Description
Multiwalled carbon nanotubes (MWCNT) and nanocarbon black (NCB) possess intrinsic self-sensing capabilities and show promising potential for structural health monitoring. The self-sensing performance of MWCNT and NCB concrete at elevated temperatures has rarely been studied to assess its feasibility for long-term monitoring applications. In this study, the mechanical properties and piezoresistivity of MCNT/NCB nanocarbon material sensors based on calcium aluminate cement (CAC) was investigated at different temperatures (25, 100, 200, 300, and 500 °C) to develop an efficient MCNT/NCB sensor that experienced minimal degradation in piezoresistive sensitivity during stress/strain monitoring. The specimens were designed based on CAC cementitious materials, and MWCNT/NCB dosages (MWCNT:1.0% and NCB:0.80%) were used as the cementitious binder weights. The specimens were evaluated under monotonic compression loading to determine the ultimate strength and different cyclic compression stress amplitudes to evaluate piezoresistive sensitivity and repeatability. The results showed that the repeatability and sensitivity of the frictional changes in the resistivity (FCR) of the CAC-based sensors exhibited acceptable linearity and excellent reversibility at 25, 100, 200, and 300 °C. Moreover, there was no spalling after the heat treatment, which improved the piezoresistivity at elevated temperatures. For the specimen without heat treatment, the FCR reached 35% at 14MPa and 45% after heat treatment at 300 °C. However, after heat treatment at 500 °C, explosive spalling was observed in the CAC-based sensor, which was no longer conductive because of the explosive spalling of the nanocarbon carbon oxidation. The CAC-based MWCNT/NCB sensors exhibited good mechanical properties and high sensing performance at normal and elevated temperatures of 100, 200, and 300 °C compared with those at 500 °C, which demonstrates that they promote the application of smart CAC-MWCNT/NCB-based sensors for structural health monitoring at elevated temperatures and contribute to improved piezoresistivity.
