UNDERWATER CONCRETING

PART 2-4

IT IS THE TECHNIQUE OF

PLACING CONCRETE

UNDERWATER FOR

CONSTRUCTION MEANS

TYPES OF UNDERWATER CONCRETING

1.METHOD•TREMIE METHOD

2.METHOD•BUCKET PLACING

3.METHODS•PLACING IN BAGS

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4.METHODPREPACKED CONCRETE

1.TREMIE METHOD

1.This is a method on how to place concrete underwater, this method

place a big role in offshore concreting, since cement looses

its strength and fade away under water, Tremie method is to be

used. 2.Tremie Concrete is done by using

a formwork/pipe which will have one end of the formwork/pipe above water and other bottom

end immersed under the water and with the help of gravity. 

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IT IS DONE BY PLACING PIPE’S ONE END IN THE

WATER AND ONE OUTSIDE.

T HE PIPE HAS A FUNNEL SHAPED HOPPER AT ONE END AND A LOOSE

PLUG AT OTHER HAND.

THE PLUG IS USED TO DEWATER THE PIPE AND

CONTROL SUPPLY OF CONCRETE

.

.

• Before concreting air and water must be excluded keeping the pipe full of concrete all the time.

• For this the funnel and the pipe should have equal capacity.

• Firstly plug is inserted in the pipe with pressure of fresh concrete so that the air is displaced

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1.THE PIPE SHOULD BE PLACED BENEATH THE PlACED CONCRETE

AND THERE SHOULD BE NON STOPPOURING OF CONCRETE.

2. AFTER PLACING THE WHOLE CONCRETE ,THE PIPE SHOULD BE

LIFTED OUT VERTICALLY AVOIDING ANY HORIZONTAL DISTURBANCE

TOTAL MECHANISM1.Coarse Aggregate: Gravel of 3/4” (20mm) max. size.  Use 50-55 % of the total aggregate by weight.Sand, 45-50% of the total aggregate by weight.2.Cement: Type II ASTM (moderate heat of hydration), 600 lbs/yd33.Pozzolans: ASTM 616 Type N or F, 100 lbs/ yd34.Water/Cement Ratio: 0.42 (0.45 Maximum).5.Do not use superplasticizers.6.Air-Entrainment Admixtures:  To give 6% total air.7.Retarding Admixture:  To increase setting time to 4-24 hours, as required.8.Slump:  6 1/2" ± 1"9.This mix will develop compressive strength in the range of 5,600 – 7,000 psi at 28 days.

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2.UNDER WATER

CONCRETING BY BUCKET PLACING METHOD

The buckets are usually fitted with drop-bottom or bottom-roller gates which open freely outward when tripped. The bucket is fully filled along with concrete and its top covered along with a canvas cloth or a gunny bag to avoid the disturbance of concrete as the bucket is lowered within water.

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1.The bucket is lowered through a crane up to the bottom surface of concrete and then opened by a suitable arrangement provided at the top.2. The concrete should be discharged straightly against the surface on that it is deposited. Early discharge of bucket, that allows the fresh concrete to drop through water, must be prevented.

PRECAUTIONS WHILE BUCKET PLACEMENT1.THE CONCRETE SHOULD BE HARD ENOUGH TO SETTLE.

2.EARLY DISCHARGE OF CONCRETE SHOULD BE

AVOIDED,SO AS TO AVOIDENTRY OF WATER IN CONCRETE.3.THIS TECHNIQUE SHOULD BE

USED ONLY ON SHALLOW WATER

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PART 3-4

PLACING IN BAGS

IN,THIS METHOD THE CONCRETE IS FILLED INGUNNY/COTTON SACKS.

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In this method, properly concrete filled bags are lowered into water and placed carefully

in a header and stretcher fashion as in brick masonry

with the help of divers.

. A work is slow and laborious, as the accurate positioning of the bags in place can be only accomplished by the divers.

The bags and labour necessary to fill and tie them are

relatively expensive. This method is only suited for

placing the concrete in shallow water.

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4.PREPACKED CONCRETE

In this method, the aggregate should be wetted before placing in position. This

method is also called as grouted concrete. It consists of placing the coarse aggregate only in the forms and thoroughly compacting it to

form a pre-packed mass.

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In this method, the aggregate should be wetted before placing in position. This method is also called as grouted concrete. It consists of placing the coarse aggregate only

in the forms and thoroughly compacting it to form a pre-packed

mass.

This mass is then grouted with the cement mortar of the required

proportions. The mortar that grouts the concrete displaces water and fills the voids. Dense and compact concrete should be prepared by using well

graded aggregates

The maximum size of aggregate conveniently used is 80 mm. The

coarse aggregate may also be allowed to fall from heights of up to

4 m, without causing any appreciable segregation. Just

shutter vibrations could be used for compact the coarse aggregate.

A mortar consists of fine sand, pozzlanic filler material and as chemical agent that serves the

penetration, early setting of cement, and the dispersion of

particles and to increase the fluidity of mortar.

An air-entraining agent is also added to the mortar to entrain about 4% of air. A small

variation of the procedure of preparation of the cement mortar for grouting leads to a process called colcrete. In this procedure, the mortar grout is prepared in a special

high-speed mixer. No admixtures are used within this procedure.

• The grout pressure will be about 0.2 to 0.3 MPa. The quantity of grout should be estimated from the void contents of the coarse aggregates. The pre-packed concrete has lower drying shrinkage and higher durability, especially freezing and thawing resistance compared to ordinary concrete for the same proportions.

• (c) Pumping the grout into aggregate mass from bottom at carefully designed positions through a network of pipes. The formwork should be constructed at the top of the coarse aggregate in this method

• (b) The grout could be poured on the top surface of aggregate and allowed to penetrate to the bottom. The method is particularly useful for grouting thin sections.

• (a) The mould could be filled with grout and the coarse aggregate can be deposited in the grout.

METHODS OF

CONCRETE

PREPACKED

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SOIL REINFORCING TECHNIQUES

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USING GEOTEXTILES

• Geotextiles are fabrics which are used to filter,drain or reinforce the soil.1.GEOTEXTILES

They are made of

polypropylene

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MAJOR FUNCTIONS OF GEOTEXTILES

1.GEOTEXTILES AS GEOGRIDS

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GEOGRIDS ARE USED FOR

WALL CONSTRUCTIO

N

DRAINAGE CONSTRUCTIO

N

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1.GEOGRIIDS ARE PLACED ON THE SUBSOIL.

• 2.THEN THE ELEVATIONS ARE MARKED .

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4.AFTER THIS THE LAYER IS COMPACTED AND AGAIN GEOGRID SHEET IS PLACED.

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5.IN THIS MANY LAYERS AREFORMED UPTO DESIRED

HEIGHTS HENCE A STRONG LAYER IS FORMED TO CARRYAND DISTRIBUTE THE LOAD

OF HEAVY STRUCTURES

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6.SIMILARLY IF ACONSTRUCTION OF A WALL

IS DONE THEN THE LAYER OFHARD ROCKS ARE PLACED

FIRST

7.THEN GEOGRID SHEET THENAGAIN ROCKS.

8.ROCKS AR PLACED ON THE BORDERS AND THE AREA BETWEEN

IS FILLED WITH SAND AND AGGREGATES

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9.IN THIS WAY UPTO REQDHEIGHT THE LAYERS ARE

FORMED.

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THANK

YOU!

END OF

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