Roller-Compacted Concrete

New Application Used Along Shoulders of Atlanta Perimeter

by Sheila Bacon

Construction crews along Atlanta's Interstate 285 are doing more than reconstructing the roadway's shoulders; they're making history.

Georgia Department of Transportation's use of roller-compacted concrete instead of asphalt or standard portland cement concrete in the replacement of nearly 35 lane mi. of shoulder along the Atlanta Perimeter/Beltway marks the first time the material has been used on a highway reconstruction job.

"In some areas where asphalt shoulders are used, they're failing," said Matthew Singel, specialty pavements engineer for the Southeast Cement Association of Lawrenceville, Ga. "So RCC is being considered (as an alternative)."

The $20.1 million contract is being handled by general contractor Pittman Construction of Conyers, Ga. A.G. Peltz of Birmingham, Ala., is the RCC contractor. The RCC rehab is just part of the overall contract, which also includes PCC rehab, joint sealing, guardrail upgrades and striping.

The I-285 shoulder repaving project is expected to be complete in September.

RCC contains the same ingredients as conventional concrete but with a low water-cement ratio, creating a zero-slump mixture.

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"By its nature, it looks like a damp aggregate rather than a concrete product," Singel said.

The mixture is placed with conventional or high-density asphalt paving equipment, then compacted with 10- to 12-ton steel drum and pneumatic tire rollers. Typically, RCC is constructed without joints. It needs neither forms nor finishing, nor does it contain dowels or steel reinforcing.

Initial costs are comparable to asphalt or PCC, but significant savings are expected down the line.

"These (existing) shoulders have required a lot of maintenance and they continue to get potholes at the edge of the existing PCC pavement," said James M. "Mickey" McGee, district construction engineer for GDOT. With the application of the new roller-compacted concrete, "we're hoping they'll be virtually maintenance-free."

Whereas asphalt is typically placed in several lifts of 2 or 3 in. each, RCC can be placed in one lift - usually between 5 and 10 in. thick - delivering a finished pavement in quick fashion. Compaction of the mix shortly after it is placed results in early strength, which translates into a quick return to traffic.

Crews along I-285 are completing between 1.5 and 2 mi. of the 10-ft.-wide shoulder each weekend, McGee said.

The portion of I-285 where work is being performed is intersected by Interstate 20. South of I-20, crews are milling out the existing shoulders and replacing the pavement with 6 in. of RCC.

North of I-20, 16-in.-thick sections of existing pavement are being removed and replaced with 8 in. of graded aggregate topped with 8 in. of RCC, anticipating possible future use of the shoulder as a traffic lane.

Roots in Logging

Roller-compacted concrete originated in the late 1970s in the Canadian timber industry. The industry found that the heavy-duty RCC was a good candidate for its sorting yards because it was quick and easy to place and provided the durability necessary to hold up under heavy equipment and loads.

More recently, RCC has been used in auto-manufacturing facilities, intermodal port facilities, military bases and warehouse facilities. The Tennessee Valley Authority used 8,000 cu. yds. of RCC as structural fill to support the turbine-building slab at the Bellefonte Nuclear Power Plant in Scottsboro, Ala.

In 1980, the Ocoee No. 2 Dam in Ocoee, Tenn., was the first use of RCC for overtopping protection. And in 2001, Honda chose RCC for more than 100 acres of pavement for its new car-manufacturing plant in Lincoln, Ala.

The Southeast Cement Association has recently been pitching RCC as a product that is appropriate for smaller projects. Industrial park roads, small-scale site paving and residential projects can all be candidates for RCC, Singel said.

"Though (RCC) has typically been promoted for large-scale projects, we're finding that large projects are not necessary to realize its cost effectiveness," he added. "We've found that these alternative pavements have a place in the market, so we're creating awareness."

The association sold the Georgia DOT on RCC after taking several GDOT decision-makers to General Motors' Saturn manufacturing plant in Spring Hill, Tenn. The facility is the largest RCC pavement project ever built, encompassing 134 acres of plant roads, vehicle storage yards and delivery areas.

The condition of the roads after more than a decade of continual use convinced the GDOT to give the product a try on its I-285 shoulder reconstruction project.

"The durability, useful life, constructability, structural value and ease of maintenance were some of the key reasons why (GDOT) elected to try it," said Bryant Poole, District 7 engineer with GDOT, who viewed RCC project sites in Tennessee before casting his vote to use the durable mix on the I-285 shoulders. "GDOT is always interested in utilizing the latest technology, safety devices and roadway materials."

Though the long-term durability and cost-effectiveness of RCC on the Atlanta Perimeter won't be confirmed for some time, Poole said he is pleased with the product so far. GDOT has used its own forces to place RCC on small-scale jobs along interstate ramps in the past, and the department is continuing to consider RCC as a viable paved shoulder alternate.