Building Materials and construction technology
- 1. UCV343C: BUILDING MATERIALS & CONSTRUCTION TECHNOLOGY Dr. Adarsh S. Chatra Associate Professor Dept. of Civil Engineering, BEC Bagalkot-587102
- 2. Introduction • Building Materials - Materials which are required for construction of buildings are referred as building materials. Building materials are classified - 1. Natural Materials: - These are naturally occurring materials namely wood, stone, mud or clay etc. 2. Artificial materials: - These are man-made materials namely bricks, cement, glass & steel. 3. Composite materials: - These are combination of two or materials namely concrete, plywood etc.
- 3. Building Materials • Stones are naturally occurring building materials which is widely use in construction of buildings. • Nowadays it has become an important source of aggregate (coarse & fine) for manufacturing concrete. • Stones used for civil engineering works may be classified in the following three ways: Geological Classification Physical Classification Chemical Classification
- 4. Building Materials • Bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and brining these blocks.
- 5. Building Materials • Mortar - The term mortar is used to indicate a paste prepared by adding required amount of water to a mixture of binding material like cement or lime and fine aggregate like sand. Timber • The word timber is derived from an old English word “timbrian” which means to build. • The timber thus denotes wood which is suitable for building or carpentry or various other engineering purposes
- 6. Building Materials Aggregates • Aggregates are defined as inert, granular and inorganic materials that normally consist of stone or stone like solids. • Aggregates can be used alone, in road bases and various types of fill or can be used with cementing materials (such as Portland cement or asphalt cement) to form composite materials or concrete.
- 7. BRICKS
- 8. Bricks Classification of brick earth 1) Loamy, mild or sandy clay: This type of earth consists of considerable amount of free silica in addition to alumina. The presence of sand helps in preventing cracking, shrinkage and warping of bricks. The addition of lime in such clay helps to fuse sand and there by increases the hardness of bricks. 2) Marls, chalky or calcareous clay: This clay consists of considerable amount of chalk in addition to alumina and silica. Such clay generally makes good bricks. 3) Plastic, strong or pure clay: This clay consists of alumina and silica which is sometimes referred as strong or fat clay. The raw bricks will crack, shrink and wrap during drying, if pure clay alone is used in making of bricks. Hence such clay is corrected by the addition of sand and ash. The sand prevents shrinkage and ash provides lime to act as flux.
- 9. Manufacturing of clay bricks Following are the considerations which governs the selection of brick field for manufacturing of bricks: • It should be linked up with communicating roads so that the materials can be conveyed easily. • It should be situated on a plain ground • It should be selected in such a way that the earth required for manufacturing of bricks is readily and easily available. • It should offer all the facilities to the workers employed in the manufacturing process.
- 10. Manufacturing of clay bricks • In the process of manufacturing bricks, the following four distinct operations are involved. a) Preparation of clay b) Moulding c) Drying d) Burning
- 11. Preparation of clay • Unsoiling: The top layer of soil about 200mm in depth is taken out and thrown away. The clay in top soil is full of impurities and hence is to be rejected for the purpose of preparing bricks. • Digging: The clay is then dug out from the ground. It is spread out on the levelled ground, just a little deeper than the general level of ground. The height of heaps of clay is about 600mm to 1200mm. • Cleaning: The clay as obtained in the process of digging should be cleaned of stones, pebbles, vegetative matter etc. If these particles are in excess, the clay is to be washed and screened. Such a process naturally will prove to be troublesome and expensive. The lumps of clay should be converted into powder form in the earth crushing roller.
- 12. Preparation of clay Weathering: The clay is made loose and any ingredient to be added to it, is spread out at its top. • The blending indicates intimate or harmonious mixing. • It is carried out by taking small portion of clay every time and turning the mixture up and down in the vertical direction. • The blending makes clay fit for the next stage of tempering. Tempering: In the process of tempering, the clay is brought to a proper degree of hardness and it is made fit for the next operation of moulding. • The water in required quantity is added to clay and the whole mass is kneaded or pressed under the feet of men or cattle. • The tempering should be done exhaustively to obtain homogeneous mass of clay of uniform character.
- 13. Moulding Hand Moulding: In case of hand moulding, the bricks are moulded by hand i.e., manually. • The moulds are rectangular boxes which are opened at both top and bottom. They may be of wood or steel. • A typical wooden mould is shown in Fig. it should be prepared from well seasoned wood. • The longer sides are kept slightly projecting to serve as handles. • The strips of brass or steel are sometimes fixed on the edges of wooden moulds to make them more durable.
- 14. Moulding • A typical steel mould is shown in Fig. It is prepared from the combination of steel plates and channels. • It may even be prepared from steel angles and plates. The thickness of steel mould is generally 6 mm. They are used for manufacturing bricks on large scale. The steel moulds are more durable than wooden moulds and they turn out bricks of uniform size. • The bricks shrink during drying and burning. Hence the moulds are made larger than size of fully burnt bricks. The moulds are therefore made longer by about 8 to 12 percent in all directions.
