Concrete Admixture used in Building Construction
Concrete Admixture used in Building Construction
Concrete is the most versatile material in the construction field. In order to modify the properties of concrete so as to make it more suitable under a wide range of climatic conditions and circumstances, admixtures are used in concrete. This standard covers the chemical and air entraining admixtures including superplasticizers, solid or liquid or emulsion, to be added to cement concrete at the time of mixing so as to achieve the desired property in concrete, in the plastic or hardened state.
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An Concrete Admixture are the ingredients in concrete other than water, aggregates and cement that added to the mix batch immediately before or during mixing.
The following are the commonly used Admixtures
(i) Water reducing Admixtures
(ii) Air entrained Admixtures
(iii) Setting and hardening Admixtures
(i) Water reducing Admixtures
Water reducing admixtures are used in concrete to reduce the quantity of mixing water. Desired slump, required consistancy, high early strength, better durability can be achived by adding this admixture. Plasticizers and super plasticizers are common water reducing admixtures.
(ii) Air entrained Admixtures
Air entraining admixtures are generally ued for increasing the workability and resistance to freezing and thawing (Frost resistance) in concrete. These admixtures generate air bubbles to facilitate frost protection. Natural wood resins, animal and vegetable fats and oils, hydrogen peroxide and aluminium powder are the commonly used air entraning admixtures.
(iii) Setting and Hardening Admixtures
- Set Retarders
These agents are primarily used for delaying the setting time of concrete. The most common retarder is calcium sulphateor gypsum, which is used as an ingredient in the manufacture of Portland cement.
- Set Accelerators
An accelerating admixture is a material added to the concrete for the purpose of shortening the setting time and accelerating early strength development of concrete. Soluble chlorides, carbonates, silicates and alumina cements have been used for this purpose.
More Info Chemical Admixtures for Concrete
