To increase concrete flow mixing additional water or admixture on TM at site is impact on strength of concrete or any ??

Dnyan Deshmukh

Staff member
Everybody while working on a site do face a situation where sometime the slump or the workability of the concrete drops down and placing of such concrete becomes a huge task as nobody wish to place with reduced workability.

Various factors do impact the workability such as retention time, performance of admixture, increased waterabsorption in aggregates, moisture correction for maintaining correct WC ratio, temperature of atmosphere and of cement.

One need to identify the causes of slump drop and need to take action on it accordingly to prevent its recurrence.

IS code do specify the addition of admixture to regain the workability is allowed up to some extent and trails should be conducted for same to assess the effect of additional admixture quantity on setting time of the concrete for deciding the upper limit of admixture dose which can be added safely in case concrete looses its workability.

Addition of admixture may impact on the setting time of concrete but will not affect the strength parameter.

Addition of water do always results into reduction in strength of the concrete, so it is always better not to experiment with water.
 
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Everybody while working on a site do face a situation where sometime the slump or the workability of the concrete drops down and placing of such concrete becomes a huge task as nobody wish to place with reduced workability.

Various factors do impact the workability such as retention time, performance of admixture, increased water absorption in aggregates, moisture correction for maintaining correct WC ratio, temperature of atmosphere and of cement.

One need to identify the causes of slump drop and need to take action on it accordingly to prevent its recurrence.

IS code do specify the addition of admixture to regain the workability is allowed up to some extent and trails should be conducted for same to assess the effect of additional admixture quantity on setting time of the concrete for deciding the upper limit of admixture dose which can be added safely in case concrete looses its workability.

Addition of admixture may impact on the setting time of concrete but will not affect the strength parameter.

Addition of water do always results into reduction in strength of the concrete, so it is always better not to experiment with water.
In this situation how much dosage of admixture to be added ? It shall be as per approved design mix ??
 

Dnyan Deshmukh

Staff member
In this situation how much dosage of admixture to be added ?
It depends on the situation and can be from 0.1 % to 0.4%.

It shall be as per approved design mix ??
At the time of mix design trials, some trials should be taken with increased % of admixture to see the effect of additional admixture on retention, setting time of concrete and strength at various ages.
This gives you idea about maximum % of admixture you can consume in concrete safely above which it creates huge impact or various scenarios.
 

Aakash Dudhat

Apprentice

Why is admixture used?​

Admixture in concrete use for the modification of setting time of concrete, Workability of concrete, air-entrainment dispersion etc

In recent time the development increased in extremely large scale so we started using high strength concrete for bridge construction project and high rise building like skyscrapers So makings concrete manually on-site by labours is not possible so that use of ready mix concrete has really promoted and use of RMC has really promoted the use of concrete admixtures

In the market various types of admixtures used in concrete available like accelerators, retarders, air-entraining agents, pozzolanic materials, waterproofing admixture etc which are used in practice by civil engineer constructors in the construction industry

The admixture dosage in concrete normally used in small quantity like 0.005 to 2% by the weight of cement but we tested first before applying

Most of the admixture used in concrete are provided in ready-to-use liquid form and are added into the concrete at the construction site
 
Since some of the discussion mentions initial set time & workability, let us be mindful that most specifications have maximum time limits between introduction of water to the mix & initial mixing and final placement of the mix. While plasticizers can be added to the mix on-site to help with workability, allowable mix times must be met. Concrete placement delays can happen - Mechanical breakdowns, too many concrete trucks showing up on-site at one time, etc. can force delays in depositing the mix. While dosing an aging batch of concrete might help your workability issue, be mindful that your total mix time requirements still need to be satisfied.
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