Electrically conductive concrete for heating using steel bars as electrodes

The steel bars with good electrical conductivity were used as two kinds of electrodes in the making of carbon fiber (CF) electrically conductive concrete for heating. The results of the pertinent experiments illustrate the design is viable. The change in electrical resistivity over three years’ hydration time was studied when steel bars were used as lateral face electrodes and top bottom surface electrodes respectively. The temperature rise test was conducted to verify the heating properties of two kinds of concrete. Not only the study can reduce the CF volume content of electrically conductive concrete for heating to 0.58% or 0.36% according to different design, but also it will enhance the carrying capacity of the concrete roadway for heating.     

电极对碳纤维导电发热混凝土性能的影响

研究了四电极法和埋入电极法得到的电阻差异性规律，同时也研究了埋入不锈铜片电极及埋入网状电极在电阻率、电热效果方面的差异，提出了可采用上下式电极来制作导电发热混凝土的方案，并将路面融雪化冰用碳纤维导电混凝土所需的碳纤维体积含量降低到了0．22%，不仅可以大幅降低制作发热混凝土的成本，而且还可以提高发热混凝土铺层的强度。     

融雪化冰用碳纤维混凝土的导电性能研究

阐述了将用于路面融雪化冰的导电性能优良的碳纤维混凝土的制作过程，特别说明了一种效果较好的电极的制作方法，并通过实验分析了该种导电混凝土电阻率与碳纤维的种类、电极大小的关系以及电阻随龄期及温度的变化情况，结果说明制作出的导电混凝土具有良好的性能，可用于工程实际。     

导电混凝土研究进展

综合国内外文献分析了导电混凝土的导电机理,介绍了石墨、碳纤维、钢纤维及钢屑等常用导电组分材料及其导电混凝土的性能、导电混凝土电性能的影响因素,分析了导电混凝土的压敏性、温敏性、力电效应和电热特性的研究进展,介绍了导电混凝土在室内采暖、变电站接地网和电热除冰化雪中的应用,指出了目前导电混凝土研究和应用方面存在的不足。     

导电混凝土电热除冰化雪的功率分析

分析了目前常用除冰化雪方法的利弊，介绍了导电混凝土电热除冰雪的工作原理；从能量守恒的角度分析了导电混凝土电热除冰雪的最低功率需求；实验测试了碳纤维混凝土电热功率与电压的关系，表明碳纤维混凝土通电后产生的热量能够满足冬季路面除冰化雪的需要。     

Compression sensibility of magnetic-concentrated fly ash mortar under uniaxial loading

The electrical conductivity, compression sensibility, workability and cost are factors that affect the application of conductive smart materials in civil structures. Consequently, the resistance and compression sensibility of magnetic-concentrated fly ash (MCFA) mortar were investigated using two electrode method, and the difference of compression sensibility between MCFA mortar and carbon fiber reinforced cement (CFRC) under uniaxial loading was studied. Factors affecting the compression sensibility of MCFA mortar, such as MCFA content, loading rate and stress cycles, were analyzed. Results show that fly ash with high content of Fe3O4 can be used to prepare conductive mortar since Fe3O4 is a kind of nonstoichiometric oxide and usually acts as semiconductor. MCFA mortar exhibits the same electrical conductivity to that of CFRC when the content of MCFA is more than 40% by weight of sample. The compression sensibility of mortar is improved with the increase of MCFA content and loading rate. The compression sensibility of MCFA mortar is reversible with the circling of loading. Results show that the application of MCFA in concrete not only provides excellent performances of electrical-functionality and workability, but also reduces the cost of conductive concrete.     

Influence of Water Content on Conductivity and Piezoresistivity of Cement-based Material with both Carbon Fiber and Carbon Black

The influence of water content on the conductivity and piezoresistivity of cement-based material with carbon fiber (CF) and carbon black (CB) was investigated. The piezoresistivity of cement-based material with both CF and CB was compared with that of cement-based material with CF only, and the changes in electrical resistivity of cement-based material with both CF and CB under static and loading conditions in different drying and soaking time were studied. It is found that the piezoresistivity of cement-ba...     

Electrical resistance behavior of vinylester composites filled with glass-carbon hybrid fibers

Vinylester (bismethacryloxy derivative of a bisphenol-A type EP resin, VE) composites with glass-carbon hybrid fibers (CF-GF) weight fraction of 50%, were prepared by the compress molding method. The distribution of carbon fiber in the hybrids was observed by stereomicroscope. The electrical resistance behavior of the composites filled with different carbon fiber (CF) weight contents (0.5% to 20%) was studied. The experimental results show that the electrical resistance behaviors of CF-GF/VE composites are different with those of CF/VE composites because carbon fibers’ conducting networks are broken by the glass fibers in the CF-GF/VE composites. The carbon fibers distribute uniformly in the networks of glass fibers (GF) like single silk and form the semi-continuous conducting networks. Composite filled with GF-CF hybrid has a higher percolation threshold than that filled with pure CF. At that time, the resistivity of CF-GF/VE composites varies little with the temperature increasing. The temperature coefficient of resistivity in GF-CF/VE composite is less than 317 ppm and the variation of the resistivity after ten thermal cycles from 20 °C to 240 °C is less than 1.96%. Funded by the Natural Science Foundation of Hubei Province (No. 2007ABA028)     

