Performance grade of asphalt mixtures based on mixture performance test thresholds

Abstract

At present, the way of fingerprinting a multi-binder, heterogeneous asphalt mixture systems involves the testing of extracted and recovered binder from lab specimens or field cores. However, concerns have been raised over the recovery of a truly representative binder sample from mixtures with modified binder system (additives, recycled binder, etc). On the other hand, mixture performance tests have been shown to: a) distinguish between different constituents of an asphalt mixture, and b) correlate well to the field performance. This study attempts to establish necessary groundwork to allow the development of a mixture-based, usable temperature grading system as an alternative to the existing grading system for recovered binders. A novel Mixture Performance Grading system is proposed that utilizes two mixture tests, namely, the Hamburg wheel track test (HWTT) and Disk-shaped compact tension (DC(T)) test, to compute a mixture-based performance grade. Both tests have shown excellent correlation with field performance data, and permit high and low temperature grading along with the computation of a mixture-based Usable Temperature Interval (UTI). The grading system involves conducting the tests at multiple temperatures and then using appropriate thresholds to find a failure temperature, analogous to current specification to determine failure temperatures of recovered binder. Eight mixtures were tested in this study including mixtures placed on Missouri roads (referred to as Level 1 mixes) and mixtures with various modifications (referred to as Level 2 mixes). The mixture grading approach was found to appropriately credit mixtures composed of high-quality aggregate structures, binders, additives, interactions between mixture ingredients, and those with good mixture volumetric designs. Obviously, the ability to evaluate the efficacy of mixture-based ingredients and mixture design variables is a key evolutionary step over traditional (and cumbersome) binder grading for modern, heterogeneous recycled asphalt mixtures.