Page 10 - Mechanics of Asphalt Microstructure and Micromechanics

Introduction and Fundamentals for Mathematics and Continuum Mechanics 3

The complexities described above can be summarized as the effect of non-linearity,
non-uniformity, rate dependency, temperature dependency, large deformation, and
complex coupling in terms of mechanics. The overall consequence is that the predic-
tion of the pavement performance based on properties characterized in laboratories
may be several magnitudes different from the performance observed in the field.
While the author began with an objective to document most of the studies relevant
to the mechanics of AC, the study identified thousands of articles and reports. It is not
the intent of this book to document all these studies, which may require an indepen-
dent book of several hundred pages. Instead, this book will focus on the more rigor-
ous theories of mechanics and their related applications. Laboratory discoveries, em-
pirical correlation, relatively simple models such as isotropic elasticity models, and
viscoelasticity models are not discussed in this book. Since systematic and fundamen-
tal research looking into the mechanisms of deformation and failure, stress-path de-
pendency, and anisotropy is not available, it is difficult to present the book in such a
way where concepts in different chapters are tied together to develop the various dis-
tress models.

1.2 Phenomenological Behavior of Asphalt
Phenomenologically, AC demonstrates behavior of non-linearity, rate dependency, tem-
perature sensitivity, anisotropy, heterogeneity, irrecoverable deformation, fracturing,
healing, hardening, softening, dilatancy, etc. Theories to cover all these phenomena and
their couplings are too complicated to be realistic. Phenomenological models that de-
scribe AC behavior are typically elasticity, anisotropic elasticity, non-linear elasticity,
elastoplasticity, linear or non-linear viscoelasticity, viscoplasticity, fracture mechanics,
and continuum damage mechanics.

1.3 Need for This Book
The need for a book such as this one is two-fold: industrial and educational. Histori-
cally, the characterization of AC has been dominated by empirical approaches. In the
last two decades an (M-E) approach for pavement design has been developed. Under
this driving force, more rigorous theories have been developed or applied to solve
problems encountered in asphalt industries. The variety of theories is so large that even
researchers in this field would become lost seeking the links among these theories and
understanding their capabilities and limits. An introduction to the fundamentals of
these theories would be helpful to industrial researchers and practicing engineers to
identify viable methods. The educational needs are relatively straightforward, as was
indicated in the preface. So far, there is no such textbook. It is anticipated the book could
serve as a textbook for characterization, modeling, and simulation courses on AC and
pavements.

1.4 Logical Link of Chapters
There are many books in mechanics dealing with topics such as stress, strains, kinemat-
ics, tensor analysis, and fundamental laws of conservation and objectivity. Excellent
books are available on these topics. There are also excellent textbooks on elasticity, vis-
coelasticity, plasticity, viscoplaticity, fracture mechanics, continuum damage mechanics