What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting?

  What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting? The size of tremie pipe is about 300mm with sections having flange couplings fitted with gasket to prevent water leakage. The tremie pipe should be closed initially to prevent water from entering the pipe. It should be designed with sufficient thickness and weight so that it would not be buoyant when empty inside water. The placement of tremie concrete is commenced by putting the closed pipe underwater to the location for concreting, followed by partial filling of tremie pipe with concrete. In order to have tremie concrete flowed out of the pipe, it is necessary to fill the pipe with concrete of sufficient height to overcome the water pressure and frictional head. After that the tremie pipe is raised about 150mm to allow concrete to flow out. To enhance sufficient bonding, each succeeding layer of concrete should be placed before the preceding layer has reached
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RCC WINDOW SILL//Important point to be noted while doing RCC window sill//how to find window sill upstand width

RCC WINDOW SILL

Following points to be noted while doing RCC Window Sill.

1) Window sill to be cast with proper shuttering, line and level.

2) Upstand portion to be cast simultaneously with main part of RCC window sill without having any joints between the main parts and upstand.

3) For better finish and correct alignment of upstand use M.S. angle (ISA 40x40x5mm).

4) Window sill to be cast upto the column face, & if column is far away from window face ( say 5’ ) window sill will be cast minimum upto 2 ft. from the face of window.

5. Window sill to be cured for 7 days covered with Hessian cloth.

6. Wherever living room windows has Grill with wooden railing on top, the upstand width of the RCC window sill will be 75 mm (as shown in the figure), so that Grill fits properly in the side wall provided the window has boxing wall on both sides and the beam is 75 mm outside building line so that rough ground ( sub frame ) do not hang outside.

FINDING OF WINDOW SILL UPSTAND WIDTH (Y)

FOR EXAMPLE

(A). Finding of window sill upstand width (Y)

Window sill width = Thickness of wall + Projection of window sill

= 125 + 75

= 200 mm

X = 110 mm

Plaster Margin = 15 mm

Y = ?

Therefore Y = 200 – (110+15)

= 200 – 125

= 75 mm

Therefore Window sill upstand width = 75 mm.

(B). Height of upstand (Z) will be height of track.

(i). If track is coming along with Gutter section, upstand height will be 40 mm.

(ii). If track is coming along without Gutter section, upstand height will be 25mm.

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