- 15. The bricks prepared by hand moulding are of two types Ground-moulded bricks - • The ground is first made level and fine sand is sprinkled over it. • The mould is dipped in water and placed over the ground. • The lump of tempered clay is taken and it is dashed into the mould. • The clay is pressed or forced in the mould in such a way that it fills all the corners of mould. • The extra or surplus clay is removed either by wooden strike or metal strike or frame with wire. • A strike is a piece of wood or metal with sharp edge. It is to be dipped in water every time. • The mould is then lifted up and the raw bricks are left on the ground. • The mould is dipped in water and it is placed just near the previous brick to prepare another brick.
- 16. • The process is repeated till the ground is covered with raw bricks. • A brick moulder can mould 750 bricks per day with working period of 8hrs. • When such bricks become sufficiently dry, they are carried and placed in the drying sheds. • The bricks prepared by dipping the mould in water every time are known as the slopmoulded bricks. • The fine sand or ash may be sprinkled on the inside surface of mould instead of dipping it water. Such bricks are known as sand-moulded bricks and they have sharp and straight edges.
- 17. Table moulded bricks Table moulded bricks: The process of moulding these bricks is just similar as above. But in this case, the moulder stands near a table of size about 2m × 1m. the clay, mould, water pots, stock board, strikes and pallet boards are placed on this table. • The bricks are moulded on the table and sent for the further process of drying. • However the efficiency of moulder decreases gradually because of standing at same place for long duration. • The cost of brick moulding also increases when table moulding is adopted.
- 18. Machine moulding • The moulding may also be achieved by machine. • It proves to be economical when bricks in huge quantity are to be manufactured at the same spot in a short time. • It is also helpful for moulding hard and strong clay. These machines are broadly classified into two categories: a) Plastic clay machines: Such machines contain a rectangular opening of size equal to length and width of a brick. • The pugged clay is placed in the machine and as it comes out through the opening, it is cut into strips by wires fixed in frames. • The arrangement is made in such a way that strips of thickness equal to that of the brick are obtained. As the bricks are cut by wire, they are called wire cut bricks.
- 19. Dry clay machines • In these machines, the strong clay is first converted into powder form. • A small quantity of water is then added to form a stiff paste. • Such paste is placed in mould and pressed by machine to form a hard and well shaped bricks. • These bricks are known as the pressed bricks and they do not practically require drying. They can be sent directly to the process of burning. • The wire cut bricks and pressed bricks have regular shape, sharp edges and corners. • They have smooth external surfaces. They are heavier, stronger and exhibit uniform dense texture than ordinary hand-moulded bricks. • Drying: The damp brick, if burnt, are likely to be cracked and distorted. Hence the moulded bricks are dried before they are taken into next step of operation i.e., burning. • For drying, the bricks are arranged longitudinally in stacks (means racks) of width equal to two bricks. A stack may contain 8 to 10 tires. • The bricks are arranged along and across the stacks in alternate layers. All bricks are placed on edge. The bricks are allowed to dry till they become hard with moisture content of about 2% or so.
- 20. Dry clay machines a. Artificial burning: The bricks are generally dried by natural process. But when bricks are to be rapidly dried on a large scale, the artificial drying may be adopted. • In such case, the moulded bricks are allowed to pass through dryers which are in the form of tunnels or hot channels or floors. Such dryers are heated with the help of special furnaces or by the hot flue gases. The tunnel dryers are more economical compared to hot floor dryers. a. Circulation of air: The bricks in stacks should be arranged in such a way that sufficient air space is left between them for circulation of air. b. Drying yard: For the drying purpose, special drying yards should be prepared. It should be slightly on a higher level and it is desirable to cover it with sand. Such an arrangement would prevent the accumulation of rain water. c. Period for drying: The time required by moulded bricks to dry depends on prevailing weather conditions. Usually it takes about 3 to 10 days for bricks to become dry. d. Screens: It is to be seen that bricks are not directly exposed to the wind or sun for drying. Suitable screens, if necessary, may be provided to avoid such situations.
- 21. Dry clay machines (ii) Burning: This is a very important operation in the manufacturing process of bricks. It imparts hardness and strength to the bricks and makes them dense and durable. The bricks should be burnt properly. If bricks are over burnt, they will be brittle and hence break easily. 1. If they are under burnt, they will be soft and hence cannot carry loads. 2. The reactions between the mineral constituents of clay are achieved at higher temperature and these reactions are necessary to give new properties such as strength, hardness, less moisture absorption, etc. to the bricks. • When the temperature of about 11000C is reached, the particles of two important constituents of brick clay minerals namely, alumina and sand, binds themselves together resulting in the increase of strength and density of bricks. Further heating is not desirable and if the temperature is raised beyond 11000C, a great amount of fusible glassy mass is formed and the bricks are said to be vitrified. The bricks begin to lose their shape beyond a certain limit of vitrification.
