1. STONE
Introduction
Rock and Stone
Formation of Rocks
Classification of Rocks
Geological classification
Metamorphism
Physical classification of rocks
Chemical classification
Classification based upon hardness of the stone
Composition of Stone (Rock-forming Minerals)
Igneous rock forming minerals
Sedimentary Rock Forming Minerals
Texture of the Rocks
Types of Fractures of Rock
Uses of Stone
Natural bed of Stone
Seasoning of Stones
Characteristics or Qualities of Stones
Characteristics of principle Building Stones
Properties
Decay or Deterioration of Stones
Preservation of Stone
Artifical Stone
Important point to be Considered before Starting Quarrying
Methods of quarrying Stone
Various Operations of Blasting
Precautions in Blasting
Blasting materials
Making of Primer Cartridge
Storing of explosives
Handling of misfires
Dressing of Stone
Machines Required for Quarrying Stone

2. BRICKS AND OTHER CLAY PRODUCTS
Introduction
Brick Earth and its Constituents
Sources of Brick Earth
Qualities of Brick Earth
Chemical composition of Brick Earth
Functions of the constituents of Brick Earth
Harmful Ingredients
Pebbles of Stones and Gravel
Alkaline-Salts
Limestone and Kankar
Vegetation and Organic Matter
Manufacture of Clay Bricks
Selection of site
Preparation of Clay
Weathering Process
Tempering process
Moulding of bricks
Soft mud process
Procedure
Stiff Mud Process
Semi Dry Process
Drying of Bricks
Natural Drying
Artificial Drying
Burning of Bricks
Clamp
Intermittent Kilns
Continuous Kilns
Classification of Burnt Clay Bricks
Introduction
Properties of Burnt Clay Bricks
General Quality of Bricks
Dimensions and Tolerances
Water Absorption of Bricks
Efflorescence
Strength of Bricks
Testing of Bricks
Test for Compressive Strength
Test for Water Absorption
Test for efflorescence
Test for warpage
Special Bricks
Specially shaped Bricks
Burnt Clay Facing Bricks
Heavy Duty Bricks
Perforated building bricks
Sand lime Bricks
Sewer Bricks
Acid Resistant Bricks
Refractory Bricks
Manufacture
Acid bricks
Basic Bricks
Neutral Bricks
Building Tiles
Process for Manufacturing Roofing Tiles
Process for Manufacturing Flooring and Wall Tiles
Specifications for Building Tiles
Earthenwares
Glazed Earthenware Tiles
Terracotta
Stoneware

3. LIME
General
Properties of Lime
Uses of Lime
Source of Lime
Some Important Terms and their Definitions
Varieties of lime
Classification of Lime
Uses of fat lime
Classification of Lime According to I.S. 712-1984
Indian Standard Specification for Lime
Manufacturing process
Description of Each Stage of Operation
Field Control Test for Assessing Quality of Lime
Manufacture of Fat Lime
Advantages of continuous kiln
Manufacture of Natural Hydraulic Lime
Manufacture of Artificial Hydraulic Lime
Storage of Lime
Field Slaking of Lime and Preparation of Putty
Objective of Slaking
Slaking Process
Determining the Slaking Nature of Lime
Slaking Procedure for Quick Slaking Lime
Initial Preparation
Methods of Slaking Lime
General Precautions in Slaking
Slaking Procedure for Medium and Slow-slaking Limes
Running
Maturing
Making Coarse Stuff and Putty from Hydrated Lime or Powder
Coarse Stuff
Putty
Storage after slaking
Testing of Lime
Classification of binding materials
Precautions to be taken in handling lime
Properties of Lime

4. MORTARS
Definitions
Sand
Classification Based on Fineness
Bulking of Sand
Desirable Properties of Sand
Function of Sand in Mortars
Fineness Modulus of Sand
Tests for Sand
Selection of Sand for Use
Substitutes for Sand
Types of Mortars
Special Mortars
Properties of Good Mortar
Test for Mortars
Precautions in using Mortar

5. CONCRETE
Introduction
Lime Concrete
Preparation of lime Concrete
Laying of Lime Concrete
Properties of Lime Concrete
Use and Precautions
Water
Coarse Aggregate
Grading of Aggregate
Proportioning of Fine Aggregate to Coarse Aggregate
Maximum Size of the Aggregate
Measurement of Cement Concrete Ingredients
Significance of Bulking of Sand
Water Cement Ratio (W/C Ratio)
Proportioning of Concrete Mixes
Cube strength of Concrete
Properties of Cement Concrete
Slump Test
Factors Affecting Proportions of Concrete
Strength of Concrete
Mixing of Concrete
Transporting the Concrete
Placing of Concrete
Consolidation or Compaction of Concrete
Finishing
Curing of Concrete
Removal of Form Work
Joints in Concrete
Some other Types of Cement Concretes
Form Work

6. ASBESTOS
Introduction
Commercial Focus
Asbestos Sheets and Boards
Asbestos Cement Pipes

7. ASPHALT, BITUMEN AND TAR
Introduction
Terminology
Asphalt/Bitumen
Other Allied Terms
Bituminous Materials
Bitumen Felt/Tar Felt
Specifications and use
Other Bituminous Materials
Tests for Bitumen
Tar

8. GRAY IRON
The Metastable Iron-Iron Carbide System
Solidification of an Fe-C-Si Alloy
Chemical Composition Effects
Carbon
Silicon
Silicon Content and Graphitization
Sulfur and Manganese
Phosphorus
Gray-iron Specifications
Heat-treatment of Gray Iron
Machinability
Wear Resistance
Strength
Stress Relief
Alloying Elements
Effect on Microstructure  
Chromium
Molybdenum, Molybdenum-Nickel
Nickel
Silicon
Copper
Aluminum and Titanium
Effect on Properties

9. CAST IRON
Definitions
Chemical Composition
Composition and Graphitization
Solidification Process
Microstructure
Graphite
Cementite
Ferrite
Pearlite
Steadite
Austenite
Properties of Cast Irons
White Irons
Chilled Iron

10. STEEL CASTINGS
Introduction
Molding Processes And Sands
Green-sand Molding
Refractoriness
High permeability and Low Moisture Content
Organic and Other Additions
Green-sand-molding Casing Defects
Dry-sand Molds and Skin-dried Molds
Other Types of Molds
Molding Methods
Cores
Hot-tear Formation
Metal penetration
Burn-on
Ceroxides
Core and Mold Washes

11. ALUMINIUM AND MAGNESIUM ALLOYS
ALuminum Alloying Principles
Copper
Heat-treatment of Cu-Al Alloys
Silicon
Magnesium
Magnesium and silicon

12. DUCTILE IRON
Solidification Of Ductile Iron
Development of Graphite Spheroids
Role of Magnesium
Control of the Common Elements
Carbon
Silicon
Sulfur
Phosphorus
Other Elements
Melting Practices
Acid Cupola Melting
Desulfurization
Basic Cupola Melting
Induction-furnace Melting
Magnesium Treatment
Inoculation
Engineering Properties

13. MALLEABLE IRON
Melting
Batch-Melting Process
Engineering Properties
Pearlitic Malleable Irons
Other Malleable Irons

14. RESIN CHARACTERIZATION
Introduction
Scope
Mechanical Properties of a Partially Cured Resin — DMA Characterization
Chemical Advancement of a Partially Cured Resin—Differential Scanning Calorimeter Characterization
Chemical-Mechanical Relations
Moisture Content as a Variable
Flake Bonding
Measurement of Pressing Environments
Resin Penetration
Practical Application

15. THERMO-GRAVIMETRY OF WOOD REACTED WITH FLAME RETARDANTS
Introduction
Experimental Methods
Results and Discussion
Phosphorus And Nitrogen
Thermogravimetry
Flame Test
Conclusions

16. WETTABILITY AND WATER REPELLENCY OF WOOD
Introduction
Experimental
Wood materials
Automated surface tension analyzer
Computer program: wood wettability study
Graph
Contact angle from attractive force
Contact angle from work of adhesion
Surface free energy estimation
Interaction parameter calculation
Aging effect
Results and Discussion
Aging effect
Surface free energy estimates
Interaction parameter calculation

17. FLAME RETARDANT TREATMENT OF
WOOD
Introduction
Materials and Methods
Preparation of specimens
Treatment of specimens
Leaching
Dimensional stability tests
Thermogravimetric analysis
Results and Discussion
Treatment of specimens
Leach resistance
Dimensional stability
Thermal degradation
Conclusions

18. FUNGAL AND TERMITE RESISTANCE OF WOOD
Introduction
Materials and Methods
Fungal evaluations
Termite evaluations
Reaction time and chemical analysis
Results and Discussion
Decay Resistance
Chemical Analysis
Conclusions

19. WEATHERING OF WOOD
Introduction
Early History
The Weathering Process
Weathering Factors
Property Changes
Weathering of Wood-Based Materials
Protection Against Weathering
Film-forming Materials
Penetrating Finishes
Summary

