DIGEST 2006 - Sabita

delays because of traffic diversion
or pre-laying preparation of the
road, the asphalt is often unusable
when the time comes for it to be
laid. The road authority frequently
has to allow for losses of up to
10% – even in the very warm
months.
The trial asphalt was
manufactured with a 320 viscosity
grade bitumen (similar to
penetration grade 40/60),
modified with 1.5% FT wax, and
was loaded into the trucks at
180 0 C. It was covered using a
heat shield sheet laid over the top
of the asphalt, together with three
layers of carpet under-felt, and
finally the usual tarpaulin covers.
The first truck arrived at
approximately
10h30 after a 9.5
hour drive. On
arrival the asphalt
temperatures at the
side walls were as
low as 112 0 C, while
the surface and
core temperatures
were in the region
of 130 0 C and
160 0 C, respectively.
Although the trial
was planned for a
very hot day it had rained the day
before, and the ambient
temperature was only 24 0 C in the
morning.
The road was profiled and cleaned,
and paving then began as usual
with a 25mm layer. During the
laying operation the temperature
of the asphalt dropped to 100 0 C
on the sides of the paver (surface
temperature), with the
Total haulage
times of up to
12 hours
before the
asphalt could
be loaded into
the paver
temperature in the middle being in
the region of 135 0 C. The ambient
temperature at this time was
about 30 0 C.
After the asphalt had been laid the
edges were hand-worked to
smooth them off, and a vibratory
roller was used to compact the
asphalt. Once the road had
reached a surface temperature in
the region of 65 0 C, a 17 ton
pneumatic roller was used with a
coverage of 6 passes to complete
the compaction. The road surface
temperature after finishing was
approximately 45 0 C. After a few
minutes the road was opened to
traffic and the other half of the
road was tackled. Total elapsed
time from profiling until the road
was opened to traffic was 2.75
hours.
The second truck
carrying the next
two loads of asphalt
had been waiting
for a few hours,
resulting in a total
transit time of
approximately 12
hours before the
asphalt was loaded
into the paver. This
asphalt temperature
in the truck had reached as low as
100 0 C near the side walls, and was
115 0 C and 135 0 C at the surface
and core respectively.
Construction proceeded as with
the previous lane, and only a few
lumps of asphalt (150 kg) were
found to be unusable.
In the cases mentioned above, the
asphalt was laid as if in close
proximity to the plant, and was
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