Introduction
Asphalt pavement is a complex system that involves multiple layers
of different materials, various combinations of irregular traffic loading,
and varying environmental conditions. The realistic prediction
of the long-term service life of asphalt pavements is one of the most
challenging tasks for pavement engineers. The performance of an
asphalt pavement structure is closely related to the performance of
the asphalt material used in the upper-bound layers. To predict the
performance of asphalt concrete with reasonable accuracy, a better
understanding of its behavior under realistic loading and environmental
conditions is needed.
Asphalt concrete is a material that exhibits both rate-dependent
viscoelastic and viscoplastic behavior. Rutting, one of the major
distress types of flexible pavements, is directly related to ratedependent
behavior under compressive loading. To predict this performance,
a significant amount of research has been undertaken to
develop laboratory test methods, analysis techniques, and models
focused on the permanent deformation growth of hot-mix asphalt
(HMA) concrete materials. However, little attention has been given
to the importance of microcrack-induced damage and its role in
accelerating the accumulation of permanent deformation. Undercompressive loading, microcracks principally develop in a direction
parallel to the loading direction, indicating for compression that the
cracks are oriented vertically in the pavement structure. In this configuration,
the microcracks tend to promote an overall reduction in
material modulus, signifying more total strain. Hence, permanent
strain develops and also tends to increase the dilative tendencies of
HMA, which further promotes material degradation.