Role of hollow glass microspheres (HGM) in improving piezoresistive response of CNT/cement composites exposed to water ingress condition

Cement-based sensors have attracted considerable attention due to their potential for self-sensing applications, particularly in the realms of structural health monitoring and traffic management, as they eliminate the need for external sensors. However, the performance of these sensors can be adversely affected by various environmental factors, with water ingress being a particularly critical concern that can destabilize their piezoresistive sensing capabilities. In this study, hollow glass microspheres (HGM), recognized for their superhydrophobic properties, were incorporated into cement-based sensors to improve their piezoresistive sensing stability under conditions of water ingress. Carbon nanotubes (CNT) were employed as the conductive filler, and the hybrid effects of CNT and HGM were systematically investigated using a range of characterization techniques. The study experimentally assessed the impact of HGM on the compressive strength, electrical resistivity, and water absorption characteristics of the cementitious composites. Furthermore, the enhancement in sensing performance due to HGM was evaluated with respect to sensitivity, linearity, and stability under both monotonic and cyclic loading scenarios. The experimental findings revealed that while HGM initially reduces water absorption, this effect diminishes over prolonged periods of water exposure. Additionally, HGM prevents CNT-based conductive networks from water ingress, thereby improving sensing stability after water exposure. Consequently, the utilization of HGM is anticipated to enhance the sensing stability of cement-based sensors under water ingress conditions.