What is air entrained concrete?

Asked By: Marcene Lazpiur | Last Updated: 10th May, 2020
Category: business and finance construction industry
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Air entrainment is the intentional creation of tiny air bubbles in concrete. A concrete maker introduces the bubbles by adding to the mix an air entraining agent, a surfactant (surface-active substance, a type of chemical that includes detergents).

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Moreover, where 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. Another related use is for deicer-scaling resistance.

One may also ask, how does air entrainment 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. When workability of concrete increases, its compressive strength decreases.

Beside this, 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.

Why is air content in concrete important?

AIR CONTENT AND DURABILITY Entrained air greatly improves the resistance of concrete to damage resulting from freezing and thawing cycles. Microscopic air bubbles produced by admixtures called air-entraining agents relieve pressures caused by water freezing in the small voids present in hardened cement paste.

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Can you trowel air entrained concrete?

to hard-trowel air-entrained con- crete. The risks associated with this requirement include: ACI 302.1R-96, “Guide for Concrete Floor and Slab Construction,” states that entrained air is not recommended for concrete to be given a smooth, dense, hard-troweled finish.

Is all concrete air entrained?

Air entraining was introduced in the 1930s and most modern concrete, especially if subjected to freezing temperatures, is air-entrained. The bubbles contribute to workability by acting as a sort of lubricant for all the aggregates and large particles in a concrete mix.

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.

What does troweling concrete do?

Trowels. Troweling produces a hard, smooth, dense surface and should be done immediately after floating. Troweling can be done by machine or by hand. Putting a long handle on the trowel allows finishers to trowel the concrete without walking out onto the slab.

How do you reduce air voids in concrete?

Use aggregate that is more uniform in shape. Irregular shaped pieces of aggregate tend to make the concrete less fluid. Techniques used during vibration can eliminate most surface voids. Vibrating both the outside and inside of your mold will draw most air and water bubbles away from the surface of the concrete.

How is concrete tested for strength?

Compressive strength is measured by breaking cylindrical concrete specimens in a compression-testing machine. Compressive strength is calculated from the failure load divided by the cross-sectional area resisting the load and reported in units of pound-force per square inch (psi) or megapascals (MPa).

How many types of concrete are there?

Typically, there are twenty-four different types of concrete used in the building and construction industry depending on the type of construction.

Is concrete porous?

Concrete is inherently porous, although a sealer can be added to the concrete surface to prevent water penetration. It's practically impossible to make an absolutely nonporous concrete where water won't penetrate even a fraction of an inch.

Should air entrained concrete be vibrated?

Entrapped air is not beneficial to the concrete and should not be confused with entrained air, which helps concrete durability in climates with freeze-thaw and is created with an air entraining admixture.

What is lightweight structural concrete?

Structural lightweight concrete has an in-place density (unit weight) on the order of 90 to 115 lb/ ft3 (1440 to 1840 kg/m3) compared to normalweight concrete with a density in the range of 140 to 150 lb/ ft3 (2240 to 2400 kg/m3). The concrete mixture is made with a lightweight coarse aggregate.

Why are air entraining agents used in concrete?

Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The benefits of entraining air in the concrete include increased resistance to freeze-thaw degradation, increased cohesion (resulting in less bleed and segregation) and improved compaction in low-workability mixes.

How do you measure air entrainment in concrete?

When you measure air in concrete, the percentage reading represents the total amount of air—entrapped and entrained air. For example, if the reading on an air meter is 6% air, it means that approximately 1.5% of the total is entrapped air and 4.5% is entrained air.

How do you harden concrete trowel?

Trowel the surface
Smooth the surface with a steel trowel after it's partially hardened. Hold the trowel almost flat and swing it in large overlapping arcs while applying pressure. Float the concrete when you're done grooving and edging (Photo 6).

What is the admixture?

Admixture is defined as a material other than cement, aggregate and water used as an ingredient of concrete, added to the batch immediately before or during mixing, to modify the properties of ordinary concrete to make it more suitable for required situation.

What is consolidation of concrete?

Consolidation of Concrete. Definition: the process of reducing the volume of voids, air pockets, and entrapped air in a fresh cementitious mixture, usually accomplished by inputting mechanical energy.- ACI Concrete Terminology.

What is air entrainment medical?

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.

Does slump affect concrete strength?

"Wetness" of concrete as measured by the slump test is directly related to its compressive strength - the 28 day compressive strength of concrete is reduced by about 1.5 MPa for each additional 20mm of slump produced by adding water.