PULSE-ECHO METHODS IN INSPECTION OF CONCRETE STRUCTURES

This paper presents Two cases of in-situ investigations of concrete st ructures by NDT methods based on the pulse-echo principle. The first i s an evaluation of defects in concrete by combined Impact-Echo and Ult rasonic Pulse Velocity (UPV) methods. While demonstrating that each me thod has its unique character in analysing defects, it also shows that there are theoretical problems to be clarified for example it indicat es a possible wave propagation mode change of UP for the signals recei ved under the 'shadow' of a crack ora structural corner. The second ca se demonstrates the use of high- frequency Ground Penetration Radar (G PR), which is an electromagnetic pulse-echo system, to locate the rein forcement in concrete. Its effectiveness in fairly accurately estimati ng the lateral position and depth of the objects of interest is shown. A field investigation on the electrical resistivity of concrete is al so shown here as a complementary study for use with the radar techniqu e.