Electrical properties of low dosage carbon nanofiber/cement composite: Percolation behavior and polarization effect

Electrically conductive cement-based composites have been widely used to build functional and smart constructions. In these composites, carbon nanofibers (CNFs) can be used as electrically conductive fillers to reduce the electrical resistivity of the cement matrix. Unlike other CNF modified composites, such as CNF/polymers or CNF/ceramics, which have porosity lower than 5%, the CNF/cement composites, however, have porosity various from 10 to 20%. As a result, the electrical conduction phenomenon of these composites is more complicated than the others. Previous studies have investigated the electrical conduction phenomenon of CNF/cement composites by using CNF dosage as the main factor; however, the water content and temperature coefficient were not systematically discussed. In this study, the percolation of the electrical conduction was analyzed by using external applied DC voltage, CNF dosage, and water contents as parameters. Specifically, the percolation critical exponents were used to calculate the percolation backbone density. It was found that there is a critical DC voltage, which turns the electrical-resistivity temperature coefficient of the CNF/cement composites from positive to negative. Furthermore, the results demonstrate that the percolation of the CNF/cement composites is also governed by the polarization phenomenon of the CNFs. This study not only elucidates the synergistic effects of CNF dosage, water contents, and temperature coefficient on the electrical resistivity of CNF/cement composite but also helps to understand the mechanisms of the dynamic electrical resistivity variation with applied DC voltage. The results will be beneficial to design and manufacture cost-effective functional CNF/cement composites for smart structures.