Tremie concreting

The most satisfactory method of placing concret under water is by the use of tremie pipe.

The word tremie is derived from the French word hopper.

Tremie method

A tremie is a watertight pipe.

Generally 250mm in dia.

Funnel shaped hopper at its upper end and a loose plug at the bottom.

It is supported on a working platform above water level.

Method of tremie concreting

A tremie pipe of 200mm to 250mm diameter is used. The length of pipe can be easily increased or deceased by using coupling. A funnel is provide at the top end of pipe to facilitate pouring of concrete. The bottom end is closed with a plug or thick polyethylene sheet to prevent entry of water into the pipe.

The pipe is lowered and made to rest at the point where the concrete is going to be placed. The concrete having a very high slump of about 15 to 20 cm is poured into the funnel. When the whole length of pipe is filled up with the concrete. The tremie pipe is lifted up and a slight jerk the plug is forced out and the concrete gets discharged.

After concreting has started the lower end of the tremie should be kept as deeply submerged in the previously placed concrete to prevent entry of water into the pipe from bottom end.

The tremie should be lifted slowly to prermit the concrete to flow out, care being taken not to loose the seal at the bottom. In this way, concrete work is progressed without stopping till the concrete level comes above the water level.

Precautions to be taken during concreting by tremie method

Cofferdams or forms should be sufficiently tight to reduce the flow of water to less than 3m per minute through the space to be concreted.

All the time, the lower end of the tremie pipe should be kept well embedded in the wet concrete.

Once concreting has started the tremie should not be moved laterally through the deposited concrete as this will again disturb the concrete. If it is necessary to shift the tremie. It should be lifted out and moved to the new position.

Pumping of water should not be allowed whilst concrete is being placed, nor 24hr thereafter. If simultaneous pumping is done it may suck the cement particles.

Under water concreting need not be compacted. As concrete gets automatically compacted by the hydrostatic pressure of water.

High water ratio is required for high consistency which reduces the strength of concrete. But at present with the use of super plasticizers it is possible to place a concrete with as low a water ratio as 0.3.

When large quantities of concrete are required to be placed over an extensive area it is advisable to use a number of tremies.

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