Question

Which of the following constituent, present in excess quantity, changes the colour of the brick from red to yellow?
1. Alumina
2. Silica
3. Limestone
4. Iron Pyrite

Answer 1

Correct Answer - Option 3 : Limestone

Explanation:

Harmful ingredient in bricks:

1) Lime:

• If lime is present in clay brick excess amount it causes a change of colour of brick from red to yellow and when lime is burn-in lamp it absorbs water and swells and brick becomes disintegrated.
• So lime should be present in bricks as finely graded material if there is present it might be removed in the beginning process.

2) Iron Pyrite:

• Iron pyrites is a necessary ingredient of red clay brick it is a small amount burn in the presence of Oxygen and provide red colour to bricks, but excess amount of pyrites decolorise the bricks to dark red-black or blue-black colour of brick.

3) Pebbles gravels And grits:

• It can not be allowed to mix with pebbles gravels and grit , because it can make brick porous and lose its strength and water-absorbing capacity is increased.

4) Alkalies:

• Excess of alkali metal causes bricks to melt and lose their shape this causes efflorescence.
• When bricks with alkalies come in contact with moisture is absorb and alkali material crystallized on drying of bricks when water is evaporated and crystallized material form white powder deposit on the bricks which destroy and spoil the appearance of bricks this phenomenon is known as effluorescence.

5. Sulphur:

• If sulphur is present in the clay or brick it provides oxidation of carbon and sulphur.
• During burning sulphur provides the spongy and swelling structure of white patches on brick and brick become discolored due to white patches.