When the new Interstate 5 Willamette River Bridge in Eugene-Springfield, Ore., is open to traffic in 2013, it will be a fitting high point to the Oregon Department of Transportation’s (ODOT) OTIA III State Bridge Delivery Program, a $1.3 billion program to address 365 aging bridges statewide, begun in 2003.

The $204 million bridge is an elegant solution to a behemoth construction challenge. The southbound and northbound structures will be approximately 1800 feet long, with 9 and 10 approach spans, respectively, to traverse a railroad, a 4-lane local highway, and 2 parks in addition to the river. The deck-arch design places only a single pier in the water, leaving plenty of room for salmon migration upstream and river recreation downstream.

Most impressive of all, the southbound bridge alone is made up of 17 specialized concrete mixes, customized for each component—drilled shafts, columns, arches, and deck—out of 27 created as options.

The recently completed southbound bridge has 20 shafts, 6 of which extend below the riverbed. They posed an environmental challenge for Knife River, Portland, Ore., the project’s concrete subcontractor. Even though the shafts were surrounded by rock, there was a chance that the concrete could leak into the river during placement. To protect the riparian habitat, Knife River created a mix that included a special anti-washout additive to hold the concrete together.

According to Randy Kessler, concrete quality coordinator in the construction-structures section of the ODOT Materials Lab, the use of an anti-washout additive is unusual. “I can only think of a few other projects where it has been used,” says Kessler. “Even though the concrete was contained, the anti-washout additive was an extra measure that protected the river.”