DIGEST 2006 - Sabita

Conclusions
The following conclusions related
to the mechanisms of failure were
drawn:
1. Permanent deformation:
• lack of proper support from
the underlying structural
pavement layers or the
existing asphalt layer(s);
• lack of resistance to
permanent deformation of
the new asphalt overlay.
2. Cracking:
• premature
ageing of the
binder where
the asphalt
layers were
found to be
permeable;
• stripping and
disintegration
of old/new
asphalt layers
resulting in a
lack of support
provided to the overlays.
During the forensic investigation,
it also became apparent that
current procedures to ensure that
only approved mixes materialised
on site were not satisfactory and
required urgent attention. The
same applies to the recording of
“as built” data.
Recommendations related to the
design and performance of asphalt
overlays included the following:
• The design of new asphalt
overlays should meet the
Forensic study:
Mix design
needs to be
better aligned
with the
design
environment
demands of the site where it
will be applied;
• Designs should be based on
reliable traffic loading
information and not only on
nominal traffic volumes;
• There is a need to develop
mixes that depend more on
the stone skeletons and less
on the binder stiffness for use
on sites subjected to slow
moving traffic such as at
intersections;
• More attention should be paid
to the mechanisms of distress
of the existing
pavement.
The following main
recommendations
were made as a
result of the
investigations:
• Asphalt and
structural
designs need to
be based on
appropriate
rehabilitation
investigations;
• SMA design procedures
should be reviewed;
• The Bailey Method should be
validated for South African
conditions and be used as an
aid to optimise HMA
aggregate packing
characteristics and also as an
aid to quality control.
Aggregate packing
As a part of a desk top study for
the forensic investigation, an
international literature study was
conducted to identify new tools
that could be used to improve the
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