Multiple Stress Creep and Recovery and Time Sweep Fatigue Tests: Crumb Rubber Modified Binder and Mixture Performance

Crumb rubber modification (CRM) is an effective means of improving neat asphalt performance. Numerous studies have investigated the effects of CRM using the current Superpave® laboratory tests. Recent studies have shown that the assumption of linear viscoelastic behavior or employing insufficient stress or strain levels makes current tests inadequate for properly assessing the performance of binders, especially when modified. This problem has resulted in the development of improved test methods such as the time sweep binder fatigue test and the multiple stress creep and recovery (MSCR) test for permanent deformation. The present study assesses the performance of binders modified with a wide range of crumb rubber content using these newly developed test methods. Additional binder and mixture performance tests were used to compare and validate the results. The results showed that the new tests performed well in predicting performance. Current Superpave criteria also showed good conformance with mixture test results for CRM binders. Tests results suggest that the MSCR can complement current rutting prediction testing. Also, the time sweep test produces results similar in accuracy to current Superpave tests, but it requires longer testing time and is thus not recommended for performance grading.