AASHTO T 320-07 (2020) PDF Download

AASHTO T 320-07 (2020) is a standard method of test that provides procedures for determining the permanent shear strain and stiffness of asphalt mixtures using the Superpave Shear Tester (SST). This standard applies to both modified and unmodified asphalt mixtures and can be used for specimens prepared in a laboratory or cored from a pavement for postconstruction analysis.

It is important to note that the nominal maximum aggregate size should not exceed 19 mm, as larger aggregate sizes may interfere with the material response and affect the repeatability of the test. The SST is capable of testing specimens with a maximum diameter of 150 mm and a preferred height of 50 mm. However, in cases where roadway cores have a layer thickness of only 38 mm, specimens with a height less than 38 mm cannot be tested due to equipment constraints.

The standard also states that the diameter-to-height ratio for shear test specimens should be 3:1 or greater. As a result, the use of 100-mm diameter specimens is effectively eliminated because of the minimum height requirement for testing.