Two new standards have recently been approved by ASTM International Committee D04 on Road and Paving Materials. The standards are D 6931 Test Method for Indirect Tensile (IDT) Strength of Bituminous Mixtures, and D 7312 Test Method for Determining the Permanent Shear Strain and Complex Shear Modulus of Asphalt Mixtures Using the Superpave Shear Tester (SST).
According to Rich May, performance testing laboratory manager for SemMaterials, D 6931 will serve several purposes for pavement design engineers, mix designers and laboratory technicians. “This test has been used for evaluating many types of asphalt concrete performance, such as fatigue cracking propagation, rutting and moisture susceptibility or stripping, where half of the specimens are subjected to conditioning to evaluate the loss in strength compared to unconditioned specimens,” says May. However, D 6931 is not a new test. It has been used by many in the pavement field over the last 40 years to predict performance and evaluate reasons for distress, such as stripping and segregation.