Abstract
This investigation focuses on experimental study of the effects of the exciting frequency and the grain (aggregate) size upon the ultrasonic P-wave velocity and the wave attenuation characteristics such as the peak-to-peak amplitude and dominant frequency-shift when performing the ultrasonic nondestructive evaluation of concrete. Furthermore, this presentation studies the extent of wave attenuation as influenced by different grain (aggregate) sizes with or without the well-distributed embedded micro-damage under different exciting frequencies. The damage index or damage assessment of concrete is certainly linked to the reduction in the ultrasonic P-wave velocity, the reduction in the peak-to-peak amplitude response, and the increase in frequency-shift through a damaged concrete specimen.
In this study, we cast concrete cylinders with five different aggregate sizes in our laboratory, including some mortar samples without coarse aggregates. In addition, small styrofoam particles are mixed into the control samples in all batches to simulate microvoids in damaged concrete. The exciting frequency ranges from a low frequency at 50 kHz to a demium frequency at 300 to 400 kHz to demonstrate the frequency effect upon the ultrasonic NDE of concrete for each batch. The grain size also affects the concrete microstructure and influences the propagation and attenuation of ultrasonic waves through undamaged and damaged concrete specimens.
