Virginia's Interstate 81 runs for 325 miles along the state's northwest spine from West Virginia to Tennessee. The Virginia Department of Transportation (VDOT) is rehabilitating a 3.7-mile, two-lane section of southbound Interstate 81 in Augusta County between exits 217 and 213. It's using a specific combination of three reconstruction processes to recycle and reuse existing pavement material for the first time on this type of a project in the United States.
The processes are cold in-place recycling, cold central-plant recycling and full-depth reclamation. "This project will save VDOT millions of dollars by reusing the resources at hand, rather than buying and transporting tons of new material to the site and disposing of the old," says Dr. Brian Diefenderfer, a Virginia Center for Transportation Innovation and Research (VCTIR) pavement researcher.
The contract for the in-place pavement recycling project was $7.64 million and was awarded to Lanford Brothers Co., a specialty contractor located in Roanoke, VA.
The project was awarded in December 2010 and is expected to be finished by November 2011. The in-place pavement recycling portion of the project took two months to complete.
This part of I-81 was built in the late 1960s. VDOT has routinely maintained the surface asphalt by periodically patching and replacing it. The original foundation of compacted stone aggregate and soil had weakened to the point it no longer provided a stable base for the overlying asphalt layers.
Fatigue cracking, caused by years of heavy traffic loads, had deteriorated the pavement structure from bottom to top. Symptoms of this deterioration could be addressed by milling the existing surface and repaving it, but the underlying condition would remain. The cause of this extensive wear could only be remedied by reworking all the material down to the subgrade.
Unless the foundation was repaired, simply repaving the road surface was only going to be a temporary improvement. If VDOT were to do nothing to this section of road, the pavement would crack more. Pieces up to the size of a golf ball could come out of the road.
The fatigue cracks were also allowing a direct path for water to seep down to the pavement foundation. The water saturated the subgrade, further reducing its load-carrying capacity. This condition could lead to deep rutting (surface depressions) within the wheel paths that can affect skid resistance and even steering ability.
The repairs were slightly different for the right and left lanes. Since most heavy traffic loads use the right (travel) lane, it has more underlying damage than the left (passing) lane.
Right lane: The asphalt layers were milled down to the top of aggregate layer (about 10 inches from the surface) by Lanford Brothers. This material was stockpiled on-site for reuse in the new pavement structure. The next 12 inches of material (aggregate and soil) were strengthened with a stabilizing agent (cement and lime) by subcontractor Slurry Pavers Inc. This material was recompacted to form a platform for the next step.
The stockpiled milled material from the asphalt layers was processed in an on-site mobile plant where a foamed asphalt binding agent was added. The resulting material was repaved at ambient temperatures to a depth of 6 inches and compacted. Four inches of traditional hot mix asphalt material was placed, followed by an additional 2-inch stone matrix asphalt (SMA) overlay used as the riding surface.
The challenge with the right lane was following the sequence exactly, says Landford Brothers Co. President Ken Lanford. "We were constantly adjusting so we could control the schedule and sequence," he explains. "This project was definitely a partnering project. We had a great, dependable team of subcontractors. We were also equal partners with the highway department - we recognized each other's goals and worked with each other to achieve them."