For an air-entrained concrete, air content measurements are reported in the mixture design submittal, and air content is measured in the field to ensure compliance. The entrapped air that remains in the mix creates an air void. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. For given water content, workability decreases if the concrete aggregates contain an excess of, a. Lime : Silica : Alumina : Iron oxide : 63 : 22 : 6 : 3, b. Silica : Lime : Alumina : Iron oxide : 63 : 22 : 6 : 3, c. Alumina : Silica : Lime : Iron oxide : 63 : 22 : 6 : 3, d. Iron oxide : Alumina : Silica : Lime : 63 : 22 : 6 : 3, 32. As much as 50% of entrained air may be lost after 3 minutes of vibration. Workability of concrete increases. The mechanism of entraining concrete with air is presented to focus on the instability of the air bubbles while concrete is in a fresh state in terms of the effect of the pumping operation and the air bubble system. The main benefit of small air bubbles within the mix is they increase the concrete’s resistance to freeze-thaw cycles. As for the mix, it should be designed to take account for the increase in air content. Another related use is for deicer-scaling resistance. 4. The process of mixing, transporting, placing and compacting concrete using Ordinary Port land Cement should not take more than, A. 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. n a low-density type of concrete throughout which small air bubbles are dispersed in order to increase its frost resistance: used for making roads. He is now asking that the entire slab be removed and replaced a day later? Margi Eglinton, in Lea's Chemistry of Cement and Concrete (Fourth Edition), 1998. The air entrained concrete has increased the workability of concrete without increase the water-cement ratio. 40 minutesC. Vibration • Excessive vibration will reduce air content. 20 cm, 10 cm, 30 cmd. By and large, the compressive strength of concrete is reduced by use of air entrained admixture, as shown in Fig. 13.The removal of excess air after placing concrete helps in increasing the strength of concrete by (a)15 to 20%Ans) (b)20 to 30% (c)30 to 50% (d)50 to 70%. 20 cm, 30 cm, 10 cm, 66. Reduced bleeding and segregation and reduction of water cement ratio reduces the overall permeability of the concrete. It is highly used as an insulator to the exterior wall of all types of buildings. An aggregate is said to be flaky if its least dimension is less than, 26. The paper presents compressive strength test results of several high performance concrete mixtures with total air contents ranging from two to six percent. After mixing, air can be lost during transport and pumping. between 350 to 600 kg/cm2C. (1)and(4) C. ((2)and (3) D. (3)and (4) Mcq Added by: Muhammad Bilal Khattak. Air Entrained Concrete. 1 : 1 : 2, 69. 1. better workability 2. better resistance to freezing and thawing 3. lesser workability 4. less resistance to freezing and thawing The correct answer is: A. WHERE TO APPLY All of the positive properties of air-entrained concrete are best utilized in dams, bridges, tunnels and road construction in countries with harsh winters-such as USA, Canada, Finland, Estonia, Iceland, Greenland, Mongolia, Russia, Kazakhstan and many others. These voids are stabilized by the air-entraining admixture and … a. has strength less than 10% to 15% b. has more resistance to weathering c. is more plastic and workable d. is free from segregation and bleeding. for the mcq The entrained concrete is used in lining walls and roofs for making Air voids, however, also improve the workability of concrete. Its unit weight is less than air-entrained concrete. Written by Saad Iqbal. sodium chloridesc. The cement concrete prepared by mixing aluminium in it , is called (a)Air entrained concrete (b)Cellular concrete (c)Aerated concrete (d)Any one of these(Ans) 15. silicad. The process of hardening the concrete by keeping its surface moist is known, 77. Advantages. iron oxidec. Air entraining chemical component creates bubbles of air in concrete mixture. Percentage of pozzolanic material containing clay upto 80% used for the manufacture of pozzolana cement, is. Air entrained concrete is found to be more resistant for alkali-aggregate reaction. Q: How does hard-troweled air-entrainment impact strong concrete? 1 : 1: 2D. plastic, 42. However, if the owner decides to use air-entrained concrete, and the slab delaminates, the cost burden shifts to the contractor. [Neither (A) Nor (B)] [BOth (A) and (B).] Air-entrained concrete is produced using air-entraining portland cement, or by the introduction of air-entraining agents, under careful engineering supervision, as the concrete is … If aggregates completely pass through a sieve of size 75 mm and are retained on a sieve of size 60 mm, the particular aggregate will be flaky if its minimum dimension is less than, 58. Correct Answer. The mixture of different ingredients of cement, is burnt at, b. larger proportion of maximum size aggregate, 13. 14.The cement concrete prepared by mixing aluminium in it , is called (a)Air entrained concrete (b)Cellular concrete (c)Aerated concrete (d)Any one of these(Ans) Unit-8 Modern Trends and Research Development in Concrete Technology. Question is ⇒ While designing an air entrained concrete., Options are ⇒ (A) water cement ratio is reduced, (B) proportion of aggregates is reduced, (C) an allowance for the entrained air is made, (D) all the above., (E) , Leave your comments or Download question paper. The main object of compaction of concrete, is: c. To provide intimate contact between concrete and embedded materials, 21. 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). Any thoughts? none of these, 64. both A and B of the above, 61. Ease with which it can be mixed, transported and placed in position in a homogeneous state. The top diameter, bottom diameter and the height of a slump mould are : a. medium sandD. 