Keeping the neighbors happy
In addition to lasting longer, RCC streets are good for public relations, since they can be built quickly and allow residents almost unlimited access while under construction.
In June 2013, Streamwood completed its most recent project in three days as scheduled. The public works paving crew installed about 300 cubic yards of RCC a day to reconstruct Edgewood Drive, a 1,850-foot residential street.
Twelve Streamwood dump trucks and three leased semi-trailers hauled the mix from Prairie Material’s Addison, Ill., plant to the jobsite, seven to 10 cubic yards at a time. The zero-slump material was kept covered by tarps to prevent it from drying. One after another, the trucks backed up to a Blaw Knox paver to place the road base. The crew then compacted the material to its specified 6 inches with a 10-ton Ingersoll Rand roller.
“We are fortunate to have our own equipment and paving crew that was already proficient with asphalt paving equipment,” says Mann. They adapted easily to working with RCC, since the dry material behaves much like asphalt during placement.
Immediately after compaction, a third-party materials testing consultant used a nuclear gauge for determining in-place density to confirm the RCC had reached its required 98% minimum density.
Before the adjacent lane was placed, workers sprayed the fresh edge joint with BASF’s Confilm evaporation reducer to retain moisture and ensure better hydration and density development at the joint interface. An asphalt emulsion was then sprayed on, doubling as a curing compound to seal in moisture and a tack coat for the asphalt topping.
Residents had almost immediate access. “After the roller compactor goes over the concrete, the cars aren’t heavy enough to bother it,” says Mann. “We just ask that people don’t drive on it while we’re paving, and we keep the garbage trucks off for about a week.”
The next morning, a sawing contractor cut transverse control joints in the RCC base every 30 feet to control cracking. The joints were sealed with an IDOT-approved hot-poured joint sealant once the entire stretch of RCC was placed.
Although an asphalt overlay can be added within 24 hours, Mann takes a more conservative approach. “Prairie recommends waiting a few days to allow the RCC to obtain significant strength, so we usually give it seven days,” he says. RCC achieves a compressive strength of 6,000 to 10,000 psi in 28 days (IDOT requires 4,500 psi).
Streamwood uses a two-step process to place the asphalt, adding a leveling binder to smooth the surface one day and placing the final layer the next day. This allows residents full access to their driveways throughout the entire project.
Public works professionals from several nearby cities and IDOT officials visited the jobsite. Although they were interested in the nuts and bolts of the process, cost savings was their top concern. With asphalt prices increasing, using RCC has saved Streamwood more than the expected 15% in material costs compared to full-depth asphalt, and 25% in pavement thickness.
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