What’s the Number One reason to test asphalt binders?
Asphalt binders (also called bitumen, liquid asphalt) hold an asphalt mixture together as the glue. Binder testing standardizes the product used in making asphalt mixtures to ensure it will perform as expected. That means the Number One reason we test a binder is to make sure it conforms to the standards required by agency specifications.
Specifications help achieve uniformity among asphalt pavements to ensure the pavements can withstand environmental stresses and traffic loads. They’re designed to conform to local seasonal temperature variations and help prevent premature pavement failure that can cost the customer or taxpayer thousands or even millions of dollars. Falling short can result in rejected loads, penalties, or worse — a complete repave.
Testing of binders helps ensure they will meet AASHTO M 320 or AASHTO M 332 specifications. Labs should be able to test all types of binders, including polymer-modified, rubber-modified, or additive-modified binders. Look for a state-of-the-art laboratory that utilizes the latest equipment, including the Dynamic Shear Rheometer (DSR) AASHTO T 315, the Bending Beam Rheometer (BBR) AASHTO T 313, a Rolling-thin Film Oven (RTFO) AASHTOT 240, and Pressure Aging Vessel (PAV) AASHTO R 28. Both the RTFO and PAV are used to accelerate the long-term aging and oxidation of asphalt binders, which are then tested with the DSR and BBR.
The latest testing methods can predict binder aging quality by using 20- or 40-hour PAV conditioning and then measuring the stiffness and slope in the BBR to determine Delta Tc.
Tests for additives can be accomplished through blending/formulation, which includes the use of high shear blending of polymers. Whether you need basic spec testing, or a more detailed, fundamental analysis, look for a lab that doesn’t simply check a box when completing a test, but one that fully analyzess the binder and provides feedback to help you understand how it will perform in the mix.
This article was prepared by asphalt materials engineer Phil Blankenship, PE, MSCE. He and other members of the BATT Team work with agencies, producers, and contractors to evaluate asphalt mixture performance and extend pavement life. He has authored or co-authored numerous peer-reviewed papers on asphalt technology.
