constituents of good brick

What are the constituents of good brick earth?What constituents render brick earth unsuitable for manufacturing bricks?
What is brick earth and its constituents?

Constituents of good brick earth as follows--

(i) Alumina: It is the principal component of the brick earth and a good brick earth must contain about 20-30% alumina. Alumina gives plasticity to the earth thereby making the moulding of brick earth easier. However excess of alumina leads to shrinkage and warping of bricks.


(ii) Silica: 50-60% silica in good brick earth is desirable. Silica exists in clay either free or in combined form. It preventsshrinkage,
warping and cracking of bricks apart from imparting uniform shape to the bricks. However excess of silica destroys the cohesion between the particles of the brick earth and the bricks become brittle.


(iii) Iron Oxide: About 5-6% iron oxide is desirable in a god brick earth. Iron oxide gives red color to bricks. Excess of iron oxide leads to dark coloration in bricks like dark blue or blackish color. However less quantity of iron oxide makes the bricks yellowish in color.


(iv) Lime: About less than 5% lime should be present in a good brick earth. It should be in the very finely divided powder form. It prevents shrinkage of bricks. Excess of lime causes bricks to meltt there by  loosing its shape


(v) Magnesia: A very small quantity of magnesia gives yellow color to bricks. It also decreases shrinkage.


Which component is harmful to bricks?

Constituents which make the brick earth unsuitable :-

(i) Pebble: Pebbles in brick earth does not allow uniform mixing of clay thereby leading to weak and porous bricks.


(ii) Iron pyrites: Iron pyrites cause the brick to disintegrate on burning because of oxidation of iron.


(iii) Alkalies: Alkalies (particularly soda and potash) acts like a flux in the kiln and they cause bricks to fuse. Also alkalies absorb water from the brick masonry. This moisture on evaporation leaves behind white patches  on the surface of brick masonry.


(iv) Vegetation: Presence of vegetation and other organic matter in brick earth aids in burning. However such matter if remains partially burnt then bricks will become porous due to evolution of gases on burning.

Some Questions-
Which constituent in the earth gives plasticity to Mould bricks?
answer is ALUMINA which is clearly mensioned in above paragraph


How does excess of each of the constituents of brick earth affect the quality of bricks?
excess of everything is bad, but why these are unsuitable due to excessnes it is clearly mensioned in above paragraph please read carefully.




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