Building Material (Part-II) (GENERAL ENGINEERING) (SSC JE)

Total Questions: 50

41. Plaster of Paris is obtained by calcining : [RRB JE 27.08.2015 (Shift-II)]

Correct Answer: (a) Gypsum
Solution:• Plaster of Paris is prepared by heating calcium sulphate dihydrate, or gypsum to 120-180ºC. • The plaster gets its name because, it main ingredient gypsum is found abundantly in Paris.
• Plaster of Paris is used to make casts and moulds.

42. A sample of cement is said to be sound when it does not contain free. [RRB JE 27.08.2015 (Shift-I)]

Correct Answer: (a) Free Lime
Solution:

If free lime is in excess, it makes the cement unsound, cause it to expand and finally disintegrate.

• Iron oxide–Impart strength, hardness and colour to cement.

• Alumina–It imparts quick setting property to the cement.

• Silica–It imparts strength to cement.

43. Which is the purest form of iron? [RRB JE 27.08.2015 (Shift-I)]

Correct Answer: (b) Wrought iron
Solution:

Purest form of iron is wrought iron.

Carbon content in various iron material

MaterialCarbon content
Cast iron2–4.5%
High carbon steel0.7–1.5%
Mild steelup to 0.25%
Medium carbon steel0.25–0.7%
Very low carbon steel< 0.1%
Wrought ironDoes not exceed 0.15%

44. The strength of timber is maximum when load applied is– [RRB JE 28.08.2015 (Shift-I)]

Correct Answer: (a) Parallel to grain
Solution:

• Compression strength of the timber section is found to be maximum parallel to the grains (along the longitudinal direction)

• Tensile strength of the timber section is found to be 2 to 4 times greater than its compressive strength parallel to the grains (weak in joint making not using the tension member acts).

45. Addition of pozzolana to ordinary portland cement increase– [RRB JE 28.08.2015 (Shift-I)]

Correct Answer: (b) Shrinkage
Solution:

Addition of pozzolana to ordinary portland cement increase in shrinkage, sulphate resistance and decrease in cost of cement, bleeding, permeability and heat of hydration.

46. A tight knot free from decay, which is solid across its face, and at least as hard as the surrounding wood. [RRB S.S.E. (Secunderabad) 02.09.2015 (Shift-I) ]

Correct Answer: (d) Sound knot
Solution:

Sound knot– A sound knot that is solid across its face, as hard as the surrounding wood, and shows no indication of decay.

47. Which of the following cement has maximum percentage of C₃S : [RRB JE 28.08.2015 (Shift-II) ]

Correct Answer: (d) Rapid hardening cement
Solution:

• Rapid hardening cement is produced by finely grinding the cement clinkers such that SSA ≮ 3250 cm² /kg and by increasing the proportion of C₃S (≈ 56%)

• It is the type of cement, which attains higher rate of gain of strength in comparison to OPC.

48. On the basis of durability test, Forest Research Institute of India, Dehradun, a tree is highly durable if its average life is more than– [RRB JE 29.08.2015 (Shift-III)]

Correct Answer: (b) 10 years
Solution: 

Based on the durability, timber is classified as–

High durability–Average life is more than 10 years

Moderate durability–Average life between 5 to 10 years

Low durability–Average life less than 5 years.

49. The setting and hardening of cement after addition of water is due to– [RRB JE 29.08.2015 (Shift-II) ]

Correct Answer: (c) Hydration of some of the constituent compounds of cement
Solution:

• The setting and hardening of cement after addition of water is due to hydration of some of the constituent compounds of cement such as tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetra calcium aluminoferrite.

Tricalcium silicate (C₃S)–

• This is also called alite.

• Tricalcium silicate hydrates quickly and contributes more to the early strength.

Dicalcium silicate (C₂S)–

• This is also called as belite.

• The contribution of dicalcium silicate takes place after 7 days and may continue for up to 1 year.

Tricalcium aluminate (C₃A)– 

• This is also called celite

• It is the quickest one to react when the water is added to the cement.

• It is responsible for flash setting.

Tetra Calcium Alumino Ferrite (C₄AF)– 

• This is called as felite •

Tetra calcium alumino-ferrite is comparatively inactive.

50. A condition of timber during seasoning in which the different layers of wood are under stress by being under compression across the grain (usually due to rapid surface drying in the kiln). [RRB S.S.E. 03.09.2015 (Shift-I)]

Correct Answer: (a) Case hardening
Solution:

Case hardening : It is due to the unequal drying of the exterior surface under compression and the interior surfaces under tension due to rapid drying.

• This happens at heavily loaded bottom stacks kept for seasoning.