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I-5, Northgate Bridge Deck Repair

Schedule: Good The contractor had 25 working days to complete the project. He was able to open all travel lanes to the public in 22 working days. Cost: Mixed Engineer’s estimate: $1,292,460 Contractor’s bid amount: $1,378,852 Anticipated final payment: $1,563,463 The variance between the engineer’s estimate and the anticipated final payment is primarily attributable to an overrun in the planned quantity of polyester concrete used in resurfacing the bridge decks. The original contract plan called for a ¾ inch overlay on the bridge decks but the actual overlays were closer to an inch in depth. While the additional depth of the overlays increased the cost, they will provide a long-term benefit by increasing the life expectancy of the bridge decks. The primary difference between the engineer’s estimate and the contractor’s bid was the estimated cost of the polyester concrete. Both WSDOT and the contractor had limited experience with this type of concrete and the contractor bid a more conservative price to ensure his costs were covered.

WSDOT's contractor, Concrete Barrier Inc., performed a major rehabilitation of three concrete bridge decks in North Seattle beginning last August. During this project, contractor crews improved the roadway surface and prolonged the life of the northbound structures that carry I-5 through the Northgate area and north through Shoreline.

The pavement condition on these bridge decks was very poor with deep wheel ruts and missing pavement. Crews used a polyester-based quickset concrete - yes, a close chemical relative to the material used in 1970s-era leisure suits. The mixture, tested several years ago but never before used on a major urban corridor in Washington state, shortens the cure time from three days to as little as three hours. This allows lane closures to be kept to nighttime and off-peak hours, and as a result greatly reduces traffic disruption.

The bridge deck-resurfacing project improved the quality of the roadway and also preserved the life of the structure supporting the road. This concrete overlay traditionally lasts longer and was foreseen as a 20-year fix for these decks. The more obvious benefit was the improved ride quality of the roadway. A majority of the work was performed at night, to minimize impact to motorists.

Lessons Learned:
The decision to change from the traditional concrete overlay, which would have required much longer, round-the-clock lane closures, to the fast curing polyester concrete was the result of using new technology to mitigate forecasted traffic impacts. The switch in materials and redesign of traffic control plans forced a late start in the 2002 construction season. An earlier start would have allowed the contractor more time to plan, arrange for suppliers, and practice with new material before applying it onto the roadway. The lessons learned in using this new material benefits not only future projects in Washington state, but representatives from Oregon's Department of Transportation came to watch the placement of the overlay. Southbound bridge decks in the same section of I-5 will be resurfaced next year using the same material.

Contact: Brian Nielsen, Project Engineer
Phone: 206-764-6444

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