Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/142598
HighwayContractor HIR After Gallagher Asphalt's HIR train passes comes compaction – then traffic. Photo courtesy of Gallagher Asphalt is HOT in Georgia For the right road with the right problem, hot-inplace recycling works. N ot every road that is failing is failing at the same rate and in the same way. For some of those roads that are not prime arteries and not collapsing hot in-place recycling (HIR) offers a valuable alternative choice to road managers. "Hot in-place recycling is a low-cost maintenance strategy that we were able to implement," says Brian Frix, traffic/ transportation engineer for Rockdale County, Georgia. "It was obviously eco-efficient. And mainly it was less expensive to surface-recycle our roads than to mill and inlay them." HIR heats, scarifies, and rejuvenates asphalt pavements. Frix says the county used HIR on 68,000 square yards of roads last year, and is looking at another 200,000 square yards this year. The savings with HIR run about 15 to 20 percent, Frix figures. To mill the pavements, haul the RAP to the plant, remix it, and inlay the surface back at 1.5 inches deep would have cost $9.00 per square yard, Frix says. By contrast, the surface recycling – plus a 1-inch overlay – cost the county $7.50 per square yard. "The savings are very attractive," says Frix. Gallagher Asphalt of Thornton, Illinois, performed the HIR process on four roads for the county last year. Frix says the roadways had experienced some environmental cracking, and had some structural deficiencies, which the county patched and repaired before doing the HIR. "So basically what was left was some cracking, some minor rutting and some low areas," says Frix. "The existing roads were full-depth asphalt, with anywhere from 3 to 5 inches of hot mix. Some of them may have been on graded aggregate base, others might have been on soil cement, and some may have been on dirt." Patrick Faster, national sales director for Gallagher As- phalt, says he recommends HIR for structurally sound asphalt roads that have the typical seven- to ten-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. 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 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-c and-fill." Says Frix: "We actually completed the project under budget and well in advance of the project completion date." Better Roads July 2013 11 HighwayCon_BR0713.indd 11 6/26/13 4:43 PM