Arkansas' Experience with Crumb Rubber Modified Mixes Using Marshall and SHRP Level 1 Design Methods Author(s): Gowda, Dary V.; Hall, Kevin D. and Elliot, Robert P., University of Arkansas Origin: Arkansas Date: January, 1996 Categories: Performance Key Words: crumb rubber modifier, asphalt-rubber, rubber modified asphalt concrete, Marshall mix design, SHRP level 1 mix design Summary: 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 25C. 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 significance.