DIGEST 2006 - Sabita

intensive and time consuming
projects such as deep patch
maintenance are even more
troublesome.
A deep patch maintenance project
in Sydney, Australia, required that
a stretch of road pavement 67
meters long, approximately
400mm deep and 3 meters wide
be removed, profiled and repaved
in four layers within 9 hours —
working at night, in the middle of
winter. No rutting was to be
observed the next morning or
shortly thereafter as a result of
elevated asphalt temperatures.
The road carries a traffic loading of
approximately 60 000 vehicles/
day, and road authority
specifications on compaction, ride
quality etc. had to be met.
Project
requirements
The project
requirements could
only be achieved by
producing and
delivering “warm
mix” asphalt to site,
and laying it at
considerably lower
temperatures than
normal. This was achieved by
modifying the bitumen with FT
wax at 1.5% of the binder
content.
The project started at 20h30 with
the profiling and removing of the
old asphalt and base layers. Once
the area had been cleaned,
200mm of stabilised base was
compacted into the affected area
and finished to ensure that exact
levels were attained. This process
No extraordinary
precautions
were taken
during the
paving or
compaction
processes
lasted until approximately 00h30,
by which time the ambient
temperature had dropped to 10 0 C.
Wind chill effects made workability
and effective compaction even
more difficult.
The asphalt was to be laid in two
base layers of 60mm each, and
two wearing course layers of
45mm each. The 60mm base
layers were produced at 130 0 C,
and the two top layers at 140 0 C.
Paving of the first layer began at
approximately 00h45. In addition
to the low paving temperatures,
the paver burners were also
limited to 120 0 C to minimise
introduction of any extra heat into
the system.
Temperature probes were inserted
into the core of
each asphalt layer
to measure
variations in the
temperature of each
mat throughout the
whole process. The
probes were placed
in the middle of
each layer (probe 1
in the bottom and 4
in the top layers)
and not directly on
top of each other to
make sure that the wires were not
cut during the rolling. The
temperature increase is due to the
subsequent layers being deposited
on top of the underlying
layers.The detailed temperature
profiles in Figure 3 show the core
start temperatures and the time
frames taken to finish all four
layers.
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