Flaw Detection in Concrete Using the Impact-Echo Method

Abstract

A technique called the impact-echo method has been developed for flaw detection in concrete. The technique is based on a simple concept using transient stress wave propagation. Mechanical impact is used to generate a short duration stress pulse which travels into the test object as P- and S-waves. The waves are reflected by internal discontinuities or external boundaries. A displacement transducer located close to the impact point measures the time history of the surface displacement caused by the arrival of reflected waves. This paper discusses the theoretical basis of the method and gives representative examples of the results of analytical and experimental studies. A procedure called spectral peak plotting is described which simplifies interpretation of data from scans across a structure. By using this procedure a profile view of the interior of the test object can be constructed.