Difference between the type of air meters used to measure air content of fresh concrete.

There are three types of air meters used to measure the air content of fresh concrete are as follows.

• Pressure method
• Volumetric method
• Free air method

Pressure meter	Volumetric meter	Free air meter
Based on Boyles law.	Based on volumetric method	Based on alcohol added to free the air.
Pressure is used to compress the present air inside the concrete.	Agitation is used to remove air from the concrete.	Alcohol is used to measure the air content of the sample.
Press-Ur-Meter is used to measure the air content.	Sight gauge is used to measure the air content.	Change in alcohol denotes the air content.
Standards for this type of measurement is ASTM C 231 AASHTO T-152	ASTM C 173 AASHTO T-192	AASHTO T-199

The difference of the types of air meters are important due to the standards of concrete used for the specific purpose. The correct choice of air entraining measure technique is necessary.