Concrete shall be composed of cementitious material, water, fine and coarse
aggregates, and admixtures. Class F flyash or Class N Pozzolan, if used
with non alkali reactive aggregates, shall consist of not less than 15
percent of the cementitious material by mass and not more than 35 percent.
GGBF slag, if used with non alkali reactive aggregates, shall consist of
not less than 20 percent of the cementitious material by mass and not more
than 50 percent. If Class F fly ash, Class N pozzolan, or GGBF slag is
required to mitigate potential alkali-aggregate reactivity, the percentage
by mass, as determined from the modified ASTM C 1260 testing shall be used
in the mixture proportioning studies. Class F pozzolan or GGBF slag shall
be used in all concrete mixtures. Class F pozzolan shall consist of not
less than 25 percent of cementitious materials by mass and not more than 40
percent. GGBF slag shall consist of not less than 40 percent of the
cementitious material by mass and not more than 50 percent. The total
cementitious material content shall be at least [280 kg/cubic meter 470
lb./cu. yd.] [310 kg/cubic meter 517 lb./cu. yd.]. Admixtures shall
consist of air entraining admixture [and shall also include] [and may also
include, as approved] [accelerator] [retarder] [water-reducing admixture].
2.11.2
Proportioning Studies
Trial design batches, mixture proportioning studies, and testing
requirements shall be the responsibility of the Contractor. Trial mixtures
having proportions, slumps, and air content suitable for the work shall be
based on methodology described in ACI 211.1, modified as necessary to
accommodate flexural strength.
2.11.2.1
Water-Cement Ratio
At least three different water-cement ratios, which will produce a range of
strength encompassing that required on the project, shall be used. The
maximum allowable water-cement ratio required in paragraph: Specified
Flexural Strength will be the equivalent water-cement ratio as determined
by conversion from the mass ratio of water to cement plus pozzolan, and
ground granulated blast furnace (GGBF) slag by the weight equivalency
method as described in ACI 211.1. In the case where GGBF slag is used, the
mass of the GGBF slag shall be included in the equations in ACI 211.1 for
the term P, which is used to denote the mass of pozzolan. Laboratory trial
mixtures shall be proportioned for maximum permitted slump and air content.
2.11.2.2
Trial Mixture Studies
Separate sets of trial mixture studies shall be made for each combination
of cementitious materials and each combination of admixtures proposed for
use. No combination of either shall be used until proven by such studies,
except that, if approved in writing and otherwise permitted by these
specifications, an accelerator or a retarder may be used without separate
trial mixture study. Separate trial mixture studies shall also be made for
concrete for each placing method proposed. The temperature of concrete in
each trial batch shall be reported. Each mixture shall be designed to
promote easy and suitable concrete placement, consolidation and finishing,
and to prevent segregation and excessive bleeding.
2.11.2.3
Mixture Proportioning for Flexural Strength
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NOTE: The first option, "Beams", includes items a
through i; the second option "Cylinders/Beams"
includes the second listing of items a through j.
SECTION 02753
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