AASHTO T 393-21 PDF Download

The AASHTO T 393-21 standard provides guidelines for assessing the cracking resistance properties of asphalt mixtures at intermediate temperatures. This test method utilizes the semicircular bend geometry, where specimens in the form of half discs with notches parallel to the direction of load application are subjected to testing.

The test aims to determine the fracture energy (Gf) and post-peak slope (m) of the load-load line displacement (LLD) curve, which are key parameters in quantifying the asphalt mixture's resistance to Mode I cracking, specifically tensile opening during crack propagation. These parameters are then used to calculate a flexibility index (FI) that serves as an indicator of the asphalt mixture's fracture resistance at intermediate temperatures.

The standard applies to test specimens with a maximum nominal aggregate size (NMAS) of 19 mm or smaller. It allows for testing of laboratory compacted specimens as well as pavement core samples. However, if the thickness of pavement cores is less than 45 mm, a thickness correction factor needs to be developed and applied during testing. The results obtained from this test method can be utilized as part of the approval process for asphalt mixtures.