Page 246 - MODELING OF ASPHALT CONCRETE

224 Cha pte r Ei g h t

1. Elastic:
Young’s modulus E
Poisson’s ratio n

These parameters can be treated as variable functions of stress such as mean pressure p
and shear stress J . The resilient modulus is a special case of such nonlinear model.
2 D
2. Elastoplastic:
Elastic parameters E and n
Plasticity parameters:
von Mises: cohesive or yield stress, c (s )
y
or, Mohr-Coulomb: cohesion c and angle of
friction, f
or, Drucker-Prager: two parameters
or, hierarchical single surface plasticity (HISS) as
follows:
Ultimate: g and b
Hardening: a and h
1 1
Phase change: n
Proportional to cohesion: 3R
3. Creep: Here, four overlay options are available:
Elastic: E, n
Viscoplastic: Γ, N
Viscoelastic, viscoelasticviscoplastic parameters
depending on the model (Fig. 8-9) described in
(Desai 2001).
4. Disturbance:
Ultimate disturbance D
u
Parameters A and Z
5. Thermal Effects:
Parameter l, Eq. (8-9)
It is important to note that only the parameters for a specific option are needed. The
foregoing parameters for the general DSC model are needed only if elasto-viscoplastic
and disturbance (microcracking, fracture, softening) characterization is desired.
It may be noted that for the general and all significant capabilities provided by the
DSC model, the number of above parameters is not large. For similar capabilities,
other models used for pavement often entail a greater number of parameters (Desai
2001); for example, in SHRP/SUPERPAVE approach. Also, the above parameters have
physical meanings; in other words, most are related to specific states during the
material behavior.

Determination of Parameters
The foregoing parameters can be estimated on the basis of standard uniaxial, shear,
and/or triaxial tests on specimens of materials. In general, three triaxial tests under
different confining pressures, temperature, and rates (if needed) are required to find the
parameters. The procedures for finding the parameters are straightforward and given
in Desai and Ma (1992); Desai et al. (1986), and Desai (2001).