Page 40 - Mechanics of Asphalt Microstructure and Micromechanics

CHAPTER2

Mechanical Properties

of Constituents

rom the microscopic view, the properties of asphalt mixtures are determined by
the properties of the constituents and the spatial arrangement of the constituents.
FThis chapter will focus on the properties of the constituents and the implication
of how these properties affect the mixture behavior. For consistency, the binder-filler
mixture is defined as Mastics. The mastic is modeled as a homogeneous and isotropic
viscoelastic medium. This chapter consists of five sections. Section 1 focuses on the
properties of asphalt binder; Section 2 focuses on the properties of aggregates; Section
3 focuses on the properties of mastics; Section 4 focuses on the characterization of mix-
ture properties; and Section 5 discusses nano-characterizations. There are various kinds
of properties such as chemical, physical, and mechanical properties. For the interest of
this book, discussion will focus on the mechanical properties only, although chemical
and thermal properties affect mechanical properties in a complex coupling mode. In
addition, as far as pavement performance is concerned, only properties at pavement
temperatures regularly encountered will be addressed. In order to study the compac-
tion properties, the properties at the compaction temperature and below will be the
focus of this book. In this temperature range, asphalt binder is viscous, viscoelastic, or
viscoplastic.
Asphalt concrete (AC) consists of approximately 5% air void by volume (not porous
asphalt pavement) and 5% asphalt binder by mass, and the volumetric composition
of AC is roughly 5% air void, 12% binder/mastics, and 83% aggregates plus fillers.

2.1 Binder Properties
Binder properties are very much related to temperatures. They can behave like a vis-
cous fluid, a viscoelastic solid, or a viscoplastic solid. Depending on the temperature
range, the parameters to represent these properties are significantly different. In addi-
tion, due to the variability in properties of asphalt binder as a result of composition and
sources, these properties are quite different as well. Therefore, for binder properties,
only models are presented. The model constants (material properties) should be char-
acterized for any specific type of binder. These properties mainly fall into the category
of deformation. Other properties such as toughness (fracturing), anisotropy, and fail-
ure/healing have not been well studied.

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