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HOW TO REDUCE THE SLUMP LOSS IN CONCRETE

Hello Every one. In today blog we will learn about HOW TO REDUCE THE SLUMP LOSS IN CONCRETE. The Slump of concrete is find out by workability test. Workability is the property of concrete through which we can safely transform, place the concrete in a desire shape. So now lets discuss the steps for reducing the slump loss in concrete.
HOW TO REDUCE THE SLUMP LOSS IN CONCRETE





Slump Loss: One of the most important nagging site problem is the loss of slump.
Slump at mixing point is not of much importance, but the slump at placing point is of primary
importance. Often there is delay between mixing and placing. Achieving high slump at the
mixer, only to be lost with time, before placing is a bad economy. Loss of slump is natural even
with un-plasticized concrete, but rate of loss slump is little more in case of super-plasticized
concrete. Fig. 5.8 indicates the slump loss with time.



Many users demand the slump value at mixing or batching plant and also specify the
slump value after a delay of 1 or 2 or 3 hours period at placing point. It is not a correct
specification. User should only specify the slump value at placing point after a delay of 1 or
2 of 3 hours. It should be left to the super plasticizer manufacturers or concrete supplier to
supply concrete of slump value as demanded by user at the time of placing of concrete.

Steps for Reducing Slump Loss:

The slump loss can be managed by taking any one or more of the following actions:
  1.  Initial high slump.
  2. Using retarders & retarding plasticizer or super-plasticizer.
  3. By repetitive dose.
  4. By dosing at final point.
  5. By keeping temperature low.
  6. By using compatible super-plasticizer with cement


·    Initial high slump: When very high slump is managed at the mixing point, even if loss of slump takes place, still the residual slump will be good enough for satisfactory placing of concrete. Although this method is not a good and economical method.



·    Using retarders & retarding plasticizer or superplasticizer:Pure retarders are used at the time of mixing. This will keep the concrete in a plastic
       condition over a long time. Just before adding an appropriate dose of plasticizer or super plasticizer which will give desirable slump value for placing requirements. This is possible only when concrete is conveyed by transit mixers. Sometime instead of using pure retarders and plasticizer separately, a retarding plasticizer, or r e t a r d i n g super-plasticizer is used in an appropriate dose in the initial stage itself. The retarding plasticizer or super plasticizers retains the slump for longer periods which may be sufficient for placing.


·         By repetitive dose: One of the common methods to combat the slump loss is to give repetitive doses at intervals and thereby boosting the slump so that required slump is maintained for long time.
Below Figure shows the typical repetitive method of using plasticizer. The time interval should be chosen in such a way that the concrete will have such a residual slump value which can be boosted up.




·        By dosing at final point: Sometimes a small dose of super plasticizer is added at the beginning and the slump is boosted up. When the concrete arrives at the pouring point, it will still have some residual slump but not good enough for placing by pump or by tremie. For pumping concrete you need a slump of around 100 mm and tremie placing the desirable slump is 150 mm. At this point an appropriate dose of super plasticizer is added to boost up the slump to required level.

·    By keeping temperature low:It is a common knowledge that hydration process can be retarded by keeping the temperature of the concrete low. At low temperature the slump loss is also slow. Use of ice flakes instead of water is resorted to reduce the slump loss. Often the use of ice flakes is an additional step to reduce the slump loss. 

·    By using compatible super plasticizer with cement:Use of highly compatible admixture with the given cement or vice versa will also reduce the problem of slump loss. A cement with low C3A content will be of use in this regard. In one of the limited trial conducted, 43 grade cement has shown better compatibility and performance than 33 or 53 grade cement.

I hope that this articles will help you to understand about HOW TO REDUCE THE SLUMP LOSS IN CONCRETE

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WHAT ARE THR QUALITIES OF GOOD BRICK WORK
WHAT ARE THE GOOD QUALITIES OF TILES
WHAT ARE THE SITE TESTS OF CEMENT
WHAT IS THE STANDARD SIZE AND WEIGHT OF BRICK


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