导电掺和料形态与水泥基材料压敏性的相关性

研究了含有碳纤维、石墨、钢纤维的水泥基材料的导电性及其在压应力作用下电阻率的变化规律;探讨了掺有导电掺合料的水泥石电阻率的变化机理。研究表明,水泥基材料具备压敏效应的前提条件是其导电网络达到渗流区,而碳纤维由于长径比大、密度小,极小掺量即可使水泥石进入渗流区,产生压敏效应。      

碳纤维水泥基材料的机敏特性研究

水泥基材料是一种高电阻率的惰性材料,通过掺入一定体积含量(0.2 vol%~1.2 vol%)的短切碳纤维,可显著提高其电导率。本文作者研究了碳纤维水泥基材料表观电导特性与其内部微观结构的关系,探讨了电阻率的变化与材料所受外部荷载的关联性。结果表明碳纤维水泥基材料具有实时诊断内部损伤的机敏性:当水泥基材料内部裂纹产生或扩展时,表现为材料电阻率上升;而当水泥基材料内部裂纹闭合时,其电阻率下降。碳纤维水泥基材料的电阻变化与所受荷载呈良好的线形关系;而不含碳纤维的普通水泥基材料在整个受荷过程中,其电导特性则无明显变化。碳纤维水泥基材料电导特性的变化反映了水泥基材料内部损伤状况丰富的信息,根据这一特性可以及时预报水泥基材料内部潜在的损伤状况,有效地防止灾难性的破坏。     

用交流阻抗法研究碳纤维混凝土导电性

随着水泥基材料的发展 ,人们对水泥基材料提出的更新的要求 ,其中水泥基导电复合材料的研究引起了广泛的兴趣。制备水泥基导电复合材料的方法是在水泥基材料中掺入各种导电组分 ,目前较常用的是掺入碳纤维 ,它不仅可以大幅度提高水泥基复合材料的电导率 ,还能够改善水泥基材料的力学性能、增加其韧性。本研究主要通过对碳纤维混凝土的交流阻抗谱进行分析 ,研究其导电性能与内部微结构的关系。     

用交流阻抗法研究碳纤维混凝土导电性

随着水泥基材料的发展,人们对水泥基材料提出的更新的要求,其中水泥基层电复合材料的研究引进了广泛的兴趣,制备了水泥基导电复合材料的方法是在水泥基材料中掺入各种导电组分,目前较常用的掺入碳纤维,它不仅可以大幅度提高水泥基复合材料的电导率,还能够改善水泥基材料的力学性能,增加其韧性,本研究主要通过对碳纤维混凝土的交流阻抗谱进行分析,研究其导电性能与内部微结构的关系。     

应力自感知水泥基复合材料及其传感器的研究进展

应力自感知水泥基复合材料是在传统的水泥或砂浆中添加特定导电材料或纳米材料复合而成的具有压阻效应的材料。利用这类材料的电阻率与其自身压应力存在一定对应关系的特性, 可以制成性能独特的应力自感知水泥基复合材料传感器。此类传感器因具有造价低、耐久性好、埋设工艺简单以及与混凝土材料相容性好等特性, 有望成为混凝土结构长期健康监测的新一代传感装置。本文作者从原材料选择、搅拌工艺、电阻测试方法以及传感器测试系统等多方面综合评述了应力自感知水泥基复合材料的研究进展。同时指出, 为促进其在工程中的应用, 对碳纤维水泥石电阻率的离散性、稳定性以及多向约束受力下电阻率的变化曲线等问题都必须进一步深入研究。      

气相生长碳纤维增强水泥基复合材料的制备及性能

研究了脱油沥青(De-oiled asphalt)基气相生长碳纤维(VGCFs)增强水泥基复合材料的制备方法及其性能。以脱油沥青作原料,采用化学气相沉积法(CVD)制备出气相生长碳纤维,以此纤维制备水泥基功能复合材料。结果表明:低含量VGCFs的碳纤维增强水泥基复合材料具有良好的抗压强度和导电性能,在VGCFs的掺量由0增至0.6 %范围内,随着VGCFs掺量的增加,碳纤维增强水泥基复合材料的电阻率下降,抗压强度提高。当VGCFs为0.4 %时,VGCFs水泥基复合材料电阻率降低2个数量级,从3.25 ×105 Ω·cm 降为1.49 ×103 Ω· cm ,抗压强度提高28.8 %,为最佳掺量。      

