7-5
0)
gff --------------------------
> -W--C1-02
t-
15 ---- Avg
0 5 10 15 20
Frequency (Hz)
Figure 4-16. Phase angle of GAC1 mixture at 40C
Master Curve Construction
The dynamic modulus and phase angle of mixtures can be shifted along the
frequency axis to form single characteristic master curves at a desired reference
temperature or frequency. In the proposed "2002 Guide for the Design of Pavement
Systems" currently under development in the NCHRP Project 1-37A, the modulus of the
asphalt mixture, at all analysis levels of temperature and time rate of load, is determined
from a master curve constructed at a reference temperature. The procedure assumes that
the asphalt mixture is a thermorheologically simple material, and that the time-
temperature superposition principle is applicable.
Typically, the shift factors a(T) are obtained from the WLF equation (Williams et
al., 1955).
c (r T )
loga(T) = C2 V-_- (Eq. 4-1)
C2T TF
Where Ci and C2 are constants, Tr is the reference temperature, and T is the temperature
of each individual test.