Fatigue Cracking
Witczak et al. (2002) performed numerous complex modulus tests to perfect the
recommendations for fatigue and cracking in asphalt mixtures. The results led to the
development of a fatigue distress model in which the number of repetitions to failure, Nf,
is a function of the horizontal tensile strain, St, which represents the largest of the
transverse and longitudinal horizontal strain, and dynamic modulus of the mix, E*|:
5 14
Nf = FK- (Eq. 2-12)
The adjustment factor, F, that indicates the stress or strain controlled fatigue
behavior in the pavement structure, is a function of the dynamic modulus and pavement
thickness,
hac:
13909E -4-1
F=+ + e 354h1-5 408) (Eq. 2-13)
A volumetric adjustment factor, Ki,, corrects the number of repetitions to failure
by taking into account the binder and mix properties. In the equation 2-14, PI is the
binder penetration index and Vb is the volume of binder in the mix:
K1, = [0.0252PI 0.00126PI(Vb)+ 0.00673Vb -0.0167]5 (Eq. 2-14)
Equation (2-12) can be reduced to the following equation, where the constants o3n
and kn can be assigned to nationally calibrated fatigue model constants:
N, = Pf k I (Eq. 2-15)