A good brick earth can easily be moulded and dried without cracking and warping.
A good brick earth should have the following composition:
Alumina or clay 20 to 30 percent by weight.
Silica or sand 35 to 50 percent by weight
Silt 20 to 35 percent weight.
Remaining ingredients which include : Lime (cao) , Oxide of iron ,Manganese oxide , Manganese , Sodium potash etc. 1 to 2 percent by weight
Alumina :
It is the principal constituent of every kind of brick earth. A good brick earth should contain about 20 percent to 30 percent of alumina.
It imparts plasticity to the brick earth, which is essential for proper moulding of bricks alumina or clay in brick earth shrinks and cracks on drying. It also warps and becomes very hard on burning unless mixed with sand.
Silica :
A good brick earth should contain about 50 percent to 60 percent of silica. Sand alone is in fusible but it fuses in the presence of lime and oxides of iron at kiln temperature.
Sand or silica in brick earth prevents the shrinkage, cracking and warping of bricks. It also makes the bricks durable. Excess of silica makes the bricks brittle and weak.
Lime :
A small quantity of lime not exceeding 5 percent is desirable in good brick earth.
It helps to bind the particles of brick earth together. It also reduces shrinkage of bricks.
Oxide of Iron :
A small quantity of oxide of iron to the extent of about 5 to 6 percent is desirable in good brick earth and binds the particles of clay together.
It also provides the required red colour to the bricks on burning but excess of oxide of iron makes the bricks dark blue.
Magnesia :
Small quantities of magnesia in bricks of yellowish colour and reduce shrinkage. But excess of magnesia leads to the decay of bricks.
Manganese :
The presence of manganese in small quantity in brick earth makes the bricks darker or even black.
Three Following Types of Perforation or Cavities Bricks :
Perforated bricks
Hollow bricks
Channeled bricks
Perforated Bricks :
These form a modern class of building bricks.
Four perforated bricks of white, yellow and red colors with round and rectangular holes on a pallet with bricks on the background other bricks on a warehouse
In perforated bricks cylindrical, rounded or rectangular holes are made in the bricks after the moulding stage. These holes are called perforations.
They are properly spaced from the side of the brick, minimum distance being 15mm. further, distance between any two perforations is not less than 10mm the volume of the perforations. May be as much as 20-50 percent of the total volume of the brick.
Advantages :
These bricks are light in weight.
Less quantity of clay is required for their manufacture;
Less time is required for drying and burning of perforated bricks.
These offer better resistance against rain penetration and better insulation against heat. As such they are ideally suited for tropical countries.
Efflorescence is least in perforated bricks.
These are specially suitable for construction of brick panels in- multi-storeyed structures.
Hollow Bricks :
A brick also called cavity brick or cellular brick has a few well- defined sets of cavities with specified dimensions made in the body of the brick.
Its net weight may be only one- third to one- half of the solid brick. It is important that the thickness of brick wall near the cavity should not be less than 2 cm. Hence cavity extends throughout the body of the brick.
The hollow bricks are made from special type of brick clay (which should have higher clay content).
Advantages :
Being
light in weight, they can be handled more conveniently and the output of the
mason may be three to four times compared with ordinary bricks.
They
offer better insulation against heat and sound.
They
are ideal and economical for non- load bearing walls, e.g in partition walls.
Channel or Gutter Bricks :
They are actually special purpose bricks having a continuous central semicircular cavity or depression running through their length very often they are glazed to make them impervious.
King Closer : the brick is so cut that it has length and width on one side only.Uses splayed jambs,blunt corners of walls.
Queen Closer : it is also a cut brick. The cut is lengthwise so that brick has only one half of the length of the full bricks. Uses bonding of brick works.
Squint Brick : it is also cut brick.the portion of cut forms angles other than right angle. Uses exterior or interior corners are to be built at some angle and also for ornamental purposes.
Splay Bricks or cant bricks : these have a level or portion taken off, widthwise, lengthwise, or in both directions. Uses for pillars , on top course of plith,on exterior walls etc.
Plinth Header : it has a full length on one face. On the other face, a slope (bevel) is made from 3/4th of the length (D)
Plinth Stretcher : it has slope from one half of the width that extends along the entire length (E).
