BUILDING. MATERIALS. (THIRD REVISED EDITION). 5. K. Duggal. B.E., M.E., Ph.D. Professor and Head. Civil Engineering Department. Motilal Nehru Institute . The Book Building Materials By S.K. Duggal is considerably modified version of the edition. In thrid edition of the book extensive revisions have been made . Book FormatPDF. Language English. Pages Views 11, Size MiB Building Materials by S K Duggal is available for free download in PDF format.
|Language:||English, French, Portuguese|
|ePub File Size:||17.42 MB|
|PDF File Size:||12.75 MB|
|Distribution:||Free* [*Registration needed]|
Geotechnical Engineering Principles and Practices BUILDING MATERIALS BY picscobenreatttas.ga PDF · Reinforced Cement Concrete(RCC) for. Building Materials & Construction Planning Textbook free. Pages·· MB·19, K. Duggal B.E., M.E., Ph.D. Professor and Head Civil Buil. The Book is considerably modified version of the edition. In thrid edition of the book extensive revisions have been made. New materials.
All inquiries should be emailed to rights newagepublishers. Preface to the Third Edition The book is considerably modified version of the edition. In third edition of the book extensive revisions have been made. New materials have been introduced due to the advances in the technology and progress in industry. The information presented includes characteristics of the materials in regards to their physical and mechanical properties with emphasis on their strength and durability qualities.
The material presented can be supplemented by the information from I. Codes and various product manufacturers. This edition embodies material changes in the chapters dealing with Cement, Concrete, Lime and many others.
Testing procedures of the materials have been updated for most of the materials as some of the codes have been revised. Especially, in chapter 3 on Rocks and Stones the section on testing of Stones has been completely rewritten. Chapter 8 on Lime has been completely rewritten to make it more reader friendly. Logical changes in chapter 5 on Cement, chapter 10 on Concrete and chapter 20 on Special Cements and Cement Concretes have been made. Admixtures for concrete have been placed in chapter 10 and section on Pointing has been removed from chapter 12 on Building Mortars.
Many newer and upcoming more important concretes such as Self compacting Concrete, Bacterial Concrete have been introduced in chapter 20 on special Cements and Cement Concrete. Numerous revision of data and substitutions in description have been made not only in these chapters but in other chapters also. Smart materials and composite materials have been introduced in chapter 21 on Miscellaneous Materials. The author will be grateful to the readers for their comments and suggestions for further improvement of the book.
Duggal 5. Preface to the Second Edition The second edition of this book deals with properties of building materials and techniques for their manufacturing. Applications of building materials have been presented with emphasis on engineering and economic approaches for determining the optimum kind of materials, best suited to specific conditions of service in buildings.
This edition provides a thorough and practical groundwork for students of civil, architecture and construction technology. The expanded and updated text can also serve as a refresher and reference for practicing civil engineers, architects, contractors, and other workers who must be aware of new building materials and techniques. The building materials industry is in continual development, the range of products is being expanded, and novel techniques for optimizing production processes are being introduced.
The main purpose of the book is to present a basic course of study with a detailed coverage of basic theory and practice of the manufacture of building materials. The present edition embodies material change in the chapters dealing with lime, cement, concrete, and many other minor revisions. Since concrete Chapter 10 is the most widely and extensively used building material, its production, properties, and testing have been thoroughly revised and discussed in more details and depth.
Chapter 11 on mix design has been introduced to make the used understand better the manufacture and properties of concrete. Standards laid by Bureau of Indian Standards have been followed. Extensive addition in Chapter 20, miscellaneous materials, include elaboration of geotextiles, new types of cements and concretes—their properties and production processes.
All this was possible due to the suggestions, and comments received form many individuals and students. I would like to thank all of them.
Acknowledgement is also made to New Age Publishers for publishing the second edition. Duggal 6. Preface to the First Edition The primary purpose of writing this book is to give engineering students up-to-date information on building materials. The book has been prepared after referring to a number of text books, references and standards. An attempt has also been made to present to the reader some of the more general uses and applications of the different materials.
