Lecture notes Construction Materials

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Construction Materials LECTURER DEPARTMENT OF CIVIL ENGINEERINGTable of Contents Chapter No Title Page No 1 Stones – Bricks – Concrete Blocks 1.1 Characteristics Of Good Building Stone 1 1.2 Testing of Stones 2 1.3 Deterioration Of Stones 8 1.4 Durability of Stones 9 1.5 Preservation of Stones 9 10 1.6 Selection of Stones 1.7 Bricks 10 1.8 Classification of bricks 11 1.9 Manufacturing Of Bricks 13 1.10 Testing of Bricks 19 1.11Fire-Clay Bricks Or Refractory Bricks 22 Lime– Cement– Aggregates – Mortar 2 2.1 Lime Mortar 24 2.2 Composition Of Cement Clinker 25 28 2.3 Hydration Of Cement 29 2.4 Rate Of Hydration 2.5 Manufacture Of Cement 29 2.6 Testing of Cement 32 2.7 Types Of Cement 45 2.8 Testing Of Aggregates 50 3 Concrete 3.1 Concrete 59 3.2 Ingredients 59 3.3 Manufacturing Process 59 3.4 Ready Mixed Concrete ( R MC) 66 3.5 Properties of Fresh Concrete: 68 3.6 Properties Of Hardened Concrete 693.7 Mix Design 70 3.8 High Strength Concrete 71 3.9 High Performance Concrete 71 3.10 Self Compacting Concrete 72 3.11 Durability of Concrete 72 4 Timber And Other Materials 4.1 Timber 75 4.2 Market Forms of Timber 75 4.3 Plywood 75 4.3.1 Types 75 4.3.2 Grades 76 4.3.3 Applications 76 4.4 Veneer 79 80 4.4.1 Types of Veneer 4.4.2 Advantages of using veneers 80 4.5 Thermocol 81 4.6 Panels of Laminates 81 4.6.1 Types 81 4.6.2 Sizes 81 4.6.3 Applications 81 82 4.7 Steel 82 4.7.1 Manufacturing Methods 4.7.2 Properties and Uses 83 4.7.3 Properties of Steel 83 4.8 Aluminum 87 4.8.1 Applications 90 4.8.2 Other names 91 4.8.3 The selective use of ACP 91 4.9 Composition 924.10 Characteristics Of An Ideal Pain 96 4.10.1 Preparation Of Paint 96 5 Modern Materials 5.1 Glass 98 5.1.1 Constituents 98 5.1.2 Manufacture 99 5.1.3 Classification 101 5.1.4 Commercial Forms 101 5.2 Ceramic 103 5.3 Fibre glass reinforced plastic 103 5.4 Clay products 104 5.4.1 Clay And Its Classifications 104 5.4.2 Physical Properties Of Clays 105 5.5 Fire-Clay Or Refractory Clay 106 5.6 Composite materials 107 5.7 Applications of laminar composites 109 5.8 Fibre textiles 109 5.9 Reinforced Earth 109CE 6401 Construction Materials CE6401 CONSTRUCTION MATERIALS L T P C 3 0 0 3 OBJECTIVES:  To introduce students to various materials commonly used in civil engineering construction and their properties. UNIT I STONES – BRICKS – CONCRETE BLOCKS 9 Stone as building material – Criteria for selection – Tests on stones – Deterioration and Preservation of stone work – Bricks – Classification – Manufacturing of clay bricks – Tests on bricks – Compressive Strength – Water Absorption – Efflorescence – Bricks for special use –Refractory bricks– Cement, Concrete blocks– Light weight concrete blocks. UNIT II LIME– CEMENT – AGGREGATES – MORTAR 9 Lime – Preparation of lime mortar – Cement – Ingredients – Manufacturing process – Types and Grades– Properties of cement and Cement mortar– Hydration– Compressive strength– Tensile strength– Fineness– Soundness and consistency– Setting time– Industrial byproducts– Fly ash–Aggregates – Natural stone aggregates – Crushing strength – Impact strength – Flakiness Index– Elongation Index– Abrasion Resistance– Grading– Sand Bulking. UNIT III CONCRETE 9 Concrete – Ingredients – Manufacturing Process – Batching plants – RMC – Properties of fresh concrete – Slump – Flow and compaction Factor – Properties of hardened concrete –Compressive, Tensile and shear strength – Modulus of rupture – Tests – Mix specification– Mix proportioning – BIS method – High Strength Concrete and HPC – Self compacting Concrete–Other types of Concrete– Durability of Concrete. UNIT IV TIMBER AND OTHER MATERIALS 9 Timber– Market forms– Industrial timber– Plywood– Veneer– Thermacole– Panels of laminates–Steel – Aluminum and Other Metallic Materials – Composition – Aluminium composite panel –Uses– Market forms– Mechanical treatment– Paints– Varnishes– Distempers– Bitumens. UNIT V MODERN MATERIALS 9 Glass – Ceramics – Sealants for joints – Fibre glass reinforced plastic – Clay products –Refractories – Composite materials – Types – Applications of laminar composites – Fibre textiles – Geomembranes and Geotextiles for earth reinforcement. TOTAL: 45 PERIODS OUTCOMES: On completion of this course the students will be able to  compare the properties of most common and advanced building materials.  