in the dry state is 0.99. When latex is present with the fiber, the corresponding value is 0.72-0.78. The ratio of the wet ionic conductivity to the dry ionic conductivity is much increased by fiber surface treatment and is higher when latex rather than silica fume is used. The wet ionic conductivity is much higher than the dry overall conductivity when latex is present, but is lower than or comparable to the dry overall conductivity when silica fume is present; the wet ionic conductivity is lower than the dry overall conductivity when the fiber is not treated and silica fume is present.     

Potential for the formation of respirable fibers in carbon fiber reinforced plastic materials after combustion

Fundamental aspects for the thermal decomposition and formation of respirable fragments of carbon fibers are investigated to assess the health hazard of carbon fiber reinforced plastic material after a fire. The influence of temperature (600°C‐900°C)/heat flux (30‐80 kW/m²), time of thermal load (up to 20 minutes), and oxygen exposure is analyzed by means of mass loss and fiber diameter of intermediate modulus and high tenacity fibers with initial diameters of 5 to 7 μm. Various types and concentrations of flame retardants were tested with respect to fiber protection. Epoxy‐based composite specimens (RTM6/G0939) additionally containing aluminum or magnesium hydroxide and/or zinc borate (1‐25 wt% per resin) were analyzed by cone calorimetry. Carbon fiber decomposition increases with combustion/irradiation time and temperature/heat flux, after a threshold temperature (ca 600°C) is exceeded. Critical fiber diameters below 3 μm are reached within minutes and are predominantly observed close to the panel surface in contact with air. Effective fiber protection is achieved by flame retardants acting beyond 600°C, forming thermally resistant layers such as zinc borate. A new field of research is opened identifying flame retardants, which protect carbon fibers in carbon fiber reinforced plastic.     

Modeling the electrical percolation of mixed carbon fillers in polymer blends

A model based on excluded volume theory is proposed for describing the electrical percolation of mixed carbon fillers in polymer blends by adjusting the unit volume of the previous model concerning mixed carbon-filler-filled single polymer systems. An equation capable of predicting the percolation threshold from those of individual carbon fillers in the single matrix polymer is developed from the model and further corrected to suit the actual situation. The corrected equation fits the experimental results obtained from multi-walled carbon nanotubes/carbon black-filled polybutylene terephthalate/styrene–acrylonitrile (SAN), polycarbonate (PC)/SAN and PC/acrylonitrile–butadiene–styrene blends well. The model and equation show clearly the advantages of using both mixed fillers and polymer blends, and can provide an important theoretical basis for designing the structures and predicting the electrical properties of conductive polymer composites.     

Effect of electrical field on TSA failure of cement-based materials

The impact of electrical field on the sulfate attack of cement-based materials at low temperatures was studied to rapidly detect Thaumasite Sulfate Attack (TSA) in the laboratory and in future engineering. Sulfate attack of cement paste with 30 wt% replacement of CaCO₃ powder soaked in Na₂SO₄ solution, MgSO₄ solution, or CaSO₄ solution was measured under the condition of 5 ± 2 °C when an electrical field was applied. Appearance changes and compressive strength of the samples were tested to evaluate the corrosion degree. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopic measurements were applied to study the microstructure of the corrosion product. The test results indicate that sample damage was obvious, compression strength declined rapidly, and ettringite and/or thaumasite were found in the corrosion product after applying the electrical field for 90 days. A muddy product with TSA characteristics was formed, and thaumasite composition was found in the corrosion product after applying the electrical field for 120 days when MgSO₄ solution was used as the corrosion medium. It is confirmed that an electrical field can accelerate TSA failure in cement-based materials.     

加固混凝土构件用碳纤维增强胶粘材料中的界面效应

对建筑结构胶粘剂中加固混凝土构件用碳纤维增强胶粘材料中的部分界面效应对性能影响及改善方法作了简要综述。     

表面处理对玻纤/碳纤增强橡胶基密封复合材料性能的影响

采用压延成张工艺制备碳纤维和玻璃纤维混杂增强非石棉橡胶基密封复合材料(NAFC),以横向抗拉强度作为表征混杂增强橡胶基密封材料中纤维与橡胶界面粘结性能的指标.通过扫描电镜(SEM)对材料横向拉伸试样断口进行形貌分析,及对材料的耐油、耐酸、耐碱性能进行测试,探讨了不同表面处理工艺对纤维与基体界面粘结效果的影响.研究结果表明,对玻璃纤维采用偶联剂KH-550浸渍后涂覆环氧树脂涂层,对碳纤维在空气氧化后涂覆环氧树脂涂层,可有效增强纤维、基体的界面粘结,所制得的混杂纤维增强复合材料具有较好的机械性能和耐介质性能.     