20. ARCHITECTURAL PAINTS
Introduction
Exterior Paints for Wood
Characteristics of Wood Siding
Binders for Exterior House Paints
Pigments for Colored Paints
Microorganisms in Paints and Coatings
Formulating Exterior Paints for Wood
Interior Paints for Plaster and Wallboard
Exterior Emulsion Paints for Masonry
Exterior Solution Type Paints for Masonry
Interior and Exterior Enamels
Enamels for Wood and Concrete Floors

21. BUILDING CONSTRUCTION ADHESIVES
Introduction
Advantage of Using Adhesives in Construction
Elastomeric Adhesives
Gap-Filling Phenol Resorcinol Adhesives
Polyurethane Adhesives
Resorcinol Resin Adhesives
Casein Adhesives
Polyvinyl Acetate Resin Emulsion
Phenolic Resin Adhesives
Melamine-Urea Resin Adhesives
Urea Resin Adhesives
Epoxy Resin Adhesives
Contact Cement

22. FLOORING
Domestic Flooring
Institutional Flooring
Industrial Flooring
Types Of Epoxy Flooring
Self-levelling Floors
Trowelled Floors
Epoxy Terrazzo
Future Developments In Epoxy Floors

23. MINING
Adhesion And Grouting
Remedial Uses
Concrete Crack Repair
Bonding Concrete to Concrete
Bonding Reinforcements
Epoxy Bonding in New Structures
Fire Resistance
Bulk Mechanical Properties
Creep
Miscellaneous Bonding Applications

24. GROUTS FOR LEVELLING: MISC.
APPLICATIONS
Miscellaneous Applications
Soil consolidation
Tile grouts
Epoxy laminates for concrete moulds
Resin concrete

25. GLASS
Structure
Composition
Single-Phase Glasses
Properties
Manufacture and Processing
Economic Aspects

26. CEMENT
Clinker Chemistry
Hydration
Cement Paste Structure and Concrete Properties
Manufacture
Portland Cements
Special Purpose and Blended Cements
Nonportland Cements
Economic Aspects, Production, and Shipment
Specifications and Types
Uses

27. INSULATING MATERIALS
Introduction
Thermal Insulation
Terminology Related to Thermal Insulation
Requirements of Thermal Insulating Materials
Types of Insulating Materials
Air Spaces
Aerated Concrete
Gypsum
Expanded Blast Furnace Slag
Sprayed Asbestos
Vermiculite
Coconut Fibres
Cork Board
Rock Wool
Cellulose
Cellular Plastics
Fibre Glass
Sound Insulation
Terminology
Units of Sound
Velocity of Sound
Acoustics
Noise
Requirement of Sound Insulating Materials
Types of Acoustical Materials
Acoustic Pulp
Acoustical Plaster
Unifil Acoustical Plaster
Limpet Asbestos
Thermacoustic
Prefabricated Boards or Tiles
Glass Fibres
Composite Units

^ Top

STONE

All the engineering structures are made from some materials. Each material, which is used in the construction, in one form or the other, is known as engineering material. Engineering materials are also, sometimes, termed, as building materials or materials of construction. Every engineer has to come across various materials, in carrying out various engineering works and projects and as such he is supposed to be fully conversant with their properties and behaviour.

No material, existing in the universe, is useless. Every material has its own field of application. An engineer has to be conversant with the properties of most of them. Stone, bricks, timber, steel, lime, cement, metals etc. are some commonly used materials by a Civil Engineer. Even engineers in branches of Mechanical Electrical, Electronics etc. are required to know the properties of these materials. Selection of building material, to be used in a particular construction, is done on the basis of strength, durability, appearance and permeability. In order to carry out safe constructions, some standards for the materials to be used, are fixed. These standards are fixed by Indian Standards Institutions (ISI). These standards are continuously reviewed and modified from time to time to suit to the changed conditions. All the commonly used Engineering Materials have been discussed in this book, in regard to their properties, place of occurrence, manufacture, and uses. In the first chapter stone has been discussed.

It is likely that our country may face shortage of common building materials like cement, lime, bricks, aggregates, plywood, plastics etc. It is therefore an urgent need to handle the situation by manufacturing cheap building materials and also by developing new building materials. Shortage of building materials and the high costs are likely to hamper many projects and developmental programmes. It is therefore imperative to lay greater emphasis on the growth of such industries which use local raw material resources for producing less costly building materials.

Rock and Stone

Rock is the term used to name a solid portion of the earth's crust. It has no definite shape and chemical composition. It is generally very big in size. The rocks have one or more than one minerals. Rocks having only one mineral is known as mono-mineralic rock and those having several minerals as Poly-mineralic rocks. Quartz, sand, pure gypsum, magnesite are examples of mono-mineralic rocks and granite, basalt, etc. those of poly-mineralic rocks. The rocks are named after the predominant mineral present in it.

A rock having calcium carbonate mineral as predominant mineral, is termed as calcarious rock. Similarly rock predominant in clay is called argillaceous rock. Quartz, felspar, hornblend, mica, augite, dolomite are some of the common rock forming minerals.

Stone

The stone is always obtained from rock. The rock quarried from quarries is called stone. Quarried stone may be in form of stone blocks, stone aggregate, stone slabs, stone lintels, stone flags, etc. Stone has to be properly dressed and shaped before it is used at the place of its use.

Formation of Rocks

Solar system consists of sun as the centre and all other planets revolve around it. Our earth is one which originally was in form of mass of incandescent gases. The mass of gases after cooling, first converted into molten mass and then on further cooling, the surface of the molten mass converted into solid crust. The process of cooling of earth is still continuing and thus process of solidification of molten matter is also continuing. Existence of molten matter under earth's crust is reflected by eruption of volcanos from time to time. The molten matter, of which the earth and other planets were originally made up and, existence of which is confirmed by the volcanic eruptions, is known as Lava or Magma.

Classification of Rocks

The stone which is used in the construction works, in one form or the other, is always obtained from the rocks. The rocks may be classified in following four ways.

1. Geological classification

2. Physical classification

3. Chemical classification and

4. Classification based on hardness of the stone.

Geological classification

According to this classification, rocks may be divided into following three categories.

(i) Igneous rocks

(ii) Sedimentary rocks and

(iii) Metamorphic rocks.

(i) Igneous rocks. As already explained in article 1.3 "formation of rocks," the in side portion of the earths surface is very hot and it can cause fusion even at ordinary pressures. The molten lava or magma, occasionally tries to come out of the earth's surface through cracks or other weak spots. This magma when gets exposed to the outside cooling effect solidifies in the form of a rock, known as igneous rock. Hence, igneous rocks are formed as a result of solidification of molten lava lying below or above the earth surface due to cooling effect. Depending upon the cooling effect, following different types of igneous rocks are formed.

(a) Volcanic igneous rocks. This type of igneous rock is formed when molten lava or magma gets exposed to atmosphere, at the surface of the earth. In this case, cooling of magma is very rapid and, hence, structures of these rocks are extremely fine grained. This rock may contain some quantity of glass which is non-crystalline. Example of Volcanic igneous rock is Basalt.

(b) Hypa-byssal rocks. This rock is formed when magma is allowed to cool at, comparatively, slower rate. Such conditions of cooling, generally, prevail at relatively shallow depth under earth crust. Since rate of cooling is not as fast as in case of volcanic rocks, the structure of resulting rocks, is fine grained and crystalline, but not as fine as in case of volcanic rocks. The best example of hypa-byssal rock is Dolerite.

(c) Plutonic rocks. These rocks are formed when cooling of magma takes places at a very slow rate. Such conditions of cooling generally, exist at a considerable depth from the surface of the earth. The structure of these rocks is coarse grained, and crystalline. Stone, obtained from Plutonic rock is most commonly used in building industry. The best example of plutonic igneous rock is granite.

All the igneous rocks contain minerals like Augite, Felspar, Horn blende, mica, quartz etc. Before solidification, all these minerals are in molten state, along with some gases, forming magma.

(ii) Sedimentary rocks. The rocks are formed by the deposition of broken up materials like sand, clay, Disintegrated rocks, dead sea organisms etc., with the aid of water, wind, frost etc. on the pre-existing rocks. Earth's crust, when subjected to weathering cause disintegration, which results in the formation of clay, sand and pebbles. The disintegrated mass is carried by rain water, streams, wind etc. and settles as and when conditions become favourable to it. The process of deposition of new disintegrated matter continues in regular layers. With age this deposited mass becomes a rock, known as Sedimentary rock. Since the sediments get consolidated in horizontal or nearly horizontal layers, these rocks show different layers distinctly. All the layers of this rock may have same or different composition, colour and structure, as all the layers have deposited under varying conditions. The formation of these rocks is shown in Fig 1. These rocks can be easily split, along the bedding plane. Sand stone, limestone, slate and shale, are some common Sedimentary rocks.

