Antioxidant Effect of Bio-Oil Additive ESP on Asphalt Binder

Bio-oil is a dark brown, mobile liquid derived from the thermo-chemical processing of bio-mass. Bio-oils generally contain water and lignin. Lignins are highly-available, well-studied carbohydrate derivative known for their antioxidant properties. For asphalt pavements, oxidation can cause deterioration, a longterm aging process, and eventually result in cracking. Therefore, bio-oil could potentially serve as an antioxidant additive in asphalt mixtures. The main objective of this study is to evaluate the effects of lignin-containing bio-oil for utilization in asphalt binder. 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 (FHWA’s) Materials Reference Library (MRL), AAM-1 and AAD-1, as well as a locally produced polymer modified asphalt binder (LPMB). Bio-oil was added to the asphalt binders in three different percentages by weight, 3%, 6%, and 9%. The Superpave testing and 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, performance tests for an asphalt mixture containing the bio-oil modified asphalts were conducted. 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. Statistical methods are applied and used to determine the statistically significant bio-oil treatment effects. Generally, 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. 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.