understand the typical and potential applications of these materials  understand the relationship between material properties and structural form  understand the importance of experimental verification of material properties. TEXT BOOKS: 1. Varghese.P.C, "Building Materials", PHI Learning Pvt. Ltd, New Delhi, 2012. 2. Rajput. R.K., "Engineering Materials", S. Chand and Company Ltd., 2008. 3. Shetty.M.S., "Concrete Technology ( T heory and Practice) ", S. Chand and Company Ltd.,2008. rd 4. Gambhir.M.L., "Concrete Technology", 3 Edition, Tata McGraw Hill Education, 2004 th 5. Duggal.S.K., "Building Materials", 4 Edition, New Age International , 2008. SCE Dept of CivilCE 6401 Construction Materials REFERENCES: 1. Jagadish.K.S, "Alternative Building Materials Technology", New Age International, 2007. 2. Gambhir. M.L., & Neha Jamwal., "Building Materials, products, properties and systems", Tata McGraw Hill Educations Pvt. Ltd, New Delhi, 2012. 3. IS456– 2000: Indian Standard specification for plain and reinforced concrete, 2011 4. IS4926–2003 : Indian Standard specification for ready–mixed concrete, 2012 5. IS383–1970: Indian Standard specification for coarse and fine aggregate from natural Sources for concrete, 2011 6. IS1542–1992: Indian standard specification for sand for plaster, 2009 SCE Dept of CivilCE 6401 Construction Materials Chapter 1 Stones – Bricks – Concrete Blocks Stone as building material – Criteria for selection – Tests on stones – Deterioration and Preservation of stone work – Bricks – Classification – Manufacturing of clay bricks – Tests on bricks – Compressive Strength – Water Absorption – Efflorescence – Bricks for special use –Refractory bricks – Cement, Concrete blocks – Light weight concrete blocks. 1.1 Characteristics Of Good Building Stone A good building stone should have the following qualities. Appearance: For face work it should have fine, compact texture; light-coloured stone is preferred as dark colours are likely to fade out in due course of time. Structure: A broken stone should not be dull in appearance and should have uniform texture free from cavities, cracks, and patches of loose or soft material. Stratifications should not be visible to naked eye. Strength: A stone should be strong and durable to withstand the disintegrating action of weather. 2 Compressive strength of building stones in practice range between 60 to 200 N/mm . Weight: It is an indication of the porosity and density. For stability of structures such as dams. retaining walls, etc. heavier stones are reauired, whereas for arches, vaults, domes, etc. light stones may be the choice. Hardness: This property is important for floors, pavements, aprons of bridges, etc. The hardness is determined by the Mohs scale Toughness: The measure of impact that a stone can withstand is defined as toughness. The stone used should be tough when vibratory or moving loads are anticipated. Porosity and Absorption: Porosity depends on the mineral constituents, cooling time and structural formation. A porous stone disintegrates as the absorbed rain water freezes, expands, and causes cracking. Permissible water absorption for some of the stones is given in Table 1 Table 1 24-Hours Water Absorption of Stones by Volume Water absorption (% S.No. Types of Stone not greater than) 1. Sandstone 10 2. Limestone 10 3. Granite 1 4. Trap 6 5. Shale 10 6. Gneiss 1 7. Slate 1 8. Quartzite 3 Seasoning: The stone should be well seasoned. Weathering: The resistance of stone against the wear and tear due to natural agencies should be high. Workability: Stone should be workable so that cutting, dressing and bringing it out in the required shape and size may not be uneconomical. Fire Resistance: Stones should be free from calcium corbonate, oxides of iron, and minerals having different coefficients of thermal expansion. Igneous rock show marked disintegration principally because of quartz which disintegrates into small particles at a temperature