Small and large strain rheological characterizations of polymer- and crumb rubber-modified asphalt binders

Nowadays, polymers and crumb rubber (CR) are extensively used modifiers in bituminous pavements. The objective of this paper is for characterizing the response of polymer- and CR-modified asphalt binders under small and large deformations to fully understand the behavior of such blends under various possible conditions. Under small strains, the complex modulus was measured and analyzed; while the large amplitude oscillatory shear (LAOS) test was carried out to characterize the non-linear behavior at strains beyond the linear viscoelastic region (LVER) of these materials. Styrene-butadiene-styrene (SBS) and ethylene vinyl acetate (EVA) as elastomeric and plastomeric polymers, respectively, and CR, at different concentrations were used to prepare the modified asphalt binders. For the large strain analysis, the waveforms for each material were collected for strain amplitudes of 0.5%, 10%, 20%, 30%, and 40% at 30 °C and 1 Hz. The small strain rheology was applied to discuss the linear properties, while the viscoelastic non-linearities of the studied asphalt binders were analyzed as a function of strain through the use of Lissajous-Bowditch plots and elastic and viscous non-linearities of an oscillatory shear cycle. The rheological measurements at small strain showed distinctive properties can be attained by the addition of polymers over CR, especially the EVA-modified binder. The analysis of Lissajous-Bowditch plots showed that higher deformations can dramatically change the behavior of the binder and it is worth be studied in conjunction with the small strain properties to capture the overall performance. Moreover, the polymer-modified binder showed higher ability to resist high strains and exhibited strong strain stiffening compared to the CR-modified binders. A continuous shear thinning was registered for the polymer- and CR-modified binders with the increase in strain amplitude.