Bio-oil is a dark-brown, mobile liquid derived from the thermo-chemical processing of biomass. Bio-oils generally contain water and lignin. Lignin is a highly-available, well-studied carbohydrate derivative known for its antioxidant properties. For asphalt pavements, oxidation can cause deterioration via long-term aging and eventually result in cracking. Therefore, bio-oil could potentially serve as an antioxidant additive in asphalt mixtures. The main objective of this research is to evaluate the effects of lignin-containing bio-oil for utilization in asphalt binders, and attempt to optimize the bio-oil modification formula by adding other additives. Using bio-oil as an antioxidant in asphalt production could prove to be an economical alternative to conventional methods while being conscious of the environment and increasing the longevity and performance of asphalt pavements.

Three bio-oils derived from corn stover, oak wood, and switch grass are tested and evaluated by blending with three conventional asphalt binders. The binders, in order of their susceptibility to oxidative aging, include two binders from the Federal Highway Administration's Materials Reference Library, AAM-1 and AAD-1, as well as a locally produced polymer modified asphalt binder. Bio-oil was added to the asphalt binders in three different percentages by weight, 3%, 6%, and 9%. Moreover, tall oil fatty acids, which is a viscous yellow odorous liquid as a by-product obtained from the southern kraft pulping process, was introduced to optimize the bio-oil modified binders. The Superpave testing and binder performance grading procedure from AASHTO M 320 was used to examine the antioxidant effects and determine the optimum fraction of bio-oil added to the binders. In addition, simple performance tests for an asphalt mixture were conducted to rank the performance properties of the different binders and bio-oil combinations. The experimental asphalt samples for dynamic modulus testing were mixed by adding optimum percentages of bio-oil modified asphalt in the aggregate with a common gradation. Following by the dynamic modulus testing, the flow number tests were carried out with the same specimens as well. Besides ranking the performance, the statistical methods are applied and used to determine the statistically significant bio-oil treatment effects.

In general, the corn stover, oak wood, and switch grass derived bio-oil indicate that there is potential to increase the high temperature performance of asphalt binders. However, the increase in high temperature performance adversely affects the low temperature binder properties. The overall performance grade ranges vary depending on the combinations of three different binders and bio-oils. Tall oil does provide significant rehabilitation effects to the bio-oil modified binders at low temperatures. According to the data, some binders show antioxidant effects. Interestingly, the dynamic modulus test results do not necessarily coincide with the asphalt binder test results and suggest greater mix performance improvement than identified by the binder test results.