The Cline Avenue Bridge (SR 912) is a predominately cast-in-place post-tensioned structure located in northwest Indiana that leads to steel mills along Lake Michigan, the Majestic Star Casinos in Gary and the Ameristar Casino in East Chicago. The bridge mainline is over 6,000 LF, has two adjacent segments nearly 35 feet wide each, and contains four connecting ramps. An inspection and analysis team was assembled to perform a thorough investigation of the bridge. The team concentrated on the existing post-tensioning system and interior and exterior concrete cracks. The engineer retained VSL to assist with the inspection of the tendons.
VSL approached the Cline Avenue project with a guideline that outlines a statistically sound method of sampling the tendons. A statistical sample pool (which consisted of the mainline structure and the ramps) was defined by referencing the American National Standard Institute’s (ANSI) guideline “Sampling Procedures and Tables for Inspection by Attributes as published by the American Society for Quality Control (1993).”
The probable void locations throughout the structure’s mainline segments and ramps were initially identified by VSL to appropriately distribute the sampling population. Such areas consisted of high points, areas approaching and leaving the high points, and couplers.
Using non-destructive Ground Penetrating Radar (GPR) and field layout drawings, VSL located existing post-tensioning tendons. Once the layout was performed, specific tendons throughout the bridge and ramp structures were sampled by drilling into the duct and exposing the tendon for visual inspection. The use of a borescope allowed for detailed visual inspection of the tendon and also captured video footage to share with the owner and the engineer. After review of each inspection, VSL placed epoxy in the borescope hole to protect the tendons from air and moisture intrusion. When voids were encountered, the project team observed and documented the condition of the strand based on the PCI Journal guideline, “Evaluation of Degree of Rusting on Prestressed Concrete Strand.” VSL used vacuum grouting technology to fill the void, thereby protecting the previously exposed strand.
The tendon inspection data was analyzed with other findings (such as crack survey findings) to determine what type of rehabilitation was required. VSL’s goal to establish a statistically sound sample of physically inspected tendons that provided valid data as to the current state of the existing PT system was accomplished.