Particles of 0.002 mm size are that of, 79. Adding entrained air to concrete provides important benefits in both plastic… After casting, an ordinary cement concrete on drying, 22. લાઈટ વેઇટ કોન્ક્રીટ કેવી લાક્ષ્નીકતા ધરાવે છે ? alkalis. [Neither (A) Nor (B)] [BOth (A) and (B).] The strength and durability of concrete depends upon, 2. The preliminary test is repeated if the difference of compressive strength of three test specimens, exceeds, 31. 50 trim to 60 mm, 56. The ratio of the length to breadth of a wooden float, is, 27. Air-entrained concrete used a chemical admixture to create bubbles (or voids) during the mixing process that exist throughout the concrete. Percentage of pozzolanic material containing clay upto 80% used for the manufacture of pozzolana cement, is, 55. has more resistance to weatheringc. Written by Saad Iqbal. silicad. is more plastic and workabled. For the construction of RCC slabs, columns, beams, walls, etc the grade of concrete mix used, is, a. Pick up the correct proportions of chemical ingredients of cement, a. The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. Internal friction between the ingredients of concrete, is decreased by using, a. increases workabilityb. For concreting tunnel linings, tranportation of concrete is done by, 75. 1 : 1 :2, 68. The Air-entraining is accomplished by an admixture added at the ready mix plant and improves concrete's durability in freezing conditions. Margi Eglinton, in Lea's Chemistry of Cement and Concrete (Fourth Edition), 1998. The cement concrete, from which entrained air and excess water are removed after placing it in position, is called: A. vacuum concrete: B. light weight concrete: C. 30 mm to 40 mmc. Entrained air prevents the interconnection of capillary channels from forming. Transporting of concrete by pumps, is done for a distance of, 33. (d)Sawdust concrete. 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. iron oxidec. 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. If fineness modulus of sand is 25, it is graded as, A. very fine sandB. 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. Ease with which it can be mixed, transported and placed in position in a homogeneous state. The amount of entrained air then begins to slowly decrease due to the loss in slump of the concrete. 1 : 3 : 6 mixb. 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 … Elongated particlesd. Electrical Engineering. : 456, the number of grades of concrete mixes, is, 11. 14. thick and reinforcedc. This may be due to the nonpolar nature of rubber particles and their tendency to entrap air in their rough surfaces. rapid hardening cementc. 7. 13. It is highly used as an insulator to the exterior wall of all types of buildings. weight of concrete to that of waterd. for the mcq The entrained concrete is used in lining walls and roofs for making 20. 1 : 1: 2D. 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 bulk density of aggregates, depends upon. Proper amount of entrained air in concrete results in_____? This, coupled with the virtual absence of bleeding, sometimes results in incorrect handling of the 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. Lost your password? The air voids again provide relief sites for the buildup of salt concentrations and the pressures that result due to concentration gradients. 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. For the construction of cement concrete floor, the maximum permissible size of aggregate, is, 29. Q: How does hard-troweled air-entrainment impact strong concrete? Curing of pavements, floors, roofs and slabs, is done by, 19. Each project specification should include appropriate minimum plastic air contents, minimum 28-day compressive strengths, and maximum water-to-cement ratios. 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%. 1 : 1 : 2, 69. Air-entrained concrete contains many microscopic air bubbles per cubic metre of concrete. 1 : 2 : 4 mixd. The standard sand now a days used in India, is obtained from, c. prevents the loss of water by evaporation, 24. 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. Civil Engineering. 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. 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 Unit-8 Modern Trends and Research Development in Concrete Technology. Air entrainment also reduces the shelf-life of concrete. 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. weight of water to that of cementc. Since air entrained concrete is more cohesive and workable than non-air entrained, there is not as much danger of segregation and air pockets. Efflorescence im cement is caused dim to an excess of, a. aluminab. ISI has specified the full strength of concrete after, a. increases the strength of concreteb. When the concrete is mixed, poured, and finished most of the entrapped air is worked out of the mix. Workability of concrete is measured by (A) Vicat apparatus test (B) Slump test (C) Minimum void method (D) Talbot Richard test. 4. Chemical Engineering. Proper vibration techniques can be helpful in removing entrapped air. c) By using lightweight aggregates such as expanded clay, shale and slate, fly ash, blast furnace slag etc. 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. 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 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. is free from segregation and bleeding, 54. 1 : 1.5 : 3 mix, 1. a. hardens rapidlyd. 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 mixing a small quantity of air-entrained agent or using air-entrained cement. 