Page 451 - Mechanics of Asphalt Microstructure and Micromechanics

Multiscale Modeling and Moisture Damage 443

Where w(x,y), t yz (x,y), f(x,y), D y (x,y), j (x,y), and b y (x,y) are the anti-plane mechani-
cal displacement, stress, in-plane electric potential, electric displacement, in-plane mag-
netic potential, and magnetic induction.
Some other theories, including the 3M continuum (Eringen, 1999), are briefly de-
scribed as follows. Eringen (1999) assumes the Helmholtz free energy Ψ in the follow-
ing format for micro continuum (or continuum for a single material):
ψ = { ζ , Γ ∂ , , θ ε BX } (13-11)
Ψ
;
,
,
KL KLM KL K K
ζ ≡ x x , ∂ ≡ x x = ∂ , Γ ≡ x x
,
,
KL k K Lk KL kK kL LK KLM Kk kL M
x k,K micro-deformation tensor, x inverse micro-deformation tensor
Kk
Here z KL is called the deformation tensor, KL the microdeformation tensor, and Γ KL
the wryness tensor; θ absolute temperature, X coordinate in the reference configuration,
x coordinate in the deformed configuration, and B in the magnetic flux vector, e K = e k x k,k ,
B K x k,k .
This way, the mechanical-electromagnetic coupling can be considered.
While the electronic-mechanical coupling may not have direct applications in as-
phalt mechanics, it may help characterize the electron-magnetic properties of asphalt
concrete that can enhance the understanding of electron-magnetic wave propagation in
asphalt concrete.

13.3 Moisture Damage of AC

13.3.1 Overall Review
Among asphalt pavement distresses, moisture damage still remains a primary cause of
its premature failure (Fromm, 1974; Graf, 1986; Curtis, 1993; Kandhal, 1994; Scholz et
al., 1994; Roberts et al., 1996; Alam et al., 1998; Mohammad et al., 2005) as water or
moisture penetrates and settles within its layers (Hicks, 1991; Epps et al., 2000; Solaima-
nian et al., 2007). Moisture damage also strongly influences other types of distresses
such as rutting, raveling, and cracking, which significantly reduce the performance and
service life of HMA pavements resulting in high maintenance costs for state and fed-
eral highways (Izzo and Tahmoressi, 1999; Bhasin, 2006).
In the Superpave volumetric mix design SP-2 (2001) process, evaluation of a mix-
ture’s moisture susceptibility is the final step and is accomplished using the AASHTO
T-283 standard. Research performed in the last three decades or so showed that mois-
ture susceptibility is influenced by the aggregate mineralogy and surface texture, as-
phalt binder chemistry, and the interaction between the aggregate and asphalt binder.
Although bitumen properties and aggregate characteristics are determinant factors
(Mohammad et al., 2003), aspects such as hot mix processing, mixture characteristics,
quality control during construction, water in the aggregate-asphalt interface, dynamic
effect of traffic, and type and properties of anti-stripping additives also influence the
hot mix asphalt (HMA) moisture susceptibility.
Generally, moisture damage occurs in AC pavements due to a loss of adhesion and/
or cohesion that accelerates structural degradation of the mixtures in conjunction with
cracking and plastic deformation. Moisture in pavements typically reduces strength or
stiffness of the binder and mastic through diffusion and weakens the adhesive bond