The 28 days cube strength of mass concrete using aggregates of maximum size 5 cm for gravity dams should be, A. between 150 to 300 kg/cm2B. When the concrete is mixed, poured, and finished most of the entrapped air is worked out of the mix. 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%. While compacting the concrete by a mechanical vibrator, the slump should not exceed, 25. Although no air entraining agent is used in rubberized concrete mixtures, higher air contents are measured as compared with control mixtures. That’s because all those air voids provide pressure relief to the concrete … Types Of Grouting In Construction | Advantages & Application Of Grouting, Top Civil Engineering Project Topics For Final Year Students, How To Calculate Unit Weight Of Steel Bars. The separation of water or water-cement mixture from the freshly mixed concrete is known, 4. Tricalcium silicate (C3S) has more resistance to sulphate attack, a. hydrates rapidlyb. Benefits of Air Entrained Concrete. Thin particlesb. 1 :3 :6b. iron oxidec. 44. 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. Air entrainment is standard practice in many countries to improve the frost resistance of concrete. The strength and durability of concrete depends upon, 10. 10 cm, 20 cm, 30 cmb. 43. calcium chorides, a. volume of water to that of cementb. These air bubbles act as flexible ball bearings and modify the properties of plastic concrete (such as workability, segregation, bleeding and finishing quality. Air entrained concrete results from using either an air-entraining cement or an air-entraining admixture during mixing. Because of enhanced workability and uniformity of the concrete matrix, the pore structure of the concrete is modified. Define air-entrained concrete. Mechanical Engineering. Air entrained concrete consists of microscopic air bubbles in the concrete mixtures. MCQ Concrete Technology Edit Practice Test: Question Set - 09. Flat particlesc. MasterAir AE 90 air-entraining admixture is for use in concrete mixtures. Computer Engineering. 1. As a result, the cured concrete is far more durable to freezing temperatures than non-air-entrained concrete. below 200 kg/cm2, a. full capacity of the ware houseb. plastic, 42. By and large, the compressive strength of concrete is reduced by use of air entrained admixture, as shown in Fig. 1. generates less heat of hydrationc. If 1500 g of water is required to have a cement paste 1875 g of normal consistency, the percentage of water is, 6. 1 : 1 : 2, 69. Wp and Wf are the weights of a cylinder containing partially compacted and fully compacted concrete. For the construction of the retaining structures, the type of concrete mix to be used, is, a. The ratio of various ingredients (cement, sand, aggregates) in concrete of grade M 200, is, A. If the deptl-eof moist sand in a cylinder is 15 cr the depth of the sand when fully inundated with watel cm, the bulking of the moist sand, is, 70. 100 cm, 76. It is highly used as an insulator to the exterior wall of all types of buildings. a) By cellular construction. light weight concrete [C]. An aggregate is known as cyclopean aggregate if its size is more than, 57. 30 mm to 40 mmc. Elongated particlesd. However, the ACI Flatwork Finisher Certification program does not recommend troweling air-entrained concrete, as the formation of blisters and delaminations can occur even when troweled by the most experienced finishers. 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. If the slump of a concrete mix is 60 mm, its workability is, 67. For concreting tunnel linings, tranportation of concrete is done by, 75. What is Entrapped Air in Concrete? Air-entrained concrete used a chemical admixture to create bubbles (or voids) during the mixing process that exist throughout the concrete. 20 mm to 30 mmb. [Neither (A) Nor (B)] [BOth (A) and (B).] The entrained air in concrete (A) Increases workability (B) Decreases workability (C) Decreases resistance to weathering (D) Increases strength. 1 : 3 : 6C. Any thoughts? A concrete having a slump of 65 cm, is said to be, a. dryb. (1) and (2) B. 7 people answered this MCQ question BOth (A) and (B). To determine the modulus of rupture, the size of test specimen used is, 41. Various laboratory and field experiments conducted by others are examined and considered in … Pick up the correct proportions of chemical ingredients of cement, a. 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) Electrical Engineering. Admixtures make concrete water proofc. Air pockets, or irregularly sized air voids, are spread throughout the concrete and have negative effects on product appearance, strength and durability. Engineering :: Concrete Technology @ : Home > Civil Engineering > Concrete Technology : The cement concrete, from which entrained air and excess water are removed after placing it in position, is called [A]. aluminad. Terms* 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. ISI has specified the full strength of concrete after, a. increases the strength of concreteb. for the mcq The entrained concrete is used in lining walls and roofs for making These air-entrained agents in concrete generate millions of non-coalescing air bubbles, These air bubbles act as flexible ball bearings and will modify the properties of plastic concrete regarding workability , segregation, bleeding, and finishing quality of concrete. The need for fundamental research regarding the mechanism by which entrained air functions is suggested and methods of tests are out- lined. medium sandD. Unit-7 Prevention and Repair Technique of Cracks, 15. (i) and (ii) B. A: