Road breaks new ground: RCC used to replace shoulders in Atlanta.
Georgia DOT (GDOT) used roller-compacted concrete (RCC) instead of asphalt or portland-cement concrete (PCC) to replace nearly 35 lane miles of shoulder along both directions of the Atlanta Perimeter/Beltway, marking the first time RCC has been used in this fashion in the southeast.
"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. "RCC is being looked at as a more durable solution."
RCC contains the same ingredients as conventional concrete but has a very low water-to-cement ratio, creating a zero-slump mixture. The RCC is placed with conventional or high-density asphalt paving equipment, then compacted with 10- to 12-ton steel-drum and pneumatic-tire rollers. RCC typically is constructed without joints. It does not require forms or finishing and contains no dowels or steel reinforcing. Initial costs are comparable to asphalt or PCC, but significant savings are expected down the line.
Before the I-285 shoulders were replaced, potholes at the edge of the PCC pavement were common, said James M. "Mickey" McGee, district construction engineer for GDOT. With the application of the new RCC, "we're hoping they'll be virtually maintenance-free," he said.
Unlike asphalt, which is typically placed in several lifts of 2 or 3 inches each, RCC can be placed in one lift--usually between 5 and 10 inches--quickly delivering a finished pavement. Compacting the mix shortly after placement results in early strength, which translates into a quick return to traffic.
The portion of I-285 that was involved--part of a $20.1 million project that also includes PCC rehab, joint sealing, guardrail upgrades, and striping--is intersected by Interstate 20. South of I-20, crews milled out the existing shoulders and replaced the pavement with 6 inches of RCC. North of I-20, 16 inches of pavement were removed and replaced with 8 inches of graded aggregate topped with 8 inches of RCC, anticipating possible future use of the shoulder as a traffic lane. Pittman Construction of Conyers, Ga., served as the general contractor, and A.G. Peltz of Birmingham, Ala., was the RCC contractor.
Once crews overcame the learning curve and the expected snags associated with using a new material and technique, the job went smoothly, said McGee. RCC's rough texture differs greatly from smooth PCC pavement, requiring numerous visual inspections at the outset. Once the job was underway, workers managed to complete 1 1/2 to 2 miles of the 10-foot-wide shoulder each weekend.
Crews finished the RCC portion of the project in September 2005, so it is still too early to tell if the application outperforms its counterpart as expected, said Bryant Poole, District 7 engineer with GDOT, but state crews are regularly monitoring it. "This is on one of the most heavily traveled truck routes, so its durability should show itself very quickly," he said.
Though RCC has been around for years, its use in highway reconstruction is relatively new. The practice originated in the late 1970s in the Canadian timber industry. The industry deemed RCC a good candidate for log-sorting yards because it was quick and easy to place, and it provided the durability necessary to hold up under heavy equipment and loads. RCC also has been used around the world to construct gravity dams.
More recently, RCC pavement has been used in parking lots, auto manufacturing plants, intermodal ports, military bases, and warehouses. The Tennessee Valley Authority used 8000 cubic yards of RCC as structural fill to support the turbine building slab at the Bellefonte Nuclear Power Plant in Scotts-boro, Ala. In 1980, the Ocoee No. 2 Dam in Ocoee, Tenn., was home to 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 been pitching RCC as a product that is appropriate for smaller projects, and for the large-scale jobs on which it has historically been used. Industrial park roads, small-scale site paving, and residential projects all are 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 said.
MEETING WITH SUCCESS
The association sold GDOT on RCC when it took some of its 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 outstanding condition of the roads after more than a decade of continual use convinced the DOT 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 Poole, 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 using the latest technology, safety devices, and roadway materials in our efforts to provide the safest and best roads in the nation."
RCC's use on the shoulders of high-traffic roadways has passed muster. GDOT recently OK'd plans to place RCC on the shoulders of a 6 1/2-mile-long stretch of State Route 6 in Cobb and Douglas counties. Here, crews will place RCC on the 6 1/2-foot-wide shoulders and median of the five-lane roadway. The pavement sits on a heavily traveled route and is adjacent to a railroad transfer terminal where numerous tractor trailers will haul heavy loads across the surfaces.
According to Poole, GDOT also has used its own forces to place RCC on small-scale jobs along interstate ramps and has been pleased with its performance. The department also is considering using RCC on several park-and-ride lots, although none are yet confirmed.
--Bacon is a Seattle-based business writer.
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|Title Annotation:||Roadway construction & maintenance|
|Date:||Jan 1, 2006|
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