Composition of brick :



SILICA:

   1. Silica prevents the cracking, shrinkage and warping of the bricks, thereby imparts uniform shape of it.

  2. It decreases shrinkage in burning and increases refactorines.

 3. If it is in excess it destroy cohesion between the particles, hence bricks become too brittle.

ALUMINA:

1. Alumina imparts plasticity to the brick so that it can be easily moulded in any desired shape.

2. If it in excess , it causes shrinkage and warping drying of bricks and makes the brick too hard during the working process.

LIME:

1. Lime also prevents the shrinkage of the brick.

2. It helps silica in clay to melt and helps in binding but if it in excess, it causes the brick to melt during the burning thereby it results in loss of the shape of bricks.

NOTE:
         During the burning of the bricks , calcium carbonate ( lime stone) is converted in to quicklime,
that undergoes slaking process which process in turn, results in the cracking & integration of the bricks due to increase in volume.

OXIDE OF IRON:

1. Oxides of iron ( ferrous) helps silica and lime to fuse with each other, hence leads to the development of strength in the brick.

 2. Excess of iron ( ferric) makes brick DARK BLUE.

 3. It also imparts Reddish brown colour in bricks

 4. Improves impermeability.

MAGNESIA:

1, Magnesia also prevents the shrinkage and imparts yellowish tint in bricks .

HARMFUL INGREDIENTS IN BRICK:

1. LIME SLAKING:

     1) Slaking - volume increase - cracking and disintegration.
     2) Changes the colour of brick from Red to yellow .

2.Iron pyrites:

 1. Presence of the iron pyrites leads to crystallization and disintegration of bricks during burning due to the oxidation of the pyrites during burning process .

2. The brick may split into pieces.

3. ALKALIES:

 1. Alkali act as a flux during the burning of bricks but if it is in excess it causes the bricks to fuse with each other there by resulting in its twisting and warping.

2. Presence of alkalies also leads to effloresence and staining in bricks.

4. PEBBLES OR STONE:

    Presence of stone and pebbles brick earth leads to the formation of weak and porous brick, loads carrying  capacity of which is comparatively reduced.
  

5. ORGANIC AND VEGETATIVE MATTER:

 Presence of organic and vegetative matter helps in the burning of bricks but if they are left unburnt, it results in the formation of gases during the decomposition which when escapes throughout the body of the bricks leads to the development of numerous voids , which results in decreasing the load carrying capacity of bricks.