In this paper, the micromorphology of asphalt binders with wax warm additives is investigated by atomic force microscopy (AFM) and optical microscopy before and after aging. Performance grade (PG) 64-22 asphalt binder is used to produce warm mix asphalt binder containing two wax additives, LEADCAP and Sasobit, and then the warm binders are artificially short-term and long-term aged using the rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Microstructure and rheology properties of the binders are characterized using AFM tapping-mode imaging techniques and the Superpave asphalt binder test, respectively. The results of this study indicate that (1) the wax type and aging level have a significant effect on the micromorphology of the binders; (2) the binders with LEADCAP exhibit no “bee-like” structures; (3) the addition of Sasobit into the binder increases the dimension of the bee-like structures regardless of the aging level and binder types; (4) the dispersed domain has higher stiffness than does the para phase; (5) the aging of the binders increases the bee shape but reduces the number of the structures; (6) the expanded peri phase is observed after the aging; and (7) the binder roughness increases after aging and shows a good relationship with the stiffness results.

The study describes the laboratory assessment (physical and rheological properties) of the binders (PG 64-22 and PG 76-22) modified with Styrene Butadiene Rubber (SBR), and a comprehensive comparison between these two modified binder types. PG 64-22 and PG 76-22 were used as base binders. Both of the base binders were blended with SBR at four different percentages of content (0%, 4%, 6%, and 8% by the weight of the binder). The base and modified binders were artificially short-term and long-term aged using a rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were conducted on the SBR modified binder using rotational viscometer (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR). In depth rutting performance was investigated using Multiple Stress Creep Recovery (MSCR). The results of this study indicated that (1) the addition of SBR into both binders increased the viscosity and polymer modified asphalt (PMA) binders observed to have more significant effect on its viscosity property; (2) the higher the SBR content, the better the rutting resistance of the binder and it is observed that the effect is prominent on the control binder; (3) MSCR test results showed that the SBR modified binders improved the binder percentage recovery and found to have a more significant effect on the PG 76-22 binder compared to PG 64-22; and (4) both the control PG 64-22 and PMA PG 76-22 binders resulted in similar trends on the cracking properties and were found to have insignificant effects due to the addition of an SBR modifier.

Crumb rubber binder with thermoplastic polyurethane (TPU) has been experimented with to characterize the performance properties considering the workability, rutting, fatigue cracking and cracking resistance at low temperatures depending on the temperatures and aging states. Physical and rheological properties were evaluated to proceed with the study by applying Superpave asphalt binder testing and multi-stress creep recovery (MSCR). Based on the targeted experiments, the binder samples were produced at three aging states (original, short-term aged and long-term aged) using a rolling thin film oven (RTFO) and pressure aging vessel (PAV). The results revealed that (i) the addition of TPU into CRM binders has a potential effect on increasing viscoelasticity at the original condition, (ii) CRM binders containing TPU showed improved anti-aging performance based on results of RTFO residues and (iii) the inclusion of TPU made it possible for CRM asphalt binder to improve its fatigue and cracking resistance at low temperature.

The effect of wax additives on the characteristics of polymer modified asphalt (PMA) binders (SIS, SBS and CRM) was investigated in this study. The binders were blended using the two wax additives (LEADCAP and Sasobit) and then artificially aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were conducted to determine viscosity, G^∗/sin δ, G^∗sin δ and stiffness values. Multiple Stress Creep Recovery (MSCR) test was carried out to evaluate the rutting resistance properties, in original and RTFO aged states. In general the results showed that (1) after the addition of wax additives, the viscosity of PG 64-22 and PMA binders was decreased; (2) higher cracking resistance (i.e., lower stiffness and G^∗sin δ values) was observed at the binders with LEADCAP; (3) by adding the wax additives, the percentage increase of rutting resistance (G^∗/sin δ) was found to be higher for PG 64-22 binder, compared to the PMA binders; (4) it was found that the effect of wax additives cannot be identified using MSCR test results; (5) the MSCR test was observed to be potentially inappropriate to measure the rutting performance of CRM binder.

In this study, thermoplastic polyurethane (TPU) and styrene-isoprene-styrene (SIS) were utilized to enhance asphalt binder properties. Superpave asphalt binder tests and multiple stress creep recovery (MSCR) were conducted to evaluate the physical and rheological performance (viscosity, rutting, and cracking properties) of the asphalt binders before and after short-term aging and after the long-term aging process. The results showed that (i) TPU has a positive effect on workability, including the mixing and compaction processes, which was evident from the reduced binder viscosity; (ii) asphalt binders with TPU and SIS showed better rutting resistance compared to the SIS binders without TPU; (iii) the cracking resistance of asphalt binders was found to be improved significantly with the addition of TPU; and (iv) TPU has the potential to be considered as a sustainable polymer modifier for producing bearable asphalt binders by improving rutting and crack resistance without increasing the melting temperature of the asphalt binders.