Pure mode I fracture specification of molybdenum disulfide nanoparticles (MDS)-reinforced hot mix asphalt (HMA) under long-term conditions

Abstract

Low and intermediate temperature cracking are two key factors for fracture and failure of hot mix asphalt (HMA), which impose huge costs on transportation departments and related agencies around the world. These two kinds of cracking may apear in the short- or long-term owing to states such as freezeing-thawing damage (FTD) and the aging mechanism. On the other hand, due to its unique features, nanomaterials are a suitable option for improving the mechanical features of bituminous mixes, which can affect the short-term performance and long-term performance. In this study, low and intermediate temperature fracture specification of Nano-molybdenum disulfide (MDS)-reinforced hot mix asphalt (HMA) under long-term conditions was evaluated. For this goal, two semi-circular bend (SCB) geometries comprising 90 degree and angled cracks, which were called symmetric SCB and classical-reinforced SCB-2, were made. Then, two various conditions, i.e. three freeze–thaw cycles and six days of aging operation were performed on various mixes in order to simulate the long-term performance of the bituminous mixes. Finally, the HMA samples with and without MDS were subjected to the three-point SCB test at the final temperatures of −15 °C and + 15 °C. The findings demonstrated that mixes comprising 0.3 % and 0.6 % MDS had more increased fracture energy (FE), fracture toughness (KIC), and stiffness under pure tension at low and medium temperatures (short-term and long-term fracture specification). In fact, MDS caused an increase in the fracture indices by increasing the maximum force (Pmax) and displacement at the time of fracture. At ± 15 °C and for the geometry comprising the 90 degree and 35 degree cracks, the HMA and Nano MDS-reinforced HMA mixes had more suitable flexibility under 3 FTC compared to 0 FTC; while, the flexibility of the HMA and Nano MDS-reinforced HMA mixes decreased under aging mechanism. In discussing the long-term performance of HMA mixture (with and without modifiers), the findings showed that applying three FTD's cycles to the mixes caused a decrease in KIC, FE, and Pmax. Also, reducing the stiffness of various mixes under 3 FTC, and increasing the flexibility of the mixes were other findings of this study. In addition, the simultaneous use of both SCB geometries comprising 90 degree and 35 degree cracks was proposed to study the fracture specification of bituminous mixes owing to the more inferior average FE and KIC. Finally, the application of 3FTC on bituminous mixes can more suitable simulate the long-term performance of asphalt pavement (compared to aging mechanism).