Slight changes introduced to pontoon construction process


Massive concrete pontoons built in Aberdeen for the Highway 520 Bridge showed minor leaks as they made the trip from Aberdeen to Lake Washington earlier this month. But officials with the state Department of Transportation say the leaks were easily repaired.

Contractor Kiewit-General is now in full swing of its second cycle of pontoons at the construction site at the mouth of the Chehalis River. This time, the contractor is using recommendations from an expert review panel to improve the way the pontoons are constructed to reduce the number of cracks.

“We’re completely confident that the pontoons we floated to Lake Washington in July are safe and structurally sound,” said Julie Meredith, SR 520 program director, said in a press release. “They’ll last 75 years or longer and so will all the rest of the pontoons we build.”

To eliminate cracks and chipped concrete, experts recommended decoupling the end walls from interior walls to reduce cracking, according to the state agency. There’s also been changes in the way post-tensioning is done when construction crews tighten metal strands within the concrete for additional strength.

“We believe these improvements will eliminate spalling (flaking) and reduce cracking in the next construction cycles,” said Jeff Carpenter, WSDOT state construction engineer, said in a press release.