What is a air entrainment test?
What is a air entrainment test?
Concrete air entrainment testing is typically performed on plastic, or fresh, concrete. Pressure method ASTM C 231 is the preferred test for determining air void spacing and volume in concrete. In order to perform the pressure test, you will need an air entrainment meter capable of performing Type B or SAM tests.
How is air entrained in concrete measured?
Petrographic testing on hardened concrete uses a microscope to count and measure the size of the air bubbles. With proper magnification, even very small bubbles are counted. The test also provides a measure of the average bubble size called the specific surface.
What is a good air content for concrete?
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.
Why air content test is done?
This test’s purpose is to get the air content of a sample of concrete using a pressure meter. In the meter you have a known volume of air at a known pressure in a sealed air pot with an unknown volume of air being contained inside the sample of wet concrete.
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 petrographic analysis of concrete?
Petrographic Testing (ASTM C856) is a method that uses microscopes to examine the mineralogical and chemical characteristics of concrete and minerals. Each of these characteristics gives the engineer a sense of what is going on with the concrete and its physical properties.
How do you calculate air content?
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. 151.7 lbs/cu. ft.
When performing an air test on concrete you are measuring?
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. The pressure is then released and the water level rises. The difference in the two levels is the apparent air content.
What does air entrainment do for concrete?
Air-Entraining Admixtures and What They Do: Air-entraining admixtures facilitate the development of a system of microscopic air bubbles within concrete during mixing. They increase the freeze-thaw durability of concrete, increase resistance to scaling caused by deicing chemicals, and improve workability.
What causes high air content in concrete?
Air content rises rapidly at mixing speed, then plateaus or decreases slightly at agitating speed. Big swings in air content can be caused by changes in concrete materials, proportions, batching sequence, or mixing methods.