of about 575°C. Limestone, however, can withstand a little higher temperature; i.e. up to 800°C after which they disintegrate. Specific Gravity: The specific gravity of most of the stones lies between 2.3 to 2.5. Thermal Movement: Thermal movements alone are usually not trouble-some. However, joints in SCE 1 Dept of CivilCE 6401 Construction Materials coping and parapets open-out inletting the rain water causing trouble. Marble slabs show a distinct distortion when subjected to heat. An exposure of one side of marble slab to heat may cause that side to expand and the slab warps. On cooling, the slab does not go back to its original shape. 1.2 Testing Of Stones Building stones are available in large quantity in various parts of the country and to choose and utilize them for their satisfactory performance, it is necessary to test the stone for its strength properties, durability and quality. Durability Test: Some of the tests to check the durability of stone are as follows. Of these tests, the crystallization test is prescribed by Bureau of Indian Standards. The durability ( soundne ss) test is performed to find out the capacity of stone to resist disintegration and decomposition. Smith Test: Break off the freshly quarried stone chippings to about the size of a rupee coin and put them in a glass of clean water, one-third full. If the water becomes slightly cloudy, the stone is good and durable. If water becomes dirty, it indicates that the stone contains too much of earthy and mineral matter. Brard’s Test — for frost resistance — Few small pieces of freshly quarried stone are immersed in boiling solution of sulphate of soda (G lauber’s salt) and are weighed. These are then removed and kept suspended for few days and weighed again. The loss in weight indicates the probable effect of frost. Acid Test — to check weather resistance — confirms the power of stones to withstand the atmospheric conditions. 100 g of stone chips are kept in a 5 per cent solution of H SO or HCI for 3 days. Then the 2 4 chips are taken out and dried. The sharp and firm corners and edges are indication of sound stone. This test is used to test the cementing material of sand stone. Crystallization Test ( IS 1126): Three test pieces of 50 mm diameter and 50 mm height are dried for 24 hours and are weighed (W ). The specimens are suspended in 14 per cent sodium sulphate solution 1 3 ( de nsity 1.055 kg/m ) for 16 to 18 hours at room temperature (20° to 30°C) . The specimens are then taken out of the solution and kept in air for 4 hours. They are then oven dried at a temperature of 105° ± 5°C for 24 hours and then cooled at room temperature. This process is repeated for 30 cycles. The specimens are weighed ( W ) and the difference in weight is found. This test is repeated thirty times and 2 the loss in weight after every five cycles is obtained. The change in weight indicates the degree of decay of stone. Durability should be expressed in percentage as change in the weight. The average of three test results should be reported as durability value. Change in weight = W 2 W 1 where W is the original weight of the specimen and W is the weight of the specimen after 30 cycles of 1 2 the test. Crushing Test Compressive Strength Test ( IS : 1121 (P art I)) Samples of stone weighing at least 25 kg each of the unweathered spcimen should be obtained from quarry. To test stone for compressive strength, specimen pieces in the form of cubes or cylinders are made from samples of rock. The lateral dimension or diameter of test piece should not be less than 50 mm and the ratio of height to diameter or lateral dimension should be 1:1. A minimum of three specimen pieces are tested in each saturated and dry conditions. Separate tests should be made for the specimen when the load to parallel to the rift and perpendicular to the rift. In all twelve test pieces should be used. The specimen pieces of diameter or lateral dimension 50 mm are immersed in water at 20 to 30°C for 72 hours and are tested in saturated condition. The specimen pieces are also tested in dry condition by drying them in an oven at 105 ± 5°C for 24 hours and then cooled in a desiccator to 