Page 157 - MODELING OF ASPHALT CONCRETE

Complex Modulus fr om the Indir ect Tension Test 135

FIGURE 5-8 Phase angle mastercurves for I19.0D-Fine mixture. (Kim et al. 2004, with
permission from Transportation Research Board.)

averaged phase angles are close to the values from the axial compression testing. This
finding needs to be refined further using a more rigorous approach. Kim et al. (2005)
contains more phase angle comparisons between IDT and axial compression tests.

Poisson’s Ratio
In order to investigate the cause(s) for the difference in the phase angles determined
from the horizontal and vertical strains, Poisson’s ratios of the four representative
mixtures were calculated from the IDT test results and plotted in Fig. 5-9. First to note
from this figure is that the average values of Poisson’s ratio at different temperatures
seem to be reasonable, that is, about 0.18 at −10°C, about 0.25 at 10°C, and around 0.45
at 35°C. Some of Poisson’s ratio values at lower frequencies and 35°C exceeded the
linear elastic limit of 0.5, indicating that at these conditions specimens were damaged
during the dynamic modulus test.
Another important observation from Fig. 5-9 is that there is a slight dependence of
Poisson’s ratio on the loading frequency. This frequency dependence of Poisson’s ratio
results in the phase lag between the vertical and horizontal strains, which in turn
produces different phase angles calculated from the vertical and horizontal strains in
Figs. 5-7 and 5-8.

Conclusions
In this chapter, an analytical solution for the dynamic modulus of asphalt mixtures
tested in the IDT mode is developed using the theory of linear viscoelasticity. The
accuracy of this solution was successfully validated using the experimental data