What is the difference between entrapped air and entrained air?
Entrapped Air: The air content of concrete is made up of entrained and entrapped air voids. Entrained air refers to microscopic air bubbles intentionally incorporated into concrete during mixing, usually by use of a surface-active agent.
Is air entrained concrete stronger?
Concrete with entrained air will have a lower strength than the same mix without entrained air, but the concrete can attain strengths required for most purposes by an increase in the cementitious factor of the mix or by reducing the water content.
Does adding water to concrete increase air content?
A.: Adding water at the jobsite increases both slump and air content. The rule of thumb for slump is that 1 gallon of water added to a cubic yard of concrete increases slump by 1 inch. Air entraining agents form air bubbles by a frothing action. The wetter the concrete, the more frothing action you get.
Where do you use air-entrained concrete?
It is beneficial to use air entrained concrete when placing concrete in areas with freeze-thaw conditions. Freeze-thaw conditions occur when the temperature of an environment fluctuates between above freezing temperatures and below freezing temperatures.
What is meant by entrained air?
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 are the two main benefits of air entrained concrete?
Air entrainment reduces the overall density of the concrete mixture and also increases the yield derived from the mix. There is an improvement in the concrete’s level of deicer-scaling resistance. There is an improvement in their general resistance to sulphate attacks.
How do you prevent bubbles in concrete?
Lower the viscosity of cement by adding sand or fly ash. This allows large aggregate to move more freely and reduces the amount of air entrapment. Use aggregate that is more uniform in shape. Irregular shaped pieces of aggregate tend to make the concrete less fluid.
How do you reduce air in 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.
How is air entrainment done?
Air entrainment: Air entrainment is an effective way of protecting concrete from freezing and thawing damage. It is achieved by adding a surface active agent in very small dosages to the concrete mixture. This action creates a large number of small, closely spaced air bubbles in the hardened concrete.
What is entrainment in oxygen?
The venturi mask, also known as an air-entrainment mask, is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy. The mask was invented by Moran Campbell at McMaster University Medical School as a replacement for intermittent oxygen treatment.
Why would an engineer specify an air entrained concrete?
Air entrainment makes concrete more workable during placement, and increases its durability when hardened, particularly in climates subject to freeze-thaw cycles.
Can you trowel air entrained concrete?
Because of the danger of scaling or blistering, troweling of air-entrained exterior flatwork is not recommended. Don’t hard trowel air-entrained concrete surfaces that will be exposed to freezing and thawing, deicing agents or both.
Can you trowel air-entrained concrete?
Can you vibrate air-entrained concrete?
Don’t Worry About Over Vibrating Entrained air bubbles are considerably smaller in size than entrapped air bubbles. Workers commonly under vibrate concrete from fear that over vibration may reduce the entrained air content or damage the microscopic air void system decreasing the freeze/thaw resistance of the concrete.
What is the best book on stability of particle stabilized bubbles?
Google Scholar Du, Z., Bilbao-Montoya, M. P., Binks, B. P., Dickinson, E., Ettelaie, R. and Murray, B. S., Outstanding Stability of Particle Stabilized Bubbles, Langmuir, 19, 3106–3108, 2003. Google Scholar (58) Baetes, P. J. M., Foam Films Drawn from Dispersions, Eindhoven University of Tech, Eindhoven, Netherlands, 1993.
How do hydrophobic particles act as stabilizing agents?
Partially hydrophobic small particles have the potential to act as stabilizing agents in many foaming processes, and they behave fairly similar in some ways to chemical surfactant molecules in that they can adsorb (attach) at the bubble interface. However, particles show several distinct differences from chemical surfactants.
Can particles act as stabilizers in industrial foaming?
For a considerable period of time it has been well known that particles acted as stabilizers in many established industrial foaming processes, such as froth flotation of mineral particles (1), deinking flotation (2) and food processing (3).