碳纳米管增强水泥砂浆梁弯曲性能试验研究

以水泥砂浆为基体,多壁碳纳米管(MWCNT)为增强组分,采用不同的分散剂和分散方法制备碳纳米管水泥砂浆(MWCNTRM).通过对碳纳米管水泥砂浆标准试件的三点弯曲试验,研究了分散剂类型及其掺量、水灰比、碳纳米管掺加量对碳纳米管水泥砂浆梁弯曲性能的影响.结果表明:分散剂与碳纳米管的质量比存在一个临界值(分散剂为CTAB时...     

Synthesis and characterisation of multi-walled carbon nanotubes (MWCNTs)

ABSTRACT

Carbon nanotubes are one of the major research areas in the field of nanotechnology, due to its mechanical and electro-conductive properties in the field of engineering and medical sciences. This paper focuses on preparation of multi-walled carbon nanotubes (MWCNTs) for the mass production using thermal catalytic chemical vapour deposition method. The synthesis of MWCNTs was made by breakdown of acetylene (C₂H₂) gas and Fe/MgO acting as catalyst. The surface morphology and structure of MWCNTs were characterised by scanning electron microscopy (SEM). Also phase identification and crystalline size of the nanopowder were determined by XRD. The particle size of MWCNTs was verified by SEM analysis and it was in the range of 20–30?nm and elemental analysis was carried out through energy dispersive analysis X-ray. Furthermore, thermal decomposition of the material property was studied by thermogravimetric analysis.     

Deformation adjustment of concrete beams laminated with carbon fiber mats

A carbon fiber mat is a sheet composed of intercrossing short carbon fibers, which has more stable and lower electrical resistivity compared with dispersed short carbon fiber mixed in cement. Thereby carbon fiber mats can be used in cement and then make cement structures exhibit obvious electro-thermal effect. In this paper, Electro-thermal properties of carbon fiber mats and an elementary strengthening experiments against deformation of carbon fiber mat cement laminated beams were researched. Firstly, electro-thermal properties of carbon fiber mats were studied. Secondly, carbon fiber mat laminated beams are designed and experiments were conducted to get temperature and deformation responses driven by the electro–thermal effects of the carbon fiber mat cement laminated beams. Finally, some experiments of deformation adjustment were done according to the above experimental results. The results show that deformation of concrete beams upon loads can be reduced even removed, and the beams can be strengthened against deformation.     

Advanced cement based nanocomposites reinforced with MWCNTs and CNFs

Cementitious materials reinforced with well dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) at the nanoscale were fabricated and tested. The MWCNTs and CNFs were dispersed by the application of ultrasonic energy and the use of a superplasticizer. Mechanical and fracture properties including flexural strength, Young’s modulus, flexural and fracture toughness were measured and compared with similarly processed reference cement based mixes without the nano-reinforcement. The MWCNTs and CNFs reinforced mortars exhibited superior properties demonstrated by a significant improvement in flexural strength (106%), Young’s modulus (95%), flexural toughness (105%), effective crack length (30%) and fracture toughness (120%).     

Vibration analysis of multi-walled carbon nanotubes embedded in elastic medium

We propose a method to estimate the natural frequencies of the multi-walled carbon nanotubes (MWCNTs) embedded in an elastic medium. Each of the nested tubes is treated as an individual bar interacting with the adjacent nanotubes through the inter-tube Van der Waals forces. The effect of the elastic medium is introduced through an elastic model. The mathematical model is finally reduced to an eigen value problem and the eigen value problem is solved to arrive at the inter-tube resonances of the MWCNTs. Variation of the natural frequencies with different parameters are studied. The estimated results from the present method are compared with the literature and results are observed to be in close agreement.     

Adsorption of 2,4,6-trichlorophenol by multi-walled carbon nanotubes as affected by Cu(II)

Adsorption equilibrium of 2,4,6-trichlorophenol (TCP) on multi-walled carbon nanotubes (MWCNTs) was investigated to explore the possibility of using MWCNTs for concentration, detection and removal of TCP from contaminated water. The adsorption of TCP on MWCNTs at pH 4 was nonlinear, reversible and best fit by a Polanyi-Manes model. Oxidation treatment increased surface area and introduced hydrophilic carboxylic groups to the defect sites of MWCNTs, hence increased the sorption of TCP and Cu(II) individually. Cu(II) suppressed the sorption of TCP on oxidized MWCNTs15A, but had little effect on as-grown MWCNTs15. TCP had no influence on Cu(II) sorption to either. The mechanisms of Cu(II) suppression effect on TCP adsorption are ascribed to the formation of surface complexes of Cu(II), which was verified by X-ray absorption spectroscopy. Cu(II) exerts a cross-linking effect of functional groups on adjacent tubes, creating a more tightly knit bundle and suppressing the condensation of TCP in the pore spaces between the tubes. The large hydration sphere around surface complexes of Cu(II) may also intrude or shield hydrophilic sites, leading to the “crowding out” of TCP around the Cu(II)-complexed sites.     

