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.

This research project is proposed in three phases (three-year project) with a specific scope for each phase. To meet the objectives of this research, four tasks are proposed and briefly discussed through each phase. The proposed tasks include: Task 1: Literature Review, Task 2: Laboratory Tests, Task 3: Analysis of Test Results, and Task 4: Documentation and Presentation.

Phase 2 of 3 - Second year: Effect of Soybean Oil on Performance of Asphalt Binders -
To make a definitive conclusion about the applicability of the above treatments discussed in the phase 1, further investigations in binder level is vital. In this year, we will verify the findings of first year using a multiscale approach which integrates chemical-physical-rheological properties of asphalt binders modified with corn oil. The focus in this year will be on the long-term performance, moisture resistance, and thermal behavior of asphalt binders modified with the soybean oil. To achieve this, one commonly used asphalt binder will be purchased. The asphalt binder will be modified with soybean oil in different dosages with/without other modifiers (e.g., antioxidant). The modified binders will be mixed with field aged binders. The control and treated binders with modifiers will be aged through different aging protocols and be tested using Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) to evaluate their long-term performance. In addition, the effect of soybean oil on the moisture susceptibility and thermal characteristics of
modified binders will be examined using Wilhelmy plate and TGA-DSC methods, respectively. Any modification proposed in the first year to improve the performance of soybean oil will also be considered and evaluated. The schematic diagram of the experiments conducted in this phase is presented in Figure 2. The research team will update research progress to the NSB TAC members on a quarterly basis. A final report including all data collected from the literature review, survey, laboratory tests, and conclusions will be delivered at the completion of this phase. We expect that the combination of asphalt binders with crude and high oleic soybean oil and other modifiers would provide the best long-term performance, moisture damage resistance, and thermal stability. The applicability of obtained results from this phase in mixture level will be examined in the next phase of the project.

Updated May 26, 2023:

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We aim to implement this research by placing and testing the asphalt mixture containing improved soybean oil and recycled materials (e.g., RAP) on a one-mile section of Nebraska road and monitor the performance of this section for a few years. If successful, the outcomes of this research will ultimately provide new use of soybean and create an expanded market for this oil. In addition, Nebraskans may find themselves with an improved economy and more sustainable asphalt roads.

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.