It’s pretty well known in the concrete industry that hard-troweled surfaces and air-entrained concrete don’t mix. Accordingly, vibration need not be prolonged. Air voids, however, also improve the workability of concrete. The pressure method is the most commonly used, and in this method a calibrated air meter is used to test a known volume of concrete that is subjected to a defined pressure. The risks associated with this requirement include: 1) increased probability of delamination or blistering; 2) reduction in surface air content; and 3) change in hardened air void parameters. It was first used in early 1930 especially in USA. The amount of entrained air then begins to slowly decrease due to the loss in slump of the concrete. નો ફાઈન કોન્ક્રીટ ______રીતે બનાવામાં આવે છે ? An aggregate is said to be flaky if its least dimension is less than, 26. for the mcq The entrained concrete is used in lining walls and roofs for making The process of proper and accurate measurement of concrete ingredients for uniformity of proportion, is known, 30. Periodically check batch sequencing to verify the proper order of material ingredients. Percentage of pozzolanic material containing clay upto 80% used for the manufacture of pozzolana cement, is, 55. Air content of the freshly mixed concrete can be measured by gravimetric, volumetric, or pressure methods. 40 nom to 50 mmd. The air entrained concrete is manufactured by introduction of any air entraining agents or using air entrained cement which is in turn manufactured by inter grinding air entraining agents to clinkers formed. Air entrained concrete is made by mixing a small quantity of air-entrained agent or using air-entrained cement. No fines concrete is manufactured by _____________. Proper amount of entrained air in concrete results in (i) Better workability (ii) Better resistance to freezing and thawing (iii) Lesser workability (iv) Less resistance to freezing and thawing. Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete … It is highly used as an insulator to the exterior wall of all types of buildings. 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. Air entrained concrete is made by just mixing a small amount of air-entraining admixture or by using air-entraining cement. 1 : 1 : 2, 71. 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). [Neither (A) Nor (B)] [BOth (A) and (B).] 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) The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. After casting, an ordinary cement concrete on drying, 22. Air entrainment reduces the density of the mix and increases yield. Concrete is unsuitable for compaction by a vibrator if it is. Ease with which it can be mixed, transported and placed in position in a homogeneous state. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Admixtures make concrete acid proofd. Up to now, various commercial air-entraining admixtures (AEAs) have had years of success that facilitate the air void system in concrete for improving FT resistance of concrete . that: “Concrete for slabs to receive a hard-troweled finish shall not contain an air-entraining admixture or have total air content greater than 3 percent.” “Guide to Concrete Floor and Slab Construction (ACI 302.1R-15)” provides the rationale behind this specifica-tion requirement in Section 8.4.7: “Air-entraining … Pick up the incorrect statement from the following : a. Tricalcium silicate (C3S) hydrates rapidlyb. vacuum concrete [B]. (d)Sawdust concrete. : 456, the number of grades of concrete mixes, is, 11. However it provides no different R value than standard concrete. Chemical Engineering. 4. 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. 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). air-entrained concrete synonyms, air-entrained concrete pronunciation, air-entrained concrete translation, English dictionary definition of air-entrained concrete. The high strength of rapid hardening cement at early stage, is due to its, 36. The process of mixing, transporting, placing and compacting concrete using Ordinary Port land Cement should not take more than, A. The Air-entraining is accomplished by an admixture added at the ready mix plant and improves concrete's durability in freezing conditions. 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 paper presents compressive strength test results of several high performance concrete mixtures with total air contents ranging from two to six percent. 1: 3 : 6b. Air entrained concrete is found to be more resistant for alkali-aggregate reaction. It is claimed that, the place-ability of an air entrained concrete having 7.5 cm slump is better than a non-air entrained concrete with a slump of 12.5 cm. provides less ultimate strength to cement, a. reacts fast with waterb. 1 : 2 : 4B. 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. For example, in the U.S., air entrained concrete specifications should be clearly written and comply with Chapter 19 of ACI 318R-14 (Building Code Requirements for Structural Concrete). c) By using lightweight aggregates such as expanded clay, shale and slate, fly ash, blast furnace slag etc. silicad. If a concrete slab does not meet the required air-entrainment, can the slab be rejected entiriely? 2. 60 minutesD. The ratio of the length to breadth of a wooden float, is, 27. is more plastic and workabled. 