Florida’s Approach Using Ground Tire Rubber in Asphalt Concrete Mixtures Document available through TRB Author(s): Page, Gale C.; Ruth, Dr. Bryon & West, Randy C. Origin: Florida Date: January, 1992 Categories: Performance Key Words: Asphalt rubber; Binder content Summary: In 1988, under a legislative mandate, the Florida Department of Transportation (FDOT) began a concentrated effort to evaluate the potential uses for reclaimed tire rubber in asphalt pavement construction. The approach taken by FDOT in this evaluation was to consider the most beneficial manner in which ground tire rubber could be utilized in asphalt pavements. FDOT identified that the most advantageous use of rubber would be as a binder modifier to improve the performance of our friction course mixtures. Specifically, it was desired to improve the durability of open graded friction courses and the deformation resistance of dense graded friction courses. Three demonstration projects were constructed to determine the optimum amount and size of rubber to be used, and to evaluate constructability and short- term performance of plant produced mixtures containing asphalt-rubber. With the asphalt cement prior to mixing with aggregate, the construction operations with the rubber modified mixtures was essentially the same as with conventional friction course mixtures. Presently all of the test sections are performing well. The optimum rubber content for open- graded friction course mixtures was determined to be 15 percent (by weight of asphalt cement using a 40-mesh ground tire rubber. In open-graded mixtures, the rubber has allowed a significant increase in the total binder content and therefore an increase in the film thickness on the aggregate particles. The increased film thickness should slow oxidation of the binder and result in improved durability of these mixtures. The optimum rubber content for dense- graded friction course mixtures has been identified as 5 percent (by weight of asphalt cement) using an 80-mesh ground tire rubber. It is believed that the rubber will provide improved elasticity to the binder and therefore greater resilience for these mixtures in recovery from repeated strains. Based on these demonstration projects, specifications have developed for using ground tire rubber in friction course mixtures as a standard practice.