Methods Of Concreting Under Water

DIFINATION OF CONCRETE UNDER WATER.

VARIOUS difficulties are faced in concreting under water. The major problem is the danger of dissolution of concrete in water. The second problem is that of invisibility of work under water. so it is difficult to place the concrete at the exact site. Also the proper jointing of concrete with already placed concrete is difficult. Under the present circumstances concrete work can be done up to the depth of 250 m (800 ft)

Method of concreting under water.

Various methods of creating under water are adopted important of these are:

• Termite pipe Method
• Bucket Method
• Grouting Method
• Bags Stacking Methods.

Tremie pipe method

According to this method a pipe is used to place concrete in water. This remains dappled in water during concreting. This pipe s called Tremie. Its loses end is remind dipped in already placed fresh concrete. This pipe reminds s filled with concrete during work. In this way this method is resembles to pumping method. But in this method concrete is placed with the help of force of gravity. Plus is used in the pipe at the of placing concrete in the pipe for the first time. Or a ball at empty bag of cement is put in to the pipe for this purpose. And concrete is put on it. In doing so the concrete remain safe instead of dissolving in water present in the pipe. The lower part of the pipe remains dipped in concrete during concrete work. This prevents work to enter to pipe. By making the upper end of the pipe higher the presence of the concrete in the pipe can be increased. While the presence can be decreased by lowering it.

BUCKET Method.

In this method of concrete work under water special buckets are used. These buckets are or from the top while they have doors in their lower part. These buckets are filled with concrete and covered with canvas and then placed at the proper places in water. The buckets are drawn out of water after placing the concrete. This method is also called drop bottom or Skip Method.

GROUTING METHODS.

According to this method of concrete works under water. First of all form work is set out at the desired place. Thin dry aggregates are put in this from work. Then the grout of cement and sand is prepared. The ration of cement and sand in this case is kept as 1:1 or 1: 1.5. This grout is placed on the aggregate put in the form work with the help of a pile. This reaches the voids in aggregates due to its weight. Concrete is prepared in this manner.

BAGS STACKING METHOD.

According to this method of concrete work under water. Concrete is filled in bags of jute or porous cloth, after its preparation. Then bags are filled up to three or fourth only. Then the bags are sewn. These are then placed at the desired place. These bags are placed length-wise called stretcher. These other layer is paced breadth wise called the header. In this way by setting out layers concreting is done up to the desired height. The slurry of cement from the bags comes out and makes the bags united. To see the masonry in the deep water the services of Divers are engaged.
The concrete placed under water should be so that its slum should remain in between 15 to 25 cm (6 to 10 inches). Admixtures should also be added in this preparation. These will save concrete to dissolve in water. The use of these will enable the concrete to flow like a solution in Dynic mode. While concrete remains solid in static mode. In addition to this cement is used in extras quantity. In this concrete. These minimum quantity of cement in the concrete should be 360 kg/m3 (20lb/cubic ft). To increase its work-ability 15 % Pazzolana should also be used in it. The temperature of concrete increases in working under it he water. Then the danger of cracks in concrete increases in working under the water.
Then the danger of crack in the concrete is there. To control this problem 16% cement, 78% powdered slag and 6 % silica fume should be added in the concrete at eh time of prorating. Before placing the concrete its temperature should be kept up to 4 degree centigrade less. For the working of concrete under water, the water cement ratio should be 0.40 to 0.45.

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