Nano-structure and sensitivity of self-sensing geopolymer composites containing nano carbon black

Geopolymer has unique microstructure, high concentration of alkali cations and low carbon footprint features, which is a promising substitute to ordinary Portland cement (OPC) to produce self-sensing cementitious composites. However, the effects of replacing OPC with a geopolymer matrix and incorporating conductive fillers on the self-sensing behavior and consequent mechanisms of self-sensing geopolymer composites (SSGCs) remain unclear. This study investigates the modification effects of nano carbon black (NCB, 0–6.0 wt%) on the mechanical, electrical, and self-sensing properties of SSGCs. To comprehensively elucidate the sensing mechanism, the roles of NCB and multiphases of SSGC matrix, were analyzed through microstructural and chemical characterizations from the geopolymerization process to self-sensing behavior under compression. Experimental results showed that SSGCs containing NCB demonstrated excellent electrical and sensing properties, particularly in detecting initial crack formation and the ultimate failure. The sensing mechanism was primarily governed by the migration of free ions in pore solutions, the establishment of charge balance and the formation of local dipoles under compressive load. SSGCs having low concentration of NCB exhibited poor sensitivity. With NCB content increasing, the rearrangement of NCB particles and the reconstruction of the conductive network contribute to the enhanced sensing properties. SSGCs integrated structural and self-sensing advantages are promising to advance structural health monitoring throughout the life cycle.