Page 428 - Mechanics of Asphalt Microstructure and Micromechanics

T
420 Ch a p t e r w e l v e

0.016
Verticle, SL=0.25
0.014 Inclined, SL=0.25
Horizontal, SL=0.25
Verticle, SL=0.5
0.012 Inclined, SL=0.5
Permanent Strain
0.010 Horizontal, SL=0.5

0.008
0.006

0.004

0.002
0.000
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000
SL=Stress Level No of Load Repetitions

FIGURE 12.21 Permanent deformation of asphalt mixes at 10 psi confi ning stress (courtesy
Robert Liang).

compared with experimental results. His simulation results and experimental results
show a significant permeability difference between vertical (the compaction direction)
and horizontal directions, while the horizontal direction permeability is statistically the
same (k xx and k yy ).
⎛ u ⎞ k ⎡ k k ⎤ ⎡ ∇ P ⎤
⎜ x ⎟ 1 ⎢ xx xy xz ⎥ ⎢ x ⎥
⎢
P
⎜ u y⎟ =− k ⎢ yx k yy k ⎥ ∇ ⎥ (12-27)
yz
y
⎜ ⎟ γ n ⎢ ⎥ ⎢ ⎥
eff
⎝ u ⎠ ⎣ k ⎢ k k ⎥ ∇ P z ⎦ ⎥
zz ⎦ ⎣ ⎢
z z zx zy
12.9 Anisotropic Behavior of Permanent Deformation
Liang et al. (2006) presented a study on evaluating the anisotropic properties of AC
using regular binder and 5% SBS modified binder (PG-76-22). They discovered that
the vertical modulus and strength (against permanent deformation) are larger than
those in the horizontal and inclined (45º to the vertical direction) directions (Figure
12.21). Anisotropy is more significant for the modified binder mixture (based on their
limited study).