Friday, January 31, 2014

Pontoon repairs successfully moving forward

Crews continue making progress on design modifications to four Cycle 1 pontoons built in Aberdeen. Design modifications on two pontoons were completed in dry docks last summer. The other two pontoons are being repaired on Lake Washington using a coffer cell to create a dry work environment.

The design modification work involves epoxy injections into pontoon cracks greater than .006 inches, crystalline waterproofing smaller cracks, transverse post-tensioning, and application of carbon-fiber wrap.

Last week crews completed repairs on the first of four ends of the remaining two massive, concrete pontoons that will help support the new SR 520 floating bridge. From inside a nearly 660-ton coffer cell attached to Pontoon V, construction workers completed crack repairs on one end of the 360-foot-long structure. After placing the coffer cell on the pontoon’s other end, crews began the next round of repairs on Thursday, Jan. 30.

While crews repair these cracks, they also take the opportunity to repair other construction anomalies previously identified during dive inspections of the pontoons. Some of these involve sections where steel rebar is exposed to water. To conduct these repairs, crews remove the concrete to expose the rebar and clean the steel with brushes and sandblasting. Workers then prepare the area for sealing by applying a special bonding agent to the cleaned rebar and surrounding concrete, followed by layers of a high-strength grout, and finally two to four layers of carbon-fiber wrap to help ensure a waterproof repair.

The procedures were developed by an outside expert and reviewed by WSDOT to ensure that the new, six-lane floating bridge lasts at least 75 years with standard maintenance along the way. We anticipate that the design modifications on these two remaining pontoons on Lake Washington will be complete this spring.

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