Determination of critical asphalt pavement voids through laboratory aging

Abstract

This research attempts to determine critical asphalt pavement voids through laboratory aging. The critical voids are defined as void levels in the asphalt pavement system above which aging occurs rapidly. A comprehensive literature review is compiled at the beginning of this dissertation. The review is intended to present a state of the art on research directed to understanding the phenomenon of asphalt pavement aging and to identify some promising aging and test methods. An oven heating procedure is selected to duplicate long-term field aging. In this procedure, pavement samples are prepared at predetermined void levels and placed in the oven maintained at 140 degrees Fahrenheit (60 degrees Ce1cius) for a period of 24 hours. During this period, air at low pressure is applied to the samples. After the aging is completed, the asphalt in the aged sample is extracted following the Abson recovery method. The effect of aging is then quantified in terms of percent penetration retained (PPR) and viscosity aging index (AI). The asphalt viscosity temperature susceptibility is also examined before and after aging. The results show that the relative aging rate of the asphalt in the mixture increases with air voids. The critical voids are determined to be between 9 and 13 percent, using the percent penetration retained, or between 9 and to 11 percent, using the viscosity aging index. It is also found that the viscosity temperature susceptibility of the asphalt tends to decrease after aging. The critical voids determined can be used to establish an upper limit for asphalt pavement voids with the intent of controlling oxidative aging. It is recommended that such an upper limit should not exceed 9 percent.