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admixtures (singular or combination of admixtures) are added to concrete or mortar or grout mixture to achieve or improve desired properties in the fresh or hardened state. The admixtures are added to concrete based on their functions which they are play.
Retardation or acceleration of concrete setting time, reduce segregation and water to cement ratio, improve pumpability, accelerate rate of strength development etc. are examples of function of admixtures.
Functions of Admixtures to Modify Fresh Concrete, Mortar, or Grout Properties
- Increase workability without increasing water content or to decrease the water content at the same workability. water-reducing and retarding admixtures.
- Retard or accelerate both initial and final setting times. water-reducing and retarding admixtures.
- Reduce or prevent settlement.
- Create slight expansion in concrete and mortar.
- Modify the rate or capacity for bleeding or both.
- Reduce segregation of concrete, mortars and grouts for instance air entrainment admixture.
- Improve penetration and or pumpability of concrete, mortars and grouts.
- Increase the slump or slump-flow without increasing the water content.
- Improve finishability which is performed by water-reducing and retarding admixtures.
- Modify rheological properties for instance Rheology/viscosity-modifying admixture.
- Reduce the rate of slump loss like water-reducing and retarding admixtures, high range water reducing admixtures
- Increase placement rate for example high range water reducing admixtures
Functions of Admixtures to Modify Hardened Concrete Properties
- Retard or reduce heat generation during early hardening.
- Accelerate the rate of strength development.
- Increase the strength of concrete or mortar (Compressive, tensile, or flexural). This function is conducted mainly water-reducing and retarding admixtures, high range water reducing admixtuers
- Reduce scaling caused by deicing salts
- Increase resistance to freezing and thawing such as air entrainment admixture.
- Decrease the capillary flow of water.
- Decrease the permeability to liquids for instance high range water reducing admixtures.
- Control the expansion caused by the reaction of alkalis with certain aggregate constituents, such as Lithium admixtures
- Produce cellular concrete.
- Increase the bond of concrete to steel reinforcement. high range water reducing and Bonding admixtuers
- Increase the bond between old and new concrete such as Bonding admixture.
- Improve impact resistance and abrasion resistance.
- Inhibit the corrosion of embedded metal which is play by Corrosion-inhibiting admixtures.
- Produce colored concrete or mortar.
- Reduce drying shrinkage and curling which is performed by Shrinkage-reducing admixtures.
While modifying any particular property, care should be taken to ensure that other properties of concrete are not affected adversely.