Method for Determining Internal P-Wave Speed and Thickness of Concrete Plates

摘要

The objective of this paper is to develop a new method for determining the internal P-wave speed of a plate-like concrete structure. The method is based on the time-of-flight of the P-wave reflected from the bottom surface of a concrete plate and is called the time-of-flight reflection method. The combination of the time-of-flight reflection method with the impact-echo technique in a two-step test procedure provides a means for measuring the internal P-wave speed and the thickness of concrete plates. This paper performed both numerical and experimental studies to investigate the fundamental behavior of P-wave reflection and to identify its arrival in the waveform recorded by a receiver located on the impact surface. Results obtained from the studies show that as the distance between the receiver and the impact point is longer than 2.43 times the plate thickness, the arrival of the P-wave reflected from the plate bottom surface causes a noticeable upward disturbance in the waveform, and the arrival time is easy to identify. Thus, the travel time of the reflected P-wave from the impact point to the receiver can be determined. The travel time and the thickness frequency obtained from the impact-echo test can be used to determine the internal P-wave speed and the accurate thickness of the concrete plate.