•Clay products are one of the most important classes of structural materials. The raw materials used in their manufacture are clay blended with quartz, sand, chamatte (refractory clay burned at 1000–1400°C and crushed), slag,

sawdust and pulverized coal.

•Bricks, tiles, pipes, terracotta, earthenwares, stonewares, porcelain, and majolica are well recognized and employed in building construction.

•Clay bricks have pleasing appearance, strength and durability whereas clay tiles used for light-weight partition walls and floors possess high strength and resistance to fire. Clay pipes on account of their durability, strength, lightness

and cheapness are successfully used in sewers, drains and conduits.

Classifications It is an earthen mineral mass or fragmentary rock capable of

mixing with water and forming a plastic viscous mass which has a property of retaining its shape when moulded and dried. When such masses are heated to redness, they acquire hardness and strength.

A. BY ORIGIN

1. RESIDUAL

known as Kaolin or China clay,

are formed from the decay of underlying

rocks and are used for making pottery.

2. TRANSPORTED OR SEDIMENTARY CLAYS

Result from the action of weathering

agencies. These are more disperse, contain

impurities, and free from large particles of

mother rocks.

B. RESISTANCE TO HIGH TEMPERATURES

1. Refractory

The refractory clays are highly disperse and very plastic. These have high content of alumina and low content of impurities

2. High melting clays

Have high refractoriness (1350–1580°C) and are used for manufacturing facing bricks, floor tiles, sewer pipes, etc.

3. Low melting clays

Refractoriness less than 1350°C and have varying compositions.

These are used to manufacture bricks, blocks, tiles, etc.

Physical Properties Plasticity, tensile strength, texture, shrinkage, porosity, fusibility and colour after burning are the physical properties which are the most important in determining the value of clay.

1. Plasticity

the property which wetted clay has of being permanently deformed without cracking. The simplest and the most used test is afforded by feeling of the wetted clay with the fingers.

2. Tensile strength

Since clay ware is subjected to considerable stress in moulding, handling and drying, a high tensile strength is desirable.

3. Texture

measured by the fineness of its grains. In rough work the per cent

passing a No. 100 sieve is determined. Very fine grained clays free from sand are more plastic and shrink more than those containing coarser material.

4. Shrinkage

Knowledge of shrinkage both in drying and in burning is required in order to produce a product of required size.

5. Porosity

the ratio of the volume of pore space to the dry volume. Large pores allow the water to evaporate more easily and consequently permit a higher rate of drying than do small pores.

6. Fusibility

Fine textured clays fuse more easily than those of coarser texture and the same mineral composition

7. Color after burning

If the kiln atmosphere is insufficiently oxidizing in character during the early stages of burning, the removal of carbon and sulphur will be prevented until the mass has shrunk to such an extent as to prevent their expulsion and the oxidation of iron. When this happens, a product with a discoloured core or swollen body is likely to result

Heavy Duty Burnt Clay Bricks These are similar to burnt clay bricks and of the same size but with

high compressive strength.

Water Absorption: should not be more than 10 % after 24 hours immersion in water.

Burnt Clay Perforated Bricks Perforated Bricks contain cylindrical holes throughout their thickness,

have high compressive strength and less water absorption. Perforated Bricks contain cylindrical holes throughout thier thickness, have high compressive strength and less water absorption. These are used in building walls and partitions.

Water Absorption: should not be more than 15 %.

Burnt Clay Paving Bricks The iron content is more than that in the ordinary clay bricks. Excessive

iron causes vitrification of bricks while burning at a low temperature, gives natural glaze to the brick, making it more resistant to abrasion.

Water Absorption: should not be more than 5 % by weight after immersion for about 24 hours

Burnt Clay Hollow Blocks Hollow blocks, also known as cellular or cavity blocks, are

manufactured from a thoroughly ground, lump free, well mixed clay mass of medium plasticity to allow moulding. They also reduce the transmission of heat, sound and dampness.

Water Absorption: should not be more than 20 %.

Burnt Clay Jallis These are normally used for providing a screen on veranda and

construction of parapet or boundary walls. These are generally hand moulded but superior qualities can be produced by machines.

Water Absorption: average value should not exceed 15 %.

Clay Tiles Tiles are thin slabs of low melting clays used for various purposes in

engineering constructions. These give a very pleasing appearance and good service properties.

