Graduate Thesis Or Dissertation
 

Development of the simplified method to evaluate dynamic mechanical analysis data on asphalt-aggregate mixtures

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  • Testing of asphalt binders and asphalt-aggregate mixtures using dynamic mechanical analysis is becoming popular with improvements in high-speed computers, precision equipment, and computer software. Researchers are trying to describe the behavior of asphalt binders and asphalt-aggregate mixtures in terms of their time- and temperature-dependent linear viscoelastic behavior. The objectives of this thesis were to develop a simplified pneumatic test to perform dynamic mechanical analysis (DMA), to evaluate the performance of the pneumatic and hydraulic test systems using the computer software developed to perform DMA tests, and, to develop a simplified method to evaluate the experimental data obtained from DMA tests on aged asphalt-aggregate mixtures. A simplified pneumatic test system was developed to perform DMA. Computer software was also developed to perform DMA testing on both the simplified pneumatic and hydraulic test systems. DMA was performed on both test systems to compare their performance, and on aged asphalt-aggregate mixtures to evaluate the application of the simplified method. The results from the pneumatic and hydraulic test systems show that there is about a 20 percent difference in the complex modulus, especially at high loading frequencies. This is due to the compressibility of the air used in the pneumatic test system. The compressibility of air is greater at warmer temperatures than at cooler temperatures. Therefore, the application of the pneumatic test system to perform dynamic testing should be limited to low frequencies ( < 2 Hz), low temperatures ( < 25°C), and low load ( < 454 kg (1000 lbs.)) applications unless a modification can be made to increase the pneumatic cylinder's response time to match the hydraulic cylinder's response time. The simplified analysis method developed in this thesis divides the DMA results into four complex modulus and five phase angle parameters. These parameters describe the shapes of the master stiffness and phase angle curves and distinguished between the different asphalt-aggregate mixtures and the aging methods performed on the aged asphalt-aggregate mixtures. The phase angle parameters were reduced into two variables, peak frequency and peak angle, which vary with the aging of each asphalt-aggregate mixture. The peak frequency and peak angle decrease as the aging severity increases and the change of peak frequency and peak angle vary with the asphalt-aggregate mixture and aging treatment. Therefore, the complex modulus parameters and peak frequency and peak angle may be good indicators to describe how a master curve's shape varies with asphalt, aggregate, and aging type.
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