Page 455 - Mechanics of Asphalt Microstructure and Micromechanics

Multiscale Modeling and Moisture Damage 447

asphalt mixes moisture damage. Properties evaluated were indirect tensile strength,
resilient modulus, creep compliance, creep rate, fracture energy limit, and dissipated
creep strain energy limit and results showed that neither one of these properties consis-
tently reveals the effects of moisture damage on the mixtures. To measure the fracture
resistance of mixtures, the energy ratio (ER) was introduced:

•
DCSE aDCSE
ER = f = f (13-18)
2
DCSE . 098 • m • D
min 1
3
where DCSE f = dissipated creep strain energy (kJ/m )
3
DCSE min = minimum DCSE for adequate cracking performance (kJ/m )
D 1 , m = creep parameters (1/psi)
–3.1
a = 0.0299 s t (6.36 − S t ) + 2.46 10 –8
s t = tensile stress of asphalt layer (psi)
S t = tensile strength (MPa)
Fracture model (crack growth model) based on dissipated pseudostrain energy
(DPSE) was investigated by Masad et al. (2006) and Arambula et al. (2007a,b) for mois-
ture susceptibility of asphalt mixes. The crack growth index for assessing the damage
was calculated using an equation derived from Paris’s law expressed in terms of the J-
integral (Lytton et al., 2005):
dr
= AJ () n (13-19)
dN R
where r = average crack radius
N = number of load cycles
A, n = material constants
J R = J integral
Further, J R can be expressed as a function of the change in pseudostrain energy/unit
volume (W R ) of the intact material over the change in crack surface area (CSA) using the
equation:
∂ W DPSE
J R ,with W =
R ∂( CSA) R S (/)
S
i l (13-20)
where DPSE = dissipated pseudostrain energy/load cycle
S i = pseudostiffness for each load cycle
(max. applied stress/pseudostrain)
S l = maximum pseudostiffness in the first load cycle
Using a linear regression model based on ultrasonic energy, McCann and Sebaaly
(2001) showed that the rate at which the asphalt binder is removed from the surface of
an aggregate can be quantified. Also, Pinzon and Such (2004) used a complex modulus
approach for assessing the damage by moisture in AC cores having various dimen-
sions. Via this approach, an empirical model for evaluating the extent of deterioration
was under development based on classifying the modulus loss levels before and after
immersion for each mix design under given temperature and immersion time condi-
tions. They concluded that the stiffness modulus alone cannot provide reasonable