碳纤维混凝土的机敏特性研究

制作了体积掺量分别为(0.0%、0.2%、0.4%、0.8%和1.2%)的碳纤维水泥基材料,试件为100 mm×100 mm×100 mm的立方体.并比较其电导性能,试验研究了不同碳纤维掺量的混凝土在单调和循环荷载作用下其压应力和电阻率的关系.结果表明:随碳纤维掺量增大,阻抗曲线逐渐向左移动,在三维空间随机分布的纤维逐渐聚集并彼此连接,使复合材料的电导性能大幅增加.当碳纤维体积掺量同为1.0%时,不同龄期材料的交流阻抗谱相差很大,随着水化龄期的增长,C-S-H凝胶大量形成,水泥基材料中的溶液电阻逐渐增大,此时作为导电性分散相的碳纤维将起电导的主导作用.随着外部荷载的增加,基准水泥基材料的导电性几乎无变化,直到破坏时,电阻变化率剧烈增大,而碳纤维水泥基材料在弹性阶段其电阻变化率随内部应力线性增加,当接近峰值荷载时,电阻率才逐渐增大,预示试件即将破坏.     

碳/钢混杂纤维水泥基复合材料的性能研究

研究了碳 /钢混杂纤维水泥基复合材料的电性能和力学性能。结果表明 :单一碳纤维水泥基复合材料的体积电阻率在碳纤维用量为 0 .5 %时出现了“渗滤”现象 ,而当碳纤维与钢纤维混杂使用时可使水泥基复合材料的电性能出现明显的混杂效应 ,但是其力学性能并没有明显的混杂增强效应。     

掺碳纤维和石墨水泥砂浆电学性能研究

利用四电极法研究了内掺水泥基渗透结晶防水材料(CCCW)的碳纤维石墨水泥砂浆试样水化期间和硬化后的导电特性及在压缩循环荷载作用下的压阻特性.结果表明:随着养护龄期的增加,碳纤维石墨砂浆试样的电阻值逐渐增加,并且逐步趋于稳定;石墨掺入量越大,试样电阻达到稳定值所需的养护时间越短;试样的体积电阻率随石墨掺量的增加而下降,并存在渗流现象,渗流阈值为20%左右;此外,在循环荷载作用下,石墨掺量为水泥质量分数的20%时,碳纤维石墨砂浆试样的体积电阻率与压应力之间呈现良好的可重复性,电阻值在应力加载时几乎以线性下降,而卸载时增加.     

基于界面效应的碳纤维水泥基复合材料压敏性实验研究

碳纤维水泥基复合材料具有应变-电阻效应。通过碳纤维水泥基复合材料单丝拉伸实验,探究碳纤维水泥基复合材料载荷作用下电阻变化的主要因素。结果表明,在纤维拔出过程中,试样电阻随界面力增大而增大,界面力达到最大值时电阻迅速增大。试样电阻变化规律与界面结构变化一致,弹性变形导致的电阻变化可逆。碳纤维拔出过程中试样电阻的变化主要是由碳纤维—水泥基体界面因素引起的。     

裂纹对碳纤维水泥基复合材料性能的影响

研究了裂纹对碳纤维水泥基复合材料导电性能和发热效果的影响规律。裂纹对碳纤维水泥基复合材料的电阻(率)有明显影响,裂纹长度越长,电阻增大得越多,电阻增大的幅度与试样原始电阻有关。在输入功率一定的情况下,裂纹长度越长,发热时在混凝土内部造成的温度分布越不均匀,裂纹尖端的温度越高,因此可根据温差的大小大致判断出混凝土中裂纹的长度。     

智能水泥基复合材料的电学性能

为研究智能水泥基复合材料的电学性能,推动土木工程材料和结构向智能化方向发展,以碳纤维为导电填料,制备了碳纤维水泥基复合材料试样,通过电学试验和理论分析,建立等效电路模型,分析试样的阻抗频率特性,研究水灰比及碳纤维质量分数对养护过程中试样的本体电阻、本体电阻稳定值以及时间特征值的影响。结果表明,不同水灰比和碳纤维质量分数的智能水泥基复合材料的阻抗性能、本体电阻及本体电阻趋于稳定的速度不同。在水灰比为0.39、碳纤维的质量分数为0.10%时,试样的时间特征值最小,本体电阻趋于稳定的速度最快。本研究的理论模型和试验研究对进一步探索智能水泥基复合材料的电学性能及其应用有一定的指导意义。     

