The aim of this research study is to evaluate the effect of soybean oil, as a locally available, affordable, sustainable, and
environmentally – friendly recycling agent, on the performance of asphalt pavements containing recycled materials. To
accomplish this, the chemical and physical properties of the soybean oil will be characterized by employing different analyses.
The stability of the soybean oil against oxidation will be increased with various treatments to enhance its performance as the recycling agent for the asphalt pavements. Next, the effect of soybean oil on chemical-rheological properties of different asphalt binders will be studied and finally, the obtained results will be verified in the asphalt mixture (blend of asphalt binder and aggregate) level. 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.

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.

In the first year we will focus on developing treatment methods for increasing oxidative stability of the crude and high oleic soybean oil. The research team will conduct a literature review to summarize the effects of chemical species in recycling agents on asphalt binder and mixture properties and performance. In addition, any possible solutions and modifications reported in the literature will be reviewed. We will evaluate crude soybean oil instead of refined/purified edible soybean oil which results in significant savings in materials cost. Using chemical and physical techniques (see Figure 1), undesirable species in the soybean oil that may negatively affect asphalt binders and asphalt mixtures will be identified. We will also consider and examine high oleic soybean oil as an available option in this phase. Then, possible modifications will be performed for increasing the oxidative stability and improving the performance of soybean oil as recycling agent. Removal of free fatty acids, non-oil materials such as proteins and phospholipids from the crude oil by refining process is important since it increases quality and oxidative stability of the oil. However, bleaching and deodorization may not be needed as they are more important for edible oils. Oxidative stability of soybean oil can be increased by a simple chemical/physical process such as activated carbon adsorption. If the crude oil shows desirable properties after such process based on the chemical analysis, the study will continue and rely on this oil. If not, the crude oil will be subjected to refining process that includes degumming and/or alkali treatment.
Since soybean oil is highly unsaturated oil, it is highly susceptible to lipid oxidation. Inhibition from the oxidation of
unsaturated acids in the soybean oil and increasing their stability to thermal degradation will be achieved by addition of asphalt binder modifiers such as a synthetic antioxidant or antioxidant mixtures such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) in different concentrations. The PI and Co-PIs will update the NSB Technical Advisory Committee (TAC) members on the progress of the proposed tasks on a quarterly basis and a final report will be delivered at the end of this phase. We expect to find a procedure to modify soybean oil to be used as a satisfying recycling agent. The outcomes of this phase will be used as an input for the next phase.

Updated May 19, 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.