Asphalt-Rubber Design and Construction Guidelines

Theme of San Jose Workshop 

Dr. Gary Hicks,P.E., Professor Emeritus, Dept. of Civil Engineering, Oregon State University (left) and Theron Roschen,P.E., Sr. Civil Engineer, Sacramento County and Director of the Northern California Rubberized Asphalt Concrete Technology Center (NCRACTC), look pleased at the conclusion of the February 20, 2002 seminar on the Guidelines at the County of Santa Clara auditorium in San Jose, CA. The one day workshop, organized by RPA under contract with NCRACTC was attended by 145 representatives of cities, counties, consulting engineering firms and Caltrans personnel throughout northern California.

The NCRACTC, funded through tire disposal fees administered by the California
Integrated Waste Management Board (CIWMB), contracted with Dr. Hicks and Oregon State University in the fall of 2000 to prepare Design and Construction
Guidelines for Asphalt-Rubber. The purpose of the guidelines is to assist local agencies in California in utilizing scrap tire rubber in asphalt pavement. (California discards over 31 million tires annually.)

The RPA was a partner in the project, providing funding for travel and other expenses incurred in the guideline development. RPA Past President Mark Belshe and Technical Advisor, Jack Van Kirk also served on the Expert Task Group which included representatives of the CIWMB , FHWA, California Asphalt Paving Association, and the Directors of the California RAC Technology Centers.

The Guidelines provides answers for frequently asked questions such as: What is Asphalt-Rubber? This question is addressed due to the confusion in California concerning the many products offered under the Rubberized Asphalt Concrete (RAC) terminology used in the state. RAC can be many things including the "terminal" blends in which the crumb rubber content is 10% or less and the "dry process" which substitutes larger rubber particles for aggregate. Asphalt-Rubber is defined as containing 18% or more crumb rubber which is reacted with hot asphalt in a field blender prior to introduction to the aggregate at the hot plant. The Guideline offers comprehensive instructions on "How" and "Where" to use the material. Blending and laydown temperatures and ambient air temperature during construction are identified as critical elements in successful projects. Construction procedures for A-R Hot Mix, Chip Seals and Interlayers are also discussed.

An important element of the Guidelines is the discussion on the use of the Design tables developed by Caltrans which allows the thickness of the Asphalt-Rubber to be reduced to up to 50% when compared to convention-al hot asphalt mixes.

While the Guidelines were developed for use in California, we feel the information will be of interest and value to local agencies elsewhere. The full Guidelines are available on the California Rubberized Asphalt Concrete Technology Center's website: www.rubberizedasphalt.org.