UNDERWATER CONCRETE

SANTHINI K.P

S8, CE 28GUIDED BY

MANASWI C.M

Concrete is the premier construction material across the

world and the most widely used in all types of civil

engineering works.

During the construction of bridges , dams or any other

structure where the foundation part of the structure is lie

underwater, we have to opt for underwater construction

When concrete is placed under water, it induces concrete

to deteriorate uniformity

Therefore should be follow proper mix design, concrete

production and placement and quality control.

PRODUCTION OF UNDER WATER

CONCRETE

Proper mix design

Proportioning underwater concrete are same as conventional concrete

According to its performance there are two classes of concrete mixture

standard mixture

high-performance mixture

Concrete placed underwater is susceptible to

cement washout

laitance

Segregation

CONT…….

Mix design influence certain workability

characteristics such as

Flowability

Self-consolidation

Cohesion

Mix design also influence by rheology

o It describes flow and deformation of materials

o The behaviour of fresh concrete can be described

by two parameters-yield stress and plastic

viscosity

Cont….

o water content is the important factor affecting

the rheology of concrete

o water content in a mixture can be classified

into two categories

o water absorbed in the aggregate

o free water

PLACEMENT METHODS

Tremie method.

Pump method

Toggle bags

Bags work.

TREMIE METHOD

A Tremie is a watertight pipe

Generally 250mm in dia.

Funnel shaped hopper at its upper end and a loose plug at the bottom.

It is supported on a working platform above water level.

LAYING OF CONCRETE BY USING TREMIE

Fig. 2.2 Tremie method

PUMP METHOD:

Pumping concrete directly into its final position,

involving both horizontal and vertical delivery of

concrete.

Pumping concrete has the advantage of operational

efficiency with potential savings of time and labour.

For massive underwater concrete construction of

navigation structures, the pump method should be

prohibited.

PUMP METHOD OF LAYING CONCRETE

CONT….

TOGGLE BAGS

• Toggle bags are ideal for small amounts of concrete

placement.

• The bag is filled in the dry with wet concrete

• Used for repair work.

• The concrete is squeezed out by a diver.

BAGWORK

• Bags are made of open weave material.

• Diver-handled bags are usually of 10 to 20 litres capacity

but 1cub.m bags can be placed using a crane.

Concrete production

The standard requirements of underwater concrete is same as conventional concrete

Production and delivery system be capable of producing concrete at the required placement rate

It is essential that the materials can be supplied to the batch plant at the required rate

The logistical planning should include

Provision for alternative supplies

Provision of all the accessory items

CONSTRUCTION TECHNIQUES

Caissons

Watertight retaining structure .

Permanent in nature.

Used to work on foundation of bridge pier, construction

of concrete dam or for the repair of ships.

Constructed in such a manner so that the water can be

pumped out.

Keeps working environment dry.

CONT…..

Box caisson Pre fabricated concrete box, it is set down on the prepared

bases

Once in place it is filled with concrete as part of placement

work

Must be ballasted or anchored to prevent this phenomenon

the floating of hollow concrete structures

Open caisson similar to a box caisson but does not have bottom face

Used in soft clays not having large obstructions

beneath

During sinking it may filled with water

CONT…….

Compressed-air caisson

It has the advantage of providing dry working

conditions

Compressed air is used to keep the water and

mud out

Used to work on river bed

Monolithic caisson

It is more suitable for off shore construction

larger than the other types of caisson, but similar

to open caissons

COFFERDAM

Temporary enclosure

Built within or in piers across a body of water

Allows the enclosed space to be pumped out, creating a

dry work environment .

Cofferdams are usually welded steel structures

With components consisting of sheet piles, and

cross braces

For dam construction, two cofferdams are usually built,

one upstream and one downstream

Fig. 3.2 coffer dam

QUALITY CONTROL

Five critical items should be observed throughout

concrete placement

Rate of concrete placement

Depth of concrete at various locations

Volume of concrete produced versus volume of

in-place concrete measured by sounding

Concrete delivery system

Embedment depth of the tremie

CONT…….

Specific recommendations for quality control include

The workers should have been properly trained

Contractor should conduct frequent testing of

concrete

Continuous soundings should be taken

The concrete placement rate and sequence

should be carefully monitored and controlled

Compare vol.of concrete produced and fed into

the tremie

Periodic checking of concrete delivery and

placement equipment

DAMAGES AND MAINTANANCE

Damage and Problems

Rebar corrosion

Scaling and Cracks

Spallingconcrete

Scour

CONT….

Rebar corrosion Rebar is steel reinforcement bars passively

embedded within the concrete before it sets

Occurs when chloride ions migrate to material like steel bars

Type of corrosion that occurs in most highway bridges

Spalling concrete The concrete that has broken up, flaked, or

become pitted

It is occurred due to poor installation and environmental factors

It can also result in structural damage

CONT…..

Scour Scour is the removal of sediments from

around bridge abutments or piers

It caused by swiftly moving water, can scoop out scour holes

It is one of the three main causes of bridge failure

Scaling and Cracks It is very common for concrete to have cracks, scaling,

crazing and pitting

Concrete expands and shrinks with changes in moisture and temperature

Irregular cracks are unsightly and difficult to maintain but generally do not affect the integrity of concrete.

MAINTENANCE

Maintenance procedure consists of initial inspection, deterioration prediction, inspection, evaluation, and remedial measures

During construction the engineering as well as social and economical aspects should be required.

Adequate protection from corrosion can be achieved by using anticorrosion or protective products

By placing concrete carefully spalling of concrete can be avoid up to an extend

CONCLUSION

For in-the-wet construction of navigation structures,

underwater concrete construction is a critical

component

underwater concrete construction can be

accomplished with the same degree of reliability as

above water construction

it is not carried out properly, with the proper

concrete mixture and placement, it can result in a

major overrun in construction cost and schedule.

CONT…..

The essential difference between underwater

concrete and conventional concrete is in the

workability requirements

Underwater concrete must flow laterally and

compact itself under its own buoyant weight, while

conventional concrete is compacted with

mechanical vibration

REFERENCESi. Yao, S.X., Berner, D.E., Gerwick, B.C., “Assessment of Underwater

Concrete Technologies for In-the-Wet Construction of Navigation Structures”, U.S. Army Corps of Engineers Publication, TR INP-SL-1, 1999.

ii. Neeley, B. D, Netherlands Committee for Concrete Research, “Underwater Concrete”, HERON, 1973 ACI 304R-00, "Guide for Measuring, Mixing, Transporting, and Placing Concrete", Chapter 8 "Concrete Placed Under Water", American Concrete Institute, 2000

iii. Yao, S. X., and Gerwick, B. C., “Underwater Concrete Part II: Proper Mixture Proportioning” and “Underwater Concrete Part III: Construction Issues”, Concrete International, February and March 2004

iv. Nagataki, S. (1992). "Use of antiwashout underwater concrete for marine structures," Tokyo Institute of Technology, Tokyo, Japan.

v. Saucier, K. L., and Neeley, B. D. (1987). "Antiwashout admixtures in underwater concrete," Concrete International 9(7), 42-47.

vi. Strange, C. (1970). "Submarine placing of concrete by the tremie method," Offshore Technology Conference 2(1311), 813-18.

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