Effect of mixing time and temperature on the viscosity of asphalt rubber containing waxy additives.

Crumb rubber from end-of-life tyres can be employed in the production of asphalt rubber binders by means of the so-called “wet” mixing technology. However, since the physical and chemical interaction between rubber particles and neat binder causes a significant viscosity increase, corresponding bituminous mixtures require higher mixing and compaction temperatures than those of standard mixtures. Such a need leads to the overall increase of energy consumption and to the emission of a greater quantity of fumes during laying operations, thus partially reducing the eco-friendly character of asphalt rubber technology. The problems highlighted above can be in part balanced by making use of viscosity-reduction additives. In the research work described in this paper, the effects of a waxy additive on the flow properties of asphalt rubber were studied by means of viscosity measurements. Tests were carried out by considering both commercial and laboratory-prepared asphalt rubber products. Factors which were analyzed during the experimental investigation included mixing technique, time and temperature. Obtained results suggest that additive efficiency is strongly related with asphalt-rubber mixing time and temperature. When these two parameters are kept constant, a similar viscosity reduction is recorded for both the commercial and laboratory asphalt-rubber.