Developing Simple Binder Indices for Cracking Resistance of Asphalt Binders at Intermediate and Low Temperatures

Abstract

Oxidative aging causes hardening of asphalt binders and, consequently, contributes to deterioration of asphalt pavements. Non-load related cracking of asphalt pavements (i.e., transverse and block cracks) is related to original properties and hardening of the asphalt binder. In recent years, researchers have proposed new indices derived from Superpave Performance Graded (PG) testing to identify changes in asphalt cracking susceptibility with aging. These indices include the parameter G′/(η′/G′) and the difference between continuous low temperature binder grade measured via Superpave creep stiffness and m-value (ΔTc). This study aims to develop interrelationships between tests allowing choice selection for the determination of simpler parameters that could be used for specification tests of asphalt binders. Two simpler asphalt binder indices for cracking resistance are investigated by means of Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) and Single Edge Notched Bending (SENB) tests results. At intermediate temperatures, the slope of the |G*|-frequency curve obtained from a simple frequency sweep test is proposed as an alternative approach to directly calculate the durability parameter G′/(η′/G′). At low temperatures, results indicated a direct correlation between failure energy at fracture obtained from SENB and ΔTc. To confim the validity of these indices and the changes at molecular level, Gel Permeation Chromatograph (GPC) results are presented to indicate that asphalts with higher content of large molecular size (LMS) molecules are likely to crack. Limits for specifcations for the slope of |G*|-frequency curve and ΔTc can be derived based on testing a wide range of binders and field experience.