Admixtures confer certain beneficial effects to concrete, including reduced water requirement, increased workability, controlled setting and hardening, improved strength and better durability. Admixtures are materials other than cement, aggregate and water that are added to concrete either before or during its mixing to alter its properties, such as workability, curing temperature range, set time or color.
Many approaches have been adopted to investigate the role of admixtures. One approach is to determine the stage of the admixture in concrete at different times of curing. The admixture may remain in a free state as a solid or in solution, or interact at the surface or chemically combine with the constituents of cement or cement paste.
Admixtures are generally used for the following purpose.
- Impart to water proofing properties.
- To accelerate curing
- Improve workability of fresh concrete
- Improve durability of entraining air in the concrete
- To accelerate setting or hardening of the concrete
- To disperse the cement particles when mixed with water
- To reduce shrinkage during setting
- To impart desired colour or tint
- Check some adverse chemical reaction
- Reduce heat of hydration
- To reduce blending
Admixtures are additions to a concrete mix that can help control the set time and other aspects of fresh concrete. Common admixtures include accelerating admixtures, retarding admixtures, fly ash, air entraining admixtures, and water-reducing admixtures.