Concrete admixtures are additives added to concrete to strengthen,chemically resist,color resist,reduction in water and cement requirement and to enhance working properties of concrete.
Types of admixtures
- Shrinkage reducers
- Corrosion inhibitors
- Hydration-control admixtures
- Retarding admixtures
- Accelerating admixtures
- Plasticizers
- Water-reducing admixtures
- Air-entraining admixtures
- Alkali-silica reactivity inhibitors
- Coloring admixtures
Source-http://www.admixtures.com/images/Ctrl_BoomImage/boom_uid5192009313442.jpg |
WATER-REDUCING ADMIXTURES
Water-reducing admixtures are used to reduce the quan-tity of mixing water required to produce concrete of a certain slump, reduce water-cement ratio, reduce cement content, or increase slump. Typical water reducers reduce the water content by approximately 5% to 10%. Adding a water-reducing admixture to concrete without reducing the water content can produce a mixture with a higherslump.The rate of slump loss, however, is not reduced and in most cases is increased . Rapid slump loss results in reduced workability and less time to place concrete. An increase in strength is generally obtained with water-reducing admixtures as the water-cement ratio is cracks in concrete. Using a water reducer to reduce the cement and water content of a concrete mixture—while maintaining a constant water-cement ratio—can result in equal or reduced compressive strength, and can increase slump loss by a factor of two or more (Whiting and Dziedzic 1992).
Reasons for using admixtures
- To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in ad-verse weather conditions.
- To achieve certain properties in concrete more effectively than by other means.
- To reduce the cost of concrete construction
- To overcome certain emergencies during concreting operations.
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