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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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Ten asphalts, including seven Strategic Highway Research Program (SHRP) asphalts and three Texas asphalts, plus naphthene and polar aromatic Corbett fractions for five of the seven SHRP asphalts were aged at laboratory conditions. The oxygen content by direct measurement and the FTIR carbonyl content were obtained for samples which were aged to varying degrees. It was found that, for each material, the oxygen content correlates linearly with the carbonyl content. The correlation is independent of aging temperature and aging pressure over the ranges studied. Furthermore, each material has a unique correlation coefficient, and the correlation slope for a whole asphalt is smaller than those of its fractions, except for asphalt AAM-1. Since the major oxidation products, including ketones, carboxylic acids, and anhydrides, have different oxygen content−carbonyl content ratios, the correlation coefficients provide qualitative information about the distribution of oxidation products. Relations between oxygen, carbonyl, and asphaltene production are deduced from these and earlier results.