Bitumen, as with all civil construction materials, is characterized by
its mechanical properties. The first classification used in the past,
and actually still working in many Countries nowadays, is based on
empirical properties, such as penetration, softening point, breaking
point and ductility. The importance of a performance analysis
has been developed only in the last 20 years: by adopting empirical
test procedures, bitumen mechanistic behaviour is not investigated,
the test procedures are influenced by the operators and innovative
binders cannot be properly tested.
Also, the traditional classification (such as penetration or viscosity
grade) provides ambiguous results.
In fact, two bituminous binders may have the same properties at
different test temperature and much different behaviour at other
ones.
The need to understand the mechanical properties and relation
between the material and the damage that occurs during the service
life of road pavement (low temperature cracking, fatigue cracks
and rutting deformations) was the motivation behind the development
of a new classification system known as Superpave: Superpave
is an acronym for Superior Performing Asphalt Pavements
and it is a new, comprehensive asphalt mix design and analysis
system, developed by Strategic Highway Research Program (SHRP)
to improve the performance and durability of roads. This method is
different from the previous one and it is based on PERFORMANCE:
focusing on bituminous binder, the modern classification introduced
by Superpave is based on Performance Grade (PG).
A unique feature of the Superpave system is that the tests are performed
at temperatures and aging conditions that more realistically
represent those encountered by in-service pavements. The Superpave
PG binder specification requires the testing of the asphalt
binder under project’s expected climatic and aging conditions in
order to help in reducing pavement distress. SHRP researchers
developed new equipment standards as well as incorporated equipment
used by other industries to develop the binder tests.
The new performance-based classification system introduces
the binder rheology based innovative testing conditions that
real replicate the binder behaviour from the construction phase
including the concept of properties evolution due to ageing. Employing
the new Superpave approach measures physical properties that
can be related directly to field performance utilizing engineering
principles. The key detail is that the Superpave tests characterize
asphalt at a wide range of temperatures and aging. Superpave
characterizes them at the actual pavement temperatures that they
will experience, and at the periods of time when the asphalt distresses
are most likely to occur.
