Assessment of concrete beams with irregular defects using surface waves

The propagation of surface waves provides information about the properties of materials. Variations in material conditions can be inferred from changes in phase velocity and attenuation. These surface wave characteristics are successfully used to detect the individual surface-breaking cracks in concrete elements, whereas assessment of the elements with irregularly distributed defects requires more investigation. In this paper, six lab-scale concrete beams, each with a different defect volume, are tested using ultrasonic methods to develop a global condition assessment methodology for the concrete elements. The relationships between the defect volume and the wave characteristics—namely, P-wave and R-wave velocities, attenuation coefficient, material damping ratio, and the recently proposed dispersion index (DI)—are investigated. The signal processing techniques in time, frequency, and wavelet domains are used to extract the most accurate diagnostic feature. The attenuation coefficient is found as an optimum parameter to evaluate the damage in terms of reliability and sensitivity, which is followed by the DI and wave velocities