Past, Present, and Future of Asphalt Binder Rheological Parameters

The notion of an aging and under-funded infrastructure in the United States is widely accepted. Current legislation calls for performance targets to be established to aid not only in the administering of funds, but also to assist states in identifying high-risk practices and roadways within their own networks. In addition to the performance targets, agency officials are looking to design and construct longer-lasting pavements through performance specifications.

In the late-1980s and early-1990s, the Strategic Highway Research Program developed a performance-based purchase specification for asphalt binders. High, intermediate, and low temperature performance is considered at single time or frequency points evaluated at different temperatures to meet American Association of State and Highway Transportation Officials (AASHTO) thresholds. Over the last 20 years, members of the asphalt pavement industry have expressed concerns over the ability of the performance-grading thresholds to accurately assess field performance. That concern has been magnified in recent years due to the increasing representation of polymers, recycled materials, and other products in asphalt pavements.

As industry experts explore refinements to the performance-grading system, rheological analysis of asphalt binders is coming to the forefront. This analysis may include interconversions between other viscoelastic properties (i.e., creep compliance to relaxation modulus) or master curve determination. This more comprehensive look at material behavior is likely needed because modifiers and other additives may render some of the more basic rheological assumptions invalid. While this is not necessarily indicative of poor performance, the behavior across the expected temperature and frequency conditions is beneficial nonetheless. More information is provided on these methods throughout the E-Circular.