Page 249 - MODELING OF ASPHALT CONCRETE

Unified Disturbed State Constitutive Modeling of Asphalt Concr ete 227

FIGURE 8-12 Comparison between predicted and observed test data for T = 25°C,
displacement rate = 5 mm/s.

loading, thermal and fluid effects. They include computation of displacements, strain
(elastic, plastic, creep), stresses, pore water pressures and disturbance during the
incremental and transient loading. Specifications of critical values of disturbance D
permit identification of the initiation of microcracking leading to fracture and softening,
and cycles to fatigue failure. Plots of the growth of disturbance, that is, microcracking
to fracture, are obtained as a part of the computation. Accumulated plastic strains lead
to the evaluation of the growth of permanent deformations and rutting.

Loading
The codes allow for quasi-static and dynamic loading for dry and saturated materials.
The repetitive loading on pavement can involve a large number of cycles. An approximate
procedure is described below.

Repetitive Loading: Accelerated Procedure
Computer analysis for 3- and 2-D idealizations can be time consuming and expensive,
especially when significantly greater number of cycles of loading need to be considered.
Therefore, approximate and accelerated analysis procedures have been developed from
a wide range of problems in civil (pavements) (Huang 1993; Lytton et al. 1993),
mechanical engineering, and electronic packaging (Desai et al. 1997). Here, the computer
analysis is performed for only a selected initial cycles (say, 10, 20), and then the growth
of plastic strains is estimated on the basis of empirical relation between plastic strains
and number of cycles obtained from laboratory test data. A general procedure with
some new factors has been developed (Desai and Whitenack 2001). This procedure is
modified for pavement analysis and is described below.