Floor tiles are extensively used in houses and industrial buildings. These are durable and impervious to water, resist abrasion well and wash easily. White burning and red burning clays, fire clays and shales are used in

making tiles for floor surfaces.

Tiles for surface of walls differ from floor tiles principally in design in degree of burning. Wall tiles are burned at a comparatively low temperature, glazed, and fired again in muffle kiln at a still lower temperature.

Characteristics Uses

A good roofing tile should have the following properties:

1. uniform texture.

2. accurate size and shape.

3. free from defects like flaws, cracks and non-uniform burning.

4. water absorption (less than 15 per cent).

5. resistant to atmosphere and dampness.

6. durability.

They are used as roofing material for low cost houses in big cities and also used to give a pleasing look from architectural point of view.

Testing of Tiles 1. Transverse Strength Test

2. Water Absorption Test

3. Impact Test

4. Breaking Test

Plain Tiling

Hip Tiling

Pan Tiles

Pan Tiling

Spanish Tiling

Italian Tiling

Ridge Tile

Ceiling Tile

Double Lug Type (Length of Ceiling tile at the botom)

Single Lug Type (Width of ceiling tile at the bottom)

Manufacturing of Clay Tiles Tiles are made in the same manner as bricks, but are thinner and lighter, so

require greater care. These are manufactured from a clay mass with or without admixtures of colouring impurities by moulding and subsequent burning until baked, up to about 1300 °C.

The clay should be highly plastic with lean admixtures and fusing agents to lower the melting point.

Fire-Clay or Refractory Clay Fire-clay is a term, loosely applied, to include those sedimentary or

residual clays which vitrify at a very high temperature and which, when so

burnt, possess great resistance to heat. The fire clay is used for manufacturing fire bricks used in furnace linings, hollow tiles, and crucibles.

Fire-Clay Bricks or Refractory Bricks

Fire-clay bricks are made from fire-clay. The process of manufacturing is as of an ordinary brick, burnt at very high temperatures in special kilns (Hoffman’s kiln).

Properties

1. The colour is whitish yellow or light brown. 2. The water absorption of fire-clay bricks varies from 4–10% 3. The minimum average compressive strength of the bricks should be 3.5 N/mm2.

Porcelain

A hard, vitreous, translucent ceramic material consisting essentially of kaolin, feldspar, and quartz, fired at a very high temperature

Enamel

A vitreous, usually opaque, decorative or protective coating applied by fusion to the surface of metal, glass, or pottery.

Earthenware

Low fired, opaque, non- vitreous ceramic ware.

Stoneware

High-fired, opaque, vitrified ceramic ware. Earliest example found in China.

Majolica Glazing

It is Italian earthenware coated with an opaque white enamel, ornamented with metallic colour. It is used in doorways, window casings, and facing tiles.

Bricks, tiles, earthenwares and stonewares are glazed by an impervious film to protect the surface from chemical attack and other weathering agencies.

1. TRANSPARENT

2. LEAD

3. OPAQUE

Application of clay products Universal availability of raw materials, comparative simplicity of

manufacture and excellent durability of ceramic materials have put them in the forefront among other constructional materials. The various applications of clay products in the building industry are as follows.

1. WALL MATERIALS

2. BRICK FOR SPECIAL PURPOSES

3. HOLLOW CLAY PRODUCTS FOR FLOORS

4. FACADE DECORATION

5. CLAY PRODUCTS FOR INTERIOR DECORATION

6. ROOF MATERIALS

7. ACID-RESISTANT LINING ITEMS

8. SANITARY CLAY ITEMS

9. AGGREGATE FOR CONCRETE

•Any of various hard, brittle, noncorrosive, and nonconductive materials formed by the ionic bonding of a metal and a non-metal, as brick, concrete and

natural stone.

•The word is of Greek origin and derives its name from Keromos meaning potter’s earth or clay.

•Nowadays the term ceramic is applied to a wide range of silicates, metallic oxides and their combinations.

