Non-destructive evaluation techniques are used to assess the conditions of concrete structures, predict future performance, and minor repair systems.  The best-known non-destructive evaluation techniques use ultra sonic waves for non-destructive testing.  Changes in the frequency spectrum indicate the presence of anomalies in the material; yet do not enable predicting the severity of the position of the anomalies.  This research presents the findings of an experimental and analytical study conducted to interpret and characterize the ultrasonic wave signals received from different kinds of anomalies in concrete bridge decks.  The frequency spectra of the recorded waveforms were obtained by using the Fast Fourier Transform technique.  Specimens differing artificial voids were tested in order to develop the relationships between the crack depth, crack width, crack type and the spectral responses in concrete bridge decks.

The project utilizes an ultrasonic device, owned by NASA and housed at UAH.  The ultrasonic velocity instrument that was originally designed and used by NASA for gas bubbles identification has been re-calibrated for identification of voids and cracks in concrete beams and slabs.  Concrete samples, whose mix and dimensions were carefully controlled, were used to validate the instrument for crack/void identification.       

The sizes of the voids were estimated using the information obtained from the data files in the LAB VIEW software.  Results show that the instrument can be successfully used for providing information about the internal conditions of concrete bridge decks and identifying flaws and cracks in concrete materials.