Admixtures are the special ingredients added during concrete mixing to enhance the properties and performance of fresh concrete. Various types of admixtures are available in the market which is used in construction work.
Function Of Admixtures:
1. To accelerate or retard the setting time of fresh concrete.
2. To improve the workability or flowability of concrete.
3. To increase the strength and durability of concrete.
4. To reduce the heat of hydration.
5. To reduce the segregation and bleeding.
6. To decrease the permeability.
7. To achieve other desired properties.
Types Of admixtures:
1. Accelerating Admixtures:
This admixture is added in concrete or mortar for increasing the rate of hydration of hydraulic cement and for shortening the setting time. Calcium chloride (CaCl2) is the most widely used accelerating admixture.
2. Retarding Admixtures:
Retarding admixtures delay the initial rate of hydration of cement and extend the setting time of cement paste. This admixture can be used in high temperature and where the concrete has to be transported to a long distance. It is also suitable for using in grouting oil wells.
3. Air-Entraining Admixtures:
Air entraining admixtures help to produce a certain amount of air bubbles in the concrete mixture. The main goal of this admixture is to increase the resistance against freeze-thaw degradation and cohesion. It also improves the workability of fresh concrete without changing the setting or the rate of hardening.
4. Water Reducing Admixtures:
As the name suggest, water reducers are added to a concrete mixture, mortar or grout to increase the flowability without increasing the water content.
Advantages Of Water Reducing Admixtures:
- The rate of concrete placement is faster.
- Strength, durability, density etc. are significantly improved.
- Segregation, permeability, and cracking are reduced.
- Superplasticizing admixtures.
- Corrosion-inhibiting admixtures.
- Grouting admixtures.
- Coloring admixtures etc.
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