Rolling
With Some Concrete Changes

by Scott Judy

After an initial recent trial of roller-compacted concrete on the shoulders of a section of Interstate 285 in Atlanta, the Georgia Department of Transportation is looking to expand its use of the paving material, including possibly on mainline pavements.

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"We've had good results, so that gives us an opportunity to see if it'll work in a different application," said Georgene Geary, state materials and research engineer with the Georgia DOT.

The transportation agency first used RCC for approximately 35 lane mi. of shoulders on Interstate 285 in 2005. Contractor A.G. Peltz of Birmingham, Ala., placed the concrete material for the 10-ft.-wide shoulders using an asphalt paver and several 10- to 12-ton steel drum and pneumatic tire rollers.

GDOT was looking for a cost-effective option to its previous use of asphalt for interstate shoulders. Geary said the RCC alternative came in at a comparable price to asphalt.

RCC contains the same ingredients as conventional concrete but has a low water-cement ratio, creating a zero-slump mixture. Additionally, RCC can usually be placed with just one lift-of about 8 to 10 in. thick-whereas asphalt is typically placed in several lifts of 2 to 3 in. each.

Essentially, RCC provides similar strength and durability characteristics as conventional concrete, but at a lower price and increased ease of application, said Allan Childers, Georgia state director for the American Concrete Pavement Association.

"It's just a different way of putting it down," said Childers, who previously worked for the Georgia DOT for more than 30 years. "They've been pleased with it."

Increased Applications

The initial results from that I-285 project have GDOT working on another, second project using RCC on State Route 6 in Cobb and Douglas counties, as well as a planned upcoming shoulder project on I-985, both near Atlanta.

On the S.R. 6 project, GDOT is reconstructing a five-lane highway that includes a four-lane travelway and a center turning lane, plus shoulders. The mainline pavement will consist of conventional concrete pavement, while the center lane and shoulders are being constructed with RCC.

Though there are no smoothness or ride specifications for the center-lane section, Geary said the department is interested in discovery how smooth an RCC pavement can become.

For example, Geary said the agency is "batting around the idea" of using RCC as a mainline pavement on low-volume roads. While the typical RCC mix is not as smooth as a conventional concrete mix, Geary was optimistic that the industry could achieve better ride characteristics without altering the material makeup.

"It has to do with construction techniques and the contractors getting more comfortable with the technique," she said. "Over time, we're going to find those little tricks in RCC that will build smoother roads."

In addition to road projects, GDOT also is starting to use the material for park-and-ride lots as well as for some of its own maintenance facility lots.