Laboratory Investigation of Crack Resistance Based on Fracture Mechanics Properties of Hot Mix (HMA) Asphalt Containing Recycled Polyester Fibers an‎d Crumb Rubber

5/22/2026 12:00:00 AM

Abstract: Asphalt pavements are subjected throughout their service life to a combination of thermal stresses, repeated traffic loading, an‎d environmental variations. These factors directly intensify the initiation an‎d propagation of cracks, ultimately reducing pavement service life an‎d increasing life-cycle costs. Meanwhile, the growing accumulation of polymeric wastes such as PET bottles an‎d scrap tires has created serious challenges in waste management an‎d environmental protection. Therefore, developing innovative approaches to improve the mechanical performance of asphalt mixtures through the recycling of polymeric materials is considered a necessity aligned with sustainability goals an‎d the enhancement of pavement durability. On this basis, the present study was conducted to eva‎luate the cracking resistance of hot mix asphalt containing two recycled additives, namely polyethylene terephthalate (PET) fibers an‎d crumb rubber (CR). In this study, the base materials included a PG 64-22 asphalt binder, filler, an‎d limestone aggregates with a nominal maximum aggregate size of 12.5 mm. The optimum fiber content was determined based on the Marshall test from among 0.15%, 0.30%, an‎d 0.45% by total weight of the mixture, an‎d 0.30% was identified as the optimum value. In addition, rubberized asphalt binder was prepared by blending crumb rubber at 10% an‎d 15% by weight of binder using the wet process with a high-shear mixer at 6000 rpm for 60 minutes. Gyratory-compacted specimens were produced using rubberized binders containing 10% an‎d 15% crumb rubber together with the optimum PET fiber content of 0.30%, which was added to the aggregates through the dry process. Fracture behavior was eva‎luated using the three-point bending test on notched semi-circular bend (SCB) specimens with a diameter of 100 mm at three temperatures of -18, 0, an‎d +20 °C under different loading modes, including Mode I, Mode II, an‎d mixed-mode I/II. Fracture parameters were measured using a concrete plastic loading jack under static loading at a constant rate of 5 mm/min. To analyze fracture behavior, fracture energy (Gf) was calculated as an indicator of resistance to crack propagation, an‎d the effective stress intensity factor (Keff) was determined as a measure of resistance to crack initiation. At 20 °C, due to the deviation of mixture behavior from linear elastic fracture mechanics, the flexibility index (FI) was used instead of the effective stress intensity factor (Keff) for result interpretation. The results showed that the fracture behavior of the investigated mixtures was simultaneously influenced by temperature, loading mode, an‎d additive content. At -18°C, the mixtures exhibited stiff an‎d brittle behavior, resulting in higher values Keff, whereas increasing temperature led to reduced stiffness an‎d a change in the failure mechanism. Crumb rubber had the greatest effect on improving fracture energy, especially under shear an‎d mixed-mode loading conditions, while PET fibers mainly enhanced resistance to crack initiation an‎d propagation through a bridging mechanism. Among the different combinations, the CR10F0.3 mixture demonstrated the most stable an‎d balanced performance under all temperatures an‎d loading modes, simultaneously increasing both Gf an‎d Keff while preventing performance loss at higher temperatures an‎d under mixed-mode loading. In contrast, increasing crumb rubber content to 15% reduced fracture energy an‎d decreased stability at intermediate an‎d high temperatures, which may be attributed to increased binder viscosity an‎d the formation of microstructural discontinuities. Performance an‎d economic eva‎luations also indicated that the CR10F0.3 mixture, by providing an appropriate balance between stiffness an‎d toughness an‎d yielding the lowest life-cycle cost, can be introduced as the optimum functional an‎d economic alternative. Overall, the findings of this study indicate that the controlled an‎d simultaneous use of PET fibers an‎d crumb rubber can provide an efficient, economical, an‎d environmentally friendly approach to enhance cracking resistance an‎d improve the durability of asphalt mixtures under various thermal an‎d loading conditions. Keywords: hot mix asphalt, fracture resistance, fracture mechanics, fracture energy, fracture toughness, PET Fiber, crumb rubber, mixed-mode loading

مخلوط آسفالتي داغ , مقاومت ترك‌خوردگي , مكانيك شكست , انرژي شكست , چقرمگي شكست , الياف پلي‌اتيلن ترفتالات , خرده لاستيك , مود بارگذاري تركيبي

hot mix asphalt , fracture resistance , fracture mechanics , fracture energy , fracture toughness , PET Fiber , crumb rubber , mixed-mode loading

Fahim Faryabi

Dr. Mahmoud Ameri – Dr. Hasan Ziari