where
S= Reduced time
t = Real time
aT = Temperature shift factor
The shift factor is another very important parameter obtained from constructing the
master creep compliance curve. On a log creep compliance log time scale, log (1/ at)
corresponds to the horizontal distance of the shifting. Two equations are commonly used
to obtain shift factors for asphalt binders:
For T > Td, the Williams-Landel-Ferry (WLF) (15) equation (2.30) is used:
a 19(T- T,,
Log -9(TT (2.30)
a d 92+(T-T,)
For T < Td, the Ahrennius function (2.31) is used:
Log =j 230 (2.31)
aTd 2.303R T Tdj
where:
aT/aTd = the shift factor relative to the defining temperature
T = Temperature at which properties are desired, ( K)
Td = Defining Temperature, ( K)
Ea = Activation energy for flow below Td 261,000 J/mol
Rg = Ideal gal constant, 8.34 J/mol- K
SK= C + 273