Cold Mills, Twin Reclaimers Widen and Rebuild County Road

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."