Road Science Tutorial
The new Rocky Mountain West partnership includes the transportation agencies of Alaska, Arizona, California, Colorado, Hawai’i, Idaho, Montana, Nevada, New Mexico, Oregon, Utah and Washington State, and through three task forces will focus on promoting the pavement preservation concept, refining terminology, definitions and communication, and affirming standard guidelines for chip seal materials.
Coordinating Thin-Lift Research
The regional groups do more than just meet once or twice a year and conduct regional workshops. For example, this year the Northeast Pavement Preservation Partnership (NEPPP) is coordinating field demonstrations of thin-lift hot asphalt mix pavement applications incorporating highly polymer modified asphalt binders.
NEPPP members Vermont Agency of Transportation and the New Hampshire, Rhode Island and Pennsylvania DOTs, are being joined by Midwest member Minnesota DOT and Southeast member Tennessee DOT to make this research on highly polymer modified, thin-lift asphalt overlays happen in 2011.
At press time, planning for four thin-lift asphalt mix field demonstrations was underway, to be executed in 1- to 3-mile sections included in existing asphalt overlay or mill-and-fill transportation agency contracts.
The demos will follow regional mix design specifications with testing protocols developed by NEPPP participating agencies, with guidelines for the new specifications distributed by Dr. Walaa Mogawer, P.E., professor, and director of the Highway Sustainability Research Center at the University of Massachusetts-Dartmouth.
Kraton Polymers is funding the project to minimize participating agency expenses, and also is donating the cost of Mogawer’s lab services, as well as the additional polymer needed for demonstrations.
The NEPPP regional specifications, titled Superpave 9.5 mm Highly Polymer-Modified Thin Overlay Specifications (PMTOL), describe the mix design as a pavement preservation strategy used to extend a pavement’s service life without improving its structural capacity. It further says the mix design is a preventive maintenance strategy that can be applied to pavements in good condition that do not require structural rehabilitation.
The thickness of the PMTOL ranges from 0.75 to 1.5 inches (19.0 mm to 37.5 mm), and consists of coarse aggregate, fine aggregate, mineral filler if needed, and a polymer modified asphalt binder. Specifications allow the use of up to 25-percent recycled asphalt pavement in the mixture. In addition, the performance grade of the polymer modified asphalt binder must be either PG 76-34 or PG 82-28, with PG 76-34 recommended for roadways exhibiting low-severity cracking and PG 82-28 recommended for roadways with little or no distresses.
However, for these demonstrations, a 1-inch-thick lift is planned. The concentration of polymer – a styrene-butadiene-styrene (SBS) polymer – allowed in the asphalt binder will be up to 8 percent, more than twice the polymer content usually allowed in traditional polymer-modified binder.
Although the modification of asphalt binders with polymers improves resistance to rutting and raveling in asphalt mixes, there is a practical limit to polymer concentration. Usually, as the concentration exceeds 3 percent, the viscosity of the binder increases, making the mix more difficult to produce in the plant and less workable for the paving crew. The polymer being used in the demonstrations will be a new type of polymer manufactured by Kraton Polymers that meets the requirements of the new regional specifications without increasing viscosity.
Indiana Embraces Preservation
The state of Indiana has embraced pavement preservation as a means of optimizing its program funding, and is implementing it from border to border.
“We have a comprehensive pavement preservation approach for Indiana statewide, using both in-house and contract work,” says Will Wingfield, public information officer, Indiana DOT. “It’s part of a larger, asset management-approach to how we manage our transportation network.”
Two distinct programs are ongoing at Indiana DOT, Wingfield says. “We have the Major Moves program, brought about by the 75-year lease of the Indiana Toll Road,” Wingfield tells Better Roads. “For that we received an upfront payment of $3.85 billion. Once our bonds were paid off, the rest of the money was dedicated to economic development and transportation infrastructure, much for state highways. In 2006, this provided a program for major reconstruction and capacity increases that had been discussed for decades, but never were able to move forward due to funding.”
In 2008, a separate Major Preservation program was started. “One of the people who helped bring it about now is our DOT commissioner [Michael B. Cline, P.E.], and he initiated the program in part to maintain and preserve both our existing infrastructure, and the new infrastructure coming online from Major Moves.”
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