What is air entrained concrete?/ Why the air-entrained concrete is produced?

       

 The concrete that contains tiny air pockets or bubbles throughout its structural volume is called air-entrained concrete.

Air-entrained concrete is produced by adding air-entraining agents or admixtures into the production process of the concrete.

These admixtures produce a large number of tiny air bubbles of 0.3mm. or lesser size in the concrete structures. When the concrete gets hardened, these bubbles create a space for air cells.

Now the question that arises is,

Why the air-entrained concrete is produced?

Water molecules expand and contract due to the freezing & thawing action of the atmosphere. When the concrete freeze, the moisture or the water molecules present in the concrete, tries to expand within the body of the structure. These water molecules regain their normal volume when the climate becomes normal. These regular expansion & contraction in the volume of the water generates cracks or fissures in the concrete structures. 

The deliberate intrusion of air pockets within the concrete provides the required space for the water molecules when they expand. This extra air space relieves the water pressure over the concrete structures. So, air-entrained concrete enhances the life span of the structure, when used in such atmospheric conditions.

Generally, 4 -7% of air bubbles (by volume) are produced in the total volume of the concrete. 

When compared to the normal concrete, the compressive strength of the air-entrained concrete is less, due to these air pockets. Larger the percentage volume of air cells, the lesser the strength of the entrained concrete & vice-versa.

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