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 both the control
chart for percent air and the chart for range, and for determining 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 an upper action limit line and lower action limit
line 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 type of mixture shall be plotted
on a single control chart for range on which an upper action limit is
set at 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 mixer and
the placement, correlation samples shall be taken at the placement site
as required by the Contracting Officer and the slump at the mixer
controlled as directed.
d. Slump Corrective Action - Whenever points on the control chart for
slump reach the upper warning limit, an adjustment shall be immediately
made in the batch weights of water and fine aggregate. The adjustments
are to be made so that the total water content does not exceed that
amount allowed by the maximum W/C specified, based upon aggregates
which are in a saturated surface-dry condition. When a single slump
reaches the upper or lower action limit, no further concrete shall be
delivered to the placing site until proper adjustments have been made.
Immediately after each adjustment, another test shall be made to verify
the correctness of the adjustment. Whenever two consecutive slump
tests, made during a period when there was no adjustment of batch
weights, produce a point on the control chart for range at or above the
upper action limit, the concreting operation shall immediately be
halted and the Contractor shall take appropriate steps to bring the
slump under control. Also, additional slump tests shall be made as
directed. All this shall be at no additional cost to the Government.
e. Temperature - The temperature of the concrete shall be measured
when compressive strength specimens are fabricated. Measurement shall
be in accordance with ASTM C 1064/C 1064M. The temperature shall be
reported along with the compressive strength data.
f. Compressive-Strength Specimens - At least one set of test specimens
shall be made each day on each different concrete mixture placed during
the day. Additional sets of test cylinders shall be made, as directed
by the Contracting Officer, when the mixture proportions are changed or
when low strengths have been detected. A random sampling plan shall be
developed by the Contractor and approved by the Contracting Officer
prior to the start of construction. The plan shall assure that
SECTION 03301A
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