A look at three Northeast U.S. states
By Greg Harder, P.E.
Back in the early 90s the advent of Superpave gave us a performance-graded (PG) binder specification known as AASHTO M320. The new PG specification considered the climate including both high and low pavement temperatures, traffic loading rates including both speed and volume plus incorporated aging of the binder within the testing framework to consider the binders performance with respect to permanent deformation and cracking.
Developed around neat asphalt binders, it was soon recognized that M320 did not properly characterize modified binders – especially those modified with elastomeric polymers. The PG specification was refined with the introduction of the Multiple Stress Creep Recovery (MSCR) test (AASHTO T-350) along with its corresponding specification AASHTO M332. While this change has been a significant improvement in the characterization of asphalt binders, its implementation nationally has been quite slow. (more…)