Effect of frequency on the evaluation of the concrete defects by ultrasonic shear wave tomography

Ultrasonic Shear Wave Tomography (USWT) is recommended as a modern non-destructive method that uses ultrasonic shear waves to detect objects, interfaces, and anomalies in the structure. The entire structure can be analyzed quickly and economically without destruction of any structural element. Thus, ultrasonic transition properties can be visualized in three dimensions by means of this method. In this work, results of experimental studies conducted on the effect of frequency on the analysis of the concrete by USWT are explained. The test device used in experimental studies has 24 transducers and its operating frequency range is 25-250 kHz. 50x50x22 cm sized three concrete specimens were produced in the laboratory for the experiments. Different materials were embedded in the concrete specimens to represent reinforcement and defects. Experiments were carried out at four different frequency values (25-50-100-200 kHz) on each specimen. The tomographic cross -sections obtained at each frequency value were studied. The reinforcement and defects obtained in tomography sections were tried to match the known properties of placed objects in the concrete specimens. According to the results obtained in this study the accuracy of the results obtained depending on the frequency value varies according to the characteristics of the defect. The materials placed in the specimens tested at 25 kHz and 50 kHz values were determined with high accuracy whereas the values of 100 kHz and 200 kHz were only satisfactory to determine the specimen sizes, in other words, the boundaries of the concrete element.