The AASHTO M332 specification includes a relationship between the non-recoverable creep compliance at 3.2 kPa ( Jnr3.2) and the percent of elastic recovery ( R3.2) from the multiple stress creep and recovery (MSCR) test. Justification for the exact position of this curve based on binder performance is largely undocumented in the technical literature as is the singular effect of higher or lower R3.2 values on mixture performance. In this study, nine binders were tested to evaluate the effect of R3.2 on the performance of asphalt mixtures. Binders with similar Jnr3.2 and varying MSCR R3.2 were divided into four groups based on their Jnr3.2 value. Comparisons were made based on results obtained from the dynamic modulus test, Hamburg wheel tracking test, and axial fatigue test. Based on these tests, it was shown that R3.2 had a strong relationship to the dynamic modulus of asphalt mixtures especially at intermediate and high temperatures. Binders with lower R3.2 had a higher dynamic modulus but showed no correlation to phase angle. Both modulus and phase angle of the mixture correlated to the binder shear modulus and phase angle. Binders with high R3.2 had a greater fatigue resistance and the effect is quite noticeable. However, R3.2 was shown to have little to no effect on the rutting resistance of the asphalt mixtures for the temperatures tested in this study. Finally, an alternative Jnr3.2 versus R3.2 relationship based on the results of this study is also presented.
It has been recognized that there exists a potential benefit from using synthetic fibers to reinforce asphalt mixtures. In these mixtures, the state of the fibers may play an essential role in their reinforcement function. This study aims to quantify the state of synthetic fiber distribution for two different aramid fiber–based asphalt mixtures and then show the impacts of fiber dispersion on modulus, rutting, and fatigue performance of each asphalt mixture in comparison with one another and with respect to an equivalent non-reinforced asphalt mixture. Both a quantitative and qualitative assessment of aramid fibers distribution as well as state of fiber are investigated using a fiber extraction procedure and microscopy imaging, respectively. The results suggested that a higher level of micro-fibrillation as well as high distribution of aramid fibers improved the rutting resistance of asphalt mixtures, while the distribution level of aramid fibers and fibers state did not affect the modulus and fatigue. These results are specific to the mixture studied but provide the first objective and detailed study describing fiber state, fiber dispersion, and performance.
The selection and specification of asphalt binder is one of the factors that ultimately affect the long-term performance of asphalt pavements. Many agencies currently follow AASHTO M320 for their binder specifications, where the ratio of dynamic modulus to the sine of the phase angle, | G*|/sin δ, is the binder rutting parameter. However, an alternative now exists, AASHTO M332, which uses the non-recovered creep compliance, J nr , for this purpose. In this paper, the relative merits of these two parameters are compared using experimental results from 21 different asphalt mixtures from Arizona. The rutting parameters according to AASHTO M332 and M320 were determined for each of the binders in these mixtures and, for each mixture, two rutting performance tests were conducted: Hamburg wheel tracking test and repeated load permanent deformation test. The two binder rutting parameters demonstrated very high correlation to one another for non-polymer modified asphalts, but inconsistent correlation for polymer modified asphalts. Both Hamburg wheel tracking tests and repeated load permanent deformation tests showed positive correlations to both | G*|/sin δ and Jnr. It was concluded that, while both parameters showed good correlation, the Jnr of the binder relates better to mixture rutting than does | G*|/sin δ. Considering the results in this study, it is believed that Jnr is a slightly better rutting parameter for binder specifications.
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