Automated NDE of Post-Tensioned Concrete Bridges Using Imaging Echo Methods

Test problems for NDE of post-tensioned concrete bridges are to deter- mine the thickness of concrete, to locate metallic tendon ducts and reinforcement bars as well as to determine the grouting condition in tendon ducts. Impulse-radar, ultrasonic echo and impact-echo are applied in combination within a scanning system. For applying the imaging echo methods it is necessary to take data in a two dimensional, rather dense grid (mesh width between 2 cm and 5 cm). Therefore time and personel requirements for manual measurements are extensive. In order to enhance the efficiency of the non-destructive measurements several automated systems were developed at BAM. Applying those systems, sensors for different methods can be automatically moved in a pre-selected grid width. Using these systems large measurement areas up to 4 m x 10 m were investigated on several post-tensioned concrete bridges. Automated measurements were carried out also in areas with limited accessability (e.g. box girders). Special data processing and data imaging is used for a more detailed interpretation of the results. Constituents of the data processing are 3D-reconstruction and fusion of data sets, derived from measurements with different methods or configurations. The detected reflectors and scatterers of the acoustic and electromagnetic measure- ments can be visualised in slices and movies. From radar data sets, measured in perpendicular directions of antenna polarisation, images of the perpendicularly arranged bars of a reinforcement layer can be generated. The results of 3D-reconstructions of ultrasonic echo data allow to recognise tendon ducts up to a measurement depth of approximately 55 cm. In summary the combination of the electromagnetic and acoustic methods allows improving and simplifying the interpretability of data.