Detection of Small Voids by Impact-Echo and Signal Processingby A. K. Maji, Univ of New Mexico, United States,
M. L. Wang, Univ of New Mexico, United States,
Abstract: The Impact-Echo method was used to detect slab thickness, presence of small voids and reinforcement locations in a concrete slab. Studying the frequency response of the slab, it is possible to verify the size and depth of voids inside the slab. Detection of small voids is complicated by the need to generate higher frequency waves with wavelengths small enough to be influenced by the small inhomogenieties. An additional limitation of the traditional impact-Echo method is the need to impact the slab at a point directly at the location of the defect. These issues were addressed using digital signal processing techniques: 'Autocorrelation and 'cross-correlation'. The extent of cross-correlation between the transducer responses for different wave propagation paths could then be used to detect the presence of voids. Digital filtering to eliminate lower frequency components of the transducer response was found to improve this technique.
Subject Headings: Voids | Slabs | Signal processing | Correlation | Reinforced concrete | Detection methods | Thickness
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