Abstract
An essential element of understanding and predicting long-term asphalt binder performance is understanding asphalt oxidative aging and its effect on physical properties. High-temperature, high-pressure laboratory kinetic studies, pressure aging vessel (PAV) aging, and aging at pavement conditions are compared. The consequences of running the PAV at conditions far from road conditions are examined. An aging model previously reported in the literature was used to describe the data. Important asphalt aging parameters include the pressure reaction order (α), activation energy (E), initial jump in carbonyl content, and hardening susceptibility. All of these parameters are asphalt dependent. PAV tests were performed on asphalts for which kinetic data were available, and the results were compared with the kinetic model and with results obtained after 135 days of aging at 333 K (140°F) air. The high temperature and pressure used in the PAV test sometimes results in serious errors in the performance ranking of asphalts of different E and α. Nevertheless, the test often ranks asphalts remarkably well because of fortuitous cancellation of several effects of pressure and temperature and the dampening effects of diffusion. Diffusion slows the oxidation rates, and asphalts with higher rates harden at the surface faster, increasing the diffusion resistance and slowing the observed bulk rate. The relative hardening of different asphalts is affected by the choice of PAV time, temperature, and pressure.
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