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Why is concrete air content important?

Why is concrete air content important?

The principal reason for entraining air in concrete is to increase resistance to the destructive effects of freezing and thawing and deicing salts. The entrainment of air also increases the workability of the concrete for placement purposes and permits a reduction in the sand and water contents of the mix.

How does low air content affect concrete?

Air entrainment affects compressive strength of concrete and its workability. It increases the workability of concrete without much increase in water-cement ratio. Compressive strength of concrete is inversely proportional to workability of concrete.

How do you measure air content in concrete?

Air Content – Air content is calculated by subtracting the unit weight, ρ, from the theoretical unit weight, T, divided by the theoretical unit weight, T, multiplied by 100 as shown below.

How is the air content of concrete measured?

Concrete Air Meters yield fast and accurate results using a method that is easy to run in the field. After proper placement of concrete in the bowl of the meter, air content is measured by pressurizing the upper chamber and releasing the volume of air into the lower chamber.

How does aggregate correction factor affect air content?

Field testing on this concrete without the use of the aggregate correction factor shows an air content reading of 4.0%, and the concrete is reported as meeting specifications. However, in reality this concrete may or may not meet specifications because even a very small correction factor would result in this concrete having a lower air content.

Why does fresh concrete have air in it?

In fresh concrete, the air bubbles reduce the water demand of the concrete and make the mix stickier, which helps to reduce segregation and reduces bleeding when air content is around 3%. If the air content is higher, the increased stickiness makes the concrete more difficult to finish,…

When to use rollermeter to test air content in concrete?

This method is only used for regular weight concrete that has relatively dense aggregate. Lightweight concrete is typically done with the volumetric method (the infamous rollermeter) because the aggregate is too porous and the test results will be thrown off with so much entrapped air.