Concrete tremie is one of the most effective methods for placing concrete underwater or in deep foundations where conventional pouring isn’t possible. It ensures high-quality, dense, and uniform concrete placement without segregation or contamination. This article explains in detail what a concrete tremie is, how it works, its components, applications, advantages, and best practices for successful underwater concreting.
What Is a Concrete Tremie?
A concrete tremie is a long, vertical pipe or tube used to place concrete below water or in deep foundations without disturbing the surrounding environment. The bottom end of the tremie remains submerged in freshly placed concrete to prevent the inflow of water, while the top end is supplied with concrete from above.
The tremie method ensures that concrete flows smoothly through the pipe and fills the underwater formwork or pile bore without washing out the cement paste. It’s commonly used in bridge piers, pile foundations, diaphragm walls, cofferdams, and marine structures.
Components of a Tremie System
A standard tremie setup consists of several key components that work together to deliver concrete safely and efficiently under water.
| Component | Description |
|---|---|
| Tremie Pipe | A vertical steel or plastic pipe, usually 200–300 mm in diameter and 3–4 m long, with flanged sections for easy connection. |
| Hopper | A funnel-shaped top attached to the upper end of the tremie pipe, used to pour concrete smoothly into the system. |
| Plug or Piston | A sealing device placed between the first batch of concrete and water to prevent direct contact. |
| Lifting Equipment | Cranes or winches used to position and lower the tremie into the desired location. |
| Concrete Pump or Bucket | Used to feed concrete continuously into the hopper. |
These components form a sealed system that minimizes segregation and maintains concrete quality.
Working Principle of Concrete Tremie
The working principle of a concrete tremie is based on maintaining a continuous column of concrete inside the tremie pipe to prevent water from entering. The process starts with sealing the lower end, placing the pipe at the desired location, and gradually filling it with concrete.
As fresh concrete enters from the top, it pushes the existing mix downward and outward, displacing water while maintaining a consistent head pressure. The lower end always remains submerged in concrete to ensure that no water can dilute or wash away the cement content.
Step-by-Step Tremie Concrete Placement Procedure
The tremie concreting process must be executed carefully to maintain quality and prevent defects. Here’s a detailed step-by-step guide:
1. Preparation of Site
- Ensure the work area is stable and free from debris.
- Check water depth, formwork, and reinforcement placement.
- Set up all equipment and verify that the tremie pipe is clean and watertight.
2. Assembly of Tremie Pipe
- Assemble pipe sections to the required length using flanges or couplers.
- Attach the hopper at the top and secure the lower end with a plug or tape to prevent water entry before pouring.
3. Positioning the Tremie
- Lower the tremie vertically into position using a crane.
- The bottom of the pipe should rest at or slightly above the placement level.
4. Initial Charging
- Pour the first batch of concrete into the hopper.
- Use a plug or “go-devil” (rubber ball) to separate the concrete from water during the first charge.
- Once the plug reaches the bottom, concrete starts flowing out smoothly.
5. Continuous Concrete Placement
- Maintain a continuous flow of concrete to avoid interruptions.
- The lower end of the pipe must remain embedded 0.6 to 1.0 m in fresh concrete at all times.
- Raise the tremie gradually as the concrete level rises, but never lift it completely out.
6. Finishing
- Continue placement until the formwork or pile is completely filled.
- Slowly withdraw the tremie, ensuring no air gaps or segregation occur.
- Allow the concrete to set and cure properly under water.
Key Requirements for Tremie Concrete
Concrete used for tremie placement must meet specific performance criteria to ensure stability under water.
- Slump: 150–200 mm for high workability.
- Cement Content: Higher than conventional concrete (350–400 kg/m³).
- Aggregate Size: Not more than 20 mm.
- Water-Cement Ratio: 0.45 to 0.55 for good flow.
- Admixtures: Anti-washout and plasticizing agents to enhance flow and cohesion.
These parameters ensure smooth placement without segregation or dilution.
Applications of Concrete Tremie
Concrete tremie methods are widely used in civil and marine construction, especially where underwater concreting is required. Common applications include:
- Pile foundations for bridges and buildings
- Underwater footings and caissons
- Diaphragm and retaining walls
- Bridge piers and abutments
- Cofferdams and harbor structures
- Offshore platforms
Anywhere concrete must be placed below the waterline, the tremie method offers the most reliable solution.
Advantages of Using Tremie Concrete
- Prevents Segregation: Maintains uniform mix composition throughout the placement.
- Ensures Quality: Cement paste isn’t washed out, leading to higher strength.
- Suitable for Deep Water: Can be used in depths exceeding 50 meters.
- Continuous Placement: Minimizes cold joints and weak zones.
- Versatile: Applicable for piles, caissons, and marine structures.
- Improved Durability: Produces dense, watertight, and durable concrete.
Limitations of Tremie Method
Despite its many benefits, the tremie method also has certain limitations:
- Requires Skilled Operators: Any mistake in maintaining the concrete head may cause washout.
- Expensive Setup: Equipment and handling increase project costs.
- Difficult Inspection: Visual inspection of concrete quality is limited under water.
- Risk of Blockage: Improper cleaning or segregation can clog the pipe.
Best Practices for Tremie Concreting
To ensure quality and prevent common defects, follow these best practices:
- Keep the bottom of the tremie submerged in fresh concrete at all times.
- Avoid stopping concrete flow during placement.
- Use anti-washout admixtures to improve cohesiveness.
- Ensure the pipe diameter is at least 8 times the maximum aggregate size.
- Do not raise the tremie too quickly.
- Maintain a constant supply of concrete in the hopper to prevent air entry.
Common Problems and Remedies
| Problem | Cause | Remedy |
|---|---|---|
| Segregation | Poor mix design or excessive slump | Use anti-washout admixture and proper water-cement ratio |
| Blockage in Pipe | Improper cleaning or aggregate size | Flush tremie before use and use smaller aggregates |
| Cold Joints | Interruption during concreting | Maintain continuous concrete flow |
| Honeycombing | Insufficient embedment or improper placement | Keep the tremie submerged and raise gradually |
Difference Between Tremie Concrete and Pumped Concrete
| Aspect | Tremie Concrete | Pumped Concrete |
|---|---|---|
| Placement Method | Gravity flow through vertical pipe | Pressure-driven through hose or pipeline |
| Application | Underwater or deep foundation work | Ground-level or elevated structures |
| Workability | High slump (150–200 mm) | Medium to high slump (100–160 mm) |
| Equipment | Tremie pipe and hopper | Concrete pump and hoses |
| Key Feature | Prevents water contamination | Efficient for high-rise or long-distance pumping |
Frequently Asked Questions (FAQs)
What is the minimum diameter of a tremie pipe?
The pipe diameter is typically 150–300 mm, depending on aggregate size and placement rate.
Why must the tremie remain embedded in concrete?
To prevent water from entering the pipe and causing cement washout or segregation.
What type of concrete is used in tremie work?
Highly workable, cohesive concrete with anti-washout admixtures is used.
Can tremie concreting be used above water?
While designed for underwater applications, it can also be used for deep or inaccessible foundations above water.
How is segregation avoided in tremie concreting?
By maintaining continuous concrete flow, keeping the pipe submerged, and using cohesive mixes.
Conclusion
The concrete tremie method is one of the most reliable techniques for underwater concreting, ensuring dense, durable, and uniform placement even in challenging conditions. By maintaining a continuous flow and using high-quality materials, engineers can achieve exceptional strength and performance in marine and deep-foundation structures. Whether constructing bridge piers, piles, or caissons, the tremie method stands as a cornerstone of modern underwater construction technology—combining precision, safety, and quality.
