When the road construction season draws to a close, innovative contractors find a way to complete one more project. That was the case this past fall on a county road in South Central Illinois, where cold milling machines played the role of a road widener by taking millings from the center of a thick hot mix asphalt (HMA) pavement and placing them in a 10-inch-deep widening trench on either side of the existing pavement.
Then, twin Wirtgen WR 2500 S reclaimer/stabilizers — operating in tandem — pulverized and full-depth recycled the road and new shoulders using a proprietary asphalt emulsion, prior to its resurfacing with hot mix asphalt.
The innovative operation drew government road agency observers from all over Central Illinois and gained kudos for its contractor, Dunn Company of Decatur, IL.
The 2.5-mile stretch of Christian County Highway 1 was in serious need of reconstruction, and was completely rebuilt near the end of the construction season, about 10 miles south of Taylorville, IL, just north of the Montgomery County line.
Studying CIP for Illinois agencies
Among the visitors was the esteemed Marshall Thompson, P.E., professor emeritus, civil engineering, of the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign, member of the Hot Mix Hall of Fame of the National Asphalt Pavement Association (NAPA), and now associated with the new Illinois Center for Transportation (ICT), founded in 2005. In July, he and Prof. Sam Carpenter began researching cold in-place recycling with asphalt products at ITC. Their project is scheduled to conclude by June 30, 2008. His visit to Hwy. 1 was part of that research.
"We're studying cold in-place recycling with asphalt emulsions, and foamed asphalt, and Dunn Company has extensive experience with both processes," Thompson says. "Our ultimate goal is to develop local road and street specifications that could be used throughout the state, without the agency having to go through a so-called experimental project review. It would make CIP a routine construction process, rather than something exotic and new."
This project used value-added Fortress proprietary asphalt emulsion from SemMaterials LP, and manufactured under license by Emulsicoat Inc. of Urbana, IL. The Fortress product has an engineered design, adheres to a set of performance-related specifications, and is a new-chemistry emulsion formulated specifically for the stabilization process, according to SemMaterials.
Thompson has studied conventional asphalt emulsions, and identified potential problems. "One of their limitations is the curing time required for the moisture to evaporate from the mix, Thompson says. "That's caused them to lose favor in some areas over the last few years, because of the associated delays in the construction process. With engineered emulsion the break is now chemically controlled and the process goes very quickly. Crews are able to blade and compact immediately after adding the emulsion. This is a very significant improvement."
Also making this project possible is the Wirtgen WR 2500 S and its pump-meter systems. "The Wirtgen asphalt additive system is totally integrated, with travel speed, pump speed, amount of emulsion added, it's all controlled," Thompson says.
"One of the major issues we used to have was quality control in terms of amounts of additive blended with the material."
The WR 2500 S and its companion machines, the WR 2000 and the new WR 2400 solve that problem.
The task force will also study foamed asphalt stabilization and recommend specifications for Illinois local government agencies. "These same machines can also produce foamed asphalt which has been done at other locations in Illinois," Thompson says. "Both the foamed asphalt and engineered emulsion stabilization projects are part of our study."
Tremendous savings can benefit local governments if they can reliably use these CIP recycling processes. "They will be able to reclaim and reuse their old asphalt pavements," Thompson says. "You can use them as a road base with a 3-inch hot mix asphalt surface, as here, or you can go through an existing thin asphaltic concrete surface and blend it with an aggregate base, and the total blend of AC surface plus agg base can be stabilized with either emulsion or foam. It's very cost-effective and allows you to maximize your in-place recycling potential. And while we're not evaluating them for our study, there are environmental problems that cold in-place recycling can solve."
Recycling very deep lift
Dunn's machines were recycling a very deep layer of existing HMA pavement, anywhere from 10 to 14 inches thick, 22 feet wide. Also, the road was being widened 3 feet on each side.
"Using a W 2000 and W 1900 we milled two inches of asphalt off the existing pavement and placed it in a widening trench that was cut with a Wirtgen W 1900 Combo cutter," says Phil Koeberlein, P.E., project manager, Cummins Engineering Corp., Springfield, IL. The widening trenches were 10 inches deep and 3 feet wide, each located 11 feet off the centerline. Then, after the millings were placed directly off the cold-mill conveyors, the existing 11-foot lane and the new 3 feet of millings were cold in-place recycled as one in two passes.
"Use of the two Wirtgen machines was fundamental to the process," Koeberlein says "Besides normal day-to-day traffic, this road leads to a local limestone quarry which handles 350 to 400 loaded trucks per day. We had to keep this road open to traffic, and needed to do one lane at a time, as quickly as possible. Having the two machines we were able to pulverize in one day and process the length of the job in one day, 10 inches deep."
The cross section of recycled material is 28 feet wide, paved 26 feet wide. The lanes are striped for 22-foot-lanes and 2 feet of paved shoulders, along with 2-foot aggregate shoulders outside the finished pavement.
Success on Hwy. 1 was assured by the recycling contractor, which orchestrated the flow of trucks, equipment and materials.
"The biggest challenge is getting the trucks lined up, with good people who know what's going on," says Tim Milhauser, senior construction manager, Soil Modification & Stabilization, Dunn Co. "Compaction is key to the success of a full-depth project like this, and everyone must be in synch."