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M.Tech Structural Concrete Admixtures — practice questions

Explore 4 free Concrete Admixtures questions in M.Tech Structural Civil Engineering. Open each question or exercise to read its content, reference answers and available explanation.

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Concrete Admixtures questions and exercises with answers

Showing questions 1–4 of 4.

Per §4.7, air entrained in concrete typically consists of minute spherical bubbles in the size range of:Read the answer and worked solution →Per §4.7.4, the dosage of air entrainment for ordinary concrete should generally be kept within the range:Read the answer and worked solution →Per §4.9, the most commonly used gas-forming admixture in concrete is:Read the answer and worked solution →Per §4.12, superplasticizers can typically reduce the water content of a concrete mix by as much as:Read the answer and worked solution →

Worked practice questions

Per §4.7, air entrained in concrete typically consists of minute spherical bubbles in the size range of:

  1. About 5 to 80 microns in size
  2. Less than 1 micron in size
  3. About 200 to 500 microns in size
  4. About 1 to 5 mm in size
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Correct answer: A. About 5 to 80 microns in size

1. §4.7: 'Entrained air is minute spherical bubbles of size ranging from 5 microns to 80 microns distributed evenly in the entire mass of the concrete.' 2. These bubbles act like ball bearings, improve workability, and interrupt capillaries — they are NOT large entrapped voids. _Source: IGNOU ET-522 Block-1 Unit-4 Admixtures, §4.7, p. 49_

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Per §4.7.4, the dosage of air entrainment for ordinary concrete should generally be kept within the range:

  1. 0.1 to 0.5 percent of the mix
  2. 10 to 12 percent of the mix
  3. 2 to 6 percent of the mix
  4. 15 to 20 percent of the mix
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Correct answer: C. 2 to 6 percent of the mix

1. §4.7.4 closes: 'In any case air entrainment should not be less than 2 percent and more than 6 percent.' 2. For mass concreting 2-3 percent is recommended; thin sections take 5-6 percent; reinforced concrete typically 3-4 percent. _Source: IGNOU ET-522 Block-1 Unit-4 Admixtures, §4.7.4, p. 51_

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Per §4.9, the most commonly used gas-forming admixture in concrete is:

  1. Hydrogen peroxide
  2. Calcium carbide
  3. Sodium bicarbonate
  4. Aluminium powder
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Correct answer: D. Aluminium powder

1. §4.9: 'Aluminium powder is used most commonly as gas forming agent. Hydrogen gas is produced due to reaction of aluminium with Ca(OH)2.' 2. Dosage is 0.005 to 0.02 percent by weight of cement; larger doses give light-weight concrete (Siporex blocks). _Source: IGNOU ET-522 Block-1 Unit-4 Admixtures, §4.9, p. 52_

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More Civil Engineering topics

GATE Civil — Core TopicsCementStrength of MaterialsAggregatesTesting of ConcreteConcreting EquipmentWorkability of Fresh ConcreteConcrete Mix Design