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Publication Number: FHWA-RD-00-056
Date: February/March 2000
When the Kansas Department of Transportation (DOT) switched to the Superpave performance-graded binder specification several years ago, the agency became concerned that the specification might be too restrictive, compelling them to select a binder that might be "softer" than needed for the winter months, yet not hold up as well in the summer months, when a "harder" binder is needed. The reason: the original binder specification developed under the Strategic Highway Research Program (SHRP), which is based on expected high and low temperatures at a site, uses the lowest air temperature in a region instead of the lowest pavement temperature.
During the first 72 hours of a portland cement concrete (PCC) pavement's life, temperature, moisture, and other factors have a significant effect on its long-term durability and performance. For example, if a paving crew applies curing compound to newly placed concrete, they may feel they have adequately protected the concrete from excessive stress during its early age. However, the concrete may still experience a significant temperature drop or other temperature changes within the slab due to wrongly timed placement and/or a change of environmental conditions. These temperature changes can cause excessive tensile stresses that cause the pavement to crack.
Since the introduction of FHWA's LTPPBind software in 1998, pavement engineers have used the program to more easily select the correct performance graded (PG) binder to use for a specific location when implementing the Superpave mix design system. Now college engineering students studying the Superpave binder specification, which classifies binders based on their suitability in a range of climatic conditions, are finding the software to be an equally effective aid.
FHWA will hold a "train the trainer" Pavement Technology Workshop at its Midwestern Resource Center in Olympia Fields, Illinois, on March 27-30, 2000, for pavement and materials engineers in its four resource centers. This workshop will help familiarize the engineers with the LTPP program, Superpave, and other products and marketing materials. For more information, contact Charlie Churilla at FHWA (phone: 202-493-3142; fax: 202-493-3161; email: email@example.com).
The long-anticipated Superpave software has arrived. The software, which made its debut at the Transportation Research Board annual meeting last month in Washington, DC, allows users to design asphalt mixes using the Superpave mix design procedures.
The American Association of State Highway and Transportation Officials (AASHTO) Task Force on SHRP Implementation, which has been a key player in the nationwide program to get the products of the Strategic Highway Research Program (SHRP) into the hands of State agencies and industry, has embarked on its "farewell tour," says Task Force Chairman John Conrad of the Washington State Department of Transportation (DOT). The Task Force is scheduled to sunset in fall 2000, with its mission largely accomplished.
The Strategic Highway Research Program (SHRP) may have ended 6 years ago, but "one of the greatest success stories in the history of applied research continues to make a difference," declared John Horsley of the American Association of State Highway and Transportation Officials (AASHTO) at the 12th annual SHRP/LTPP Coordinators Meeting in January. The gathering, held in conjunction with the Transportation Research Board (TRB) annual meeting in Washington, DC, drew representatives from State highway agencies, AASHTO, the Federal Highway Administration (FHWA), and others to hear updates on SHRP implementation efforts and the progress of the long-term pavement performance (LTPP) program.
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