Using Polymer Modified Asphalt Emulsions in Surface Treatments A ...

2.1.3 Asphalt Composition
Asphalts are generally characterized as colloids containing high molecular weight,
relatively insoluble and nonvolatile compounds known as “asphaltenes”, dispersed
within a liquid, continuous, lower viscosity phase comprised of low molecular weight
compounds called “maltenes”. Asphaltenes are believed to be the component of
asphalt that imparts hardness, while maltenes provide ductility and facilitate adhesion.
Maltenes consist predominately of oils (aromatics and saturates) and resins
(compounds which represent a transition between asphaltenes and oils). Typical
asphalts normally contain between 5% and 25% by weight of asphaltenes.
The asphaltene content of asphalt cements is chiefly responsible for influencing the
overall viscosity of the composite system – that is, higher asphaltene contents generally
lead to higher composite viscosities. In addition, research has shown that maltene
phases possessing a comparatively high aromatic content generally result in better
dispersal of the asphaltenes, leading to high temperature susceptibilities, high ductility,
low complex flows, and lower rates of age-dependent hardening (3).
Conversely, low aromatic maltenes generally lead to the formation of agglomerates of
asphaltenes which form a network-like structure and are referred to as “gel-type”
asphalt cement. Gel-type asphalt may also be formed from mixtures where the
asphaltene to maltene ratio is inordinately high, because maltenes are needed to
disperse the asphaltene fractions. Gel-type asphalts are generally characterized by low
temperature susceptibilities, low ductility, increased elastic component content,
thixotropic behavior, and rapid age-dependent hardening (3). In this sense, the addition
of polymer modifiers when used in conjunction with compatible asphalts, can lead to
improved high and low temperature performance combined with increased flexibility and
resistance to deformation. Compatible asphalts are those that when blended with a
polymer modifier, produce a two-phase mixture that is characterized by a well dispersed
polymer phase that is stable at high temperatures.
Many of the compounds contained in asphalt are polar molecules due to the presence
of alcohol, carboxyl, phenolic, amine, thiol, and other functional groups. As a result of
this polarity, the molecules self-assemble to form large, complex structures with
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