Not be deposited under water if it is practicable to

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Unformatted text preview: ng water. 4.12.1.1 No concrete shall be placed in water colder than 2°C ( or 35°F ). When the water temperature is below 7°C ( or 45°F ), the temperatrue of the concrete when deposited shall be between 15 to 25°C The difference between the temperature of water and (or 60 to 80°F). temperature of concrete shall in no case exceed 5°C ( or 40°F). The cement content shall be not less than 390 kg of cement per cu m ( or 658 lb of cement per cu yd) of concrete. The limits for the slump shall be 10 cm and 18 cm ( or 4 in and 7 in ), the actual slump being decided by the engineer-in-charge. 4.12.1.2 Cofferdams or forms in running water .shall be sufficiently tight to reduce the velocity of the water to less than 0.3 cu m ( or 10 cu ft ) per minute through the space to be filled with concrete. Cofferdams or forms in still water shall be sufficiently tight to prevent the loss of mortar. Pumping or bailing shall not be conducted while the concrete is being deposited, and within 24 hours after placing of the concrete. 4.12.2 Methods of Depositing Under Water-Concrete shall be deposited continuously until it is brought to the required height. While &positing, the top surface shall be keGt as nearly level as possible and the formation of seams shall be avoided. The methods to be used for depositing concrete under water shall bc one of the followinga) Tremie - When concrete is deposited under water by means of a rremie, the top section of the tremie shall be a hopper large enough to hold one entire batch of the mix or the entire centents of the 23 IS : 457 - 1957 transporting bucket when one is used. The trcmic pipe shall be not less than 20 cm ( or 8 in ) in diameter and shall be large enough to allow free flow of concrete and strong enough to withstand the external pressure of the water in which it is suspended, even if a partial vacuum sl~ould develoij inside the! pipe. Flanged steel pipe of adequate strength to sustain the greatest length and weight required for the job should preferably be used. A separate lifting device shall bc provided for each tremic pipe with its hopper at the upper end. Unless the rower end of the pipe is equipped with an approved automatic check valve, the upper end of the pipe shall be plugged with a wadding of gunny sacking or other approved material, before delivering the concrete to the tremie pipe through the hoppei. The plug of sacking or other material is forced out at the bottom end of the pipe by filling the pipe with concrete. It is necessary to raise slowly the tremic in order to cause iI uniform flow of the concrete, but care shall be taken not to empty the tremie SW that water enters above the concrete in the pipe. At all times, .after the placing of concrete is started and until all the concrete is placed. the lower end of thcb tremip pipe shall be below the top surface of t!le plastic concrete. This causes the concrete to build up from below instead of flowing out over the surface and If the charge in the t...
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This document was uploaded on 10/01/2013.

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