改善新老混凝土界面粘结性能的措施研究

通过16组共48个100mm×100mm×100mm四种纤维混凝土与既有混凝土粘结的立方体试件劈拉试验,研究了新混凝土中纤维种类、纤维掺量对粘结试件劈拉性能的影响。结果表明各种纤维的加入总体上均有利于新老混凝土粘结性能的提高。效果最佳的是碳纳米管,其次是聚丙烯腈纤维,然后是玄武岩纤维和钢纤维。然后通过64组共192个100mm×100mm×100mm纤维增强聚合物改性混凝土与既有混凝土粘结的立方体试件劈拉试验,研究了新混凝土中纤维种类、纤维与聚合物掺量组合对粘结试件劈拉性能的影响。苯丙乳液的复合掺入总体上可进一步提高新老混凝土的粘结劈拉强度。各种纤维与苯丙乳液复掺时,均存在一个苯丙乳液掺量的最佳值。     

碳纤维水泥基复合材料电阻变化规律研究

研究了碳纤维水泥基复合材料在水化期间及固化后的电阻变化特性。研究发现：当碳纤维体积分数较低时，试样的电阻率随着固化时间的增大而明显增大；反之，当碳纤维体积分数超过某一个范围后，会出现电阻（率）随水化时间的延长而变小的规律。此外，对于已固化好的碳纤维水泥基复合材料，随着电流（电压）的增大，电阻会出现一定程度的降低，碳纤维体积分数越低（即电阻率越大时），电阻下降的趋势越明显。     

An Improvement in Electrical Properties of Asphalt Concerete

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Self-monitoring application of asphalt concrete containing graphite and carbon fibers

The self-monitoring application of asphalt concrete containing graphite and carbon fibers using indirect tensile test and wheel rolling test were introduced. The experiment results indicate that this kind of pitch-based composite is effective for strain/stress self-monitoring. In the indirect tensile test, for a completely conductive asphalt concrete specimen, the piezoresistivity was very weak and slightly positive, which meant the resistivity increase with the increment of tensile strain at all stress/strain amplitudes, with the gage factor as high as 6. The strain self-sensing ability was superior in the case of higher graphite content. However, when the conductive concrete was embedded into common asphalt concrete specimen as a partial structure function, the piezoresistivity was positive at all stress/strain amplitudes and with the gage factor of 13, which was much higher than that of completely conductive specimen. Thus, the strain self-sensing ability was superior when conductive asphalt concrete was taken in as a partial structure function. In the wheel-rolling test, the piezoresistivity was highly positive. At any stress amplitude, the piezoresistivity was strong, with the gage factor as high as 100, which was higher for a stress amplitude of 0.7 MPa than that of 0.5 MPa.     

纳米碳纤维增强混凝土的介电特性

为研究纳米碳纤维增强混凝土的介电特性,发现纳米碳纤维增强混凝土对电磁波的反射与损耗规律,采用波导法测试纤维掺量为0、0.1%、0.2%、0.3%、0.5%的纳米碳纤维增强混凝土在1.7～2.6 GHz频率范围内的介电常数。分别从相对复介电常数实部、相对复介电常数虚部、损耗角正切等方面分析了纤维掺量、频率对纳米碳纤维增强混凝土介电特性的影响,并对比分析0.3%纤维掺量下纳米碳纤维和普通碳纤维对混凝土材料介电特性的影响。结果表明:纳米碳纤维的掺加提高了混凝土材料相对复介电常数实部和虚部、损耗角正切,增强了混凝土材料对电磁波的损耗能力;纤维掺量越大,纳米碳纤维增强混凝土介电特性越强,对电磁波的损耗能力越大;纳米碳纤维对混凝土材料介电特性的提高效果强于碳纤维。     

Preparation and Performance of Corona-proof Conductive Composite Coatings

Because of its merits,acrylic resin was chosen to improve the mechanical,conductive and hydrophobic properties.Carbon fiber powders (CF),carbon nanotubes (MWCNT),and nano-TiO₂ were incorporated into the acrylic resin to prepare the corona-proof conductive composite coatings.The incorporation of CF and MWCNT may improve the conductivity and mechanical strength of the coatings.However,the addition of nano-TiO₂ may increase the hydrophobicity of the coatings.Thus,the effects o...     

