This study examined the effect of amorphous poly alpha olefin (APAO) on the rheological behavior of asphalt binder. In order to modify asphalt binder, several percentages of APAO (0, 2, 4, 6, 8%, and 10% by the weight of asphalt binder) were used. The penetration grade, softening point, ductility, and viscosity tests were performed. Also, the multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests were conducted to evaluate the rutting and fatigue behavior of asphalt binder. The storage stability test was implemented to measure the ability of modified asphalt binder against separation. Based on the results, using APAO reduced the penetration grade and increased the softening point due, maybe, to the asphalt binder stiffening. The PI values increased with the addition of APAO, which indicated that the temperature susceptibility of all modified asphalt samples was reduced compared to the base asphalt binder. The increase in the viscosity of virgin asphalt binder due to APAO addition caused the mixture placement/compaction operations to become harder. The G*/sinδ parameter for all types of pre-post-aging RTFO asphalt binders was improved for APAO-modified asphalt binder, meaning that the latter stiffened and thus increased the respective rutting resistance of mixtures. The low temperature performance of asphalt binder indicated that the stiffness of asphalt sample increased with an increase in the APAO percentage, which indicates that the addition of APAO improved the cracking potential of modified asphalt binders and had negative effects on the asphalt binders. The storage stability test results indicated that the phase separation of asphalt binder was related to the APAO content. Results revealed, ignoring the levels of stress, that using APAO reduced the non-recoverable creep compliance (Jnr) value of virgin asphalt binder, indicating the production of an asphalt binder benefitting higher rutting resistance with APAO modification. APAO increased the %R of asphalt binder. Based on the LAS test results, the addition of APAO led to an increase in the fatigue life of asphalt binders, and by increasing the additive content, the fatigue life increased. The FTIR analysis indicated that no chemical interaction was observed between asphalt binder and APAO.

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