Sellwood Bridge: Patching the patches
While a Citizen Community Task Force ponders problems of rebuilding or replacement (see separate article), Multnomah County road crews maintain an ailing and aging bridge over the Willamette River.
Drivers crossing the Sellwood Bridge can see -- and feel -- its poor condition. But the good news, according to Multnomah County officials, is that the bridge really is still safe to use.
With the 80-year-old bridge closed for repairs on September 10th, we hiked the span to observe its condition, and to watch a Multnomah County road crew prepare its southernmost Willamette River span for winter.
We see small cracks, missing chunks of cement railing, expansion joints bulging, and workers patching the road surface, and we find ourselves wondering, 'Is this bridge safe?'
'The condition of the bridge is poor, but safe,' is how the county's Michael Pullen puts it. He adds the caveat: That is, safe for the posted loads under 10 tons.'
Other bridges are typically scheduled for inspections once every two years, Pullen says; 'But, because the Sellwood Bridge is in poor condition, we inspect it quarterly. [This time] they didn't find any more significant damage. Since we've gotten the heavy vehicles off the bridge, it has stabilized, and it is not deteriorating further.'
Patching the patches
We ask a bridge worker about the patches we see. He says, 'Because the bridge is relatively narrow, it focuses vehicle tires to hit the same relatively small edges of the pavement near the expansion joints. This wears down the pavement; and opens it to potential water damage.'
At a glance, it looks like workers are merely smearing the worn pavement with asphalt. But, we discover, the crew carefully prepares the area, and then uses high-tech materials to preserve the roadway.
First, the crew breaks away loose gravel and sweeps up debris. The area to be treated is lightly sandblasted to assure maximum adhesion of the patch.
Then, workers apply a thin layer of 'neet', the same kind of two-part epoxy used in the patch mix. They wait 15 minutes for the neet to set up. Finally, workers mix small stones - called aggregate - with a two-part epoxy compound which then forms the binding base.
'The epoxy must be mixed precisely, and mixed for exactly five minutes,' a worker tells us, 'but the result is a paving material some say is stronger than steel.'
'This should last a couple of more years,' a worker says, 'this bridge gets a lot of traffic.'
The crew also repairs expansion joints and applies a new coating over the steel-plate 'splints' that hold the cracking concrete girders in place at the bridge's west end.
After eight decades of service, word is that this bridge will continue to require a great deal of tender loving care to keep it standing for another decade or two, until it can be rebuilt or replaced.