ASPHALT OXIDATION -- AH OVERVIEW INCLUDING A NEW MODELFOR OXIDATION PROPOSING THAT PHYSICOCHEMICAL FACTORS DOMINATE THE OXIDATION KINETICS

Oxidative aging of asphalt is the primary cause of asphalt hardening in pavements, thus contributing to various forms of pavement cracking. The major identifiable functional groups formed on oxidation at use temperatures are ketones and sulfoxides. Anhydrides are formed in significant amounts at the higher levels of oxidation, apparently not via carboxylic acids, but at specific aromatic bridgehead positions from the same precursors that form the ketones. Only trace amounts of carboxylic acids are formed. The sulfoxides formed have thermal sensitivity to subsequent decomposition, thus they reach a “steady state” concentration which is a function of temperature and oxygen diffusion rate. A differential infrared technique has been developed to quantitatively determine the major oxygen-containing functional groups present and/or formed on oxidation. The technique is based on the use of selective chemical reactions and selective solvents.