Effect of polymer molecular weight on the rheology of SBS polymer-modified asphalt binder

The properties of asphalt are known to change significantly when modified with polymer, and such shift is often attributed to polymer content, structure and density. On the other hand, there is a significant difference in polymers’ properties with constant density and structure but varying molecular weight. In this research work, the effect of styrene butadiene styrene (SBS) polymer molecular weight on the hot storage stability, viscosity, rutting, and fatigue resistance of asphalt binder was investigated using the standard test methods on SBS-modified binders. Three SBS polymer with different molecular weight was used to modify 60/70 pen grade unmodified asphalt binder at 3%, 5%, and 7% by weight of the unmodified asphalt binder. It was found that increase in the polymer content and the molecular weight within the modified asphalt binder showed a significant improvement in the rutting resistance of the binder. The effect of the molecular weight on the rutting behaviour of the modified binder was more evident at 5% and 7% polymer content with up to 92% reduction from the unmodified non-recoverable creep compliance. The |G*|.sinδ parameter of the fatigue resistance analysis shows that the higher molecular weight of the polymer led to the improvement of the anti-fatigue performance parameter. The use of polymer with a high molecular weight value is not suitable for hot storage and reduces the viscosity of the binder.