# Physical and Chemical Methods to Assess Performance of TPO-Modified Asphalt Binder
## 5 Conclusions  
The road to sustainable infrastructure must include effective asphalt binder additives. Currently, only physical properties are considered for performance standards, but asphalt modification and aging can affect physical and chemical properties. Through this study, physical and chemical testing were performed on unaged, short-term aged, and long-term aged TPO-modified asphalt binders.  
The main conclusions are as follows:  
* Due to the reactivity of TPO, blending the material resulted in physical and chemical variability. The physical variability was reduced as the testing temperature increased. Physical testing temperatures above 58 \({}^{\circ}\)C are recommended to homogenize the modified binder matrix. The chemical variability was more subtle, but FTIR analysis indicated that no new IR-sensitive functional groups were formed during mixing.
* Physical testing alone could not explain the unexpected stiffening of the 2% sample. FTIR testing indicated a higher amount of water and C=O in the blend. NMR analysis resulted in an increased primary relaxation time, indicating a less mobile system. These chemical results indicate that some TPO components introduced water and stiffened the binder matrix.  
Figure 15: NMR relaxation times for TPO blends\({}^{\prime}\) (**a**) primary relaxation times and (**b**) secondary relaxation times.  
Adding 8% TPO hindered the high PG from 64 \({}^{\circ}\)C to 58 \({}^{\circ}\)C, reducing the resistance to rutting. This physical testing was supported by the decrease in the NMR primary relaxation time, indicating a more mobile system. None of the TPO blends enhanced the intermediate PG. The similar physical properties were supported by the similarities in chemical testing. FTIR analysis showed little variation from aging. The carbonyl indices indicated that long-term aging had the largest carbonyl content across most samples. Further analysis was complicated due to the carbonyl groups present in the TPO. The primary NMR relaxation times indicated a connection to physical testing. Since NMR depends on the binder matrix, the impact of the TPO and aging could be seen. Some connections could be made between the secondary relaxation times, but more testing is needed to determine a correlation. This testing showed a correlation between physical and chemical testing that can be applied to other asphalt additive materials. Chemical testing was shown to be a useful tool to indicate additive quality and binder performance. While chemical testing cannot be used in all situations due to noisy samples, ineffective indices, or unknown reactions, further research should focus on chemically characterizing the quality and performance, including low PG, of other modified asphalt blends. Chemical testing should be further developed as a tool to better understand the impact of chemical microstructure environments on physical pavement performance. Conceptualization, R.M.H. and M.A.; methodology, R.M.H. and K.W.; formal analysis, R.M.H. and J.B.; writing--original draft preparation, R.M.H. and J.B.; writing--review and editing, M.A. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The dataset is available on request from the authors. Acknowledgments: The authors would like to acknowledge both the civil engineering and chemistry departments for this collaborative effort. The S&T NMR Institute also played a role in providing chemical materials for this study. Specifically, we would like to acknowledge [PERSON], [PERSON], [PERSON], and [PERSON]. We would like to thank [PERSON], [PERSON], [PERSON], and [PERSON] for their help in the civil department. Conflicts of Interest: The authors declare no conflicts of interest.