, Professor, Civil, Environmental and Geo-Engineering
Gene Skok, Former University Researcher, Civil, Environmental and Geo-Engineering
This research project consisted of laboratory testing to determine the complex modulus and phase angle of asphalt mixtures. Laboratory tests were performed on four different asphalt mixtures from the MnROAD site. Testing was performed at six temperatures and five frequencies. Data from the tests were processed through a nonlinear regression curve fit to generate master curves of dynamic modulus and phase angle vs. frequency. These master curves were compared to results obtained from Witczak's predictive equations. It was found, as expected, that the dynamic modulus increased with an increase in frequency and a decrease in temperature. The model used to fit dynamic modulus master curves provided a good fit for the experimental data. The modulus values calculated using the 2000 predictive equation fit the test data reasonably well for two of the four mixtures, but the differences for the two other mixtures were more significant. Smooth master curves for phase angle could not be obtained. An exploratory study to use a vibration exciter to measure dynamic modulus proved unsuccessful. This study was done under the framework of NCHRP Projects 1-37A, 9-19, and 9-29 that recommends dynamic modulus both as a design parameter and a simple performance test.