Page 386 - Mechanics of Asphalt Microstructure and Micromechanics

378 Ch a p t e r E l ev e n

Notation
σ ij , e ij The total stress and strain tensor
ε ij The elastic strain stress tensor
el
D ijkl The elasticity tensor
1
p The hydrostatic pressure, p =− σδ
3 ij ij
S ij The deviatoric stress tensor, S = σ + pδ
ij ij ij
q The effective Mises stress, q = 3 S S
2 ij ij σ = ( )
σ y The yield stress of the fully dense material (f = 0), y σ ε m pl
y
ε m The equivalent plastic strain in matrix ε = 2 ε ε pl
pl
pl
pl
m
3 ij ij
f The void volume fraction
q 1 , q 2 , q 3 Material parameters
⎡ 2 ⎤
f 1 ⎛ ε pl − ε ⎞
A A = N exp − ⎢ ⎜ m N ⎟ ⎥
s 2π ⎢ 2 ⎝ s N ⎠ ⎥
N ⎣ ⎦
ε N The mean value of nucleation strain
s N The standard deviation of nucleation strain
f N The volume fraction of the nucleated voids (in tension)
EVOL Element volume

VVF Void volume fraction

The application of this model to the simulation of the field compaction will be pre-
sented following a discussion about the field compaction process and influencing fac-
tors.
Considering the field conditions, more properties need to be considered. According
to Wang et al. (2007), factors that affect compaction can be generally classified into three
categories: properties of the materials, environmental variables and boundary condi-
tions, and compaction equipment and operation control. The properties of the materials
include the gradation, shape, angularity, and texture of aggregates, the grade, and the
amount and the temperature sensitivity of the binder. The environmental variables and
boundary conditions include air and base temperatures, humidity, sunshine or cloudi-
ness and wind velocity, layer thickness, stiffness of the underlying layer, and mix lay-
down temperature. Layer thickness is one of the most important variables that affect
other influencing factors such as the rate of cooling of the asphalt mixtures, and the
particle movement during compaction. Compaction equipment and operation control
include types of roller, rolling patterns, number of passes, and rolling speed. These fac-
tors can be adjusted during the compaction. An understanding of the compaction
mechanism plus the intelligent compactor technique (Briaud, 2003) will certainly en-
hance the compaction quality significantly (intelligent compaction requires a funda-
mental understanding of the compaction mechanism to make it wise; wrong under-
standing would make it unwise). The factors in the three categories are listed as follows
(see Figure 11.11).