碳纤维水泥基复合材料电学性能研究进展

掺入碳纤维对提高水泥基材料的电导率有很大的作用.综合评述了近十年来碳纤维水泥基复合材料力电、电热性能的研究进展.近年来对碳纤维水泥基材料的研究表明,这类材料受载后电阻率将发生明显变化,试件通电后可以作为发热元件使用,并且其热电效应可以将热能转变成电能.认为今后对碳纤维水泥基复合材料的研究重点应放在提高测量精度和电磁屏蔽等方面,并开发材料的新性能.     

聚羧酸减水剂对水泥基材料中碳纤维分散性的影响

通过简单有效的技术措施提高碳纤维在水泥基材料中的分散性有助于提高其应用效果。通过浊度法对比了碳纤维在聚羧酸减水剂(PC)和甲基纤维素(MC)溶液中的分散效果,测试了碳纤维增强水泥砂浆(CFRM)的电阻率和孔结构,并采用扫描电镜观测碳纤维增强水泥砂浆(CFRM)中碳纤维分布情况。结果显示,PC浓度提高不同长径比的碳纤维分散性明显改善,配制的CFRM导电性显著增加;而甲基纤维素仅对长径比小的碳纤维有较好的分散效果,CFRM导电性仅在水灰比较高时有提升;萘系减水剂溶液分散后的碳纤维所配制的CFRM导电性无明显变化。PC具有良好的碳纤维分散效果在于PC极性基团吸附在碳纤维表面,导致纤维表面斥力增加,有效改善了碳纤维的分散性;扫描电镜观察和孔结构分析均证实PC对碳纤维有良好的分散效果。     

纳米碳纤维增强水泥基复合材料的探讨

纳米碳纤维(Carbon nanofibers,CNFs)是近年来国内外纳米材料界的研究热点。介绍了纳米碳纤维的结构特点、性能、应用以及水泥基材料的各项性能和特点,并对纳米碳纤维增强水泥基力学性能的可能性进行了系统的探讨及研究,总结出现阶段需要解决的问题是纳米碳纤维在水泥基材料中的均匀分散及纳米碳纤维与水泥基体的相容性,并提出一些解决方案,为后期的工程应用及研究奠定了基础。     

磷酸盐水泥碳纤维复合材料的导电性能研究

以高掺量粉煤灰磷酸盐水泥为基体,短切碳纤维为功能材料,制备出了磷酸盐水泥碳纤维复合材料(PCFC),同时制备了碳纤维硅酸盐基复合材料(CFRC),并利用压力试验机、交流电桥和SEM对二者的基本力学性能、导电性能及内部碳纤维分布进行了对比研究。此外还考察了碳纤维掺量、龄期对PCFC导电性能的影响。结果表明,PCFC相比CFRC在同等碳纤维掺量的情况下力学增强效果更好、导电性能更为优越;机理分析表明PCFC中存在二次"渗流"现象,而CFRC试体中则没有。SEM照片显示碳纤维掺量较高时,PCFC中的碳纤维分散得更好;龄期实验结果表明,当碳纤维掺量超过1.4%时,龄期对PCFC的导电性影响较小,具有良好的导电稳定性。     

掺CCCW的碳纤维石墨水泥基复合材料的导电及压阻特性

利用四电极法研究了内掺水泥基渗透结晶防水材料(CCCW)的碳纤维石墨水泥基复合材料试样(40 mm×40 mm×40 mm)的导电特性及其在循环荷载作用下的压阻特性,分析讨论了碳纤维石墨水泥砂浆的体积电阻率及压阻特性随石墨掺量的变化规律。碳纤维和CCCW的掺量分别为水泥质量的1%和4%;石墨掺量分别为水泥质量的0%、10%、20%、30%、40%和50%。结果表明,添加CCCW的碳纤维石墨砂浆试样的体积电阻率随石墨掺量的增加迅速下降,并存在渗滤现象,渗滤阈值为20%左右。在循环荷载作用下,不同石墨掺量试样的电阻和应力存在一定的对应关系。石墨掺量为水泥质量的20%～30%时,碳纤维石墨水泥砂浆试样的体积电阻率与压应力呈现良好的可重复性,电阻值在应力加载时几乎呈线性下降,而卸载时增加。     