The author gratefully acknowledges the considerable encouragement, splendid help and valuable suggestions received form his colleagues.
Appreciation and thanks are also due to those students who went through the preliminary and final scripts. Finally thanks are due to my wife Suman and children Swati and Shashank for their tolerance during this trying time. Efforts have been made to keep errors to a minimum. However, they are inevitable. Suggestions are welcomed from all concerned pointing out any oversights. Duggal 7. This page intentionally left blank 8. Principal Properties of Building Materials 1 1.
Structural Clay Products 8 2. Rocks and Stones 52 3. Wood and Wood Products 91 4. Contents xi 4. Materials for Making Concrete-I Cement 5. Cement Exercises Objective Type Questions 9. Puzzolanas 9. Concrete Contents xiii Concrete Mix Design Building Mortars Ferrous Metals Non-Ferrous Metals Ceramic Materials Polymeric Materials Paints, Enamels and Varnishes Contents xv Tar, Bitumen and Asphalt Gypsum Special Cements and Cement Concretes Miscellaneous Materials Although their most important use is in construction activities, no field of engineering is conceivable without their use.
Also, the building materials industry is an important contributor in our national economy as its output governs both the rate and the quality of construction work.
There are certain general factors which affect the choice of materials for a particular scheme. Perhaps the most important of these is the climatic background. Obviously, different materials and forms of construction have developed in different parts of the world as a result of climatic differences.
Another factor is the economic aspect of the choice of materials. The rapid advance of constructional methods, the increasing introduction of mechanical tools and plants, and changes in the organisation of the building industry may appreciably influence the choice of materials.
Due to the great diversity in the usage of buildings and installations and the various processes of production, a great variety of requirements are placed upon building materials calling for a very wide range of their properties: Also, materials for interior decoration of residential and public buildings, gardens and parks, etc.
Specific properties of building materials serve as a basis for subdividing them into separate groups. For example, mineral binding materials are subdivided into air and hydraulic-setting varieties.
The principal properties of building materials predetermine their applications.
Only a comprehensive knowledge of the properties of materials allows a rational choice of materials for specific service conditions. It requires the quality of materials and manufactured items to be not below a specific standard level. However, the importance of standardisation is not limited to this factor alone, since each revised standard places higher requirements upon the products than the preceding one, with the effect that the industry concerned has to keep up with the standards and improved production techniques.
Thus, the industry of building materials gains both in quantity and quality, so that new, more efficient products are manufactured and the output of conventional materials is increased. Todevelopproductsofgreatereconomicefficiency,itisimportanttocomparetheperformance of similar kinds of materials under specific service conditions.
Expenditures for running an installation can be minimised by improving the quality of building materials and products. Building industry economists are thus required to have a good working knowledge, first, of the buildingmaterials,second,oftheiroptimumapplicationsonthebasisoftheirprincipalproperties, and, third, of their manufacturing techniques, in order that the buildings and installations may have optimum engineering, economic performance and efficiency.
Having acquired adequate knowledge, an economist specialising in construction becomes an active participant in the development of the building industry and the manufacture of building materials.
For most materials, bulk density is less than density but for liquids and materials like glass and dense stone materials, these parameters are practically the same. Properties like strength and heat conductivity are greatly affected by their bulk density.
Bulk densities of some of the building materials are as follows: For almost all building materials ro is less than 1. It is also used in fluid dynamics as a property of the fluid e. The terms specific gravity, and less often specific weight, are also used for relative density. U U s a w The absolute specific gravity is not much of practical use.
Apparent or mass specific gravity Gm If both the permeable and impermeable voids are included to determine the true volume of solids, the specific gravity is called apparent specific gravity. It is the ratio of mass density of fine grained material to the mass density of water. It is expressed as a ratio of the volume of pores to that of the specimen. Dense materials, which have low porosity, are used for constructions requiring high mechanical strength on other hand, walls of buildings are commonly built of materials, featuring considerable porosity.
Following inter relationship exists between void ratio and the porosity.
