The Nevada Department of Transportation (NDOT) has been successfully performing cold in-place recycling (CIR) since the mid 1990s, and this past summer it decided to put the process to the test on Interstate 80 west of Elko. The Humboldt County project, between MP 29.38 and 42.19 was probably not the easiest debut of NDOT's interstate CIR attempt, due largely to the heavy traffic volume and steep grade required to traverse the Golconda Summit, but the resulting success proved it to be a most viable approach to rehabilitating the state's main east/west corridor.
The construction strategy consisted of CIR three inches of the existing asphalt surface and then placing four inches of NDOT's specified Plant-mix Bituminous Surface overlay (a dense-graded mix) followed by a ¾ inch of open-graded wearing course. Based on the existing condition of this portion of I-80, NDOT believed this rehabilitation strategy would be the most cost-effective approach; however, since it was the first interstate recycling project in the history of NDOT, there was a lot of anxiety leading up to construction.
The amount of traffic that I-80 carries was of primary concern in the planning and safe execution of the recycling project. The Annual Average Daily Traffic (AADT) at the time of recycling was 6,620, with approximately 50 percent of that volume being truck traffic. Based on the AADT, percentage of trucks, truck equivalency factor, and the projected growth rate of vehicle usage, the 20-year Equivalent Single Axle Loads (ESALs) was calculated to 14,988,198. To protect the recycled mat from a high percentage of truck traffic, public traffic was not allowed to run on the recycled surface for a minimum of three days. Once the first two-inch lift of dense graded hot mix was placed, public traffic was allowed to travel on the surface for a maximum of 14 days before the second lift had to be placed.
Another factor that posed an added challenge was whether or not the CIR train could traverse the steep incline over Golconda Summit (a six percent grade). Normally, the recycling train would travel downhill due to the weight of the equipment. However with safety concerns over the recycling train traveling against the flow of traffic, NDOT requested that construction activities flow with traffic. As a contingency to assist the train up the steep grade, a Cat 988 loader was attached to the front of the train and used several times to help pull the recycling train up the steepest portion of the grade.
The final concern in executing a recycling project on this major interstate was completing the work to protect the CIR mat from the harsh winter weather conditions the Golconda Summit endures. Timing was critical and NDOT wanted the recycled mat covered with the new hot mix overlays to prevent any weather-related damage to the recycled material. But the timing and coordination between the recycling contractor, Valentine Surfacing, and the paving contractor, Frehner Construction, allowed the work to begin in March and to be completed in September. NDOT allowed 220 working days for the project, which was finished in only 140 working days. For NDOT, the project was hailed as a complete success.
Vancouver, WA-based Valentine Surfacing performed the CIR of the existing asphalt roadway, milling 563,000 square yards at a depth of three inches of the old pavement surface on the 13-mile-long project.
To minimize traffic disruptions, the interstate project was divided into approximate six-mile segments in east and westbound directions, allowing milling and paving to be conducted simultaneously throughout the duration of the work. Working with general contractor, Frehner Construction, a paving contractor based in Las Vegas, Valentine milled the inside 12-foot-wide travel lane along with the inside 4-foot-wide shoulder using a CMI Roto-Mill, which conveyed the millings to a screen and crusher (specifications required that all milled material had to be sized at minus 1-1/4 inches), which then transferred the processed millings to a pugmill where the cationic medium set (CMS-2S) emulsion was added. The recycled asphalt was then deposited in a windrow behind the CIR train for laydown and compaction.