THE CONCRETE BRIDGE MAGAZINE

WINTER 2018

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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CBP Concrete Bridge Preservation color that was selected on site by the historian to be within the range of the original concrete color. Mock-ups and field trials were implemented to evaluate the contractor's materials and methods and conformance with the project specifications. The long-term durability of these concrete repairs was augmented with a film-forming coating throughout the bridge, as well as passive cathodic protection at targeted locations in the corners of the arch ribs. Several key factors contributed to the success of the project: • a thorough, early investigation accurately identified the deterioration mechanisms and allowed for selection of appropriately targeted rehabilitation alternatives; • due consideration of historic preservation principles led to the decision to protect vulnerable historic fabric by using a high-performance, water-resistant, opaque concrete coating; • cathodic protection systems were targeted to slow corrosion at the most vulnerable locations and detailed to be less visible from the ground; • step-by-step mock-ups validated the color, texture, and quality of the repair methods before full-scale implementation; and • historic concrete assessment and rehabilitation experts collaborated with bridge analysis and design experts; historic preservation agencies; county engineers, technicians and inspectors; community stakeholders; and a contractor experienced in historic concrete repair. References 1. Enser, Dan, Arne P. Johnson, John S. Lawler, and Paul Backer. 2017. "Franklin Avenue Bridge." ASPIRE Winter 2017: 24-27. 2. Johnson, Arne P., John S. Lawler, Dan Enser, Travis Konda, and Paul Backer. 2017. "The Franklin Avenue Bridge Part 1: History, Investigation, and Rehabilitation." Concrete International 39(6): 33–42. 3. Enser, Dan, Mario Grenville Ratnaraj, Arne P. Johnson, John S. Lawler, and Paul Backer. 2017. "The Franklin Avenue Bridge Part 2: Analysis, Design, and Accelerated Bridge Construction." Concrete International 39(8): 29–36. _____________ Arne P. Johnson, principal, was Wiss, Janney, Elstner Associates' project manager for this project, and he was assisted by John S. Lawler, associate principal at Wiss, Janney, Elstner Associates, both in Northbrook, Ill. Dan Enser is a project manager with HNTB in Golden Valley, Minn. Paul Backer is a senior construction engineer with Hennepin County Transportation Department. of deck expansion joints from 15 to 6, with none of the 6 joints located above a pier. This design reduces future leakage potential, which is expected to extend the life of the vulnerable historic concrete. Concrete surface repairs were specified and detailed for all locations where delaminations and spalls were present. The specifications demanded high-quality concrete repair techniques, including perimeter saw cutting, removal to sound concrete using light chipping hammers, substrate preparation via sandblasting, sandblast cleaning and coating of exposed reinforcement, and anchorage using epoxy- grouted bars. The specifications were designed to allow the contractor to choose form-and-pour, form-and-pump, or shotcrete methods with either prepackaged or ready- mixed concrete for each type of repair. The contractor chose prepackaged dry-mix shotcrete for most repairs. In portions of the bridge most visible to the public, the new concrete repairs were specified with a board-form finish to match the original surface texture. The new surface-coating and concrete-repair materials were colored to a light-buff Cutaway view of arch rib showing Melan truss reinforcement and typical con- crete repairs. Figure: WJE. A – epoxy-grouted dowels for anchorage; B – saw cuts at repair perimeter; C – tooled joint with sealant; D – clean and coat existing steel; E – crack-control reinforcement; F – properly prepared, sound concrete substrate; G – intermittent slots and wire connections to existing steel; H – continuous zinc anode in sawcut slot; J – Melan truss reinforcement; K – typical surface repairs; L – grout and seal crack

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