碳纤维增强复合材料的应用现状

碳纤维复合材料以其优异的综合性能成为当今世界材料学科研究的重点。介绍了碳纤维的概念及其性能,简述了碳纤维复合材料作为结构型复合材料、结构功能型复合材料及功能型复合材料的一些具体应用。     

Impact damage sensing in glass fiber reinforced composites based on carbon nanotubes by electrical resistance measurements

In this article, we report an interesting employment of multi‐walled carbon nanotubes as a filler in the epoxy matrix of a glass fiber reinforced composite (FRP). The intrinsic electrical conductivity of carbon nanotubes made the development of a nanocomposite with enhanced electrical properties possible. The manufactured nanocomposite was subsequently employed in the production of a glass FRP. Due to the high aspect ratio of carbon nanotubes, very small amounts of these particles were sufficient to modify the electrical properties of the obtained glass fiber composites. Basically, a three‐phases material was developed, in which two phases were electrically insulating—epoxy matrix and glass fiber—and one phase highly conductive, the carbon nanotubes. The main goal of this study was to investigate the possibility of developing a glass fiber reinforced nanocomposite (GFRN), which is able to provide measurable electrical signals when subjected to a low‐velocity impact on its surface. Following this goal, the drop in the mechanical performance of the composite was evaluated before and after the impact. At the same time, the variation in its electrical resistance was measured. The results have shown that it is possible to associate the increase in electrical resistance of the composite with the formation of damages caused by impact. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ion-conduction in cement-based materials

Those factors which control electrical conduction in cement based materials, namely, the concentration and mobility of ions in the pore solution and the porosity and pore size distribution, are discussed in terms of the time dependency of the electrical conductivity. An experimental study has been made of the influence of water/cement ratio and age of the cement on the various parameters which can be determined from conductivity measurements. While the measurements have been made on dense silica-cement, the conclusions are applicable to other Portland cement based materials.     

Mechanical,electrical, and dielectric properties of polyvinylidene fluoride/short carbon fiber composites with low‐electrical percolation threshold

In this investigation, polyvinylidene fluoride (PVDF)/short carbon fiber (SCF) composites have been prepared by solution casting technique to enhance electrical and dielectric properties with very low‐electrical percolation threshold (0.5 phr SCF). The effect of SCF content on mechanical, thermal and morphological properties of the composites have also been investigated. The mechanical properties of the composites are found to reduce compared to neat PVDF due to poor polymer–filler interaction which can be concluded from FESEM micrographs showing poor bonding between PVDF and SCF. The PVDF/SCF composites exhibit either positive temperature coefficient effect of resistivity or negative temperature coefficient effect of resistivity depending on the loading of SCF in the polymer matrix. The change in conductivity during heating–cooling cycle for these composites shows electrical hysteresis along with electrical set. The melting point of the composites marginally increases with the increase in fiber loading in PVDF matrix as evidenced from DSC thermograms. X‐ray diffraction analysis reveals the crystallinity of PVDF decreases with the increase in SCF loading in matrix polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39866.     

Tribological behavior and applications of carbon fiber reinforced ceramic composites as high-performance frictional materials

Due to the favorable tribological, mechanical, chemical, and thermal properties, carbon fiber reinforced ceramic composites, especially carbon fiber reinforced carbon and silicon carbide dual matrix composites (C/C–SiC), has been considered as high-performance frictional materials. In this paper, current applications and recent progress on tribological behavior of C/C–SiC composites are reviewed. The factors affecting the friction and wear properties, including the content of silicon carbide and carbon matrix, carbon fiber preform architecture, as well as the matrix modification by alloy additives and C/C–SiC composites under various test conditions are reviewed. Furthermore, based on the current status of researches, prospect of several technically available solutions for low-cost manufacturing C/C–SiC composites is also proposed.     

