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Special Feature: Concrete Roads

SpecialFeature by Dan Brown, Contributing Editor AMERICAN CONCRETE PAVEMENT ASSOCIATION Superthin concrete Overlays S purred forward by some brave new thinking, the concrete pavement industry is working toward 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 concrete overlays (formerly called ultrathin whitetopping). These applications, as well a stubborn economy is leading the American Concrete Pavement Association (ACPA) to advance overlay technology in new directions. “Very thin overlays are the next 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 reverse-engineer a new overlay material 10 October 2012 Better Roads that would have durability, uniform thickness, compressive strength, and all the qualities of conventional concrete overlays. But instead of trying to ﬁt conventional concrete into a thinner section by adjusting panel sizes and joint spacings, Voigt says the industry should rethink and ﬁt the material to thin applications. The ﬁrst thinking should be to design the needed characteristics of a good-quality overlay, he says. With speciﬁc engineered qualities like durability, ﬂexibility and toughness in mind, the next effort would be to design – or reverse engineer – a version of concrete to ﬁt those qualities. Voigt says the new overlay may be a shorterterm solution – it may not last 30 or 40 years, as people have come to expect from conventional concrete. Thinner Can Work “I think we need to strive to achieve “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. at least 3 inches,” says Voigt. “A 2-inch layer would really be pushing the envelope. But if we can get to a 3-inch layer by modifying our material and looking 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 wearing surface material. Called ﬂowable ﬁbrous concrete (FFC), the mixture incorporates a hybrid of synthetic ﬁbers to give the concrete toughness 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.

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