Comparison of NDT techniques on a post-tensioned beam before its autopsy

Following the complete demolition of a prestressed concrete bridge in southern France, a suspected weak post-tensioned beam was retained for non-destructive testing (NDT). Ground penetrating radar, Ferroscan(R) (covermeter), gamma-ray radiography and impact-echo methods have all been tested and their results then discussed after the autopsy of the beam by means of hydro-demolition. This paper describes the extent to which NDT surveys are able to respond to the needs of structural engineers, through the use of complementary NDT approaches. The introduction of a second technique should provide a more pertinent response while eliminating certain ambiguities either by improving measurement reliability or by focusing on questionable zones to obtain more precise local measurements. Afterwards, the problems still not adequately resolved by these techniques are pinpointed. This step concludes with the set of needs heretofore unmet by such techniques. (C) 2002 Elsevier Science Ltd. All rights reserved.