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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What Is The Procedure Of STP WATER TESTING

 

STP Water Testing.

This procedure is applicable to check Quality of STP Water.

1.0 Purpose:  To Check Quality of STP Water using O- Tolidine, Universal  Indicator, Hardness A, B, & R. 

2.0 Apparatus:  Measuring Jar 50ml capacity.

3.0 Material:  STP Water, O- Tolidine, Universal Indicator, Hardness A, B, & R.

4.0 Procedure:

4.1 For Checking of Free Chlorine

a)Take 10ml of S.T.P. water in a cylinder and add approximately 6 drops of O- Tolidine to it.

b)Shake the cylinder and observe the change in colour.

c)Then match the colour with the PPM tube sample and note the PPM.

 4.2 For Checking of pH

a)Take 25ml of STP water in a cylinder and add 0.5ml of universal indicator to it.

b) Shake the cylinder and see the colour change.

c) Match the colour change with the pH sample colour on the pH universal indicator bottle.

d) Note the pH in standard format.

4.3 Hardness Test

a)Take 25ml of STP water in a cylinder and add a pinch of Hardness ‘A’ indicator.

b)The colour changes to pink.

c)Then add approximately 17 drops of hardness ‘B’ indicator to the sample.

d)The sample turns dark pink.

e)Then take hardness ‘R’ and add drop by drop to the sample till the sample turns colourless.

f)Note the drops of hardness ‘R’ indicator added to the sample to turn colorless.

g)Hardness of water is calculated by the formula:

Hardness = Number of hardness ‘R’ drops x 5.

5.0 Observation/Conclusion:

1)Free Chlorine in STP water should be within 1to3 PPM. If found more or less than 1 to 3PPM, than accordingly the addition of Chlorine is increased or decreased.

2)PH value of STP water should be within 7.5 to 7.8. If found more or less than, required than accordingly the addition of Alum & Lime is increased or decreased.

3)Hardness of STP water should not be more than 500PPM.

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