Underwater concreting - Explained By Converge

April 23, 2023

Concreting on dry land is not an easy task, there are a lot of aspects to consider. One of these aspects are, for example, weather conditions. Concreting can very well be affected by mundane things such as hot weather or rain. However, if you think concreting in rainy weather provides challenges, then imagine doing underwater concreting. 

Not a lot of people know how underwater concreting is executed, yet we see the results of it almost every day. Keep reading to learn more about this exciting topic while we answer some of the most common questions regarding underwater concreting. 

Read more: Learn more about long term effects of hot weather on concrete and the long term effects of cold weather on concrete.

What is underwater concreting?

Underwater concreting is the process of placing concrete below the water line. Concreting under water will provide a couple of issues. One of these problems is that the water can disrupt the concrete mix ingredient ratio. If more water is added to the concrete mix it can cause washout of the cement. You can avoid this by, for example, using a specific cement. 

Another important aspect of placing concrete under water is the increased demand for high quality formwork. In normal conditions the formwork is used to create the desired shape of the concrete. However, while concreting under water it also has to protect the concrete mixture from water current and other water related aspects. 

When do you use underwater concreting?

Concreting under water is regularly used to build things such as:

  1. Ports and harbours
  2. Bridges
  3. Piers
  4. Metro projects
  5. Dams
  6. Marine works
  7. Sewage

Can concrete cure underwater?

Concrete has to keep its moisture in order to cure. So despite what some people might think, concrete curing and concrete drying is not the same thing. If concrete dries up prematurely it will be weakened and will not be able to reach its full strength. 

With that said, concrete that is placed under water actually keeps its moisture a lot better than concrete on dry land. This further leads to the concrete curing process being highly successful under water. 

Using special materials

To ensure that concrete placed under water will be sustainable and long-lasting, a concrete mixture that has been optimised for this specific purpose is used. This concrete contains  hydraulic cement, which minimises the risk of cement washing away once placed in water. 

The Portland Cement Association provide recommendations regarding the quality of underwater concrete. One of the most important aspects mentioned is that the underwater concrete needs to be both cohesive and at the same time have a good flowability. To acquire this the concrete will need to have a high slump, around 150 to 180 mm. 

Read more: We explain how to measure the temperature of concrete, how humidity affects concrete curing and which weather conditions are best for concreting.

A dam by some beautiful mountains

Underwater concreting methods

There are many different types of methods which can be used for underwater concreting. Two common methods with many advantages are the Tremie method and the Bucket placing method. 

Tremie method

The tremie method is carried out by using a water tight tremie pipe with a funnel shaped hopper at the top. The pipe also has an adjustable plug at the bottom. Follow these steps to execute the tremie method:

1. Place tremie pipe on top of the desired location for concrete placement. 

2. Fill up the pipe with concrete through the funnel.

3. Adjust the plug while slowly lifting the tremie pipe upwards to release concrete onto the ocean/lake floor.

4. Continue lifting the pipe upwards until you need to refill the pipe or until the concrete reaches above the water surface. 

One important thing to keep in mind is that once you start moving the pipe upwards, the bottom opening of the pipe must always be submerged in the freshly poured concrete. The fresh concrete creates a seal that prevents water from entering the pipe. 

Bucket placing method

This concrete placing method is pretty much exactly what it sounds like. A bucket that allows you to place concrete at considerable depths. The bucket is usually constructed with a bottom that opens up outwards and a cover on top to protect the concrete from water. These are the steps to follow for this method:

1. Fill the bucket with concrete.

2. Lower the bucket into the water by using a crane.

3. Let the bucket reach the ocean/lake floor.

4. Deposit the concrete by opening the bottom of the bucket.

Frequently asked questions

How long does it take for concrete to cure underwater?

For concrete to reach its full strength it takes 28 days no matter if you are on dry land or underwater. 

What is the lifespan of concrete?

The lifespan of concrete depends on how much wear and tear the concrete has to endure. A solid building could last up to a 100 years with the right care. 

Does concrete get stronger in water?

Yes, when cement gets in contact with water the hydration process begins. This process makes the concrete strong. This means that concrete can get stronger in water than on land.

Read more: What happens to concrete when it freezes and how to protect concrete from rain and frost

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