Effect of Rubber Characteristics on Asphalt Binder Properties

The use of scrap tires in ground tire rubber (GTR) modified binders has continued to evolve since its introduction in the early 1960s. Currently, many states have developed recipe specifications requiring contractors to blend GTR with asphalt binders using specified rubber sizes, percentages, and grinding methods. While these specifications were developed based on early research, the GTR industry has developed new methods and techniques which might improve the quality of GTR in asphalt binders. The objective of this research was to assess how rubber properties affect the properties of an asphalt binder. This objective was completed by blending 12 unique GTR samples with a singular asphalt binder at a loading of 10% rubber. Two of the selected rubbers were additionally tested at 15% loading. These 14 GTR-modified asphalt binders were then tested using the performance grade (PG), multiple stress creep recovery (MSCR), cigar tube separation test, and softening point methodologies. Statistical analyses were conducted to determine how particle size, grinding temperature, rubber chemistry, and surface area affected the four test results. GTR particle size was the most influential parameter on the majority of the test results. The smaller particle sizes improved the high and low temperature performance grade and particle separation as tested by cigar separation tubes and the softening point.