Pulse-echo methods in inspection of concrete structures

摘要

This paper presents two cases of in-situ investigations of concrete structures by NDT methods based on the pulse-echo principle. The first is an evaluation of defects in concrete by combined Impact-Echo and Ultrasonic Pulse Velocity (UPV) methods. While demonstrating that each method has its unique character in analysing defects, it also shows that there are theoretical problems to be clarified, for example it indicates a possible wave propagation mode change of UP for the signals received under the 'shadow' of a crack or a structural corner. The second case demonstrates the use of high-frequency Ground Penetration Radar (GPR), which is an electromagnetic pulse-echo system, to locate the reinforcement in concrete. Its effectiveness in fairly accurately estimating the lateral position and depth of the objects of interest is shown. A field investigation on the electrical resistivity of concrete is also shown here as a complementary study for use with the radar technique.