Fig. 1. Sedimentary Rock formation

(iii) Metamorphic rocks. These rocks are formed, when igneous as well as sedimentary rocks are subjected to a very large heat and pressure. The process of change due to heat and pressure is known as metamorphism. The rocks change their character, due to metamorphism, and the resulting mass of rock change into hard and durable foliated structure; Marble, quartzite and slate are common examples of metamorphic rocks.

Metamorphism

All the rocks of igneous and sedimentary origin, represent a mass of mineral composition. This mass remains in equilibrium under the general atmospheric conditions. When either temperature, or pressure, or even both are increased, the equilibrium of the mass gets disturbed and its minerals realign themselves to re-establish the equilibrium. Re-alignment of minerals change the texture of the rock. This process is known as metamorphism. It should be remembered that weathering action and sedimentation action, are not included in metamorphism.

Heat, pressure, and chemically active fluids, are the three agents which bring about the changes of metamorphism.

Heat may be supplied by the general rise of temperature inside the earth or by hot magma and pressure may be caused due to heavy overlay rocks or due to movement of the earth during earthquakes. Chemical liquids do not take any active part in the process of metamorphism. Following four types of metamorphisms occur.

(a) Plutonic metamorphism.

(b) Thermal metamorphisms.

(c) Cataclastic metamorphism.

(d) Dynamo-Thermal metamorphism.

(a) Plutonic metamorphism. The metamorphic change takes place at large depths under the earth. Uniform pressure and high temperature are responsible for this change. This is due to the fact that rocks become plastic mass at certain depths, and plastic mass can be in equilibrium only under uniform pressure.

(b) Thermal metamorphism. The changes brought about in this metamorphism are predominantly due to high temperature.

(c) Cataclastic metamorphism. The metamorphism or change is brought about by directed pressure only and temperature, uniform pressure do not play any role in it. This change takes place at the surface of the earth.

We have used two terms above-uniform pressure and directed pressure. Directed pressure can be applied to solids only. Directed pressure when applied to liquids is converted into uniform pressure. Uniform pressure can be applied to liquids and solids both.

(d) Dynamo-thermal Metamorphism. Temperature increases with depth inside the earth. The changes brought about in the rock by combination of heat and directed pressure are known as Dynamo-Thermal metamorphism. This change takes place not at very large depths, but at moderate depths.

As a result of metamorphosis, limestone and marl become marble, Basalt and trap are converted to schist and laterite and granite becomes Gneiss.

Physical classification of rocks

According to general structure, the rocks may be classified into following three categories.

(i) Stratified rocks

(ii) Unstratified rocks and

(iii) Foliated or laminated rocks.

(i) Stratified rocks. These are such rocks which possess planes of stratification or cleavage. These rocks can be easily split along these planes. An experiences supervisor at the quarry site, can easily locate these planes. All the sedimentary rocks have distinct layers of stratification and thus are stratified rocks.

(ii) Unstratified rocks. The structure of these rocks is compact granular. They do not show any layers of stratification or cleavage. All the igneous rocks of volcanic origin, are the examples of unstratified rocks.

(iii) Foliated or laminated rocks. These rocks comprise of thin laminations. They can be split in definite direction and size. Metamorphic rocks come under the category of foliated rocks.

Chemical classification

Based upon chemical composition, the rocks can be classified into following three categories:

(i) Silicious rocks

(ii) Argillaceous or clayey rocks

(iii) Calcareous rocks.

(i) Silicious rocks. These rocks consist of silica, as their predominant constituent. These rocks are very hard and durable and are not easily affected by weathering agencies.

Granite, quartzite, trap, basalt, sandstone, etc. are the examples of silicious rocks. Presence of weaker materials may cause their disintegration.

(ii) Argillaceous rocks. Predominant constituent of these rocks is clay. The principle constituent alumina, which is nothing but clay, remains mixed up in varying proportion with siliceous, calcareous and carboneous matter. These rocks are hard, durable, dense and brittle, in nature. Laterite, slate, porphyry, are the best example of argillaceous rocks.

(iii) Calcareous rocks. The predominant constituent of these rocks is calcium carbonate. The durability of these rocks is greatly dependent upon the constituents of surrounding atmosphere. Lime stone, marble, dolomite, kankar etc. are the examples of this type of rocks.

Classification based upon hardness of the stone

According to this classification stone may be classified as soft, medium, hard and very hard.

Very hard rocks. Granite, trap taconite, are the very hard varieties of rocks. Hard rocks. Granite, basalt, trap, gravel, quartzite are the hard varieties of rocks. Medium rocks. Dolomite and lime stone are the medium varieties.

Soft rocks. Talc, gypsum, sand stone, slate etc. are the soft varieties of stones.

Scale of hardness of various minerals, starting from hardest to softest, have been given as follow.

Diamond (Hardest)-Corundum-Topaz-quartz-Felspar-Apatite-Flouspar-Calcite-rocks salt-Talc (softest).

Composition of Stone (Rock-forming Minerals)

Chemically the rocks are composed of mineral earths, alkalies, oxides or iron and manganese etc. Silica (SiO2), alumina (Al2O3), lime (CaO), and magnesia (MgO) are the mineral earths, which are usually found is rocks in one form or the other. Soda (Na2O) and Potash (K2O) are the usual alkalies present in the rocks. Presence of alkalies in the rocks is not preferred, as it causes stone to disintegrate when exposed to weather. Generally stones comprise of more than one mineral earth.

BRICKS AND OTHER CLAY PRODUCTS

This chapter deals with construction materials such as bricks, tiles, refractory bricks, earthenwares and stonewares. All these materials are made from clay and are also known as clay products. Burning of moulded clay products makes them sufficiently strong for use as construction materials. Though tiles, refractory bricks, earthenwares and stonewares serve different construction purposes, brick is the most commonly used building material. It is light, easily available, uniform in shape and size, and relatively cheaper except in hilly areas. Bricks are easily moulded from plastic clays, also known as brick clay or brick earth.

BRICK EARTH AND ITS CONSTITUENTS Sources of Brick Earth

Brick earth is derived by the disintegration of igneous rocks. Potash feldspars, orthoclase or microcline (K2O: Al2O36SiO2) is mainly responsible for yielding clay mineral in the earth. This mineral decomposes to yield kaolinite, a silicate of alumina which on hydration gives a clay deposit Al2 O3 2H2O known as Kaolin.

Qualities of Brick Earth

A good brick earth should be such a mixture of pure clay and sand that when prepared with water it can be easily moulded and dried without cracking or warping. It should contain a small quantity of lime which causes the grains of sand to melt and helps bind the particles of brick clay together. It should also contain a small amount of oxide of iron which acts in the same way as lime and moreover lends the brick its peculiar red colour.

Functions of the constituents of Brick Earth

Silica or sand in brick earth prevents shrinkage, cracking and warping of bricks but too much of sand will make the bricks brittle. Clay or alumina makes brick earth plastic and lends the brick its hardness; but unless mixed with sand it will shrink, crack and warp in the process of drying and burning. Lime and oxides of iron both act as fluxes helping the grains of sand to melt and bind the particles of clay together. Oxides of iron also impart a red colour to the brick but excess of it makes the brick dark blue. Magnesia present in clay with oxide of iron make the brick yellow.

Pebbles of Stones and Gravel

These do not allow the clay to be mixed uniformly and thoroughly and result in weak and porous brick. Bricks containing grits are likely to crack and cannot be readily cut or worked.

Alkaline-Salts

Alkaline salts, if present, act as hygroscopic substances. They absorb moisture from the atmosphere in due course of time and create damp conditions. The moisture on drying leaves behind a greyish white deposit known as efflorescence on account of which the appearance of the building is spoiled. Common salts generally present in soils are sulphates of calcium sodium and potassium. The presence of Reh or Kallar consisting of sodium sulphate, with more or less of sodium carbonate and sodium chloride, renders the clay utterly unsuitable for brick making. Presence of Reh or Kallar can be easily detected by the efflorescence on the sides of fresh excavation, if the soil is moist, but it would be appropriate in all cases to moisten the soil with water and subject it to evaporation and check for efflorescence.

Limestone and Kankar

Presence of large quantity of lime and limestone in lumps is detrimental to brick earth, as lumps of limestone, if burnt in a brick, slake afterwards and split the brick. Thus limestone should be present in very finely divided state.

Vegetation and Organic Matter

Organic Matter if present in brick earth will produce porous bricks. This is due to the evolution of gas during the burning of the carbonaceous matter, resulting in the formation of small pores.

MANUFACTURE OF CLAY BRICKS

Bricks are made by treating suitable brick earth or clay, moulding it to shape and size (allowing for shrinkage), drying it, and then baking, burning or firing it at high temperatures in order to fuse the constituents to a hard, homogeneous mass: The process of manufacture can be described under the following heads.

1. Selection of site

2. Preparation of clay

3. Moulding of bricks

4. Drying of bricks

5. Burning of bricks.

Preparation of Clay

According to IS: 2117-1975, brick clay should be prepared in two stages:

1. Weathering

2. Tempering

Weathering Process

The soil is left in heaps and exposed to weather for at least one month in cases where such weathering is considered necessary for soil. The soil is turned at least twice and it is ensured that the entire soil is wet throughout the period of weathering. The purpose of weathering is to disintegrate big boulders of clay under the action of atmospheric agencies to make it a uniform mass and also to eliminate the impurities which get oxidized.