Building Materials By S.K.Duggal
To the vacant spaces between the particles of aggregate the name voids is applied. Necessarily, the percentage of voids like the specific weight is affected by the compactness of the aggregate and the amount of moisture which it contains. Generally void determinations are made on material measured loose.
There are two classes of methods commonly employed for measuring voids, the direct and the indirect. The most-used direct method consists in determining the volume of liquid, generally water, which is required to fill the voids in a given quantity of material.
Since in poring water into fine aggregate it is impossible to expel all the air between the particles, the measured voids are smaller than the actual. It therefore becomes evident that the above direct method should not be used with fine aggregate unless the test is conducted in a vacuum. By the indirect method, the solid volume of a known quantity of aggregate is obtained by pouring the material into a calibrated tank partially filled with water; the difference between the apparent volume of material and the volume of water displaced equals the voids.
If very accurate results are desired void measurements should be corrected for the porosity of the aggregate and moisture it contains. Hygroscopicity is the property of a material to absorb water vapour from air.
It is influenced by air-temperature and relative humidity; pores—their types, number and size, and by the nature of substance involved. Water Absorption denotes the ability of the material to absorb and retain water. It is expressed as percentage in weight or of the volume of dry material: The properties of building materials are greatly influenced when saturated. The ratio of compressive strength of material saturated with water to that in dry state is known as coefficient of softening and describes the water resistance of materials.
For materials like clay which soak readily it is zero, whereas for materials like glass and metals it is one. Materials with coefficient of softening less than 0. Weathering Resistance is the ability of a material to endure alternate wet and dry conditions for a long period without considerable deformation and loss of mechanical strength. Water Permeability is the capacity of a material to allow water to penetrate under pressure.
Materials like glass, steel and bitumen are impervious. Frost Resistance denotes the ability of a water-saturated material to endure repeated freezing and thawing with considerable decrease of mechanical strength. Under such conditions the water contained by the pores increases in volume even up to 9 per cent on freezing. Thus the walls of the pores experience considerable stresses and may even fail. Heat Conductivity is the ability of a material to conduct heat. It is influenced by nature of material, its structure, porosity, character of pores and mean temperature at which heat exchange takes place.
Materials with large size pores have high heat conductivity because the air inside the pores enhances heat transfer. Moist materials have a higher heat conductivity than drier ones. This property is of major concern for materials used in the walls of heated buildings since it will affect dwelling houses.
Thermal Capacity is the property of a material to absorb heat described by its specific heat. Thermal capacity is of concern in the calculation of thermal stability of walls of heated buildings and heating of a material, e.
Fire Resistance is the ability of a material to resist the action of high temperature without any appreciable deformation and substantial loss of strength. Fire resistive materials are those which char, smoulder, and ignite with difficulty when subjected to fire or high temperatures for long period but continue to burn or smoulder only in the presence of flame, e.
Non-combustible materials neither smoulder nor char under the action of temperature. Some of the materials neither crack nor lose shape such as clay bricks, whereas some others like steel suffer considerable deformation under the action of high temperature. Refractoriness denotes the ability of a material to withstand prolonged action of high temperature without melting or losing shape.
Natural stone materials, e. Durability is the ability of a material to resist the combined effects of atmospheric and other factors. Strength is the ability of the material to resist failure under the action of stresses caused by loads, the most common being compression, tension, bending and impact.
Compressive Strength is found from tests on standard cylinders, prisms and cubes—smaller for homogeneous materials and larger for less homogeneous ones.
Prisms and cylinders have lower resistance than cubes of the same cross-sectional area, on the other hand prisms with heights smaller than their sides have greater strength than cubes.
This is due to the fact that when a specimen is compressed the plattens of the compression testing machine within which the specimen is placed, press tight the bases of the specimen and the resultant friction forces prevent the expansion of the adjoining faces, while the central lateral parts of the specimen undergoes transversal expansion.
The only force to counteract this expansion is the adhesive force between the particles of the material. That is why a section away from the press plates fails early. The test specimens of metals for tensile strength are round bars or strips and that of binding materials are of the shape of figure eight.
