The Air Content Percentage may be entered in the ‘Air Content’ field on a Mix Design Form. It is defined as the percentage of entrained and entrapped air by volume in the freshly mixed concrete.
Entrained air is considered to comprise small, separate air bubbles, whose presence is caused intentionally by air entraining agents, in distinction to normal entrapped air, which is usually present as relatively large voids, that may be interconnected.
It is impractical to measure the entrained air and entrapped air separately. However the total air content can be determined by the Volumetric, Gravimetric or Pressure Tests (see References 19, 20, 21 and 22), although measurements are problematic for lightweight concrete, since air contained in the voids of the coarse aggregate particles may be incorrectly included.
The following table gives likely percentages of entrapped air and typical values of the air content percentage needed to provide adequate frost protection, for concrete made with a particular maximum size of coarse aggregate.
| Maximum size of aggregate | mm | 10 | 20 | 40 |
| In. | 0.375 | 0.75 | 1.5 | |
| Probable Entrapped Air | % | 3 | 2 | 1 |
| Air content for Mild Exposure | % | 4.5 | 3.5 | 2.5 |
| Air content for Average Exposure | % | 6 | 5 | 4 |
| Air content for Severe Exposure | % | 7.5 | 6.5 | 5.5 |
The figures are taken from table 6.3.3 of ACI 211.1-91 (see References 21)
Range: 1 - 6%