The same process was followed on the outside 12-foot travel lane, and again on the 10-foot-wide outside shoulder, according to Chuck Valentine, owner of Valentine Surfacing.

"Each CIR project is a little different, and on this one Nevada specified the emulsion we used as well as adding a lime slurry during the milling process," Valentine says. "The lime slurry acts as an anti-stripping agent, and helps cure and strengthen the recycled asphalt."

The end result of the CIR process is a treated base course, after it has several days to cure, ready for a new hot mix overlay.

Ready for the hot mix

With the concern NDOT expressed about leaving the recycled mat unprotected over the winter, Frehner established an aggressive paving schedule to complete the project in one construction season. Frehner outfitted two paving crews, one to place the recycled cold mix and one to place the hot mix.

According to Gary Isaman, Frehner's Elko, NV area manager, about the only difference in placing the cold mix versus the hot mix was the lag time between placement and compaction.

"We had to wait a half hour to 45 minutes after the paver laid the cold mat before we could begin our rolling pattern, because it took that time for the lime to begin setting the emulsion," Isaman says. "Once we could get on it, we were able to achieve 90 to 92 percent density."

Project specifications required up to 10 days for moisture content in the recycled mat to drop to 2 percent before Frehner could begin placing the hot mix, but due to weather conditions, the curing process took only three to five days.

Once the recycled mat reached the specified moisture content, Frehner's hot mix crew, using a Blaw-Knox 5510 paver, began placing the first of two 2 1/2-inch mats of dense-graded asphalt. The new 5-inch overlay was then covered with a ¾-inch open-graded wearing course.

"We used pneumatic rollers on the cold mix, finishing with a steel-drum roller, and steel and pneumatic rollers on the hot mix," Isaman say. "We achieved are required 92 percent density on the 2C (hot mix) and the only time we operated our rollers in a vibratory mode was when we did a re-roll of the cold mat prior to placing the hot mix. NDOT specified the re-roll for additional compaction density before placing the new asphalt. We also achieved the required Type A smoothness spec required by NDOT, which meant we didn't have any grinds to correct any detected surface deviations. (NDOT's Type A smoothness index allows 5 inches of ¼-inch deviations per lane mile).

CIR continues to perform

As Nevada continues to use CIR as a cost-effective maintenance approach, its past success supports the efforts to expand its use on interstate road projects.

"For the past 15 years, Nevada has been successful in cold recycling low-volume (traffic) roads, and I knew they could be successful in cold recycling an interstate road," Valentine says. "A lot of the restrictions concerning traffic and preventing traffic on the recycled mat until it could be covered with new asphalt had to do with NDOT's desire to make this first interstate cold recycling project successful. But as the project moved along, we were able to convince them (NDOT) that they could allow traffic on the recycle mat and not worry about damaging it before the new asphalt was placed."

The CIR process saved a considerable amount of time and money compared to Nevada's conventional Road Bed Modification rehabilitation, where 8 to 10 inches of road surface is pulverized and 2 percent cement slurry is added to stabilize and strengthen the pulverized base before a 4-inch hot mix overlay is placed.

"Once NDOT started to use cold in-place recycling on roads, they started to realize the cost benefit through the number of miles they could reconstruct versus the number of miles they were reconstructing with the Road Bed Modification approach," Valentine says.

"They realized that by being able to improve more miles with the same dollars they were spending on their old rehabilitation approach, they would be able to raise the overall quality of their road system," he continues. "In fact, Nevada's road quality rating has gone from a #30 to a #4 during the time the state has been using CIR as a preferred rehabilitation approach.