Tempering Process

After weathering, the required quantity of water should be mixed with the soil to obtain the right consistency for moulding. Addition of sand and other materials, if necessary, may be made at this stage to modify the composition of the soil.

The quantity of water to be added, may range from ¼ to 1/3 of the weight of soil, sandy soils requiring less water and clayey soils more water. But the nature and degree of wetness of the soil at this stage should also be duly considered.

The moistened soil is kneaded with spades or other manual or mechanical equipment into a plastic mass. After the addition of water and kneading, the soil may be pugged in a pug mill of suitable size corresponding to quantity of bricks to be manufactured. The pug mill may be mechanically operated or hand operated, as shown in fig. 1a and 1b.

Moulding of Bricks

Bricks may be moulded by any one of the following methods:

1. Soft mud process (Hand moulding)

2. Stiff mud process (Machine moulding)

3. Semi dry process (Machine moulding)

Soft Mud Process

The clay prepared by using 25 to 30% of water is pressed into the mould by hand. Some typical moulds of timber or metal are shown in fig. 2.

Fig. 1 (a) Manually operated pug mill (b) Mechanically operated pug mill.

Moulds are made either of wood or of thin steel plates. Seasoned wood should be used to prevent changes in the dimensions of the mould. The edges are protected with strips of brass or steel. Steel moulds, made of plates 6 mm thick, are used if the bricks are to be manufactured on large scale. Normally shrinkage allowance, varying from 10% to 12% is provided. Thus, the size of the mould is such that it would give the finished brick its required size.

As per IS: 2117-1975 the mould should be constructed preferably of metal. The thickness of the sides of the mould shall not be less than 3 mm if made of metal and not less than 10 mm, if made of wood.

The process of moulding bricks with the help of moulds is also called hand moulding. According to IS: 2117-1975, handmade bricks may be either ground moulded or table moulded. In case it is ground moulded, a level firm surface should be used. Typical specifications for accessories used in table moulding are given below and in Fig. 3.

Moulding table. The moulding table is 1.2 to 1.8 m long and 0.6 to 1.0 m wide and is made of wood or iron. It is smoothly finished at the top and supported horizontally at a height of 1m to 1.2 m. Also there are holes to accommodate accurately the bottom pins of the stock-board.

Stock board. It is a wooden board with iron lining around the upper edge and with such dimensions as to fit accurately but loosely the interior of the mould (Fig. 3.4.). The stock board is provided with four pins one at each corner of the bottom side, which when fitted into the corresponding holes on the moulding table hold the board tightly in position during moulding. The stock board should also have a projection at the top so as to form the frog of the brick being made.

Pellet boards. These are rectangular pieces of wood of size 30 cm x 15 cm x 10 mm thick with a smooth surface on one side. Pellet boards are used for conveying moulded bricks to the drying yard.

Fig. 3 Stock board.

Procedure

Before moulding, the inside of the mould is cleaned and then sprinkled with sand or ash. If slop moulding is adopted then the mould is dipped in water and cleaned. The mould is then set firmly on the level surface.

A quantity of clay slightly more than the volume of the mould is taken and rolled in sand. It is then shaped suitably into a single lump and dashed firmly into the mould with a force that is to be judged by the moulder by experience, so that the clay completely occupies the mould without air pockets and with minimum surplus for removal. The surplus soil is scrapped off with a sharp straight edge, known as a style, or a stretched wire and the top surface is levelled.

The whole assembly of the mould is then lifted, given a slight jerk, and, inverted to release the moulded brick on a pellet board in the case of table moulding or on a dry level surface of the ground in the case of ground moulding.

The ground may be advantageously sprinkled with sand before releasing the brick over it, so that bricks do not stick to the ground. When a frog is not needed a bottomless mould may be adopted in which case inversion to release the moulded bricks from the mould will not be necessary. It may be added that each moulder can make on an average about 500 to 1000 bricks per day.

Stiff Mud Process

The selected clay, after proportioning of the ingredients is mixed with water up to about 12 to 18% and is thus initially prepared for being put in the machine. There are two stages in machine moulding:

Fig. 5 Pug mill and extruding machine.

1. The final mixing when kneading and tempering is done in the pug mill.

2. In the second stage bricks are formed by extruding stiff clay through a mould or orifice in the extruding machine.

The pug mill and the extruding machine may be combined in one unit, as shown in Fig. 5.

The upright cylinder or barrel of the machine, known as the pug mill, is kept filled with prepared clay which is mixed well and pressed down against the coarse threads of a horizontal spiral screw. The pressing screw is fixed near the top of the horizontal axle called `auger'. At one end of the auger, power is applied for driving the machine and at the other end is fixed a metal die through which the clay extrudes with the desired section. The extruding clay is a continuous mass and is received on a conveyor to be further cut into pieces of the correct sizes of bricks.

The bricks are cut either by a single wire or by a number of wires fixed on a frame as shown in Fig. 6. The bricks obtained by this method have a smooth rectangular finish.

Semi Dry Process

In this method only 7 to 10% of water is added so that it forms just a damp powder. It is then pressed under a pressure of 1000 to 1200 kg/cm2 with the aid of a plunger machine to form the bricks. At the first plunger machine the material is automatically measured off, fed into a steel mould and pressed by plungers (heated to prevent sticking) on two opposite sides. It is then expelled from the mould and transferred to another plunger machine where it is again pressed, one of the beds receiving the frog at this stage. Pressed bricks do not require drying and could be put into the kiln directly for burning. They are very strong and compact and on account of the latter quality they are more durable than bricks moulded by the stiff mud process.

Machine moulding can also be employed for the soft mud process to press pugged clay into moulds with the aid of the plunger. It is possible to mould 4 to 8 bricks at a time as against one by hand-moulding.

LIME

General

Lime is a very important building material. It has been in use since ancient times. Egyptians used to use lime for plastering works and Romans for plastering, mortar, and concrete works. In India, there are numerous historical constructions, where lime had been used in the form of cementing material. Even today, lime is a very important material not only for building purposes, but also in so many other manufacturing processes.

Source of Lime

Lime does not occur in nature in free state. It is obtained from substance having lot of calcarious content in it. Lime stone, chalk, Kankar are the usual raw materials from which lime is obtained. All the materials containing calcarious substance have calcium carbonate (CaCO3) as the chief constituent. When calcarious materials are heated, carbon dioxide and moisture are driven out, leaving behind calcium oxide (CaO), which is called lime. Raw material from which lime is obtained by heating vary in chemical composition as well as physical properties from place to place and as such lime of uniform quality can not be obtained at all the places. Besides this, methods of burning, slaking, storing and using also affect the properties of the lime.

MIX-OF-LIMESTONE & COKE

Fig. 3 Lime burning crude clamps.

(i) More fuel is required for burning as, it is wasteful method.

(ii) There is no control on temperature during burning.

(iii) Fire cannot be regulated properly.

(iv) Quality of lime is not uniform. Limestone pebbles near surface generally remain unburnt or under burnt, while those very near to the fire are over burnt.

(v) Supply of burnt lime is intermittent and small.

2. Intermittent Kilns. There are many types of intermittent kilns in use. But the most commonly used kilns are following:

(i) Intermittent Flame kiln and

(ii) Intermittent flare kiln.

(i) Intermittent Flame kiln. It consists of a round encloser, open at the top. The encloser is lined by fire clay bricks from sides. It has fire places and draw holes suitably located in the walls. The kiln is loaded by crushed lime stone and fuel, arranged in alternate layers. Horizontal as well as vertical flues are formed at the time of loading. The loaded kiln is lastly covered with some unburnt material, which may be clay. The kiln is fired and allowed to burn for about 3 days. The kiln is then allowed to cool and lastly unloaded.

MORTARS

Definitions

The mortar is a paste like substance prepared by adding required amount of water to a dry mixture of sand or fine aggregate with some binding material like, clay lime or cement.

When clay is used as a binding material, the resulting mortar is known as mud mortar. If, it is lime, the resulting mortar is lime mortar. Similarly, if cement is the binding material it is known as cement mortar.

Before properties and uses of different types of mortars are explained, let us gain some knowledge about the fine aggregate which is commonly known as sand. Sand is mostly used as inert material in mortars and concretes.

Sand

It is a form of silica (SiO2) which may be siliceous, argillaceous, according to composition. Sand particles consists of small grains of silica. It is formed by the decomposition of sand stone due to various weathering effects. It is mostly obtained from pits, shores, river beds and sea beds. Sand may be classified into three categories as follows.

1. Pit sand

2. River sand.

3. Sea sand.

A brief description of each type of sand has been given.

