Underwater Concreting:
Concrete is often placed underwater or in a trench filled with bentonite slurry. In such cases, the use of a bottom-dump bucket or a tremie pipe is used.
In the bottom-dump bucket, the concrete is taken out of the water in a water-tight box or bucket, and when it reaches the end of storage, the bottom is opened by some procedure and the entire concrete is slowly poured.
This method does not give a satisfactory result because a certain amount of cement washing occurs. In some cases, dry or semi-dry cement mixture, fine and coarse aggregates are filled in cement bags, and such bag concrete is stored on the bottom bed of water.
This method does not provide satisfactory concrete, since the concrete mass is filled with vacuums filled with rotting sack bags. The most satisfactory method of placing concrete underwater is the use of tremie pipe.
The word “tremi” comes from the French word hopper. Tremie pipe is a pipe with a diameter of about 20 cm, which is easily attached to increase or decrease the length. A funnel is installed at the top end to facilitate the pouring of concrete.
The bottom end is covered with a plug or thick polyethylene sheet or other material and rested in a place where the water is taken down and concrete. Has been placed. Because the end is blocked, no water can enter the pipe.
The concrete is poured into the tube, about 15 to 20 centimeters high. When the entire length of the pipe is filled with concrete, the tremie pipe is lifted and some traction is provided by the winch and pulley system.
When the pipe is lifted and given traction, due to the weight of the concrete, the bottom
The plug falls off and the concrete is discharged. At this stage, special care must be taken to ensure that the end of the tremie pipe stays in the concrete so that water does not enter the pipe from the bottom.
In other words, the tremie pipe is plugged into the lower end of the concrete. Again the concrete is poured over the funnel and when the entire length of the tremie pipe is filled with concrete, the pipe is lifted up again and given some traction.
Underwater Concreting | Watch for better understanding:
Care is taken at all times to make the lower end of the tremie pipe well embedded in damp concrete. The concrete in the tremie pipe is discharged. In this way, the concrete is in progress without stopping until the concrete level reaches the water level.
Fig. 6.22 shows the underwater concreting by tremie. If this method is implemented correctly It has the advantage of not being affected by concrete water other than the top layer. The top layer is scrubbed or cut to remove the affected concrete at the end of the entire operation.
During concreting, pumping of water should not be allowed. If Pumped simultaneously, it can suck cement particles. Underwater Concrete Concrete does not automatically have to be compressed due to the hydrostatic pressure of the water.
Second, concrete has such consistency that it is not usually necessary Contraction. The disadvantage of underwater concrete in this method is that a higher water/cement ratio is required for greater stability which reduces the strength of the concrete.
But currently, with the use of superplasticizer, this is not a constraint. Concrete with a w / c ratio of 0.3 or less can be placed by the tremie method. Another method that is not commonly used to place concrete underwater is the prepackaged aggregate grouting process.
The coarse aggregate is thrown to predict the entire dimension of the concrete mass. Cement mortar grout is pierced through the pipes, which extends to the bottom of the entire bed. The pipes are slowly withdrawn as the grouting progresses. Grout expels water from the gap and occupies the space.
This method is often adopted to plug a good foundation. Concrete can be placed underwater with the use of pipes and concrete pumps. The pipeline is plugged into one end and lowered until it rests on the bottom. Then the pumping is started.
When the pipe is filled, the plug is forced out, closing the concrete pipe that surrounds the lower end of the pipe. The pump is made against the pressure of the plug at the lower end. When the pumping effort required to overcome the pressure is too large, the pipe is withdrawn and the operation is repeated. This process is repeated until the water reaches the upper level of the concrete.
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