Asphalt Rubber Technology Information Center
Arkansas' Experience with Crumb Rubber Modified Mixes Using Marshall and SHRP Level 1 Design
Gowda, Dary V.; Hall, Kevin D. and Elliot, Robert P., University of Arkansas   
January, 1996  
Key Words:
crumb rubber modifier, asphalt-rubber, rubber modified asphalt concrete, Marshall mix design, SHRP level 1 mix design  
Unmodified and crumb rubber modified mixes conforming to the Arkansas State Highway and Transportation
Department (AHTD) Type II Surface Course specifications were designed for heavy traffic conditions and environmental
conditions typical to the state of Arkansas using the Marshall and Superpave Level I methods. Specimens prepared at
appropriate design asphalt contents were evaluated from both volumetric and performance considerations. Three mix
types, including an unmodified hot-mix asphalt concrete, a “dry process” rubber modified asphalt concrete (in which the
crumb rubber is added to the aggregate prior to mixing with asphalt cement), and a “wet process” asphalt-rubber mix (in
which the crumb rubber is blended with the asphalt cement prior to mixing with aggregate) were included in the
investigation. For the asphalt cement, crumb rubber, aggregate type and aggregate gradation used in this study, the
design asphalt content was reduced for the SHRP level I method relative to the Marshall method. Incorporation of crumb
rubber into hot-mix asphalt concrete provided increased rutting resistance; however, the rubber modified mixes did not
show enhanced resilient and tensile properties when tested at 25C. Also, the performance related properties of the
SHRP Level I asphalt-rubber mixes (5, 10 and 15& A-R blends) evaluated did not differ significantly at 5% level of
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