DIGEST 2006 - Sabita

calcium oxide is not fully hydrated,
the presence of water can cause
hydration and the further breaking
down of the aggregate. In a steel
slag asphalt mix this is characterised
by isolated white deposits of
calcium carbonate, which is
formed by the hydration and
carbonation of free lime close to or
at the surface of the aggregate.
Consequently steel slag destined
for use as an asphalt aggregate
should be stockpiled outdoors for
up to 18 months to expose the
material to moisture, either from
natural precipitation or the
deliberate application of water, to
ensure that potentially destructive
hydration and its associated
expansion takes place prior to its
use as an aggregate in asphalt.
The properties that have to be
evaluated for the suitability of slag
as an aggregate relate to the
chemical, physical and mechanical
nature of the material. Table 1
gives indications of the typical
properties of steel slag, dolerite
and quartzite.
Physical properties
The unique properties of steel slag
improve the performance
characteristics of asphalt materials
in a number of ways. These are
discussed below.
Density: Particle density of the
steel slag aggregate compared to
the dolerite and quartzite
aggregates in Table 1 indicate that
steel slag is a more dense and,
hence, heavier material. The
disadvantageous financial effect of
this higher tonnage demand has to
be offset by the price of steel slag
aggregate compared to
conventional aggregates to render
mixes using steel slag
economically viable.
Property
Steel slag
13.2mm
Steel slag
9.5mm
Steel slag
-3.0mm
Dolerite
13.2mm
Quartzite
Free lime (%) 2.36 2.36 2.36 N/A N/A
pH 12.8 13.1 13.1 8 5
Particle density
(kg/l) 3.239 3.188 3.319 3.069 2.7
Water absorption 1.1 2.1 2.4 0.7 0.3
Flakiness index 3.9 7.7 - 20 23
Ten Percent Fines
Value
Wet
Dry
Aggregate
crushing value
Wet
Dry
Polished stone
value
460
490
7.3
-
460
490
7.3
-
- 315
350
-
-
13
11
236
299
20
15
63 63 63 52 55
Table 1: Steel Slag, Dolerite and Quartzite Properties
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