Ternary Role of Carbon Black-Nickel-Silica Nanoparticles in Cement Mortars for Structural Health Monitoring

This study developed mechanically robust and electrically conductive self-sensing composites (SSC) by integrating carbon black (CB), nickel (Ni), and silica dioxide ( SiO 2 ) nanoparticles. Three formulations, namely, CB-SSC, CB/Ni-SSC, and CB/Ni/ SiO 2 -SSC, were systematically compared to evaluate their structural and piezoresistive performance. The percolation thresholds were identified through electrical resistance testing, revealing that 5 wt.% CB was optimal for enabling tunneling-dominated conductivity. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy analyses revealed the critical role of SiO 2 in enhancing nanoparticle dispersion, reducing Ni agglomeration, and facilitating the distribution of CB, thereby refining conductive pathways. Cyclic and monotonic loading tests demonstrated the superior performance of the hybrid CB/Ni/ SiO 2 -SSC, achieving a 41.8% fractional change in resistivity at failure, which was threefold higher than that of CB-SSC, alongside exceptional linearity and repeatability. Further, SiO 2 enhanced compressive strength by 15% by forming extra calcium-silicate hydrate, counteracting the CB-induced porosity. These results underscore the functionality of the hybrid addition of CB, Ni, and SiO 2 in enhancing mechanical properties and piezoresistive sensitivity, with the ternary system demonstrating precise failure-detection capability during loading. This work highlights the necessity of balancing strength and conductivity in SSCs, providing a scalable strategy for advancing structural health monitoring (SHM) systems through nanomaterial synergy.