Correct Answer - Option 4 : gravel, grits
Concepts:
Harmful ingredients in Bricks and their effect on bricks:
1. Lime:
- A small quantity of lime is required in brick earth. But if present in excess, it causes the brick to melt and hence brick loses its shape.
- Also, if lime is present in the form of lumps, then it is converted into quick lime after burning. This quick lime slakes and expands in presence of moisture, causing splitting of bricks into pieces.
2. Iron Pyrites:
- The presence of iron pyrites in brick earth causes the brick to get crystallized and disintegrated during burning, because of the oxidation of the iron pyrites.
- They also discolourise the bricks.
3. Alkalis:
- They exist in the brick earth in the form of soda and potash. It acts as a flux in the kiln during burning and it causes bricks to fuse, twist and warp. Because of this, bricks are melted and they lose their shape.
- The alkalis remaining in bricks will absorb moisture from the atmosphere when bricks are used in masonry. With the passage of time, the moisture gets evaporated leaving grey or white deposits on the wall surface (known as efflorescence). This white patch affects the appearance of the structure.
3. Pebbles (Gravel, Grits):
- Pebbles in brick earth create problems during the mixing operation of the earth. It prevents uniform and thorough mixing of clay, which results in weak and porous bricks.
- Bricks containing pebbles will not break into shapes as per requirements.
4. Vegetation and Organic Matter
- The presence of vegetation and organic matter in brick earth assists in burning. But if such matter is not completely burnt, the bricks become porous. This is due to the fact that the gasses will be evolved during the burning of the carbonaceous matter and it will result in the formation of small pores.
