  Increasing the HMA base thickness and modifying the HMA mixture properties to
improve the resistance to fatigue cracking are among the most popular methods
for achieving long-lasting pavements. Such methods are based on the idea of
reducing the tensile strain at the bottom of the HMA layer below the Fatigue
Endurance Limit (FEL), a level of strain below which no cumulative damage
occurs to the HMA mixture. This study investigates the effectiveness of several
design strategies involved in long-life, perpetual pavement design. A 3D Finite
Element model of the pavement involving a linear viscoelastic constitutive
model for HMA materials and non-uniform tire contact stresses is developed
using ABAQUS 6.11. The effects of asphalt base course thickness and mixture
type, rich binder layer, and aggregate subbase layer are examined. Four asphalt
base course mixture types, namely dense graded, polymer modified, high modulus,
and standard binder, are studied as a function of the asphalt base course
thickness. The results underline a better performance of the high-modulus
asphalt base, as compared to the other base course mixtures. The aggregate
subbase layer on top of subgrade soil showed a relatively minor effect on the
longitudinal and lateral strain response at the bottom of asphalt base course.
The addition of a rich binder layer at the bottom of the asphalt base course
showed a significant reduction in tensile strains. Tables are provided as a
guideline to assess the different alternatives in design of long-life perpetual
pavements.
