Evaluating the Characteristics of Crumb Rubber Modified Asphalt Binders Produced with Neat Bitumen—Case of Kuwait

This research study evaluated the characteristics of crumb rubber modified (CRM) asphalt binders produced with neat bitumen. Two different percentages of crumb rubber (CR); 10 and 15% and one bitumen type with penetration (Pen) grade 60/70 were evaluated. The evaluated characteristics included viscosity, ductility, Penetration, and softening point of the produced asphalt binders. Additionally, images obtained by Scanning Electron Microscopy (SEM) were used to investigate the surface topographies and compositions of the neat and produced CRM binders. SEM images were used to check for separation between the crumb rubber and the bitumen. Furthermore, the Multiple Stress Creep Recovery (MSCR) test was conducted in order to evaluate the rheological properties of the produced CRM asphalt binders. MSCR results showed that the addition of CR to the neat bitumen significantly improved the performance grade (PG) of the produced binder as per AASHTO M332 standards. The traffic loading level for both 10 and 15% CRM asphalt binder increased from “Heavy” for neat to “Extreme” level. Both 10 and 15% CRM binders passed local Kuwaiti requirement for modified binders. Based on AASHTO M332 standards, the 15% CRM binder is said to be not modified with an elastomeric polymer, unlike the 10% CRM binder, which was found to be modified with an acceptable elastomeric polymer. This can be attributed to the lack of full blending between the CR particles and the binder’s bulk due to the increase in CR percentage as shown by the SEM images