composition of bricks

BRICKS

Brick are the oldest building material which may be made of burnt clay or mixture of sand and lime or of Portland cement concrete. Clay bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks. As bricks are of uniform size, they can be properly arranged, light in weight and hence bricks replace stones.

Composition of good brick earth

A good brick earth may contain the following constituents

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. Presence of silica prevents cracks, 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 not exceeding 5 percent should present in good brick earth. It helps in preventing shrinkage and cracking. The excess of lime causes the brick to melt and hence its shape is lost during the process of drying and burning.

4.     Oxide of iron

The quantity of iron oxide generally present in the good brick earth should be 5 to 6%. When the brick earth is heated the iron oxide gives bricks a red color. It also acts as a flux and helps in melting the sand or silica particles at lower temp. If the quantity of the iron oxide is less, the color of the brick will be yellowish and if the quantity of the iron oxide is more, the color of the bricks will be 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.

The ingredients like, lime, iron pyrites, alkalies, pebbles, organic matter should not present in good brick earth



** basic civil engineering notes for bput students.