The parking lot outside of the Illinois Department of Transportation’s new materials lab is ordinary. So, seeing a crowd of workers and on-lookers and hearing the gears of eight mix trucks –– all with a different redi-mix producers name emblazoned across the side –– may have seemed odd. But this was no common parking lot repaving project.
The IDOT job is part of a demonstration to experiment with “whitetopping” –– the process of placing a thin layer of concrete over existing asphalt as an alternative method of rehabilitation. What IDOT, and the rest of the state’s paving industry, are looking at is how whitetopping matches up to other methods in terms of quality and cost-effectiveness.
“That’s pretty much the foundation of what we are doing out here and what’s drawing so much attention,” said George Houston, mixture control area supervisor of IDOT.
IDOT will test the effects of cut depths, joint spacing and structural fibers on the load bearing capacities of the concrete panels used in the system to determine if the alternative technology is worth adopting into its specifications.
“It is the saw cutting that really takes the costs through the roof,” said Houston. “The depth of cut and spacing directly affects the productivity with the saws.”
The sawing and spacing of the concrete are very important for maintaining load carrying capacity and controlling cracking. The spacing is determined by the thickness of the overlays, which vary from 2 to 6 in. on the project. The joints vary from 2 to 5 ft.
Referred to as “early-cut,” the joint’s cuts are made to relieve environmental and load stresses.
“Sawing the cut while it is still ’green’ creates less dust and noise during the operation, but more importantly reduces wear and tear on the blades and allows cutting at a faster rate,” said Houston.
Two different structural-fiber-content concrete mixtures also will be investigated during the experiment. The fiber amount in each will be determined by the thickness of the overlay: 4 lbs./cu. yd. for 2 and 3 in. overlays, and 7.5 lbs./cu. yd for 4 and 6 in. overlays. “The purpose of this is to determine if we can have overlays that will produce a flexible enough surface,” said Mel Kirchler, district bureau chief of materials of IDOT.
“What we find is that at a minimum we get about a 20 percent potential increase in joint spacing by going to the fibers,” said Randy Riley of the American Concrete Pavement Association (ACPA). “The fibers may give us the advantage of extension of the joints with the same traffic carrying capacity.”
Kirchler pointed out that the technology being tested by IDOT is not new but the approach is. “We are taking all of the technology of the United States and combining it in to one to create an overlay system that may be unique to this area, but is really what is being done all over the United States in various forms.”
Houston said this application may be particularly good for roads where daily traffic surges in a short time because of development. “You find that your roadway has exceeded its design capacity,” said Houston. “[Whitetopping] might be one alternative to beefing up the roadway without raising curbs and changing your drainage,” he said.
Len Swederski, president of Swederski Concrete Construction Inc. in Spring Grove, IL, and one of the contractors on the project, also noted whitetopping is environmentally friendly and it is life-cycle cost effective.”
Swederski’s company spent three days laying several thousand square yards of 2, 3, 4 and 6 in. whitetop overlays on the existing asphalt of the parking lot.
Swederski Concrete is using a Somero SD-240 laser screed with a 3D-Profiler system. “It works off a fully robotic Geodimeter total station linked to a laptop on the screed,” said Swederksi.
With servos controlled by radio link to control the grades and the slope of the concrete, the system can be used for multi-sloped interior and exterior grading operations, he said.
According to Houston, just about every local concrete supplier has donated not only money but also manpower and trucks.
“It’s quite amazing the kind of logistics that are involved when you try this type of endeavor,” he said. “IDOT is getting what appears to be a free parking lot out of this, but our own crews have been involved in the prep work, as well as several other people in the industry. It is definitely a partnering effort.”
The demonstration is co-sponsored by the Illinois Department of Transportation, the Illinois chapter of ACPA and the Illinois Ready Mixed Concrete Association.
Swederski’s focus in the last few years has been developing the exterior concrete paving market. “It’s a pretty low market in the northern Illinois area,” he said. “It’s a new developing market.”
“The marketplace could be huge if [local, county and municipal governments] are allowed a choice when designing their pavements,” said Jimie Wheeler of ACPA. “For IDOT to adopt these specifications to allow for thin concrete overlays as opposed to the traditional asphalt overlays is very, very significant. Certainly for the intersection market and service roads and truck routes.”
According to Wheeler, it has been promised that the letting this March should include several whitetopping projects.
“We believe this is very significant for the taxpayers,” said Wheeler. “This culminates a long process of working with the state of Illinois to adopt a specification for thin concrete overlays of existing deteriorated asphalt pavements. We are very pleased. We’ll watch as time goes by to see how the durability holds up. The proof will be in the pudding.”