7. Efflorescence im cement is caused dim to an excess of, a. aluminab. Air-entrained 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. The ratio of the length to breadth of a wooden float, is, 27. 30% b. સિમેન્ટ કોંક્રિટ, જ્યાંથી અંદરની હવા અને વધારે પાણી ને દૂર કરવામાં આવે છે, તેને ________ કહેવામાં આવે છે? a. 7 people answered this MCQ question BOth (A) and (B). If you need to entrain air, as in concrete that will be exposed to cycles of freezing and thawing while wet, you do as little finishing as possible. 1: 3 : 6b. The high strength of rapid hardening cement at early stage, is due to its, a. finer grindingb. between 150 to 500 kg/cm2D. Lost your password? 30 minutesB. Air entrainment also reduces the shelf-life of concrete. Internal friction between the ingredients of concrete, is decreased by using, a. increases workabilityb. (d)Sawdust concrete. The workability of concrete is defined as the. civil engineering mcqs with answers on topic of concrete technology for interview, entrance test and competitive examination freely available to download for pdf export. To determine the modulus of rupture, the size of test specimen used is, 41. b) By using no fines concrete. The use of air-entraining agents in portland cement concrete shows considerable promise, particularly in highway concrete where resistance to scaling is an important factor. Rebar Couplers Vs Lapping Vs Welding – Which Is Best? Chemical Engineering. (1) and (2) B. For the construction of the retaining structures, the type of concrete mix to be used, is, a. Mechanical Engineering. Air-entrained concrete contains many microscopic air bubbles per cubic metre of concrete. As a result, the cured concrete is far more durable to freezing temperatures than non-air-entrained concrete. is free from segregation and bleeding, 54. below 200 kg/cm2, a. full capacity of the ware houseb. Proper amount of entrained air in concrete results in_____? For construction of structures in sea water, the cement generally preferred to, is, 18. prestressed concrete [D]. This natural air is known as entrapped air. Unit-6 Special Concrete & Concreting Techniques, 13. The diameter of the Vicat plunger is 10 mm and its length varies from, a. A: It’s pretty well known in the concrete industry that hard-troweled surfaces and air-entrained concrete don’t mix. 13. Finishing Air-Entrained Concrete Used in many applications, air-entrained concrete uses a chemical admixture (or sometimes, air-entraining cement) to produce a system of small voids during the mixing process. Cost for Air entrained concrete is rather inexpensive ( a couple of dollars per yard). 7 people answered this MCQ question BOth (A) and (B). The place-ability of an air entrained concrete having 7.5 cm slump was found better than a non-air entrained concrete having a slump of 12.5 cms. Flaky particles, 8. higher content of tricalcium, 51. to construct a massive dam, the type of cement you will use, is, a. ordinary Portland cementb. weight of concrete to that of waterd. In slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for, a. Vi b r ation time with air entrained mixes should be s h o r tened and kept reasonably con- … This rule of thumb was developed from research on normal strength concrete, but there is little data on the strength reduction due to entrained air in high performance concrete. These air bubbles increase the workability of the concrete and lower the water cement ratio. A concrete using an air entrained cement. The minimum percentage of chemical ingredient of cement is that of, a. magnesium oxideb. Lorem ipsum dolor sit amet, consectetur adipiscing elit.Morbi adipiscing gravdio, sit amet suscipit risus ultrices eu.Fusce viverra neque at purus laoreet consequa.Vivamus vulputate posuere nisl quis consequat. 1 : I: 3c. The American Concrete Institute. However, air content measurements are rarely specified for non-air-entrained concrete. has no effect on the strength of concreted. Please enter your email address. Air pockets, or irregularly sized air voids, are spread throughout the concrete and have negative effects on product appearance, strength and durability. Admixtures give high strength. For this reason, air-entrained concrete is typically restricted to outdoor applications exposed to freezing and thawing, and it is infrequently intended for indoor, protected structures. The standard sand now a days used in India, is obtained from, c. prevents the loss of water by evaporation, 24. air-entrained concrete synonyms, air-entrained concrete pronunciation, air-entrained concrete translation, English dictionary definition of air-entrained concrete. is the answer among Neither (A) Nor (B),BOth (A) and (B). For road pavements, the cement generally used, is, 16. The impurity of mixing water which affects the setting time and strength of concrete, is, a. sodium sulphatesb. Workability of concrete is directly proportional to, 14.For concreting of heavily reinforced sections without vibration, the workability of concrete expressed as compacting factor should be, 15. AIR ENTRAINED CONCRETE Air entrained concrete A major advance in concrete technology in recent years is the introduction of tiny disconnected air bubbles into concrete called air entrainment. light weight concrete [C]. 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For concreting tunnel linings, tranportation of concrete, isa of small air bubbles help to intimate... Specified for non-air-entrained concrete ( a ) and ( B ). drying... Than non-air-entrained concrete of tiny spherical shaped air bubbles help to provide the good of!: 45 by pumps, is known, 30 for given water content, workability if. Amount of entrained air to concrete provides important benefits in BOth specimen used is,.. Capillary channels from forming admixture, as shown in Fig voids,,. Aggregates ) in concrete mixture the weights of a concrete having a slump mould are: a, hydrates! Are measured as compared with control mixtures is found to be flaky if its is! B of the mix design countries to improve the frost resistance of concrete, is, finer...