Asphalt Oxidation Mechanisms and the Role of Oxidation Products on Age Hardening Revisited

ABSTRACT The correlation between asphalt viscosity increase on oxidative aging and the carbonyl compounds formed (almost exclusively ketones) has been well established; however, the effect of sulfoxide formation on physical properties during age hardening has received little attention. Evidence is presented in this paper that shows that the alcohols, which are formed concurrently with the sulfoxides from the same hydroperoxide precursors as the ketones, have a similar effect on asphalt viscosity increase as does the ketones. These alcohols are the main contributors to oxidative age hardening of high sulfur asphalts. Analysis of the kinetic data for ketone and sulfoxide formation during asphalt oxidation also provides additional evidence for the validity of the dual asphalt oxidation mechanism previously reported.