Entrainment of a small amount of air in the cement/concrete has been found to improve considerably the durability of concrete. The recommended limits specified for the air content are between 3% and 6.5%.
Smaller percentages may result in deterioration taking place more quickly and larger percentages may reduce the strength without any improvement in durability of the concrete.

The Air Entrainment meter consists of a pressure-tight flanged cylindrical measuring bowl, fitted with a removable flanged and conical cover assembly with a seal between.
The conical cover has an air valve and pet cock for bleeding off the water. A cylindrical stand pipe which is graduated in per cent air content is fixed on the conical cover assembly.