Ceramic ware

Any of Various products made by firing clay or similar materials in a kiln, as brick, tile, and pottery

Firing

The process of hardening or glazing ceramic ware by heating in a kiln to a specified temperature

Vitrify Vitreous Semi vitreous

Resembling a glass as in transparency, hardness, brittleness, luster, or having low or no porosity

Having a moderate water absorption of slightly under 6%

To make a clay body vitreous by firing at a specified temperature

HARD-BURNED – fired at a high temperature to near vitrification and having relatively low absorption and high compressive strength

SOFT-BURNED – Fired at a low temperature and having relatively high absorption and low compressive strength

Non vitreous

Having a water absorption greater than 7%

(ALSO SOFT BURNED)

A thermochemical bond between materials resulting from exposure to temperatures approaching the fusion point of the mixture

The structural portion of a ceramic article or the clay material or mixture from which it is made.

Ceramic Bond Body

Bisque-fired

Fired to harden a clay body

Bisque

Earthenware or porcelain that has been fired once but not glazed. Also called Biscuit.

Glaze-fired

Fired to fuse a glaze to a clay body

Glaze Frit

A Vitreous layer or coating fused to a clay body to color, decorate, waterproof, or strengthen its surface.

A fused or partially fused material that is ground to introduce a soluble or unstable ingredients into glazes or enamels.

Ceramic tile Glazed wall tile

Any or various fired clay tiles used for surfacing walls, floors, and countertops.

A ceramic tile having a non vitreous body and a bright, matte, or crystalline glaze, used for surfacing interior walls and light-duty floors.

Ceramic mosaic tile Quarry Tile

Small ceramic tile having a porcelain or natural clay body, glazed for surfacing walls or unglazed for use on both floors and walls, and usually face or back-mounted on sheets to facilitate handling and speed installation.

Unglazed ceramic floor tile having a natural clay body. Also called promenade tile.

Paver tile

Unglazed ceramic floor tile similar in composition to ceramic mosaic tile but thicker and larger in surface area.

Structural clay tile

A hollow tile of fired clay having parallel cells or cores, used in building walls and partitions.

LB

Load-bearing structural clay tile suitable for masonry walls not exposed to frost action, or in exposed masonry where protected by a facing of 3 in. (76.2mm) or more of stone, brick, terra cotta, or other masonry.

LBX

Load-bearing structural clay tile suitable for masonry walls exposed to weathering or frost action.

Hollow tile Structural facing tile

Any of various cellular building units of fired clay, concrete, or gypsum, used for building walls, floors, and roofs, or for fireproofing steelwork.

Structural clay tile facing a glazed surface, used for facing walls and partitions, esp. In areas subject to heavy wear, moisture problems, and strict sanitation requirements.

FTS FTX

Structural facing tile suitable for exposed exterior and interior masonry walls and partitions where moderate absorption, slight variation in face dimensions, minor-defects in surface finish, and medium color-range are acceptable.

Smooth structural facing tile suitable for exposed exterior and interior masonry walls and partitions where low absorption and stain resistance are required, and where a high degree of mechanical perfection, minimum variation in face dimensions, and narrow color range are desired.

Terra cotta Architectural terra cotta

A hard, fired clay, reddish-brown in color when unglazed, used for architectural facings and ornaments, tile units, and pottery.

Hard-burned, glazed or unglazed terra cotta, hand-moulded or machine-extruded to order as a ceramic veneer for walls or for ornamentation.

Adobe Rammed earth

Sun-dried brick made of clay and straw, commonly used in countries with little rainfall

A stiff mixture of clay, sand or other aggregate, and water compressed and dried within forms, as a wall construction. Also called pise, pisay, pise de terre.

Mechanical Properties Tensile strength

Theoretically the tensile strength of ceramics is very high but in practice it is quite low. Tensile failures of ceramics are attributed to the stress concentrations at the pores and micro-cracks at grain corners.

Compressive strength The compressive strength is high and it is usual to use ceramics like clay, cement

and glass products in compression.

Shear strength Ceramics have very high shear strength with resistance to failing in a brittle

manner.

Transverse strength is difficult to ascertain and ceramics are not used in the places where

such strength is the criteria.

Thermal Properties Thermal capacity, conductivity and resistance to shocks need to be

considered while using a ceramic.

The heat in ceramics is conducted by phonon conductivity and by the interaction of lattice vibration. The ceramic materials do not have enough free electrons to bring out electronic thermal conductivity

Electrical Properties Ceramic materials have no free electrons so they have low electrical

conductivity. However, at high temperatures the ionic diffusion is accelerated. For example glass is an electrical insulator, but in the glass melting furnace, its conductivity becomes quite high.