Abstract

Crumb rubber has been used to enhance the performance of hot mix asphalt pavements since the 1960s by improving the rheological properties of the crumb rubber modified (CRM) binders. Several researchers have identified the CRM-binder interaction as diffusion of the lighter binder fractions into the CRM particles. This physical interaction is two-fold: (1) the rubber particles swell and (2) the viscosity of the binder matrix increases due to removal of a portion of the oily fraction. While this interaction has been the major consideration with CRM binders, the effect of the CRM particles acting as fillers has not received much attention. This investigation
resulted in a method to quantify both the interaction effect (IE) and particle effect (PE) of CRM, which contribute to the increased rheological properties of CRM binders. These effects were determined using a rotational viscometer and a dynamic shear rheometer (DSR) to measure the rheological properties of CRM binders produced with three sizes of CRM, two crumb rubber processing methods (ambient and cryogenic grinding), two CRM contents, and three binder sources. It was concluded that binder source had a significant effect on the IE, followed by CRM
content. The PE was most significantly affected by the CRM content, followed by the CRM particle size.

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