The Utilization of Agriculturally Derived Lignin as an Antioxidant in Asphalt Binder

Asphalt pavements undergo long-term aging due to oxidation of the asphalt binder. As a pavement oxidizes, it stiffens and eventually cracks. The use of an antioxidant in an asphalt binder could retard aging, thus increasing the pavement’s service life. Lignin is a known antioxidant and is highly available from timber and many agricultural products. A wet-mill ethanol process produces several co-products, some of which contain lignin. The utilization of lignin from an ethanol plant could provide benefit to asphalt pavements, along with increasing the value of these lignin containing coproducts. Three different lignin containing co-products were added to four asphalt binders with varying amounts to find the optimum amount of lignin that would provide the greatest benefit to the asphalt binders. The asphalt-lignin blends were evaluated according to Superpave specifications and performance-graded on a continuous scale. The blends were also tested for separation tendencies. The results illustrate that the addition of lignin has a slight stiffening effect on the binder. The more lignin added, the greater the stiffening. However, separation effects are significant at high lignin levels. Binder stiffening increases the high-temperature properties, while the low-temperature properties are slightly decreased. However, the low-temperature stiffening effects are small and do not change the actual performance grade. The lignin has an overall effect of widening the performance grade range of the asphalt binders.