Background
Crumb rubber modifiers (CRM) have been used in highway applications since the 1960s. Numerous technologies have been evaluated, with varying degrees of success. Asphalt rubber, which has the longest history of use in highway applications, must meet the requirements given in ASTM D-6114 "Standard Specification for Asphalt-Rubber Binder" including the following:

• a blend of asphalt cement, extender oil, and crumb rubber
• the crumb rubber (minimum of 15%) is a combination of scrap tire rubber and high natural rubber (HNR) additive
• the binder is reacted at elevated temperatures for a minimum of 45 minutes
• the reacted asphalt rubber binder must meet specified physical properties
  

Asphalt rubber binders are most widely used in the states of Arizona, California, and Texas for preventive maintenance and for structural and non-structural overlays.
Decisions regarding when and where to use asphalt rubber must be based on cost and expected performance. The Federal Highway Administration (FHWA) and several state highway agencies are advocating the use of life cycle cost analysis (LCCA) to aid in determining the most appropriate rehabilitation and maintenance strategies for a given situation. This paper presents results of a study sponsored by the Rubber Pavements Association (RPA) to evaluate the cost effectiveness of asphalt rubber for a number of different applications.

Objectives
The specific objectives of this paper are as follows:

• Briefly describe the history of asphalt rubber use
• Outline the life cycle cost analysis approach used
• Present examples of the LCCA for selected applications
• Provide tentative guidelines for cost effective uses of asphalt rubber
  It includes an analysis of different maintenance and rehabilitation scenarios used by local agencies in the states of Arizona and California.