Gilsonite was selected
as the best asphalt modifier at Finland’s international
Vantaa Airport for the new third runway. A high level of
confidence was required in the asphalt surfacing chosen
for the 3,000m new-build runway construction.
The onerous asphalt specification required high stability, good
ductility properties and extremely good low temperature performance
as temperatures below -30°C would be encountered during
the winter months. A further requirement was that the Ring &
Ball softening point must not change by more than 3°C after
sample storage in de-icing fluid. The key to obtaining the low
temperature performance was the timing of the introduction of
the Gilsonite into the asphalt mixer.
For the high stress
areas of the runway the selected surface course was an
AC 16/100 with 0.4% Gilsonite content. The binder course
was an AC 20/120 with 0.4% Gilsonite content. The Gilsonite
was added during the mixing process where it was introduced
several seconds before the bitumen was added. This is standard
practice in Finland where use of Gilsonite is routine.
The mixing and paving operations were trouble free and
the asphalt concrete pavement is performing well.
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In
the USA a recent study has demonstrated that only small
additions of Gilsonite are required to reduce the effective
penetration of a refinery bitumen. For example, replacing
6.6% of a 50 pen bitumen with Gilsonite will result in
a penetration of 30. Similarly, an 8% replacement will
reduce 30 pen to 16 pen.
Reduced water sensitivity has
been demonstrated in trials with a highly water sensitive
gneiss aggregate. Replacing 4% of the binder with Gilsonite
dramatically improved the Marshall stability of soaked
specimens.
Dynamic Modulus studies of Gilsonite modified
materials have shown an increase in complex moduli that
strongly suggests increased fatigue life in practical applications.
Further studies have shown that other beneficial properties
can be obtained through combined use with polymers. Gilsonite
is compatible with all known commonly used asphalt polymer
modifiers. |
