56) The principal constituent of every kind of brick earth is alumina.

• (a) True
• (b) False

57) A first class brick should have a minimum crushing strength of

• (a) 7 MN/m2
• (b) 10.5 MN/m2
• (c) 12.5 MN/m2
• (d) 14 MN/m2

58) The percentage of alumina in a good brick clay should vary from

• (a) 20 to 30%
• (b) 30 to 40%
• (c) 40 to 50%
• (d) 50 to 60%

59) The percentage of silica in a good brick clay should vary from

• (a) 20 to 30%
• (b) 30 to 40%
• (c) 40 to 50%
• (d) 50 to 60%

60) Excess of alumina in the clay

• (a) makes the brick brittle and weak
• (b) makes the brick crack and warp on drying
• (c) changes colour of the brick from red to yellow
• (d) improves impermeability and durability of the brick