Influential Factors on Deicing Performance of Electrically Conductive Concrete Pavement

The deicing experiment of carbon fiber reinforced electrically conductive concrete （CFRC） slab was conducted in laboratory at first, then the deicing process of CFRC parement was analyzed by means of finite element method （FEM）. At last, based on the energy conservation law and the computing restdts of finite element method, the influential factors including the setting of electric heating layer, environmental temperature, the thickness of ice, material parameters, and deicing power on deicing performance and energy consumption were discussed.     

Mechanical Properties of Phenolic-Resin Composites Reinforced with CF/BF Interlayer Hybrid Fibers

Phenolic-resin composites reinforced with carbon fiber (CF) and basalt fiber (BF) interlayer hybrid fibers plain fabric were fabricated. The tensile strength, compressive strength and interlaminar shear strength of the prepared composites were studied. The results indicated that hybrid fibers reinforced composites possessed the advantages of both CF and BF. When resin content was 35% by volume fraction, the comprehensive mechanical performance of BF/CF reinforced phenolic resin composites reached the optimal values with the warp and weft direction tensile strength, compressive strength and interlayer shear strength being 252 MPa and 487 MPa, 105 MPa and 129 MPa, 21 MPa and 20 MPa, respectively. The scanning electron microscope (SEM) observations showed that the BF/CF hybrid fibers reinforced composites had better interfacial adhesion.     

Effect of Aluminum Tri-polyphosphate on Corrosion Behavior of Reinforcing Steel in Seawater Prepared Coral Concrete

Atri-polyphosphate was used as a corrosion inhibitor in the seawater prepared coral concrete, and its influence on the corrosion behavior of carbon steel, 304 austenitic stainless steel, and 2205 duplex stainless steel was studied by the open-circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization, respectively. The results reveal that the corrosion potential and impedance of the reinforcing steel increase, while the corrosion current density decreases with the content of aluminum tripolyphosphate in the coral concrete. A low content of the corrosion inhibitor significantly retards the corrosion of the two stainless steels, but it cannot effectively inhibit the corrosion of the carbon steel in the coral concrete.In general, the carbon steel is unsuitable for the coral concrete for its poor corrosion resistance. In contrast,the stainless steels, especially the 2205 duplex stainless steel, shows an excellent anti-corrosion property in the seawater prepared coral concrete containing a certain amount of inhibitor, which is one of the satisfactory candidate methods to build the long-life coral concrete constructions.     

Influence of surface state on moisture sensitivity of carbon fiber and its composite interfacial properties

The influence of surface state on the moisture sensitivity of carbon fiber was analyzed by applying a T800 grade carbon fiber with five different surface conditions, namely, with and without surface oxidation, in the presence or absence of sizing agent. The interfacial properties of their composites in the presence of two epoxy matrices (respectively EP07 and EP10) were also characterized by micro-droplet tests. The overall results show that both oxidized and sizing-coated fibers have higher moisture equilibrium content than that of the pristine unsurface-treated fiber, due to higher amount of activated carbon groups. After moisture absorption of the carbon fibers, almost all the fiber/epoxy systems show decrease in the interfacial shear strength and the unsurface-treated fiber system exhibits the largest decline. Moreover, both interfacial shear strength and interlaminar shear strength of carbon fiber/EP10 composite demonstrate better water resistance performance than that of the carbon fiber/EP07 composite, consistent with DSC results of the two resins.     

无电极电阻率法研究水泥基复合材料的导电机理

采用无电极电阻率法监测了分别掺入碳纤维、钢纤维和碎石骨料的水泥基复合材料在72 h内的电阻率,并用Hymstruc3D建立了微观结构模型分析导电机理。结果表明:水泥浆体的电阻率受电解质液相饱和度、孔隙率及孔结构曲折度的影响。掺入的导电纤维能明显降低水泥基复合材料的电阻率;而掺入骨料时,其电阻率明显增加。水泥基复合材料的导电现象是由水泥浆体中液相离子导电和导电纤维中的电子导电的共同作用所致。水泥基复合材料的电阻率与其导电相的含量密切相关。无电极电阻率法为估算水泥基复合材料中导电相或非导电相的含量提供了新的思路。     

融雪化冰用钢渣导电沥青混凝土的电阻稳定性

探讨了不同石墨掺量下钢渣导电沥青混凝土(conductive asphalt concrete using steel slag as aggregate,CACS)的电阻稳定性,研究了温度、氯盐溶液、载荷变化对钢渣导电沥青混凝土电阻率的影响.试验表明,钢渣作为集料复掺石墨制备出的钢渣导电沥青混凝土,电阻随时间变化小,在氯盐溶液中其电阻稳定性也良好.钢渣导电沥青混凝土的电阻呈现明显的正温度系数效应(positive temperature coefficient,PTC),电阻率随着温度的升高而逐渐增加,具有良好的温敏性;电阻率随着压力的增大而减小,卸载后电阻率有所增加,但不能完全恢复到原来的电阻率.