Assessment of bonding defects in FRP reinforced structures via ultrasonic technique

Fiber reinforced polymer (FRP) composite systems are widely used for the rehabilitation of concrete structures such as building that need to resist to seismic loads, bridges that have to carry heavier traffic loads. The technique consists in bonding the composite plate to the concrete surface element in order to increase the flexural capacity. A proper attachment of the FRP plate to the concrete surface is necessary for the efficiency of the load transfer between the reinforcement and the substrate. In this work, the quality of composite bonding is characterized through ultrasonic testing. The proposed technique is relative to a time domain analysis of the ultrasonic signals and couples the Akaike Information Criterion (AIC), used as automatic onset signal detection, and the Equivalent Time-Length (ETL), used as an indicator of the quantity of energy propagating through the bonding. It has been tested both numerically and experimentally, in vitro, using samples with imposed well- known defects.