Underwater concrete was specifically designed to increase construction efficiency and performance in water environments. It can be characterized by concrete resistance to washout, segregation, bleeding, and affected by the mix proportioning, aggregate shape and gradation, admixtures, vibration, and placement conditions.
During any construction where the lower part of the structures is probably to lie under water, we can use underwater concrete.
Here we learn about underwater concrete, properties of underwater concrete & much more.
Introduction to underwater concrete:
There are often situations such as basements, sewerage, ducts, ports, bridges and marine works in which concrete is to be placed under water.
Special care must be taken whenever concrete is to be placed under water, it should be plastic and cohesive but have good flow capacity.
Many difficulties in water formation, especially in places where the depth is large therefore proper mixing design, concrete production, placement, and quality control must be followed.
Properties of underwater concrete:
- Adequate safety from corrosion can be achieved by using anti-corrosion or protecting merchandise.
- Spalling of concrete can be avoided by expanding the concrete carefully.
- The better maintenance process includes initial inspection, worsening prediction, inspection, evaluation, and remedial measures.
- During construction, social as well as economic aspects are minimum along with engineering works.
Methods of Underwater concrete:
Tremie pipe is a satisfactory method of underwater concreting, diameter tremie pipe is about 20 cm.
A funnel is mounted at the top end to facilitate concrete pouring, the lower end of the pipe is closed with a plug or thick polythene sheet.
As the end of the vibrating pipe is blocked, no water will enter.
Concrete is poured over the funnel and when the entire length of the pipe is filled with the concrete, vibrating pipe is lifted up and given a slight shock.
Care must be taken while concreting, the lower end of the pipe is embedded in the well-wet concrete and it has a very high deceleration of about 15 to 25 cm.
Underwater Concrete with a low water/ cement ratio can be kept to 0.3 or even less.
2.Bucket Placing Method:
This method has an advantage that concrete can be carried out at considerable depth.
The main disadvantage of the bucket method is the difficulty in keeping the upper surface of the placed concrete at a reasonable level.
3.Placing in bags Method:
In this method, gunny bags are partially filled with concrete in such a way that they can readily be accommodated on which they are placed.
4.Packed Concrete Method:
This method is also called grouted concrete.
This technique consists of placing the coarse aggregates uniform thoroughly to form a replaced mass and grouted with cement mortar.
Underwater Concrete Construction Techniques:
Caissons are a watertight retaining structure & permanent in nature used in bridges pier, the development of concrete dams, or the repair of ships.
It is constructed in such a way that water can be pumped and underwater concrete keeps the working environment dry.
It is a temporary enclosure & built within a body of water or in piers, the enclosed space permits for pumping and making a dry working environment.
Cofferdams are usually welded steel structures with sheet piles and cross braces components.
For dam construction two cofferdams are normally constructed, one upstream and other downstream.
Advantages of underwater concrete:
- It allows construction and excavation in a poor environment.
- It provides a harmless environment for working.
- Sheet piles are easy to install and remove.
- The material can usually be reused on other projects.
Disadvantages of underwater concrete:
- Rapidly rising water can eject the scour hole & it is one of the main fundamental causes of bridge failure.
- Cracks, scaling, crazing, and potting are very common in concrete.
- Rebars are steel reinforcement bars that are passively located within the concrete, they undergo corrosion.
- The concrete broke, flattened, or piled up due to poor installation and environmental factors.
Also read: Mass Concrete, Translucent Concrete & Reinforced Cement Concrete
For the wet development of navigation constructions, underwater concrete are crucial element, this concrete construction can be skillful with the same degree of consistency.
If construction is not accomplished properly in water, then with correct concrete mixing and placement, it may result in the main overvaluation in construction prices and schedule.