Improved impact-echo technique by signal processing

Abstract

Abstract An experimental study was performed to modify the conventional impactecho technique to detect small diameter spherical voids in concrete. High velocity impact of steel balls was used to generate the high frequency waves in concrete necessary for detection of small voids. Elastodynamic wave propagation in concrete, type of impact source, and the size of the flaw that can be detected were studied. These laboratory studies were carried out on a 4 in. (10.2 cm) thick 4 ft. × 4 ft. (1.22 m × 1.22 m) concrete slab that contained a variety of artificial spherical flaws embedded at known locations. Analysis of the frequency spectrum of the response of the slab was used to determine the slab's thickness and presence of voids. Signal processing techniques were applied for a better interpretation of the slab's response. Autocorrelation and cross-correlation algorithms were used to determine the characteristics of the slab at different locations. The problems associated with determination of flaws and voids in concrete have been delineated. Some practical and easy to implement solutions have been proposed and ways of using the impact-echo technique more efficiently for field applications have been discussed.