Asphalt Recycling Section
| July 01, 2010 |
A New Road at a Good Price
By Daniel C. Brown, Contributing Editor
The Utah Department of Transportation estimates that it saved more than $1.2 million with the Full Depth Reclamation (FDR) process for SR-68 near Saratoga Springs – compared to remove-and-replace reconstruction.
FDR saves money by eliminating the hauling of base materials involved in removal and replacement. Moreover, the state said it also saved approximately $1 million by not having to identify and relocate utilities under the existing roadway.
The SR-68 project included reconstruction of an existing two-lane roadway with upgraded accesses and intersections, and widening to a five-lane roadway for about 12 miles. The general contractor, Geneva Rock Products, of Orem, Utah, subcontracted the FDR portion of the project to Valentine Resurfacing, of Vancouver, Wash. Construction extended from the summer of 2008 into the fall of 2009.
Valentine used a Roadtec SX-7 reclaimer to pre-pulverize the roadway to a depth of 8 inches, working 8 feet wide. Valentine also added water to the pulverized material to attain the optimum moisture content for adequate dispersion of a solventless emulsion, which was supplied by Road Science, LLC, of Tulsa, Okla. The contractor then regraded the material to a new profile, pulverized again to add 4.5 percent of solventless emulsion, and compacted the roadway.
The stabilized base was overlaid with 5 inches of asphalt and a 1.25-inch layer of open-graded friction course. It is a 20-year design.
The FDR process for this roadway saved hauling more than 20,000 dump truck loads of excavated and imported materials, according to the state. What’s more, says Utah, the FDR option resulted in an energy savings of 37 percent compared to conventional removal and replacement – and a 19-percent reduction in carbon dioxide emissions. v
Go Green – Save Green
Full-depth reclamation rejuvenates existing materials to build a new road base.
Green, sustainable road construction is thriving in the in-place asphalt recycling world. Proving that, the full-depth reclamation (FDR) process saved approximately 80 percent of the cost of complete reconstruction of a two-lane road for Grady County, Ga. Briefly, the FDR process calls for full-depth in-place mixing and stabilization of an existing asphalt roadway.
To reconstruct the 11.5-mile stretch of Old State Route 179 and cap it with 2 inches of hot mix asphalt would have cost more than $10 million, estimates Rusty Moye, Grady County administrator. By contrast, the FDR process – plus a 2-inch asphalt overlay – cost just $2.24 million. “It costs about $1 million per mile for complete reconstruction,” says Moye. “For that we would remove the old roadway, regrade it, put a new 8-inch base under it, and repave it.”
This is one of the longest FDR projects ever performed in Georgia. Even so, the in-place reclamation plus overlay took just 3.5 weeks, compared to three or four months that complete reconstruction would take, said David Faust, project manager for Blount Construction Co. of Marietta, Ga., the FDR contractor. Plus, FDR did not require closing the road, as reconstruction would have.
Blount’s first move in the FDR process was to spread 60 pounds of Portland cement per square yard on the original roadway. It consisted of a 1.5- to 2-inch layer of a bituminous-sand mixture placed atop a base of sandy clay. The county’s consultant, Watkins & Associates, Tifton, Ga., recommended the 60-pound rate, and the county used a state specification for the FDR work.
Next, Blount ran two large CMI-made reclaimer-stabilizers in echelon down the roadway. (CMI has since been absorbed by Terex Corp.) The two reclaimers, an RS-800 and an RS-650, first worked a total of one 11-foot lane and stabilized the old asphalt to a depth of 8 inches, Faust said. The reclaimers accomplished a thorough mixing of the cement into the existing asphalt and base. A motor grader shaped the reclaimed material. Next, three rollers – a Hamm 3412 padfoot and two 25-ton rubber-tired rollers, one a Hamm and the other an Ingersoll Rand-handled the compaction chores.
Faust said the two reclaimers worked from the outside edge to the centerline to cover one lane, then reversed their paths and reclaimed the second lane in the same way. “We could cover a little over a half-mile per day, working the full width of the road,” said Faust. “We were spreading 10 tankers per day of cement.”
The 2-inch hot mix overlay followed, as placed by The Scruggs Co., Valdosta, Ga.
“Over the years, we have done some large volumes of FDR work for various counties in Georgia,” says Faust. “I would estimate we have done FDR work in 20 to 30 counties, either working directly for the county or for a general contractor.”
