Construction crews along Georgia's Interstate 285 have done more than reconstruct the roadway's shoulders—they have made history.
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.HUMBLE BEGINNINGS
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.