ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306858
MAINTENANCE, REPAIR, and REHABILITATION OF CONCRETE BRIDGES To perform efficient and cost-effective repairs on bridge abutments, the Ohio Department of Transportation places activated-zinc anode strips (in red) parallel to epoxy-coated reinforcement (green) after the delaminated concrete is removed. The anodes provide global protection for the abutment reinforcement and extend the abutments' service life. The project shown is the Kirkwood Bridge in Sydney, Ohio. ASPIRE , Winter 2009 | 41 Repairing deteriorating bridges without causing considerable impact to users creates a difficult balancing act. The Ohio Department of Transportation has found a solution for its abutment repairs by using activated-zinc anode strips distributed throughout a new reinforced concrete facing. Compared to previous repair methods, the galvanic encasement combination extends the bridge's service life and provides global protection to the abutment in a quick and economical way rather than protection only to the patched area. The department's designs for cast- in-place concrete, continuous, slab bridges typically have a construction joint located over the abutment. This exposes the abutment to chloride penetration from deicing salts and subsequent corrosion of the abutment reinforcement. Typically, the slabs re m a i n i n g o o d c o n d i t i o n , w i t h only the abutment under the joint deteriorating. Previously, to repair the damage, temporary shoring would be placed under the slab and the abutments would be replaced. This required either complete bridge closure or phased construction. Both of these created traffic delays and disruptions. But the other options of doing nothing or replacing the bridge were not feasible either for safety or economic reasons. Ohio began using discrete activated-zinc anodes several years ago, first as a localized repair. The puck-sized anode units, supplied by Vector Corrosion Technologies, Tampa, Fla., attach to the exposed reinforcement using integral tie wires, and consist of a zinc core surrounded by a highly alkaline cementitious matrix. The zinc has a higher corrosion potential than the reinforcing steel, allowing the anode to corrode rather than the steel. Providing this galvanic protection allowed isolated patch repairs to be accomplished quickly, with minimal impact on traffic and at a low cost. However, the localized benefit provided by the discrete zinc anodes assured protection only around the patch to mitigate the "halo" effect. This effect involves the area around the patch that begins to corrode at an accelerated rate. To provide extra protection for the entire abutment face, the department has completed several projects that now supply global protection through the use of activated distributed zinc "strip" anodes. In this process, the delaminated concrete is removed, and the new reinforcing steel is installed along the face of the exposed concrete. Zinc anode strips are placed parallel Minimizing RepaiR impact by Craig A. Shutt