revealing the cause for high air content in concrete

Revealing the cause for high air content in concrete

Revealing the cause for high air content in concrete 19 September 2017 A study carried out in Aalto University showed that the effectiveness of the mixing process has ...

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Revealing the cause for high air content in concrete

Sep 19, 2017  It was found out that one significant cause of the strength problems was increased air content in the concrete. In order to improve frost resistance, the air content of concrete is increased to...

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The effect of air content on concrete strength

How does air content affect strength? A. Intentionally entrained air voids improve the resistance of concrete to damage from cycles of freezing and thawing. Any air voids reduce the strength of concrete, with about a 5% reduction in strength for each 1% increase in the volume of air voids.

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Causes for Air Content Fluctuations Concrete Construction ...

Jan 01, 1993  Air entraining agents form air bubbles by a frothing action. The wetter the concrete, the more frothing action you get. So up to a point, the higher the slump, the higher the air content. If the concrete gets too sloppy, however, some air may be lost. Adding 10 gallons of water to 7 yards of concrete probably increased the air content slightly.

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What Factors Affects Air Content of Concrete? - The ...

Jun 05, 2018  5. Effects of Mixing Action on Air Content of Concrete Air content increase by mixing for up to 15 minutes and mixing beyond this time will decrease air content. Entrained air will vary with type, physical condition, speed of the mixer and quantity of concrete that is being mixed.

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Factors Which May Influence Air Content

Pumping Concrete – May result in air content reductions of 2%-3% at the discharge end of the pump boom. Higher air losses usually are the result of boom configuration causing free fall of the concrete and will sometimes actually create a vacuum in the pump boom.

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high air entrainment - Structural engineering general ...

Mar 11, 2010  Air content up to about 6 percent helps with freeze-thaw resistance. When the air content goes much higher, the permeability is affected, thus creating more problems with freeze-thaw than lower air content. Further, scaling might be a problem as the finishing process might have trapped more air just below the surface.

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What Factors Affects Air Content of Concrete? - The ...

5. Effects of Mixing Action on Air Content of Concrete Air content increase by mixing for up to 15 minutes and mixing beyond this time will decrease air content. Entrained air will vary with type, physical condition, speed of the mixer and quantity of concrete that is being mixed.

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Effects of Too Much Air Concrete Construction Magazine

Oct 01, 1999  But if the air content exceeds the maximum by a percent or two, how does that affect the concrete? A.: Strength loss is the major effect of too much air. Each percent increase in air content can reduce compressive strength by 2% to 6% for moderate-strength concrete. The degree of strength loss depends on the cement, admixtures, and other ...

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Volume 19/Number 1 Control of Air Content in Concrete ...

Control of Air Content in Concrete Air-Void Analyzer Figure 1. Freeze-thaw deterioration of non-air-entrained concrete railing. (S44517) Control of Air Content in Concrete New manual provides concrete producers and users with tips on achieving and controlling air in concrete. Air entrainment is a necessary com-ponent of concrete mixtures exposed

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High slump and air entrainment in exterior concrete ...

Jul 31, 2008  The high air content might cause finishing problems by creating blisters in the top surface layers of the slab. When troweling occurs, the dragging force and the vibration of the equipment compels the air to rise to the surface at the same time that the equipment is denisfying the top layers, prohibiting the air from getting out.

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Comparison of Air Contents in Fresh and Hardened Concretes ...

that for air-entrained concrete, the air content of hardened con- crete can be 0.5 to 1.1% smaller than a 5.1% air volume mea- sured with a pressure airmeter on fresh concrete.

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Revealing the Mystery of Admixtures

May 29, 2010  Table 3 presents some minimum limits for key parameters. Note that concrete must have an air content of at least 3 percent to be classified as air-entrained; however, this is typically too low for protection against freezing and thawing. Freeze-thaw durable concrete typically contains a total air content of between 5 percent and 7 percent.

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Revealing the thermal environmental quality of the high ...

Sep 15, 2018  On the other hand, under a cloudy sky, air temperatures in a warm day stay around 20 °C. In typical cooler days air temperatures can go as high as 24 °C, or slightly higher, due to the impact of solar radiation, whereas in a cooler cloudy day, air temperatures hardly get above 15 °C. 4. Method

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Effect of W/C Ratio on Durability and Porosity in Cement ...

Apr 15, 2014  Water is often added to concrete placing for easy workability and finishability in construction site. The additional mixing water can help easy mixing and workability but causes increased porosity, which yields degradation of durability and structural performances. In this paper, cement mortar samples with 0.45 of W/C (water to cement) ratio are prepared for control case and durability ...

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Science to reveal how long highway construction should ...

Aug 29, 2019  "Concrete pavement patching has to achieve a certain strength level to accommodate truck traffic due to the load and pavement curling and warping. ... Revealing the cause for high air content in concrete. Sep 19, 2017. Soybean oil driving technology to improve roadways ... inaccuracy or would like to send an edit request for the content on this ...

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Vibration Study of Consolidation of Portland Cement Concrete

American Concrete Institute (ACI), tends to have an entrapped air content of 5 to 20 percent ( 4). Consolidation by vibration attempts to remove the entrapped air. When plastic concrete is vibrated, it passes through two stages. The first stage is the slumping of the concrete. The harmonic vibration causes the particles to behave as a near liquid.

