Evaluation of lignin as an antioxidant in asphalt binders and bituminous mixtures.

The chemical process of oxidative age-hardening in asphalt pavements is one of the major distressesleading to hot mix asphalt (HMA) pavement failure as evidenced by fatigue and thermal (low temperature)cracking.Research investigations at the Western Research Institute (WRI) prior to 2005 suggested the additionof lignin may reduce the oxidation rate of asphalt binder. Research efforts by Bishara, Robertson, andMahoney (2006) at the Kansas Department of Transportation\u2019s Research Chemistry Laboratory in 2005 alsosuggested the addition of lignin to asphalt binder appeared to reduce the oxidation rate of the binder, andtherefore, had the potential to be an antioxidant for HMA pavement.The objective of this 2007 limited laboratory research project was to determine the potential ofreducing the oxidation rate of HMA pavements by adding lignin to the asphalt binder used to produce theHMA mixture. The testing matrix for this study consisted of two binders, two basic aggregate mixtures, andone hardwood lignin at one concentration. Eight total mixtures with and without lignin were tested afterlong-term aging to determine if the lignin had any effects on the material properties. The test results fromthis project showed minimal differences between the lignin test specimens and the control specimens.Based on the results from this limited study, there is no clear evidence adding lignin to HMAmixtures reduces oxidation or the lignin acted as an antioxidant