Effect of chloride penetration on electrical resistivity of CNT-CF/cement composites and its application as chloride sensor for reinforced mortar

This study was conducted to investigate the effect of chloride (Cl) penetration on the resistivity of highly conductive composites containing carbon nanotubes (CNTs) and carbon fibers (CFs). First, Cl ions were penetrated into the hardened composite specimens with the application of an electrical charge, and the profiles of the Cl contents, conductivity, hydration, and pore structures were then evaluated. Second, the composite sensors were embedded in a reinforced mortar and immersed in a NaCl solution. Third, the ion distribution in the composite sensor immersed in the NaCl solution was visualized via element mapping using a scanning electron microscopy-energy-dispersive X-ray analysis and an electron probe micro-analyzer. It was found that the resistivity of the composites increased as the Cl penetrated the specimens, and this phenomenon was presumably due to the clogging of the CNT network. The results indicated that the Cl penetration could be monitored by checking the trend of change in the resistance value of multiple sensors over time (trend analysis), and not just by measuring the instantaneous resistance value of a single sensor (deterministic measurement).