Smart Behavior of Carbon Fiber Reinforced Cement-based Composite

The electrical characteristics of cement-based material can be remarkably improved by the addition of short carbon fibers.Carbon fiber reinforced cement composite (CFRC) is an intrinsically smart material that can sense not only the stress and strain, but also the temperature. In this paper, variations of electrical resistivity with external applied load, and relation of thermoelectric force and temperature were investigated. Test results indicated that the electrical signal is related to the increase in the material volume resistivity during crack generation or propagation and the decrease in the resistivity during crack closure. Moreover, it was found that the fiber addition increased the linearity and reversibility of the Seebeck effect in the cement-based materials. The change of electrical characteristics reflects large amount of information of inner damage and temperature differential of composite, which can be used for stress-strain or thermal self-monitoring by embedding it in the concrete structures.     

Hydration monitoring of cement-based materials with resistivity and ultrasonic methods

Two test setups, the electrical resistivity and ultrasonic techniques, were used to monitor the hydration process of cement-based materials. In the electrical resistivity method, a non-contacting device was used. In the ultrasonic method, a wave was transmitted and measured by the embedded piezoelectric ultrasonic transducers, which had good coupling with the surrounding materials. The focus of the study was to detect the setting and hardening behaviors of cement paste during the first 7 days of hydration using the above techniques. Immediate after placing the cement paste into the mould, the measurement started and continued throughout the hydration process. The obtained resistivity and ultrasonic data were used to interpret the hydration process of the specimens. The correlation of two techniques was also studied. The results illustrated that both electrical resistivity and ultrasonic techniques were effective to accurately monitor the hydration of cement pastes. The resistivity method was able to study both the chemical reaction and physical change during hydration, while ultrasonic method was sensitive to physical change of cement only.     

CVI处理短碳纤维在CFRC中分散性的评价

碳纤维增强水泥基复合材料(CFRC)是一种新发展起来的、很有潜力的功能材料.丙烯作前驱体,对短碳纤维在高温下(900～1300℃)进行100个小时左右的化学气相浸渍(CVI)表面处理,丙烯在高温下分解,生成热解碳,沉积在碳纤维表面.借助超声波预分散技术及新型分散剂羟乙基纤维素(hydroxyethyl cellulose,HEC)和超细颗粒硅灰的分散作用,实现了CVI处理碳纤维在水泥基体中的均匀分散.HEC水溶液的质量分数控制在1.56～1.77%之间为宜.分别运用扫描电镜法(SEM)、新拌料浆法(FM)、硬化试件电阻率测试法(ERM)及模拟试验法(SE)四种方法评价了CVI处理后短碳纤维的分散性.每种方法均有自身的优缺点和适应环境,四种方法中,模拟试验法(SE)是评价制备CFRC复合材料前期、碳纤维第一步分散的最方便的方法,此法不仅可节约时间和大量的原材料,而且可预测制备CFRC过程中应选择何种分散剂及碳纤维第二步分散的情况.     

掺碳系屏蔽介质的水泥基复合材料的屏蔽性能研究

以石墨、炭黑、碳纤维和纳米碳管等为屏蔽介质,采用不同的方法分散碳系屏蔽介质,然后掺入到水泥材料中制得水泥基复合屏蔽材料,研究了普通碳系屏蔽介质对屏蔽性能的影响及碳纤维和碳纳米管掺量的变化与屏蔽效能之间的关系;利用四探针测试仪、电子探针等手段表征了复合材料的电导率和屏蔽介质的分散均匀性.结果表明,掺碳纤维的水泥基复合材料...     

