DIGEST 2006 - Sabita

Figure 1: A typical example of deformation
(Courtesy of CSIR)
• The need to assess the
implications of contact stress
magnitudes and distributions
on the performance of HMA.
An HMA research programme was
proposed consisting of:
• Desk-top studies;
• Forensic investigations;
• Laboratory studies; and
• Accelerated Pavement
Testing (APT) involving both
the HVS and the MMLS.
Forensic investigation
The forensic investigation was
conducted in two phases, namely
a preliminary and a detailed
investigation. The purpose of the
preliminary investigation was to:
• Assess the quality of the mix
designs in broad terms;
• Identify the differentiating
characteristics of good and
poor performing sections;
• Attempt to identify the
causes of the failures; and
• Identify sections for the
detailed forensic study.
The preliminary forensic study
concluded that:
• Mix design needed to be
better aligned with the design
environment;
• More attention should be
devoted to aggregate
packing;
• More rut resistant mixes
should be selected for
intersections; and
• Design protocols for SMA
needed to be developed
and/or refined.
The objectives of the detailed
forensic investigation were to
better understand the typical
characteristics of good and poor
performing HMA mixes, and to
identify mix design aspects that
require further study in the HMA
project.
Detailed investigations were
conducted on several sections of
the provincial road network which
were classified as both good and
poor performers. As part of these
investigations, non-destructive
testing, such as FWD deflections,
Dynamic Cone Penetrometer and
seismic testing, were conducted,
as well as laboratory tests on
cores extracted from the sections.
The forensic investigation included
a range of stone mastic asphalt
(SMA) mixes, medium
continuously graded mixes and a
bitumen rubber continuously
graded asphalt mix.
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