Wednesday, May 25, 2016

Crews plan to get crackin’ on southbound I-5 in SeaTac, Des Moines

By Tom Pearce

We’re about six weeks out from the start of weekend lane reductions on southbound I-5 in the Tukwila, SeaTac and Des Moines areas. Southbound I-5 will be reduced to two lanes from Friday nights through Monday mornings the weekends of July 8-11, 15-18 and 22-25, and Aug. 12-15 and 19-22.

A concrete cracking machine used on one of our projects in Skagit County in 2011.
The work is part of the southbound I-5 South 320th Street to Duwamish River Bridge concrete pavement rehab project. For the past couple of months the crews have been working nights, replacing concrete panels and grinding ruts and cracks over this 13-mile section of freeway. The work is scheduled to continue until fall 2017.

Weekend-long lane reductions
Replacing 235 panels scattered along the 13-mile section of I-5 and grinding the concrete with nighttime lane closures works for most of this project. But a 2.7-mile section in the SeaTac-Des Moines area needs more than that, so during three weekends in July we’re repaving it with asphalt.

Our contractor will use the first two weekends to replace 96 concrete panels with asphalt to create a smooth transition area. On the third weekend they’ll repave the rest using a process called crack, seat and overlay. What’s that? It’s pretty much what it sounds like.

A crew member helps remove a concrete panel on a different project.
Our contractor will use a large concrete cracking machine with a heavy blade that drops like a guillotine, cracking the concrete panels into smaller pieces. Then a 35-ton compactor rolls over the cracked concrete to “seat” it firmly. Finally, we will overlay this with asphalt, creating a new, long-lasting smooth driving surface.

I sense some questions about this:
Why do you have to reduce the freeway to two lanes on weekends to do this?
Working entire weekends without interruption gets the project done much more quickly.

Why do you have to crack the concrete to put asphalt on top of it?
You’d think a 12-foot by 15-foot, nearly foot-thick slab of concrete won’t move. Actually, they do move, especially after decades of cars and large trucks rolling over them. If we put asphalt on top of the panels without cracking and seating them first, those panels would continue to move, which would crack the asphalt. Cracking and seating the concrete provides a much more stable base.

Why are you only doing this on a 2.7-mile section of the freeway?
The 2.7-mile section between SeaTac and Des Moines has more than 500 broken panels. We could replace each of these individually, but that would take years. Doing crack, seat and overlay repairs this section in a few weeks.

What are you doing during the two weekends of lane reductions in August?
Our contractor crews will replace four expansion joints on the southbound I-5 Duwamish River Bridge. They’ll also do drainage repair and panel replacement near the bridge during one of those weekends.

There are a lot of activities every weekend. Don’t you look at those when you schedule weekend work?
Yes, we consider events very carefully. We’ll discuss that more in our next blog about this project.