Evaluating the Fatigue Behavior of Hot Mix Asphalt Reinforced by Recycled PET Fiber by 4-Point Bending Test

This research evaluates the effect of recycled polyethylene terephthalate (PET) fibers on the fatigue properties of hot mix asphalt. Based on micro-structural analysis, fiber contents were taken into account as equal to 0.5, 1.0, 1.5 and 2.0% by weight of bitumen. Fibers used with two lengths of 1 and 2 cm and an average diameter of 30 µm. For comparison, crumb PET with the particle size of 0.425-1.180 mm was used in two contents of 1 and 2% by weight of bitumen. Slab specimens of the reference and reinforced mixes were compacted by laboratory roller compactor to achieve 4±0.2 % air void. After that, the specimens were removed from the mold and sawed to obtain beam-shaped specimens. Then, the 4-point bending test was performed to evaluate the fatigue response of the modified and unmodified specimens by EN12697-24 standard. The fatigue tests were performed at 20oC and initial strain levels of 300, 500 and 700 microstrain using universal testing (UTM-14) apparatus. Based on the obtained results, the flexural stiffness of mixes containing both additives was lower than the reference mix. The reduction in the flexural stiffness continued as the fiber and crumb PET content increased. The fatigue life of fiber reinforced mixes was higher than the reference one. At initial strain of 300 microstrain, the most increase in the fatigue life of fiber reinforced mixes containing 1 and 2 cm fibers were equal to 149 and 177% of the reference mix, respectively. Also, at 700 microstrain the increases in the fatigue life of aforementioned mixes were 138 and 163% of the unmodified mix, respectively. The most increases in the fatigue life of the specimens containing 1 and 2% of the crumb PET were 148 and 163% of the reference one, respectively. Based on the obtained results and performed analyses, the optimum PET fiber and crumb PET contents were 1 and 2% by weight of bitumen, respectively.