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.

中文翻译：

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通过超声测量监测钢筋混凝土粘结结构的健康状况：应用于再生骨料混凝土

本工作介绍了一种实验超声方法，该方法允许在加载条件下评估钢筋混凝土粘结结构的健康状况。通过包括传统和再生骨料混凝土在内的拉拔试验，已在实验室条件下成功实施了这种新方法。将两个超声传感器，一个发射器和一个接收器放置在拉出样品的相对侧面上，以使钢筋（钢筋）位于直接超声路径的中心。在钢筋拔出期间，测量了发射信号和接收信号之间的时间间隔（即飞行时间）的变化。首先，研究了这种飞行时间变化与钢筋混凝土粘结行为之间的潜在相关性。然后，讨论了再生混凝土骨料的影响。特别地，提出了砂浆机械性能对钢筋混凝土粘结性能的重要作用。最后，提出了这种飞行时间变化与钢筋混凝土界面附近发生的损伤和断裂机理的关系的解释。这种基于超声波的方法可能会更大规模地扩展到常规和再生钢筋混凝土结构的健康监测应用。