Bricks

UNIT – II

Chapter - 4 (A)

BRICKS

BRICKS

First man was using stone in the construction of huts and houses. In some places, where stone was not available, man thought of alternative material. Bricks are artificial blocks manufactured from good Brick Earth, i.e., Clay, by moulding it in rectangular boxes.

1. COMPOSITION OF GOOD BRICK EARTH

A good Brick Earth (Clay) contains the following Constituents / Ingredients:

1. Alumina: A good brick earth should have 20 - 30% of Alumina. Alumina imparts plasticity to the clay so that it can be moulded and shaped. If Alumina is present in excess, raw bricks shrink and warp during drying and burning.

2. Silica: A good brick earth should contain 50 - 60% of Silica. Presence of Silica prevents cracking, shrinking and warping of raw bricks. It gives uniform shape and durability to the bricks. Excess of Silica makes the brick brittle and useless. Lime: A good brick earth should contain up to 5% of Lime. Lime prevents shrinkage of raw bricks.

3. Lime enables the Silica to melt in burning and bind the particles of brick together. Excess lime will cause the brick to melt and the shape will be lost.

4. Iron Oxide: A good brick earth should contain 5 - 6% of Iron Oxide. It enhances the durable quality. It also imparts red colour to brick.

5. Magnesia: A small quantity of Magnesia in brick earth decreases shrinkage. It gives a yellow tint. Excess of Magnesia leads to the decay of bricks.

6. Alkalis (mainly Soda and Potash): Alkalis in bricks absorb moisture from air. However, they cause the brick to fuse, twist and warp during burning.

2. PROPERTIES or QUALITIES OF GOOD BRICKS

1. Colour: Brick should have uniform deep red or cherry colour.

2. Perfect Edges: The brick should have perfect and sharp edges, free from cracks or flaws.

3. Shape and Size: It should have proper rectangular shape of standard size 19 × 9 × 9 cm.

4. Burning Equally and Evenly: Bricks should be burnt equally and evenly. Over-burnt Bricks form into irregular mass. Under-burnt Bricks are soft and crumble on light crushing.

5. Metallic Ringing Sound: Brick should give clear metallic ringing sound when struck with each other or with hammer.

6. Homogeneous Structure: The brick, when broken, should show homogeneous and compact structure and free from voids.

7. Hardness: The brick should be sufficiently hard. No impression should be left on the brick surface, when scratched with finger nails. The brick should not break when dropped flat on hard ground from a height of about one meter.

8. Water Absorption: Brick is kept immersed in water for 16 hours. Then, it should not absorb water more than 20% of its own weight.

9. Low Thermal Conductivity and High Sound Insulation: The brick should have low thermal conductivity (should not conduct most heat). Also, it should be sound proof.

10. Crushing Strength: Crushing strength of brick varies from 3.5 N/mm2 to 7 N/mm2, depending upon the type of bricks. Better the durability, better is the crushing strength.

11. Presence of Soluble Salts: A brick should not show deposits of white salts like Sulphates of They Calcium, Sodium, Potassium and Magnesium, when immersed in water and dried. keep the masonry in a damp condition permanently. This results in the decay of bricks.

12. Weight: The average weight of a brick should be 3 to 3.5 kg.

13. Fire Resistant: The brick should have very high resistance to fire.