Watertight pontoons "critical" to construction of SR 520 bridge in Wash.

12/22/2011 | SeattlePI.com

A critical part of building the world's largest floating bridge is making sure that the 33 massive concrete pontoons that will hold up the bridge are crack-free. Getting just the right mix of concrete -- with fly ash and microsilicia -- ensures that they don't crack or take on water once they are in the water. The new $4.6 billion State Route 520 bridge in Washington will also be able to withstand a 1,000-year seismic event and 92 mph winds.

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