Rutting of heavy-duty pavements has been increasingly experienced in recent years primarily because of high tire pressures and increased wheel loads. Many asphalt technologists believe that the use of large size stone (maximum size of more than 1 in. ) 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 by 76% of the states in the united states consists of a 4-in. Diameter compaction mold intended for mixes containing aggregate up to 1 in. Maximum size only. This has inhibited the use of large stone mixes. A standard method for preparing and testing 6-in. Diameter specimens has been presented. Theproposed method has the following significant differences from astm d 1559: (a)hammer weighs 22.5 Lb, (b) specimen size is 6 in. In diameter and 3 3/4 in. In height, (c) specimen weighs about 4, 050 g, and (d) the number of blows needed is1 1/2 times the number of blows needed for a standard marshall specimen to obtain equivalent compaction levels. Comparative test data (4-in. Versus 6-in. Diameter specimens) obtained from various highway agencies and producers indicate that the compaction levels are reasonably close. The average stability ratio (stability of 6-in. Specimen/stability of 4-in. Specimen) and flow ratio (flow of 6-in. Specimen/flow of 4-in. Specimen) were determined to be very close to the theoretically derived values of 2.25 And 1.50, Respectively. A typical mix design by using 6-in. Specimens along with limited field data is also given. It is believed that the proposed test method will be useful in determining the optimum asphalt content of large-stone asphalt mixes. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Abstract