Evaluation of Asphalt-Rubber Interlayers Author(s): Estakhri, Cindy K.; Pendleton, Olga and Lytton, Robert L. Origin: Texas Date: February, 1994 Categories: Performance Key Words: asphalt rubber, interlayer, stress absorbing membrane interlayer, SAMI, reflective cracking, crumb rubber modifier, scrap tire rubber Summary: 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.