Lee Smith, president of the hot-in-place recycling (HIR) subcontractor Paveover, Albuquerque, N.M., says Highway 141 recycled well. “You’ve got to use the right process on the right road at the right time,” he says. “This is a case where they did that. Even if the cost of the hot recycling was the same as cold milling with an overlay, the hot-in-place recycling is a good thing to do. It saves substantial amounts of new aggregates and virgin asphalt.” The general contractor was Mays Construction Specialties in joint venture with United Companies of Mesa County, Colo.

CDOT’s Ray says he likes the in-place heating and remixing process. “I think you can do a lot with your smoothness too, because the recycling train allows you to add virgin mix to smooth out ruts or replace the asphalt in low areas,” says Ray. In fact, Ray says the smoothness and overall quality of the new roadway won an award from the Colorado Asphalt Paving Association – Best Overall Quality for Rural Resurfacing.

Multi-Machine Train

The total project consisted of 22 lane miles of two-lane roadway. Paveover performed its HIR on 168,246 square yards of pavement. The first two machines in the HIR train are preheaters. Sometimes only one is needed, but on Highway 141, Paveover used two. Both machines apply intense heat using banks of propane-fueled infrared heaters, says Mike Smith, Paveover project administrator.

The next machine, called the A unit, is a heating-and-milling machine that mills the pavement to a depth of 1 inch and places it into a windrow. “The next thing that happens is that the second heating-and-milling unit shows up and that’s what we call the B unit,” says Mike Smith. “The B unit has a windrow pickup machine that picks up the asphalt from the A unit, heats the milled surface again and mills off 1 more inch. So now we have milled off a total of 2 inches.”

The B unit can also receive virgin hot mix. On the Highway 141 project, Ray estimates that Paveover added an average of about 30 percent virgin asphalt to the total recycled material. The recycled asphalt plus the virgin material, plus any rejuvenator needed, go to a twin-shaft pugmill unit on the rear of the B unit.

Because Highway 141 had received chip seals, that asphalt mixed in well with the recycled material and precluded the need for a rejuvenator.

Ray says that a contributing factor to the project’s award was the smoothness that Paveover and Mays/United achieved. At a minimum, a section of pavement must have a Half-Car Roughness Index (HRI) of 65 inches per mile to receive a smoothness bonus. For an HRI of less than 45, a contractor can win the maximum bonus.

On Highway 141, the contractors received the maximum bonus on many one-tenth-mile segments. And the team averaged 61 inches per mile on the southbound side and 62 on the northbound side. The total of bonuses awarded was $28,000, Ray says.

“You have to look at what process gives you the best life cycle cost,” says Lee Smith. “And on this project, everyone agrees that we got it right.”