Description

AASHTO T 320 – Standard Method of Test for Determining the Permanent Shear Strain and Stiffness of Asphalt Mixtures Using the Superpave Shear Tester (SST)

AASHTO T 320-07 (2020) provides performance-related test procedures for the determination of stiffness and permanent shear strain of asphalt mixtures using the Superpave Shear Tester (SST). Modified and unmodified asphalt mixtures can be tested and analyzed using this standard.

This standard is applicable to specimens prepared in a laboratory or cored from a pavement for postconstruction analysis.

Note 1- Nominal maximum aggregate size is defined in R 35 as the sieve greater than the first sieve to retain more than 10 percent 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.

Note 2 – The SST is only capable of testing specimens with a maximum diameter of 150 mm. The specimen height of 50 mm is preferred, but may not be available in roadway cores where layer thickness may only be 38 mm. Specimen heights less than 38 mm cannot be tested because of equipment constraints.

Note 3 – 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).