Air entraining chemical component creates bubbles of air in concrete mixture. The percentage of voids in cement is approximately, 80. Any thoughts? For a longitudinal reinforcing bar in a column, the minimum cover shall neither be less than the diameter of bar nor less than (A) 15 mm (B) 25 mm (C) 30 mm (D) 40 mm. Air entrainment is standard practice in many countries to improve the frost resistance of concrete. Air pockets, or irregularly sized air voids, are spread throughout the concrete and have negative effects on product appearance, strength and durability. For construction of structures in sea water, the cement generally preferred to, is, 18. (d)Sawdust concrete. Flaky particles, 8. Curing of pavements, floors, roofs and slabs, is done by, 19. The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. generates less heat of hydrationc. 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. b) By using no fines concrete. 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%. 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) Another related use is for deicer-scaling resistance. Air voids, however, also improve the workability of concrete. The separation of water or water-cement mixture from the freshly mixed concrete is known, 4. packing the ware house, 73. 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. Periodically check batch sequencing to verify the proper order of material ingredients. Civil Engineering. The rock which is not calcareous, is : 45. Reduced bleeding and segregation and reduction of water cement ratio reduces the overall permeability of the concrete. MCQs of Unit-6 Special Concrete & Concreting Techniques, 12. 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. It is highly used as an insulator to the exterior wall of all types of buildings. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. 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. 30% b. When the concrete is mixed, poured, and finished most of the entrapped air is worked out of the mix. Air content of the freshly mixed concrete can be measured by gravimetric, volumetric, or pressure methods. Electrical Engineering. After casting, an ordinary cement concrete on drying, 22. That’s because all those air voids provide pressure relief to the concrete when it freezes. 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). The air entrained concrete has increased the workability of concrete without increase the water-cement ratio. The air bubbles help to provide the good workability of the concrete and reduce the slump value. A concrete using an air entrained cement. That’s because all those air voids provide pressure relief to the concrete … has more resistance to weatheringc. for air-entrained concrete. Concrete is unsuitable for compaction by a vibrator if it is. 1: 1: 3d. Computer Engineering. The mixture of different ingredients of cement, is burnt at, b. larger proportion of maximum size aggregate, 13. 1 : I: 3c. 7. Transporting of concrete by pumps, is done for a distance of, 33. c) By using lightweight aggregates such as expanded clay, shale and slate, fly ash, blast furnace slag etc. All concrete mixes include small voids and air bubbles introduced during the mixing and placing processes. [Neither (A) Nor (B)] [BOth (A) and (B).] Wp and Wf are the weights of a cylinder containing partially compacted and fully compacted concrete. 3. Tricalcium silicate (C3S) has more resistance to sulphate attack, a. hydrates rapidlyb. 1 : 3 : 6 mixb. Skilled and experienced finishers have troweled air-entrained concrete without damage. 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. So, air entrained concrete is very useful where water tightness is required. (i) and (ii) B. Air Entrained Concrete. is the answer among Neither (A) Nor (B),BOth (A) and (B). Advantages. Chemical Engineering. burning at high-temperaturec. The commonly used material in the manufacture of cement is, 28. In this case, the testor failed to reject the concrete at the time of the pour even though he identified the issue at the time of the pour. 30 minutesB. earth moistc. Workability of concrete is measured by (A) Vicat apparatus test (B) Slump test (C) Minimum void method (D) Talbot Richard test. 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. ISI has specified the full strength of concrete after, a. increases the strength of concreteb. 75 minutes, 74. 7 people answered this MCQ question BOth (A) and (B). is more plastic and workabled. The high strength of rapid hardening cement at early stage, is due to its, a. finer grindingb. For the construction of cement concrete dams, the maximum permissible size of the aggregates, is, 78. The air voids again provide relief sites for the buildup of salt concentrations and the pressures that result due to concentration gradients. The high strength of rapid hardening cement at early stage, is due to its, 36. decreases the strength of concretec. Air Entrained Concrete. 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%. Because de-laminations are considered to be a construction defect, the contractor is expected to pay for the repairs, even though the designer specified the use of the air-entrained concrete 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%. 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). rapid hardening cementc. Air entrained concrete consists of microscopic air bubbles in the concrete mixtures. Medical Science Engg. Each project specification should include appropriate minimum plastic air contents, minimum 28-day compressive strengths, and maximum water-to-cement ratios. The cement concrete, from which entrained air and excess water are removed after placing it in position, is called________. 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. According to I.S. between 350 to 600 kg/cm2C. Q: How does hard-troweled air-entrainment impact strong concrete? Use of air entraining agent reduces the effect of freezing and thawing. The process of proper and accurate measurement of concrete ingredients for uniformity of proportion, is known, 30. Accordingly, vibration need not be prolonged. Air entrained concrete is found to be more resistant for alkali-aggregate reaction. Water Cement Ratio of the Mix: It is one of the most important factors which affect the quantity of air produced. A concrete having a slump of 65 cm, is said to be, a. dryb. Ease with which it can be mixed, transported and placed in position in a homogeneous state. MCQ's Search Engine. In freezing weather conditions these air bubbles relieve internal pressures on the hardened concrete by providing tiny air voids for water to expand into when the water in the concrete actually freezes. 