Asphalt Rubber Technology Information Center
Polymerized Crumb Rubber Modified Mixtures in Minnesota - Final Report
Newcomb, David; Stroup-Gardiner, Mary; Kim, Jong, Allen, Bruce & Wattenhoffer-Spry, Jeff, University of Minnesota  
January, 1994  
Performance, Noise  
Key Words:
Crumb rubber, CRM, polymerized
This research program was based on laboratory and field studies.  All work was limited to the use of a 10-mesh crumb
rubber in the dry process.  An evaluation of the asphalt-rubber interactions indicated that there should be a reasonable
level of interaction between the crumb rubber and the asphalt cement selected for the project.  A suggested criterion for
defining an acceptable level of interaction would be to establish a minimum viscosity of 15 poise for a neat asphalt
cement modified with 20 percent crumb rubber.  When designing a crumb rubber modified mixture, the aggregate
gradation should be substantially gapped.  The target gradation used in the construction of the Babbit, Minnesota test
sections should be considered as a guideline for an acceptable gapped gradation.  Stockpile gradations should be
adjusted for crumb rubber gradations volumetrically; generally, 1 gram of crumb rubber occupies the same volume as 3
grams of aggregate for a given sieve size.  The optimum asphalt content for CRM mixtures should be based on air voids
form 1.5 to 3 percent.
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