Asphalt Concrete Rutting Resistance Assessment by the Flow Number Test

This study was conducted to evaluate the effect of recycled asphalt pavement (RAP) amounts on the rutting resistance of plant-produced SUPERPAVE asphalt concrete (AC) mixtures in the laboratory. RAP amounts ranged from 0 to 25 percent by weight of mixture. Tests conducted included the dynamic modulus test at multiple temperatures and the flow number (FN) test at 54°C to characterize the stiffness and rutting resistance of the mixtures, respectively. Significant differences in rutting resistance were observed even though the mixtures considered were designed for similar levels of traffic (between 3 million and 10 million design equivalent single-axle loads). The effect of RAP amount on rutting resistance was unexpected as FN decreased as the RAP amount increased from 10 percent to 25 percent. The practice of allowing softer binders for AC mixtures containing high RAP amounts (>20%) was suggested as a possible reason for the relatively lower rutting resistance at the 25 percent RAP level. It was concluded that the use of a high RAP amount in combination with the softer binder may have the inadvertent effect of reducing the rutting resistance of certain AC mixtures. Future work involving a larger set of AC mixtures than presented in this paper is recommended.