Effect of tire rubber grinding method on asphalt-rubber binder characteristics

The results of a study carried out to evaluate the effect of rubber grinding processes on the properties and characteristics of the resulting asphalt-rubber binder are presented. Several ambient and cryogenic ground tire rubber (GTR) materials were evaluated using measurements of surface areas and bulk densities. The rubber materials were then, respectively, mixed with an AC-30 asphalt; the resulting blends were tested to determine the corresponding viscosity, settlement during storage, and potential for binder draindown. The findings indicate that the asphalt-rubber binders produced with rubber from the different grinding processes have measurable differences in properties and storage characteristics that are critical to the performance of the binder in open-graded mixtures. The wet-ground rubber material had substantially lower bulk densities and larger surface areas than rubber resulting from other grinding methods. GTR materials with greater specific surface areas and more irregularly shaped particles produced asphalt-rubber binders with higher viscosities. Binders with the cryogenic ground rubber had the greatest amount of settlement and the least resistance to draindown.