Nevada?s Department of Transportation initiated a second cold in-place recycling (CIR) project on its major east/west corridor - I-80 - and the agency is convinced the cost-effective approach bodes well for maintaining a high-quality road network.
The first CIR I-80 project was performed in Humboldt County at Golconda Summit three years ago. Nevada DOT has been successfully performing CIR road rehabilitation since the mid 1990s, and the Golconda project was the first real test of using the technique on its main east/west I-80 corridor, which supports heavy traffic volume. At the time of the project, the Annual Average Daily Traffic (AADT) volume was 6,620, with approximately 50 percent of that volume being truck traffic. The construction strategy consisted of CIR three inches of the existing asphalt surface and then placing four inches of NDOT?s Plant-mix Bituminous Surface overlay (a dense-graded mix) followed by a ¾-inch open-graded wearing course. The Golconda I-80 project has performed well over the past three years and the DOT expects it to continue to perform well as projected traffic volume increases puts additional demand on the road.
Round Two
This past summer NDOT implemented the second I-80 CIR rehabilitation project east of Elko, an approximate 21-mile stretch of the divided four-lane interstate from 1.11 miles east of the Moor Interchange to 1.87 miles east of the Oasis Interchange. As with the first I-80 CIR project, this particular contract included traversing a high-elevation point - Pequop Summit - and completing work with minimal disruption to traffic flow.
Road and Highway Builders of Reno, NV was awarded the general $33-million contract, with Valentine Surfacing Co. of Vancouver, WA subcontracted to perform the CIR work. The project called for 215,662 tons of Nevada DOT Type 2C plant mix, 37,640 tons of open-graded plant mix, 859,590 square yards of existing asphalt to be recycled with 22,000 tons of quicklime and 2,200 tons of cationic medium-set (CMS-2S) emulsion.
The project is being constructed over two seasons, with approximately 60 percent completed in 2007. It was divided into one-third sections, with the east and west portions completed during the first year of construction and the center portion scheduled for completion in 2008.
The project required this approach due largely to the amount of drainage pipe work required in the center portion of the contract, which prohibited the CIR and overlay work to be completed during the 2007 construction season. Also, numerous traffic control limitations and limitations regarding how long the cold recycled material could remain without being overlaid proved to be a logistical challenge that could only be addressed by executing the project over two construction seasons.
The middle portion of the project also requires traversing the Pequop Summit, which consists of four to six percent grades on either side of the summit, and that in itself requires additional logistical and execution planning.
CIR, paving coordination
Executing the Pequop project required a coordinated effort on the part of Valentine and the general contractor.
Some of the notable limitations/requirements outlined in the project contract included:
- Regardless of traffic control operations, do not stop public traffic on I-80 at anytime and do not delay public traffic for more than 10 minutes total.
- For I-80 cold recycle and paving operations, limit work zones to two in each direction, not to exceed 7 miles per work zone. Maintain 5 miles between work zones in the same direction.
- Do not allow public traffic on recycled mat for a minimum of 48 hours. The contractor, at his own risk, may open the recycled surface to public traffic for a period not to exceed five days.
- Cold recycled surface will be constructed to a common point, full width, and overlaid with full-depth plant mix prior to winter shutdown.
- After initial compaction, allow the recycled mixture to cure a minimum of three days and then take three randomly selected samples from the recycled surface to be overlaid. If the moisture content, as determined by Test Method Nevada T112, of the samples is 2 percent or less and a minimum of three days have passed since initial compaction, overlay the recycled surface.
- Do not allow traffic on the first lift of dense-graded plant mix for more than 72 hours before placing the second lift.
- Place the full-depth dense-graded plant mix surface over the recycled mat with 45 days after it has been processed.
Limitations/requirements specific to placing hot-mix asphalt over the CIR mat included:
If the average moisture content is greater than 2 percent, delay paving until the moisture content from three or more samples is 2 percent or less. Perform re-compaction (proof rolling) a maximum of 48 hours prior to placing the first lift of dense-graded hot mix. Do not perform rolling when the surface temperature is below 90 degrees F.
According to Chuck Valentine, president of Valentine Surfacing, coordinating the CIR portion of the project with the paving work required to cover the CIR mat as specified by the contract is a significant challenge in the successful execution of this type of project.
?Fortunately, we?ve worked a lot with Road and Highway Builders in the past, so it?s easier when you have a good working relationship with the paving contractor,? Valentine says.
Project coordination
Beginning at Moor Interchange on the west end of the project, Valentine?s CIR train headed east, recycling the 12-foot-wide inside travel lane and the 4-foot-wide inside shoulder in one 16-foot-wide pass.
In the CIR process, Valentine?s crew milled the old pavement and blended it with the quicklime and CMS-2S emulsion before depositing the new material in a windrow behind the CIR train - consisting of 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), followed by a pugmill mixing process to add the emulsion and lime before depositing the cold mix back on the road.
The paving contractor followed with a windrow pick-up device and paver to place the cold mix back down on the road surface.
Bert Truxal, Road and Highway Builders? project manager, says roller operators then had to wait two to three hours before beginning compaction of the cold-mix lift in order to allow the moisture content time to evaporate.
?Then after approximately 48 hours (when the moisture content dropped to 2 percent during the curing process) we had to re-roll the mat for final compaction before we could begin placing the two 2-inch-thick mats of new (NDOT specified) dense-graded plant mix,? Truxal says. ?There were times when we had to wait longer for the cold recycle to cure and the moisture content to drop to the contract specifications before we could begin placing the new overlays.?
After completing the full 3 1/2-inch recycled depth of the 6- to 7-mile stretch, the CIR crew then moved to the westbound lanes to repeat the process on the inside travel lane and shoulder.
After completing the inside travel lanes and shoulders on the west section of the project, Valentine?s CIR crew then moved to the east end of the project to repeat the process on the inside travel lanes and shoulders of that 6- to 7-mile stretch of the project.
?When we were working on the inside travel lanes and inside shoulders (CIR the 16-foot-wide surface in one pass), we were able to process approximately 1 to 1 1/4 miles a day,? Valentine notes. ?After completing one pass in one direction, then moving to the other side of the project, we were able stay ahead of the paving crew and limit the (construction) congestion in the individual work zones.?
After completing the inside lanes of the two project sections, Valentine?s CIR crew began work on the 12-foot outside travel lanes and the 10-foot outside shoulders.
?We moved back to the west end of the project and began the process all over,? Valentine says. ?This time we had to make two separate passes in order to process the travel lane and the shoulder. When operating in a 12-foot-wide or 10-foot-wide (shoulder width) mode, we were able to process 1 1/2 to 2 miles a day.
?On the east end of the project, the grades are a little steeper and more abrupt, so we had to take that into consideration when estimating how fast our CIR train could travel and whether or not we needed additional equipment to help pull the train up the grades,? he adds.
With some initial delays in staging and preparing aggregate for the mix required, completing the two portions of the project before colder weather set in also proved challenging.
?We began recycling in late July, later than we originally planned to start, so we only had approximately two months to complete the work prior to the winter shutdown,? Valentine says. ?So on this project in particular; we had to work closely in order to keep the project moving forward and on time.?
When the center section of the project is recycled and overlaid with dense-graded mix this year, the entire project will be capped off with an open-graded wearing course, and the NDOT will have rebuilt another challenging stretch of I-80 using a time-tested, cost-effective CIR approach to maintaining its road network.
