Modification mechanism of asphalt binder with waste tire rubber and recycled polyethylene

- WTR and RPE were used to modify asphalt binders in combination.
- Morphological and rheological properties of modified asphalts were investigated.
- The modification effect greatly depends on the concentration of WTR and RPE.
- The interaction among WTR, RPE and light components guaranteed the performance.
- The high temperature performance grade was remarkably increased.
- The low temperature performance grade was not sacrificed after the modification.

In this paper, the fundamental modification mechanism of asphalt binder modified with waste tire rubber (WTR) and recycled polyethylene (RPE) was studied through a comprehensive laboratory program. The base asphalt binder was mixed with 5% and 10% WTR of the mass of the asphalt binder, respectively. The modified asphalt binder is then prepared with additional 2% and 4% RPE of the mass of the base asphalt binder, respectively. Morphological analysis methods, which included Fourier transform infrared spectroscopy (FT-IR), fluorescence microscopy, thermogravimetric (TG) and differential scanning calorimetry (DSC), were employed to understand the modification mechanism. Conventional tests, dynamic shear rheometer and bending beam rheometer were used to assess the rheological characteristics under different temperatures. From the testing results, it is found that the deformation resistance, high-temperature stability, and flexibility of asphalt binder are all improved after WTR and RPE were added. The modification mechanism of WTR and RPE on asphalt binder is the combination of physical process and chemical process. With proper modifying agent content, the interaction among WTR, RPE and light component guaranteed the homogeneity of asphalt binders, the WTR and RPE distributed uniformly in modified asphalt binder and the thermal stability was enhanced. The penetration decreased and softening point increased, which means that the deformation resistant was enhanced and the high-temperature stability was improved. The complex shear modulus (G∗) increased and the phase angle (δ) decreased after modification. When WTR dispersed in the bitumen, it formed a continuous elastic network. Furthermore, the increment of G∗/sin δ proved that high-temperature deformation resistance was enhanced. The decrease in creep stiffness after modification with WTR and RPE suggested that the flexibility of asphalt binder was improved. The capacity to relax the load induced stresses was weakened at −6 °C, −12 °C, and −18 °C but the ability increased at −24 °C. The performance was more stable after modification and the effect was better at lower temperatures. The high temperature performance grade changed and low temperature performance grade kept unchanged after modification, the PG 64-22 base asphalt binder changed into PG 76-22 for base asphalt binder with 5% WTR and 2% RPE and PG 82-22 for base asphalt binder with 10% WTR and 2% RPE.