A Rheological Comparison of Low Dosage Crumb Rubber Modified Binders as an Anti-Aging Additive

Abstract: The performance enhancing effects of crumb rubber modified (CRM) binders has received considerable research attention and their benefits are well understood. However, research has typically considered high dosages (>20%) in gap and open graded asphalt blends, whereas the potential of low dosage CRM binders (5-15%) as an anti-aging modifier has received comparatively little attention. To better understand these potential benefits, low dosage CRM binders (5, 10 and 15% rubber by weight of binder) were prepared using both short and long blending durations, and were subjected to thermo-oxidative aging through the use of a rolling thin film oven (RTFO), and 20 and 50 hour cycles in a pressure aging vessel (PAV). Rheological analysis using a dynamic shear rheometer (DSR) subjected binders to temperature-frequency sweeps to better understand intermediate temperature responses post-aging. It was observed that increasing crumb rubber contents resulted in improved high-temperature performance whilst maintaining reduced stiffness in the low temperature test regions. Further analysis of master curves and Black space diagrams, in addition to rheological properties such as Glover-Rowe parameter, R-value (rheological index), GC (crossover modulus) and other index parameters, found that increasing rubber contents improved binder durability and reduced thermo-oxidative aging impacts. While higher dosages (15%) were observed to perform best, it was apparent that the incorporation of any amount of crumb rubber provided anti-aging benefits relative to the unmodified base binder.