When a single test result reaches either the upper or lower action
limit, a second test shall immediately be made. The results of the two
tests shall be averaged, and this average shall be used as the air
content of the batch to plot on the control charts for air content and
range and to determine the need for any remedial action. The result of
each test, or average as noted in the previous sentence, shall be
plotted on a separate chart for each mixture on which an "average line"
is set at the midpoint of the specified air content range from
paragraph AIR CONTENT. An upper warning limit and a lower warning
limit line shall be set 1.0 percentage point above and below the
average line. An upper action limit and a lower action limit line
shall be set 1.5 percentage points above and below the average line,
respectively. The range between each two consecutive tests shall be
plotted on a control chart for range where an upper warning limit is
set at 2.0 percentage points and an upper action limit is set at 3.0
percentage points. Samples for air content may be taken at the mixer;
however, the Contractor is responsible for delivering the concrete to
the placement site at the stipulated air content. If the Contractor's
materials or transportation methods cause air content loss between the
mixer and the placement, correlation samples shall be taken at the
placement site as required by the Contracting Officer and the air
content at the mixer controlled as directed.
b. Air Content Corrective Action - Whenever points on the control
chart for percent air reach either warning limit, an adjustment shall
immediately be made in the amount of air-entraining admixture batched.
As soon as is practical after each adjustment, another test shall be
made to verify the result of the adjustment. Whenever a point on the
control chart range reaches the warning limit, the admixture dispenser
shall be recalibrated to ensure that it is operating accurately and
with good reproducibility. Whenever a point on either control chart
reaches an action limit line, the air content shall be considered out
of control and the concreting operation shall immediately be halted
until the air content is under control. Additional air content tests
shall be made when concreting is restarted. All this shall be at no
extra cost to the Government.
c. Slump Testing - In addition to slump tests which shall be made when
test specimens are fabricated, at least four slump tests shall be made
on randomly selected batches in accordance with ASTM C 143/C 143M for
each separate concrete mixture produced during each 8-hour or less
period of concrete production each day. Also, additional tests shall
be made when excessive variation in workability is reported by the
placing foreman or Government's quality assurance representative. Test
results shall be plotted on control charts which shall at all times be
readily available to the Government. Copies of the current control
charts shall be kept in the field by the Contractor's quality control
representatives and results plotted as tests are made. When a single
slump test reaches or goes beyond either the upper or lower action
limit, a second test shall immediately be made on the same batch of
concrete. The results of the two tests shall be averaged and this
average used as the slump of the batch to plot on the control charts
for percent air and for range and to determine the need for any
remedial action. An upper warning limit shall be set at 13 mm 1/2 inch
below the maximum allowable slump on separate control charts for
percent air used for each type of mixture as specified in paragraph
SLUMP, and upper and lower action limit lines shall be set at the
maximum and minimum allowable slumps, respectively, as specified in the
same paragraph. The range between each consecutive slump test for each
SECTION 03373
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