Fatigue Behavior of Rubber-Modified Pavements

Over the last 18 years, a number of rubberized pavement projects have been built in Alaska. Initial laboratory and field investigations sponsored by the Alaska Department of Transportation and Public Facilities (AKDOT&PF) and conducted by Raad et al. indicated improved fatigue performance of the rubberized sections in comparison with conventional asphalt concrete pavements. The results of a follow-up investigation to develop design equations for rubberized pavements in Alaska are presented. Laboratory studies were conducted on field specimens using the flexural fatigue test in the controlled-displacement mode. Specifically, the rubberized mixes included asphalt-rubber concrete with AC-2.5 (wet-process) and PlusRide RUMAC with AC-5. Tests were performed for a range of temperatures varying between 22°C and –29°C. Fatigue relationships were developed in terms of repeated flexure strain, dynamic flexure stiffness of the mix, and repetitions to failure. Relationships for the dynamic flexure stiffness as a function of temperature were also developed. Dissipated energy associated with repeated flexure stress and strain was determined and used to assess the damage behavior of conventional and rubberized mixes. The proposed fatigue equations were used to compare the behavior of the rubberized mixes with conventional AC-5 mixes at 20°C and 0°C. Results of the analysis show that at 20°C, asphalt-rubber and AC-5 mixes exhibit essentially similar fatigue resistance, whereas PlusRide has the least fatigue life. However, at 0°C, the fatigue resistance of PlusRide and asphalt-rubber exceeds that of the conventional AC-5 mix. The fatigue equations were also used to compare the fatigue life of conventional and rubberized pavements for different surface layer temperatures and foundation support conditions.