DIGEST 2006 - Sabita

HMA research programme:
Forensic investigation into
premature distress in asphalt
Elzbieta Sadzik
Materials Engineer
Gauteng Department of Public Transport, Roads and Works
As part of a drive by the
Gauteng Department of
Public Transport, Roads
and Works (GPTRW) to
re-examine a number of
unresolved issues associated
with hot mix asphalt, a project
was launched not only to
define these issues, but also to
serve as a catalyst for
solutions to be sought jointly
by the asphalt industry and
consulting engineers.
The project incorporates forensic
and laboratory studies to define
and, ultimately, redress premature
distress of hot mix asphalt. This
initiative seeks to bring about a
common understanding of the
issues at stake, a systematic
response through innovative
designs, and an accelerated
pavement testing programme
(APT) to evaluate the various
proposals and to develop
standards for hot mix asphalt over
a range of operating conditions.
In the last few years several
incidents of unsatisfactory
performance of HMA have been
encountered on provincial roads in
Gauteng. The poor performance
was manifested in excessive
deformation, especially at
intersections, and premature
cracking. In many instances, the
HMA design life reduced from 8-10
years to 4-6 years. Consequently,
the financial viability of HMA
became questionable.
Research
The GPTRW commissioned the
CSIR Built Environment to develop
an HMA research programme not
only to investigate the causes of
this unsatisfactory performance,
but also to address several other
unresolved issues associated with
HMA, including:
• The need for reliable test
procedures and acceptance
criteria for the assessment of
permanent deformation and
fatigue;
• The need for reliable test
methods to assess the
durability of HMA; and
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