Comparative Evaluation of 4-Inch and 6-Inch Diameter Specimens for Testing Large Stone Asphalt Mixes

摘要

Increased incidence of premature rutting of heavy duty asphalt pavements has been experienced in recent years. There is a general agreement among most asphalt paving technologists that the use of large size stone in the binder and base courses will minimize or eliminate the rutting of heavy duty-pavements. However, the wide acceptance of the Marshall and Hveem mix design procedures inhibits the use of large stone mixes because these methods use standard 4-inch (101.6 mm) diameter specimens and limit the maximum aggregate size to one inch (25.4 mm). Modified Marshall equipment and Gyratory Testing Machine (GTM) are now available for compacting and testing 6-inch (152.4 mm) diameter specimens to accommodate aggregate up to 2-inch (50.8 mm) maximum size. However, some agencies continue to use 4-inch diameter specimens for mixes containing 1- 1/2 inch (38.1 mm) maximum size aggregate. This study compares the mix properties such as Marshall stability and flow, indirect tensile strength, and permanent deformation (from static creep test) obtained on 4-inch and 6-inch (101.6 and 152.4 mm) diameter specimens. Both Modified Marshall and GTM equipment were used to compact the specimens of these two sizes. The maximum aggregate size ranged from 1/2 to 1 1/2- inches (12.5 to 38.1 mm). The test data indicates increased coefficient of variation when testing 4-inch (101.6 mm) specimens of the mix containing aggregate larger than one inch (25.4 mm) compared to 6-inch (152.4 mm) specimens. The 6-inch (152.4 mm) diameter specimens also had lower variability in creep test compared to 4-inch (101.6 mm) specimens. Laboratory and rationally derived data indicating the ratios by which stability and flow values increased is also given in the paper. It has been recommended to use 6-inch (152.4 mm) diameter specimens for large stone asphalt mixes.