DIGEST 2006 - Sabita

air permeability recommended in
TRH8 (1987) which is less than
1,0 x 10 6 cm 3 /second.
The required Voids Filled with
Binder (VFB) should lie between
65% and 75% (Superpave 2001).
The values of VFB obtained in the
mix design are slightly on the high
side, due to the high VMA, which,
along with the voids in the mix,
determine the VFB.
Additional testing
Gyratory Testing: This test gives
an indication of the compactability
of a mix, and reasonably simulates
in-service compaction under
traffic. From Table 2 it can be seen
that the steel slag mix at various
binder contents satisfies the
gyratory testing requirements
given in the Interim guidelines for
the design of hot mix asphalt in
South Africa 2001.
(MMLS) apparatus. The results
obtained can be seen in Table 3.
These test results indicate that the
steel slag asphalt displays
somewhat better resistance to
deformation than the Dolerite
asphalt and SMA samples
evaluated.
Volume Expansion: As
mentioned before, it is of utmost
importance that the steel slag
aggregate used for road construction
is volumetrically stable. To
evaluate the stability of steel slag
aggregate once it has been
subjected to weathering, volume
expansion testing is undertaken as
a quality control measure. Typically,
the volume increase of the
steel slag aggregate is dependent
on time, and this behaviour, for all
steel slag, is usually asymptotic,
with a high rate of initial volume
expansion decreasing with time to
virtually zero.
Percentage
binder
Voids @ 125
gyrations
Voids @ 300
gyrations
Design
Specification
4.7% 4.8% 4.9% 5.0% 5.1% Voids E80s
5.1 4.9 4.8 4.3 5.4 Min 4.0 >10x10 6
3.9 2.6 2.6 2.7 3.3 Min 2.5 >10x10 6
Table 2: Gyratory Test Results
The results indicate that the mix is
not easily compacted under traffic,
and is therefore considered to be a
rut resistant mix which will
perform well in service.
Wheel Tracking Test: Cores of
150mm diameter were removed
from four locations for
comparative testing using the
Model Mobile Load Simulator
Soluble Deleterious Material
Test: Steel slag is further required
to be tested for soluble deleterious
materials.The required minimum
according to SABS 1083 is 85%,
and therefore the sample is
considered to be acceptable.
Grip Tester Friction
Measurements: Grip Tester
friction measurements were
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