Concrete Technology and Design

61. Efflorescence in cement is caused due to an excess of

1. Alumina
2. Iron oxide
3. Silica
4. Alkalis

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62. Examine the following statements:
(i) Factor of safety for steel should be based on its yield stress,
(ii) Factor of safety for steel should be based on its ultimate stress,
(iii) Factor of safety for concrete should be based on its yield stress,
(iv) Factor of safety for concrete should be based on its ultimate stress.
The correct statements are

1. (i) and (iii)
2. (i) and (iv)
3. (ii) and (iii)
4. (ii) and (iv)

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63. Expansion joints are provided if the length of concrete structures exceeds

1. 10 m
2. 15 m
3. 15 m
4. 45 m

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64. Finer grinding of cement

1. Affects only the early development of strength
2. Affects only the ultimate strength
3. Both (A) and (B)
4. Does not affect the strength

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65. For a cantilever of effective depth of 0.5 m, the maximum span to satisfy vertical deflection limit is

1. 3.5 m
2. 4 m
3. 4.5 m
4. 5 m

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66. For a concrete mix 1:3:6 and water cement ratio 0.6 both by weight, the quantity of water required per bag, is

1. 10 kg
2. 12 kg
3. 14 kg
4. 16 kg

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67. For a continuous slab of 3 m × 3.5 m size, the minimum overall depth of slab to satisfy vertical deflection limits is

1. 50 mm
2. 75 mm
3. 100 mm
4. 120 mm

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68. For a good concrete

1. Aggregates should be hard and durable
2. Water should be free from organic materials
3. Cement should be sufficient to produce the required strength
4. All the above

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69. For a longitudinal reinforcing bar in a column, the minimum cover shall neither be less than the diameter of bar nor less than

1. 15 mm
2. 25 mm
3. 30 mm
4. 40 mm

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70. For a reinforced concrete section, the shape of shear stress diagram is

1. Wholly parabolic
2. Wholly rectangular
3. Parabolic above neutral axis and rectangular below neutral axis
4. Rectangular above neutral axis and parabolic below neutral axis

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