Oxidation of bitumen in the presence of a constant concentration of oxygen

The rate of oxidation of bitumens oxidised in an approximately constant concentration of oxygen (300 psi air in a pressure vessel) can be accurately described by an equation derived assuming two concurrent simple first order reactions. The equation was successfully fitted to oxidation rate data obtained in terms of viscosity increase of neat bitumen under 300 psi of air at 60 degrees C, 70 degrees C and 80 degrees C, and carbonyl group content in solution (6-15%) at 30 degrees C. Bitumen oxidation can be generalised as consisting of a group of fast reactions obeying approximately first order kinetics, and involving carbonyl and sulphoxide formation and a much slower process involving carbonyl formation which is approximately constant over the experimental time frame. Parameters in the equation can be used as a simple means to compare the durability of bitumens oxidised at temperatures characteristic of field conditions.