6.0 5.0 4.0 . , . . AAA-1 Original AAG-1 Original --AAA-l Aged --AAG-1 Aged --The oxidation of asphalt is a major cause of pavement failure. The low-temperature oxidation kinetics of 14 asphalts are presented. A t constant temperature and oxygen pressure, asphalt oxidation occurs in two stages: (1) a relatively rapid-rate period, followed by (2) a long period of constant rate. Activation energies for the constant-rate region vary ji-om 64 to 109 kJ/mol, and reaction orders relative to oxygen pressure vary from 0.25 to 0.61. This variation in activation energy and reaction order leads to skepticism regarding the present practices of eualuating road-condition asphalt-hardening rates at a single elevated temperature and perhaps at an elevatedpressure. The asphalts occur in essentially two groups, one at high values of both activation energy and reaction order and the other at low values of each. The data indicate the existence of an isokinetic temperature near 100°C. The degree of oxidation that occurs during the initial rapid-rate region varies inversely with the oxygen reaction order of the constant-rate region.Aging temperatures 170", 180", and 190°F; aging pressures 0.2 atm and 20 atm.

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