Week of June 5, 2006

County smoothing out the process for sidewalks and streets

Our late spring rain may be putting a damper on the schedule, but crews from the King County Road Services Division are excited about recent innovations that are smoothing out the process for laying asphalt and cement.

If the weather permits, county crews will begin the annual street repaving program this week in South King County, while another crew is waiting for some sunshine to pour curbs and gutters on a first-of-its-kind project near Woodinville. Both projects involve new techniques and materials that should save time and money.

This summer, the county will be repaving approximately 63 center lane miles of roadway mostly in unincorporated King County and also in a few contract cities. The total cost for 2006 paving is $6.6 million. The first road on the overlay schedule is Cedar Grove Road south of Issaquah for the South County program. The North County program will start about a week later in Shoreline and work its way clockwise through the north and east parts of the county. To track the work of the paving crews, visit the overlay project webpage.

Saving money couldn’t come at a better time for the county paving program. As petroleum prices soar, so do the cost of related products such as asphalt. This year, the county will be paying almost $10 a ton more for asphalt than in 2005. A very costly price hike when you consider that the county will be purchasing a total of 124,000 tons of asphalt this summer just for the overlay program.

“Petroleum-based products like asphalt have gone sky high, so we’re looking at ways to be as efficient as possible with our available dollars,” said Rick Brater, Engineering Services Section manager. “We are using monies saved through efficiencies to do the most we can to preserve the road systems in the unincorporated areas.”

Last summer, the Roads Division staff implemented two new items to the paving program to allow for more efficient paving and a more durable pavement surface. Both will return again this year based on last year’s success. One involves placing a material transfer device between the paving machine and the large trucks carrying the asphalt. The transfer device holds more than a truckload of asphalt and continuously mixes the hot asphalt to allow for non-stop paving that speeds up the process and creates a new surface with fewer lumps and bumps caused by short-term stops and starts.

The other innovation was buying a different type of asphalt mix called “Super Pave,” which is longer lasting requiring less frequent repaving on the same stretch of road. Brater said the division is also looking at varying the thickness of the overlay on roads that don’t have heavy truck travel as another way to make the asphalt go further.

Most of the resurfacing is done in short stretches, with priority given to key arterials and busy residential streets. Laying down a new coat of asphalt not only improves driving surfaces, but it also reduces maintenance costs and extends the life of the roads.

In another innovative application, the Roads Division is also exploring how it can use slag cement, a by-product of steel production, in some of its projects – particularly sidewalks, curbs and gutters. Mixed in with other materials to form fresh concrete, it saves on the cost of brand new cement and reuses materials that were once sent straight to the landfill.

It is being used for the first time by the county on a walkway project near Hollywood Hills Elementary east of Woodinville. The slag cement will be used on the curb and gutter next to the roadway, and on the back curb next to a hillside.

Slag is a by-product generated in the blast furnaces used to produce steel. Once a waste material, slag is becoming increasingly useful as a substitute for up to 50 percent of the portland cement used to make concrete. This substitution can reduce greenhouse gas emissions because slag is a by-product of the energy already used to produce steel. The division’s Roads Material lab conducted a full battery of tests on different slag blends and applications to determine their suitability and usability on King County road and infrastructure projects.

Roads staff wanted to experiment with the slag cement first on a small scale project like the walkway out at Hollywood Hills to see how the finishing and curing works. The report from the lab testing was that it seems to take a little longer to harden, but takes less work to get a smooth finish and ends up stronger as it cures. It also has a lighter color than regular cement.

Now that the testing is done, the crews are ready to try it out in the field – if the rain ever stops long enough.

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