Self-sensing performance of nanoengineered one-part alkali-activated materials-based sensors after exposure to elevated temperature

One-part alkali-activated binders offer advantages such as low carbon footprint and enhanced thermal stability, making them a promising alternative to ordinary Portland cement for manufacturing self-sensing cementitious composites (SSCCs). This study aims to develop a nanocarbon black (NCB)-engineered one-part alkali-activated slag composite (CBAS) for a fire safety monitoring system, and thus the residual resistance-based and capacitance-based sensing performances after exposure to 300 °C and 600 °C were investigated. The results indicate the developed CBAS exhibits enhanced residual self-sensing capabilities and retains adequate mechanical strength after high-temperature exposure. The influence of elevated temperatures on the self-sensing mechanisms was thoroughly explored through analyses of phase evolution, microstructure, and the innovatively proposed paired equivalent circuit models of ((R(QR))(RQ)(RW)) and (QR). The exclusive presence of Maxwell–Wagner type interfacial polarization, resulting from NCB/matrix(microdefects)/NCB structures, ensures highly sensitive and improved capacitance-based responses after high-temperature exposure. The compressive and flexural strengths follow the same minor-then-severe strength loss pattern after exposure to 300 °C and 600 °C, with the retention rates of 48.3–93.1 % and 51.1–73.2 %, respectively. The sensitivity of DC and AC resistance-based sensing follows the same increasing–then–decreasing trend, with DC-based sensing exhibiting higher sensitivity. In contrast, capacitance-based sensing shows a monotonically increasing sensitivity with rising exposure temperature and the maximum FCC of 63.1–207.3 % under 6 MPa cyclic compression. The insights from equivalent circuit analysis align well with the theoretical polarization mechanism evolution observed in both resistance- and capacitance-sensing responses, demonstrating the accuracy and reliability of the proposed equivalent circuit model and mechanistic analysis.