Page 251 - MODELING OF ASPHALT CONCRETE

Unified Disturbed State Constitutive Modeling of Asphalt Concr ete 229

3. Compute disturbance in all elements using Eq. (8-12).
4. Compute cycles to failure N by using Eq. (8-13), for the chosen value of D .
f c
The above value of disturbance allows plot of contours of D in the finite element
mesh, and based on the adopted value of D , it is possible to evaluate extent of fracture
c
and N .
f
Loading-Unloading-Reloading
Special procedures are integrated in the codes to allow for loading, unloading, and
reloading during the repetitive loads; details are given in Desai (2001).

Validations and Applications
The DSC 2-D and 3-D procedures have been used to predict the laboratory and/or field
behavior of a wide range of engineering problems, for example, static and dynamic-
soil-structure interaction, dams and embankments, reinforced earth, tunnels, composites
in chip-substrate systems in electronic packaging (Desai 2001) and microstructure
instability or liquefaction (Desai 2000c). In the area of multicomponent systems like rail
tracks and pavements, its specialized versions have been used to predict the field
behavior (Desai and Siriwardane 1982; Desai et al.1983; Desai et al. 1993).
It is believed that the DSC approach can be applied successfully for 2-D and 3-D
nonlinear response of both the bound and unbound materials in rigid and flexible
pavement (Desai et al. 2001; Desai 2002). The DSC models are applied herein to illustrate
the capabilities of 2-D and 3-D analyses of flexible pavements subjected to monotonic
and repetitive loading including permanent deformations, fracture, and reflection
cracking; in view of the length limitation, application for thermal cracking is not
included at this time. Also, only the DSC model with HISS plasticity as RI behavior is
used. The DSC multicomponent model is capable of including the viscoelastic and
viscoplastic creep; this will be included in future work based on available test data.

Material Parameters
Table 8-1 shows the DSC parameters for pavement and unbound materials for the
following 2-D and 3-D analyses.
The parameters for the asphalt concrete were determined from the comprehensive
triaxial tests reported by Monismith and Secor (1962); the quasi-static and creep tests
were conducted under various confining pressures and temperatures. The disturbance
parameters were also evaluated on the basis of uniaxial tests on asphalt concrete reported
by Scarpas et al. (1997). The unbound materials were characterized as elastoplastic by
using the HISS model. Their parameters were determined from the triaxial tests reported
by Bonaquist (1996). The parameters for concrete are adopted from Desai (2001).
Typical applications involving pavement geometrics and loading are given below.
Example 1: Multilayered Asphalt Pavement
Linear and nonlinear elastic models such as the resilient modulus have limited
capabilities, and in particular, they cannot account for plastic deformations or rutting
and fracture. Hence, it is necessary to use models that can allow for plastic deformations.
This example is intended to illustrate the difference between the results from the
elasticity and plasticity models.