- 22. Dry clay machines • The burning of bricks is done either in clamps or in kilns. The clamps are temporary structures and they are adopted to manufacture bricks in small quantity to serve a local demand or a specific purpose. The kilns are permanent structures and they are adopted to manufacture bricks on a large scale.
- 23. Qualities of good brick 1. The bricks should be table-moulded, well-burnt in kilns, copper-colored, free from cracks and with sharp and square edges. The color should be uniform and bright. 2. The bricks should be uniform in shape and should be of standard size. 3. The bricks should give a clear metallic ringing sound when stuck with each other. 4. The bricks when broken or fractured should show a bright homogenous and uniform compact structure free from voids. 5. The bricks should not absorb water more than 20 percent by weight for I class brick and 22 percent by weight for II class brick when soaked in water for 24hrs. 6. The bricks should be sufficiently hard. No impression should be left on brick surface, when it is scratched with finger nail. 7. The bricks should not break into pieces when it is dropped on hard ground from a height of 1 meter. 8. The bricks should have low thermal conductivity and they should be sound- proof. 9. The bricks when soaked in water for 24hrs should not show deposits of white salts when allowed to dry in shade. 10. No brick should have the crushing strength less than 3.5 N/mm2.
- 24. Tests on Bricks (1) Absorption: A brick is taken and it is weighed dry. It is then immersed in water for a period of 16 h. It is weighed again and the difference in weight indicates the amount of water absorbed by brick. It should not in any case exceed 20% of weight of dry brick. (2) Crushing strength: The crushing strength of a brick is found out by placing it in a compression testing machine. It is pressed till it breaks. As per the code IS: 1077-1970, the minimum crushing strength should not be less than 3.5 N/mm2. The brick with crushing strength of about 7 to 14 N/mm2 are graded as A and those having greater than 14N/mm2 are graded as AA. (3) Hardness: In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, the brick is treated to be sufficiently hard.
- 25. Tests on Bricks (4) Presence of soluble salts: the soluble salts, if present in bricks, will cause efflorescence on the surface of bricks. • For finding out the presence of soluble salts in a brick, it is immerse in water for 24hrs. • It is then taken out and allowed to dry in shade. The absence of grey or white deposits on its surface indicates the absence of soluble salts. • If the white deposits cover about 10% surface, the efflorescence is said to be slight and it is considered as moderate, when the white deposits cover about 50% of surface. • If grey or white deposits are found on more than 50% of surface, the efflorescence becomes heavy and it is treated as serious.
- 26. Tests on Bricks 5) Shape and size: In this test, a brick is closely inspected. It should be of standard size and its shape should be truly rectangular with sharp edges. For this purpose, 20 bricks (19cm X 9cm X 9cm) are selected at random and they are stacked lengthwise, along the width and along the height. For good quality bricks, the results should be within the following permissible limits. • Length: 3680mm to 3920mm • Breadth: 1740mm to 1860mm • Height: 1740mm to 1860mm (6) Soundness: In this test, the two bricks are taken and they are struck/hit with each other. The bricks should not break and a clear ringing sound should be produced. (7) Structure: A brick is broken and its structure is examined. It should be homogeneous, compact and free from any defects such as holes, lumps etc.
- 27. Classification of bricks • Burnt bricks • Un-burnt bricks • 1. The un-burnt or sun-dried bricks are dried with the help of heat received from sun after the process of moulding. These bricks can only be used in the construction of temporary and cheap structures. Such bricks should not be used at places where they are exposed to heavy rains. • 2. The bricks used in construction field are burnt bricks and they are classified into following four categories:
- 28. I Class Bricks: • These bricks are table-moulded and of standard shape and they are burnt in kilns. • The surface and edges of the bricks are sharp, square, smooth and straight. • They satisfy all the qualities of good bricks which are mentioned earlier. • These bricks are used for superior work of permanent nature.
- 29. II Class Bricks: • These bricks are ground-moulded and they are burnt in kilns. • The surface of these bricks is somewhat rough and shape is also straightly irregular. • These bricks may have hair-cracks and their edges may not be sharp and uniform. • These bricks are commonly used at places where brick work is to be provided with a coat of plaster.
- 30. III Class Bricks: • These bricks are ground-moulded and they are burnt in clamps. • These bricks are not hard and they have rough surfaces with irregular and distorted edges. • These bricks give dull sound when strucked with each other. • They are used for unimportant and temporary structures and at places where rainfall is not heavy.
- 31. IV Class Bricks: • These are over-burnt bricks with irregular shape and dark colored. • These bricks are used as aggregate for concrete in foundations, floors, roads etc. • Because of the fact that the over-burnt bricks have a compact structure and they are seems to be stronger than I Class bricks.