Evaluation of Lignin/Phenol Derived from Bio-oil Production for use as an Antioxidant in Asphalt

Grant # 07-04
Principal Investigator: R. Christopher Williams
Co-Principal Investigator: Justinus Satrio
Organization: Iowa State University
Technical Area: Renewable Energy

EXECUTIVE SUMMARY
Many different performance enhancing additives and modifiers exist for asphalt binders for the purpose of improving their high or low temperature properties to combat permanent deformation or low temperature cracking.  These modifiers are commonly used for high volume roadways for permanent deformation, or for maintaining the low temperature properties and enhancing the high temperature properties.  However, very rarely are modifiers used for lower volume roadways as their predominant mode of failure is from environmental effects, e.g. oxidative aging, and results in fatigue or raveling distresses later in a low volume roadways’ life.

Substantial technological developments in the production and fractionation of bio oil, a product derived from fast pyrolysis of biomass, has the potential to be a beneficial asphalt additive/modifier/extender.  Three biomass sources consisting of switch grass, corn stover and oak wood were pyrolized and fractionated in a pilot plant.  The electrostatic precipitant (ESP) from the three biomass sources were blended with three different asphalt binders at 3, 6, and 9 percent by mass of the total binder and characterized. Characterization was done according to AASHTO M320 for grading a standard asphalt binder.  Substantial benefits of blending the oak wood and switch grass ESP fractions with a polymer modified asphalt binder were identified.  Namely the grade range of the binders utilizing the oak wood and switch grass ESP bio oil fractions were increased.  The increase of the grade range was due to greater increases in the critical high temperatures than the increases in the low critical temperatures as a result of the antioxidant activity

Work to Date – Summary and Conclusions (August 2008)
The research work summarized here clearly illustrates the value of utilizing bio oil electrostatic precipitant fractions in asphalt binders.  The key finding is that the use of oak wood and switch grass ESP bio oil fractions can increase the performance grade range of polymer modified asphalt binders in with the oak wood source by nearly six degrees Celsius.  The addition of oak wood and switch grass ESP bio oil fractions also tend to improve the grade range of binder AAM-1, but not as much as the polymer modified binder.  An increase in the grade range of the aged binder shows the antioxidant activity of the asphalt portion of the binder as the high critical temperatures are increased more than the low critical temperatures.  Generally, the corn stover ESP bio oil fraction did not improve the grade ranges of any of the three studied binders although the grade range did not significantly decrease either.  It is thought that the higher ash content of the corn stover ESP bio oil fraction is facilitating/initiating more detrimental chemistry than the oak wood and switch grass ESP bio oil fractions.

The effects of the bio oil has been shown to be dependent upon the base asphalt, source of the bio mass, and amount of bio oil blended with the asphalt binders.  It was also shown that the various levels of the main effects can vary depending upon the aging and subsequent rheological properties tested and resulting critical temperatures (Tc).  Statistical analysis on the expanded experimental plan utilizing tall oil will need to be done.  General observations of the bio oil/tall oil/asphalt blends illustrate that the tall oil addition tends to improve the ESP bio oil fractions for all three sources when used in AAD-1 binder, but the results vary with the other combinations studied.

It is important to understand that this research examined the effects of the ESP bio oil fractions on asphalt binders and that a formulation process would produce bio oil asphalt blends that would meet grades for hot mix asphalt use.  It appears that depending upon the asphalt binder and bio oil source that up to 9 percent bio oil could be used in asphalt binders.  This research illustrates the market potential of using green technology to produce products for use in the asphalt industry.  Laboratory work is also underway evaluating the performance of mixtures containing various bio oil asphalt blends.  It will be important for this technology to demonstrate its laboratory performance in rutting, fatigue and thermal cracking, and moisture damage resistance prior to field sections being placed.

More chemical and physical characterization on the bio oil will need to be done and determine which properties have a relationship to the rheological properties of the bio oil/asphalt blends.  Further work on blending time and in fact examining higher bio oil contents also need to be examined and understand their effects on the rheological properties of the blends.

Industry partners have found the research work to have substantial application value and are in the midst of building a full size commercial pilot plant with fractionation capabilities that will be able to process 50 to 100 tons of biomass daily.  This facility will allow for large enough quantities of the ESP fraction so that mixtures for demonstration pavements can be built.  This will allow for the evaluation of production and construction processes as well as in-situ performance.