Acid-treated carbon nanotubes and their effects on mortar strength

In the present study, multi-walled carbon nanotubes (MWCNTs) were treated in an acidic mixture solution, made with nitric and sulfuric acids in a ratio of 3:1 by volume. The durations of the treatment were 100 and 180 min. The defects of these treated MWCNTs were examined using Raman spectroscopy. The attachment of hydroxyl functional groups to the walls of the MWCNTs were verified using FTIR spectroscopy. The dispersion of CNTs with acid treatment is assessed using UV-Vis spectroscopy and Scanning Electron Microscopy (SEM). The results indicate that the duration of the acid treatment has significant effect on both the degree of defects and functionality of the MWCNT. The compressive strength of mortar increased with the addition of the acid-treated MWCNTs; however, no appreciable difference was noted for the two treatment durations under this study.     

Chromium removal by combining the magnetic properties of iron oxide with adsorption properties of carbon nanotubes

The adsorption features of multiwall carbon nanotubes (MWCNTs) with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. Composites of MWCNT/nano-iron oxide were prepared, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR). XRD suggests that the magnetic phase formed is maghemite and/or magnetite. FESEM image shows nano-iron oxides attached to a network of MWCNTs. The adsorption capability of the composites was tested in batch and fixed bed modes. The composites have demonstrated a superior adsorption capability to that of activated carbon. The results also show that the adsorptions of Cr(III) on the composites is strongly dependent on contact time, agitation speed and pH, in the batch mode; and on flow rate and the bed thickness in the fixed bed mode. Along with the high surface area of the MWCNTs, the advantage of the magnetic composite is that it can be used as adsorbent for contaminants in water and can be subsequently controlled and removed from the medium by a simple magnetic process.     

火灾后用碳纤维增强聚合板对钢筋混凝土梁的加固-试验和分析

经历火灾后，钢筋混凝土梁的承重能力和硬度都会降低，使用碳纤维增强聚合物板（CFRP）对其进行加固是一种新的加固方法。研究比较了6根钢筋混凝土梁在火灾前后的最终强度、变形、开裂和延展性。试验结果显示，材料性能的降低对火灾后梁的承载力影响巨大。探讨了如何提高钢筋混凝土梁的延展性和承载力。在采取了适当耐火保护方法后，加固结构具有了较强的抗火能力。在试验结果基础上，提出了用CFRP板对火灾后钢筋混凝土梁进行加固的方法。这种加固方法与试验结果相当吻合并具有很高的安全性。     

Effects of priming with multi-walled carbon nanotubes on seed physiological characteristics of Hopbush (Dodonaeaviscosa L.) under drought stress

This paper reports the effects of different dosages of multi-walled carbon nanotubes (MWCNTs) on seed germination of hopbush, a medicinal multipurpose plant. After nano-priming and drying under room temperature, the seeds were placed in a germinator under 20 °C constant temperature and 65% relative humidity with a photoperiodic regime of 16 h light/8 h dark at 1000 lux fluorescent light. The results show that MWCNTs can dramatically improve seed germination percentage, mean germination time (MGT), root and stem lengths, as well as fresh and dry weights of root and stem. When no drought stress was applied, germination percentage of 10 and 200 mg/l nano carbon treatments was found to be 100%, and MGT in all the studied treatments had a marked decrease as compared to that of the control counterparts. The best results were gained at zero osmotic pressure, in which the effect of CNTs treatment on the mentioned traits was maximal at 30 mg/l. Increasing the level of drought stress revealed that 50 and 100 mg/l dosages of MWCNTs could more favourably affect both the hopbush growth parameters and seed germination. Therefore, nano-priming with carbon tubes can be recommended for enhancing seed germination and plant growth in work on afforestation with hopbush, an evergreen shrub suitable for desert conditions.     

纤维表面处理对碳纤维水泥基复合材料功能特性的影响

通过单丝拔出微观力学试验研究了纤维表面处理对碳纤维水泥基复合材料功能响应的影响.未经表面处理的碳纤维表面惰性大,与基体的结合强度低,容易脱黏,界面韧性和稳定性差,以脱黏破坏为主的界面结构变化,使试样电阻上升较快;碳纤维经过表面处理后,其与基体的结合强度提高,纤维拔出过程中试样电阻的变化平缓,显示了随着界面黏结强度及界面...     

多壁碳纳米管/氧化亚铜的制备及其对N-甲酰吗啉的光催化性能

采用液相还原法制备多壁碳纳米管/氧化亚铜(MWCNTs/Cu2O)复合微球。利用傅立叶变换红外光谱仪(IR)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)等对样品进行官能团分析、物相分析和形貌观察,结果表明:多壁碳纳米管以纵横穿插方式与氧化亚铜形成复合微球。对比氧化亚铜和多壁碳纳米管/氧化亚铜对目标有机物N-甲酰吗啉的光催化活性,结果表明:多壁碳纳米管/氧化亚铜复合催化剂的催化效果明显优于氧化亚铜。     

残余碳对掺萘系减水剂水泥浆体流变性的影响

以木炭模拟研究了残余碳对掺萘系减水剂水泥浆体流变性的影响,测试了水泥颗粒对萘系减水剂的吸附量以及浆体的流动度、Marsh时间、饱和掺量、表观黏度及剪切应力,同时观察了浆体絮凝情况.结果表明：随着残余碳含量的增加,萘系减水剂的表观吸附量逐渐增大;掺萘系减水剂水泥浆体的流动性随着残余碳含量的增加而下降,表现为浆体流动度下降、Marsh时间增大、饱和掺量增大、分散性下降、浆体絮凝结构数量及强度增大、剪切应力及表观黏度增大;浆体流动性与萘系减水剂的表观吸附量存在反向对应关系.     

