Measurement of Air Content in Concrete

This article describes five techniques for the measurement of the air content of fresh concrete and one technique for hardened concrete. The tests discussed are: AASHTO T 152, Standard Method of Test for Air Content of Freshly Mixed Concrete by the Pressure Method; AASHTO T 196, Standard Method of Test for Air Content of Freshly Mixed Concrete by the Volumetric Method; AASHTO T 121, Standard Method of Test for Density (Unit Weight), Yield, and Air Content [Gravimetric] of Concrete; AASHTO T 199, Standard Method of Test for Air Content of Freshly Mixed Concrete by the Chace Indicator; and ASTM C457, Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete. The authors focus on identifying potential sources of errors, notably failure to maintain and calibrate equipment and to properly follow test procedures. One section briefly explains the use of the air void analyzer (AVA) to determine the volume and size distributions of air voids. Readers are referred to the appropriate AASHTO or ASTM standard for full details of each procedure.