【作者】 郑立霞；

【导师】 李卓球；

【作者基本信息】 武汉理工大学 ， 固体力学， 2011， 博士

【摘要】 机敏混凝土不仅具有优异的结构性能,而且具有多种功能特性,可用于工程结构健康监测,因而受到工程界日益广泛的关注。机敏混凝土的功能特性大都基于其导电性。为了更深入了解机敏混凝土的导电性及传感特性,本文从导电相、导电路径、导电载流子以及供电方式等方面对机敏混凝土的导电性及传感特性进行了研究。另外,机敏混凝土传感器埋入大体积混凝土结构中时,往往是处于三向应力状态,所以本文又针对机敏混凝土在三向应力状态下的传感特性进行了研究。主要研究内容和创新成果如下：1.开展了机敏混凝土导电相的导电性及传感特性研究。研究了连续碳纤维单丝和碳纤维束的应变电阻效应,获得了它们的应变电阻灵敏系数,发现连续碳纤维束的应变电阻灵敏系数比单丝的要大,且随着纤维根数的增多灵敏系数越来越大；同时分析了连续碳纤维束的静态传感特性。2.开展了机敏混凝土导电路径研究。首次通过局部叠层碳纤维机敏混凝土的应变电阻效应研究,探讨机敏混凝土的导电路径问题。综合分析了连续碳纤维束、连续和局部叠层碳纤维机敏混凝土以及短切碳纤维机敏混凝土的应变电阻效应,并结合碳纤维束的拉拔实验,得出如下结论：机敏混凝土的3条导电路径(碳纤维、混凝土基体、纤维与基体间的界面)中,“纤维与基体间的界面”这条路径状态的变化是引起其电阻变化的主要原因,界面越多,材料的应变电阻灵敏系数越高,但电阻越不稳定。3.开展了机敏混凝土导电载流子研究。首次将Hall效应实验用于研究机敏混凝土的导电性,由此不仅获得了不同纤维含量机敏混凝土的电阻率,以及纤维含量的渗流阈值,而且还知晓了不同纤维含量下机敏混凝土的主要载流子类型、载流子浓度和载流子迁移率,为机敏混凝土导电性研究提供了一种新的、有效的方法。分析了机敏混凝土基于载流子浓度的传感机理；揭示了机敏混凝土电阻测量时出现暂态效应的原因。4.开展了不同供电方式下机敏混凝土传感特性及工程应用研究。发现采用不同的供电方式时,机敏混凝土的传感灵敏性和稳定性是不同的；建立了交流供电下机敏混凝土的电学模型；并探讨了机敏混凝土的传感特性在工程上的应用,结果表明,机敏混凝土作为混凝土结构的修补材料,在修补的同时,还可利用其传感特性对修补质量进行在线评估。5.开展了机敏混凝土在三向应力状态下的传感特性研究。首次研究了机敏混凝土试样在三轴受力情况下的应变电阻效应,并首次得到如下结论：(1)在弹性阶段,轴向电阻随着轴压的增大而减小,而随着围压的增大而增大；试块的最终受力状态相同时,无论加载次序如何,其电阻相对变化率均近似相等。(2)电阻的变化取决于应变的变化,并且轴向应变是引起试样轴向电阻变化的直接和根本原因,即,不管其它量如何变化,只要影响轴向应变,轴向电阻就会相应地发生变化。(3)同单轴受力时相比,三向应力状态下试样传感灵敏系数有所降低,但线性更好、传感极限提高；两种受力情况下稳定性变化不大,但三向受压时电阻变化滞后较严重。更多还原

【Abstract】 Smart concrete has not only excellent structural performances, but also prominent multi-functional characteristics, which mostly based on its electric conductivity. So, it is of the increasing concern for structural health monitoring (SHM) of civil engineering structures. For further understanding of the electric conductivity and the strain sensing effect within smart concrete, in this dissertation, dependence of electric conductivity and sensing characteristic of smart concrete on conductive phase, conductive path, conductive carrier, power supply mode, etc. is studied. Further, smart concrete sensors embedded in large-scale concrete structures often work in the stress state of triaxial stress, so, its sensing characteristic under applied triaxial stress has been performed in this dissertation. The main conclusions and innovations are listed as follows:1. Research on electric conductivity and sensing characteristic of conductive phase of smart concrete has been carried out. The strain resistance effect of the single continuous carbon fiber and the bundle of carbon fiber was studied. It is found that the gauge factor of carbon fiber bundle is larger than that of single continuous carbon fiber. The gauge factor increases with the count of the carbon fiber increasing.In the meantime, the static sensing properties of single continuous carbon fiber was analyzed.2. Research on the conductive paths of smart concrete has been carried out. For the first time, the conductive pathes of smart concrete is explored by the study of strain resistance effect of part-stromatolithic carbon fiber reinforced concrete. The strain resistance effect of continuous carbon fiber bundle, continuous carbon fiber reinforced concrete, part-stromatolithic carbon fiber reinforced concrete and short-cut carbon fiber reinforced concrete was analysed by synthesis. The pull-out tests of carbon fiber bundle from concrete have been also performed. Conclusions were as following:Among the three conductive paths in smart concrete such as paths through carbon fiber, paths through concrete matrix and paths through the interface between fiber and matrix, the change of resistance is mainly caused by the change of interface between fiber and matrix. The more the fiber-concrete interface, the larger the gauge factor is, but the unstabler the electrical property is.3. Research on conductive carriers of smart concrete has been carried out. A new effective method, based on the Hall effect experiment, is proposed to obtain the electric resistivity of smart concrete, and the percolation threshold of fiber content. Also, the main type of charge carrier, its concentration and mobility in smart concrete with different fiber content is given. Sensing mechanism of smart concrete based on carrier concentration is analyzed. And the reason of the transient effect, which happens as the resistance of smart concrete is measured, is revealed.4. Research on sensing characteristic under different power supply modes and engineering application of smart concrete has been carried out. Sensing characteristic of smart concrete under different power supply modes is studied. The results show different modes of the applied electrical current for electrical resistance measurement of smart concrete can affect both stability and sensitivity of smart concrete. An electrical model of smart concrete under AC power supply has been established. For the application of smart concrete in civil engineering structures, smart concrete can be used as a kind of patching material for concrete structures to evaluate the repair quality online by use of its sensing characteristic, meanwhile, reinforced concrete structures.5. Research on sensing characteristic in state of triaxial stress of smart concrete has been carried out. The strain resistance effect of smart concrete under triaxal compression is performed for the first time. The following conclusions are drawn up. (1) During elastic stage, axial resistance in the cylindrical smart concrete specimens decreases with the increasing axial load, while it increases with the increasing confining pressure. When the final strainedcondition is the same, the relative rate of change of the resistance is approximately equal regardless of the loading sequences. (2) Variations of resistance depend on the change of strain greatly, while have no direct link with stress. The axial strain is the direct cause for the change of axial resistance, which has no direct relation with the hoop strain or the volume strain. That is, axial resistance changes with the axial strain, while do not depend on the stain in other directions. (3) Comparing with uniaxial compression, the gauge factor of smart concrete under triaxial stress decreases. However, it owns better linearity and the wider sensing limit. The hysteresis effect is more serious under triaxal compression.更多还原