Effect of temperature on the self-sensing behavior of carbon nanotubes/cement composites

Concrete structures, such as pavement slabs, bridges, and dams, which are excellent candidates for the application of self-sensing composites, are usually exposed to a wide range of temperature variations. These variations can be originated from different sources such as heat release from cement hydration, day/night cycles, or seasonal weather changes. The implementation of most self-sensing composites to monitor concrete structures is based on measurement of their electrical resistivity. It is known that the electrical resistivity of cement-based composites with carbon fibers is inversely proportional to temperature; nevertheless, there is little information available in the literature on how temperature variations affect the self-sensing capacity of carbon nanotube (CNT)/cement composites. This work studies how the electrical resistivity and piezo-resistive response of CNT/cement composites changes when temperature increases. First, the composites were heated from room temperature to 70 °C, allowing free deformation, to determine a relationship between temperature, thermal expansion, and electrical resistivity. Subsequently, piezo-resistivity experiments in steady temperature regime were performed at 25°C, 50°C and 70°C. It was found that if temperature is steady when deformation is imposed on a CNT/cement composite, the sensitivity and linearity of its electrical response are maintained. On the other hand, when temperature is in transient condition, CNT/cement composites work as a thermistor and such behavior must be considered when interpreting fractional resistivity change curves.