By: Lee Geistlinger
Just shy of 25,000 residents, Glen Ellyn, Ill., is a modestly sized suburb of Chicago. However, with almost 10 years' experience with fast-track concrete-paving projects under its belt, the village can rightly call itself a "paving leader" in the Land of Lincoln.
"We were the first to lay [fast-track concrete] in a residential area in Illinois," says Cathy Radek, administrative assistant for the village's public works department. "We put that down sometime in the late '80s. We have used it in several other projects, as well. There are probably about five miles of fast-track pavements in the village. We had such good success with it that we decided to put it in [our Main Street project]."
As the name implies, Main Street cuts through the heart of the primarily residential community. In early 1995, the village embarked on an ambitious plan that would almost completely renovate a 3,800 lin-ft section of Main Street and 464 lin ft of an intersecting road, Hillside Avenue.
The village's plan called for removing existing pavement on the two-lane road along with its curbs; constructing new sanitary and storm sewers, water mains, combination curbs and gutters; and laying a portland cement concrete (PCC) pavement on the existing subbase.
Work on the project officially began on March 21, with crews instituting tree-protection measures along the strictly residential project corridor. The sewer work was done in phases, so that residents living along the project route would not be inconvenienced for any extended period. The road was often closed to all but local traffic; other vehicles were rerouted just a block east of construction.
Water main work took some time, as did removal of the existing road surface. Originally a 6-in.-thick PCC road with 6-in.-high curbs, the pavement had been overlaid with asphalt to improve ridability. The thickness of the overlay was 4 in., leaving only 2 in. of curb remaining. All this was removed, leaving only the 4-in.-thick subbase. Actual work on the road itself began on Aug. 30, five months after project initiation.
Faced with a completion deadline that left little time for the traditional set-up times associated with PCC, the village elected to finish the nonintersection portions of the project using fast-track concrete paving. Andrew Miller is a design engineer for the Kudrna & Associates Ltd., the Westmont, Ill.-based firm hired by the village to oversee and document the project, and he describes what is actually involved in a fast-track project.
"It is a procedure that is based on the equipment," he explains. "You have this large 'Cat In the Hat' machine that is on four hydraulic pods-it's a track unit. It runs pretty slowly-about 10 ft per minute-and there is an auger in front of the machine to take the concrete that is poured in front of the machine and feed it back to the screed."
The unit used on this job was a SF-350 slipform paver from CMI Corp.; the contractor was K-Five Construction, a company based in nearby Lemont. The unit paved the entire 20 ft 10 in. width of the road in a single pass, inserting epoxy-coated rebar every foot and a half in the middle of the 71¦2-in.-thick PCC lane, as well as along the edges, where curbs were later added.
"The mix used is a 71¦2-bag mix, which is pretty strong," Miller says, "but it gave us compressive strengths of 3,500 psi in 24 hours, as compared to about a week for a normal mixture." Two weeks after installation, one reading went as high as 7,300 psi.
In addition to the heavy mix, additives helped the concrete set up in that short a period. Fly ash was one component, as were two W.R. Grace products: an air-entrainment additive, Daravair; and Daraccel, a water reducer.
According to Miller, Illinois DOT specifications call for AstroTurf to provide texture for the concrete. "There is actually burlap hanging off the back end of the paver," he says, "and then the turf is on a beam that bridges the whole pavement. The paving crew drags that behind the burlap over the concrete."
Even with a day lost to rain, the K-Five crew managed to finish their portion of the paving in three days: They began on Sept. 6, when they completed 1,800 lin ft; were rained out Sept. 7; and finished up on Sept. 8.
This ended the "fast track" portion of the job, although other portions of the job used the same mix that went into the slipformed sections. Other work delayed the complete opening of the road until late October; mid-November saw pavement markings that signified project completion.
While the actual cost of fast-tracking can be construed as higher than that of conventional PCC paving-the paver is a specialized piece of equipment and the additives increase any given mix's cost-other factors make the process cost effective: The quick setting of the mix, as well as its high strength, help mollify concerns over cost differentials. And since the entire effort is a highly coordinated process that gets as much pavement as humanly possible laid in a given period, labor costs are kept in line.
Fast-track paving enables municipalities to pave in a manner similar to that of asphalt paving, but with a longevity asphalt cannot match. In the case of Glen Ellyn's Main Street project, the pavement is rated for a 20-year life span. And since the curbs and driveway aprons replaced used the same mix as went into the roadway, local residents won't soon be inconvenienced for any major roadwork on this stretch. The end result of fast-tracking is a strong, long-lasting pavement that does not have to be closed off for an extended curing period, which minimizes traffic interruptions.
Miller says the fast-track method certainly proved itself in this instance: Martam Construction, formerly based in Glen Ellyn but since relocated to Elgin, Ill., was responsible for the intersections in the project. Martam did these sections by hand using a vibratory screed; the intersection had to be done in phases so as to not completely block traffic. It took Martam's crews from Oct. 3 to Oct. 21 to complete this portion of the project.
"Yes, it was getting colder then," Miller notes, "and it was taking the same mix used in the fast-track portions of the project longer to set up. It took about 48 hours to get to 3,500 psi."
He says the road appears to have held up well thus far, although it is really too soon to tell. Miller's only complaint is the areas surrounding the roadway fixtures. These areas, such as around manhole covers, were boxed-out with lumber and then, after the fast-track paving, filled in by Martam. Not only are these transitions less perfect than the very consistent surface the fast-track paving providing, but the stress cuts to these areas (to prevent cracking) had to be done in such a way that some sections of the road are covered with a "web" of cuts.
Other municipalities considering fast-track paving should also be aware that stringing the wire necessary to guide the paving unit is a time-consuming process: The 4,200-ft Main Street project required a week for guide-wire installation. However, this carefully installed line enabled the paver to, in some instances, stay within 3¦100th of an in. of design specs. The grader preparing the subgrade also used the guide wire: Miller says the operator used a sonar attachment on the unit that echoed off the wire and allowed the grader to sometimes get 5¦100-in. tolerances.
Overall, Miller says he is very pleased with the way the Main Street project turned out. "This is my first [fast-track] project, but it really blows away bituminous material, both in terms of durability and time closed."
Radek says the entire cost for the roadway, including curbs, sidewalks and storm sewers, was $1,254,000. Other costs, including the design work provided by Walter E. Deuchler Associates Inc., Aurora, Ill., raised the final cost of the entire project to approximately $1,800,000. The project was not a bond issue; it was paid for by the city's utility tax, with contributions from its water and sewer funds.
Time will be the final judge of the success of the Main Street project; right now, the idea is that it will be a long time before any judgment is necessary.
