Current methods can measure only the total air content of fresh concrete, not the gradation of air bubbles. Even so, it's important to measure the total air content in fresh concrete for two practical reasons. First, specifications may require a minimum or maximum air content. Testing shows if the concrete meets specified requirements. Second, a consistent air content indicates uniform materials and batching, and is essential to a consistent yield.
Total air content in fresh concrete is determined by one of three standard tests: the unit weight test, the roll-o-meter test, and the pressure meter test.
Microscopic evaluation of the hardened concrete air-void system is performed to:
- Evaluate placing, consolidating, or finishing operations
- Evaluate the effectiveness of air-entraining admixtures
- Determine compliance with specified requirements for characteristics of the air-void system.
- Estimate the frost resistance of the concrete in-place, often when frost resistance is questioned based on fresh concrete air content
Microscopic analysis of hardened concrete is done by a trained specialist under laboratory conditions - it is not a field test, nor should it be done by amateurs.