What is the meaning of air entrainment?
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.
Why is air entrained concrete used?
The primary use of air-entraining concrete is for freeze-thaw resistance. The air voids provide pressure relief sites during a freeze event, allowing the water inside the concrete to freeze without inducing large internal stresses.
What is the difference between air entrained and non air entrained concrete?
The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. The water content for an air-entrained mix will be 3 to 5 gallons per cubic yard less than for a non-air-entrained mix having the same slump.
What are some causes of entrained air?
Improper addition of make-up fluid — Air may be entrained in the fluid if splashing occurs when fluid is added, or if the added fluid causes increased agitation in the reservoir. Contamination — One common source of increased air entrainment and foaming is fluid contamination by surface-active compounds.
What is Portland cement entraining?
Air-entrained portland cement is a special cement which has air bubbles introduced in the cement or concrete that provides the space for expansion of minute droplets of waters in the concrete due to freezing and thawing and protects from cracks and damage of concrete.
What is the difference between air entrainment and air entrapment?
When the bubbles are smaller than 0.04 inch, the air is called entrained; larger, and it’s called entrapped. Entrapped air voids are usually irregular in shape while smaller entrained air bubbles are spherical. Air-entraining admixtures stabilize bubbles at a smaller size.
What is meant by admixture?
An admixture is defined as “a material other than water, aggregates, cementitious materials, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing” (ACI Committee 212, 2010).
What is Colour cement?
Coloured cements are made by grinding 5 to 10 percent of suitable pigments with white or ordinary gray portland cement. Air-entraining cements are made by the addition on grinding of a small amount, about 0.05 percent, of an organic agent that causes the entrainment of…
Do you vibrate air entrained concrete?
Don’t Worry About Over Vibrating Air-entrained concrete is produced by adding air-entraining admixtures during batching and the microscopic size bubbles form during mixing. Therefore, workers should vibrate between 5 and 15 seconds to ensure the second phase of consolidation or de-aeration is achieved.
How do you remove entrained air from water?
The most common short-term solution to air problems is to add a chemical defoamer product. A wide variety of chemical formulations has been found to be effective to promote coalescence of air bubbles within papermaking stock and white water or to break bubbles at the surface of water.
What is an air entraining admixture?
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 is superplasticizer in concrete?
Superplasticizers (SP’s), also known as high range water reducers, are additives used in making high strength concrete. Plasticizers are chemical compounds that enable the production of concrete with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more.