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up the remaining 10 percent. Approximately 75 percent of the blast furnace slag generated
annually is used in aggregate applications, a smaller percentage is used in concrete, and the
remainder is disposed or stockpiled.
b. Technically proven uses. It is technologically and economically feasible to process
granulated blast furnace slag into an additive for cement and concrete. The granulated slag
is ground into a consistency somewhat finer than Portland cement. GGBF slag replaces a
portion of the Portland cement in concrete mixtures. In some concrete mixtures, GGBF slag
can replace up to 75 percent of the Portland cement, on a pound for pound basis. Most
concrete mixtures containing GGBF slag use between 25 and 50 percent slag, however.
FHWA commented that there are three basic types of blended cement containing
GGBF slag: Type IS, which contains 25-50 percent GGBF slag; Type ISM, which contains
less than 25 percent GGBF slag; and Type S, which contains over 70 percent GGBF slag.
FHWA stated that Type IS is the most commonly used blended cement,, while Type S is,
rarely used due to its slow setting rate.
Like coal fly ash, GGBF slag can improve the performance of concrete, although
there is some inconsistent data about the performance of GGBF slag-Portland cement
concretes, as discussed above. According to information provided by the GGBF slag
producers and some state agency commenters, GGBF slag can result in higher strength;
lower heat; lower permeability; better durability in marine, salt, and chemical environments;
and lighter color. FHWA, several state agencies, and the Province of Ontario commented
that GGBF slag can help to reduce alkali-silica reactions. FHWA also stated that GGBF slag
can help provide an increased resistance to sulfate attack.
In the proposed CPG, EPA noted that the GGBF slag producers had informed EPA
that GGBF slag can be used compatibly with coal fly ash and other cementitious and
pozzolanic-materials when used in concrete. The American Portland Cement Alliance
commented that it supported the proposed designation, indicating that use of GGBF slag is
accepted by the cement and concrete industry.
In the proposed CPG, EPA stated that there is approximately 1.2 million tons of
domestic cement industry grinding capacity specifically devoted to the manufacture of GGBF
slag. EPA also stated that five Portland cement companies operate six grinding plants to
produce GGBF slag; that two Portland cement companies may begin producing GGBF slag at
three locations, and that a third company recently bought a GGBF slag plant.
Corrected information provided by commenters indicates that there is 1.95 million
tons of blast furnace slag granulation capacity at four locations. Ten cement companies in
nine states currently grind granulated blast furnace slag into GGBF slag. According to the
slag granulators, three more companies, in three additional states, will begin grinding
commercial quantities of GGBF slag in 1995.

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