Non-linear ultrasonic investigation of interface debonding of steel-concrete composites

In this paper, the second harmonic generation (SHG) method, a non-linear ultrasonic technique, is employed to investigate the interface debonding of steel-concrete composites. The quadratic parameter of non-linear constitutive relationship for the steel-concrete composites is adopted as a measure of the debonding between a steel component and a concrete component. The quadratic parameter is calculated based on the amplitude measurements of probing ultrasonic waves and the corresponding second harmonic generated by the non-linear response of the debonded steel-concrete interface. The ultrasonic experiments are conducted on both scaled-down laboratory samples and full-size structures. Results from both experiments show that the defined parameter is highly correlated with the debonding condition of the composite interface, indicating an excellent feasibility for its use in the detection of the variation of interface microstructure. The SHG experimental results are further compared with results from the amplitude attenuation, a conventional ultrasonic method. It is shown that the change in the defined parameter is orders of magnitude larger than the traditional attenuation coefficient. The results of the comparison demonstrate the higher sensitivity of the developed SHG method in terms of the assessment of interface debonding of steel-concrete composites, particularly in the early phase of structural deterioration.