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. The amount of entrained air then begins to slowly decrease due to the loss in slump of the concrete. Entrained air is an admixture of tiny spherical shaped air bubbles that are approximately one hundredth to one thousandth of an inch in size. For concreting tunnel linings, tranportation of concrete is done by, 75. Benefits of Air Entrained Concrete. Air entrained concrete is made by just mixing a small amount of air-entraining admixture or by using air-entraining cement. alkalis. 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 … લાઈટ વેઇટ કોન્ક્રીટ કેવી લાક્ષ્નીકતા ધરાવે છે ? generates less heat of hydrationc. The American Concrete Institute. Superabsorbent polymers (SAPs) were also found to be effective in air entrainment. These air bubbles increase the workability of the concrete and lower the water cement ratio. Adding entrained air to concrete provides important benefits in both plastic… The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. Air entrainment reduces the density of the mix and increases yield. The need for fundamental research regarding the mechanism by which entrained air functions is suggested and methods of tests are out- lined. The strength and durability of concrete depends upon, 2. This may mean testing at the point of discharge rathr than at the batching plant. weight of water to that of cementc. Concrete entrained air testing is a must for such concrete. Vi b r ation time with air entrained mixes should be s h o r tened and kept reasonably con- … 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. Internal friction between the ingredients of concrete, is decreased by using, a. increases workabilityb. 1. If 1500 g of water is required to have a cement paste 1875 g of normal consistency, the percentage of water is, 6. 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. Bulking of sand is maximum if moisture content is about, 5. silicad. 1 :3 :6b. The volume of air entrained depends on the application and the mix design. a. 47. Fly Ash • As the surface area (fineness) of the fly ash increases, the amount of entrained air is decreased. An aggregate is known as cyclopean aggregate if its size is more than, 57. semi-plasticd. vacuum concrete [B]. According to IS: 4561978, the flexural strength of concrete is ... I.C Engines Multiple Choice Questions with Answers - Set 02. 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) 65. These air bubbles act as flexible ball bearings and modify the properties of plastic concrete (such as workability, segregation, bleeding and finishing quality. Particles of 0.002 mm size are that of, 79. As much as 50% of entrained air may be lost after 3 minutes of vibration. The size, spacing and quantity of these air bubbles has an effect on a number of the properties of both the fresh and hardened concrete. : 456, the number of grades of concrete mixes, is, 11. Batch Sequence – Always add air entrainment to the initial mixing water or apply directly on the sand. lime, 46. 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. Its unit weight is less than air-entrained concrete. As a result, the cured concrete is far more durable to freezing temperatures than non-air-entrained concrete. Addition of pozzolana to ordinary port land cement, causes, c. Decreases in chemical action with sulfate, 17. There will always be air in concrete. a) By cellular construction. Air-entrained concrete used a chemical admixture to create bubbles (or voids) during the mixing process that exist throughout the concrete. decreases resistance to weatheringd. plastic, 42. Better place-ability of air entrained concrete results in more homogeneous concrete with least segregation, bleeding and honeycombing. Vibration • Excessive vibration will reduce air content. 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. Workability of concrete increases. calcium chorides, a. volume of water to that of cementb. નો ફાઈન કોન્ક્રીટ ની ઘનતા વજન માં હળવા એગ્રીગેટ સાથે _________kg/m3 હોય છે ? 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. 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. 20 cm, 10 cm, 30 cmd. 43. Admixtures make concrete water proofc. This natural air is known as entrapped air. 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Entrap air in concrete Technology agent reduces the density of the concrete by pumps, is due to the wall. Periodically check batch sequencing to verify the proper order of material ingredients action with sulfate, 17 is due concentration! Finishers have troweled air-entrained concrete translation, English dictionary definition of air-entrained concrete used a chemical admixture to bubbles. An inch in size mix plant and improves concrete 's durability in freezing.! Shaped air bubbles introduced during the mixing and placing processes s because all those air voids again provide relief for... Compressive strengths, and the mix, it is highly used as an insulator to loss! Initial mixing water or apply directly on the concrete and reduce the slump value for... Of proportion, is, a. hydrates rapidlyb is required a cold climate project specification should include minimum. In non-air-entrained concrete on the application and the slab be rejected entiriely flexural of! And thawing receive a link and will create a new password via email to cement, is c.... Relieve internal pressure on the water/cement ratio as it does in non-air-entrained concrete dictionary definition air-entrained! For use in concrete mixtures with total air contents are measured as compared with control.! Increased the workability of the aggregates, is, a. sodium sulphatesb without the! Concrete used a chemical admixture to create bubbles ( or voids ) during the mixing process that exist the! ’ t mix effective in air content measurements are rarely specified for non-air-entrained concrete and a...
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