# Value-Added Use of Waste PET in Rubberized Asphalt Materials for Sustainable Payement
## 4 Summary and Conclusions  
In this study, PET wastes were first chemically recycled into derived additives, namely PET-TEA and PET-EA, by amine treatment from TETA and EA, respectively. Afterwards, the Superpave high- and low- temperature rheological properties of the 18 CRMA binder modified by both additives at 2 wt.% were assessed. Finally, the engineering performances of the corresponding SMA10 mixtures were validated in terms of rutting, fatigue, and dynamic modulus. The following valuable and interesting findings were obtained:  
* The rutting factor results indicate that 2 wt.% PET-TETA and PET-EA can slightly increase the rutting failure temperature of the asphalt rubber from 82.2 \({}^{\circ}\)C to 85.5 \({}^{\circ}\)C and 84.2 \({}^{\circ}\)C, respectively, and exhibit no change in the high grade of PG 82.
* The BBR analyses indicate that both PET additives slightly compromise the low-temperature performance of the rubberized binder, just causing a decrease in the corresponding grade from PG-28 to PG-22, which means that it can be subjected to the climate of many field practices worldwide.
* Marshall test results show that these two PET additives have almost no influence on the thermal stability and deformation resistance of the rubberized asphalt mixture.
* The ITFT analyses illustrate that PET-TETA exhibits a strong capability to extend the fatigue life of the rubberized asphalt mixture, but PET-EA fails to do so.
* The WTT results demonstrate that both additives slightly compromise the rutting resistance of the rubberized asphalt mixture, leading to a decrease in the rut depth from 3.10 mm to around 3.70 mm, which is an insignificant difference.
* The results of the dynamic modulus and phase angle tests indicate that the addition of a small amount of PET-TETA does not affect the viscoelastic characteristic of the rubberized asphalt mixture over a wide frequency range, but for PET-EA, it tends to slightly enhance the viscous behavior of the 18 CRMA mixture at a low frequency (below approximately 1 Hz).  
Overall, PET-TETA is regarded as a more suitable and valuable additive in contrast with PET-EA from the research findings. We recommended that it be applied in rubberized asphalt pavement due to its significant capacity to extend the fatigue life of asphalt rubber. The recycling approach proposed in this study can not only seriously alleviate the environmental pressures caused by the landfilling and stockpiling of waste PET and scrap tires, but it also makes these waste products more valuable in durable pavement. Furthermore, a determination on the feasibility of using the recommended waste-PET-derived additive in  
Figure 10: Phase angle master curves of CRMA mixtures incorporating PET additives.  
other asphalt mixture types, such as porous asphalt and glassphal, through performance evaluations, still needs to be carried out in the laboratory and in the field.  
Conceptualization, X.X. and S.S.; data curation, Y.C.; formal analysis, Q.W. and X.C.; funding acquisition, S.S.; investigation, Y.L.; methodology, X.X.; resources, Q.W., X.C. and S.S.; supervision, X.X.; writing--original draft, Y.C. and Y.L.; writing--review & editing, Y.C. and Y.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Research Project of the Education Department of Hubei Province (B2021084) and the Science Foundation of the Wuhan Institute of Technology (K201932 & K201731).  
Not applicable.  
The authors declare no conflict of interest.