A hot, in-place in the sun
Hillsborough County, Fla., takes a torch to its road maintenance costs by making hot-in-place recycling of asphalt pavements a key element in its program.
by Larry Flynn
The Tampa Bay Buccaneers have a new football stadium, Raymond James Stadium, and thanks to hot-in-place recycling (HIP), their fans drive to the stadium on a new asphalt pavement that is as black as a pirate's eye patch.
Worn and tattered like a quarterback unable to allude the grasp of Buccaneers defensive lineman Warren Sapp, three miles of Columbus Drive, which lies in the shadow of the stadium, was given a new life by the Hillsborough County Public Works Department early this year. In all, 101,650 sq yd of asphalt was reclaimed, recycled and placed in a single pass on the four-lane road. In addition, 20,325 sq yd of asphalt was recycled and placed on nearby Armenia Avenue.
"We get a good sound product and we're only adding one additional inch of asphalt and recycling the rest," Michael B. McCarthy, P.E., project manager for the county public works department, told Roads & Bridges. "You get a lot of miles for your dollar this way."
Hillsborough County is one of the latest counties in Florida to add hot-in-place recycling to its road maintenance program. The trend was started several years ago by Orange County and followed by Manatee County, according to John Rathbun, vice president of sales for Cutler Repaving, Inc., Lawrence, KS. Cutler, which has performed HIP in all three counties, performed the Tampa project as part of a two-year contract with the county.
"You're cutting maintenance costs by 50% when compared to a 2-in. overlay," Rathbun said of using the HIP recycling technique on the job. "From the yields we're getting, it appears as though this job will be under budget," McCarthy said. Estimated to cost $418,000, the Columbus Drive and Armenia Avenue projects, which began in 1998, came in at $408,677, according to the contractor.
Orange County has realized a 35% saving in costs on its projects, while Manatee County saved 40% in costs over that of milling, leveling and overlaying. In general, Cutler estimates an 18-35% cost saving can be expected from the process in relation to milling and overlay projects. Bob Hall, Cutler's area manager, brought HIP to Manatee County when he was the county's pavement engineer. "It made me look like a hero," said Hall, who subsequently joined Cutler because of his familiarity with the process.
Cost is only one saving realized from the process. According to the contractor, HIP takes half the time of a standard milling and overlay project. The repaver machine, manufactured by Cutler, also reprofiles the pavement as it recycles. In reusing the existing asphalt, the process also reduces the build up of pavement as a result of multiple overlays.
The HIP train is led by a preheater that provides the initial heating of the asphalt. A Mack dump truck filled with virgin asphalt follows behind the preheater on the softened roadway. The repaver then heats the pavement a second time and typically removes 1-1/4 in. of asphalt from the pavement. The repaver then mixes and processes the reclaimed asphalt, adding 1/10th gal per sq yd of ACR1 polymer-modified recycling agent from Koch Materials. The recycled mix is laid with the help of a vibratory recycling screed. The recycled layer then is topped with a 1 in. hot-mix asphalt overlay, which is laid with a second screed on the machine. "The process creates a good monolithic bond between the new and recycled layers," said Cutler's Rathbun.
Because Columbus Drive is a heavily traveled urban arterial with an ADT of 45,000-60,000, an S-3 structural asphalt mix is used as the surface layer to add strength and life to the roadway. The repaver is followed by two compaction rollers: an Ingersoll-Rand DD-90 double-drum breakdown roller followed by a steel-drum finish roller.
During the repaving process the county utilized the services of a sheriff's deputy to enhance traffic control. According to Hillsborough County's McCarthy, the county has adopted the use of a deputy as standard practice on road projects. "A sheriff's deputy makes all the difference in the world," said McCarthy. Aside from enforcing traffic speeds and calling attention to the project, the deputy also has the ability to operate traffic boxes when necessary.
HIP is one of five different maintenance processes used by the county in its program. The other techniques include resurfacing (overlay), rejuvenation, microsurfacing and chip sealing for dirt roads. McCarthy said the county also is considering a cold-mix application in environmentally sensitive areas, such as park lands, to reduce the risk of runoff problems.
The county-wide budget for its resurfacing program is between $5 million and $7 million a year for a county that has seen itself become increasingly urbanized in the past six years. Of that amount, repaving and microsurfacing total approximately $2 million a year, according to McCarty. Hillsborough maintains arterial roads within Tampa, such as Columbus Drive, through a co-op agreement with the city.
"Next year we are considering adding another item to the program; roadway reconstruction," said McCarthy.
McCarthy credits Bernardo Garcia, the county's director of public works, with modernizing the county's street maintenance program. According to McCarthy, Garcia implemented a new pavement management system that has helped prioritize maintenance needs so that dollars are spent wisely. "Pavement management has been very helpful," said McCarthy. "I hope to see it grow."