碳纤维水泥基材料性能试验的正交分析

采用正交试验法分析了分散剂掺量、消泡剂掺量和水灰比三个因素对碳纤维水泥石电阻率、抗压强度以及水泥浆工作性的综合作用,同时比较了两种不同粘度分散剂的作用效果,研究结果表明:分散剂可以有效地提高碳纤维分散,但会降低水泥石的抗压强度和水泥粒子的分散度,且分散剂的掺量越多、粘度越大越明显;消泡剂可以提高水泥浆的流动度以及水泥石的导电性和抗压强度;水灰比增加能增强整个纤维-水泥浆体系的均匀性,因而可明显地提高水泥浆的流动性和水泥石的导电性。正交试验是多性能指标受多因素影响的碳纤维水泥基材料性能研究的有效方法。     

碳纤维加固技术在建筑工程中的应用

介绍了碳纤维加固技术的原理,对碳纤维增强水泥、预应力碳纤维板、碳纤维复合力筋的特性及其在建筑工程中的应用技术进行了阐述,并分析了碳纤维材料与传统材料相比所具有的优越性,以促进其进一步的推广应用。     

Consumption of carbon fiber plates in the reinforced concrete beams strengthened with CFPs

Four-point bending flexural tests were conducted to one full-size reinforced concrete (RC) beam and three full-size RC beams strengthened with carbon fiber plates (CFPs). The experimental results showed that the consumption of CFP had significant effects on failure modes and the flexural capacity. An analytical procedure, based on the limit failure mode and ductility, was presented to predict the applied area of CFP. An analytical program, based on Smith-Teng model and Cheng-Teng model, was provided to calculate the bonding length of CFP. The test results are used to validate the proposed procedure. The results are also applied to the design and construction of RC beam strengthened with CFP. __________ Translated from Journal of Hunan University (Natural Sciences), 2006, 33(6): 16–20 [译自: 湖南大学学报 (自然科学版)]     

Carbonized nano/microparticles for enhanced mechanical properties and electromagnetic interference shielding of cementitious materials

In the present work, carbon nano/microparticles obtained by controlled pyrolysis of peanut (PS) and hazelnut (HS) shells are presented. These materials were characterized by Raman spectroscopy and field emissionscanning electron microscopy (FE-SEM). When added to cement paste, up to 1 wt%, these materials led to an increase of the cement matrix flexural strength and of toughness. Moreover, with respect to plain cement, the total increase in electromagnetic radiation shielding effect when adding 0.5 wt% of PS or HS in cement composites is much higher in comparison to the ones reported in the literature for CNTs used in the same content.     

碳纤维在水泥基体中的分散性研究进展

基于碳纤维的分散性在水泥基复合材料中的重要性,阐述了碳纤维的基本性能、生产工艺及碳纤维在水泥基体中的分散方法,探讨了碳纤维分散性的发展趋势。     

碳纤维布加固开裂低配筋混凝土梁试验研究与有限元分析

为了给受损开裂低配筋混凝土结构加固维修提供依据,按3种低配筋率0.127%、0.189%、0.251%设计了6根钢筋混凝土梁。先将混凝土梁加载至出现宽度为0.3mm的可见裂缝时卸载,再粘贴碳纤维布进行加固,养护后重新加载至破坏。试验结果表明:粘贴碳纤维布能有效提高开裂梁的承载能力,随着加固量的增大加固梁承载力提高,但变形能力降低;在低配筋情况下,配筋率越高,承载力提高比例越大。用有限元方法数值模拟碳纤维布加固受损低配筋梁受力全过程,计算结果与试验结果吻合较好,为进一步参数分析提供了工具。     

High strength characteristics of cement mortar reinforced with hybrid fibres

An experimental study was conducted on high strength mortar reinforced with steel fibres and hybrid fibres consisting of steel fibre, palm fibre and synthetic fibre (Barchip). The inclusion of fibres was maintained at a volumetric fraction of 2%. The compressive strength, splitting tensile strength, static modulus of elasticity, shrinkage, flexural strength, and flexural toughness were determined to study the effect of the hybrid fibres on the properties of high strength cement mortar (HSCM). The results showed that hybridization of fibres in the quantities 1.5% steel fibres + 0.25% palm fibres + 0.25% Barchip fibres, improved the compressive strength and flexural toughness significantly, and also enhanced the splitting tensile strength and flexural strength of the mortar by about 44% and 140%, respectively.