Description
Asphalt rubber has been utilized for many years in Arizona as a Stress Absorbing Membrane (SAM) or Stress Absorbing Membrane Interlayer (SAMI) for both rigid and flexible pavement overlay systems to reduce reflective cracking. The SAMI asphalt rubber in 1977 was a mixture of 75% hot paving grade asphalt and 25% ground tire rubber. To this mixture 7.5% diluent(kerosene) was added for spray application. This mixture is also referred to as the asphalt rubber wet process or McDonald process. In 1977, a very novel experimental application of asphalt rubber was used to build a low volume highway pavement between the town of Dewey and Interstate 17 on State Route Highway 169. Several experimental pavement sections were placed to determine to what degree partial encapsulation (waterproofing the subgrade) in combination with a very thin pavement section could provide good pavement performance for a relatively low volume highway. Most of the test sections failed within two years after construction. After 22 years of service only the two SAMI test sections with bound subgrade and an open graded friction course are still performing. This extraordinary long life in retarding shrinkage cracks, further confirms an earlier finite element analysis study.
