Brick properties in Detail, types of bricks and Special brick in detail

                BRICK THEORY

Introduction:- 

A brick is rectangular in shape and of size that can be conveniently handled with one hand. Brick may be made of burnt clay or mixture of sand and lime or of Portland cement concrete. Clay bricks are commonly used since these are economical and easily available. The length, width and height of a brick are interrelated as below:

Length of brick =   2  x  width of brick +   thickness of mortar.

Height of brick = width of brick

Size of standard brick (also known is modular brick) should be 19 x 9 x 9 cm and  19 x 9 x 4 cm . In masonry 19 x 9 x 9 cm bricks with mortar becomes 20 x 10 x 10 cm. And bricks are used for Constructing walls, columns, roofs, paving floors etc.

Frog:-  

The purpose of providing frog is to form a key for holding the mortar and therefore, the bricks are laid with frogs on top. Frog is not provided in 4 cm high bricks and extruded bricks. (provided in 9 cm high bricks).

Standard size of frog:- 10 x 4 x 1 or 2 cm

Classification of Bricks:- 

 Clay bricks are classified as first class, second class, third class and fourth class based on their physical and mechanical properties.

   First Class Brick:-

·         These are thoroughly burnt and are of deep red, cherry or copper colour.

·         The surface should be smooth and rectangular, with parallel, sharp and straight edges and square corners.

·         These should be free flaws, cracks and stones.

·         These should have uniform texture.

·         No impression should be left on the brick when a scratch is made by a finger nail.

·         The fractured surface of the brick should not show lumps of lime.

·     A metallic or ringing sound should come when two bricks are struck against each other.

·      Water absorption  should not be more than 20% by weight after 24 hours immersion in cold water.

·     The crushing strength of the brick should not be less than 10 N/mm² .

·     Uses:-  First class bricks are recommended for pointing, exposed face work in masonry structures, flooring and reinforced brick work.

      Second Class Bricks:-

·         Not well burnt and are not of uniform shape, size and colour.

·         Small cracks and distortions are permitted.

·         Water absorption not more than 22% by weight.

·         The crushing strength should not be less than 7 N/mm² .

·         Uses:-  Second class bricks are recommended for all important or unimportant hidden masonry works and centering of reinforced brick and reinforced cement concrete (RCC) structures.

      Third Class Brick:-  

·         These are under burnt and not uniform in shape and Size, also called pilla bricks.

·      They are soft and light-coloured producing a dull sound when struck against each other.

·         Water absorption not more than 25% by weight.

·         The crushing strength should not be less than 5 N/mm² .

·         Uses:-  it is used for building temporary structures.

Over burnt bricks / Jhama bricks:-

·         Over burnt and irregular shape and size.

·         Uses:- used as Aggregates for making concrete to be used in foundations, floors etc. and as road metals for Soling coat.

Special Bricks:-

1.       Bull nose Brick:-  If one side (Corner) is rounded of brick.
2.       Cow nose Brick:-  If both corner rounded of brick.
3.       Refractory Bricks:- A good refractory brick should have the capability of with standing high temperature and low Co-efficient of expansion and contraction. It is also known as Fire Bricks.

·         High compressive stresses up to 1500 to 2000 kg/cm² .

·         Water absorption is 4 to 10 %.

·         Unit weight of refractory bricks is 2400 kg/m³ .

·         Standard Size of refractory brick is 230 x 65 x 113 mm.            

Characteristics of Good Bricks:-

• The essential requirements for building bricks are sufficient strength in crushing, regularity in size, a proper suction rate, and a pleasing appearance when exposed to view.

• Size and shape:  The bricks should have uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges.
• Colour:- The brick should have a uniform deep red or cherry colour as indicative of uniformity in chemical composition and thoroughness in the burning of the brick.
• Texture and compactness:  The surfaces should not be too smooth to cause sleeping of mortar. The brick should have pre compact and uniform texture. A fractured surface should not show fissures, holes grits or lumps of lime.
• Hardness and soundness:  The brick should be so hard that when scratched by a finger nail no impression is made. When two bricks are struck together, a metallic sound should be produced.
• Water absorption:  Should not exceed 20 percent of its dry weight when kept immersed in water for 24 hours.
• Crushing strength:-  should not be less than 10 N/mm² .

       Defects in Bricks:-

•       Over burning of Bricks:-   Bricks should be burned at temperatures at which incipient, complete and viscous vitrification occur. However, if the bricks are over burnt, a soft molten mass is produced and the bricks loose their shape. Such bricks are not used for construction works.
•              Under burning of bricks:-  When bricks are not burnt to cause complete vitrification, the clay is not softened because of insufficient heat and the pores are not closed. This results in higher degree of water absorption and less compressive strength. Such bricks are not recommended for construction works.
•                 Bloating:-   This defect observed as spongy swollen mass over the surface of burned bricks is caused due to the presence of excess carbonaceous matter and Sulphur in brick-clay.
•         Black core:-  When brick-clay contains bituminous matter or carbon and they are not completely removed by oxidation, the brick results in black core mainly because of improper burning.
•             Efflorescence:- This defect is caused because of alkalis present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalis crystallise. On drying grey or white powder patches appear on the brick surface. This can be minimized by selecting proper clay materials for brick manufacturing, preventing moisture to come in contact with the masonry, by providing waterproof coping and by using water repellent materials in mortar and by providing damp proof course.
•              Chuffs:-  The deformation of the shape of bricks caused by the rain water falling on hot bricks is known as chuffs.
•               Checks of cracks:- This defect may be because of lumps of lime or excess of water. In case of the former, when bricks in contact with water, the absorbed water reacts with lime nodules causing expansion and a consequent disintegration of bricks, whereas shrinkage and burning cracks result when excess of water is added during brick manufacturing.
•            Spots:-  Iron sulphide, if present in the brick clay, results in dark surface spots on the brick surfaces. Such bricks though not harmful are unsuitable for exposed masonry work.
•           Blisters:‑  Broken blisters are generally caused on the surface of sewer pipes and drain tiles due to air imprisoned during their moulding.

Manufacturing of Bricks:-

1.   Preparation of Brick Earth:-

• Unsoiling
• Digging
• Weathering
• Blending
• Tempering

      2.   Moulding
      3.   Drying 
      4.   Burning:- The burning of bricks of may be divided in three phases.

            Dehydration             ( 400 – 650^o C )

            Oxidation phase       (650 – 900^o C )

            Vitrification              (900 – 1100^o C )

•   Burning of bricks is done in a clamp or kiln. A clamp is a temporary structure whereas kiln is a permanent one.