A Research On The Electrical Properties And The Improvement Of CFRC

As a new composite material, carbon fiber-reinforced cement-matrix composite (CFRC) is gaining much attention in both the research community and engineering. It can be used not only for structural function, but also as a smart material due to its stress-sensing behavior and Seeback effect.In this thesis, the electrical properties of CFRC are studied. Firstly, a comparative study was performed on the measurement methods of resistance of CFRC. Results show that the fractional change in resistance (R-R0)/R0 obtained from two-probe method cannot represent the stress-sensing behavior of CFRC, while one from four-probe method reveals the real stress-sensing ability of CFRC.Secondly, an experimental research was performed to study the effect of moisture content, stress and loading rate on the electrical properties of cement mortar. Results show that the electrical properties of mortar vary with moisture content. When mortar is of higher moisture content, resistance increases monotonically with the increase of compressive loading and decreases during unloading. After oven-drying, an opposite phenomenon is observed. It is also shown that the electrical properties of mortar are rate-sensitive. Mechanism for these phenomena is discussed.Then, an experimental research was performed to study the effect of moisture content on the electrical properties of CFRC. Results show that the resistance of CFRC varies with moisture content. For higher moisture content, polarization is predominant in the early period of measurement and resistance increases with time. However, the later period of measurement sees the effect of electric conduction and resistance decreases with time. Under compression, there is a net decrease of resistance during each cycle of loading and unloading. In the case of lower moisture content, polarization is predominant in the whole period of measurement and resistance increases all the time. Moreover, a net increase of resistance is produced during each cycle of loading and unloading. When moisture content is appropriate, polarization and electric conduction will keep in a balance, and resistance can return to its original value after unloading. Further, mechanism of these phenomena is discussed.Finally, the improvement of CFRC was studied by the combination use of carbon fibers and nano-carbon black. Results show that the effect of moisture content and loading rate on the electrical properties of CFRC can be greatly diminished with the addition of nano-carbon black.