Monitoring of the rebar-concrete bond structural health through ultrasonic measurements: application to recycled aggregate concrete

Abstract

The present work introduces an experimental ultrasonic method allowing for the rebar-concrete bond structural health to be assessed under loading conditions. This novel method has successfully been implemented in laboratory conditions by means of a pull-out test campaign including both conventional and recycled aggregate concretes. Two ultrasonic sensors, one emitter and one receiver were positioned on opposite side faces of the pull-out sample so that the reinforcing bar (rebar) was located in the center of the direct ultrasonic path. During the rebar pull-out, a variation of the time interval between the emitted signal and the received signal (i.e. time-of-flight) was measured. First, a potential correlation between this time-of-flight variation and the rebar-concrete bond behavior is investigated. Then, the influence of recycled concrete aggregates is discussed. In particular, a significant role of the mortar mechanical properties on the rebar-concrete bond behavior is suggested. Finally, an interpretation of this time-of-flight variation in relation to damage and fracture mechanisms occurring at the vicinity of the rebar-concrete interface is proposed. This ultrasonic-based method could likely be expanded to health monitoring applications of both conventional and recycled reinforced concrete structures, at a larger scale.