Air entrained concrete

Air-Entrained Concrete | Air Entraining Cement | Air Concrete7 min read

What Is Air-Entrained Concrete?

Air-Entrained Concrete contains billions of microscopic air pockets and this air pocket relieve internal pressure on the concrete by creating a small air void for water to expand into when it freezes. Air-entrained concrete is made by using air-entraining portland cement or by use of the air-entraining agent in the concrete mix.

The method of forming a small tiny bubble in the concrete is known as Air entrainment. During the concrete making process, some air entrain admixtures are added to the concrete which forms air bubbles in it. Bubbles are created in the concrete when the concrete is in the plastic stage, most of the bubbles are surviving in the hardened stage of concrete.

The main primary purpose of the air entrainment in the concrete is to increase the durability of the hardened concrete where the climates are subject to freeze and thaw. The main secondary purpose is to increase the workability of concrete at its plastic stage. Due to air stickier is produce so it gives good less result of segregation and good attractive surface of the concrete.

Read More: What is Air-Entraining Admixture and Its Effect on Concrete


How to Make Air Entrained Concrete

how to make air entrained concrete? following material are used to make concrete,

  1. Air entraining cement
  2. Air entraining agents

1. Air Entraining Cement

Air entrained Portland cement is one of the special types of cement which creates air bubbles in the cement or concrete.

The Air bubbles provide the space for the Expansion of the concrete due to freezing and thawing and protect concrete from cracks and damage.

Air Entrained Concrete
Air Entrained Concrete

2. Air Entraining Agents

Air entraining agents or material including the following things:-

  1. Using gas-forming material:-
    1. Aluminium powder
    1. Zinc powder
    1. Hydrogen peroxide
  2. Lowering Surface tension agents:-
    • Natural wood resins
    • Animal fats
    • Wetting agent
    • Water-soluble soaps of certain acids

All materials given above are mixing with other concrete constitutes and act as a foaming agent.  Due to the lowering of the surface tension of water the stable foam creates the small tiny microbubbles in the air entrained concrete.

  • Using cement dispersing agents
  • Calcium ligno-sulfate and calcium salts of glues

Read More: What is Lightweight Concrete (Foam Concrete) – Types, Uses & Applications


Properties of Air Entrained Concrete

  1. Workability
  2. Freeze-thaw durability
  3. De-icers resistance
  4. Sulphate resistance
  5. Strength
  6. Abrasion resistance
  7. Water tightness

1. Workability

If the workability of air entrained concrete is improved then reduce water and sand requirement particularly in lean mixes of concrete.  If the air bubbles are disconnected then it reduces segregation and bleeding of plastic concrete.

2. Freeze-Thaw and Durability

In the freezing process, the water is expanding and creates enough pressure for rupture in the concrete. Air bubbles work in the concrete as reservoirs to protect the concrete from the expansion water and protect the damage in concrete.

3. De-icers Resistance

Air entrained concrete is mostly used where concrete is in contact with de-icing chemicals because entrained air prevents scaling caused by de-icing chemical use for snow and ice removal.

4. Sulphate Resistance

If concrete is made with low w/c ratio, entrained air and cement having low tri-calcium aluminate content is useful to resist the sulphate attack. Entrained air is very useful to resist the sulphate attack in concrete.

5. Strength

The strength of air-entrained concrete is basically determined from the voids to the cement ratio. In this ratio, voids define as the total volume of water plus air. 

If the air content in concrete remains constant the strength varies inversely with the w/c ratio.  If the air content increases then we can generally maintain a given strength by the help of holding the voids to the cement ratio constant.

6. Abrasion Resistance

The abrasion resistance in the air-entrained concrete is the same compressive strength as non-air-entrained concrete. If abrasion resistance increases then the compressive strength also increases.

7. Water Tightness

The water tightness of air entrained concrete is more than the non-air-entrained concrete. Entrained air prevents the interconnection of capillary channels from forming.  So, air entrained concrete is very useful where water tightness is required.


Effect of Air Entrainment on Strength of Concrete

The main thing which is affected by the air entrained concrete is workability and the compressive strength of concrete. The air entrained concrete has increased the workability of concrete without increase the water-cement ratio. If the workability of the concrete is increasing then compressive strength automatically decreases because workability and the compressive strength are always inversely proportional to each other.

  1. Effect of air entrainment on compressive strength of concrete
  2. Effects of air entrainment on flexural strength of concrete

1. Effect of Air Entrainment on Concrete Compressive Strength

Air entraining admixture commonly introduced to increase concrete workability without affecting the concrete strength very much. Form the study says that the air-entrained concrete having 7.5 cm slump is better than the slump of 12.5 cm of the non-air-entrained concrete.

If we use air-entrained admixture in large or huge quantity then the compressive strength of concrete is reduced. The common factors which affect the reduction of the strength of concrete are mix proportions, type of concrete, and grading of concrete, type of cement, and entraining agent.

The strength of concrete reduces with the use of air entrained admixtures is varied from 3 to 7%. The variation of this 3 to 7% is considered in the concrete mix design so the desired compressive strength is achieved with the required amount of admixture and workability.

Before the design trial mix designs are done and find the exact variation of strength with the use of the admixtures and then suitable corrections are done in the mix design. Generally assumed that a loss of 5% of the compressive strength of concrete occurs due to each 1% by volume entrained air in the concrete mix.

Air Entrained Concrete
Effect of Air Entrainment on Concrete Compressive Strength

For estimating of the water-cement ratio required for an air entrained concrete which allows for strength reduction is incorporated in the mix design and assumes the high target mean strength. High target mean strength for an air-entrained mix is given by:-

Target mean strength = fc + m/(1-0.055a)

where,

f = specified characteristic strength

m = the margin

a = % by volume of entrained air

2. Effect of Air Entrainment on Flexural Strength of Concrete

The reduction of flexural strength of the concrete due to air entrainment is generally not determined as in the case of compressive strength. From the report, if the air content is 4% in concrete then achieved maximum flexural strength.

From both the case it concludes that compressive and flexural strength of lean concrete mix design increase with provided that, maximum water reduction considers and small maximum aggregate size is employed. 


FAQs: Air-Entrained Concrete

Air-Entrained Concrete

Air-Entrained Concrete contains billions of microscopic air pockets and this air pocket relieve internal pressure on the concrete by creating a small air void for water to expand into when it freezes. Air-entrained concrete is made by using air-entraining portland cement or by use of the air-entraining agent in the concrete mix.

Air Concrete

Air-entrained concrete is a type of concrete that is made by introducing millions of tiny air bubbles in concrete by adding air-entrained cement or air-entraining agent. The major advantage of air concrete is that it is capable to resistant to freeze-thaw damage and scaling caused by de-icing salts or chemicals.

Air Entrainment

The method of forming a small tiny bubble in the concrete is known as Air entrainment. During the concrete making process, some air entrain admixtures are added to the concrete which forms air bubbles in it. Bubbles are created in the concrete when the concrete is in the plastic stage, most of the bubbles are surviving in the hardened stage of concrete.

Uses of Air Entraining Cement

The major benefit of air-entraining concrete is freeze-thaw and scaling resistance. The air voids in concrete work as pressure relief value during a freeze event, allowing the water inside the concrete to freeze without exerting large internal stresses.

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