Evaluation of physical properties of fine crumb rubber-modified asphalt binders

The results of a laboratory experiment aimed at evaluating the physical properties of asphalt binder containing fine crumb rubber modifier are outlined. Binder characterization procedures developed as part of the Strategic Highway Research Program (SHRP) were used in the analysis. The collective products of SHRP asphalt research are now called Superpave. The crumb rubber modifier used was produced from a wet ambient grind process. The maximum rubber particle size was 180 μm, with an average particle size of 74 μm. Testing showed that when compared with the base asphalts, the fine crumb rubber-modified binders were stiffer at high pavement temperatures, were less stiff at low pavement temperatures, and had approximately the same or slightly less stiffness at intermediate temperatures. The behavior of the asphalt rubber binders during rolling thin film over (RTFO) aging was unlike that of the base asphalts. The fine rubber-modified binders tended to veil across the RTFO bottle during aging, or in other cases it congregated in a thick film around the perimeter of the RTFO bottle during the aging process. Viscosity tests showed that the asphalt rubber binders are subject to viscosity building when they are stored at high temperatures. No other difficulties were encountered in using the Superpave binder analysis procedures to characterize fine crumb rubber-modified binders.