Which cement is used underwater?

Concrete under water

Concreting under water is used more and more often

Concreting under water. For many people this is seemingly impossible. But also for many concrete experts, concreting under water remains fascinating. After all, concrete should be processed in precisely the element that must never be added to the composite building material in excessive quantities. The need for concrete under water is actually relatively high - even with conventional house construction, concreting under water can occur:

  • Base plates made from underwater concrete
  • Bank reinforcements made of underwater concrete, which is provided with a ballast made of gravel
  • Concrete pools that have to be erected when filled
  • Bridge piers in rivers

Concreting under water when building an average house

The example of the base plate with concrete under water with a high groundwater level quickly shows that it is not always possible to put in precast concrete (18.49 € at Amazon *) parts. A base plate in particular cannot be manufactured outside and then simply embedded.

The water-cement value for underwater concrete

As for the composition of the concrete used underwater, the same concrete formulations are used as for ordinary concrete. Only a relatively high water-cement value is noticeable (w / c value up to 0.60). As for the properties of concrete underwater, even waterproof concrete can be made.

The consistency of the concrete

When producing the concrete that is to be poured under water, the most important thing is the optimal consistency. The concrete must on no account segregate during filling. This is ensured by not separating the concrete structure. This, in turn, requires a correspondingly soft and pliable cement that can be easily poured in with the concrete pump.

The concrete must not segregate when pouring

It is important that the concrete must not be poured through the water. Rather, the front end of the pump hose will always be stuck something in the fresh concrete that has already been placed. So the concrete grows from the inside out under water. Due to the pressure that prevails in the water, the concrete also compacts better under water.

Compaction and post-treatment of concrete under water

An additional compaction of the concrete is not necessary. On the contrary, subsequent compaction is actually risky, as this could cause the upper concrete layer to mix with the surrounding water. Post-treatment of the concrete is also not necessary. However, a concrete should be used that does not heat up too much during hydration, during chemical setting.

Basically, concreting underwater is not really difficult. But it requires extensive specialist knowledge and a wealth of experience. Therefore, only experienced concrete workers should pour demanding concrete components under water. Up until a few decades ago, water-permeable bags of dry precast concrete were sunk into the water. However, it was not possible to produce really high-quality concrete with consistently high quality characteristics in this way.

Author: Tom Hess

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