not stain, discolor, or affect exposed surfaces of the structures, or
damage the environment of the project area. The method of disposal shall
be subject to approval.
3.3
PLACING
3.3.1
Placing Procedures
The surfaces of horizontal construction joints shall be kept continuously
wet for the first 12 hours during the 24-hour period prior to placing
concrete. Surfaces may be dampened immediately before placement if
necessary. Concrete placement will not be permitted when, in the opinion
of the Contracting Officer, weather conditions prevent proper placement and
consolidation. Concrete shall be deposited as close as possible to its
final position in the forms and, in so depositing, there shall be no
vertical drop greater than 1.5 m 5 feet except where suitable equipment is
provided to prevent segregation and where specifically authorized.
Depositing of the concrete shall be so regulated that it may be effectively
consolidated in horizontal layers 600 mm 2.0 feet or less in thickness with
a minimum of lateral movement. The amount deposited in each location shall
be that which can be readily and thoroughly consolidated. Sufficient
placing capacity shall be provided so that concrete placement can be kept
plastic and free of cold joints while concrete is being placed. Concrete
shall be placed by methods that will prevent segregation or loss of
ingredients. Any concrete transferred from one conveying device to another
shall be passed through a hopper that is conical in shape. The concrete
shall not be dropped vertically more than 1.5 m 5 feet, except where a
properly designed and sized elephant truck with rigid drop chute bottom
section is provided to prevent segregation and where specifically
authorized. In no case will concrete be discharged to free-fall through
reinforcing bars.
3.3.2
Placement by Pump
When concrete is to be placed by pump, the nominal maximum-size coarse
aggregate shall not be reduced to accommodate the pumps. The distance to
be pumped shall not exceed limits recommended by the pump manufacturer.
The concrete shall be supplied to the concrete pump continuously. When
pumping is completed, concrete remaining in the pipeline shall be ejected
without contamination of concrete in place. After each operation,
equipment shall be thoroughly cleaned, and flushing water shall be wasted
outside of the forms. Grout used to lubricate the pumping equipment at the
beginning of the placement will not be incorporated into the placement.
3.3.3
Time Interval Between Mixing and Placing
Concrete shall be placed within 30 minutes after discharge into
nonagitating equipment. When concrete is truck-mixed or when a truck mixer
or agitator is used for transporting concrete mixed by a concrete plant
mixer, the concrete shall be delivered to the site of the work, and
discharge shall be completed within 1-1/2 hours after introduction of the
cement to the aggregates. When the length of haul makes it impossible to
deliver truck-mixed concrete within these time limits, batching of cement
and a portion of the mixing water shall be delayed until the truck mixer is
at or near the construction site.
3.3.4
Cold-Weather Placing
When cold-weather placing of concrete is likely to be subjected to freezing
SECTION 03301A
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