The aim of this research study is to evaluate the effect of soybean oil, as a locally available, affordable, and environmentally – friendly recycling agent, on the performance of asphalt pavements containing recycled materials. In continuation of phase I of this study, the effect of soybean oil (produced in phase I) on mechanical-rheological properties of asphalt binders will be studied in phase II. Next, the obtained results will be verified in the asphalt mixture level (blend of asphalt binder and aggregate) and a life cycle cost analysis and environmental assessment will be carried out to examine the applicability and suitability of the soybean oil, as a recycling agent, from economic and environmental viewpoints (phase III).

1) Identify the chemical species present in the soybean oil that may negatively affect the performance of asphaltic materials (i.e., asphalt binder and asphalt mixture) and improve soybean oil composition and oxidative stability by physical and/or chemical processes.
2) Examine the effect of soybean oil as a recycling agent and its combination with other modifiers (e.g., antioxidants and warm mix additives) on performance of different asphalt binders and mixtures.
3) Perform an environmental and economic analysis to understand how soybean oil, as a recycling agent, can positively affect the environment and economy of our state.

Phase III - Third year: Effect of Soybean Oil on Performance of Asphalt Mixtures
The focus of this year will be on the different combinations of asphalt binders with different source and gradation of aggregates used in Nebraska. Several mechanical tests based on balance mix design approach such as IDEAL Cracking Test (IDEAL CT) or Semi-Circular Bending (SCB) fracture test will be performed to find the cracking resistance of the mixtures. In addition, the Hamburg Wheel Tracker Test (HWTT) will be employed to characterize the rutting potential and moisture damage resistance of the mixtures modified with soybean oil and other modifiers recommended in phase I and verified in phase II, respectively. As shown in Figure 2 [Schematic diagram of the planned experiments in phase III], in this year, economic (LCCA) and environmental (leachability of heavy metals and organic pollutant) analysis will be performed to assure agencies such as NDOT that the proposed practice is safe and affordable. The research team will update research progress to the NSB TAC members on a quarterly basis. All research findings will be presented, and a final report including all details and conclusions will be delivered at the completion of this project. The obtained test results will provide direction as to how soybean oil should be used in the asphalt mixtures and how to move forward with the implementation potential for paving materials in Nebraska.

1) The outcomes of this research will ultimately provide new use for soybean oil and create an expanded soybean oil market. For example, the Nebraska Department of Transportation (NDOT) is planning to use high percentages of RAP (up to 65%) with these new technologies (i.e., recycling agents). Our preliminary test results show that 6% of vegetable-based recycling agent based on the total weight of asphalt binder must be added to asphalt pavements containing 65% RAP. Considering 2,000,000 tons of asphalt mixtures which are produced in Nebraska every year and 5.5% asphalt binder in the asphalt mixtures, 6,600 tons of soybean oil will be consumed annually just for NDOT projects alone, probably about twice that for all asphalt paving in Nebraska.
2) Soybean oil which is considered as “green chemical” will potentially replace petroleum-based ingredients.
3) The possible use of soybean oil will provide safer, trustworthy, and comfortable means for the transportation construction industry and can bring significant cost savings and provide longer lasting and more sustainable asphalt pavements.