Short- and long-term aging procedures were developed at Oregon State University under the Strategic Highway Research Program (SHRP) A-003A project. Several alternative methods for short- and long-term aging of asphalt-aggregate were examined. These were subjected to extensive laboratory and field validation test programs. Laboratory validation was done with an extensive testing program using 8 asphalts and 4 aggregates. Field validation utilized 20 test sites and compared the modulus of field aged and laboratory aged specimens.
For short-term aging a procedure of curing the loose mix in a forced draft oven at 135°C for 4 hours was recommended. For long-term aging, oven aging at 85°C for 4 days was recommended to represent projects of about 10 years old. Alternative procedures may be appropriate in some situations. Long-term oven aging for 2 days at 100°C could be used for stiff mixes, whereas a low pressure procedure of 4 days at 85°C may be necessary for soft mixes.
The results of the asphalt-aggregate mixture testing presented herein show that the aging of the mixture is dependant on both the asphalt and the aggregate. Also, it appears, from the evaluation of data from other SHRP contractors, that the aging and subsequent testing of asphalt alone is not a good predictor of how a mixture will behave due to the effect of the asphalt-aggregate interaction.
Continued monitoring of field projects is needed, particularly for Dry-No Freeze and Wet-No Freeze zones. Increasing the number of sites and total number of specimens tested will facilitate the use of regression analyses to develop performance prediction models.