Concrete Technology Questions and Answers - Silica Fume

1.Content of CaO in silica fume?
a) 5
b) 21
c) 40
d) <1

Answer: d
Explanation: The content of CaO in silica fume is less than 1. 21 is the content of CaO in Calcareous (ASTM C618 Class C) Fly Ash.

2. The specific surface (m2/kg) of silica fume.
a) 370
b) 15000-30000
c) 45000
d) 420

Answer: b
Explanation: The specific surface area of silica fume can be measured with the BET method or nitrogen adsorption method. It typically ranges from 15,000 to 30,000 m2/kg.

3. Specific Gravity of silica fume.
a) 2.38
b) 2.65
c) 2.94
d) 2.22

Answer: d
Explanation: The specific gravity of silica fume is generally in the range of 2.2 to 2.3.

4. Bulk density of the silica fume varies from ____________
a) 130-600 kg/m3
b) 650 kg/mm3
c) 75-150 kg/mm3
d) 750 kg/mm3

Answer: a
Explanation: The bulk density of silica fume depends on the degree of densification in the silo and varies from 130 (undensified) to 600 kg/m3.

5. Spherical particles in silica fume has diameter of _______
a) <1 μm
b) >1 μm
c) 1 μm
d) .1 μm

Answer: a
Explanation: Silica fume is an ultrafine material with spherical particles less than 1 μm in diameter, the average being about 0.15 μm.

6. Silica fume is usually added during ____________
a) Before concrete production at a concrete plant
b) After concrete production at a concrete plant
c) Concrete production at a concrete plant
d) Curing

Answer: c
Explanation: Silica fume for use in concrete is available in wet or dry forms. It is usually added during concrete production at a concrete plant.

7. Air entrainment in concrete increases ____________
a) Strength
b) Workability
c) The effect of temp variations
d) The unit weight

Answer: b
Explanation: There are following types of Air entrainment in concrete which helps to increase the workability.

8. In a dry environment, concrete strength will be loosed as much as ___________ % in moist environment.
a) 30
b) 40
c) 50
d) 60

Answer: c
Explanation: Laboratory tests show that concrete strength will be loosed as much as 50% in dry environment as compared to moist environment.

9. Concrete placed in cold weather will take ____________ time to gain strength.
a) No
b) Less
c) More
d) Equal to hot weather

Answer: c
Explanation: Concrete placed in cold weather will take longer time to gain strength, delaying form removal and subsequent construction.

10. After finishing concrete surface must be kept ___________
a) Dry
b) First dry it and then wet it
c) First wet it and then dry it
d) Wet

Answer: d
Explanation: After finishing concrete surface must be kept wet, so that it’d be prevented from evaporation.