Underwater Concrete: Techniques, Applications, and Benefits

What Is Underwater Concrete?

Underwater concreting is a form where underwater concrete is a construction material widely used in certain forms of structural engineering projects. Underwater concrete has been used for a long time now.

In every other building in which the lower parts of the buildings are expected to remain underwater, underwater concrete should be used.

Advantages of Underwater Concrete

1. Makes construction as well as excavation in a challenging atmosphere.
2. Offers an innocuous workplace environment.
3. Sheet piles become simple to construct and then uninstall.
4. Materials may typically be utilized on certain programs.

Disadvantage of Underwater Concrete

1. Quickly rising water will expel a scour gap, but this is one of the primary contributors of the bridge collapse.
2. Cracking, scaling, crazing including potting are quite popular in concrete.
3. Rebar is steel reinforcing bars that have been actively mounted only within concrete and experience corrosion.
4. Concrete bent, flattened, or stacked up due to lack of proper implementation including environmental conditions.

Application of Underwater Concrete

1. Bandra Worli Sea Link, Mumbai, where underwater cement is utilized.
2. Pamban Setu, Rameswaram.
3. Sardar Sarovar Dam.
4. Salem Hydro project, Salem, Andhra Pradesh.

Underwater cement is utilized.

1. Hydro projects.
2. Marine development.
3. Metro projects.
4. Repair of underwater concrete (solid tanks, dams, and water-driven designs).

Can Concrete Cure Underwater?

Concrete may cure underwater often effectively than that in the atmosphere. That occurs as the fragments of cement hydrate. Cement chemically reacts with water and binds sand and gravel respectively. One such method of curing requires about a couple of weeks and allows the cement to be patched.

As concrete is sprayed underwater, several of the components responds to create an exterior layer of water. Such covering stops an amount of moisture from soaking in or, worst, further diluting the cement.

After this, a further substance in the concrete responds at a slightly slower pace which brings it to its ultimate toughness 28 days later.

Although most people are agreeing that perhaps the cause of concrete fixes is that even the water is blended with evaporation, that’s not entirely true. Cement sets are due to the chemical reaction that takes place.

Afterward, much of the extra water has been used up by interacting with substances inside the cement to create fresh.

As concrete settles, it just doesn’t dry on its own, because that will disrupt the chemical reaction. This is why concrete which is submerged appears to be heavier than its equivalent which is in the air.

That being said, with non-hydraulic cement types, they use lime as well as gypsum plaster as binders is true. its method of curing relies on the evaporation of moisture. This forms of cement are suitable for special tasks such as historical preservation.

How Do They Pour Concrete Under Water?

If conditions require concrete to be installed underwater, any attempt must be taken to ensure consistency of positioning in between design segments.

Puddling or indeed any amount of physical disruption must be cautiously stopped as soon as the concrete has been in position and also any step taken must be made to eliminate segregation. Tremie has been the most popular way of treating concrete underwater.

The tremie generally comprises a vertical steel shaft, covered by a hopper, broad enough just to enter the lowest level of the underwater excavation from its work surface well above water.

Through this method, the steel tubing, with such a watertight sealing always at the top, is positioned only at the base of the excavation. Based on the level, the pipe is packed or partly filled by concrete.

Therefore the pipe is softly elevated around six inches to make the concrete start coming up across the tube. In proper positioning of the tremie, a sealing is being used to close the pipe until the concrete is placed.

As when the tremie is dropped to the base of the mold, the water pressure maintains the sheet firmly in place. The pipe as well as the tremie are then packed.

The retention wire of it’s plate shall be released whether it is individual or extracted if it is multiple, and also the tremie shall be elevated roughly 4 to 6 inches again from the bottom of the form, enabling the concrete to flood into position.

Any appropriate plug can indeed be established by pressing an inflatable rubber ball only to the top of the container. The ball is driven back either by the pressure of the concrete. The benefit of using a ball also for plug would be that it would rise to the surfaces after exiting the shaft.

Stoppages throughout tremie placement will create tremendous difficulties and any attempt should be taken to predict and stop them.

The primary reasons of the stoppage seem to be. the pipe diameter would be too short since this mixture eventually creates a bridge over the pipe walls; the shipping time is prolonged so the mixture within the pipe starts to stiffen.

The mixture is too rough or too solid, making plastic flow difficult; poor aggregate grading but, in specific, inadequate fines; the lubrication surface on the pipe walls is destroyed as well as binding occurs.

Pouring Concrete Underwater

Pouring concrete under water, there are two different methods as follows.

1. Caissons.
2. Cofferdam.

1. Caissons

Caissons is indeed a watertight supporting framework and durable in existence used for the bridge pier, the construction of concrete dams, or the maintenance of ships.

It’s also built-in a really manner that the water could be drained and the underwater concrete holds the work place safe.

2. Cofferdam

This is a short-term structure & installed inside a body of water or even in a dock, the enclosed area allows pumping as well as a dry workplace environment.

Cofferdams are typically fastened structural steel including sheet piles including cross brace elements. Two cofferdams are usually installed for the dam building, one upstream and one downstream.

Concrete Placing Methods

Concreting under water methods, like underwater concrete methods, are often intended to prevent concrete from being washed. Such techniques did not have the complete function of preventing cement washing at the initial stages of usage underwater concrete, except in situations when significant amounts of concrete were used.

However, more modern methods may have been used to accomplish the goal of avoiding washing it out concrete.

1. Tremie method.
2. Pumping technique.
3. Hydro valve method.
4. Pneumatic valve method.
5. Skip method.
6. Tilting pallet barge method.
7. Preplaced aggregate concrete.
8. Toggle bags method.
9. Bagged concrete method.

