Effect of Moisture on Electrical Resistivity and Self-Sensing Behavior of a Cement Paste

Abstract

Large structures need to be monitored to ensure safety for users and increase their service life through predictive maintenance. Self-sensing cementitious composites have been studied for structural health monitoring applications. By adding carbon nanotubes (CNTs) to a cement matrix, the resulting composite exhibits piezoresistive properties, making it capable of monitoring strain and mechanical stresses. However, due to their porous microstructure, the electrical properties of these cementitious composites are affected by moisture. This work studies the influence of water in the pores of a cement paste on the electrical resistivity, self-sensing capability, and electrification effects of cement pastes with different amounts of CNT. It was found that for pastes with lower amounts of CNT, the presence of water decreased electrical resistivity and increased electrical polarization effects and self-sensing sensitivity to strain, but not to failure. On the other hand, pastes with higher CNT content were less affected by the presence of water in the pores of the cementitious matrix. It was concluded that a minimum amount of CNT, above the percolation region, can minimize the effects of moisture variations on electrical properties. The construction industry is one of the most traditional in the world. Nevertheless, it has undergone a significant transformation and evolution through the adoption of new materials. Nanotechnology has played a pivotal role in the development of cementitious materials with novel properties, such as self-healing, energy absorption, self-cleaning characteristics, and the ability to monitor deformations, among others. It is within this context that smart cementitious composites emerge, maintaining their pre-existing properties and functionalities while incorporating new ones. Among these, self-sensing cementitious composites are specialized cement-based materials designed to monitor the safety performance of construction structures. When incorporated into structures, they can correlate their electrical properties with the deformations experienced, providing real-time monitoring of the conditions of these buildings. Self-monitoring cementitious composites serve as sensors for monitoring pavements and large structures such as dams, bridges, and viaducts. Their significant advantage lies in being manufactured from the same material as most structures, ensuring excellent compatibility and greater durability compared to other commercial sensors.