Carbon cement-based sensors for dynamic monitoring of structures

Structural Health Monitoring is a topic of growing significance in Civil and Mechanical Engineering, whereby an effective monitoring of a structure can lead to cost-effective maintenance and can enhance occupants' safety. A distributed monitoring system can better identify, localize and quantify incipient damages and variations of the structural behavior compared to a sparse utilization of off-the-shelf sensors. This is due to the spatial distribution limitation of conventional sensors, providing partial information for a subsequent structural diagnosis. They are also denoted by durability issues and high implementation cost. Owing to recent advances in Nanotechnology, new smart materials are becoming available, enabling the development of distributed sensing solutions for structural health monitoring. In particular, novel conductive piezoresistive nanofillers, such as carbon nanotubes and nanofibers, have showed promise towards realizing cementitious materials with self-sensing capabilities. In such materials, the change in strain or stress is detectable through the variation of given electrical properties, such as resistance or conductivity. The nanomodified cementitious sensors can be embedded into structural elements and therefore provides a distributed sensing system. Investigating important issues related to their composition, their fabrication and their electrical characteristics, will lead to their broad implementation. This paper is aimed at investigating the dispersion of nanoinclusions in the cement matrix, the electrical conductivity, and the strain/stress sensitivity of samples of cement paste, mortar and concrete fabricated with Multi Walled Carbon Nanotubes (MWCNTs) and Carbon Nanofibers (CNFs). The results of the electromechanical experimental tests, including tests conducted on full-scale concrete elements, show that these new sensors can be effectively used for monitoring the health of structures.