Design Of Open Graded Asphalt Friction Courses
Primary Topic: Pavement Design
Description: Efforts to improve pavement skid resistance have shown the advantages of using open-graded asphalt paving mixtures. Extensive implementation of these mixtures has been hampered, however, due to some difficulties encountered during construction and some deficiencies observed in service performance. These problems are partially attributable to a number of uncertainties involved in existing design methods. A new design method has been developed which purports to satisfy the immediate needs of the highway industry. The method is a constructive blend of past experience and a new approach to the problem. The concept used is that the open-graded asphalt friction course consists predominantly of a narrowly-graded coarse aggregate fraction with a sufficiently high interstitial void capacity to provide for a relatively high asphalt content, a high air void content, and a relatively small fraction of fine aggregate. The coarse aggregate fraction provides the structure of the composite mixture while the fine aggregate fraction acts as a filler and imparts a chocking action; to stabilize the coarse aggregate. The high asphalt content provides for mixture durability and the high air void content provides for adequate subsurface water drainage.
The described method is relatively new, but has been used successfully on several FHWA, R& Demonstration Projects. It is believed that the proposed method provides technological improvements over other existing methods, and its use is recommended for immediate experimental application.
FHWA Publication Number: FHWA-RD-74-2
Publication Year: 1974