Air Content by the Volumetric Method
Volumetric procedure
The volumetric method measures air by displacing it with water and alcohol in a calibrated meter. Fill the meter with concrete in layers, consolidate each layer, and strike off. Add water and isopropyl alcohol, then roll and invert the meter so the alcohol breaks the air bubbles and the air escapes. Continue until the water level in the graduated neck becomes stable, and read the air content at the bottom of the meniscus. The method gives a direct volume reading and requires no aggregate correction factor.
When to use it
The volumetric method is useful for concrete made with lightweight or porous aggregates, where the pressure method may be unreliable. It is also useful as a field check. The meter must be clean, calibrated, and used with the correct amount of alcohol. The concrete must be representative and must not have lost water before testing.
Traps and worked example
Traps include too little alcohol, insufficient rolling and inverting, reading the top of the meniscus, and failing to tap the meter to release bubbles. Another trap is using a dirty or leaking meter.
Rule of thumb: roll, invert, tap, and wait for a stable level. Worked example: after rolling, the water level rests at the 5.0% mark; the air content is 5.0%. If the level continues to rise, keep rolling; do not read until it is stable.