Types of Admixtures Used in Concrete and Their Uses

Admixtures are chemicals which are added to concrete at the mixing stage to modify some of the properties of the mix. Admixtures should never be regarded as a substitute for good mix design, good workmanship, or use of good materials.

Types of admixtures

Admixtures are normally categorized according to their effect:

  • Plasticizers (water-reducing agents)
  • Superplasticizers (high range water reducers)
  • Air entrainers
  • Accelerators
  • Retarders
  • Others

Many admixtures provide combinations of properties such as plasticizer/retarders or plasticizer/air entrainers.

Uses of admixtures

The most common reasons for using admixtures in concrete are:

  • To increase workability without changing water content.
  • To reduce water content without changing workability.
  • To effect a combination of the above.
  • To adjust setting time.
  • To reduce segregation and/or bleeding.
  • To improve pumpability.
  • To accelerate the rate of strength development at early ages.
  • To increase strength.
  • To improve potential durability and reduce permeability.
  • To reduce the total cost of the materials used in the concrete.
  • To compensate for poor aggregate properties.

 

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