混杂短纤维对Al2O3f＋Cf／ZL109性能的影响

用挤压铸造法制出不同体积分数的氧化铝和碳短纤维混杂增强ZL109复合材料（简记为Al2O3t Cf/ZL109）,探讨了混杂纤维对Al2O3f Cf/ZL109复合材料性能的影响,结果表明：复合材料拉伸强度在混杂纤维体积分数为8％时（氧化铝与碳纤维混合经为9：1）出现峰值;在混杂纤维体积分数不变是,复合材料 伸强度随碳纤维含量的增加而增大,复合材料的压缩强度随混杂纤维体积分数的增大而增加,热膨胀系数在各温度区间都随混杂纤维体积分数的增大而减小。     

纳米炭黑水泥基复合材料的压敏性研究

纳米炭黑水泥基复合材料具有导电性和压敏性.试验结果表明,电阻率随炭黑掺量的变化呈现渗滤特征,渗滤区炭黑体积含量为0.6%-1.5%.处于渗滤区和超过渗滤区的纳米炭黑水泥基复合材料的电阻率具有明显的压力依赖性.在受到压应力时,电阻率减小,卸载后电阻回复具有不可逆性.炭黑水泥基复合材料的压敏性与3个因素有关:试件本身的极化效应、隧道效应和渗流导电.当炭黑掺量在渗滤区以前时,极化效应占主导地位;当炭黑掺量在渗流区内时,隧道效应占主导地位,试件体现出明显的压敏性;当炭黑掺量继续增加时,炭黑聚集体接触的渗流导电占主导地位.     

P·O与R·SAC复合水泥砂浆的强度与电阻率研究

将普通硅酸盐水泥（Ordinary Portland Cement,简称为P·O）和快硬硫铝酸盐水泥（Rapid Hardening Sulphoaluminate Cement,简称为R·SAC）以不同比例混合,并掺人一定量的减水剂配制成自流平砂浆,通过测定砂浆在不同龄期的抗压强度和1440min内的电阻率,研究了这两种水泥的复合使用效果。结果表明,当快硬硫铝酸盐水泥的掺量从10％增加到90％时,砂浆抗压强度表现出明显的先降低后增大的变化趋势。随着掺量的增大,砂浆的初始电阻率也逐渐增大,水泥的早期水化逐渐加快;当掺量从60％增加到90％时,电阻率曲线开始出现峰值,并且峰值的出现时间也逐渐提前,此时砂浆的抗压强度也逐渐增大。     

水泥基复合材料界面过渡区体积分数的定量计算

为了计算水泥基复合材料的界面过渡区体积分数,采用最邻近表面分布函数和骨料比表面积2种方法,结合实际骨料的筛分曲线,给出了界面过渡区体积分数定量关系式．结果表明：单位体积水泥基复合材料中,当骨料的体积分数〈0．5,界面厚度〈50μm时,2种方法计算的误差约为10％;界面区厚度越小,2种方法计算的误差也越小．     

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 measurement to assess hydration process and the porosity formation

The change of electrical resistivity with time at early ages was used to investigate the hydration process and the porosity development. Porosity reduction process of cement-based materials hydration was developed by a proposed method. The porosity reduction is fast at the setting period. The results find that the pore discontinuity occurs faster at lower water/cement ratios than at higher water/cement ratios which is similar to the results of the Percolation method.     

Piezoresistive response extraction for smart cement-based composites/sensors

A kind of piezoresistive response extraction method for smart cement-based composites/sensors was proposed.Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding carbon nanotubes and nickel powders as conductive fillers into cement paste or cement mortar.The variation in measured electrical resistance of such cement-based composites/sensors was explored without loading and under repeated compressive loading and impulsive loading.The experimental results indicate that the measured electrical resistance of piezoresistive cement-based composites/sensors exhibits a two-stage variation trend of fast increase and steady increase with measurement time without loading,and an irreversible increase after loading.This results from polarization caused by ionic conduction in these composites/sensors.After reaching a plateau,the measured electrical resistance can be divided into an electrical resistance part and an electrical capacity part.The piezoresistive responses of electrical resistance part in measured electrical resistance to loading can be extracted by eliminating the linear electrical capacity part in measured electrical resistance.     

