The process which involves the introduction of tiny air bubbles into concrete is called air entrainment. And the concrete formed through this process is called air entrained concrete.
Using air entraining Portland cement or air entraining agents such as admixture, air entrainment is done in concrete. The amount of air in such concrete is usually between four to seven percent of the volume of concrete.
It is measured by galvanometric method, volumetric method and pressure method. The air bubbles relieve internal pressure on the concrete by providing chambers for water to expand when it freezes.
Process:
Here are the ways of incorporating air in concrete:
1-Using gas forming materials as aluminium powder, zinc powder and hydrogen peroxide.
2-Using surface active agents that reduces surface tension. They may be natural wood resins and their soaps, animal or vegetable fats or oils, alkali salts of sulfonated or sulphated organic compounds.
3-Using cement dispersing agents.
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