sampling is done in a completely random and unbiased manner. A set of
test specimens for concrete with a 28-day specified strength per
paragraph DESIGN REQUIREMENTS shall consist of four cylinders, two to
be tested at 7 days and two at 28 days. A set of test specimens for
concrete with a 90-day strength per specified paragraph DESIGN
REQUIREMENTS shall consist of six cylinders, two tested at 7 days, two
at 28 days, and two at 90 days. Test specimens shall be molded and
cured in accordance with ASTM C 31/C 31M and tested in accordance with
ASTM C 39/C 39M. All compressive-strength tests shall be reported
immediately to the Contracting Officer. Quality control charts shall
be kept for individual strength tests, moving average for strength, and
moving average for range for each mixture. The charts shall be similar
to those found in ACI 214R.
3.7.2.7
Inspection Before Placing
Foundation or construction joints, forms, and embedded items shall be
inspected for quality by the Contractor in sufficient time prior to each
concrete placement to certify to the Contracting Officer that they are
ready to receive concrete. The results of each inspection shall be
reported in writing.
3.7.2.8
Placing
a. Placing Inspection - The placing foreman shall supervise all
placing operations, shall determine that the correct quality of
concrete or grout is placed in each location as directed and shall be
responsible for measuring and recording concrete temperatures and
ambient temperature hourly during placing operations, weather
conditions, time of placement, yardage placed, and method of placement.
b. Placing Corrective Action - The placing foreman shall not permit
batching and placing to begin until he has verified that an adequate
number of vibrators in working order and with competent operators are
available. Placing shall not be continued if any pile of concrete is
inadequately consolidated. If any batch of concrete fails to meet the
temperature requirements, immediate steps shall be taken to improve
temperature controls.
3.7.2.9
Vibrators
a. Vibrator Testing and Use - The frequency and amplitude of each
vibrator shall be determined in accordance with COE CRD-C 521prior to
initial use and at least once a month when concrete is being placed.
Additional tests shall be made as directed when a vibrator does not
appear to be adequately consolidating the concrete. The frequency
shall be determined at the same time the vibrator is operating in
concrete with the tachometer held against the upper end of the vibrator
head while almost submerged and just before the vibrator is withdrawn
from the concrete. The amplitude shall be determined with the head
vibrating in air. Two measurements shall be taken, one near the tip
and another near the upper end of the vibrator head and these results
averaged. The make, model, type, and size of the vibrator and
frequency and amplitude results shall be reported in writing.
b. Vibrator Corrective Action - Any vibrator not meeting the
requirements of paragraph VIBRATORS shall be immediately removed from
service and repaired or replaced.
SECTION 03301A
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