Assessing the Reliability of Impact-Echo for the Detection of Delamination Using Wilcoxon-Mann-Whitney Statistics

Impact echo (IE) is a widely used nondestructive evaluation (NDE) technique for the detection of subsurface delamination in concrete bridge decks. Reviewing the existing literature reveals that there have been limited in-depth quantitative assessments of the reliability of IE. In most of the previous studies, the reliability of IE has either been anecdotally discussed through a visual comparison of the test results with the actual condition, by sounding, or by estimation of the probability of detection (POD) considering limited number of core samples extracted from the test object. Although POD is an important component, it is only a portion of a comprehensive reliability assessment. For optimum decision-making, reliability assessments of NDE technologies should consider both the true detection rate and also the false detection (or false alarm) rate. This manuscript aims to quantitatively assess the reliability of IE through a statistical analysis method called Wilcoxon-Mann-Whitney (WMW), which inherently considers all expected true and false detection rates. As compared to the well-known POD analysis, WMW analysis has not been widely used in the field of NDE. This analysis method was explored due to its ability to provide a quantitative reliability index and therefore, can provide the complementary information necessary for transportation agencies regarding to the performance of NDE technologies. Results of the analysis showed the effectiveness of WMW analysis for evaluating the overall reliability of NDE technologies and for assessing the capability of IE for detecting subsurface delamination in concrete bridge decks. Results demonstrated the excellent capability of IE technology for detecting subsurface voids in concrete plate-like members.


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