Dynamic Shear Rheological Properties of Polymer-Modified Asphalt Binders

Abstract

Rheological characteristics were measured using DSR (Dynamic Shear Rheometry) for two asphalts (A and B, conventional AC-20 viscosity grades) from different crude sources modified with 5% SBR, 5.5% LDPE, 5% SB, and a crumb rubber (5%)/SBS (2%) mixture. Mastercurves were constructed from DSR frequency sweeps at temperatures ranging from -20 to 80°C. The mastercurves were constructed using the method of reduced variables, similar to the WLF equation, and described all binders well except for the A-LDPE binder. Polymer network formation is suggested in the B-SB binders based on the tendency of the tan δ mastercurve to exhibit a local minimum and the lack of observable phase separated polymer domains within the resolution of the fluorescence microscope. The morphology of the SBR polymer in the asphalt was observed to be dependent on the specific asphalt source. Initiation of polymer network formation is postulated for B-SBR based on the behavior of tan δ and the asphalt swollen phase separated polymer domains as observed by fluorescence reflection microscopy. For B-LDPE, A-CR + SBS, and B-CR + SBS the response of tan δ suggests networking but is postulated to be a contribution of the clearly observable phase separated polymer domains. The overall response of B-LDPE and the CR + SBS binders are a sum of the contributions of each phase with the polymer acting more as a filler, dominating the rheological response at intermediate frequencies.