Page 22

2014SumShotcreteEMag

Bridge Preservation over the Oregon Inlet A History of Concrete Rehabilitation on North Carolina’s Outer Banks By Martin Emmrich Fig. 1: Herbert C. Bonner Bridge Photo by Smkybear, courtesy of Flickr.com via Wikimedia Commons Athe Atlantic Ocean and separates Bodie concrete mixture designs, and only a minimalepoxy-coated reinforcing steel, no advancedpaint coatings for steel members, no enhancedlong North Carolina’s Outer Banks, theOregon Inlet joins the Pamlico Sound with Island to the north from Pea Island to the south. amount of concrete cover over reinforcing steel. It is traversed by a 2.5 mile (4 km) bridge, the Like many of today’s bridges, it has out-lived Herbert C. Bonner Bridge, which serves as a its intended 30-year lifespan. Over the course lifeline for thousands of residents (Fig. 1). of over 50 years, the bridge has taken a beating, Over 2 million cars cross the bridge annually, including weathering many storms, with- providing islanders access to work, schools, and standing corrosive saltwater and air, enduring health care on the mainland while also providing harsh current, and sustaining numerous boat access for an important part of North Carolina’s crashes. The chloride-laden salt air has taken a annual $19.4 billion tourism industry. With toll on the bridge’s embedded reinforcing steel, landmarks such as the Cape Hatteras Light- creating concrete spalling, and the turbulent house, one-quarter of Dare County’s overall waters of the inlet are constantly shifting the economic impact comes from Outer Banks sand on the ocean floor, undermining the piers tourism alone. that support the bridge. “The concrete is essentially rotting from the The Bridge’s History inside out as salt has found its way to the internal The bridge was built by the North Carolina reinforcing steel causing the steel to corrode,” Department of Transportation (NCDOT) in 1963 said State Bridge Management Engineer Greg for $4.1 million to replace the existing ferry route Perfetti. “We’ve also had problems with scour that could no longer keep up with the growing over the years, where the sand around the piers traffic. It was built without technology and gets washed away” (NCDOT Press Release, methods considered standard practice today—no 9/4/2013). 20 Shotcrete • Summer 2014


2014SumShotcreteEMag
To see the actual publication please follow the link above