AIR ENTRAINED CEMENT - MANUFACTURE, PROPERTIES, ADVANTAGES AND DISADVANTAGES

Air Entrained Cement

Air Entrained Portland Cement is a special cement that contains billions of microscopic air bubbles per cubic foot.These air bubbles provides the space for expansion of minute droplets of water in the concrete due to freezing and thawing.The air bubbles increase the workability of the concrete and lower the water cement ratio.However because of air entrained the strength of concrete reduces and as such the quantity of air so entrained should not exceed 5%.

Manufacture of Air Entrained Cement

The manufacturing process of air entrained cement is same as OPC cement,when the cement clinkers are formed, during grinding process the cement clinker are added with some air entraining materials which makes the cement as air entrained cement.

Air Entraining Admixture

• Natural wood resins
• Vinsol resin and Darex 
• Animals and vegetable fatty acids.
• Water soluble soaps of resin acids.
• Aluminium powder,zinc powder and hydrogen peroxide.
• Alkali salts or sulphated and sulphonated organic compounds.
• Sodium salts of petroleum sulphonic acids,hydrogen peroxide and aluminium powder etc.
• Animals and vegitables fats and oils, such as olive oil and their fatty acids.

Properties of Air Entrained Cement

1. Workability

The workability property of air entrained cement is high due to the air bubbles which act as lubricant betweeen aggregates,which reduce water and sand requirements and increase the strength of concrete.

2. Strength

In air entrained cement water cement ratio is kept low and hence the strength parameter of the concrete is not compromised.

3. Freezing and Thawing Durability

In cold condition,due to low temperature the water inside the concrete freezed and expands.The expansion of water as it freezes in concrete can create enough pressure to rapture the concrete.These entrained air bubbles serve as reservoirs for the expanded water,thereby relieving expansion pressure and preventing concrete damage. 

4. Sulphate Resistance

The resistance ability of sulphate attack is high in the air entrained cement as the water cement ratio can be kept low which initiates the sulphate attacks.

5. Abrasion Resistance

Air entrained concrete has the same abrasion resistance as that of non air entrained concrete of the same compressive strength.Abrasion resistance increases as the compressive strength increases.

6. De-Icing Resistance

In the sloped structure,the ice is formed on the building.To remove these ice, de-icing chemicals are used.When we used this chemicals it forms a layer of scales in the concrete.Because entrained air prevents scaling caused by de-icing chemicals and is recommended for all applications where the concrete contacts de-icing chemicals.

Advantages of Air Entrained Cement

• Workability of concrete increased.
• Reduced bleeding and segregation.
• Improved cohesiveness of concrete.
• Reduces cracks formation in the concrete surface.

Disadvantages of Air Entrained Cement

• The strength of concrete decreases.
• The use of air entraining agent increases the porosity of concrete thereby reducing the unit weight.