Microwave-induced microstructure engineering for self-sensing cement-based composites: Trade-offs of elastic sensing range and short-term conductive network stability

Self-sensing concrete offers a promising solution for structural health monitoring, which is critical for infrastructure safety and longevity. However, practical application still faces significant challenges in achieving optimal sensitivity, stable performance, and sufficient elastic sensing range for reliable monitoring. Therefore, this study proposed a novel approach combining nano carbon black (nCB) for conductive network formation with microwave-induced micropore engineering to extend the linear response range of cement-based composites. Comprehensive micro and macro-level testing assessed mechanical and electrical performance, hydration characteristics, and pore structure, with additional piezoresistive tests evaluating the stress-sensing response. Specifically, ¹H NMR analysis revealed a novel three-stage microscopic convection mechanism driven by localized microwave absorption, resulting in a bimodal microporous distribution. These engineered micropores functioned purely as mechanical stress-relief zones, enabling reversible conductive network deformation without premature pathway disruption. Consequently, this engineered microstructure notably extended the elastic sensing range by 89% (from 12.2 MPa to 23.0 MPa) while maintaining a stress sensitivity of 1.11%/MPa. Furthermore, equivalent circuit modeling confirmed enhanced electromechanical coupling through reduced bulk resistance and increased interfacial capacitance. However, a distinct trade-off was observed: the 1% nCB composite achieved the widest elastic range, whereas superior cyclic signal stability required a 2% nCB dosage, albeit at the cost of compromised matrix integrity. Ultimately, the outcomes of this work establish a robust microstructural design strategy for developing next-generation smart cement-based materials.