Evaluation of Test Methods to Identify Asphalt Binders Prone to Surface-initiated Cracking

The fatigue cracking and durability performance of asphalt airfield pavements are highly dependent on the characteristics of the asphalt binder incorporated in the asphalt mixture. Asphalt binders with poor relaxation properties and that are prone to accelerated age hardening typically cause asphalt mixtures to develop issues about raveling and non-load-associated cracking, as well as being highly susceptible to premature load-associated cracking. A research study was conducted to evaluate different asphalt binder test methods that capture key asphalt binder performance parameters, which were found to be highly correlated to asphalt mixture fatigue cracking performance. In Phase 1 of the study, various asphalt binder grades and sources were conditioned at four different levels and compared to the SCB Flexibility Index and IDEAL-CT Index with identical asphalt binders. The Phase 1 work resulted in the identification of three different asphalt binder parameters that ae sensitive to asphalt mixture fatigue cracking: (1) the Glover-Rowe parameter at the intermediate temperature of the mixture; (2) the (loss tangent)(2) at the intermediate temperature of the mixture; and (3) the (loss tangent)(2) at G* = 10 MPa. In Phase 2 of the study, asphalt binder was recovered from the top 1/2" of various field cores, evaluated using the parameters identified, and compared to the observed field performance. The laboratory and field studies showed that all three parameters have the potential to be utilized within a purchase specification, as well as for use in forensic studies, to identify asphalt binders that are prone to surface-initiated cracking and durability distress.