Bending Strength tests are performed on small bars beams supported at their ends and subjected to one or two concentrated loads which are gradually increased until failure takes place. Hardness is the ability of a material to resist penetration by a harder body. Mohs scale is used to find the hardness of materials.
It is a list of ten minerals arranged in the order of increasing hardness Section 3. Hardness of metals and plastics is found by indentation of a steel ball. Elasticity is the ability of a material to restore its initial form and dimensions after the load is removed. Within the limits of elasticity of solid bodies, the deformation is proportional to the stress. Ratio of unit stress to unit deformation is termed as modulus of elasticity. A large value of it represents a material with very small deformation.
Plasticity is the ability of a material to change its shape under load without cracking and to retain this shape after the load is removed.
Some of the examples of plastic materials are steel, copper and hot bitumen. Principal Properties of Building Materials 7 1. The ductile materials can be drawn out without necking down, the examples being copper and wrought iron.
Brittle materials have little or no plasticity.
They fail suddenly without warning. Cast iron, stone, brick and concrete are comparatively brittle materials having a considerable amount of plasticity. Stiff materials have a high modulus of elasticity permitting small deformation for a given load. Flexible materials on the other hand have low modulus of elasticity and bend considerably without breakdown. Tough materials withstand heavy shocks.
Toughness depends upon strength and flexibility. Malleable materials can be hammered into sheets without rupture. It depends upon ductility and softness of material. Copper is the most malleable material. Hard materials resist scratching and denting, for example cast iron and chrome steel.
Materials resistant to abrasion such as manganese are also known as hard materials. Define the following: Write short notes on the following: Higher the bulk specific gravity, the stronger is the clay product.
This rule does not hold good for vitrified products since the specific gravity of clay decreases as vitrification advances. Bulk specific gravity of clay brick ranges from 1.
Structural Clay Products 9 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. 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. This is a result of micro-structural changes in clay and as such is a chemical property. Purest clays consist mainly of kaolinite 2SiO2. By their origin, clays are subdivided as residual and transported clays. Residual clays, known as Kaolin or China clay, are formed from the decay of underlying rocks and are used for making pottery. The 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. The refractory clays are highly disperse and very plastic. These have high content of alumina and low content of impurities, such as Fe2O3, tending to lower the refractoriness. These are used for manufacturing facing bricks, floor tiles, sewer pipes, etc. These are used to manufacture bricks, blocks, tiles, etc.
Admixtures are added to clay to improve its properties, if desired. Highly plastic clays which require mixing water up to 28 per cent, give high drying and burning shrinkage, call for addition of lean admixtures or non-plastic substances such as quartz sand, chamottee, ash, etc. Items of lower bulk density and high porosity are obtained by addition of admixture that burn out. The examples of burning out admixtures are sawdust, coal fines, pulverized coal.
Acid resistance items and facing tiles are manufactured from clay by addition of water-glass or alkalis. Burning temperature of clay items can be reduced by blending clay with fluxes such as felspar, iron bearing ores, etc. Plasticity of moulding mass may be increased by adding surfactants such as sulphite-sodium vinasse 0. Knowledge of these properties is of more benefit in judging the quality of the raw material than a chemical analysis. By plasticity is meant the property which wetted clay has of being permanently deformed without cracking.
The amount of water required by different clays to produce the most plastic condition varies from 15 to 35 per cent. Although plasticity is the most important physical property of clay, yet there are no methods of measuring it which are entirely satisfactory. The Personal equation necessarily plays a large part in such determination. Since clay ware is subjected to considerable stress in moulding, handling and drying, a high tensile strength is desirable.
The test is made by determining the stregth of specimens which have been moulded into briquette form and very carefully dried. The texture of clay is measured by the fineness of its grains.
In rough work the per cent passing a No. No numerical limit to the grain size or desired relation between sizes has been established. Very fine grained clays free from sand are more plastic and shrink more than those containing coarser material. Knowledge of shrinkage both in drying and in burning is required in order to produce a product of required size. Also the amount of shrinkage forms an index of the degree of burning.
