Electrical and piezoresistive properties of carbon nanofiber cement mortar under different temperatures and water contents

Influence of temperatures and water contents on the electrical resistance and piezoresistivity of carbon nanofibers (CNFs) cement mortar were investigated in this paper. Electrochemical impedance spectroscopy (EIS) and equivalent circuits were determined to explore the conductive and mechanical mechanism. Results indicated that the electrical resistance decreased with the increasing CNFs dosages in all environments. When CNFs content was less than 1.5%, the electrical resistance of dried specimens with environment temperature ranging from −30 °C to 20 °C increased linearly with the ascending temperature. However, when the temperature ranged from 20 °C to 40 °C, the electrical resistance decreased with one dimensional Gauss function with the increasing temperature. While, when dried CNFs mortar possessed the CNFs content of 1.5%, 2.0% and 2.5% or specimens were in water saturated state, the resistance of all specimens and temperatures conformed to one dimensional Gauss function. Moreover, when CNFs mortars were at the temperature of 20 °C, the relationship between electrical resistance and water contents could be described as exponential function of 10. Additionally, CNFs mortar with 2.5% CNFs performed favorable piezoresistivity. The strain-sensing performance of CNFs mortar deteriorated when temperature decreased from 20 °C to −30 °C. When temperature was higher than 20 °C, self-sensing property became worse with the increasing temperature. Nevertheless, the sensitivity of CNFs mortar first decreased and then increased with the increasing water contents. CNFs mortar samples in dried state and 20 °C showed the optimum self-sensing performance. Furthermore, the EIS curves were sensitive to temperatures and water contents and effective to reveal the conductive mechanism.