Today's gravel, tomorrow's roads


The sound of gravel crunching under tires and bouncing off the undersides of cars has become common this summer, particularly in the areas just outside the city limits.

Day after day, county road crews are dumping truckloads of gravel on stretches of roadway such as Abbott Road, Sturm and Bryant avenues and more -- a whole lot more.

Apparently the tons of gravel being dumped on the roads is supposed to improve them. Seriously?

What's up with that? How does dumping a bunch of little rocks on a road do anything but, well, make a dusty, loud mess?

I've been pondering that for a few weeks as I crunch my way through the gravel around the edges of Walla Walla.

I gave Randy Glaeser, the county's public works director, a call to find out just how all this gravel is improving the roads.

"The rocks get pushed in (to the road)," Glaeser said matter-of-factly. "The more traffic the better able you are to pound those rocks in ... You do it when it is hot so it stays soft."

How, I asked, do all those little rocks get pushed into the road? All I see is gravel flying everywhere.

Well, he said, it's a long process. The rocks don't become part of the road overnight -- or even in a few days.

The process -- known as chip sealing -- actually takes about a year to complete, Glaeser said.

It starts the previous year when road crews start preparing the surface by fixing cracks and potholes.

Two different crews start work in the fall. One crew fixes the cracks while the other takes out some of the potholes and imperfections.

Fixing the cracks starts when compressed air is used to blow out rocks and debris. Then the cracks are filled with hot, liquid asphalt. This leaves the roads with a lot of black stripes in different directions -- think Frankenstein's monster's neck.

This is followed by "preleveling." Although, depending on the work schedule, the tasks can be done in the opposite order without causing problems.

The preleveling crew starts by filling in potholes and fixing the shoulders. Then a thin layer of hot-mix asphalt is poured and "feathered" over the entire roadway.

It is best to give this new asphalt time -- usually over the winter -- so it can cure and strengthen, Glaeser said. But if there isn't enough time this process can be done in the spring just a few months before the chip seal is applied.

"The goal there is to restore a smoother surface to the road before we apply the chip seal," Glaeser said. "If we did not do that all those irregularities in the road (would remain after the chip seal)."

In the summer, when the weather starts to get hot, crews get to work on the actual chip seal.

Emulsified asphalt -- essentially asphalt mixed with water creating a substance with the consistency of oil -- is spread over the roadway.

Then gravel is put over the entire surface. In urban areas smaller rocks, about a half-inch in size, are used. Slightly larger gravel is used in rural areas.

A roller then comes along and smashes the gravel into the road as the emulsified asphalt, which is often called road oil, slowly begins to harden as the water evaporates.

The hot weather speeds the evaporation but keeps the oil soft so the rocks stick.

Over the next week or so traffic travels over the gravel, pounding it into the road.

"The more traffic the better to pound those rocks into the oil. We do it when it is hot so it stays soft and really gets jammed in," Glaeser said.

When the week is up a crew comes back with a sweeper and cleans the road of rocks. Glaeser said a small percentage of rocks, perhaps about 10 percent, are left after being pounded by the cars and trucks. In the urban areas just outside the city limits the rocks are collected and recycled. Out in the rural areas, the rocks are swept to the side to help build up the shoulder.

"The oil and rock is to seal, preserve and protect the structural surface of the road. The chip-sealing process essentially hardens the road, reducing the chance water can get under the roadway," Glaeser said.

Chip sealing should be done every seven to 10 years, Glaeser said. The county is on a nine-year road preservation cycle. Every county road is chip sealed during that period. The county spends about $1.5 million every year to chip seal about 60 miles of road.

This year the 60 miles being chip sealed are in the county's urban area on the edge of the city limits.

In addition, the city of Walla Walla has contracted with the county to do some city streets, such as Division Street from Bryant Avenue to Alder Street and Alder Street from Wilbur Avenue to Tausick Way. College Place is also contracting with the county to do some of its roads as is the Port of Walla Walla, which is responsible for the roads at the airport.

Chip sealing costs about one-third of what it costs to do an asphalt overlay like the one recently done on U.S. Highway 12 where it runs through Walla Walla.

The current weather -- consistently in 80s and 90s -- has been perfect for the chip seal process. Glaeser said it will be even better if the warm weather lasts through September. This will allow for a nice slow setup of the road oil and rock mix.

"The interesting thing is that as the rocks get pounded in they turn black as nature does its thing," he said, adding that the length of time before the road becomes smooth depends on the amount of traffic. It usually takes less than a year.

"This time next year you will not even realize we chip sealed it."

Rick Eskil can be reached at or 509-526-8309. If you, too, wonder what's up with that, let Eskil know about it and maybe he can find out.


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