Description
The Arizona Department of Transportation (ADOT) has used crumb rubber from ground tires since the late 1960’s to primarily reduce reflective cracking. In 1988, ADOT started to use crumb rubber mixed with hot asphalt, commonly referred to as asphalt rubber (AR) as a binder in hot mix asphalt (HMA). Typically, these mixes are either open-graded or gap-graded and from 12.5 mm (half inch) to 25 mm (one inch) or 25 mm (one inch) to 50 mm (two inches) in thickness, respectively. Open-graded mixes generally contain 9 to 10 percent AR binder, whereas the gap-graded contains generally 7.5 to 8.5 percent AR binder. To date, field performance has been very good. As an extra benefit, the ground tire rubber from over eight and one half million tires in Arizona has been recycled since 1988, in the making of HMA with AR.
