Carbon fiber-reinforced cement as a thermistor

Carbon fiber (approx. 5 mm long, 0.5% by mass of cement)-reinforced silica fume (15% by mass of cement) cement paste was found to be an effective thermistor. Its electrical resistivity decreased reversibly with increasing temperature (1-45°C), with an activation energy of electrical conduction (electron hopping) of 0.4 eV. This is comparable to those of semiconductors (typical thermistor materials) and higher than that of carbon fiber polymer-matrix composites. Without carbon fibers, or with latex in place of silica fume, the activation energy was much lower and the resistivity was higher. The voltage range for a linear current-voltage characteristic was wider in the absence of fibers. The current-voltage characteristic of carbon fiber-reinforced silica fume cement paste was linear up to 8 V at 20°C.