The shrinkage in drying is dependent upon pore space within the clay and upon the amount of mixing water. The addition of sand or ground burnt clay lowers shrinkage, increases the porosity and facilitates drying. Fire shrinkage is dependent upon the proportion of volatile elements, upon texture and the way that clay burns. By porosity of clay is meant the ratio if the volume of pore space to the dry volume.
Since porosity affects the proportion of water required to make clay plastic, it will indirectly influence air shrinkage. Large pores allow the water to evaporate more easily and consequently permit a higher rate of drying than do small pores. In as much as the rate at which the clay may be safely dried is of great importance in manufacturing clay products, the effect of porosity on the rate of drying should be considered.
The temperature at which clay fuses is determined by the proportion of fluxes, texture, homogeneity of the material, character of the flame and its mineral constitution. Owing to non- uniformity in composition, parts of the clay body melt at different rates so that the softening period extends over a considerable range both of time and temperature.
This period is divided into incipient vitrification and viscous vitrification. Experiments roughly indicate that the higher the proportion of fluxes the lower the melting point. Fine textured clays fuse more easily than those of coarser texture and the same mineral composition. The uniformity of the clay mass determines very largely the influence of various elements; the carbonate of lime in large lumps may cause popping when present in small percentages, but when finely ground 15 per cent of it may be allowed in making brick or tile.
Lime combined with silicate of alumina feldspar forms a desirable flux. Iron in the ferrous form, found in carbonates and in magnetite, fuses more easily than when present as ferric iron. 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. A determination of the fusibility of a clay is of much importance both in judging of the cost of burning it and in estimating its refractoriness. Clay bricks are used for building-up exterior and interior walls, partitions, piers, footings and other load bearing structures. Structural Clay Products 11 A brick is rectangular in shape and of size that can be conveniently handled with one hand.
Brick may be made of burnt clay or mixture of sand and lime or of Portland cement concrete. Clay bricks are commonly used since these are economical and easily available.
The length, width and height of a brick are interrelated as below: Weight of such a brick is 3. An indent called frog, 1—2 cm deep, as shown in Fig. The purpose of providing frog is to form a key for holding the mortar and therefore, the bricks are laid with frogs on top. Frog is not provided in 4 cm high bricks and extruded bricks.
First Class Bricks 1. These are thoroughly burnt and are of deep red, cherry or copper colour. The surface should be smooth and rectangular, with parallel, sharp and straight edges and square corners. These should be free from flaws, cracks and stones. These should have uniform texture.
Smart Building Systems for Architects Owners and Builders By James Sinopoli
No impression should be left on the brick when a scratch is made by a finger nail. The fractured surface of the brick should not show lumps of lime. A metallic or ringing sound should come when two bricks are struck against each other. This limit varies with different Government organizations around the country. First class bricks are recommended for pointing, exposed face work in masonry structures, flooring and reinforced brick work. Second Class Bricks are supposed to have the same requirements as the first class ones except that 1.
Small cracks and distortions are permitted. The crushing strength should not be less than 7. Second class bricks are recommended for all important or unimportant hidden masonry works and centering of reinforced brick and reinforced cement concrete RCC structures. Third Class Bricks are underburnt. They are soft and light-coloured producing a dull sound when struck against each other.
Water absorption is about 25 per cent of dry weight.
It is used for building temporary structures. Fourth Class Bricks are overburnt and badly distorted in shape and size and are brittle in nature. The ballast of such bricks is used for foundation and floors in lime concrete and road metal.
Table 2. The burnt clay bricks having compressive strength more than The water absorption of these bricks is limited to 5 per cent. Each class of bricks as specified above is further divided into subclasses A and B based on tolerances and shape. Subclass-A bricks should have smooth rectangular faces with sharp corners and uniform colour. Subclass-B bricks may have slightly distorted and round edges.
These may vary greatly in strength and durability and are used for filling, backing and in walls where appearance is of no consequence. Facing Bricks are made primarily with a view to have good appearance, either of colour or texture or both. These are durable under severe exposure and are used in fronts of building walls for which a pleasing appearance is desired. Engineering Bricks are strong, impermeable, smooth, table moulded, hard and conform to defined limits of absorption and strength.
