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First, commenters stated that water demand could be increased if GGBF slag is used.
The State of Indiana noted that it does not allow GGBF slag from a particular source whose
product has a high water absorption. The slag granulators stated that this is incorrect and
cited several studies and concrete industry practice manuals which conclude that there are
water savings from using GGBF slag. FHWA's final comments to EPA state "GGBF slag
will generally improve the workability and reduce the water demand of a concrete," but that
"some slags will have the opposite effect; that is, concrete made with them will require more
water than if made without. This is due to differences in production processes between
sources of GGBF slag. The possibility of an increased water demand is not insurmountable,
but it is important to remember that this situation can occur and is dependent on the source
of the GGBF slag."
Second, several commenters stated that concrete containing GGBF slag is more
difficult to finish (i.e., workability is decreased). The slag granulators cited several studies
and concrete industry practice manuals to the contrary. As noted in the previous paragraph,
FHWA's final comments to EPA state that GGBF slag will generally improve the workability
of concrete, but that there have been instances where the opposite is true.
Third, commenters stated that concrete containing GGBF slag sets at a slower rate
than other concretes. This can be a concern for some construction projects where it is
necessary to accelerate the construction process (e.g., to return a roadway to service after
repairs); Two states also commented that GGBF slag cements are not suitable for use in cold
months due to the slow set time. EPA notes that 70 percent of concrete is poured in warmer
months, however.
Fourth, in a related concern; commenters stated that concrete containing GGBF slag
gains strength at a slower rate than other concretes. As with set time, rate of strength gain
can be a concern for some construction projects where it is necessary to accelerate the
construction process (e.g., to return a roadway to service after repairs). Information
provided by the slag granulators indicates that the rate and level of strength gain for GGBF
slag-based concretes is addressed by the concrete mix design.
Fifth, several states questioned the freer&and-thaw durability of concrete containing
GGBF slag. One of these states admitted that it had not tried the product, however. The
State of Indiana commented that a laboratory evaluation of GGBF slag concrete questioned
its freeze-and-thaw durability. The GGBF slag producers commented that there were
problems with this laboratory evaluation, but according to FHWA, when Indiana recently
performed a second laboratory evaluation, the results also indicated a lower level of freeze-
and-thaw durability. By contrast, the GGBF, slag producers commented that the State of
`Illinois had recently completed freeze-and-thaw testing and achieved suitable results: They
further noted that both Pennsylvania and Virginia were satisfied with the freeze-and-thaw
durability of concrete containing GGBF slag. EPA also notes that the States of
Pennsylvania, Virginia, Maryland, and New Hampshire commented that they use GGBF slag
concretes, and none indicated that they had experienced' freeze-and-thaw problems with the
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