pipe shall be lifted during placement at a rate that will maintain the
bottom of the pipe embedded in fresh concrete to a level that will produce
the desired surface slope and rate of flow within the limits specified
above. It may be necessary to reduce the amount of embedment as the
differential head decreases between the concrete in the tremie pipe and the
concrete in the panel. The repeated raising and lowering of the tremie
pipe in the fresh concrete to facilitate placement shall be minimized.
Placement shall proceed without interruption until the concrete has been
brought to the required height. The Contractor shall continuously measure
and record the flow and slopes during placement with the use of a sounding
line. The tremie shall not be moved horizontally during a placing
operation, except that as the required height is reached, the tremie pipes
may be moved to the corners and low areas between the tremie pipes to bring
the lift to final elevation. A sufficient number of tremies shall be
provided so that the concrete does not flow horizontally a distance of more
than 2.1 m 7 feet from a tremie; i.e., tremies shall be placed a maximum of
4.2 m 14 feet on centers. Where more than one tremie pipe is used in the
same placement simultaneously, the concrete level at each pipe position
shall be maintained nearly level with respect to the other. Special care
shall be taken to ensure that the bottom of the tremie pipe is not lifted
out of the fresh concrete. If this occurs, the Contractor shall remove the
tremie pipe, insert a dry pipe with a temporary bottom plug, and restart
the placement. Also, as soon as practical, the Contractor shall drill a
NX-size core boring through the center of the cutoff wall to a depth of at
least 3 m 10 feet below the depth where the bottom of the tremie pipe was
lifted out of the fresh concrete. Unacceptable zones of concrete such as
honeycombed, segregated, or uncemented zones found within the core boring
shall immediately be repaired or removed and replaced by an appropriate
means. All cost incurred because of this failure, including the initial
core boring and as many additional core borings as may be required to
delineate the limits of the unacceptable concrete and the repair of the
cutoff wall, shall be borne by the Contractor and shall not result in any
additional cost to the Government. The Contractor shall submit a plan for
repairing or removing and replacing the unacceptable concrete. Placement
delays shall not be permitted for periods of time longer than 30 minutes.
3.2.5
Required Height of Concrete
Concrete that is free of laitance, scum, slurry, or other contaminants
shall be placed at the top of the wall. All scum, laitance, and
contaminated concrete shall be removed from the top of the concrete as the
placement is nearing completion and shall be disposed of in the spoil
areas. The top surface shall be finished to grade by screeding spoil areas.
3.3
CURING AND PROTECTION
The exposed concrete shall be moist cured for 14 days. Immediately after
placement, concrete shall be protected from premature drying, extremes in
temperatures, rapid temperature change, and mechanical damage. All
materials and equipment needed for adequate curing and protection shall be
available and at the placement site prior to the start of concrete
placement. Concrete shall be protected from the damaging effects of rain
for 12 hours and from flowing water for 14 days. No fire or excessive heat
including welding shall be permitted near or in direct contact with
concrete or concrete embedments at any time.
SECTION 03373
Page 23
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