concrete production. Additional tests shall be made when
excessive variation in workability is reported by the placing
foreman or Government inspector. Tests shall be made in
accordance with ASTM C 231 for normal weight concrete and ASTM C
173/C 173M for lightweight concrete. Test results shall be
plotted on control charts which shall at all times be readily
available to the Government and shall be submitted weekly. Copies
of the current control charts shall be kept in the field by
testing crews 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 air content and the control chart
for range, and for determining need for any remedial action. The
result of each test, or average as noted in the previous sentence,
shall be plotted on a separate control chart for each mixture on
which an "average line" is set at the midpoint of the specified
air content range from paragraph Air Entrainment. An upper
warning limit and a lower warning limit line shall be set 1.0
percentage point above and below the average line, respectively.
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 secondary 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 practical after each adjustment,
another test shall be made to verify the result of the adjustment.
Whenever a point on the secondary control chart for 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.
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
inspector. Test results shall be plotted on control charts which
shall at all times be readily available to the Government and
shall be submitted weekly. Copies of the current control charts
shall be kept in the field by testing crews and results plotted as
SECTION 03300A
Page 66
Previous Page
