Pipe at all times after the placing of concrete is

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Unformatted text preview: remie is 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 concrete. 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not be dumped until it rests on the surface upon which the concrete is to be deposited and when discharged shall be withdrawn slowly until well above the concrete. 4 Bugs - Bags of at least 0.03 cu m ( or 1 cu ft ) capacity of jute or other coarse cloth shall be filled about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 any way. 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 without interruption 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 suspended during excessively hot, cold, or inclement weather, or whenever conditions are 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 is likely to fall below -7’C ( or 20°F) within the subsequent 48 hours, concreting opeiations 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 temperature 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 4.13.4 During continued rainy weather or heavy do...
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