Brick|Types|Classification|Constituents|Harmful ingredients|Good quality

Types of brick:-Bricks may primarily be divided as sun dried or kachha bricks and brunt or pucca brick. Sun dried bricks are not burnt bricks generally used for temporary construction. These bricks should not be exposed to heavy rains. These bricks are primary forms of pucca bricks,

Depending upon the strength, appearance and usefulness of burnt bricks, they are further

classified as:-

1)First class brick :- First class bricks are the quantity bricks with following characteristics:-

●A first class brick should be free from cracks, stones etc.

●It should be thoroughly burnt and should have uniform deep red or cherry or copper

color.

●It should have a firm uniform and compact texture.

●It should not show efflorescence when soaked in water and dried.

●It should have rectangular plane surface with parallel sides and sharp,straight,right

angled edges.

●Compressive strength should not be less than 140 kg/cm2

●Its specific gravity should be greater than 1.8.

Its uses:

Such types of bricks are used in unimportant situations and for inter walls (where the bricks are generally hidden from view.

2) Second class brick :- Second class bricks are the inferior quality of bricks that are generally used for minor structural purposes. Following are the characteristics of second class

brick.

●A second class brick should be well brunt but may be not uniform in color,shape and size.

●It may have a rough surface.

-It should also have a fine, compact and uniform texture.

●It may have some cracks,lumps etc.

●It should have a minimum crushing strength of 7 mpa.

●Water absorption of second class bricks should exceed 22% of its dry weight.

● It should also produce a metallic ringing sound when struck.

3) Third class brick :-

●These bricks are light yellow coloured,unsuitable for the structural purposes and sometimes soluble in water.

●They are soft,easily broken and produces dull sound

when struck.

●They are used in-temporary construction.

●It is used in inferior and temporary buildings.

4) Over burnt bricks - These are vitrified bricks with irregular shape and dark or blue color. They are hard and strong. They produce a metallic ringing sound when struck. These bricks are used in foundation and in making aggregates for concrete. They may also be used in soiling and as road metal. These bricks may also be classified as machine made bricks or chimney made bricks.

Classification

Generally bricks are divided into two types:

Sun Dried bricks:

-->These bricks are dried with the help of heat received from the sun after molding. These bricks are not burnt.

These bricks are weak and can be used in the construction of temporary and cheap structures.

Such bricks should not be used in heavy structure and exposure

to water.

Burnt bricks:

They are burnt in clamps or kilns after drying.

They are hard, strong and durable and are generally used in permanent structure.

Composition of good brick

In general it is observed that clay any soil that contains one-fourth past of clay and three by fourth parts of sand and silt is suitable for making bricks. A good brick earth should be such that when prepared with water it can be easily molded, dried and burnt without cracking or warping. It should contain a small quality at finely divided lime to help in binding the particles of brick together by melting the particles of sand. A little oxide of iron should also be present which would give the brick its peculiar red color and acts as flux in the same manner as lime.

Constituents in brick

i) Alumina or clay(20%-30%): - It makes brick earth plastic,so that it can be molded and after drying impacts hardness.If bricks contain excess amount of it,they shrink,crack and wrap in the

process of drying and burning.

ii) Silica(or sand) (50% -60% ]:-Presence of silica prevents shrinkage,cracking and wrapping of bricks.Its excess amount destroys the cohesion between particles and makes the brick brittle and weak.

iii) Lime (4%-6%):-Lime and oxide of iron both acts as fluxes helping the grain of sand to melt

and bind the particles of clay together.Oxide of iron also impacts a red color to the brick,but excess of it makes the brick dark blue.Iron oxide also increases the durability and

impermeability of the bricks.

iv) Magnesia(1% -2%):-Magnesia present in clay with oxide of iron makes the brick yellow, but larger amounts of magnesia may cause bricks to decay.

v) Iron Oxide(4% -6%):-Iron oxide acts as a flux, it lowers down the softening temperature of silica and other clay components during firing. The iron oxide impacts the very characteristic red

color to the brunt brick. A deficiency of iron oxide in the clay may make their burning difficult and also give them a yellowish appearance.

Harmful ingredients of brick

i)Lime:-Lime when used in excess and in the form of stone or kankar,gets converted into quick lime.Quick lime readily absorbs moisture and swells, which causes the cracking of bricks.

ii) Alkalis:- Alkali present in the brick earth lowers the fusion point of clay and causes brick to fuse,twist and wrap during burning.Alkaline salts present in the brick absorbs moisture from the atmosphere and creates damp conditions. These bricks when dried up give a grayish white deposit around the surface known as efflorescence.This spoils the appearance of brick.

iii) Pebbles of stone and gravel:-Presence of Pebbles of stone and gravel does not harm chemically, but it reduces the workability and homogeneity of brick earth.

iv) Iron pyrite:- Iron pyrite oxidizes in the brick and splits the brick into pieces.It should be removed carefully.

v) Vegetation and organic matters:- Vegetation and organic matters mainly contain carbon which when burnt converts into carbon dioxide. The volume occupied by these materials becomes vacant and the bricks will not be sound to be used for structure purposes.

Good Quality of Bricks

(i) Size and shape: A good brick should be uniform in size(standard) and should have regular plane surface with parallel

sides and sharp straight right angled edges. Its surface should not be too smooth or, otherwise the mortar will not stick to it as the NS size of brick is (230 x 110 × 55) mm.

(ii) Colour: It should have light orange copper color. It should be uniform without a tinge of other colors.

(iii) Structure: A good brick should show fine compact and uniform structure in broken form.

(iv) Soundness: A good brick should give a clear metallic ringing sound when struck with another brick.

(v) Hardness: It should be so hard that finger nail should not be able

to make any impression on its surface when scratched.

(vi) Porosity: A good brick should not absorb more than 20% of its dry weight of water when kept immersed in water.

(vii) Strength: A good brick should have a minimum strength of 10.5 N/mm². Ordinarily it should not break when dropped from 1m height on hard flat ground.

(viii) Resistance to fire: It should have good resistance to fire. It must resist a temperature of at least 1200°C.

(ix) Efflorescence: A good brick should not contain much alkaline salts, which may cause efflorescence on its surface and decay the brick.

(x) Durability: A good brick should be able to resist the effect of weathering agencies like température variation rain, frost action

etc. and should remain in original condition for many years.