EVALUATION OF ASPHALT-AGGREGATE MIXTURE AGING BY DYNAMIC MECHANICAL ANALYSIS

Dynamic mechanical analysis (DMA) and other methods of rheological testing have been used to characterize the time- and temperature-dependent responses of viscoelastic materials. A DMA test procedure can determine the complex modulus, storage modulus, loss modulus, and loss tangent. These calculated values can be used to thoroughly characterize an asphalt-aggregate mixture. From tests done over a range of frequencies and temperatures, a master stiffness curve can be made by using the time-temperature superposition principle to transform the data to a standard temperature. From these master curves, complex moduli can be determined at the transformed temperature for frequencies other than those used in the test. At Oregon State University, a semi-closed-loop servohydraulic DMA testing system with controlling software has been developed. An evaluation of three asphalts and two aggregates was undertaken with this new testing system. A range of temperatures from 0 deg to 40 deg C and a range of frequencies from 0.01 to 15 Hz was used in the testing program. From the data collected in this program it was possible to differentiate between the different mixtures in their response and to differentiate between long-term aging procedures for some of the mixtures. It was also noted that the DMA rankings of aging susceptibility based on the complex modulus at 1 Hz are similar to the diametral resilient modulus rankings for the same asphalt-aggregate combinations.