1. Pit sand. This sand is obtained by forming pits into the soil. It is sharp, angular, porous and free from harmful

CONCRETE

Concrete is a construction material obtained by mixing a binder (such as cement, lime, mud etc.), aggregate (sand and gravel or shingle or crushed aggregate), and water in certain proportions. The mix is placed properly in moulds or forms to harden in a suitable environment. When the various ingredients are mixed, these form a plastic mass which can be moulded into the desired shape and size. The moulded mass when allowed to cure in suitable environment, hardens to become a solid mass capable of maintaining its shape and size and sustaining certain loads. Hardening in concrete is a result of the chemical/physical combination of the binding material, water and air in a given environment. The hardened concrete so obtained serves different purposes depending on the type of binding material used, quality and grade of concrete, location and size of such concrete component.

The type of concrete is basically known by its binding material. It is the binding material which plays the main role in the behaviour and characteristics of the resulting concrete. Based on the binding materials, the common concretes can be classified as:

• Mud concrete
• Lime concrete
• Cement concrete
• Polymer concrete

These concretes are used to serve certain requirements of various concrete elements cast in different situations. Behaviour of these concretes can further be modified by the use of certain admixtures, special treatments, or combination of binding materials. Properties of some of these concretes can further be improved through certain special techniques of construction (such as prestressing, reinforcing, impregnation, etc.).

Mud concrete is made by using suitable mud as the binding material. Mud is prepared from good quality clay and water by kneading. The mud is mixed with coarse aggregate or shingle to obtain mud concrete. The mud concrete is laid in suitable layers and compacted by ramming or tamping. The mud concrete properties are mainly due to interlocking of aggregate particles and filling of voids by mud. Mud concrete can easily be affected by moisture and has poor impermeability, durability and strength characteristics. This type of concrete is generally used for cheap and temporary type of constructions in foundation bases, non-load bearing walls with water proofing treatment on external faces, etc.

Lime, is very popular binding material in Civil Engineering constructions. Properly slaked lime slurry or putty is used as binding material in lime mortar and lime concrete. Lime concrete is prepared by mixing lime mortar with aggregate (shingle or gravel). Lime concrete is laid in layers and compacted suitably by ramming. Lime concrete is commonly used for foundation base layers, floor base layers, roof insulation layers over stone patties (slabs), etc. Lime concrete exhibits fairly good properties of durability, impermeability, and strength specially suitable for base courses. It has been used in many important old monumental buildings which have stood the test of time. The details of preparation, properties and used shall be dealt in a subsequent section. The advent of cement as binding material in the 19th century revolutionized construction activities. Cement concrete obtained by mixing cement, sand, gravel or shingle or crushed aggregate and water is a versatile and popular construction material. Cement concrete is used in almost all modern structures due to its superior qualities and appropriate quality controls possible during and after construction. Cement concrete is used in various forms and grades for different purposes in construction works. Certain weak points in cement concretes for specific purposes can easily be overcome by adopting suitable techniques such as steel reinforcing, prestressing, fibre reinforcing, ferrocement and polymer impregnation techniques etc. The properties of cement concrete can also modified by the use of certain admixtures during its preparation. The details of preparation, properties and uses shall be discussed later.

Recently certain polymers and epoxy resins have been developed which exhibit superior binding qualities. These polymers are now being used for preparation of special polymer concretes. Polymers concrete is obtained by mixing epoxy resins or polymers with plastic aggregates. Polymer concrete exhibits very high strength. Cost of polymers and other epoxy resins used as binding material is quite high and hence the cost of polymer concrete is also high. Due to the high cost and small production of epoxy resins, the use of polymer concrete is limited. In India, use of such polymer concrete is yet to pick up. The future potential for the manufacture and use of polymer concrete for construction of highly sophisticated structures is very good.

1. Mud concrete. This concrete does not carry any importance. It is prepared by mixing brick bats in mud mortar. Brick bats may be made from kuchha or pucca bricks. Sometimes, even crushed stone may be mixed with mud mortar to form mud concrete.

Mud concrete is used for preparing hard base. Over which lime concrete may be laid and then permanent flooring may be spread. During construction of ground floor of buildings, filling of earth is first of all consolidated by sprinkling sufficient amount of water. During consolidation process broken brick bats or crushed stone pebbles, lying waste at the site, are also spread and rammed into the fillings by rammers. Earth filling added with water and broken brick or stone bats, forms mud concrete which on setting develops a hard surface, over which permanent flooring of any form may be laid. The same processes of consolidation with mud concrete may be carried out during preparation of foundation bases.

The coarse aggregate used in mud concrete is usually of broken bricks of size 4 cm 100 m3 brick ballast is mixed with 40 m3 of prepared mud mortar.

ASPHALT, BITUMEN AND TAR

The history of these materials can be traced back to ancient times. Their importance was realized by early civilizations, who employed them for a variety of purposes ranging from mummification to building temples, palaces and vast irrigation systems and enduring highways. A ritual pool-dating back to 3000 B.C. discovered in Mohenjodaro, in the valley of the Indus, was water-proofed with a layer of bitumen on the walls. After an apparently extinct phase through the middle ages and renaissance period, bitumen was re-discovered in the form of deposits of impregnated limestone, in France, Switzerland and Germany in the eighteenth century. Put to use for side walls and pavings in different parts of the continent, it proved to be satisfactory. The utility of the material has grown ever since and today its versatility as a construction material may be well judged from its use and application for roofing, road surfacing, insulating varnishes, acid resistant paints and cold-moulded products.

For purposes of , asphalt, bitumen and tar are referred to as “Bituminous Materials’’, which are essentially hydrocarbon materials frequently accompanied by their non-metallic derivatives. They may be gaseous, liquid, semi-solid or solid in nature and are completely soluble in carbon-di-sulphide (CS2.). They possess some common properties, as follows:

1. Thermo-viscosity, i.e. variance of viscosity (which is roughly the opposite of fluidity) with temperature.

2. Adhesion to solid surfaces.

3. Durability.

4. Water-proofing characteristics under normal circumstances.

The above desirable properties of ‘bituminous materials’ render them very useful as a protective agent, an adhesive and a sealant.

GRAY IRON

Although “gray iron” denotes a certain type of cast iron, yet the chemical composition, structure, and properties of gray iron may vary over broad limits. The range of alloy compositions and properties produced as gray irons may be better understood by consideration of some of the principles of gray-iron metallurgy. The metallurgy of cast irons depends in large measure upon the nature of the iron-carbon equilibrium system.

THE METASTABLE IRON-IRON CARBIDE SYSTEM

In the phase system iron-iron carbide, carbon in the alloys occurs as the metastable compound iron carbide (Fe3C). During solidification or melting and in thermal treatments in the solid state, the iron carbide functions according to normal principles of phase relationships as expected from the equilibrium diagram. For example, freezing of a hypoeutectic alloy, less than 4.30 per cent carbon, will begin with the formation of austenite dendrites and be completed by solidification of the eutectic austenite-iron carbide. After solidification, cooling in the solid state results in transformation of the austenite to pearlite.

CHEMICAL COMPOSITION EFFECTS

All the elements normally present in gray iron exert some influence on the microstructure of the iron. Carbon and silicon, of course, are fundamental in their effect on cast irons, and may be considered first.

Carbon

Carbon in gray iron is present from about 2.5 to 4.5 per cent by weight. Two phases occur, elemental carbon in the form of graphite and combined carbon as Fe3C. The analysis reported ordinarily is the total carbon percentage in the iron. Since the two forms may be determined separately by chemical analysis, the degree of graphitization may be assessed by the following relationship:

% total carbon= % graphitic carbon + % combined carbon

If graphitization is complete, the percentage of total carbon and the percentage of graphitic carbon are equal. If no graphitization has occurred, the percentage of graphitic carbon is zero. If about 0.5 to 0.80 per cent combined carbon exists in a gray iron, it generally indicates that the microstructure is largely pearlitic since pearlite in gray iron having about 2 per cent silicon forms from the austenite eutectoid containing about 0.60 per cent carbon. Thus the relationship above offers a chemical criterion of the degree of graphitization in a gray iron. For sufficient graphitization to develop during solidification of a true gray iron, a certain minimum total carbon content is necessary, which is probably about 2.20 per cent, but this value depends on silicon percentage in the iron.

Silicon

Silicon is present in gray iron from about 1.0 to 3.50 per cent by weight. Of course, the important effect of silicon is its effect on graphitization. It may be noted that increasing silicon percentage shifts the eutectic point of the iron-carbon diagram to the left. The eutectic shift is often described by the following relationship:

Eutectic carbon percentage (in Fe-C-Si alloy)

= 4.30-1/3 x % Si (in iron)

Another term, the carbon equivalent (CE), is often used to describe the relationship of a particular iron to the eutectic point:

CE = % C (in the iron) + 1/3 x % Si

If the carbon equivalent of a particular iron is calculated to be 4.3, then that iron corresponds approximately to a eutectic alloy (even though it is not a true eutectic in the sense of the ternary phase diagram). If the carbon equivalent of an iron is less than 4.30, the alloy is a hypoeutectic alloy. The carbon equivalent is a useful expression because many properties of gray iron have been found related to it. If the combination of carbon and silicon exceeds 4.30, according to the carbon-equivalent equation, the iron is a hypereutectic one. In this case, the freezing process begins with the formation of graphite. When graphite precipitates first during solidification, the melt is said to form kish. Because of its buoyancy, kish pops out of the melt into the air and can be observed as sparkly graphite flakes floating on the surface of the iron or in the air above the iron.

