How do you test the air content of concrete?

The gravimetric method (ASTM C138) in which the air content is obtained by subtracting the sum of the absolute volumes of the ingredients in a batch from the measured volume of the mixed concrete as calculated from its density.

Why do you test for air in concrete?

The primary purpose of entraining air in concrete is to increase its durability when exposed to freeze/thaw cycles with water present. Air-entraining admixtures for concrete create small, uniform, and stable air bubbles from around 0.01mm to 1mm diameter in the cement matrix throughout a concrete mix.

What is a good air content for concrete?

about 6.5%
Concrete having a total air void content of about 6.5% seems optimal. A mix having 6.5% total air voids will have approximately 1.5% entrapped air voids and 5.0% entrained air voids. Entrapped air is the larger bubbles formed in the mixing process and does not provide much protection against freeze-thaw action.

How does air content affect concrete?

A. Intentionally entrained air voids improve the resistance of concrete to damage from cycles of freezing and thawing. Any air voids reduce the strength of concrete, with about a 5% reduction in strength for each 1% increase in the volume of air voids. Air voids, however, also improve the workability of concrete.

How does a concrete air test work?

To measure the air content of the concrete, the upper chamber is pressurized and then the volume of air is released into the lower chamber. The pressure gauge on the top of the meter indicates the change in pressure as it’s released into the concrete. Entrained air is formed in concrete using a surfactant.

What are the two most commonly used methods to determine air content of fresh concrete?

The measurement of air content in fresh concrete of normal density is typically performed using the pressure method (ASTM C 231). Another useful test is ASTM C 173. However, the pressure method is frequently preferred because it is relatively fast.

What is the volumetric method?

Volumetric analysis is a widely-used quantitative analytical method. As the name implies, this method involves the measurement of volume of a solution of known concentration which is used to determine the concentration of the analyte. This process is called titration and the solution in the buret is called the titrant.

What is a concrete air test?

An air content test is required for checking air entrained concrete. As the pressure rises the concrete becomes compressed and the water level in the graduated cylinder falls. When the pressure has reached a specified level, the reading of the water level is recorded.

How do you reduce the air content of concrete?

Adding a pumping aid along with an AEA increases air c o n t e n t . Dust on the aggregate decreases air content. Crushed-stone concrete entrains less air than gravel concrete. Diluting AEA with hard water prior to batching decreases air content.