DIGEST 2006 - Sabita

Fischer-Tropsch wax bitumen modifier:
Overcoming temperature and
time constraints
Francois Bornmann
Marketing Manager
Sasol Wax
Robbie Hiley
Marketing Manager
Sasol Wax Australia (Pty) Ltd
Stefan Strydom
Business Manager
Sasol Wax
Contractors in South
Africa, Australia and
elsewhere have achieved
optimum pavement performance
when mixing and placing
hot and warm asphalt, even
under conditions of inclement
weather and extended time
and haul distance, through the
use of bitumen modified with
Fischer-Tropsch wax.
Wax modifiers (commonly referred
to as Sasobit® or FT wax) are
produced by Sasol Wax (a division
of Sasol Chemical Industries Ltd.)
using the Fischer-Tropsch catalytic
process utilising natural gas. FT
wax is fundamentally different
from naturally occurring waxes in
bitumen, in that it is inert to
chemical and ultraviolet activation.
It further combines a low melt
viscosity with a reduction in
penetration and an increased
softening point of the modified
binder.
The physical and rheological
properties of FT wax have a
significant impact on those of the
base binder at low modification
levels. These are evident in the
improved blending, compaction
and ease of laying of the modified
asphalt and the resultant
performance characteristics of the
pavement.
Physical properties of
FT wax
Pure FT wax begins to crystallise
above 100 0 C. However, practical
experience has shown that asphalt
mixes containing this modifier can
be compacted at temperatures as
low as 80 0 C, which seems to
contradict the first statement. This
raises the question of the
mechanism of FT wax crystallisation
in asphalt mixes, since this
has a considerable influence on
the minimum temperatures of
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