Improving the accuracy of impact-echo in testing post-tensioning ducts

The need for greater accuracy in positioning metal ducts in concrete and in detecting their grouting faults motivated the application of the scanning impact-echo method on site for testing a post-tensioned beam. 2-D data display allowed recognition of signal patterns improving interpretation reliability with regard to lateral position and concrete cover of ducts, and their grouting condition. Partially grouted ducts presenting small voiding were discriminated from fully grouted ducts and findings compared with cores. New interpretation criteria were highlighted and alternative wave behavior considered.