Contractors need to demolish and rebuild the top of a future Highway 520 column in Seattle, where fresh concrete broke away from some corners, exposing steel rebar.

This structure, called a pier cap, rises above a temporarily closed part of the Interstate 5 express lanes where the Washington State Department of Transportation is adding a connecting ramp and bus-carpool lane from Highway 520 onto I-5, extending south to the Mercer Street interchange.

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WSDOT communications staff highlighted the column when it was built in July, as a conspicuous sign of progress. But when a wooden work platform was removed in October, the team discovered concrete flaws, said spokesperson Tony Black. The public can see it too from north Capitol Hill, or driving on the northbound I-5 mainline.

Walsh Construction, which is building the lane under a $68 million contract, is working with WSDOT to fix the ramp support at the company’s expense, Black said. Crews will rebuild the top crossbeam, and perhaps the top part of the column, in the next two to three months, he said.

The work isn’t expected to delay a grand opening of the new high-occupancy lane in early 2024, he said.

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Walsh’s regional office in Seattle declined to comment Tuesday and referred questions to WSDOT.

The adjacent column, covered by orange tarps, is in good condition, and the company has changed its concrete mixture, according to Black.

New concrete should fully cover the rebar, with minimal cracking throughout the pier cap, to bind the structure and guard internal steel against corrosion. WSDOT is still working to determine root causes of the concrete loss, said Black. “We certainly don’t like how it looks,” he said.