Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/86539
Superthin SpecialFeature by Dan Brown, Contributing Editor AMERICAN CONCRETE PAVEMENT ASSOCIATION Overlays concrete "D" Construction crews finish a freshly placed section of bonded concrete overlay on an existing asphalt pavement on Route 53 in Will County, Ill. The project used stringless paving technology on what was the old U.S. Route 66 alignment. thinner concrete overlays these days – down to 3 inches, even 2 inches. Some Iowa counties have paved a lot of miles of 4-inch overlays that have stood up well for years. And Illinois, Tennessee, and other states have paved many miles of thin con- crete overlays (formerly called ultra- thin whitetopping). These applica- tions, as well a stubborn economy is leading the American Concrete Pavement Association (ACPA) to ad- vance overlay technology in new directions. "Very thin overlays are the next S frontier for the concrete pavement industry," says Jerry Voigt, P.E., ACPA president and CEO. "This is where we have to go," he says with conviction. Voigt proposes that the industry re- verse-engineer a new overlay material 10 October 2012 Better Roads purred forward by some brave new thinking, the concrete pave- ment industry is working toward that would have durability, uniform thickness, compressive strength, and all the qualities of conventional concrete overlays. But instead of try- ing to fi t conventional concrete into a thinner section by adjusting panel sizes and joint spacings, Voigt says the industry should rethink and fi t the material to thin applications. The fi rst thinking should be to design the needed characteristics of a good-quality overlay, he says. With specifi c engineered qualities like du- rability, fl exibility and toughness in mind, the next effort would be to de- sign – or reverse engineer – a version of concrete to fi t those qualities. Voigt says the new overlay may be a shorter- term solution – it may not last 30 or 40 years, as people have come to ex- pect from conventional concrete. Thinner Can Work "I think we need to strive to achieve at least 3 inches," says Voigt. "A 2-inch layer would really be pushing the enve- lope. But if we can get to a 3-inch layer by modifying our material and look- ing at the concrete differently, then the number of places that could apply that solution will grow much more than it would with a 4-inch overlay." Jeffery R. Roesler, PhD, P.E., is an associate engineering professor at University of Illinois, and worked with Amanda C. Bordelon, Ph.D., to develop a new thin concrete wear- ing surface material. Called fl owable fi brous concrete (FFC), the mixture incorporates a hybrid of synthetic fi bers to give the concrete tough- ness and limit the size of cracks. "An objective of the wearing surface was to construct reasonable slab sizes and crack widths while ensuring economic feasibility," according to a paper by Roesler and Bordelon for the American Society of Civil Engineers.