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.
3.7.2.6
Concrete Mixture
a. Air Content Testing - Air content tests shall be made when test
specimens are fabricated. In addition, at least two tests for air
content shall be made on randomly selected batches of each separate
concrete mixture produced during each 8-hour period of concrete
production. Additional tests shall be made when excessive variation in
workability is reported by the placing foreman or Government quality
assurance representative. Tests shall be made in accordance with ASTM
C 231. 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 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 used as the air content of the
batch to plot on both the control chart for air content and the control
chart for range, and for determining 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 up 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
SECTION 03301A
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