Admixtures are the materials that are added to concrete immediately before or during mixing in order to improve the properties of concrete. Admixtures are used for several purposes such as to increase the flow-ability of fresh concrete, obtain high strength through lowering w/c ratio, retard or accelerate time of initial setting, increase freeze thaw resistance, and inhibit corrosion. Normal admixture dosage is about 2 to 5 % by mass of cement.
There are two broad classifications of Admixtures, they are
- Chemical Admixtures – These are the materials in the form of powder or fluids that are added to concrete. The effectiveness of an admixture depends upon the type, brand and amount of cementing materials.
- Mineral Admixtures – These are inorganic materials that also have pozzolanic properties. These are very fine grained materials that are added to concrete mix to improve the properties of concrete.
The different types of Chemical Admixtures are:
- Water-reducing admixtures.
- Air entraining admixtures.
- Corrosion inhibitors.
The different types of Mineral admixtures are:
- Fly Ash.
- Ground Granulated blast furnace slag.
- Silica Fumes.
- Rice Husk Ash.
- High-reactivity Metakaolin.