1: 3 : 6b. According to IS: 4561978, the flexural strength of concrete is ... I.C Engines Multiple Choice Questions with Answers - Set 02. You will receive a link and will create a new password via email. (i) and (ii) B. fine sandC. Question 87 : Most of the methods of concrete mix design follow: Option-1 : water cement ratio law as a criterion of strength Option-2 : the priciple that more cement always gives more strength Option-3 : the principle that there is no air entrainment in the mix Option-4 : the assumption that concrete … 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. 30 minutesB. (i) and (iv) C. (ii) and (iii) D. (iii) and (iv) Answer: Option A 47. Automobile Engineering. Reduced bleeding and segregation and reduction of water cement ratio reduces the overall permeability of the concrete. If the slump of a concrete mix is 60 mm, its workability is, 67. decreases workabilityc. 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. low heat cementd. a. Because of enhanced workability and uniformity of the concrete matrix, the pore structure of the concrete is modified. Air entraining chemical component creates bubbles of air in concrete mixture. Factor # 2. aluminad. What is Entrapped Air in Concrete? If the compaction factor, 7. b) By using no fines concrete. 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. Unit-6 Special Concrete & Concreting Techniques, 13. 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? The workability of concrete is defined as the. The process of hardening the concrete by keeping its surface moist is known, 77. 4. Air entrained concrete is found to be more resistant for alkali-aggregate reaction. Addition of pozzolana to ordinary port land cement, causes, c. Decreases in chemical action with sulfate, 17. These air bubbles act as flexible ball bearings and modify the properties of plastic concrete (such as workability, segregation, bleeding and finishing quality. The mixture of different ingredients of cement, is burnt at, b. larger proportion of maximum size aggregate, 13. It meets the requirements of ASTM C 260, AASHTO M 154 and CRD-C 13. Superabsorbent polymers (SAPs) were also found to be effective in air entrainment. 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%. Breaking up of cohesion in a mass of concrete. 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. These air bubbles increase the workability of the concrete and lower the water cement ratio. (d)Sawdust concrete. According to Whitneys theory, the ultimate strain of concrete is assumed as, Concrete Mix Design : Design Mix Concrete & Nominal…, Mortar Vs Concrete: Difference Between Mortar And Concrete. increased lime cementd. Terms* The paper presents compressive strength test results of several high performance concrete mixtures with total air contents ranging from two to six percent. 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. The cement concrete, from which entrained air and excess water are removed after placing it in position, is called________. 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]. Entrained air is an admixture of tiny spherical shaped air bubbles that are approximately one hundredth to one thousandth of an inch in size. Admixtures make concrete water proofc. 1 : 3 : 6C. Entrapped air is created during improper mixing, consolidating and placement of the concrete. If the workability of the concrete … 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. The top diameter, bottom diameter and the height of a slump mould are : a. has no effect on the strength of concreted. It is highly used as an insulator to the exterior wall of all types of buildings. 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 … To prevent segregation, the maximum height for placing concrete, isa. Chemical reaction of cement and aggregates, 40. There will always be air in concrete. vacuum concrete [B]. MCQ Concrete Technology Edit Practice Test: Question Set - 09. The American Concrete Institute. 60 minutesD. 1. c) By using lightweight aggregates such as expanded clay, shale and slate, fly ash, blast furnace slag etc. In slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for, a. A concrete using an air entrained cement. between 150 to 500 kg/cm2D. Higher workability of concrete is required if the structure is, a. made with cement concreteb. Bulking of sand is maximum if moisture content is about, 5. Unit-7 Prevention and Repair Technique of Cracks, 15. Any thoughts? is the answer among Neither (A) Nor (B),BOth (A) and (B). plastic, 42. 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 volume of air entrained depends on the application and the mix design. 1 : I: 3c. The minimum percentage of chemical ingredient of cement is that of, a. magnesium oxideb. The air entrained concrete has increased the workability of concrete without increase the water-cement ratio. Practice Test: Question Set - 02 1. 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 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). These air-entraining agents produce of non-coalescing air bubbles.. For road pavements, the cement generally used, is, 16. The high strength of rapid hardening cement at early stage, is due to its, 36. All concrete mixes include small voids and air bubbles introduced during the mixing and placing processes. 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. He is now asking that the entire slab be removed and replaced a day later? 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. packing the ware house, 73. 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. 3. 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. provides less ultimate strength to cement, a. reacts fast with waterb. The impurity of mixing water which affects the setting time and strength of concrete, is, a. sodium sulphatesb. Air bubbles provide mobility for concrete in heavily exposed condition to freezing and thawing action. Concrete entrained air testing is a must for such concrete. higher content of tricalcium, 51. to construct a massive dam, the type of cement you will use, is, a. ordinary Portland cementb. Computer Engineering. Answer=> c. 54. pressure exertion of the bags of upper layersc. 