EFFECT OF MIX INGREDIENTS ON PERFORMANCE OF RUBBER MODIFIED ASPHALT MIXTURES

Abstract

This report summarizes the results of field performance surveys and laboratory testing programs aimed at identifying the critical factors in designing and constructing rubber-modified asphalt pavements using a content of 2 to 3% of coarse (1/4 inch to #40 sieve) ground tire rubber. The benefits of adding rubber in this size range to asphalt paving mixes are those of increasing traction and reducing stopping distances. A prior study by the Alaska Department of Transportation and Public Facilities evaluated the ice-removal and stopping distance aspects and documented an average reduction of 25% in icy-road stopping distances from the addition of the rubber. Since that time, the use of such rubberized mixes has been encouraged for special situations where this benefit will offset the higher mix costs. This study has indicated that benefits of extended fatigue life may also be expected, and that the addition of rubber may be practical in normal paving mixes not specifically gap-graded to provide a high percentage of coarse (+ 1/4 inch) particles as has previously been done. Initially, implementation will take the form of field trials of such dense-graded rubber-modified mixes to evaluate their workability and field performance. The consequence of varying mixing temperatures, rubber gradations, and density levels were also evaluated. Pavement designers are encouraged to evaluate the results reported herein when proceeding to prepare specifications and trial mix designs for construction projects.