Moye says the FDR process has several benefits:
It can be done under traffic and requires no road closures;
It uses existing materials, which saves trucking and the cost of virgin materials;
It features a quick turnaround. “We started this job the last week in March, and finished the week of April 21.”
“We had a good road base to start with; we just needed to get the base materials up and rejuvenate them,” Moye adds. “Then The Scruggs Co. paved it in one pass.”
Renewing the Road to the Caverns
New Mexico success with its first FDR/asphalt emulsion project.
Full-depth reclamation (FDR) with emulsion resulted in savings of more than $1 million per lane mile, compared to a removal-and-replacement on New Mexico State Highway 7 near Carlsbad.
In this case, the FDR process reclaimed the existing 4 inches of asphalt pavement, mixed it with 4 inches of caliche base and incorporated the emulsion. The 6.5-mile project marked one of the first times that FDR with asphalt emulsion has been used in the state.
“Our total project cost was $3.5 million, or about $269,000 per lane mile,” says Shane McDade, president of Texas Road Recyclers, Fort Worth Texas. The firm provided on-site consultation, quality control testing during the job, and mix design consultation. “That represents a substantial savings over reconstructing a similar roadway,” said McDade. “We estimate that to remove the old material, build a new 8-inch base, and add a 2-inch hot mix overlay, would have cost between $1.5 million and $2 million per lane mile.” McDade bases his estimate on the most current information available from the Federal Highway Administration and various state transportation departments.
S.H. 7 is the main access road to the famous Carlsbad Caverns National Park. Although it is a New Mexico state highway, the road’s location in a national park meant that the job fell under the jurisdiction of the Federal Highway Administration. FHWA’s engineer for the project was Eric Zeller, P.E., project engineer for the Central Federal Lands Highway Division.
Field work began when McDade sampled the S.H. 7 roadway for mix design purposes. By using a Wirtgen WR-2400 recycler to reclaim to a depth of 8 inches, the mix consisted of 50-percent asphalt and 50-percent caliche base. Mix design testing was done by Maghsoud Tahmoressi of PaveTex Engineering and Testing in Dripping Springs, Texas.
Mix design testing showed the optimum emulsion content for the roadway was 3-percent. Constructors Inc., the subcontractor for the FDR and overlay, incorporated PASS-R, a patented engineered emulsion developed by Western Emulsions Inc. (WEI) and supplied by their Roswell, N.M. facility. The on-site representative for WEI was Larry Parker, regional marketing manager for the New Mexico region.
The prime contractor for the job was Briston Construction LLC, from Tempe, Ariz. Briston’s superintendent was Jard Plocher and the project manager for Constructors Inc. was Cory Burnett.v
Budget Stretching in Ingham County
Even though the hot-in-place recycling (HIR) process plus an ultra-thin overlay cost about the same as a mill-and-fill, William Conklin says the HIR process gave the Ingham County (Michigan) Road Commission a better product in the end.
Briefly, the HIR process heats the pavement surface and rejuvenates it in-place.
“We decided that the hot-in-place recycling was the best fit for our situation and generally we have been pleased with the results,” says Conklin, managing director for the commission. “We saved the cost of milling and removal of the asphalt, and the HIR doesn’t leave a milled surface underneath the overlay. If we had only milled off the top 1 inch and overlaid that, we would have been leaving an old, brittle and cracked pavement underneath. This allowed us to restore some of the substrate properties and not worry about reflective cracking in the overlay.”
For Ingham County, the total cost of HIR plus a liquid rejuvenator was $3.34 per square yard. The unit cost of the ultra-thin overlay was $85 per ton, applied at 110 pounds per square yard or about 1-inch thick. So, the overlay cost $4.68 per square yard. That adds up to $8.02 per square yard for the HIR plus overlay.
“The cost of a conventional 2-inch milling and 2-inch paving would have been about the same cost – at $8.05 per square yard – assuming conventional asphalt costs $55 per ton and milling runs $2 per square yard,” says Conklin.
Last year, the commission turned to Gallagher Asphalt Corp., Thornton, Ill., to perform the HIR process on 7.2 miles of residential streets in Meridian Township. Most of the streets were 20 or more years old, and Conklin says their distress level really exceeded that for which Gallagher normally recommends HIR.
“By all rights some of these streets should have been milled out completely and replaced,” says Conklin. “But to stretch our budget, we decided to do the HIR process. The fact that 1.5 inches of it was recycled and closed up helped the reflective cracking from coming up through the overlay.”
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.
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