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.