Unlocking the Environmentally Independent Conductivity of Nanoengineered Cement Composites with Carbon Nanotubes

Cement nanocomposites stand out as true multifunctional materials, offering not only increased strength or durability, but also advanced capabilities such as real-time strain and crack sensing, on-demand heat generation and energy harvesting. However, smart cement nanocomposites remain vulnerable to their surroundings: shifts in temperature and humidity can destabilize their electrical response and undermine their reliability as strain sensors. To address this challenge, we introduce cement composites incorporating multiwalled carbon nanotubes that deliver a stable electrical response under various working conditions. We compared the electrical response of cement mortars with carbon nanotubes using electrochemical impedance spectroscopy, capturing their behavior across a wide alternating current frequency range under different humidity conditions and, separately, under various temperatures with negligible humidity differences. Two compositions of mortars were tested with carbon nanotube dosages ranging from 0.05 wt.% to 1.0 wt.%. Three levels of humidity, including full saturation, ca. 50% saturation, and fully dried samples, as well as temperatures between 5 °C and 80 °C, were tested. The results indicate that the dosages of carbon nanotubes above the percolation threshold, i.e., 1.0 wt.%, result in high conductivity of cement composites that are stable even under changing humidity and temperature, therefore showing huge potential in their application as next-generation structural sensors, tailored to operate in real-world environments.