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Materials Notebook: Asphalt Mix Design and Field Control - February 16, 1988 Memorandum 4-1
There are presently about 1,420,000 miles of intermediate or high type flexible pavements on State highways and local roads. This represents about 70 percent of the paved mileage on all public roads and streets. In 1986, about $2 billion of asphalt concrete was placed on Federal-aid projects and this amount will likely increase in the future. Information that has been gathered over a number of years by the States, FHWA, and the asphalt industry has revealed that a number of asphalt concrete pavements are experiencing premature distress and significantly reduced pavement performance periods. Types of distress identified have included bleeding, cracking, shoving, rutting, stripping, and raveling.
Two distress types, rutting and stripping, have had a high frequency of occurrence over wide areas of the United States. The reduction in pavement performance due to rutting or stripping is potentially severe from a national perspective. Due to the continuing major investment which is being made in asphalt concrete pavements and as a result of reports indicating premature rutting and stripping problems, we appointed an Ad Hoc Task Force to examine the problems of asphalt concrete pavement rutting and stripping, and to develop FHWA policy recommendations. The Task Force has completed its assignment and a copy of its report was provided to each region and division office. In accordance with one of the Task Force's major recommendations, our Technical Advisory (TA) on this subject has been updated to reflect current knowledge. Attached for your immediate use is a copy of the TA "Asphalt Concrete Mix Design and Field Control." This TA sets forth guidance and recommendations relating to asphalt concrete paving. It covers the areas of materials selection, mixture design, mixture production, and mixture placement. The TA is intended primarily for application on high type facilities.
Each division office is to initiate an effort to compare the updated TA to present State specifications and construction practices. Differences and/or deviations are to be discussed with the State and, if appropriate, industry representatives. Some States have found it beneficial to have a formal committee composed of State, FHWA, and industry personnel to scrutinize the State's mix design, and field control procedures, and iron out differences with the TA. The TA is a consensus of current best practice, and serious consideration should be given to adopting its recommendations. Sound engineering judgment must be used in determining what is best for each particular State but deviations from the TA recommendations should be supportable.
We recognize that some States have been working in strengthening their asphalt concrete mix design and field control practices. These efforts are appropriate and continued involvement of all the field offices in encouraging conformance with the attached TA will be expected.
Other factors such as truck weights, high tire pressures, etc., also contribute to the rutting and stripping problems and we are working on these issues. We are convinced though that significant gains in solving rutting and stripping problems can be achieved by using quality materials and strengthening specifications and construction practices. We expect those States where rutting and stripping is a problem to include a priority effort to improve the design and construction of asphalt concrete pavements. The Pavement Division and the Construction and Maintenance Division are available upon request to provide technical support and guidance, which may be necessary in achieving these actions.
SIGNED R.D. MORGAN