Asphalt Rubber Technology Information Center
Evaluation of Asphalt-Rubber Interlayers
Estakhri, Cindy K.; Pendleton, Olga and Lytton, Robert L.  
February, 1994  
Key Words:
asphalt rubber, interlayer, stress absorbing membrane interlayer, SAMI, reflective cracking, crumb rubber modifier,
scrap tire rubber  
This report presents the field performance results of three asphalt-rubber interlayer test roads in terms of the
effectiveness of the interlayer at reducing the rate of reflection cracking.  Several variables were included in the field
experiments: concentration of rubber, binder application rate, type of source of rubber, and digestion (or mixing) time of
asphalt and rubber.  Control sections were made up of no interlayer and interlayer binders of polymer-modified asphalt
and conventional asphalt cement.
Results of the statistical analyses of the data indicated that, in general, asphalt-rubber interlayers are more effective at
reducing reflection cracking than no interlayer at all.  Asphalt-rubber also performed better than control sections
composed of asphalt cement interlayer and polymer-modified interlayers except in one case where the interlayer was
composed of a double application of asphalt cement/aggregate.
The data also indicated that higher binder application rates lead to improved cracking resistance; however, on many test
sections excessively high binder application rates caused flushing at the pavement surface.
Rubber type or source did not appear to be a factor in determining reflection cracking but the lower concentrations of
rubber appeared to perform better than high concentrations.
© 2015 - Rubber Pavements Association (RPA). All rights reserved.