Laboratory Study of Fatigue Characteristics of HMA Surface Mixtures Containing Recycled Asphalt Pavement (RAP)

Reclaimed asphalt pavement (RAP) has been used in the construction of asphalt pavements since the 1930’s. Conversely the use of RAP in load carrying layers has always been a sensitive issue due to the uniformity and rheological properties of the blended asphalt mixtures. Typically the inclusion of RAP will blend the long-term aged asphalt binder in the RAP with the fresh asphalt binder resulting in a stiffer mixture. Generally rutting will less likely be a problem with the inclusion of RAP. However, the fatigue crack resistance of the HMA mixtures containing RAP has been a key interest to designers and engineers. This thesis presents the results of a laboratory study, in which the laboratory fatigue characteristics of asphalt mixtures containing RAP were evaluated.

A typical surface mixture meeting the state of Tennessee “D” mix criteria was evaluated at 0, 10, 20 and 30 percent of screened RAP materials. Two types of aggregates (limestone and gravel) and two types of binder (PG 64-22 and PG 76-22) were used for this study. Fatigue characteristics were evaluated through indirect tensile strength, semi-circular bending and beam fatigue tests.

The results from this study indicated that laboratory long-term aging and the inclusion of RAP generally increased the stiffness and laboratory fatigue resistance for the mixtures studied. For the mixtures studied, the inclusion of 30 percent RAP for both binder types significantly changed the fatigue characteristics as compared to 0, 10 and 20 percent RAP. Increasing the percentage of RAP increased the fatigue resistance, however at higher percentages of RAP the mixture becomes stiffer and some fatigue characteristics are compromised by adding RAP. Based on the workability and performance in the lab, 20 percent RAP would be recommended for use in Tennessee surface mixtures. Field validations are recommended to compare laboratory performance to field performance to verify the optimum percentage of RAP to be used during pavement construction.