Not only is the eutectic point shifted by silicon in cast irons, but it also shifts the eutectoid point and the solubility limits of carbon in austenite to the left of equivalent points in the Fe-C system. For this reason pearlite in a 2.0% Si gray iron may contain only about 0.60% carbon rather than the 0.76% C value on the Fe-C diagram

Micro structurally, silicon occurs dissolved in the ferrite of gray iron. As such it hardens and strengthens the ferrite, as pointed out in Chap. 18. Ferrite in pure iron will measure 80 to 90 Bhn, whereas 2.0 per cent silicon in a ferritic iron raises the hardness to about 120 to 130 Bhn.

Silicon Content and Graphitization

Silicon promotes graphitization. Low percentages are not sufficient to cause graphitization during solidification, but will cause nucleation and graphitization in the solid state at high temperature, as, for example, during malleableizing heat-treatment. Certain silicon percentages will cause limited graphitization during solidification, and a mottled iron, partly white and partly gray, results.

A certain minimum silicon (and carbon) concentration is necessary for graphitization to proceed sufficiently during solidification to develop a satisfactory gray iron. More accurate diagrams have as their purpose a limiting description of the silicon and carbon percentages which will cause an iron to freeze gray in the section sizes of commercial castings poured into green sand molds. Although these diagrams are useful as a guide, successful metallurgical performance in the type of castings made in particular foundries remains the ultimate criterion for the carbon and silicon content. Hence foundries producing certain sizes of castings and types of gray irons will ultimately develop silicon and carbon combinations suitable to their work.

Sulfur and Manganese

Sulfur, which may be present up to about 0.25 per cent, is one of the important modifying elements present in gray irons. A low-sulfur iron- silicon-carbon alloy, under 0.010% S, will graphitize most completely. Boyles has shown that higher sulfur percentages favor the retention of a completely pearlitic microstructure in a gray iron. The latter effect causes sulfur to be known as an element restricting graphitization (carbide stabilizing). Above about 0.25 per cent sulfur is considered to contribute undesirable hardness and decreased machinability because of its retardation of graphitization.

The influence of sulfur needs to be considered relative to its reaction with the manganese in the iron. Alone, sulfur will form FeS in cast irons. The latter compound segregates into grain boundaries during freezing and precipitates during the final stages of freezing. When manganese is present, MnS, or complex manganese-iron sulfides, are found, depending on the manganese content. The manganese sulfides begin to precipitate early, and continue to do so during the entire freezing process, and are therefore usually randomly distributed. As MnS, the effect of sulfur in causing a pearlitic microstructure to be retained is lost to a major extent. The effect of Mn alone as an alloying element is to promote resistance to graphitization. Therefore manganese above that necessary to react with the sulfur will assist in retaining the pearlitic microstructure. The following rules are advanced to express the relationship involved:

1. % S X 1.7 = %Mn; chemically equivalent S and Mn percentages to form MnS.

2. 1.7 X % S + 0.15 =%Mn; the manganese percentage which will promote a maximum of ferrite and a minimum of pearlite.

3. 3 X % S + 0.35 = %Mn; the manganese percentage which will develop a pearlitic microstructure.

For commercial gray irons in which a pearlitic microstructure is desired, rule 3 offers a favourable combination of manganese and sulfur percentage.

Phosphorus

Segregation of phosphorus may result in lowering of the temperature of final solidification to about 1800 F. The percentage of steadite present in the final structure may amount to ten times the percentage of phosphorus in the iron. Because of segregation, the steadite usually adopts a cellular pattern characteristic of the eutectic cell size developed during solidification. In certain conditions of melting and chilling, iron carbide is associated with the phosphide in a ternary iron-iron phosphide-iron carbide eutectic. Then an amount of the latter constituent considerably in excess of ten times the per cent phosphorus may be formed. If the ternary eutectic is accompanied by graphitization of its carbide during solidification, expansion of the liquid occurs and beads of eutectic exude from the iron. These are often found at the surface of sprues and risers.

Because it forms a eutectic as it segregates, phosphorus is often looked upon as increasing the tendency for a particular iron composition to be a eutectic-type alloy. For this reason, the carbon-equivalent equation is sometimes modified to include a factor for phosphorus as follows:

CE = %C + 1/3 (% Si + % P)

The phosphide of iron is hard and brittle, as is the carbide. Increasing phosphorus percentage in the iron causes a proportional increase of the hard constituent, and therefore increasing hardness and brittleness of the iron, especially above about 0.30% P. To a limited degree, improved fluidity of the molten iron is a desirable property contributed by phosphorus through its influence on carbon equivalent.

Gray-iron Specifications

Because gray iron is used in so many different engineering applications, numerous specifications covering its use in special fields have been developed.

CAST IRON

Cast irons are the tonnage product of the foundry industry. Cast-iron foundries produce over a million tons of castings monthly, and thus supply more than twice as much casting weight as all other foundries combined. Iron foundries are found everywhere that manufacturing occurs. Of the 5674 foundries in India 2068 produce gray-iron, 350 nodular-iron, and 116 malleable-iron castings. These foundries send a steady stream of iron castings into every conceivable industry. The demand for iron castings is based on the nature of cast irons as engineering materials and their economic cost advantages. Cast irons offer a tremendous range of the metallic properties of strength, hardness, machinability, wear resistance, abrasion resistance, and corrosion resistance and other properties. Furthermore, the foundry properties of cast irons in terms of yield, fluidity, shrinkage, casting soundness, ease of production, and others make the material highly desirable for casting purposes. From all standpoints, the cast-iron family offers a variety of engineering properties which ensure its continued and widespread use. Since many cast irons of different properties are employed, it is desirable that a student engineer obtain an over all picture of the entire field. This chapter offers such a picture and presents some of the simpler and more fundamental differences between members of the cast iron family.

SOLIDIFICATION PROCESS

The differences between gray, mottled, and chilled irons are largely established during the freezing process. The fundamentals of the freezing process are related to the nature of the iron-carbide-silicon ternary equilibrium system (Fig. 2). However, a simplified schematic diagram presenting the essential ideas is given in Fig. 3. With reference to the diagram, the freezing and cooling of an iron, composition A, may be described by the following steps:

A. Liquid melt cools until freezing begins at point 1. At this point solid austenite dendrites begin to form and grow until the temperature at point 2 is reached. This step is omitted when the composition is eutectic, at B, on the diagram.

B. Eutectic (a liquid saturated with respect to two solids) freezing begins as the area at point 2 is entered with decreasing temperature. The eutectic solids which form may be a mixture of austenite and carbide or of austenite and graphite. If the former occurs, the iron is freezing as white iron. If the latter occurs, the iron is freezing as a gray or a nodular iron. Graphite will prevail if graphitizing factors, such as high silicon content and slow cooling rate, are operative. Low silicon content and rapid cooling will cause the eutectic to freeze as a mixture of carbide and austenite (white). When the temperature has dropped to point 3, freezing is completed. Thus an iron freezes, as white, gray, or nodular iron. Actually, the solidification of nodular cast iron is somewhat more complex than this. If the iron freezes as gray or nodular, the nature of the graphite is established during freezing Mottled irons are borderline cases where both graphite and carbide have formed.

C. At the end of freezing, the structure consists of the solids developed during steps A and B. In gray and nodular irons these are austenite and graphite, and in white irons, austenite and carbide.

D. Further cooling between points 3 and 4 results in the precipitation of carbon from the austenite present since the austenite may contain as much as 2.0% C at the end of freezing, but only about 0.60 to 0.80% as the temperature decreases to point 4. The excess of carbon in the austenite is precipitated as carbide in white irons and as graphite in gray and nodular irons.

E. Between points 4 and 5, the final change occurs in the solid state during cooling. Austenite-transforms over the temperature range of points 4 to 5. Because this change is quite complex, only a few generalizations are offered. With the most favourable of graphitizing conditions, only ferrite is formed in gray and nodular irons. With less severe graphitizing conditions, ferrite and pearlite or only pearlite is formed. In nodular cast iron, mixed structures of ferrite and pearlite form as “bull’s eyes” of ferrite around the graphite spheroid (Fig. 1). In white irons only pearlite is formed. The final microstructure of white iron such as is used to produce malleable castings.

F. Cooling below point 5 to room temperature produces little change in the iron.

From the foregoing it can be seen that the type of iron, whether white, mottled, chilled, or gray, is largely established during the freezing process. Furthermore, the room-temperature microstructure reflects the entire freezing and cooling process of the iron. Thus the properties of cast irons are greatly influenced by the thermal and chemical changes occurring during its entire history from liquid melt to cooled casting.

