3.8.2.5
Batch-Plant Control
The measurement of all constituent materials including cementitious
materials, each size of aggregate, water, and admixtures shall be
continuously controlled. The aggregate weights and amount of added water
shall be adjusted as necessary to compensate for free moisture in the
aggregates. The amount of air-entraining agent shall be adjusted to
control air content within specified limits. A report shall be prepared
indicating type and source of cement used, type and source of pozzolan or
slag used, amount and source of admixtures used, aggregate source, the
required aggregate and water weights per cubic meter yard, amount of water
as free moisture in each size of aggregate, and the batch aggregate and
water weights per cubic meter yard for each class of concrete batched
during plant operation.
3.8.2.6
Concrete
a. Air Content - At least two tests for air content shall be made on
randomly selected batches of each concrete mixture produced during each
8 hour period of concrete production. Additional tests shall be made
when excessive variation in workability is reported. Tests shall be
made in accordance with ASTM C 231. The average of each set of two
tests for each mixture shall be plotted on control charts on which the
average percent and upper and lower limits are set in accordance with
paragraph MIXTURE PROPORTIONING for each NMSA. The range between two
consecutive tests for each mixture shall be plotted on a control chart
on which the upper control limit is 3.0 percent. Samples for air
content shall normally be taken at the mixer, however the Contractor is
responsible for delivering the concrete to the forms at the proper air
content. Samples shall be taken at the placement site as often as
required, depending on the Contractors delivery method, to determine
any air loss.
b. Air Content Corrective Action - Whenever points on the control
chart approach the upper or lower control limits, an adjustment should
be made in the amount of air-entraining admixture batched. If a single
test result is outside the specification limit, immediate adjustment is
mandatory. As soon as practical after each adjustment, another test
shall be made to verify the correction of the adjustment. Whenever a
point falls above the upper control for range, the dispenser shall be
calibrated to ensure that it is operating correctly and with good
reproducibility. Whenever two consecutive points either for average or
range are outside the control limits, the Contracting Officer shall be
notified.
c. Slump Testing - At least two slump tests shall be made in
accordance with ASTM C 143/C 143M on each concrete mixture produced
during each 8-hour period or less of concrete production each day.
Additional tests shall be made when excessive variation in workability
is reported. The result of each test for each mixture shall be plotted
on a control chart on which the upper and lower limits are set as
specified in paragraph MIXTURE PROPORTIONING. The range shall be
plotted on a control chart on which the upper control limit is 50 mm 2
inches. Samples for slump shall be taken at the mixer, however the
Contractor is responsible for delivering the concrete to the placement
site at the stipulated slump. If the Contractor's materials or
transportation methods cause slump loss between the mixer and the
placement, samples shall be taken at the placement site as often as
required by the Contracting Officer.
SECTION 03700
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