Laboratory Evaluation of Crumb-Rubber Modified (CRM) Binders and Mixtures (1332-1)

CRM binders were fabricated in the laboratory and evaluated according to ten different binder tests. Some of the test procedures routinely used for CRM binders were determined to have no apparent relationship to mixture properties or field performance. The SHRP binder tests were also used to characterized CRM binders. The SHRP direct tension test and, to a lesser degree, the force-ductility test appear to measure CRM binder characteristics, which are attributed to improved cracking performance in CRM mixtures.|Nine CRM mixture were evaluated using AAMAS characterization procedures: four wet-process mixtures, four dry-process mixtures, and one control mix. It was determined that CRM has the potential to significantly improve the fatigue and thermal cracking performance of asphalt concrete pavements, but only when the wet method is used and the binder is properly designed. The dry process should produce mixtures with reduced propensity for rutting, but may have an adverse effect on cracking.|Although state DOTs must comply with the existing legislative requirements, tire rubber, as any additive, should be used whenever possible to address a given mixture deficiency or expected deficiency in a given situation.