Sept. 8, 2018 — Construction on the Siuslaw River Bridge Cathodic Protection Project enters its final stage on Monday, Sept. 10, with a projected completion time of late October or early November.
Finishing months earlier than initially expected, final work done on the bridge will include replacing railing, extending sidewalk ramps and touching up the cathodic coating.
During this time, the speed limit around the site will be temporarily reduced for worker safety until construction is fully completed.
Beginning in spring of 2015, the protection project has included other improvements such as concrete repair and seismic upgrades.
Perhaps most evident among improvements has been its brighter coating, called cathodic protection. More than just a facelift, cathodic protection is a technique used to control corrosion and thus extend the life of bridges. Coastal bridges, especially, are exposed to high levels of salt, which can find its way through concrete and come in contact with the reinforced steel at its core. The resulting corrosion expands in the form of rust, forcing the concrete to crack and eventually break away, or spall.
Cathodic protection on the Siuslaw River Bridge uses zinc as an anode. When a low voltage direct current is run through the system, the reinforced steel can better resist the salt. The zinc acts as a sacrificial barrier.
“It’s officially designed to increase bridge life by about 20 years,” said Ray Bottenberg, Oregon Department of Transportation (ODOT) Bridge Preservation Engineering Manager.
The Siuslaw River Bridge, completed in 1936, was constructed without the benefit of modern corrosion-fighting techniques. Only now has significant attention been paid to such matters.
Regardless, Bottenberg said the bridge has been resistant to corrosion despite its harsh coastal environment.
“The amount of corrosion that’s happened is a relatively low percentage compared to many of the other bridges we’ve done,” he said.
As part of the concrete repair process, workers hammer-sound the bridge, listening for dead spots where spalling might occur. After a professional assessment, compromised sections are replaced with new concrete in a spot-removal process.
As construction work paused this summer, cracks on the bridge’s south end substructure were brought to the attention of the Siuslaw News by a Florence resident. Upon site inspection of the cracks, however, ODOT said there was no need for concern.
When the bridge’s old finishing was sand-blasted away to prepare for the cathodic coating, only then the cracks became visible.
“On any cracks that we had, they would crack-inject with epoxy to seal it up,” said Shane Prohaska, ODOT Region 2 Assistant Project Manager.
In some cases, cracks would not even take the epoxy, pointing to them being merely surficial.
“It’s nothing we’re seeing as a structural issue,” said Prohaska, “but it’s something we’re always looking at on these projects, too.”
Pictures of the cracks were also passed on to Bottenberg for review.
“None of the things in those pictures is that out of place for cathodic protection,” he said, confirming that the cracks are mostly surficial and not alarming.
Even so, Bottenberg has requested more pictures over time to be certain the cracks aren’t growing.
“We take this seriously,” he said, “but we don’t expect to find a problem.”
The Siuslaw River Bridge has also received its first seismic upgrade. Classified as a Phase I retrofit, the upgrade is designed to keep spans from separating.
“The Phase I seismic retrofit is sized with the intent to prevent collapse for any known earthquake, but not to prevent significant damage,” said Bottenberg.
Galvanized steel cable restrainers on the north and south end are sized to keep the parts of the bridge that are not structurally continuous from separating longitudinally. Shear blocks are also added to keep the girders from moving sideways if the bridge should rock.
With these seismic upgrades, “the bridge can handle a reasonable amount of movement,” said Bottenberg.
The bridge’s railing are also in the process of being replaced. These so-called “stealth rails” meet modern standards and provide functional reinforcement. Keeping to bridge engineer Conde McCullough’s original recognizable design, the rails are embedded with structural steel.
“It’s much more than purely aesthetic,” said ODOT Public Information Officer Angela Beers Seydel. “It’s safer not only for the folks walking along the bridge because it’s higher … but it’s structurally more sound for cars that might hit it.”
Lastly, pedestrian access and sidewalk improvements will consist of ramps and easier approaches to the bridge’s sidewalks on both ends when construction is completed.
Final cost estimates for the project are roughly $17.5 million, with about 90 percent funded federally and the rest by the state.
Future ODOT bridge projects are also planned in the area.
“We’re working our way up and down the coast,” said Beers Seydel. “In the next two and a half years, we’re actually getting ready to kick off six more bridges.”
The projects will include a cathodic protection for the Siltcoos River Bridge in 2020.