Ultrasonic Evaluation of CFRP-Concrete Interface for Specimens under Temperature and Water-Immersion Aging Effects

Ultrasonic non-destructive evaluation (NDE) techniques are widely used for structural health monitoring of concrete/FRP structures. In this study, experimental and processing schemes of surface acoustic waves (SAW) are described for assessing concrete/CFRP specimens subjected to accelerated aging conditions. Ultrasonic waves are generated and received at one side using narrow-band transducers of 110 kHz center frequency. The received signals are filtered and amplified then digitized and processed to extract various parameters in both time and frequency domains. These parameters include ultrasound propagation speed, maximum amplitude, total power, and the slope at maximum power spectrum. Changes in these parameters due to water immersion aging at different temperatures were monitored over 10 weeks. Results indicated a notable decrease in measured ultrasonic parameters over time, particularly after the first 2 weeks. This may indicate a debonding or deterioration in the concrete/FRP samples. This behavior showed good agreement with the findings of a parallel destructive study on Mode-II fracture loading of CFRP-concrete samples, tested to obtain fracture energy and define traction-separation response under temperature and water-immersion aging effects.