ASTM D7312-07

The test procedures and associated analysis techniques described in this method can be used to determine complex shear modulus and permanent shear strain of asphalt mixtures. The shear frequency sweep test at constant height can be used to determine the complex shear modulus of a mixture. The repeated shear test at constant height can be used to determine permanent shear strain under repeated loading.

Note 4—The complex shear modulus is used to characterize the shear behavior of the mixture, and the permanent shear strain relates to pavement rutting.

1.1 This standard provides performance-related test procedures for the determination of stiffness complex shear modulus and permanent shear strain of asphalt mixtures using the Superpave Shear Tester (SST). This standard is applicable to the testing and analysis of modified and unmodified asphalt mixtures.

1.2 This standard is applicable to specimens prepared in a laboratory or cored from a pavement for post-construction analysis. It is intended for use with specimens having the following minimum dimensions:

Nominal maximum aggregate size is defined in AASHTO R35 as one sieve larger than the first sieve to retain more than 10 % of the total aggregate. Asphalt mixtures with a nominal maximum aggregate size greater than 19 mm can be tested using this procedure, but it is not recommended. The larger aggregate sizes may significantly interfere with the material response, thereby affecting the repeatability of the test.

The SST shall accommodate test specimens of 150 mm in diameter and 50 mm in height. The specimen height of 50 mm is preferred, but may not be available in roadway cores where layer thickness may be less. If the specimen height is less than 50 mm, use platen to platen fixturing (Linear Variable Differential Transformers (LVDTs) or extensometers). Specimen heights less than 38 mm cannot be tested because of equipment constraints.

The diameter-to-height ratio for shear test specimens should be 3:1 or greater. This effectively eliminates the use of 100 mm diameter specimens (because of minimum height requirement for testing discussed in NOTE 2).

1.3 The between laboratory reproducibility of this test method has not been determined, therefore this standard should not be used for acceptance or rejection of a material for purchasing purposes.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.