Entrainment of a small amount of air in cement concrete has been found to considerably improve 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 the durability of concrete.
Further, when use of admixtures is made to increase workability of concrete, the air content should be checked to ensure that the percentage of air remains between 1% and 2% for optimum performance of the concrete structure.
An Air Entrainment Meter, as specified in ASTM standards, is used to determine these percentages. It consists of a pressure-tight flanged cylindrical measuring bowl, fitted with a removable flanged and conical cover assembly with a seal in between.
The conical cover has an air valve and a pet cock for bleeding off the water. A cylindrical stand pipe, which is graduated in percent of air content, is fixed on the conical cover assembly.
The required pressure is applied to the specimen with the help of a pressure bulb. The whole assembly is mounted on a flat base. Each apparatus is supplied complete with a calibrating
cylinder, pressure gage, funnel, trowel and tamping bar.