Effect of crumb rubber particle size and concentration on performance grading of rubber modified asphalt binders

This study evaluates two aspects of the performance related Superpave(TM) binder specification methodology: 1) the applicability of the dynamic shear rheometer (DSR) to crumb rubber modified binders, and 2) the effect of crumb rubber particle size and concentration on the higher temperature performance grading of rubber modified asphalt binders. Results indicate that the Superpave(TM) DSR test protocol is applicable to the modified binders used in this study. The average coefficient of variation for the different specimen thickness and replicate testing based on the measured property G*/sin delta obtained was 6.2% and 6.5%, respectively. In general, the crumb rubber particle size did not affect the performance grading of the modified binders. A 7% crumb rubber modification increased the high temperature performance grading by one grade; whereas, the 14% crumb rubber modification increased the performance grading by two grades. For high temperature range, the unmodified and modified binders with the same performance grade appear to show similar characteristics.