Electrical Behaviors Of Carbon Fibers/Nano-sized Carbon Black Composites And Application

The electrical behaviors of cement-matrix composites containing carbon fibers or nano-sized carbon black were studied through experimental research. Results show that the relative change in resistance ((R-R₀)/R₀) varies with moisture content of the cement-matrix composites. With very high or low moisture content, the composites demonstrate the negative pressure sensitivity. However, when moisture content is appropriate, the composites present the positive pressure sensitivity. Moreover, the magnitude of pressure sensitivity is small due to high moisture content. When moisture content is low, the magnitude of pressure sensitivity increases as the magnitude of the relative change in slow polarization increases. The results also show that the non-reversibility in pressure sensitivities of the cement-matrix composites is related to both moisture content and inner damage.Further, a novel method for the strain measurement of steel bar was developed by the use of carbon fiber/carbon black epoxy-matrix composite. It is shown that the surface resistance of steel bar varies linearly with the bar tension when the bar was covered with a thin layer of carbon fiber/carbon black epoxy-matrix composite. Therefore, the strain of steel bar can be obtained by the electrical resistance measurement, which may be applicable for the long time monitoring of concrete structures.