Tremie Concrete Placement

1. Underwater concrete when using the tremie process is ideal for pouring vast volumes of high-flowing concrete.
2. The concrete is transferred to the tremie by either pumping, belt conveyor, and skips.
3. The Tremie tubing, which will have the top range attached to the tremie and the lowest levels constantly immersed in fresh concrete, is being used to put concrete only at the exact situation of the tremie at the bottom.
4. The justification for immersing the lower part of the tremie pipe would be to avoid the intermixing of both concrete as well as water.

Underwater Concrete Method Using the Tremie Process:

There seem to be a variety of considerations that should have been recognized mostly during the Tremie pipe technique for underwater concrete:

Tremie Equipment

The tremie pipe might be configured in three different ways such as constant length that is raised during concreting, pipe with different sections which dismantled during concreting and telescope pipe.

Aluminum alloy pipes can have a detrimental effect on the concrete due to reaction among them and should thus be prevented. The pipe must have an appropriate diameter to avoid blockage due to the overall size.

The normal diameter would be between 200 to 300 mm that might be used rarely between 150 mm as well as 450 mm, although the aggregate size must be regarded for instance 19 mm as well as the aggregate size of 40 mm is smaller for pipe diameter of 150 mm and 200 mm respectively.

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Tremie Seal

To stop intermingling water and asphalt in the pipe, the edge of the pipe is capped with a wooden plate plug. Which stops the water from entering the conduit and leaves it dry.

Because after the pipe reaches its desired location, the mixture is placed as well as the lock is broken. Which concrete spills out from the pipe and forms a seal by collecting at the bottom end of the pipe.

Placing Concrete for Termine

As often as its concrete has begun, the pipe mouth can be immersed up about 1 to 1.5 m in the concrete mix to stop moisture from penetrating the pipe. The rate of concrete flow is regulated by dropping.

But increasing the pipe and then lowering or rising the concrete leakage implies the failure of the seal, and as such the flow of concrete must be controlled constantly and cautiously.

Flow Pattern for Termine

Two different types of flow patterns are known, namely the layered as well as bulging. The bulging flow is preferred as it pushes the concrete evenly, leading to less laitance deformation with flatter slopes.

Steps Underwater Concrete Repair

Steps underwater concrete repair are as follows.

1. Repair of surface spalling.
2. Large-scale reconstruction of underwater reinforced concrete.
3. Pre-positioned aggregate concrete.
4. Injection procedure for underwater reconstruction of a concrete structure.
5. Gunting for the underwater restoration of a concrete structure.
6. Steel sleeve underwater concrete restoration procedure.

Frequently Asked Questions (FAQ) about Underwater Concrete

What is underwater concrete?

Underwater concrete is a specialized construction material designed for use in projects where parts of the structure will remain submerged. It is commonly used in structural engineering projects such as bridges, dams, and marine developments.

Why is underwater concrete necessary?

Underwater concrete is essential for structures that are built in or near water. It provides the necessary durability and strength to withstand the underwater environment, preventing issues like erosion and structural failure.

What are the advantages of using underwater concrete?

1. Facilitates construction and excavation in challenging environments
2. Ensures a safe working environment
3. Simplifies the construction and removal of sheet piles
4. Utilizes materials effectively for various projects

What are the disadvantages of underwater concrete?

1. Susceptibility to scour from rapidly rising water, which can contribute to bridge collapse
2. Common issues like cracking, scaling, crazing, and potting
3. Corrosion of steel reinforcing bars (rebar)
4. Potential for bending, flattening, or stacking due to improper implementation or environmental conditions

What are some notable applications of underwater concrete?

1. Bandra Worli Sea Link, Mumbai
2. Pamban Setu, Rameswaram
3. Sardar Sarovar Dam
4. Salem Hydro project, Salem, Andhra Pradesh
5. Hydro projects, marine development, metro projects, and repairs of underwater structures like tanks and dams

Can concrete cure underwater?

Yes, concrete can cure underwater effectively. This occurs as the cement hydrates and chemically reacts with water to bind sand and gravel. The curing process, which takes about 28 days, involves forming an exterior layer that prevents excess moisture from diluting the cement.

How is concrete poured underwater?

Concrete is poured underwater using methods that ensure consistency and prevent physical disruption. The most common technique is the tremie method, which involves using a vertical steel pipe with a hopper to place the concrete at the bottom of the underwater excavation.

What are the main methods for pouring concrete underwater?

1. Caissons: Watertight structures used for bridge piers, dam construction, or ship repairs, keeping the work area dry.
2. Cofferdam: Temporary structures installed to create a dry work environment by enclosing an area within a body of water.

What are the different techniques for placing concrete underwater?

1. Tremie method
2. Pumping technique
3. Hydro valve method
4. Pneumatic valve method
5. Skip method
6. Tilting pallet barge method
7. Preplaced aggregate concrete
8. Toggle bags method
9. Bagged concrete method

How does the tremie method work?

The tremie method uses a steel pipe to place concrete underwater, ensuring the pipe’s lower end is always immersed in fresh concrete to prevent water from mixing with the concrete. The pipe is gradually lifted as concrete flows out, forming a seal at the bottom.

What are the steps for repairing underwater concrete?

1. Repair of surface spalling
2. Large-scale reconstruction of underwater reinforced concrete
3. Pre-positioned aggregate concrete
4. Injection procedure for concrete structure repair
5. Guniting for concrete structure restoration
6. Steel sleeve restoration procedure