Conventional ultrasonics-based test methods such as impact-echo have some drawbacks. There may not be enough distinct echoes to permit a good fit. This method was tried out in the field during a survey of concrete bridges in the state of Maryland. It was found to work reasonably well on sound concrete. However, on damaged concrete typically only a few echoes could be identified, which was an insufficient number for accurately fitting the exponential decay function. Another drawback is that the actual decay curve is a function of other factors including geometry that are not accounted for by a simple exponential decay model based on attenuation.

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