20–30°C. These are 2 tested in universal testing machine. The load is applied gently at a rate of 14 N/mm per minute until the resistance of the specimen piece to the increasing load breaks down and no greater load is sustained. SCE 2 Dept of CivilCE 6401 Construction Materials The compressive strength of the specimen piece is the maximum load in Newtons supported by it 2 before failure occurs divided by the area of the bearing face of the specimen in mm . The average of the three results in each condition separately should be taken for the purpose of reporting the compressive strength of the sample. When the ratio of height to diameter or lateral dimension differs from unity by 25 per cent or more, the compressive strength is calculated by the following expression. C p C = c È b Ø 0.778 0.222 É Ù Ê h Ú where C = compressive strength of standard specimen piece c C = compressive strength of the specimen having a height greater than the diameter p or lateral dimension b = diameter or lateral dimension h = height 2 The crushing strength of stones varies in the range of 15–100 N/mm . Transverse Strength Test ( IS : 1121 (Part II)) : To test stone for transverse strength, specimen pieces are made in the form of blocks 200 × 50 × 50 mm. These are tested in saturated and dry conditions similar to as explained in the compressive strength test. Test apparatus used for testing is shown in Fig. 1. Each specimen piece is supported upon two self-aligning bearers Fig. 1 Arrangement for Transverse Strength Test of Stones A and B, 40 mm in diameter, the distance between centres of bearers being 150 mm. Bearer A is supported horizontally on two bearer screws C, which carry hardened steel balls D. Bearer B is supported on one such bearer screw and ball. The load is then applied centrally on the specimen piece at a uniform rate of 2 kN/min through a third bearer E, also 40 mm in diameter, placed midway between the supports upon the upper surface of the specimen S and parallel to the supports. The average of the three results ( se parately for saturated and dry condition) should be taken for the purpose of determining transverse strength of sample. Any specimen giving result as much as 15 per cent below the average value should be examined for defects. SCE 3 Dept of CivilCE 6401 Construction Materials The transverse strength of the specimen is given by 3WL 3 R = 2bd 2 where R = transverse strength in N/mm W = central breaking load in N L = length of span in mm b = average width in mm of the test piece at the mid section d = average depth in mm of the test piece at the mid section Tensile Strength Test (IS : 1121 (P art III)) Three cylindrical test pieces of diameter not less than 50 mm and the ratio of diameter to height 1:2 are used to determine the tensile strength of the stone in each saturated ( ke pt in water for 3 days at 20 to 30°C) and dry condition (dr ied in an oven at 105 ± 5°C for 24 hours and cooled at room temperature) . The general arrangement for testing tensile strength of stone is shown in Fig. 3.11. Each test piece to be tested is sandwiched in between two steel plates of width 25 mm, thickness 10 mm and length equal to the length of test piece. The load is applied without shock and increased continuously at a uniform rate until the specimen splits and no greater load is sustained. The maximum load applied to the specimen is recorded. Fig. 2 General Arrangement for Testing Tensile Strength of Building Stone 2W Split tensile strength, S = S dL where 2 S = split tensile strength (N /mm ) W = applied load (N ) d = diameter of specimen (m m), a nd L = length of specimen ( mm) The average of three results separately for each condition should be reported as split tensile strength of the sample. In case any test piece gives a value of as much as 15 per cent below the average, it should be examined for defects and if found defective the test piece should be rejected. SCE 4 Dept of CivilCE 6401 Construction Materials Shear Strength Test (IS : 1121 (Part IV) ) The test is carried out either in Jhonson shear tool ( F ig. 3) or Dutton punching shear device (Fig. 4) . Three test pieces are used for conducting the test in each of