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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Page 40 of 59

ASPIRE Winter 2018 | 39 The assessments identified widespread concrete deterioration in the original concrete piers, abutments, and arch ribs to a depths as great as 22 in. below the surface, as well as longitudinal cracking along the top and bottom surfaces of the arch ribs (generally aligned with the upturned legs of the embedded steel angles). Testing showed that the causes of the deterioration were primarily chloride-related corrosion of the embedded trusses and conventional reinforcement, long-term exposure to moisture, and freezing-and-thawing cycles. The deterioration in the various bridge elements was largely determined by their exposure to chloride-laden water from deicing salts leaking through expansion joints or by drainage of water onto the concrete surfaces. For example, the deck soffit, cap beams, and some of the spandrel columns located below expansion joints exhibited widespread and sometimes advanced delamination, spalling, and corrosion of embedded reinforcement due to chloride contamination of the concrete; in contrast, elements away from deck joints were in much better condition. High levels of chloride in the deck had also begun to produce corrosion-related damage. Rehabilitation Design and Details The investigation showed that the bridge was generally competent to support vehicle loading. However, deterioration in many of the bridge elements, particularly those located near expansion joints, along with a refined structural analysis and load rating, traffic study, historic property evaluation, and life-cycle cost analysis, prompted the following selective rehabilitation: • complete removal and reconstruction of the deck and cap beams, with a traffic configuration of two central vehicle lanes flanked by barrier-separated pedestrian and bicycle lanes along the bridge length, and a wider four-lane roadway on the east end to transition into a challenging five-legged intersection just off the bridge; • rehabilitation of the original historic concrete (piers, abutments, and arches) using historically sensitive, durable concrete repair methods supplemented with a water-resistant concrete coating and targeted corrosion mitigation along the arch rib corners; and • restoration of historic features, including historic cap beams with scrolled ends, exterior ornamental barriers, light fixtures, deck fascia entablature, and re-created observation bays over the river piers. The guiding principle behind the repair design was to detail the repairs in ways that would address the root deterioration mechanisms identified while recognizing the historic sensitivity of the structure. Based on a structural analysis of thermal effects, the new deck design reduced the number Close-up view of same pier showing loss of con- crete cover at pier corner. Photo: WJE. Concrete deterioration and reinforcement corrosion below deck expansion joints. Photo: WJE. Applying board-form finish to dry-method shotcrete repair on the underside of an arch rib. Photo: HNTB. Northwest Concrete Bridge Experts • Design • Inspection • Seismic Retrofit • Rehabilitation • Accelerated Bridge Construction SEE US IN ACTION: w w w.OBEC .com

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