Research On Surface Metallization Of Carbon Fiber Improved Conductivity And Compression Sensibility Of CFRC

Carbon fiber reinforced cement-based composite(CFRC) is a new kind of smart material, CFRC with excellent mechanical properties and functional properties has a good application prospect in the self-diagnosis and self-monitoring of dams, roads, bridges and other large infrastructure. In the preparation process of CFRC, homogeneous dispersion of carbon fiber(CF) is one of the key problems to determine conductivity and compression sensibility of CFRC, and the interface between CF and cement matrix is a bridge of transferring stress and other information, the comprehensive performance of CFRC is directly affected by the interfacial properties.In this paper, the surface of CF was coated with metal, the Copper or Nickel layer with different thickness on the surface of CF mainly by electroplating, the specimens of CFRC were made from the carbon fiber after electroplating and cement, and the influence of the surface metallization of CF on the dispersion of carbon fibers in CFRC was studied. To indirectly evaluate the effect of fiber dispersion by the change of CFRC resistivity after electroplating of CF. Then under monotonic loading and cyclic loading, the effect of the electroplating metal of CF surface on the compression sensibility of CFRC was researched, and the relationship between the thickness of CF and the conductivity and compression sensibility of CFRC was established. Finally, the influence of the surface metallization of CF on the conductivity of CFRC and the conductive mechanism of CFRC were analyzed by using AC impedance. The main conclusions are drawn as following:(1) In order to prevent the loss of the softness of CF and metal-coating caking, the current density and plating time should not be too large in electroplating, the current density and plating time should be controlled in the range of 1.5 mA/cm2 and 20 min respectively, the conductivity of CF was increased by electroplating.(2) The electroplating metal of CF surface can significantly reduce the resistivity of CFRC, the variation coefficient of resistance was reduced, the dispersion of CF was improved, and its strength is not affected. But the coating should not be too thick, the average thickness should be controlled in the range of 2 ?m. The resistivity of CFRC decreases with the increase of the coating thickness. After electroplating metal of CF surface, the resistivity of CFRC decreases with the increase of the coating thickness, And the resistivity of Nickel plating is lower than that of Copper plating, the lowest resistivity were 65 ?·cm and 246 ?·cm respectively.(3) CFRC has the piezoresistive effect under compressive stress. The resistance change rate first increases and then decreases with the thickness of the metal layer, under monotonic loading. When the volume content of CF increases, the maximum resistance change rate of CFRC corresponds to the smaller thickness of the coating, which indicates that the electroplating metal of CF surface can obtain better compression sensibility under low content. Under cyclic loading of small stress, the compression sensibility of CFRC of the nickel plated on carbon fiber surface will be more stable.(4) Through the analysis of AC impedance of CFRC, the percolation threshold of CF content in CFRC was found to about 0.6%. At the same time, with the increase of coating thickness on the surface of CF, the impedance curve moves to the left. When the coating is more than a certain thickness, and the curve moves to the right. Early stage of cement hydration, CFRC is mainly based on ionic conductivity, and the later stage of hydration, the conductivity of CFRC is established on the conductive network that is mainly formed by CF.