Study On Conductivity Of Carbon Fiber Reinforced Cement-based Material

Carbon Fiber Reinforced cement-based material (CFRM for short) is presented. Its resistivity changes with the external force, which is called piezoresistive phenomenon. According to the piezoresistive phenomenon of CFRM, some CFRM strain sensors are made. The usage, resistivity stability and electrode promotion of CFRM strain sensor are studied. The details are as follows:1. The conductive behavior of carbon fiber cement-based composites is presented. According to the phenomenon that the physical properties have a great effect on CFRM, some CFRM strain sensors are made. The CFRM strain measure system is made up of two sensors of same resistance. One is set to measure the strain of the structure; the other is set at the location of structure of zero stress for compensation. Using 100μA constant current for excitation, voltage difference of strain sensor is measured at external force. Results show that the voltage difference and the strain fit well. The CFRM strain measure system has higher sensitivity than a simple voltage measurement. It can also alleviate the impact of relative humidity, curing age, temperature and other uncertainties. This method is particularly suitable for bridge, large-span structures and so on.2. The resistance stability of CFRM strain sensors was studied during and after their curing age. Results show that:the resistance of CFRM strain sensors grows rapidly at the beginning of curing age, and then slows down. After the curing age, the resistances sustain linear growth in a long period. Resistance of CFRM is sensitive to temperature. When getting 0.105℃/h decline, the resistance change rate is 2.027Ω/h. In about 100h, the resistance difference of two strain sensors basically stable at 750Ωand the resistance change rate is 1/60 of that of a single strain sensor. So that the CFRM strain measure system with compensation can alleviate the impact of curing age and temperature, and has better stability.3. Plain stainless steel wire mesh electrode was transformed to three-dimensional stainless steel wire electrode. And the improved CFRM strain sensors'stability and resistance change under one-way or cyclic loading were studied. Results showed that:the use of three-dimensional stainless steel wire electrodes can effectively reduce contact resistance between the electrode and CFRM, so that the resistance of CFRM strain sensors was lowered. The suitable peak angle of the three-dimensional stainless steel wire electrodes was between 60°and 90°, at this time the resistance of CFRM strain sensors maintained at a relatively low level, and can quickly meet stable basically. Too small peak angle (less than 60°) would cause CFRM strain sensor resistance instability.