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Sellwood Bridge project continues, with 'strength tests'

by: DAVID F. ASHTON - These two east-side approach bents are the last to be constructed on the Sellwood side until the bridge nears completion, in 2015.Rising columns and the massive east side abutment are visible signs of progress, as the new Sellwood Bridge is built.

But, unseen to most is the behind-the-scenes testing that takes place on every batch of concrete delivered to the construction site.

An employee of KE & Associates, Inc., a quality assurance subcontractor based in Tigard, was at the construction site when THE BEE recently visited.

We learned that each batch of concrete that arrives is given a “concrete slump test” to ensure uniformity with batches of similar concrete under field conditions, by checking the workability and consistency of the fresh load.

The inspector places a tall cone on a leveled board, and fills it with concrete. How much the concrete spreads, or if it slumps over to one side, indicates the nature of the concrete. If the sample fails the test, the entire batch of concrete may be rejected for falling outside the design specifications.

Also, the quality control worker pours some concrete into cylinders, 6 inches in diameter and 12 inches in height. These cylinders are cured for 28 days and tested by compression – squeezing them under high pressure – until it they are crushed. The “compressive strength” provides engineers a measure of quality for that batch of concrete.

Mike Pullen, Multnomah County’s spokesperson for the Sellwood Bridge project observed the testing process with us and said, “This kind of testing and documentation helps us make sure we’re building high-quality project.”

Pullen pointed out that the last of the cross-beams atop a “bent” to support the east approach was being poured during our November 7 visit. “This is the last one we’ll pour on this side for two years.”

The west side of the project has been the focus of much of the work, Pullen said. “Contractors are working on the retaining walls. They are widening part of Highway 43 to get it prepared to close the ‘slip lane’ that goes under Highway 43 and underneath the bridge.” By now, that lane should be closed for good.

The next major construction work on the east side will be building and sinking box caissons, which will be on top of the foundation piers that will eventually support the arch spans that touch down on the main river pier, Pullen said.