Patrick Faster, national sales manager for Gallagher Asphalt, says he recommends the HIR process for structurally sound asphalt roads that have the typical seven- to 10-year distresses, such as longitudinal and transverse cracking, reflective cracking, rutting, oxidation, and edge raveling. By towing a series of two or three ovens over the old road, Gallagher heats the surface to approximately 300 degrees F. Propane burners heat fire bricks in the oven, which in turn reflect the heat into the pavement.

A combination of hot-in-place recycling (HIR) and thin overlays will last longer, says a Michigan county official.

Once the surface is hot and pliable, Gallagher applies a set of flexible tines, working 1.5 inches deep, to scarify the pavement. Faster says the HIR process works to the same depth as the last lift of pavement placed. Next the recycling train introduces a liquid polymer-modified rejuvenating agent at the rate of 0.10 to 0.20 gallons per square yard. Then a set of reversible augers mixes the rejuvenating agent into the asphalt. “The augers pick up the material and feed it back to the paving screed,” says Faster.

Compaction comes next, with a double-drum vibratory roller. “After the roller passes, the road can be reopened to traffic,” says Faster. “We don’t have lane closures; we have lane restrictions.”

Depending on the volume of traffic carried by the road, the owning agency typically chooses an overlay treatment to cover the recycled surface. That can range from a chip seal or a slurry seal to an ultra-thin layer of hot mix to a conventional 1.5-inch layer of hot mix asphalt.

“If you do HIR and an overlay, your savings will typically be 30 to 35 percent compared to a 3-inch mill-and-fill process,” says Faster. “And the process can be done in about half the time it takes to mill and fill.

“Even at similar cost, HIR and thin overlays should provide a longer life, as the top 1.5 inches of the existing substrate pavement is recycled in place rather than just milled,” says Conklin. “Thus reflective cracking and other distresses should be delayed longer from reaching the new overlaid surface.”v