20. Real‐time measurement of air content in fresh, air‐entrained concrete 8 CY of nominal 4000 psi, air‐entrained (6%) concrete were batched from a stationary mixer into an Oshkosh front‐discharge ready‐mix truck with an 11 CY drum, fitted with a CiDRA, “SMARThatch” acoustic air meter. Concrete entrained air testing is a must for such concrete. Since air entrained concrete is m o r e cohesive and workable than non-air entrained, there is not as much danger of segregation and air p o c k e t s. Ac c o rd i n g l y, vibration need not be prolonged. a. 7.2.6 AIR ENTRAINMENT. Entrained air content increases in concrete mixtures with addition of waste tire-rubber particles (Fig. Lost your password? The impurity of mixing water which affects the setting time and strength of concrete, is, a. sodium sulphatesb. 75 minutes, 74. The mixture of different ingredients of cement, is burnt at, b. larger proportion of maximum size aggregate, 13. Do not let other admixtures come into contact with the air entrainment while it is being added to the load of concrete during the batching process. Correct Answer. 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. The amount of air can increase or decrease the strength of the concrete, can determine whether the concrete is protected from freeze-thaw conditions or is prone to weathering, and can affect the finish and cosmetic look of the concrete (if you spend months planning out a building, you want it to look good). weight of water to that of cementc. The top diameter, bottom diameter and the height of a slump mould are : a. The main object of compaction of concrete, is: c. To provide intimate contact between concrete and embedded materials, 21. 13. alkalis. The entrainment of air in fresh concrete improves its workability. Flaky particles, 8. 7. b) By using no fines concrete. The cement concrete, from which entrained air and excess water are removed after placing it in position, is called________. In slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for, a. The process of hardening the concrete by keeping its surface moist is known, 77. Rebar Couplers Vs Lapping Vs Welding – Which Is Best? The strength and durability of concrete depends upon, 2. (1)and(4) C. ((2)and (3) D. (3)and (4) Mcq Added by: Muhammad Bilal Khattak. Adding entrained air to concrete provides important benefits in both plastic… The standard sand now a days used in India, is obtained from, c. prevents the loss of water by evaporation, 24. Use of air entraining agent reduces the effect of freezing and thawing. fine sandC. The air bubbles help to provide the good workability of the concrete and reduce the slump value. 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. Answer=> c. 54. The cement concrete, from which entrained air and excess water are removed after placing it in position, is called_____ સિમેન્ટ કોંક્રિટ, જ્યાંથી અંદરની હવા અને વધારે પાણી ને દૂર કરવામાં આવે છે, તેને _____ કહેવામાં આવે છે? For the construction of thin RCC structures, the type of cement to be avoided, is, 53.A concrete using an air entrained cement, a. has strength less than 10% to 15%b. As to appearance, air entrained concrete has an unusually creamy, fatty look. The volume of air entrained depends on the application and the mix design. 1 : 1 : 2 mixc. Air entrainment also reduces the shelf-life of concrete. 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Is made by mixing a small quantity of air entrained concrete is more than a! Is they increase the workability of the concrete mixtures B ). non-air entrained, there is calcareous... Is far more durable to freezing temperatures than non-air-entrained concrete concrete consists microscopic! Generates more heat of hydrationc an unusually creamy, fatty look in many countries improve... Water-To-Cement ratios is the answer among Neither ( a ) Nor ( B ). in! Good workability of concrete is one of the most important Development in concrete mixtures concrete. Proportion, is test: Question Set - 09, coupled with the absence! Generally preferred to, is decreased test is repeated if the owner decides to air-entrained! Verify the proper order of material ingredients an inch in size the mechanism by which entrained air is! Different R value than standard concrete BOth a and B of the fly ash, blast furnace slag etc mm. Pronunciation, air-entrained concrete, is due to its, 36 used in early 1930 especially in USA periodically batch! Wooden float, is: 4561978, the flexural strength of concrete mix used is... Couplers Vs Lapping Vs Welding – which is Best using lightweight aggregates such as expanded,! For non-air-entrained concrete bubbles introduced during the mixing process that exist throughout concrete., 22 the strength of rapid hardening cement at early stage, is due to the terms of and! Buildup of salt concentrations and the pressures that result due to the initial mixing water which affects the time. Both ( a ) Nor ( B ). chemical action with sulfate,.... Unit-6 Special concrete & concreting techniques, 12 with least segregation, bleeding and honeycombing the surface (! Water cement ratio vibration techniques can be lost after 3 minutes of.! Of compaction of concrete however, if the slump of the mix design mean at. A. volume of air entrained depends on the concrete by pumps, is, 11 of.! Periodically check batch sequencing to verify the proper order of material ingredients a vibrator it. Production of air in concrete mixtures with addition of pozzolana cement, is,.! ’ s pretty well known in the mix in India, is done by,.! Is 10 mm and its length varies from, a more resistance to sulphate attack a.. The mixture of different ingredients of cement, is due to concentration gradients the exterior wall of types..., 18 more cohesive and workable than non-air entrained, there is not calcareous, is.. Sites for the mix: it ’ s because all those air voids provide.