Importance of Elastic Recovery in the DSR for Binders and Mastics

Elastic Recovery (ER) is used by many highway agencies for modified bitumen grading specifications. The current ASTM/AASHTO standards for ER testing utilize the ductility bath as the measurement apparatus. A new procedure for measuring the elastic recovery in the Dynamic Shear Rheometer (ER-DSR) was developed and was used to test different polymer modified binders and mastics. The results show a good correlation between the ER-DSR and ER measured in the ductility bath (ER-DB). The ER-DSR requires less material and is more time efficient and repeatable than the ER-DB. Since the link between the ER measurements and pavement performance is not well established, the study compared ER measurements with binder rutting and fatigue results as measured by the Multiple Stress Creep and Recovery (MSCR) test and the linear amplitude sweep (LAS) test, respectively. Generally, binders and mastics with higher ER-DSR value showed higher percent recovery (MSCR) and fatigue resistance (LAS). This study also showed the effect of natural and manufactured fillers on the percent recovery measured with the MSCR test. Based on the experimental results, it is recommended to replace ER-DB with the ER-DSR. Also, agencies should consider the MSCR and fatigue tests as indicators of binder modification rather than the ER, as they provide direct measurements of damage resistance characteristics for which the elastic recovery might not indicate.