The rheological properties of Styrene-Butadience-Styrene (SBS) modified asphalt binders (SBS-PMAs) depend on formulation variables. The most sensitive among them may be listed as polymer amount, cross-linking agent amount(%), and other additives (PPA). The dispersion of SBS in an asphalt binder depends on blending time and temperature and base asphalt binder compatibility. In this study an incompatible and a compatible base asphalt binder were selected and modified with various amounts of SBS. Elemental sulfur was used as a cross-linking agent in various proportions. Other additives such as PPA at 0.5% concentration and wax at various amounts were also used. High shear blends of SBS-PMAs were made in the laboratory by varyingblending time until an optimum dispersion of polymer was obtained. The dispersion of the polymer was studied using a fluorescence microscope. MSCRtest was used to study creep and recovery behavior of these modified binders. It was found that MSCR test results (Jnr and %recovery) were able to characterize the extent of dispersion of SBS in these PMAs. This implies that a fundamental test method is now available to discriminate between the dump & stir type PMAs and those that have been optimally dispersed. This presentation discusses the effect of SBS dispersion and other additiveson the MSCR test results.
Abstract