Role of concrete admixture:
Concrete admixture are additives or natural or manufacturer chemicals which are added during mixing of concrete to increase the specific properties of the hardened an or fresh concrete . such as durability , workability and early and final strength of concrete admixtures.
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functions of concrete admixture:
- To modify the hardened concrete properties
- Retard or reduce heat generation
- Strength Development rate will be accelerate
- Enhance the freezing resistance
- like wise Air entrainment admixture
- To reduce the permeability
- To reduce the insulation or isolation
- To reduce the bleeding
Categories of concrete admixture:
There are two categories given below;
Mineral concrete admixture:
It make admixture more economical, enhance strength ,decrease permeability, and clout other concrete properties. Mineral admixture make alteration in the nature of the hardened concrete through hydraulic or pozzolanic activity. Pozzolans are cementitious material and include natural pozzolans such as volcanic ash used in roman ash, fly ash and silica fume. Mineral admixture can be use with Portland cement or blend cement separately or in combination.
Chemical concrete admixture:
chemical admixture are use in mixing of concrete to enhance the performance of concrete. They are use during mixing of concrete ,transporting, placement and curing to improve the quality of concrete.
Types of Chemical Concrete Admixture:
There are five types of chemical admixture given below ;
1- Air entraining Admixture:
- Improve the freezing resistance of concrete or thaw cycles
- It help to produce the enough amount of air bubbles in concrete mixture
- Enhance drying and wetting cycles resistance
- Increase the degree workability of fresh concrete without changing the setting and rate of hardening
- Enhance the degree of durability
2- Water reducing admixture:
- Water reducers are use in concrete mixture to reduce the water content in mixture
- Increase the slump in concrete mixture
- Mortar and grout are use to enhance the flow-ability without increasing the water content
- Reduce the water-cement ratio
- Reduce the cement contents
- plasticizer and super plasticizer are examples of water reducing admixture
3- Retarding Admixture:
- Reduce the setting rate of concrete
- Stamping concrete in warm weather
- Reduce the temperature to compensate the hardening rate of concrete
- Reduce the temperature to make the placing and finishing easier
- Holdup the starting rate of hydration of cement
- Boost the setting time of cement paste
4- Accelerating admixture:
- Enhance the rate of initial strength development
- Reduce the time needed for proper curing
- Reduce the required time for protection
- Enhance the speed of initiating the finishing operations
- Used to changing the properties of admixture in cold weather
5- Corrosion Preventing Admixtures:
- Used to slow down corrosion of reinforcing steel in concrete
- Used as a protective strategy for structural concrete
- Reduce the process of corrosion
- To reduce the shrinkage of concrete
- It can be effective in parking structure , bridges and marine environment
