DIGEST 2006 - Sabita

aggregate structure of asphalt
mixes. Grading characteristics of
HMA mixes investigated in the
forensic study were analysed using
the principles of the Bailey
Method, as well as related
techniques such as the Dominant
Aggregate Size Range and the
permeability characteristics of the
mix.
Based on the limited number of
mixes studied, it would seem that
these analysis techniques hold
good potential for South Africa.
Industry challenge
The asphalt industry has accepted
this challenge enthusiastically and
has come up with several
interesting designs, which will be
evaluated as part of the HVS
testing programme (see page
102). The innovative asphalt
mixes included the following:
• Stone skeletal HMA used at
airports;
• High Modulus Asphalt;
• HMA mix designed according
to the Bailey Method; and
• HMA mix manufactured with
chrome slag aggregates.
An intended APT study on durable,
rut-resistant mixes submitted by
industry in response to a challenge
issued by GPTRW has been
preceded by meetings held with
representatives of Sabita members
– asphalt suppliers, together with
their advisers and contractors. At
these meetings discussions
centred on problems encountered
in asphalt mix design, aggregate
supply logistics, consistent
production and quality
management processes.
A general conclusion was that the
COLTO specification for aggregate
grading of asphalt mixes may no
longer predicate optimal aggregate
packing given the current
aggregate shapes, and that other
methods e.g. Bailey or PRADO
may be more beneficial.
A key objective of this cooperative
effort of GPTRW and industry is to
encourage innovative thinking
without being restricted by current
specifications.
Figure 2: HVS with climatic chamber
testing a standard mix
APT and laboratory study
APT and LTPP studies have
commenced on road P159/1 (R80)
with the testing of a standard
asphalt mix commonly used in
Gauteng. These studies, which are
linked to an extensive laboratory
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