Characterization of Dense-Graded Asphalt Containing Virgin, Postconsumer, or Blended Polymer Systems

Abstract

This paper contains data related to ground tire rubber (GTR), and binder and mixture performance information is presented that validates some aspects of current practice yet shows that other areas could be improved. While GTR has been utilized in asphalt paving since the 1960s and use in dense-graded mixes began in the late 1980s to early 1990s, proper formulations (including understanding GTR's functional polymer content) have been lacking a considerable portion of the time. This paper's primary objective was to review, evaluate, and suggest enhancements to GTR modified binder characterization. One finding was that parallel plate (PP) testing at a 2-mm gap is adequate for binders with 30 mesh (0.595 mm) and finer GTR particles, while cup and bob testing is more suitable for binders with coarser GTR particles. Enhancements were suggested for GTR's use in modified binder systems related to incorporating hybrid binders containing styrene-butadiene-styrene (SBS) and GTR. Discussion is provided regarding specifying GTR based on virgin polymer replacement.