When the road construction season draws to a close, innovative contractors find a way to complete just one more project. Such was the case this past Fall on a county road in South Central Illinois.
The 2.5-mile stretch of Christian County Highway 1 was in serious need of reconstruction. The job called for it to be completely rebuilt about 10 miles south of Taylorville, IL, just north of the Montgomery County line.
Cold milling machines brought in by Dunn Co., Decatur, IL, took on the role of a road widener, taking millings from the center of a thick hot-mix asphalt (HMA) pavement and placing them in a 10-in.-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 HMA.
Studying CIP for Illinois agencies
The innovative operation drew government road agency observers from all over Central Illinois. Among the visitors was Marshall Thompson, P.E., professor emeritus, civil engineering, for the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign, and a member of the National Asphalt Pavement Association's Hot Mix Hall of Fame. He is also associated with the Illinois Center for Transportation (ICT).
Last July, Thompson and Professor Sam Carpenter began research at ICT on cold in-place recycling (CIP) with asphalt products. His visit to Highway 1 was part of that research.
One reason this particular project was possible was the use of Fortress proprietary asphalt emulsion from SemMaterials LP, manufactured under license by Emulsicoat Inc. According to SemMaterials, the 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.
One of the limitations Thompson has seen with conventional asphalt emulsions is the curing time required for the moisture to evaporate from the mix. "That's caused them to lose favor in some areas over the last few years, because of the associated delays in the construction process," he points out. "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 the project possible is the WR 2500 S and its pump meter systems. "The Wirtgen asphalt additive system is totally integrated, with travel speed, pump speed and amount of emulsion added all controlled," says Thompson. "One of the major issues we used to have was quality control in terms of the amounts of additive blended with the material." The WR 2500 S and its companion machines, the WR 2000 and WR 2400, solve that problem.
A quick completion
Dunn's machines were recycling a very deep layer of existing HMA pavement, ranging from 10 to 14 in. thick and 22 ft. wide. The road was also being widened 3 ft. on each side.
"Using a W 2000 and W 1900, we milled 2 in. 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 in. deep and 3 ft. wide, with each located 11 ft. off the centerline.
After the millings were placed directly off the cold mill conveyors, the existing 11-ft. lane and the new 3 ft. 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 that 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 and process the length of the job in one day to 10 in. deep."
The cross section of recycled material is 28 ft. wide, paved to a 26-ft. width. The repaired section is striped for 22-ft. lanes and 2 ft. of paved shoulders, with 2-ft. aggregate shoulders outside the finished pavement.
Successful completion of the project 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."