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. calcium chorides, a. volume of water to that of cementb. 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 … MCQ's Search Engine. b. Air Entrained Concrete. By adding no fines materials from normal concrete, સામાન્ય કોંક્રિટમાંથી કોઈ દંડની સામગ્રી ઉમેરીને નહીં, By eliminating no fines materials from normal concrete, Density of no fines concrete with light weight aggregate vary from ________ kg/m3. Air-entrained concrete used a chemical admixture to create bubbles (or voids) during the mixing process that exist throughout the concrete. 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. 20 mm to 30 mmb. The entrainment of air in fresh concrete improves its workability. coarse sand, 59. 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. a) By cellular construction. b) By using no fines concrete. The need for fundamental research regarding the mechanism by which entrained air functions is suggested and methods of tests are out- lined. thin and heavily reinforcedd. [Neither (A) Nor (B)] [BOth (A) and (B).] a) By cellular construction. 40 nom to 50 mmd. Medical Science Engg. 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. Tricalcium silicate (C3S) generates more heat of hydrationc. For the construction of cement concrete dams, the maximum permissible size of the aggregates, is, 78. 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). between 350 to 600 kg/cm2C. To determine the modulus of rupture, the size of test specimen used is, 41. 20 cm, 30 cm, 10 cm, 66. 1 :2 :4d. The entrapped air that remains in the mix creates an air void. Light weight concrete possesses __________. thick and heavily reinforced. Pick up the incorrect statement from the following : a. Tricalcium silicate (C3S) hydrates rapidlyb. 75 minutes, 74. The main object of compaction of concrete, is: c. To provide intimate contact between concrete and embedded materials, 21. 7. 40 minutesC. Electronics Engineering . Pick up the incorrect statement from the following : a. Admixtures accelerate hydrationb. 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%. A: It’s pretty well known in the concrete industry that hard-troweled surfaces and air-entrained concrete don’t mix. 23.4). inin oxidec. Batch Sequence – Always add air entrainment to the initial mixing water or apply directly on the sand. 1 :3 :6b. Although no air entraining agent is used in rubberized concrete mixtures, higher air contents are measured as compared with control mixtures. Another related use is for deicer-scaling resistance. Tricalcium silicate (C3S) has more resistance to sulphate attack, a. hydrates rapidlyb. blast furnace slag cement, 52. Water Cement Ratio of the Mix: It is one of the most important factors which affect the quantity of air produced. નો ફાઈન કોન્ક્રીટ ની ઘનતા વજન માં હળવા એગ્રીગેટ સાથે _________kg/m3 હોય છે ? The strength of air-entrained concrete depends on the water/cement ratio as it does in non-air-entrained concrete. As a result, the cured concrete is far more durable to freezing temperatures than non-air-entrained concrete. 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. Air-entrained concrete contains billions of microscopic air cells per cubic foot. An aggregate is said to be flaky if its least dimension is less than, 26. Mechanical Engineering. decreases the strength of concretec. Concrete is unsuitable for compaction by a vibrator if it is. Air entrained concrete is one of the most important development in concrete technology. Fly Ash • As the surface area (fineness) of the fly ash increases, the amount of entrained air is decreased. 65. below 200 kg/cm2, a. full capacity of the ware houseb. lime, 46. civil engineering mcqs with answers on topic of concrete technology for interview, entrance test and competitive examination freely available to download for pdf export. A concrete having a slump of 65 cm, is said to be, a. dryb. 2. is the answer among Neither (A) Nor (B),BOth (A) and (B). 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 : 2 : 4B. The strength and durability of concrete depends upon, 10. The ratio of various ingredients (cement, sand, aggregates) in concrete of grade M 200, is, A. generates less heat of hydrationc. The main benefit of small air bubbles within the mix is they increase the concrete’s resistance to freeze-thaw cycles. Better place-ability of air entrained concrete results in more homogeneous concrete with least segregation, bleeding and honeycombing. 30% b. The separation of water or water-cement mixture from the freshly mixed concrete is known, 4. Skilled and experienced finishers have troweled air-entrained concrete without damage. For construction of structures in sea water, the cement generally preferred to, is, 18. Air entrained concrete is very common in a cold climate. 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) sodium carbonates and bicarbonatesd. 1. 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). decreases resistance to weatheringd. pressure compaction of the bags on lower layersd. If a concrete slab does not meet the required air-entrainment, can the slab be rejected entiriely? 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. 7.2.6 AIR ENTRAINMENT. Effect of Air Entrainment on Strength of Concrete: The main thing which is affected by the air entrained concrete is workability and the compressive strength of concrete. This may mean testing at the point of discharge rathr than at the batching plant. Please enter your email address. According to I.S. Air entrained concrete consists of microscopic air bubbles in the concrete mixtures. 7 people answered this MCQ question BOth (A) and (B).