Investigating the mechanisms of rubber, styrene-butadiene-styrene and ethylene-vinyl acetate in asphalt binder based on rheological and distress-related tests

To understand the prospects of rubber-modified and polymer-modified asphaltic materials, pavement engineers must have a proper knowledge of the physical mechanisms of polymer materials in asphalt binder so that asphalt materials reflect the various rheological properties and pavement distresses along the wide range of testing conditions. Accordingly, the study reported here is aimed to present a mechanistic investigation on characteristics of rubber-modified and polymer-modified asphalt binders based on the evaluation of various rheological properties and primary modes of failure (i.e. low-temperature cracking, rutting and fatigue cracking in this study). In this experimental work, crumb rubber (hereinafter referred to as rubber), styrene–butadiene styrene (SBS), and ethylene–vinyl acetate (EVA), were introduced individually to the asphalt binder at different rates to prepare the blends. The physical and mechanical characteristics of the modified asphalt binders were discussed in the light of rotational viscosity (before and after aging), linear and nonlinear rheological measurements, rutting susceptibility, fatigue cracking, and relaxation modulus. Susceptibility to low-temperature cracking also was analyzed for all possible aging states. The results revealed that the viscosity of modified asphalt binders (using rubber, SBS, and EVA) is highly dependent on the aging state and the additive type and the content. The modified binders are able to allow good stress relaxation and better resistance to low-temperature cracking (even after short- and long-term aging), rutting, and fatigue cracking. Interestingly, the low-temperature cracking performance of the SBS-modified asphalt binder had improved much more after long-term aging compared to the unmodified binder and rubber/EVA modified binders. EVA-modified binder can sustain higher strains than rubber-modified binder (RMB), while comparing both small and large shear strain measurements. Storage and viscous moduli were determined to identify the rheological properties along the range of linear and nonlinear domains, and polymer-modified binders (PMBs) showed higher moduli in linear and nonlinear rheological conditions compared to the unmodified binder. Likely, higher cross-linking generated by polymer is the main contributory cause of such result. EVA polymer is a good choice to mitigate rutting, whereas SBS is more helpful to control fatigue cracking of the binders