DIGEST 2006 - Sabita

Figure 4: Maintenance seals can be applied
selectively while the unit is driving over the road
• Self contained and minimal
site establishment, which
facilitates a quick response
times.
Quality issues
Very few people realise how
quickly the temperature of a
bituminous binder drops once it
makes contact with the road
surface. It is exactly this
occurrence that puts the single
pass system way ahead of the
conventional or traditional two
stage system in terms of
quality.
exact same binder – in
this case only after an
initial delay of 30
seconds. It can clearly
be seen that after 2
minutes the ball has
made far less contact
with the binder. This
illustrates the
importance of
obtaining the correct
binder viscosity if good
adhesion of the
aggregate to the binder is to be
achieved.
The diagram also illustrates that
the temperature of a binder, even
if applied as hot as 170 0 C, will
reach the ambient road
temperature about two minutes
after application. This clearly
proves that any delays in the
stone reaching the binder will
definitely result in inferior
adhesion, and very likely in
stripping of the aggregate – a
phenomenon often seen on our
roads.
Figure 5 illustrates
how the ‘wetting’ of
metal balls is
affected when
making contact with
bitumen at different
time delays. The ball
at the top left is very
clearly best
submerged, just two
minutes after making
almost immediate
contact with the
binder, i.e. as per
the single pass
system. The ball top
right was brought
into contact with the
Figure 5: How the ‘wetting’ of metal balls is affected when
making contact with bitumen at different time delays.
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