Fundamental of building construction (Bricks)

Notes for bricks used for building construction.

1. BASIC MATERIALS OF CONSTRUCTION

2. BRICKS Oldest building material Obtained by moulding clay Do not require dressing Art of laying is simple Durable, Reliable, Strong, Easily available, Fire resistant.

3. COMPOSITION OF GOOD BRICK EARTH Alumina: 20-30% of alumina. Imparts plasticity to earth so that it can be moulded. If present in excess, causes shrinking and warping during burning and drying. Silica: 50-60 % silica. It prevents cracking, shrinking and warping of raw bricks. Excess of silica causes brittleness. Lime: should not be more than 5%. Prevents shrinkage of raw bricks. Excess of lime causes the brick to melt and lose its shape.

4. Oxide of iron: 5-6% is desirable. Helps lime to fuse sand. Imparts red colour to bricks. Excess of it makes bricks dark blue or blackish. Magnesia: Imparts yellow tint to bricks and decrease shrinkage.

5. Harmful ingredients of brick earth Lime Iron pyrites Alkalies- in the form of soda and potash Pebbles Vegetation and organic matter

6. Manufacturing of bricks Preparation of clay Unsoiling – top layer, about 200 mm in depth is taken out and thrown away since having impurities. Digging – Clay digged out and spread in a levelled ground. Cleaning – Stones, pebbles etc. removed. Washing to be done if needed. Weathering – Exposed to atmosphere for softening for few weeks to months. Blending – harmonious mixing makes clay fit for tempering Tempering – Required quantity of water added and made to a uniform mixture

7. Pug mill for grinding clay

8. Moulding Hand moulding – manually done Ground moulded bricks and table moulded bricks Machine moulding Plastic clay machines and dry clay machines

9. Drying – to avoid cracking, the moulded bricks are dried Artificial drying – bricks passed through special dryers which are in the form of tunnels. Circulation of air – Sufficient air space left between bricks Drying yard – Should be on a higher level and covered with sand. Period of drying – 3-10 days

10. Burning Imparts hardness and strength to bricks. Clamps Kilns Intermittent kiln-up-draught and down- draught Continuous kiln –Bull’s trench kiln, Hoffman’s kiln ,Tunnel kiln

11. Classification of bricks Unburnt Burnt -used in construction work First class –Used of for superior work. Are table moulded, burnt in kilns, standard shape, edges are sharp Second class – Ground moulded , burnt in kiln, may have hair cracks, used when plaster is provided Third class bricks – Ground moulded, burnt in clamps, not hard, rough surface, distorted edges, used in unimportant work Fourth class bricks – Overburnt bricks with irregular shape, dark colour, Used as aggregate for concrete

12. Qualities of good brick Should be table moulded, well burnt in kilns, copper coloured, free from cracks and with sharp and square edges. Should be of uniform shape and standard size. Should give a clear metallic ringing sound when struck with each other. When broken should show uniform structure. Should not absorb water more than 20% by weight for first class bricks. Should be sufficiently hard. Should not break into pieces when dropped from a height of 1 metre. Should have a low thermal conductivity. Should not show deposits of white salts.

13. Strength of bricks Factors affecting strength are Composition of brick earth Preparation of clay and blending of ingredients Nature of moulding adopted Care taken in drying and stacking Type of kiln used Burning and cooling processes Care taken in unloading

14. Tests for bricks Absorption – do not exceed 20 % by weight when immersed in water for 16 hours Crushing strength – Minimum is 3.5N/mm 2 Hardness -No impression left on the surface when scratched with nail. Presence of soluble salts – Minimum efflorescence Shape & size – Truly rectangular with sharp edges Soundness – When struck with each other, shouldn’t break Structure – Homogeneous structure when broke