Evaluation of Degradation of SBS Modified Asphalt Binder Because of RTFO, PAV, and UV Aging using a Novel Extensional Deformation Test

Styrene-butadiene-styrene (SBS) modified PG 64-22 and PG 76-22 binders are studied to investigate the degradation of polymer because of aging applied by: rolling thin film oven (RTFO), pressure aging vessel (PAV), and ultraviolet (UV). Upon observing the temperature increment of unmodified binder during high shear mixing, a polymer mixing procedure has been established. SBS (2%, 4%, and 6%), polyphosphoric acid (PPA) (0.5%, 2%, and 3.5%), and PPA (2%)-SBS (0.5%, 2%, and 3.5%) are mixed with PG 64-22 binder. Sentmanat extensional rheometer, based on dynamic shear rheometer, is used to investigate the extensional deformation characteristics in which SBS modified binders exhibit both first peak elongation force, F1, and second peak elongation force, F2, whereas, unmodified binders and PPA modified binders exhibit no F2. SBS is the most effective in increasing F2 with an increasing rate of 1.16N/% of SBS polymer. At 12°C and 16°C, F2 of RTFO aged SBS modified binder reduces, which indicates the polymer is degrading. In the case of PAV aged SBS modified binder, no F2 is found at 12°C and 16°C. With the increment of temperature, the PAV aged sample shows F2, but the value is less than the F2 of the original and RTFO aged binder of similar stiffness (F1). A normalized parameter, F2/F1, also shows that RTFO and PAV aging degrade SBS. Evaluation of UV aged SBS modified binder shows no F2 at any temperature while oven aged binder shows F2 value at similar aging temperature, duration, and thickness, indicating SBS completely degrades because of UV aging.