The volumetric challenge of crumbed rubber modified asphalt mixtures

Abstract

Significant research has demonstrated the potential benefits associated with crumb rubber modification of bituminous binders for asphalt road surface production. Most of this previous research has focused on higher (20–30%) dosages of crumbed rubber and there is now an increased interest in lower (5–15%) dosages for improved binder and asphalt ageing to extend the time between periodic local road surfacing. For Marshall designed asphalt mixtures, the volumetric composition of the mixture is important and isolating the effect of the crumb rubber modification from the effect of an increased modified binder content is critical to understanding the economic viability of low dosage crumb rubber as an anti-ageing additive. Testing of a typical 10 mm dense graded asphalt mixture showed that the rubber is partially dissolved into the bitumen and both complete dissolution (100%) or no dissolution (0%) based calculations have a significant effect on Marshall volumetric properties such as binder film thickness, air voids and voids in the aggregate. Further work is required to determine a reliable method for determining the degree of crumb rubber dissolution on a case-by-case basis.