FHWA Develops New Method of Testing Concrete
Federal Highway Administration
August 15, 2000
FOR IMMEDIATE RELEASE
Tuesday, August 15, 2000
Contact: Karen Whitney
New Approach Will Help Yield Smoother, More Durable Roads
In their search for better highways, researchers at the U.S. Department of Transportation’s Federal Highway Administration (FHWA) have developed a precise method for determining the rate at which portland cement concrete (PCC) contracts and expands during temperature changes. The information generated by this new method will lead to longer lasting, smoother roads.
About half of the roads on the 43,000-mile interstate system are composed of concrete or a combination of asphalt and concrete. The new test method provides a means of characterizing concrete that will significantly improve the pavement design process by "matching" pavement better to its environment.
"This kind of application-oriented research is part of our commitment to providing Americans with the safest, most efficient transportation system in the world," FHWA Administrator Kenneth R. Wykle said. "Our new testing procedure will take the guesswork out of one of the most critical elements of PCC pavement design, enabling engineers to fine-tune the process at the outset to significantly improve roads."
The thermal coefficient of expansion (T-coeff), the rate at which concrete contracts and expands as temperature changes, is a critical factor in pavement design. The new method determines the T-coeff by precisely measuring the change in length of a sample of the concrete when it is heated and cooled. The capability for testing T-coeff has been around for some time, but this new procedure makes it easier to collect the data, requires little additional equipment, and most important, standardizes the process.
Before FHWA’s new testing procedures, pavement designers usually relied on an average value to estimate the T-coeff of portland cement concrete. Using an average value left the design process vulnerable to incorrect assumptions about a specific pavement’s response to temperature changes. This increased the potential for producing pavements that would develop bumps, cracks and other surface irregularities after construction.
The new test method, which includes new testing equipment, was recently approved by the American Association of State Highway and Transportation Officials (AASHTO) as test number TP60-00, "Standard Test Method for the Coefficient of Thermal Expansion of Hydraulic Cement Concrete." It is included in the 2000 edition of AASHTO Provisional Standards.
The PCC Pavement Team researchers who developed the test at FHWA’s Turner-Fairbank Highway Research Center in northern Virginia are also using the test in-house to measure the T-coeff of concrete pavement cores from around the country. This data will be included in the Long Term Pavement Performance database so that it can be used to help analyze current pavement performance, as well as design better pavements in the future.
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