Evaluation Systems for Crumb Rubber Modified Binders and Mixtures

Abstract

The use of crumb rubber modified (CRM) asphalt mixtures has been increasing steadily. The reasons for this increase in use are twofold: the Intermodal Surface Transportation Efficiency Act of 1991 mandate and the potential of better performance. The technology of testing, design, and evaluation of CRM binders and mixtures has not yet caught up. Therefore, there is a need for establishing standard procedures for the design and evaluation of CRM mixtures. The outcome of a recent research project sponsored by the Nevada Department of Transportation (NDOT) is presented. The binder testing system concentrated on the newly developed Strategic Highway Research Program (SHRP) performance grading system and its applicability to CRM binders. It was concluded that the standard SHRP system will not work for CRM binders containing coarse rubber particles. The plate and cup system will have to be used for such CRM binders. However, the plate and cup system cannot adequately replace the bending beam rheometer for low-temperature testing. In the case of CRM mixtures, a modified Hveem mix design procedure was developed and validated on an actual NDOT project. Temperature susceptibility, moisture sensitivity, rutting resistance, and low-temperature cracking of CRM mixtures also are presented.