Plinth Return : it is a combination of both the header and stretcher beveling (F).
Coping Bricks : when a coping is to be provided to a wall, a special shape may be desired. The chamfered brick, the half round brick and the saddle back brick are some common coping bricks.
Bull Nose : it is otherwise a standard brick having one arris or edge rounded. Uses for decoration purposes.
Cow Nose : it is similar to a bull nose but has both edges on the side rounded. It may be called a double bullnose. Use for ornamental purpose.
Miscellaneous Shapes : these include bricks shaped for very specific purpose (not covered above) as for arches and circular walls, chimneys and culvets and wells.
Conventionally , the Bricks are classified in the following two types :
Sun dried or Katcha Bricks :
Burnt or Pucca bricks :
Sun Dried or Katcha bricks :
The bricks dried only in the sun after their moulding are called sun dried or Katcha Bricks.These should not be used at places exposed to heavy rains.
Uses : These are suitable for constructing temporary houses,enclosures etc. in rural area.
Burnt or Pucca Bricks :
These brick burnt in a clamp or klin,after moulding and drying are called burnt or pucca bricks.
These are hard,strong and durable.
Uses : These are generally in permanent works.
These further classified into the following four types :
FIRST CLASS BRICKS :
CHARACTERISTICS :
(i) Well burnt having even surface , perfectly rectangular shape & free from saline deposits.
(ii) When two bricks are struck against each other a ringing- sound is produced.
(iii) Its compressive strength shall not be less than 140kg/cm2 and its absorption after 24 hours, immersion shall not exceed 20 percent.
(iv) It should show a uniform appearance,colour , texture and structure when seen on fracturing.
(v) They shall be clean,smooth & free from cracks,chips,grits,holes , nodules of lime or kankar etc.
(vi) They shall not show any sign of efforescence on surface when dried in the shade.
(vii) They shall not absorb water more than 20% by weight after 24 hours immersion in cold water.
(viii) They shall have a minimum crushing strength of 105kg/sq.cm.
Uses : Every kind of masonry work, flooring etc. Where strength and durability is desired. They are also used for face work,reinforced brick work and as ballast for base concrete work in floors.
SECOND CLASS BRICKS :
CHARACTERISTICS :
Well burnt, even slight over burning is accepted.
Metallic-ringing sound is also a must in this case as well.
In shape, rectangular, but slight irregularity is permitted. Surface may be slightly uneven.
Compressive strength shall not be less than 70kg/cm2 and absorption value between 20-22 percent.
Slight difference in structure on fractured surface is admissible.
They have fine , compact ,uniform texture.
They may have slightly chips , flaws or surface cracks but shall be free from lime & kankar nodules.
They are not so hard & strong.
They shall have a minimum crushing strength of 70 kg/sq.cm.
They shall not absorb water more than 22% by weight after 24 hours immersion in cold water.
They shall not show any sign of efflorescence on surface either in wet or in dry state.
Uses : These used in unimportant situations where bricks are hidden from front views as in the case of interior walls. They are never used in reinforcement brick work or face works of building.
THIRD CLASS BRICKS :
CHARACTERISTICS :
Poorly and unevenly burnt, that is, may be over burnt or under burnt.
On striking a dull thud (rather than metallic sound) is produce.
Appearance, shape and size are also non- uniform and irregular.
Compressive strength lies between 35- 70 kg/cm2 and absorption between 22-25 percent.
Yellowish in colour & may be distorted and have round edges.
They are soft & weak in strength.
They shall not absorb water more than 25% by weight after 24 hours immersion in cold water.
Uses : These used in inferior and temporary buildings & in place not subjected to heavy rains . They are sometimes used for scaffolding and centring in the construction of building.
JHAMA OR FOURTH CLASS / OVER BURNT BRICKS :
CHARACTERISTICS :
Irregular in shape and dark in colour, which is due to over burning.
Quite strong in compressive strength, generally above 150kg/cm2 and low in porosity and absorption.
They shall be over burnt , vitrified & distorted bricks.
They shall be dark in colour.
They shall be irregular in shape & size and may be available in the form of lumps.
They shall be hard & strong.
Produce metallic sound when struck with one another.
Uses : They are used as aggregates for making base for concrete to be used in foundations, floors etc. and as road metal for soling coats.
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