15 Sept 99
for the existing field moisture and drainage conditions (Gupta et al. 1994 and Kneller et
Air-cooled blast-furnace slags have been used by more than 20 states and other agencies
in many construction applications in recent years. The most common uses are as
aggregates for base course, concrete, and hot-mix asphalt, but the slag is also used as an
embankment material, especially over low strength subgrades. These slags are used
worldwide wherever they are readily available. Australia has successfully employed
slags for most of the applications mentioned above (Leask 1983). Granulated blast-
furnace slag has gained some acceptance as a cementitious material. One study used a
granulated slag as an additive to a cement-bentonite mixture to provide increased shear
strength of a slurry wall (Khera and So 1997). One consideration is the use of slag in
hot-mix asphalt is the increased requirement for asphalt cement, due to the porous nature
of the slag (Ahmed 1991).
Steel slag is formed in a steel furnace as the lime flux reacts with molten iron ore, scrap
metal, and other possible ingredients. After removing any entrapped metal by magnetic
separation, the slag consists of a fused mixture of oxides and silicates, mainly calcium,
iron, unslaked lime, and magnesium (Ahmed 1991 and Collins and Ciesielski 1994).
There are three different types of steel furnaces: open hearth, basic oxygen, and electric
arc. Over one-half of the furnaces currently in use are electric arc; however, there are
still substantial quantities of open-hearth slag in stockpiles. Steel slag has a tendency to
expand when exposed to moisture, unless it is previously aged with water. This
expansion is caused by the hydration of calcium and magnesium oxides (Ahmed 1991).
One company recently developed a new method of processing steel slag that completely
eliminates possible expansion (Schriefer 1997). It has a higher unit weight than blast-
furnace slags and is relatively hard, stable, and abrasion resistant. In 1989, 7.9 million
tons of steel slag were sold by the 26 producing states in the U.S. The slag was used
mainly for constructio n purposes (Collins and Ciesielski 1994).
Steel slags have been used as aggregates for base course, concrete, and hot-mix asphalt;
although only about one-half as many states have used it as have used blast-furnace slag.
Any applications other than in hot-mix asphalt require that the steel slag be properly aged
with water. Steel slag provides a hard, tough, and durable aggregate. It has been used in
pavement surfacings because of its resistance to polishing and resulting long-term skid
resistance (Ramaswamy and Aziz 1992). There have been instances of leachate
originating from slag fills and bases, while others report satisfactory environmental
effects (Ahmed 1991, FHWA 1993, and Collins and Ciesielski 1994). However, steel
slag continues to be used in base course applications (Roads and Bridges 1998).
c. Cement and lime kiln dusts. Cement kiln dust is produced in high temperature
kilns where raw materials are used to produce a cement clinker. The dust collected
during this operation consists of fine powdery materials, the exact components of which
depend upon the component materials added to the kiln and where in the dust collection
system is located (Collins and Ciesielski 1994). As of 1992, more than 3.5 million metric
tons of cement kiln dust were generated each year (Todres et al. 1992). Lime kiln dusts