Evaluating the fatigue properties of hot mix asphalt reinforced by recycled PET fibers using 4-point bending test

Abstract

This research evaluates the effect of recycled polyethylene terephthalate (PET) fibers on the fatigue properties of hot asphalt mix. Based on micro-structural analysis, fiber contents were taken into account as equal to 0.0 (i.e. reference mix), 0.5, 1.0, 1.5 and 2.0% by weight of bitumen. Fibers used with two lengths of 1 and 2cm and an average diameter of 30µm. For comparison, crumb PET with the particle size of 0.425–1.180mm was used at the rate of 1 and 2% by weight of bitumen. Slab-shaped specimens 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. 4-Point bending test was performed to evaluate the fatigue response of the modified and unmodified specimens considering EN12697-24 standard. The fatigue tests were performed at 20°C and initial strain levels of 300, 500 and 700 microstrain using universal testing machine (UTM-14). 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 lives of fiber reinforced mixes containing 1 and 2cm fibers were equal to 149 and 177% of the reference mix, respectively. Also, at 700 microstrain the fatigue lives of aforementioned mixes were 138 and 163% of the reference mix, respectively. Likewise, the most increases in the fatigue lives of modified specimens with 1 and 2% crumb PET were 148 and 163% of the reference one, respectively. Based on the obtained results and performed analyses, the optimum fiber and crumb PET contents were 1 and 2% by weight of bitumen, respectively.