More than 2 billion waste tires are stockpiled across the country. In addition, the United States disposes of 279 million waste tires, representing over 4 million tons of scrap waste. Although a limited number of waste tires are used for resource and energy recovery, the majority go to landfills or are disposed of in an environmentally unacceptable manner. In an effort to clean up old stockpiles of used tires and to promote the recycling of today's used tires, many road agencies are evaluating the use of discarded tires to modify asphalt cement mixtures. Ground tire rubber from waste tires has been used as an additive in various types of asphalt pavements in recent years. The use of rubber is of interest to the paving industry because of the additional elasticity imparted to the binder and enhanced safety related to improved roadway skid resistance. However, it is the additional benefit of resource recovery, recycling used tires into rubber granulate for use in rubber-modified asphalt concrete, that has prompted a growing interest in its use. There are two primary reasons why rubbermodified asphalt mixes have not achieved widespread use. First, the capital costs for these surfacing alternatives is higher than conventional asphalt mixtures by 40 to 80 percent. Second, there is a lack of dissemination of information regarding properties and performance of these surfacing alternatives. Three different asphalt paving systems are described and the economics of each system is compared to conventional asphalt concrete. Also, a potential solution to the mentioned obstacles is described.

The use of ground tire rubber as an additive in various types of asphalt pavement construction has been demonstrated in recent years and is of interest to the paving industry because of the additional elasticity imparted to the binder. However, additional environmental benefits, such as resource recovery, have also been observed by creating a use for recycled waste tires. Approximately 480 million tons of asphalt are laid each year in the United States (1). If only 10 percent of this total was laid in rubber-modified asphalt concrete using 3 percent granulated rubber, all of the tires that need disposal each year would be consumed. Also, at a rate of only 10 percent of total paving, rubber-modified asphalt concrete could be laid in specific locations to fully realize the advantages of rubbermodified asphalt concrete: increased durability, reduced reflective cracking, thinner lift, and increased skid resistance. With the increased burden placed on our national roadway system by higher tire pressures and increased traffic volumes, there is a need to improve conventional asphalt concrete mixes. Rubber-modified asphalt concrete has been shown to increase the fatigue resistance and durability. Its widespread use would also have the ecological benefit of recycling some of the 279 million tires needing disposal each year (2).