This paper describes how non-destructive testing (NDT) allows the reduction of destructive testing and extends the possibilities for the assessment of concrete bridges. During the past years NDT methods in civil engineering have experienced broader public awareness and their performance was strongly improved. In this paper, the results gained during the investigation of the inner structure of posttensioned box girder webs with impulse radar, ultrasonic echo and impact-echo are presented. Two-dimensional measurements with these three NDT methods were carried out at two highway bridges in Vienna. A scanning system, developed at BAM (Federal Institute for Materials Research and Testing), was used at large areas and allowed automated data acquisition. The main objectives were the demonstration of the performance of radar, impact-echo and ultrasonic echo methods in automated measurements and the application of new tools for data processing and data visualization. By the combined application of the acoustic and electromagnetic impulse-echo methods tendon ducts could be localized at measurement depths up to 40 cm. The reinforcement on the outer side of the webs could be clearly visualized. Information about the position of tendon duct couplings and hints to ranges of incomplete grouted tendon ducts can be given. The investigations have also shown that further research is still necessary concerning the detection of grouting faults with the acoustic methods.
Abstract