碳纤维加固法在桥墩加固工程中的应用技术

在混凝土加固工程通常采用钢板粘接加固法和碳纤维粘接加固法。钢板加固法目前用的较多,设计理论和施工技术较为成熟;碳纤维布加固法是近年来发展较快的加固方法,以强度高、质量轻、耐腐蚀、施工简单等特点备受关注。本文以日本首都高速道路公司承担的首都高速3号线高架桥桥墩抗震加固工程为例,讨论碳纤维在混凝土加固工程中的实用技术。     

Thermoelectric properties of carbon nanotube reinforced cement-based composites fabricated by compression shear

Carbon nanotubes (CNTs) with weight percent of 5.0%, 10.0% and 15.0% were added into the cement matrix to fabricate CNT reinforced cement-based composites (CNTs/CC) by mixing and dry compression shear methods. Seebeck coefficient, electrical conductivity and thermal conductivity of the as-received CNTs/CC were measured and analyzed in detail. The CNTs/CC exhibits the thermoelectric behavior of p-type semiconductor. CNTs were dispersed uniformly in cement matrix by compression shear stress, which promoted a relatively high electrical conductivity (0.818 S/cm) and Seebeck coefficient (57.98 μV/°C) of CNTs/CC. Combining with their lower thermal conductivity ranged from 0.734 to 0.947 W m^?1 K^?1, the CNTs/CC shows the highest thermoelectric figure of merit (ZT) has reached 9.33 × 10^?5, Which is benefit to the applications in large-scale energy harvesting in the buildings and pavements with low cost in the future cities.     

Electrical-resistance-based damage self-sensing in carbon fiber reinforced cement

Damage self-sensing (to be distinguished from strain self-sensing) by electrical resistance measurement is effective in carbon fiber reinforced cement below the percolation threshold, as shown under uniaxial compression. Major damage that is accompanied by irreversible strain is indicated by irreversible resistivity increase ranging from 10% to 30%. Minor damage in the elastic regime is indicated by this increase ranging from 1% to 7%. The irreversible resistivity fractional change per unit irreversible strain is higher in the transverse direction than the longitudinal direction. The origin of the damage self-sensing ability is attributed to the fracture of fibers that bridge microcracks and the consequent resistivity increase. The fracture of a bridging fiber occurs upon microcrack opening or shear.     

Physical modeling of the electrical double layer effects on multispecies ions transport in cement-based materials

The transport of ions through cement-based materials is described at a microscopic scale with a pore modeled by two infinitely large flat plates. The theory of the electrical double layer (EDL) shows that (i) the overlapping between the diffuse layers occurring in the pore is more important as the pore diameter will be small (low than the Debye length) and the pore walls will be strongly charged, (ii) the fluxes of coions and counterions will be respectively increased and attenuated in such pores. The gel pores of cement based materials have similar characteristics. As the capillary pores of the cement based materials with low porosity are connected between them by the pores gel, the transport of ions at a macroscopic scale could be greatly influenced by the overlapping effect of the diffuse layers.     

短碳纤维增强铝基复合材料

通过化学镀再电镀的方法,在碳纤维表面镀上Cu镀层,制备C/Cu复合丝,并在硼酸的保护下,利用非真空条件下的液态机械搅拌法制备短碳纤维增强铝基复合材料,研究了碳纤维在复合材料中的分散程度,铜镀层存在状态及C/Al复合材料的拉伸性能.实验结果表明：在硼酸存在下,大大降低了铜的氧化程度,碳纤维分散均匀且没有损伤,少量硼酸的加入,对复合材料的力学性能没有影响,该复合材料的抗拉强度随碳纤维含量的增加而增加,其抗拉强度较基体材料提高50%以上,但塑性指标却明显下降.     

Matrix hybridization in the interlayer for carbon fiber reinforced composites

Polymeric composites have gone through a level of maturity beyond the laboratory stage with the development of the Boeing 787, the structure of which contains more than 50% composites. Nonetheless, a basic understanding of the material used in its primary structure has not been extensively investigated. For instance, micromechanical models are inadequate as they always assume an evenly distributed homogeneous matrix, without following classic lamination theory, which assumes constant stress through the laminate thickness. Our program now in its third year at the Polymeric Composites Laboratory in Seattle, supported by industry as well as government agencies, and in collaboration with several universities on a global scale, is developing such concepts for understanding and improving matrices in layered configurations. This effort focuses on the development of interlayer systems used as enablers to improve certain properties of the composite, such as fracture‐toughness and crack‐propagation inhibition. POLYM. COMPOS., 31:1965–1976, 2010. © 2010 Society of Plastics Engineers.     

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

In conductive polymer compounds, the filler volume fraction at which a network of touching particles is formed is not a constant but depends on the manufacturing process. By applying three main features—particle-particle interaction, dynamics of agglomeration, and structure of agglomerates—which are well known in colloid science to filled polymers, the electrical percolation behavior can be understood. Thus, it is possible to explain the hitherto found low percolation thresholds of less than 0.5 vol% in carbon-black-filled resins and, hence, further reduce the threshold to 0.06 vol%. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1741–1746, 1997