If major underwater concrete placement is required,
supplement this paragraph using guidance from ACI
304R. If appropriate, add special requirements for
underwater concrete to paragraphs Concrete
Proportioning Studies, Normal Weight Concrete and
General Requirements both in PART 1. If considered
necessary, require a special technical
representative in paragraph Technical Service for
Specialized Concrete in PART 1. Contractor will be
required to submit proposed procedures.
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Concrete shall be deposited in water by a tremie or concrete pump. The
methods and equipment used shall be subject to approval. Concrete buckets
shall not be used for underwater placement of concrete except to deliver
concrete to the tremie. The tremie shall be watertight and sufficiently
large to permit a free flow of concrete. The concrete shall be deposited
so that it enters the mass of the previously placed concrete from within,
displacing water with a minimum disturbance to the surface of the concrete.
The discharge end of the pump line or tremie shaft shall be kept
continuously submerged in the concrete. The underwater seal at start of
placing shall not produce undue turbulence in the water. The tremie shaft
shall be kept full of concrete to a point well above the water surface.
Placement shall proceed without interruption until the concrete has been
brought to the required height. The tremie shall not be moved horizontally
during a placing operation, and a sufficient number of tremies shall be
provided so that the maximum horizontal flow of concrete will be limited to
5 m 15 feet. Concrete shall not be deposited in running water or in water
with a temperature below 2 degrees C 35 degrees F.
3.8.7
Placing Concrete in Congested Areas
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NOTE: Delete the last sentence when not applicable.
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Special care shall be used to ensure complete filling of the forms,
elimination of all voids, and complete consolidation of the concrete when
placing concrete in areas congested with reinforcing bars, embedded items,
waterstops and other tight spacing. An appropriate concrete mixture shall
be used, and the nominal maximum size of aggregate (NMSA) shall meet the
specified criteria when evaluated for the congested area. Vibrators with
heads of a size appropriate for the clearances available shall be used, and
the consolidation operation shall be closely supervised to ensure complete
and thorough consolidation at all points. Where necessary, splices of
reinforcing bars shall be alternated to reduce congestion. Where two mats
of closely spaced reinforcing are required, the bars in each mat shall be
placed in matching alignment to reduce congestion. Reinforcing bars may be
temporarily crowded to one side during concrete placement provided they are
returned to exact required location before concrete placement and
consolidation are completed.
3.8.8
Placing Flowable Concrete
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NOTE: Delete this paragraph when flowable concrete
is not permitted.
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SECTION 03300A
Page 44
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