Toward sustainable cementitious materials: A thermally resilient CAC–MWCNT self-sensing composite for high-temperature infrastructure monitoring

This study develops a calcium aluminate cement-based multi-walled carbon nanotube composite as a thermally resilient self-sensing cementitious material for high-temperature infrastructure monitoring. MWCNTs were incorporated at 0.25–1.50 wt% to evaluate their effects on mechanical performance, electrical resistance, and microstructural stability, as well as the piezoresistive response under cyclic, monotonic, and flexural loading before and after exposure to 300 °C and 500 °C. The results show that increasing MWCNTs content significantly reduced electrical resistivity and improved cyclic sensing stability, indicating the formation of a more effective conductive network. Among the investigated mixtures, the CNT-1.25 composite showed the best balance between mechanical and sensing performance, with a compressive strength of 64 MPa, low electrical resistivity of 0.062 × 10⁴ Ω·cm, and a fractional change in resistance of −32% under cyclic compression before thermal exposure. After heat treatment, the sensing response further increased, with FCR values of −41% after 300 °C exposure and −55% after 500 °C exposure. Although thermal exposure reduced mechanical strength in some mixtures, the optimized CNT-1.25 composite maintained effective load-bearing capacity and enhanced piezoresistive sensitivity. Microstructural observations suggest that moisture removal, CAC phase transformation, moderate thermally induced microcracking, and preservation of the MWCNTs conductive network contributed to the improved post-heating sensing response. These findings demonstrate that CAC–MWCNTs composites can function as embeddable self-sensing materials for monitoring structural response in thermally demanding environments.