The air content test, also known as the air entrainment test, is used to measure the amount of entrained air in freshly mixed concrete. Entrained air is intentionally added to concrete to improve its durability and resistance to freeze-thaw damage, and to reduce cracking and segregation of the concrete mix.
Test Procedure:
- Fill a measuring container, such as a pressure gauge or volumetric flask, with a sample of freshly mixed concrete.
- Seal the container and shake it to allow the air bubbles to escape from the concrete.
- Record the volume of the concrete in the container.
- Repeat the process with the same sample after it has been allowed to stand for a few minutes.
- Measure the volume of the entrained air by subtracting the final volume of the concrete from the initial volume.
The air content test provides a quantitative measure of the amount of entrained air in the concrete mix, expressed as a percentage of the total volume of the concrete. The air content is typically in the range of 3-7% for normal weight concrete, with higher air contents required for concrete exposed to severe weather conditions.
Examples:
- For normal weight concrete, a typical air content is in the range of 3-5%.
- For lightweight concrete, a higher air content of 5-7% is typical to improve the insulation properties and reduce the weight of the concrete.
- For high-performance concrete, a lower air content of 2-3% is typical to improve the strength and durability of the concrete.
In conclusion, the air content test is an important tool for engineers and contractors to ensure that concrete has the correct amount of entrained air for its intended use. The test provides valuable information about the quality and consistency of the concrete mix, and helps to ensure that the concrete meets the required standards and specifications for a particular application.
