5 rows · Concrete Pumping Effects on Entrained Air-Voids. Author. William Elkey, Donald J.
The air entrained of concrete mixes alone results in a loss of strength in the range of 5-17% and is dependent on the content of the superplasticizer, the consistency of the concrete mix, changes
Queries on Concrete, Concrete International, August 1992, p. 71. 5. "Effects of Pumping Air Entrained Concrete," Washington Ag-gregates and Concrete Association, March 20, 1991, 12 pp. 6. Dyer, R.M., "An Investigation of Concrete Pumping Pressure and the Effects on the Air Void System of Concrete…
Road research Laboratory U.K, it is found that 5% air entrainment increases the compacting factor by 0.07, which would be equal to an increase in slump from 1.2 cm to 5.0 cms. 3. Effect on Strength of Concrete: Generally it can be said that air entrainment in concrete reduces the compressive strength of concrete.
"Entrapped air" is air that is naturally entrapped in all concrete, occurring without the use of an air entraining agent. These bubbles/voids are larger than entrained air and contribute nothing to durability. Entrapped air is also unstable and can be lost during mixing or certain placement operations, i.e. pumping, vibration. Depending on the
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The most effective method to protect concrete from F-T damage is through the addition of an air entraining agent as an admixture that creates a well distributed, closely spaced, small sized air void system in the concrete. Air content measurement in fresh concrete is a routine quality control and acceptance test procedure that helps to ensure
Dec 20, 2012 · 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. Air pockets, or irregularly sized air voids, are spread throughout the concrete and have negative effects on product appearance, strength and durability.
When Pumping Air-Entrained Concrete 1 of 3 Things Happen: bubbles when you pump. •Air void system in the fresh concrete changed due to pumping with these •Pumping effects: •Slump •Segregation •Air. Pumping Changes The Concrete 5" Slump Before the Pump After the Pump
The influence of air void parameters on the workability and rheology of concrete was then discussed. In the hardened state, the effect of air entrainment on compressive strength, freeze-thaw resistance, and fire resistance was illustrated. Moreover, the effect of binder, chemical admixture, mixing time, vibration, pumping, temperature, and low
The effect of percent of air voids, based on the experimental results will be limited on the 6 %, because after that the class of concrete will be changed rapidly.
Jul 12, 2010 · Uses and effects of air entrainment. Air entrainment is the process where many small air bubbles are distibuted into concrete and become part of the matrix that binds the aggregate together in the hardened concrete. These air bubbles are dispersed throughout the hardened cement paste but are not, by definition, part of the paste (Dolch 1984).
INFLUENCE OF PUMPING ON CHARACTERISTICS OF AIR-VOID SYSTEM OF HIGH-PERFORMANCE CONCRETE. The results of an experimental study in which a high-performance air-entrained concrete mixture (water-cement ratio = 0.29; 28-day average compressive strength of 75 MPa) was pumped at the job site horizontally and vertically are presented.
Sep 01, 1995 · A 1994 study examined the effects of concrete handling methods on normal air-entrained concrete. Concrete for a large parking lot and driveway project was placed by pump, crane and bucket, truck-mounted conveyer, and directly from the chutes of ready mix trucks. The primary goal of the test program was to determine how air content, air-void system parameters, and freeze-thaw durability of air
"Effects of Pumping Air Entrained Concrete," Washington Aggregates and Concrete Association, March 20, 1991, 12 pp. Dyer, R.M., "An Investigation of Concrete Pumping Pressure and the Effects on the Air Void System of Concrete," Master's Thesis, Department of Civil Engineering, University of Washington, Seattle, Washington, 1991.
Re-tempering with water does not usually affect the air void system but can on rare occasions result in a phenomenon called air void clustering which causes the air bubbles to cluster around the coarse aggregates causing the concrete to be structurally weaker. Re-tempering with air entrainment will restore the air void system. Higher
Question: How does air cause surface voids on my finished concrete casting? Answer: In most circumstances, air voids have an irregular shape and tend to be much larger (1/2" or 1.27 cm.) than those caused by water or release agents. The air voids are caused by air trapped between the mold surface and the concrete.
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Jul 18, 2021 · About 3 to 5 per cent air by volume of the concrete is the best amount for pumping. Too much air, over 7 to 8 per cent, can decrease pumping efficiency by absorbing some pump stroke energy as the air compress and reduce the strength of the concrete by creating porosity in concrete.
Jul 02, 1994 · The actual effect of pumping on the air content measured for the concrete is not consistent; in some cases air content has increased, while in others it has decreased. Previous work has shown that pumping causes pressure in the concrete, and this pressure can alter the air-void system.
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