Testing and Evaluation of Large Stone Mixes Using Marshall Mix Design Procedures
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1989-11-01
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Abstract:Premature rutting of heavy duty asphalt pavements has been increasingly experienced in recent years primarily due to high pressure truck tires and increased wheel loads. Many asphalt technologists believe that the use of large size stone (maximum size of more than one inch) in the binder and base courses will minimize or eliminate the rutting of heavy duty pavements. The equipment specified in the Marshall procedure (ASTM D 1559) used y 76 percent of the states in the United States consists of a 4-inch compaction mold containing aggregate up to l-inch maximum size only. This has inhibited the use of large stone mixes. A standard method for preparing and testing 6-inch diameter specimens has been presented. The proposed method has the following significant differences from ASTM D 1559: (a) hammer weighs 22.5 pounds, (b) specimen size is 6-inch diameter and 3-3/4 inch height, (c) specimen weighs about 4,050 grams, and (d) the number of blows needed is 1-1/2 times the number of blows needed for a standard Marshall specimen to obtain equivalent compaction levels. Comparative test data (4-inch versus 6-inch diameter specimens) obtained from various highway agencies and producers indicates that the compaction levels are reasonably close. The average stability ratio (stability of 6-inch specimen/stability of 4-inch specimen) and flow ratio (flow of 6-inch specimen/flow of 4-inch specimen) were determined to be very close to the rationally derived values of 2.25 and 1.50, respectively. Typical mix designs using 6-inch specimens are also given. Construction data and experience gained from six field projects in Kentucky and Pennsylvania is also included. It is believed that the proposed test method will be useful in determining the optimum asphalt content of large stone asphalt mixes. Because of the size of this document, it is broken into two sections which can be accessed from the HTML page linked in this record. References, appendices. 54p.
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