PROPERTIES OF AGED ASPHALT BINDER RELATED TO ASPHALT CONCRETE FATIGUE LIFE

The proposed Strategic Highway Research Program (SHRP) asphalt binder specification includes a parameter that is represented as a fundamental binder property that contributes to pavement fatigue life. However, it has been the observation of some that the fatigue parameter, G* sin delta, does not correlate adequately with field performance data. There has also been some concern expressed that the parameter may actually allow the use of binders which, in previous experiences, have been used in pavements that have exhibited very poor fatigue life. Thus, a study was conducted to compare binder properties with the fatigue life of mix containing various binders, including some with "extreme" properties, for which documented performance data exists. The evaluation of the binders in a controlled laboratory mix "failure" test was considered a necessary tie between the binder properties and the field performance data. The laboratory fatigue test provides for better control of variables, while the field data are a necessary reality check on the performance ranking. A part of this tie is the degree to which the laboratory failure test simulates field conditions, such as aging. While it was intentioned to address this in the fatigue testing in the SHRP research, time limitations precluded this task. Thus, for this study, the binders were all aged using binder accelerated aging procedures prior to their incorporation into a mix. This approach was chosen over long-term oven-aging of mix because, currently, the binder aging procedure has been correlated specifically with the appearance of premature fatigue cracking in the climate where the performance data exists (the desert) on some of the binders used in this study.