Detection and processing of impact echoes in concrete

The impact echo method uses transient stress waves for evaluating subsurface conditions. This method creates a transient stress wave in the object under test by means of mechanical impact, while a suitable transducer detects wave reflections on the surface. Processing of the reflection signals enables deductions to be made concerning the subsurface conditions. Details concerning the design of a high-fidelity piezoelectric transducer specifically constructed to detect impact echoes on a concrete surface are described. Processing and analysis of the surface displacement signals are discussed. Results of preliminary laboratory studies designed to detect voids in various concrete specimens are presented. Cylindrical voids in plates up to 15 in thick have been reliably found using a discrete Fourier transform signal processing method