•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
Stoneware
Low fired, opaque, non-
High-fired, opaque, vitrified
vitreous ceramic ware.
ceramic ware. Earliest example found in China.
Majolica It is Italian earthenware
coated with an opaque white enamel, ornamented with metallic colour. It is used in doorways, window casings, and facing tiles.
Glazing 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
To make a clay body vitreous by firing at a specified temperature
Vitreous Resembling a glass as in
transparency, hardness, brittleness, luster, or having low or no porosity
HARD-BURNED – fired at a high temperature to near vitrification and having relatively low absorption and high compressive strength
Semi vitreous Having a moderate water
absorption of slightly under 6%
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)
Ceramic Bond A thermochemical bond between
materials resulting from exposure to temperatures approaching the fusion point of the mixture
Body The structural portion of a
ceramic article or the clay material or mixture from which it is made.
Bisque-fired Fired to harden a clay body
Glaze-fired Fired to fuse a glaze to a clay
body
Bisque Earthenware or porcelain that
has been fired once but not glazed. Also called Biscuit.
Glaze A Vitreous layer or coating
fused to a clay body to color, decorate, waterproof, or strengthen its surface.
Frit A fused or partially fused
material that is ground to introduce a soluble or unstable ingredients into glazes or enamels.
Ceramic tile Any or various fired clay tiles
used for surfacing walls, floors, and countertops.
Glazed wall tile 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 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.
Quarry Tile 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 Any of various cellular
building units of fired clay, concrete, or gypsum, used for building walls, floors, and roofs, or for fireproofing steelwork.
Structural facing tile 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
Smooth structural facing tile
for exposed exterior and interior masonry walls and partitions where moderate absorption, slight variation in face dimensions, minordefects in surface finish, and medium color-range are acceptable.
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 A hard, fired clay, reddish-brown
in color when unglazed, used for architectural facings and ornaments, tile units, and pottery.
Architectural terra cotta 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
A stiff mixture of clay, sand or
and straw, commonly used in countries with little rainfall
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.
