Georgia’s Experience with Crumb Rubber in Hot Mix Asphalt Document available through TRB Author(s): Brown, Dan R.; Jared, David & Watson, Don, Georgia DOT, & Jones, Chris, Couch, Inc.; Georgia DOT/Couch, Inc. Origin: Georgia Date: January, 1997 Categories: Performance Key Words: crumb rubber, hot mix asphalt Summary: In 1991, Georgia DOT (GDOT) began to evaluate the production and placement of crumb rubber hot mix asphalt. The crumb rubber mix (CRM) used by GDOT was produced by adding ground tire rubber to hot mix asphalt using the wet process. A test section of CRM was placed on I-75 in Henry County, just south of Atlanta, consisting of a surface mix containing 6% crumb rubber by weight of asphalt cement (AC). The test section was evaluated from 1991 to 1995. The test section indicated that the CRM became very brittle over time, as shown by a large increase in viscosity and decrease in penetration, and by a large amount of transverse reflective cracking. The CRM did not reduce rutting compared to the control mix, and the CRM was more than twice as expensive to place. In addition to the test section, two projects were let to contract utilizing CRM. These two projects showed that CRM could be produced and placed using conventional equipment requiring only a few modifications. On-site blending units were used to combine the crumb rubber at a dosage rate of 16% by weight of AC. Pump and metering equipment was modified in order to accurately meter the stiff asphalt material, and correction factors were established for determining the AC content by vacuum extraction, since some of the rubber particles were retained in the aggregate portion of the sample.