Constituents of Bricks

 Following are the constituents of good brick earth.

 1. Alumina: 

It is the chief constituent of every  kind of clay. A good brick earth should contain 20 to 30 percent of alumina. This constituent imparts plasticity  to earth so that it  can be  moulded. If alumina is present in excess, raw bricks shrink and warp during drying and burning. 

2. Silica:

A good brick earth should contain about 50 to 60 percent of silica. Silica exists  in clay either as free or combined form.  As free sand, it is mechanically mixed with clay  and in combined form;  it exists in chemical composition with alumina.  Presence of silica prevents crackers shrinking and warping of raw bricks. It  thus imparts uniform  shape to the bricks. Durability  of bricks depends on the proper proportion of silica in brick earth. Excess of silica  destroys  the cohesion between  particles and bricks become brittle. 

3.Lime:

A small quantity of lime  is desirable in finely  powdered state to prevents shrinkage of raw bricks. Excess of lime  causes the brick to melt and hence, its shape is last due  to the splitting of bricks. 

4. Oxide of iron:

A small quantity  of  oxide of Iron to the  extent of 5 to 6 percent is desirable in good brick to imparts red  colour to bricks. Excess of oxide of iron makes the bricks dark blue or blackish. 

5. Magnesia: 

A small quantity  of magnesia  in brick earth imparts yellow tint to bricks, and decreases shrinkage. But excess of magnesia decreases shrink leads to the decay  of bricks.