STEEL CASTINGS

MOLDING PROCESSES AND SANDS

Molding for steel castings is no different from that for other casting alloys. However, because of certain characteristics of steel, certain methods cannot be used and others are not used to the extent that they are employed in other metals.

Steel can be cast into molds made by any of the sand-molding processes. Dry-sand molds, core-sand molds, skin-dried molds, and cement-bonded molds are used to a greater extent in steel foundries than for most of the other casting alloys. The reason for this is the severe conditions imposed by steel. The problems associated with various molding methods should become more apparent as these methods are discussed.

With reference to molding methods other than those using sand, the high pouring temperature required for steel prevents its being made by the permanent-mold process, except in certain special cases, or by die casting, or plaster molding. Steel can be poured in investment molds because the investment materials are sufficiently refractory. Graphite molds can be used for steel if precautions are taken to avoid carbon pickup. Ceramic molds can be and are being used.

Green-sand Molding

Many steel castings are made using green-sand molds. The general practice is no different from that for other alloys. However, steel-foundry sands differ from others chiefly in the following characteristics.

Refractoriness

Because sand in contact with steel may be heated to an excessively high temperature, the molding sand must be of sufficient purity so that it will not fuse together or deteriorate. Figure 15.6 illustrates that the sand at a metal-mold interface may reach high temperatures, but a short distance away the sand does not get so hot nor does it heat up so rapidly as at the interface. As a consequence of the demand for high thermal stability, most green-sand molding for steel is done with compounded sand mixtures; the bond is usually bentonite. Associated with refractoriness of the sand is the problem of durability. The high-temperature exposure to which the sand is subjected alters the sand and its bond both physically and chemically, leading to a gradual change in its properties unless it is amply replenished with new sand. Unfortunately, there is no simple test to indicate the occurrence of these gradual changes. In one investigation it was observed that the rate of deterioration of the sand could be linked with the development of relatively high hot strength and sensitivity to thermal shock, with progressive build-up of “cokey” coatings on the sand grains.

High Permeability and Low Moisture Content

These two requirements are linked together because they are inter, related. When sand is heated, part of the moisture in the sand is changed to steam. The air in the mold is heated and increases in volume, and organic additions may decompose to gaseous products. These gases must be vented away from the mold cavity. Steel heats the mold to higher temperatures than do other alloys; hence a greater gas volume may develop and more venting is needed. The necessary conditions can be achieved for steel by increasing the permeability above that required for other alloys and restricting the moisture content to a relatively low value (around 3 per cent). Much of the gas can escape through risers and other openings in the mold.

Organic and Other Additions

The use of synthetic sands with a relatively low binder content for steel is accompanied by a tendency toward certain casting defects such as scabs, buckling, and rattails that result from the expansion of the sand as it is heated. The addition of certain materials to the sand may reduce the tendency to form these defects.

The net effect of these special conditions imposed by steel on green sand properties results in establishing a range of properties that differ rather markedly from those for molding sand mixtures used for other alloys. These differences are demonstrated by the data in Table 5.9, which lists typical sand compositions and properties for various alloys, including steel.

Much green-sand work is done with a facing sand which is especially compounded to produce the desired properties, and a backing sand which, being essentially reused facing sand, is also controlled as to properties and grain size. This practice, although it adds to the complexity of molding since it involves delivery of both facing and backing sand to the molder, has the advantage of cutting down the quantity of sand that must be treated with additives and ensures sand properties at the metal-mold interface that are always under close control.

Green-sand-molding Casing Defects

In addition to such defects as rattails, buckles, scabs, hot tears, etc. which are discussed elsewhere in this book, and also treated thoroughly in reference material, another defect that can develop is pinhole porosity.

It is characterized by small smooth-walled holes, elongated in a direction perpendicular to the mold wall and occurring immediately below the casting skin. The exact cause of the defect is still a matter of debate, but it is generally agreed that the formation of either CO or H2O or both by a reaction at the metal surface or slightly below is responsible. The fact that the defect occurs more frequently in green-sand molds suggests that it is at least aggravated by certain conditions existing at the metal-sand interface; and since the only major difference between green-sand and dry-sand molds would be in moisture content, the formation of H2O by reaction between hydrogen and oxygen in the steel is strongly suspected as at least a contributing factor. Moisture in the sand could aggravate the condition by being dissociated to hydrogen, which could then diffuse into the steel and react with dissolved oxygen. This would explain why pinhole porosity can be prevented by deoxidizing the steel with aluminum before pouring, since the oxygen would react with the aluminum instead of the hydrogen.

Dry-sand Molds and Skin-dried Molds

Green-sand molding is preferable to other methods of molding because it is more economical and gives maximum production rates. There are times, however, when, because of the need to increase the strength of the mold or to avoid pinholes, or for other reasons, drying of the mold before pouring is desirable. Superficial drying can be accomplished by heating the surface with torches, infrared lamps, or hot air, or the molds can be dried in large car-type ovens at temperatures up to 500F.

The moisture content of the green sand used for skin-dried or dry-sand molds may be somewhat higher than for ordinary green-sand work for greater moldability, and also because a higher moisture content leads to greater dry strength.

Other Types of Molds

A few foundries have used cement as a sand binder, but the practice has not been very popular in this country.

One field where investment molding has proved effective is in the castings of the special alloys and shapes used for gas-turbine blades and other parts subject to high-temperature service that cannot be readily formed by other methods.

Shell molds have been used with some success, but there is a tendency to form surface defects. These can be eliminated by use of hill-type shell molds. Ceramic molds are also feasible. These permit pouring thinner sections than with conventional sand molds. A special process combining graphite molds and air-pressure pouring has been used to produce steel car wheels and other shapes.

Molding Methods

The usual methods of molding, such as hand ramming, jolt ramming, squeezing, and sand-slinger ramming, are used on steel sands; no difference exists in the ramming methods used for steel in comparison with other casting alloys.

ALUMINIUM AND MAGNISIUM ALLOYS

Pure aluminium and magnesium being relatively poor casting materials, aluminium and magnesium castings are actually produced from alloys. The casting alloys used are those having properties peculiarly suited to casting purposes. Since a large number of aluminum-and magnesium-base casting alloys are available, it is evident that quite widely different properties may be obtained from the various alloys. For all these alloys two types of properties should be considered: the casting properties, those characteristics of the alloy which determine the ease or difficulty of producing acceptable castings, and the engineering properties, those properties which are of interest to the designer or user of the castings. These two sets of properties can be used as a basis for studying the similarities and differences of the large number of aluminium and magnesium casting alloys.

ALUMINUM ALLOYING PRINCIPLES

The aluminium-base alloys may in general be characterized as eutectic systems, containing intermetallic compounds or elements as the excess phases. Because of the relatively low solubilities of most of the alloying elements in aluminium and the complexity of the alloys that are produced, any one aluminium-base alloy may contain several metallic phases, which sometimes are quite complex in composition. These phases usually are appreciably more soluble near the eutectic temperatures than at room temperature, making it possible to heat-treat some of the alloys by solution and aging heat-treatments. Specific instances of the application of these heat-treatments are given in subsequent paragraphs.

All the properties of interest are, of course, influenced by the effects of the various elements with which aluminium is alloyed. The principal alloying elements in aluminium-base casting alloys are copper, silicon, magnesium, zinc, chromium, manganese, tin, and titanium. Iron is an element normally present and usually considered as an impurity. Some of the simpler effects of alloying can be considered.

Copper

The diagram shows solubility of copper in aluminium increasing in the solid state from less than 0.50 per cent at room temperature to 5.65 per cent at 1018 F. Copper above the solubility limit at any temperature appears micro structurally as the phase. The latter phase has a composition approximating the formula CuAl2 (46.5% A1-053.5% Cu) and is a hard brittle constituent. By comparison the solid-solution phase is relatively soft and ductile. Structurally, then, increasing copper content in Cu-Al-base alloys result in an increasing percentage of the hard phase. The mechanical properties of hardness and strength can then be expected to increase as copper content increases while the ductility decreases. A limited percentage of copper thus has a beneficial effect of strengthening and hardening in Cu-Al-base alloys. Furthermore, ductility is reduced to a very low level and brittleness results in alloys of high copper content. Therefore copper percentages do not exceed 12 per cent in most aluminium casting alloys. Actually, the copper percentages in aluminium casting alloys are adjusted so that the lower contents, 2 to 5 per cent, are used in alloys required to have optimum ductility (or toughness), whereas the higher percentages are used when greater hardness and strength are desired.

Heat-treatment of Cu-Al Alloys

The mechanical-property curves of Cu-Al alloys are shown to be markedly shifted by solution heat-treatment and age hardening. In fact, the degree of strengthening obtainable by heat-treatment is greater than that gained by alloying alone. A few elements, namely, Cu, Mg, Zn, and combinations of Mg and Si confer heat-treating potentialities to Al-base alloys in which they are present. These are referred to as “heat-treatable” grades of aluminium alloys, and they greatly extend the range of properties available in aluminium castings.

