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avoids formation of laitancc layers.
lost while depositing, the tremic shall be raised above the concrete
surface, and unless sealed by a check valve it shall be re-plugged at
the top end, as at the beginning, before being refilled for depositing
b) Drop bottom bucket - The top of the bucket shall be open. The
bottom doors shall open freely downward and outward when
tripped. The bucket shall bc filled completely and lowered slowly
to avoid backwash.
It shall not be dumped until it rests on the
surface upon which the concrete is to be deposited and when discharged shall be withdrawn slowly until well above the concrete.
4 Bugs - Bags of at least 0.03 cu m ( or 1 cu ft ) capacity of jute or
other coarse cloth shall be filled about two-thirds full of concrete,
the spare end turned under so that bag is square ended and securely tied. They shall be placed carefully in header and stretcher
courses so that the whole mass is interlocked.
Bags used for this
purpose.shall be free from deleterious materials.
4.12.3 1‘0 mini&e
the formation of laitance, great care shall be
exercised not to disturb the conc.rete while it is being deposited.
4.12.4 If it is necessary iu raise the water after placing the concrete,
the level shall be brought up slowly without creating any waves or commotion tending to wash away ctimet;t or to disturb the fresh concrete in
24 IS : 457 - 1957
4.12.5 Concrete Exposed to Corrosive Water or Soils - Special cements
shall be specified to be used in concrete to be deposited under these conditions.
Extreme care shall be taken to secure maximum
density and durability.
The placing of any block shall continue
until the concrete is at least 45 cm ( or 18 in ) above the ground water level.
The corrosive waters or soils shall not touch the concrete during placement
or for at least 72 hours thereafter.
4.13 Weather Conditions 4.13.1 Concrete operations
shall be temporarily
hot, cold, or inclement
weather, or whenever
such that the concrete cannot be properly placed and cured.
4,.13.2 During freezing weather, all aggregates shall be free from ice,
snow, heavy frost and frozen lumps.
Whenever the temperature
to fall below -7’C ( or 20°F) within the subsequent
48 hours, concreting
shal-1 be suspended unless provision
has been made to protect
the concrete from freezing.
Under such circumstances,
the water used for
mixing shall bc heated and the temperature
of concrete shall be kept at not
less than 10°C ( or 50°F) for at least 72 hours after placement.
.4.13.3 During hot weather no concrete shall be deposited when the
within the forms is more than 50°C ( or 120°F ). Whenever
ncccssary, exposed surfaces of fresh or green concrete sha!l be shaded from
the direct rays of the sun and protcctedagainst
premature setting or drying
by being cured under cortinuous
fine spray of water
or heavy do...
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- Fall '13