Early-age Electrical Resistivity and Reactive Capacity of Mineral Admixtures in Mortars

1 IntroductionPozzolanic capacity of mineral admixture in concreteis usually tested by direct reaction with Ca(OH)2whilemonitoringthe consumption of lime (or strength develop-ment) .In theory,it is possible to completely react withall the calcium hydroxide , but this happens in practiceinfrequently.Some standards for methods ,among whichthere are chemical analysis and physical tests ,are devel-opedin some countries to allowaccurate characterizationof pozzolanic materials[1-3].And crrently,th…     

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)     

矿物掺和料-水泥浆体电学特性与其微结构的关系

采用循环伏安法和交流阻抗法系统研究了粉煤灰、矿渣粉和石灰石粉水泥浆体的电学特性,通过等效电路对电学测试结果进行拟合,并将拟合所得浆体电学参数与浆体化学结合水和压汞所测孔结构之间的相关性进行比较。结果表明：浆体的化学结合水与其电阻率具有较好的正相关性,即化学结合水越多,水化程度越大,浆体电阻率越高;粉煤灰和矿渣粉可以提高浆体电阻率,而石灰石粉在5%掺量下对浆体电阻率无影响;随着水化龄期的延长,浆体孔溶液电阻增大,其变化规律与浆体电阻率一致;浆体凝胶电容和凝胶电阻与C-S-H凝胶含量有关,二者有很好的负相关性;随着水化龄期的延长,浆体孔结构曲折程度提高,交流阻抗法所测得常相角指数减小,压汞测得的分形维数增大。     

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。     

水泥基材料早期水化特性与体积稳定性的关系

采用五路裂缝测定仪和非接触式电阻率测定仪，分别测试了水泥砂浆在干燥条件下约束收缩开裂的初裂时间与相应水泥浆体早期水化24h内的电阻率变化，分析研究了水泥浆体在非常早期水化中的电阻率极小值与相应砂浆的初裂时间的关系，结果发现二者之间具有较好的线性相关性（相关系数〉0．90）。机理研究表明在水泥类型和骨料确定的条件下，胶凝材料体系初始水化的液相特征是影响早期收缩开裂的关键；不同化学与矿物外加剂及微量组分（可溶碱）的添加将通过改变水化的液相特征而影响水化物的初始形成速率、形貌、分散性及其生长能力等，最终影响材料的体积稳定性。     

Effects of silica fume and steel fiber on chloride ion penetration and corrosion behavior of cement-based composites

This project was aimed to evaluate the chloride permeability and corrosion behavior of cement-based composites which comprised fibers and silica fume in the mixes. Resistivity, polarization resistance, ponding and rapid chloride penetration results of specimens were obtained through tests. Test results indicate that resistivity, open circuit potentials and direct current polarization of specimens with w/b ratio of 0.35 are higher than those of specimens with w/b ratio of 0.55. For length-diameter ratio of 65, resistivity and direct current polarization of specimens with fiber length of 35 mm were similar to those of 60 mm. In addition, the open circuit potentials of specimens with fiber length of 60 mm were slightly higher that those of 35 mm. The resistivity decreased with increasing steel fiber content, and the open circuit potential and direct current polarization increased with increasing steel fiber content. The specimens containing silica fume were found to provide higher resistivity, open circuit potentials and direct current polarization than the control specimens. The incorporation of steel fiber and silica fume in composites achieved more significantly decreases in resistivity and increases in direct current polarization than steel fiber composites or silica fume composites. The penetration depth and six-hour total charge passed of specimens for w/b ratio of 0.35 were lower than those for w/b ratio of 0.55. For length-diameter ratio of 65, the penetration depth of specimens for fiber length of 35 mm was similar to that of 60 mm. The penetration depth decreased with increased steel fiber content in the composites. By regression analysis, a good correlation between open circuit potential and direct current polarization, and chloride penetration depth and direct current polarization.     

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.