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Crews from Farrow Concrete place about 660 cubic yards of concrete to form the first of 17 base slabs in the Washington State Route 520 Pontoon Construction Project casting basin. Local contractor Bayview Redi-Mix provided the mix for the July 8 pour. (Photo courtesy of via Flickr)

Crews in Aberdeen, Wash., on Friday completed part of a $4.65 billion project to revamp part of State Route 520, which includes replacement of a floating bridge over Lake Washington.

The crews made the first concrete pour for a casting basin facility, which will eventually make 33 pontoons for the new bridge. The pontoons – sort of like really big, floating docks – are being made to support the new bridge. They’ll replace the current pontoons, if needed, in case the current ones are damaged in something like a big natural disaster. Some of the pontoons will be as tall as three-story buildings, as wide as two motor homes parked end to end, and as long as a football field. They’ll weigh as much as 11,000 tons each.

Pontoon construction is expected to start this summer and finish by mid 2014.

The casting basin facility  and the pontoons are themselves a $367 million project. The entire SR 520 project – which consists of a revamp of the highway from Seattle to Redmond, Wash. – will cost about $4.65 billion. Only about $2.62 billion of that has been received so far, according to the . WSDOT and contractor Kiewit-General began work in Aberdeen in February.

WSDOT has uploaded a ton of and has put up a project webcam, which you can see .