ABSTRACT
A 265 ft (80.8 m) long post-tensioned concrete tie girder was being fabricated as a cast-in-place girder at an off-site location. The 3.25 ft (1.0 m) wide and 4 ft (1.2 m) deep section included 12 empty post-tensioning ducts and a congested reinforcement cage. A lack of workability was noticed during the placement of concrete delivered by one of the trucks. This necessitated a nondestructive investigation of the girder interior for indications of insufficient consolidation. Ultrasonic tomography was selected as a suitable technique. Wave signal propagation through the reinforced concrete section (with and without ducts) was simulated to evaluate the likelihood of detecting backwall reflections. Backwall reflection detection was required for the calibration of phase values for the classification of reflector types (i.e., the internal details and voids). The simulation showed the likelihood of visualizing only the empty ducts and longitudinal reinforcement located near the scanned surface with very light reflections from the empty ducts at the 2nd column located at a distance of 19.5 in. (495.3 mm) from the vertical surface. Based on the simulation results and the understating of girder details, data collection protocols were developed and executed. This paper describes structural details of the post-tensioned concrete tie girder, simulation results, data collection plan, findings, and the capabilities and limitations of the state-of-the-art technology for visualizing the interior of concrete sections with complicated details.
