Dispersion of carbon fibers and conductivity of carbon fiber-reinforced cement-based composites

Dispersion of carbon fibers in the cement matrix remains a hot topic in the preparation of carbon fiber reinforced cement-based composites (CFRC) because it affects greatly both the mechanical and electrical properties of the composites. In this work, a new dispersant hydroxyethyl cellulose was used with the aids of pre-dispersion by ultrasonic wave to realize the uniform distribution of chopped carbon fibers in the cement matrix. The fracture surface of the prepared CFRC was observed by scanning electron microscopy, the elemental distribution was investigated by energy dispersive spectroscopy, and the components was analyzed by X-ray diffraction. Influences of carbon fiber lengths and contents, water/cement weight ratio, molding process, curing time, and silica fume content over the conductivity of the CFRC composites were studied. The mechanism of conductivity was discussed. Results shown that the electrical resistivity intended to decrease with the increasing of carbon fiber contents. The mass fraction 0.6% of carbon fibers was a turning point. The concentration of hydroxyethyl cellulose between 1.66% and 1.86% was mostly beneficial for the dispersion of carbon fibers. The resistivity was increased first and decreased then with the increase of water/cement ratio. When the CFRC sample was prepared by the vibrating pressing method, the resistivity of the sample was reduced far greatly than that of the sample by the vibrating method. The incorporation of silica fume into the CFRC composites exerted not only a good effect on the dispersion of carbon fibers, but also increased the density of the composites to further influence the conductivity of the CFRC.