Solution heat-treatment. Solution heat-treatment of aluminium casting alloys consists of a thermal cycle of heating, a suitable period of holding the metal at some elevated temperature, and then rapid cooling of the castings, usually by quenching in water. The temperature and time of holding are exceedingly important factors in the treatment. The temperature must be high enough to cause a substantially large amount of the alloying elements (usually present as intermetallic compound phases) to dissolve in the aluminium-rich solid-solution phase.

After sand casting and slow cooling to room temperature, this alloy consists micro structurally of the aluminium-rich phase k and the hard phase, copper being concentrated mainly in the latter phase. Reheating the alloy to a temperature of about 900 to 950 F causes the phase to disappear from the microstructure, since, the higher temperature permits all the copper in the alloy to be dissolved by the aluminium; hence the name “solution” heat-treating. Of course, adequate time for dissolving of the phase into the K phase must be allowed. Thus emphasis is placed on the “time at temperature” of the solution heat-treatment. A sufficient holding period at the solution heat-treating temperature is one which results in the aluminium-rich phase having reached a uniformly high percentage of dissolved alloying elements. When this condition exists, rapid cooling from the elevated temperature will retain the enriched solid-solution phase, 4% Cu-96% Al in the present case, down to room temperature. The end microstructure after solution heat-treating then is a supersaturated Al-rich solid-solution phase. In this case, the k phase contains 4 per cent dissolved copper rather than the normal amount of less than 0.50 per cent for the slow or equilibrium-cooled condition. Since solution heat-treating results in a more uniform distribution of soluble alloying elements, it also assists in minimizing the harmful effects of segregation developed during solidification.

Accompanying the microstructural effects of solution heat-treatment are improvements in mechanical properties. A marked increase in tensile and yield strengths and an improvement in ductility are revealed in Fig. 3 as a consequence of this treatment. Most important is the fact that solution heat-treatment is the necessary step in preparing the alloys for age or precipitation hardening from which further benefits may be obtained.

Solution heat-treatment by chill casting. Rapid cooling from any elevated temperature, particularly above 700 to 800 F, will cause retention of a supersaturated A1-rich phase down to room temperature. Hence casting processes such as permanent-mold or die casting which are inherently rapid in their cooling effect have this possibility. Sand casting, by contrast, is a slow cooling process. Therefore, if a given alloy, Cu-A1, for example, is cast in a metal mold, it will usually show higher hardness, strength, and ductility than if the same alloy is cast in a sand mold. This point will be considered again later.

Age hardening or precipitation hardening. Natural age hardening is a gradual increase in hardness (and strength) which occurs with the lapse of time at atmospheric temperatures. The increased hardness may reach a maximum value in a few days but may require several years in some alloys. More rapid aging can be caused to occur at elevated temperatures, 300 to 400 F. Heat-treating to cause aging is called artificial age hardening, or “precipitation” hardening. Aging effects by either method are obtained only from alloys which have been previously solution heat-treated. Or the alloy can be aged, if it has been processed so that effects similar to solution heat-treatment are retained, as, for example, by chill casting. The metallurgical changes associated with aging are exceedingly complex, so that only the more simple details are considered here.

Aging or precipitation-hardening temperatures are such as to promote precipitation from the supersaturated solid solution remaining from solution heat-treatment. In the case of the 4% Cu-96% A1 alloy considered earlier, the direction of microstructural changes during aging is toward reprecipitation of the phase from the supersaturated k phase developed by solution heat-treatment. However, the most beneficial aging effects are obtained before microstructural evidence of precipitation is revealed. In fact, when the precipitating phase is metallographically visible, overaging has occurred. Overaging results in a substantial decrease in hardness, strength, and other properties.

Temperature and time of aging are exceedingly important factors, determining the end effect of aging. High temperatures are to cause rapid aging or overaging at extended times. Low temperatures can prevent aging. Thus it is evident that a proper temperature and time interval will produce the most desirable properties. Aging treatments for specific alloys will be considered later.

MALLEABLE IRON

American malleable iron occupies the unusual position of being truly a product born of the American foundryman’s inventiveness. The first “blackheart” malleable-iron castings were developed by Seth Boyden at Newark, N.J., starting in 1826. Boyden’s work eventually resulted in the growth of the American, or blackheart, malleable-iron industry, until it has become the third largest tonnage producer in the castings field.

Malleable iron is an important engineering material, largely because its properties offer certain special advantages among the family of cast irons. Desirable properties include case of machinability, toughness and ductility, corrosion resistance in certain applications, strength adequate for wide usage, magnetic properties, and uniformity resulting from 100 per cent heat-treatment of all castings produced. Applications of malleable castings usually reflect a need for one or more of the foregoing properties. Principal users of the castings are the automotive and truck industries, construction-machinery producers, and agricultural-equipment makers.

Examples of truck malleable-iron castings are shown in Fig.1.

The properties of malleable iron are mainly related to its metallographic structure. Malleable iron may be defined micro structurally as a ferrous alloy composed of temper carbon in a matrix of ferrite containing dissolved silicon. The structure is the result of heat-treatment applied to white-iron castings. The chemical composition of the common grades of white iron which may be heat-treated to malleable iron is given in Table 1.

Heat-treatment converts the massive carbides and pearlite of the white iron to ferrite and temper carbon. Chemically, heat-treatment causes a change from combined carbon to graphite or temper carbon, the combined carbon generally being less than 0.15 per cent by weight after heat-treatment. The ferrite structure with interspersed graphite gives malleable-iron mechanical properties in the range of those specified in Table 2, under standard malleable iron. The tensile properties and Bhn are characteristic of ferrite alloyed with 1 per cent silicon.

Except for annealing or malleableizing, the manufacture of malleable-iron castings involves the same basic foundry processes used with other alloys. Molding, coremaking, cleaning, melting, pouring, etc., are adapted to the special casting properties of malleable iron, which are primarily related to its metallurgical nature. This area will therefore be considered first.

MELTING

Melting iron for malleable casting is generally performed in the air-furnace, the cupola, induction, or direct are electric furnaces, or a combination of these furnaces when duplexing is employed.

Batch-melting Process

The cold-melt air furnace shown in Fig. 3 is used for batch melting. The air furnace is a reverberatory-type furnace fired with pulverized coal or oil. Common furnace capacities range from 15 to 40 tons. The furnace hearth is rectangular and provides a molten-bath depth of generally less than 12.0 in. Tapholes are-provided on the side of the furnace. The side walls are made of firebrick supported by steel, and the bottom is either silica sand or firebrick. The furnace top consists of a series of removable firebrick arches known as “bungs.” By removing some of the bungs, the furnace may be charged with cold metal through the top. A typical furnace charge is given below:

Smaller-size charge materials are usually placed on the bottom of the furnace. Both charges listed above contain about 50 per cent sprue because this is the usual percentage of remelt in a malleable foundry. The balance of the air-furnace charge is selected so that the iron will melt down at about 2.65 to 2.85 C, phosphorus and sulfur percentages below the maximum permitted, and silicon and manganese within or slightly below the desired analysis range. Less than 0.07 per cent, and preferably less than 0.03 per cent, chromium should be in the charge, since this element interferes with annealing. Melting down is performed with a fuel-air mixture which will produce flame temperatures of about 3080 to 3150 F and hold oxidation of the metal to a minimum. A slag forms during melting down from metal-oxidation products and refractory attrition. During melting down and as the bath reaches a temperature of about 2600 F, the slag is skimmed. The bath temperature is then raised to the desired pouring temperature, usually 2800 to 2900 F. Losses of silicon and manganese occur during melting down and until the metal has reached a temperature of about 2700 F. At higher temperatures, carbon losses can occur rapidly under oxidizing atmospheres, but there may be a silicon pickup from the refractories and slag. The iron gains about 0.05 to 0.15 per cent silicon per hour at 2800 to 2900 F from reduction of silica by carbon in the iron. Typical composition changes during a heat are given in Table 3.

Carbon losses are counteracted by melting with a higher fuel-to-air ratio (reducing), by adding graphite, petroleum coke, or proprietary recarburizer, or by dropping powdered coal on the metal surface from the burners.

The analysis changes occurring in the course of an air-furnace heat are accompanied by structural changes in the solidified iron. Early in the heat, iron cast into a bar about 1¾ to 2 in. in diameter and 8 to 10 in. long will freeze gray or mottled. Mottling results from the formation of flake graphite during freezing, the iron then not being a completely white iron. As the temperature increases above 2600 F and the carbon percentage in the iron drops, mottling gradually disappears. Finally, before tapping, the test bar will cast white and will have a completely white fracture as illustrated in Fig. 5. Generally, the objective of quality malleable-iron melting is to produce a completely white iron with no free flake graphite in the castings since-flake graphite lowers the properties of malleable iron. Melting may be conducted to favor white iron by using high temperatures, oxidizing conditions, low carbon and silicon percentage in the iron, add