What is air entrained concrete?
What is Air Entrained Concrete? Air entrained concrete contains microscopic air bubbles that help alleviate internal pressure on the concrete by providing small pockets for water to expand into when exposed to freeze-thaw conditions.
What is the difference between entrapped air and entrained air in concrete?
It is important to note that entrained air is not the same as entrapped air. Entrapped air is created during improper mixing, consolidating and placement of the concrete. Entrained air is intentionally created by adding a liquid admixture specifically designed for this purpose.
What causes entrapped air in concrete?
Concrete always contains air bubbles. During concrete mixing and placement, these bubbles are first formed, then ruptured, merged, and floated out of the mix. But once the concrete has hardened, the bubbles that remain are fixed in place forming the air-void system in hardened concrete.
What is entrainment air flow?
Air entrainment, or free-surface aeration, is defined as the entrainment/entrapment of un-dissolved air bubbles and air pockets that are carried away within the flowing fluid. The resulting air–water mixture consists of both air packets within water and water droplets surrounded by air.
What is natural air in concrete?
Air entrained concrete contains millions of minute air bubbles that are distributed uniformly throughout the paste fraction of the mix. These bubbles must have a certain size and distribution to be effective. Natural or entrapped air bubbles are too large and spaced irregularly to be of any benefit.
Where does fly ash come from?
Where does fly ash come from? Fly ash is produced by coal-fired electric and steam generating plants. Typically, coal is pulverized and blown with air into the boiler’s combustion chamber where it immediately ignites, generating heat and producing a molten mineral residue.
How do you reduce entrapped air in concrete?
Hot concrete temperatures may reduce air content by 25%, while cool concrete temperatures less than 75 degrees Fahrenheit can increase air content up to 40%. Increasing the use of fly ash with high carbon content will decrease the amount of entrained air.
What is Pozzolana cement for?
PPC is special blended cement useful in general construction work and is especially suitable for applications in aggressive environmental conditions. It can be confidently employed in construction of hydraulic structures, marine works, mass concreting such as dams, dykes, retaining walls foundations and sewage pipes.
What is the difference between Portland and pozzolanic cement?
Portland Pozzolana Cement is a variation of Ordinary Portland Cement. Pozzolana materials namely fly ash, volcanic ash, are added to the OPC so that it becomes PPC. PPC is cheaper than OPC. PPC has low initial setting strength compared to OPC but hardens over a period of time with proper curing.