These are used for all load bearing structures. On the Basis of Finish Sand-faced Brick has textured surface manufactured by sprinkling sand on the inner surfaces of the mould. Rustic Brick has mechanically textured finish, varying in pattern. On the Basis of Manufacture Hand-made: These bricks are hand moulded. Depending upon mechanical arrangement, bricks are known as wire-cut bricks—bricks cut from clay extruded in a column and cut off into brick sizes by wires; pressed- bricks—when bricks are manufactured from stiff plastic or semi-dry clay and pressed into moulds; moulded bricks—when bricks are moulded by machines imitating hand mixing.
On the Basis of Burning Pale Bricks are underburnt bricks obtained from outer portion of the kiln. Body Bricks are well burnt bricks occupying central portion of the kiln. Arch Bricks are overburnt also known as clinker bricks obtained from inner portion of the kiln. On the Basis of Types Solid: Small holes not exceeding 25 per cent of the volume of the brick are permitted; alternatively, frogs not exceeding 20 per cent of the total volume are permitted.
Small holes may exceed 25 per cent of the total volume of the brick. The total of holes, which need not be small, may exceed 25 per cent of the volume of the brick. Holes closed at one end exceed 20 per cent of the volume. Small holes are less than 20 mm or less than mm2 in cross section. Size and Shape: The bricks should have uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges.
The brick should have a uniform deep red or cherry colour as indicative of uniformity in chemical composition and thoroughness in the burning of the brick. Texture and Compactness: The surfaces should not be too smooth to cause slipping of mortar.
The brick should have precompact and uniform texture. A fractured surface should not show fissures, holes grits or lumps of lime. Hardness and Soundness: The brick should be so hard that when scratched by a finger nail no impression is made. When two bricks are struck together, a metallic sound should be produced.
Water Absorption should not exceed 20 per cent of its dry weight when kept immersed in water for 24 hours. Brick Earth should be free from stones, kankars, organic matter, saltpetre, etc. After drying, it should not shrink and no crack should develop. The clay used for brick making consists mainly of silica and alumina mixed in such a proportion that the clay becomes plastic when water is added to it.
It also consists of small proportions of lime, iron, manganese, sulphur, etc. The proportions of various ingredients are as follows: It enables the brick to retain its shape and imparts durability, prevents shrinkage and warping.
Excess of silica makes the brick brittle and weak on burning. A large percentage of sand or uncombined silica in clay is undesirable. However, it is added to decrease shrinkage in burning and to increase the refractoriness of low alumina clays. Alumina absorbs water and renders the clay plastic.
If alumina is present in excess of the specified quantity, it produces cracks in brick on drying. Clays having exceedingly high alumina content are likely to be very refractory. Lime normally constitutes less than 10 per cent of clay. Lime in brick clay has the following effects: Reduces the shrinkage on drying. Causes silica in clay to melt on burning and thus helps to bind it. In carbonated form, lime lowers the fusion point.
Excess of lime causes the brick to melt and the brick looses its shape. Magnesia rarely exceeding 1 per cent, affects the colour and makes the brick yellow, in burning; it causes the clay to soften at slower rate than in most case is lime and reduces warping. Iron Iron oxide constituting less than 7 per cent of clay, imparts the following properties: Gives red colour on burning when excess of oxygen is available and dark brown or even black colour when oxygen available is insufficient, however, excess of ferric oxide makes the brick dark blue.
Improves impermeability and durability. Tends to lower the fusion point of the clay, especially if present as ferrous oxide. Gives strength and hardness. When a desirable amount of lime is present in the clay, it results in good bricks, but if in excess, it changes the colour of the brick from red to yellow.
When lime is present in lumps, it absorbs moisture, swells and causes disintegration of the bricks. Therefore, lime should be present in finely divided state and lumps, if any, should be removed in the beginning itself.
