Monday, October 7, 2013

Air-Entraining Agents

The following types of air-entraining agents are used for making air entrained concrete:

  •  Natural wood resins
  • Animal and vegetable fats and oils
  • Alkali salts or sulphated and sulphonated organic compounds
  • Water-soluble soaps of resin acids and animal and vegetable fatty acids
  • Miscellaneous materials such as the sodium salts of petroleum sulphonic acids, hydrogen peroxide and aluminum powder etc.
The most important air entraining agents which at one time enjoyed worldwide market are vinsol resin and darex.

Factors affecting air entrainment
  1. The type and quantity of air entraining agents used
  2. Water and cement ratio of the mix
  3. Type and grading of aggregate
  4. Mixing time
  5. The temperature
  6. Type of cement
  7. Influence of compaction
  8. Admixture other than air entraining agents used

The effect of air entrainment on the properties of concrete:
Air entrainment will affect directly the following three properties of concrete
  • Increase resistance to freezing and thawing
  • Improvement of workability
  • Reduction in strength
Incidentally air entrainment also affect the following properties of concrete
  1. Reduce the tendencies of segregation
  2. Reduces the bleeding and laitance
  3. Decreases the permeability
  4. Increases the resistance to chemical attack
  5. Permits reduction in sand content
  6. Improves placeability and early finishing
  7. Reduces the cement content, cost, and heat of hydration 
  8. Reduce the unit weight
  9. Permits reduction in water content
  10. Reduces the alkali-aggregate reaction 
  11. Reduce the modulus of elasticity

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