Construction and Field Evaluation of Electrically Isolated Tendons in a Prestressed Concrete Spliced Girder Bridge

Abstract

This paper describes the first application of Electrically Isolated Tendon (EIT) technology in the United States. These systems have been developed to provide a level of quality assurance for post-tensioned strand systems in bridge applications. The EIT system is intended to provide electrical isolation between the strand inside the post-tensioning duct and the reinforcement outside of the duct system thus reducing the potential for corrosion to occur. This is achieved using plastic tendon ducts, additional protection of the ducts, modified tendon trumpets, electrical isolation plates at the tendon anchorages, and encapsulation of the strand anchors. A demonstration was conducted with support of the FHWA and Pennsylvania Department of Transportation. The system consists of a three-span continuous bridge composed of pretensioned Pennsylvania Bulb tees spliced and post-tensioned. The bridge system was monitored during beam fabrication, erection, and bridge construction and an overview of the EIT installation methodology is presented. The performance of the EIT system is compared with standard recommendations on acceptable performance and was found to meet the requirements. Installation of the EIT system was not significantly different than that of a conventional post-tensioning tendon. The system provided additional assurance of the electrical isolation in the bridge and appears to be a viable approach for long-term monitoring of the performance of post-tensioned grouted tendons.