Better Roads

Photo courtesy of Asphalt Pavement Alliance RoadScience Asphalt perpetual pavement design calls for deep, robust, fatigue crackresistant layers of asphalt, of different mix formats, topped with a sacrificial friction course that can be periodically milled and overlaid. The perpetual pavement concept was first articulated in 2000 by the Asphalt Pavement Alliance (APA), a joint promotional effort of The Asphalt Institute, NAPA, and the State Asphalt Pavement Associations, representing local contractor associations in 36 states. A perpetual pavement is defined by APA as an HMA pave- ment designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction, and needing only periodic surface renewal in response to distresses confined to the top of the pavement. Perpetual pavement's increased durability is a product of mechanistic design, instead of long-standing empirical design. Its mechanistically based pavement design incorporates how traffic stresses induce strain that will affect the pavement's performance, taking into account material qualities and thickness. By contrast, an empirical design would take the results of existing experience, in the industry's case, the AASHO Road Tests, and make the design conform to a test design that successfully withstood loadings that mirror those anticipated for the new construction. By designing the pavement to keep strain below the critical level, fatigue failure is avoided and perpetual performance can be assured, proponents say, adding structural and aeronautical engineers have used mechanistic design principles for years. Another approach to ensure long-term fatigue life is to design a thickness for a stiff structure so the tensile strain at the bottom of the asphalt layers is insignificant. This allows for the use of a single mix design in the base and intermediate layers, and precludes the need to change mix types in the lower pavement structure.v Introducing... Flameless All-In-One Pothole Patcher InPaveTM Management System PATCHING SOLUTION PROVIDER! A New Patching Solution! See Us At APWA Bergkamp is your one source for unique patching solutions that support the way you maintain your roads. Booth 1500 Bergkamp Inc. 3040 Emulsion Drive, Salina, KS 67401-8966 USA Phone: (785) 825-1375 • Fax: (785) 825-4269 • sales@bergkampinc.com • www.bergkampinc.com Text INFO to 205-289-3789 or visit www.betterroads.com/info Untitled-4 1 12 August 2013 Better Roads RoadScience_BR0813_old.indd 12 7/30/13 3:12 PM 8/1/13 10:55 AM

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• BETTER Bridges: Big River Bridges Getting Smarter: The four bridges that span the Mississippi River to join Mississippi to Arkansas and Louisiana are getting major Intelligent Technology System upgrades to make them safer and to improve traffic management
• ROADSCIENCE: A Good, Long Life: In Part IV of our series Building Roads that Won't Fail, Tom Kuennen looks at some of the tools that civil engineers can use to design pavements that keep performing as they should over the longest time possible. Such thin
• APPLICATIONS & INNOVATIONS: Managing Winter: It's year-round job, but now is one of the most important periods in making sure your winter months will be safe and productive. FMI's Brian Moore says managers now should be focused on a few key areas that can
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