Experience has shown, however, that when line particles smaller than 3 mm diameter hydrate they produce only small pock mark which, provided that there are not many of them, can usually be ignored. Particles larger than this might, if present in any quantity, cause unsightly blemishes or even severe cracking. Pebbles, Gravels, Grits do not allow the clay to be mixed thoroughly and spoil the appearance of the brick.
Surveying by SK-Duggal.pdf
Bricks with pebbles and gravels may crack while working. Iron Pyrites tend to oxidise and decompose the brick during burning. The brick may split into pieces. Pyrites discolourise the bricks.
These are mainly in the form of soda or potash. However, when present in excess, alkali makes the clay unsuitable for bricks. They melt the clay on burning and make the bricks unsymmetrical. When bricks come in contact with moisture, water is absorbed and the alkalis crystallise.
On drying, the moisture evaporates, leaving behind grey or white powder deposits on the brick which spoil the appearance. This phenomenon is called efflorescence. Efflorescence should always be dry brushed away before rendering or plastering a wall; wetting it will carry the salts back into the wall to reappear later.
If bricks become saturated before the work is completed, the probability of subsequent efflorescence is increased, brick stacks should, therefore be protected from rain at all times. During laying, the bricks should be moistened only to the extent that is found absolutely essential to obtain adequate bond between bricks and mortar; newly built brickwork should be protected from rain. Organic Matter: On burning green bricks, the organic matter gets charred and leave pores making the bricks porous; the water absorption is increased and the strength is reduced.
Carbonaceous Materials in the form of bituminous matter or carbon greatly affects the colour of raw clay. Unless proper precaution is taken to effect complete removal of such matter by oxidation, the brick is likely to have a black core.
Sulphur is usually found in clay as the sulphate of calcium, magnesium, sodium, potassium or iron, or as iron sulphide. Generally, the proportion is small. If, however, there is carbon in the clay and insufficient time is given during burning for proper oxidation of carbon and sulphur, the latter will cause the formation of a spongy, swollen structure in the brick and the brick will be decoloured by white blotches.
A large proportion of free water generally causes clay to shrink considerably during drying, whereas combined water causes shrinkage during burning. The use of water containing small quantities of magnesium or calcium carbonates, together with a sulphurous fuel often causes similar effects as those by sulphur. These additives should, however, have a desirable level of physical and chemical characteristics so as to modify the behaviour of clay mass within the optimum range without any adverse effect on the performance and durability.
Some of the basic physio-chemical requirements of conventional additives are as under: Structural Clay Products 17 Fly Ash: Awaste material available in large quantities from thermal power plants can be added to alluvial, red, black, marine clays, etc. The fly ash contains amorphous glassy material, mullite, haematite, magnetite, etc.
These silicates also help towards strength development in clay bodies on firing, when mixed in optimum proportion depending on the physio-chemical and plastic properties of soils to be used for brick making. The proportion of fly ash mixed as an additive to the brick earth should be optimum to reduce drying shrinkage, check drying losses and to develop strength on firing without bloating or black coring in fired product.
The crystallites present in the fly ash should comply with the resultant high temperature phases in the finished product. Your email address will not be published. The Book is considerably modified version of the edition.
In thrid edition of the book extensive revisions have been made. New materials have been introduced due to the advances in the technology and progress in industry. The information presented includes characteristics of the materials in regards to their physical and mechanical properties with emphasis on their strength and durability qualities.
Download Building Materials by S.K. Duggal PDF
The material presented can be supplemented by the information from I. Download the Book. The Content is for Members Only!!! Civil Engineering Blog.
About the Author: Leave a Reply Cancel reply Your email address will not be published. Looking for a Job?Large pores allow the water to evaporate more easily and consequently permit a higher rate of drying than do small pores. Wall tiles are burned at a comparatively low temperature, glazed, and fired again in muffle kiln at a still lower temperature. Check your Email after Joining and Confirm your mail id to get updates alerts. Since in poring water into fine aggregate it is impossible to expel all the air between the particles, the measured voids are smaller than the actual.
The proportion of fly ash mixed as an additive to the brick earth should be optimum to reduce drying shrinkage, check drying losses and to develop strength on firing without bloating or black coring in fired product.