ADMIXTURE FOR CONCRETE

ADMIXTURE FOR CONCRETE

Admixtures are ingredients other than portland cement, water, and aggregates that may be added to concrete to impart a specific quality to either the plastic (fresh) mix or the hardened concrete (ASTM C494). Some admixtures are charged into the mix as solutions. In such cases the liquid should be considered part of the mixing water. If admixtures cannot be added in solution, they are either weighed or measured by volume as recommended by the manufacturer.

Admixtures are classified by the following chemical and functional physical characteristics:

1. air entrainers

2. water reducers

3. retarders

4. hydration controller admixtures

5. accelerators

6. specialty admixtures

The Portland Cement Association (PCA) identifies four major reasons for using admixtures (Kosmatka et al., 2008):

1. to reduce the cost of concrete construction

2. to achieve certain properties in concrete more effectively than by other means

3. to ensure quality of concrete during the stages of mixing, transporting, placing,

    and curing in adverse weather conditions

4. to overcome certain emergencies during concrete operations