Foundation Specifications 0208

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Cofferdams and Seal Courses

Tremie concrete is a name given to the method of placing concrete under water through a

pipe or tube, which is called a tremie. The tremie can either be rigid or .exible. Concrete

.ow can be either by gravity with a hopper located at the top of the pipe, or by direct

connection to a concrete pump.

The purpose of this equipment is to enable continuous placement of monolithic concrete

underwater without creating turbulence. To accomplish this, it is imperative that the

discharge end of the tremie be kept embedded in the concrete. It is also imperative that the

concrete have good .ow characteristics. Concrete placement can be accomplished by either

a tremie supported and maneuvered by a crane or the discharge end of a concrete pump.

Frequently contractors will use multiple-tremie systems with each hopper supported by

bracing or walkways in the cofferdam. In this case, tremie spacing is controlled by the .ow

characteristics of the concrete.

Brie.y described, a typical tremie operation begins with the tremie pipe being lowered into

position with a plug or other device fitted into the pipe as a physical barrier between the

water and concrete. Concrete is charged into the pipe to a sufficient height to permit gravity

.ow. The .ow itself is started by slightly lifting the pipe. Once started, the concrete .ow

must be maintained by continuing to charge the pipe. The operation must continue until

completion. The tremie pipe is immersed in concrete during placement. Some factors

which assure success for this operation are:

Tremie concrete shall have a penetration of between 3 and 4 inches.

Concrete shall contain a minimum of 7 sacks of cement per cubic yard.

Concrete placement and the maneuvering of the tremie pipe must be done

smoothly and deliberately.

Concrete delivery must be adequate and timely.

The concrete mix design should be geared to good flow characteristics.

Of the various plug devices, the in.ated rubber ball is about the most practical. However, a

tip plug can cause long tremie pipes to .oat.