# Effect of Chemical Composition of Bio- and Petroleum-Based Modifiers on Asphalt Binder Rheology
## 5 Summary and Findings  
The focus of this paper is to evaluate the impact of modifiers' chemical properties on the rheological properties of respective modified binders. Binders blended with various types of modifiers, intended to soften (reduce) the grade of an unmodified binder, were tested at various aging conditions (unaged, RTFO, PAV, 2 PAV, and 3 PAV). Performance progression indicators were used to predict their long-term performance. Low-temperature cracking susceptibility was assessed using GR and \(\Delta\text{T}_{\text{c}}\), and intermediate-temperature cracking susceptibility was assessed using black space diagrams. Chemical characteristics of modifiers were evaluated using elemental analysis, FTIR, GPC, and TLC-FID. The results show that modifier chemistry impacts modified binder performance. The presence of certain elements, chemical functional groups and molecular size can affect the rheological properties of the binder. Following are the findings of this study:  
1. Nitrogen-rich modified binders appear to have superior rheological properties. They have higher \(\Delta\text{T}_{\text{c}}\), higher phase angles, and lower GR for 2 PAV and 3 PAV conditions. Hence, it can be assumed that the presence of nitrogen would boost anti-oxidizing properties and reduce susceptibility to cracking. Further research is needed to validate this hypothesis. 2. Sulfur presence may have a detrimental impact on modified binder performance. Lower molecular size/weight of modifiers appears to be related to better cracking resistance potential of modified asphalt binders. Further research towards validating this idea is encouraged. * Modifiers A and D have similar chemical characteristics and molecular weight distributions. This suggests that modifier A may have a bio-based origin. * The methodology employed in the SARA analysis may not be able to characterize some modifiers. An alternative test method should be considered for some modifiers. * Phase angle parameter in conjunction with complex modulus (G*) was shown to be sensitive to laboratory aging of modified and unmodified binders. Therefore, such a parameter has potential to identify phase-incompatible asphalt binders, is able to distinguish potential mechanical behavior, and could be associated with field performance. In conclusion, modifier chemistry was shown to have a relationship with rheological behavior of modified binders. The experimental program presented in this paper can be used to choose modifiers that may control cracking development and could also be used as guidance to engineer asphalt binder modifiers. All authors have read and agree to the published version of the manuscript. Conceptualization, B.K.S., H.O. and I.L.A.-Q. ; Methodology, B.K.S., H.O. and I.L.A.-Q. ; Validation, P.S. and J.J.G.M. ; Formal analysis, P.S. and J.J.G.M. ; Investigation, B.K.S., H.O. and I.L.A.-Q., J.J.G.M. and P.S. ; Resources, I.L.A.-Q., H.O. and B.K.S. ; Data curation, P.S. and J.J.G.M. ; Writing--original draft preparation, P.S. and J.J.G.M., Writing--Review and editing, I.L.A.-Q., B.K.S., H.O. ; Visualization, P.S. and J.J.G.M. ; Supervision, B.K.S., H.O. and I.L.A.-Q. ; Project administration, B.K.S., H.O., and I.L.A.-Q. ; Funding acquisition, B.K.S., H.O. and I.L.A.-Q. This research was funded by the Illinois Department of Transportation, under the project number ICT R27-196 HS. This publication is based on the results of \"ICT-R27-196 HS: Rheology-Chemical Based Procedure to Evaluate Additives/Modifiers used in Asphalt Binders for Performance Enhancements (Phase 2).\" ICT-R27-196 HS is currently conducted in cooperation with the Illinois Center for Transportation (ICT); Illinois Sustainability Technology Center (ISTC); the Illinois Department of Transportation (IDOT); and the U.S. Department of Transportation, Federal Highway Administration. Special thanks to ICT and ISTC students and research staff, [PERSON], [PERSON], [PERSON], and [PERSON], for their input and support during this study.