What are the disadvantages of slump in concrete?

The deceleration value is of great importance when the concrete is in its fresh state. The bearish value represents the workability property of concrete. Because of its importance, the bearish value is usually specified by the designer. And when working on site, it is the responsibility of the engineer to ensure that the concrete should show the same slump value as specified. Hence it is necessary to check the slump before pouring the concrete. But for a variety of reasons, the bearish value gradually decreases as time passes. This decrease in bearish value over time is called bearish loss in concrete.

How to Manage Slump Damage in Concrete

Methods of controlling slump damage in concrete

The following methods are helpful for managing fall damage in fresh concrete.

  • initial high bearish
  • use retard
  • Using plasticizer or super plasticizer
  • with repetitive doses
  • dosing at the end point
  • keeping the temperature low
  • By using super plasticizers compatible with cement

1. Bearish initial high

In this method a very high slump is managed at the mixing point, so that after the loss of the slump, the residual slump is still satisfactory for keeping the concrete. This method is not economical and hence not good. But sometimes this method is adopted.

2. Using Retarders

In this method a diluent is used at the time of mixing. This will help the concrete to stay in the plastic state for a longer period of time.

3. Using retarding plasticizer or super-plasticizer

Before placing the concrete, add a suitable dose of plasticizer or super-plasticizer, which will give a desirable value of meltdown. This method is adopted only when the concrete is transported by transit mixer.

4. By Repetitive Dosing

This is one of the common methods to manage slump damage in concrete. In this method, repetitive doses are given at intervals and thus the required slowdown is maintained for a long period of time. The time interval should be chosen in such a way that the concrete has such residual deceleration value that it can be increased.

5. By dosing at the end point

Sometimes a small dose of super-plasticizer is added at the beginning and slowdown is increased. After the concrete has come to the pouring point, it will still have some residual slowdown but not enough to hold by specified methods (such as by pumping or tremie). At this point a suitable dose of super-plasticizer is added to increase the deceleration to the required level.

6. Keeping the temperature low

The hydration process of cement generates heat, which is also a cause of meltdown damage. The process of hydration can be slowed down by keeping the temperature of the concrete low. The deceleration loss is also slow at low temperatures. Snow flakes are used in place of some amount of water to reduce deceleration losses.

7. By using super-plasticizers compatible with cement

Use of highly compatible mix with the given cement will also reduce the problem of slump loss. Cement with low C3A content will come in handy in this regard.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.