Page 454 - Mechanics of Asphalt Microstructure and Micromechanics

446 C hapter T h ir te en

To calculate the surface energy of adhesion between two different materials (i and j)
without the presence of water, the following equation was used (Cheng et al., 2003):
a
ΔG ij = ΔG aLW ij + ΔG aAB ij (13-14)
where ΔG aLW ij = non-polar part of the surface energy of adhesion
ΔG aAB ij = polar part of the surface energy of adhesion
In his research, Kim et al. (2004) used the dynamic mechanical analysis (DMA) to
characterize the fatigue damage behavior and fracture of asphalt binders and mastics
by measuring the viscoelastic properties and damage characteristics. The model em-
ployed was used to study the effects of moisture on mastic sensitivity to fatigue dam-
age. The model equation is presented as follows:
fS () k
γ
N = f () −2α (13-15)
f k(.05 I C C ) α 0
P 1 2
where N f = number of loading cycles to failure
I P = initial pseudostiffness
k = 1 + (1 − C 2 )a
S f = damage parameter for fatigue failure
a = viscoelastic-related material parameter
C 1 , C 2 = regression constants from stiffness versus damage parameter relation
The measure of the free energy using suction in AC materials with different air-void
contents and gradations was studied by Kassem et al. (2006). The suction measure-
ments were used to calculate the moisture diffusion coefficient and relate it with the
moisture damage. The total suction under isothermal conditions was calculated using
the following formula:
h t = (u a − u w ) + h π (13-16)

where h t = total suction (kPa)
(u a − u w ) = matric (capillary) suction
u a = pore-air pressure
u w = pore-water pressure
h π = osmotic suction
Bhasin et al. (2006, 2007) looked into the strength of physical adhesion between the
asphalt and the aggregate in a dry condition, which is quantified in terms of the adhe-
sive bond energy. A high level of adhesive bond energy (in dry state) combined with a
low level of reduction in free energy in the presence of moisture are beneficial for HMA
to resist debonding in the presence of water. The total adhesive bond energy was calcu-
lated using the following formula, based also on Lifshitz-Van der Waals and acid-base
components:
ΔG AS = g A + g S − g AS (13-17)
where g A , g S = surface energy of unit area (asphalt and aggregate)
g AS = interfacial surface energy
Birgisson et al. (2003, 2004, 2007) employed the HMA fracture mechanics model
based on dissipated creep strain energy (DCSE) as a fundamental model for evaluating