THE KINETICS OF CARBONYL FORMATION IN ASPHALT

The oxidation of asphalt is a major cause of pavement failure. The low -temperature oxidation kinetics of 14 asphalts are presented. At const ant temperature and oxygen pressure, asphalt oxidation occurs in two s tages: (1) a relatively rapid-rate period; followed by (2) a long peri od of constant rate. Activation energies for the constant-rate region vary from 64 to 109 KJ/mol, and reaction orders relative to oxygen pre ssure vary from 0.25 to 0.61. This variation in activation energy and reaction order leads to skepticism regarding the present practices of evaluating road-condition asphalt-hardening rates at a single elevated temperature and perhaps at an elevated pressure. The asphalts occur i n essentially two groups, one at high values of both activation energy and reaction order and the other at low values of each. The data indi cate the existence of art isokinetic temperature near 100 degrees C. T he degree of oxidation that occurs during the initial rapid-rate regio n varies inversely with the oxygen reaction order of the constant-rate region.