Highly dispersed graphene oxide electrodeposited carbon fiber reinforced cement-based materials with enhanced mechanical properties

Mechanical behavior of carbon fiber (CF) reinforced cement-based materials greatly depends on the dispersion of CF and interfacial properties between the CF and cement matrix. In this study, graphene oxide (GO) was utilized to modify the surface properties of CF, including the roughness, wettability and chemical reactivity, and the graphene oxide/carbon fiber (GO/CF) hybrid fibers were fabricated by a newly designed electrophoretic depositing method. The scanning electron microscopy and contact angle measurement results indicated that GO/CF hybrid fibers not only had a rougher surface which was expected to improve the physical friction when CF was pulled out from cement matrix, but also had a higher wettability surface that made it easier to contact with cement hydrates as nucleation sites. In addition, GO/CF hybrid fibers were capable of high chemical reactivity due to the introduction of GO with many functional groups, which ensured them more likely to interact with cement hydrates due to the hydrogen bonding at interface and therefore benefited to strengthen the bonding between the CF and cement matrix. In terms of mechanical behavior, three-point bending test showed that compared with the CF reinforced cement paste, flexural strength of the GO/CF hybrid fibers reinforced cement paste was enhanced by 14.58%, and could be further improved by 10.53% when the GO/CF hybrid fibers were pre-dispersed in the GO solution and then mixed with cement powders. The larger electrostatic repulsion and steric stabilization led to the better dispersion of GO/CF hybrid fibers in GO solution, which were responsible for the further mechanical enhancement of cement paste. In conclusion, the research outcomes provided a novel way for utilizing GO as both of dispersant and surface modifier to improve the dispersion of CF in cement and strengthen its bonding with cement hydrates, consequently achieving a significant enhancement in the mechanical properties of cement paste.     

Cement-based sensors with carbon fibers and carbon nanotubes for piezoresistive sensing

Electrically conductive cementitious composites carrying carbon fibers and carbon nanotubes were developed and their ability to sense an applied compressive load through a measureable change in resistivity was investigated. Two types of cement-based sensors, one with carbon fibers alone and the other carrying a hybrid of both fibers and nanotubes, were considered. Direct comparisons were also made with traditional strain gauges mounted on the sensor specimens.Sensing experiments indicate that under cyclic loading, the changes in resistivity mimic both the changes in the applied load and the measured material strain with high fidelity for both sensor types. The response, however, is nonlinear and rate dependent. At an arbitrary loading rate, the hybrid sensor, containing a combination carbon fibers and nanotubes, produced the best results with better repeatability.     

Properties of Fabric–Cement Composites made by Pultrusion

Practical manufacturing and use of thin cement-based elements composites require an industrial cost-effective production process in addition to proper reinforcement materials to improve the tensile and flexural performance. Reinforcement by means of fabric materials is an alternative to the use of short fibers. The objective of this study was to investigate use of pultrusion technique as a cost-effective method for the production of thin-sheet fabric-reinforced cement composites. Woven fabrics made from low modulus polypropylene (PP) and glass meshes were used to produce the pultruded cement composites. The influence of fabric type, PP and glass, processing method, pultrusion vs. cast and cement-based matrix modification were examined. Tensile and pullout tests as well as Scanning Electron Microscopy (SEM) observations were used to examine the mechanical, bonding and microstructure properties of the different composites. The rheology of the mix was correlated with the mechanical behavior of the pultruded composites. The tensile behavior of the pultruded fabric–cement components exhibited strain hardening behavior. The best performance was achieved for the PP pultruded composites.     

Piezoresistivity in Carbon Fiber Reinforced Cement Based Composites

The results of some interesting investigation on the piezoresistivity of carbon fiber reinforced cement based composites (CFRC) are presented with the prospect of developing a new nondestructive testing method to assess the integrity of the composite. The addition of short carbon fibers to cement-based mortar or concrete improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFRC responsive to the smart behavior by measuring the resistance change with uniaxial pressure. The piezoresistivity of CFRC under different stress was studied, at the same time the damage occurring inner specimens was detected by acoustic emission as well. Test results show that there exists a marking pressure dependence of the conductivity in CFRC, in which the so-called negative pressure coefficient of resistive (NPCR) and positive pressure coefficient of resistive (PPCR) are observed under low and high pressure. Under constant pressures, time-dependent resisti