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Slab Surface Prevention Repair - concrete is better

attribute blistering to three principal causes: 1. An excess amount of entrapped air held within the concrete by a high percentage of material passing the 600 μm, 300 μm, and 150 μm (No. 30, 50, and 100) sieves, resulting in a sticky or tacky concrete that can become more easily sealed when floating or finishing it at any early age. Sticky

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Factors Affecting Air Entrainment

(100°F) may reduce air content by 25% while reductions from 21°C (70°F) to 5°C (40°F) may increase air content by as much as 40%. Concrete Mixer • The amount of air entrained by any given mixer (stationary, paving, transit) will decrease as the blades become worn. • Air content will increase if the mixer is loaded to less than capacity ...

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Why Do Buildings Fall Down? – Bali Advertiser

Probably the greatest risk for reinforced concrete is the penetration of salt laden air or water into the concrete which causes the reinforcing bar in the concrete to corrode. ... It can also lead to spalling where small pieces break out of the surface revealing the reinforcing bar beneath. ... the air has a high salt content. This effect can ...

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Moisture in basements: causes and solutions UMN Extension

In fact, if a dehumidifier is used in a basement with moisture problems, it may cause greater damage. By drying out the basement air, moisture is drawn into the basement more rapidly causing efflorescence and spalling of concrete and further damage to interior finishes. Interior membrane or

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Air entrainment and concrete - USDA

imum air content usually called for is 6 percent. In specifications air content is generally stated as a give n f i g u r e plus or minus a certain per-c e n t a g e, quite commonly 11⁄ 2 p e r - cent. It is not feasible to hold the p e r centage constant from batch to batch because air content is

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Loss of Air Content in Pumped Concrete — What, why, how ...

High air content concrete with low strength could, or almost surely will, be placed in the structure if boom angles are reduced or if somewhat lower slump concrete is pumped. Research has indicated that when the loss of air content is not too high (less than about 3%), the air void system in the concrete may still be adequate for freeze-thaw ...

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Revealing the Mystery of Admixtures

May 29, 2010  Table 3 presents some minimum limits for key parameters. Note that concrete must have an air content of at least 3 percent to be classified as air-entrained; however, this is typically too low for protection against freezing and thawing. Freeze-thaw durable concrete typically contains a total air content of between 5 percent and 7 percent.

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Air Entrainment versus Air Entrapment - NPCA

Dec 20, 2012  The recommended air content varies with the severity of exposure and aggregate size. For instance, 3/8-in. aggregate with a severe exposure (frequent freeze-thaw cycles) requires 7.5% air content, while the same aggregate with moderate exposure requires 6% air content. A 1-in. aggregate requires 6% for severe exposure and 4.5% for moderate ...

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Low Concrete Cylinder Strength — What, why, how ...

High air content can also be a cause of low strength. ... Look at the slump, air content, concrete and ambient temperatures, number of days cylinders were left in the field, procedures used for initial curing in the field and subsequent curing in the lab and any reported cylinder defects.

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Admixtures for Concrete - Memphis

reduced. For concretes of equal cement content, air content, and slump, the 28-day strength of a water-reduced concrete containing a water reducer can be 10% to 25% greater than concrete without the admixture. Despite re-duction in water content, water-reducing admixtures may cause increases in drying shrinkage. Usually the effect of

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Factors Affecting Strength of Concrete - The Constructor

Compaction of concrete Any entrapped air resulting from inadequate compaction of the plastic concrete will lead to a reduction in strength. If there was 10% trapped air in the concrete, the strength will fall down in the range of 30 to 40%. Temperature The rate of hydration reaction is temperature dependent.

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Moisture In Concrete - force

Apr 11, 2018  Discussion of effects of moisture on concrete slabs. Capillary Action: A capillary is a small, hollow tube which allows moisture to travel from a lower to a higher level.The force which causes a capillary movement is the result of tension on the surface of

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DEPARTMENT OF HIGHWAYS

If a specimen of concrete absorbs 10 percent water by volume and if this amount of water completely fills the voids in the concrete , the increase in volume of the specimen, upon freezing, would be approxi-mately 0,9 percent, This amount of dilation would, in all likelihood, cause the concrete to rupture, Laboratory tests have demonstrated

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"Glascrete" - Concrete with glass aggregate

The problem with the use of glass powder is its high content of ... of natural concrete components can cause environmental degradation. ... durability of concrete. The air content of concrete ...

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What Is Honeycomb In Concrete Cause of Honeycomb In ...

In setting steel spacing, both the designer and the builder should keep in mind that the concrete must be consoled.. Honeycomb is a void left in concrete due to the failure of the mortar to effectively fill the spaces among coarse aggregate particles. Rock pockets are generally severe conditions of honey-comb where an excessive volume of aggregate is found.

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Why the Towers Fell: Two Theories

The prevailing theory. The prevailing theory for the collapse of the 110-story, award-winning Twin Towers is that when jetliners flew into the 95th and 80th floors of the North and South Towers respectively, they severed several of each building’s columns and weakened other columns with the burning of jet fuel/kerosene (and office combustibles).

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What Are Safe Moisture Levels in Walls?

So, knowing the relative humidity (RH) conditions is a must when trying to determine what a “safe” moisture content for wood walls is. For example, if the temperature in the room is around 80 degrees Fahrenheit, and the RH is 50%, then a “safe” level of moisture in the wall would be about 9.1% MC.

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Concrete, The Article about Concrete, The by The Free ...

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased. Concrete, The unity in diversity, the universal in the particular; the real link between the aspects and facets of an object and knowledge of the object in the full richness of its essential relations, interactions, and contradictions. The ...

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