THE CONCRETE BRIDGE MAGAZINE

SUMMER 2012

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.

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ASPIRE , Summer 2012 | 53 Rainbow Bridge The Positive Impact of Concrete Bridge Preservation by Chris Ball, Vector Corrosion Technologies The Rainbow Bridge, completed in 1933 at a cost of $74,000, is the longest (410-ft) single-span concrete arch bridge in Idaho and a landmark structure on the Payette River National Scenic Byway. The bridge is listed in the National Register of Historic Places and designated for rehabilitation rather than replacement. Decades of exposure to freezing and thawing cycles and deic- ing chemicals began to affect the integrity of the structure. A consultant's 2004 study assessed the structure and evaluated al- ternatives to preserve the bridge. This evaluation identified the most destructive corrosion as that which was located in the sub- structure near the joints and deck drains. The repair scope included partial and full replacement of rail- ings and curbs, replacement of expansion joints, concrete patch- ing, and corrosion mitigation of the arches. After evaluating a series of alternatives, the consultant and the Idaho Department of Transportation (IDOT) specified two systems to protect dis- tinctly different sections of the structure: electrochemical chlo- ride extraction (ECE) to passivate corrosion in the concrete arch substructure and alkali-activated embedded galvanic anodes in sections that did not receive electrochemical treatment. The implementation of the concrete repair and corrosion mitiga- tion plan provided several important benefits: • Minimal impact on the aesthetics of the historic structure • Shorter construction schedule and reduced traffic impact • Sustainable, long-life bridge preservation solution The Rainbow Bridge, selected "2007 Project of the Year" by the International Concrete Repair Institute, is an example of mod- ern techniques used to preserve a unique historic structure. This signature bridge identifies a local community, serves as a re- minder of past successes, and continues to provide an important gateway for the area. Bridge preservation techniques and strategies are playing an in- creasing role in mitigating performance concerns as more than 30% of the nation's 600,000 bridges are near their theoretical 50-year service life. _________ Chris Ball is vice president of Vector Corrosion Technologies. The historic Rainbow Bridge, Valley County, Idaho. Photo: Vector Corrosion Technologies. Extending Performance Since 2008, the U.S. Highway Bridge Program provides flexibility for state transportation departments to use federal funds for bridge replacement, rehabilitation, or systematic preventive maintenance. In 2011, the Federal Highway Administration (FHWA) published the Bridge Preservation Guide: Maintaining a State of Good Repair Using Cost Effective Investment Strategies. This guide provides many examples of cost-effective interventions to extend bridge performance through pre- ventive maintenance. Two techniques detailed in this guide are cathodic protection and electrochemical chlo- ride extraction (ECE). Evaluations of existing bridges determine if these preventative maintenance approaches will achieve bridge service life requirements. Cathodic Protection Cathodic protection systems can be galvanic or impressed current (ICCP). Galvanic systems use low maintenance sacrificial anodes. These surface-installed systems in- clude: metalized galvanic anodes, galvanic jackets/en- casements, and embedded anodes in concrete repairs. ICCP systems use transformer/rectifiers to deliver protec- tion via inert anodes. The anodes are placed on the sur- face, placed in sawcuts, encased in overlays and jackets, or grouted into drilled holes. ECE Electrochemical treatments passivate active corrosion by providing temporary current that changes the environ- ment around the reinforcing steel. ECE reduces the level of chlorides and increases the pH in chloride-contaminat- ed concrete. This re-alkalization also increases the pH in carbonated concrete ASPIREBook_Sum12_R02.indb 53 6/29/12 12:39 PM

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