the saturated and dry condition. Test piece for use in Jhonson shear tool should be bars 50 × 50 mm in section and not less than 100 mm in length and that for use with the Dutton punching shear device should be slabs 30 mm in thickness, 100 mm in width and not less than 100 mm in length. Fig. 3 Detail of Modified Johnson Shear Tool (a ) D etails of Parts ( b ) A ssembled view Fig. 4 Details of Dutton Punching Shear Device SCE 5 Dept of CivilCE 6401 Construction Materials Using Jhonson Shear Tool The test piece is carefully centred in the shear tool and the bolts drawn up tightly. The tool is then centred in the testing machine with the centre of the spherical block in contact with the centre of the top portion of the plunger of the shear tool. The speed of the moving head of the testing machine during load application should not be more than 1 mm/min. During the test, the beam of the testing machine should be kept constantly in floating position. The shear strength of test piece is calculated by W S = 2A where 2 S = Shear strength (N/ mm ) W = total maximum load (N ) 2 A = area of the centre cross-section of test piece (mm ) The average of all the three results separately for each condition is calculated and taken as the shear strength of the test piece. Using Dutton Punching Shear Device Centre lines are laid over one surface of the slab. Thickness of the slab is measured at three points approximately equidistant around the circumference of a 50 mm circle centred on the intersection of the two center lines. The test piece is centred in the punching device keeping it under the plunger. The punching device is then centred in the testing machine with the centre of the spherical bearing block in contact with the centre of the top portion of the plunger of the shear device. The speed of the moving head of the testing machine during load application should not be more than 1 mm/min. During the test, the beam of the testing machine should be kept constantly in floating position. The shear strength of the test piece is calculated by W W t i S = S DT where 2 S = Shear strength (N/ mm ) W = total maximum load (N ) t W = initial load (N ) r equired to bring the plunger in contact with the surface of specimen i D = diameter (m m) of the plunger T= thickness (m m) of the specimen The average of all the three results separately for each condition is calculated and taken as shear strength of the test piece. Absorption Test (I S: 1124) The selected test pieces of stone are crushed or broken and the material passing 20 mm IS Sieve and retained on 10 mm IS Sieve is used for the test. The test piece weighing about 1 kg is washed to remove particles of dust and immersed in distilled water in a glass vessel at room temperature 20 to 30° C for 24 hours. Soon after immersion and again at the end of SCE 6 Dept of CivilCE 6401 Construction Materials soaking period, entrapped air is removed by gentle agitation achieved by rapid clock-wise and anti-clock-wise rotation of the vessel. The vessel is then emptied and the test piece allowed to drain.The test piece is then placed on a dry cloth and gently surface dried with the cloth. It is transferred to a second dry cloth when the first one removes no further moisture. The test piece is spread out not more than one stone deep on the second cloth and left exposed to atmosphere away from direct sunlight or any other source of heat for not less than 10 minutes untill it appears to be completely surface dry. The sample is then weighed (B) . The sample is then carefully introduced in a 1000 ml capacity measuring cylinder and distilled water is poured by means of 100 ml capacity measuring cylinder while taking care to remove entrapped air, untill the level of water in the larger cylinder reaches 1000 ml mark. The quantity of water thus added is recorded in ml or expressed in gram weight (C ). The water in the larger cylinder is drained and the sample is carefully taken out and dried in an oven at 100 to 110°C for not less than 24 hours. It is then cooled in a desiccators to room temperature and weighed (A ). T he room temperature during the test is recorded. A Apparent specific gravity = 1000 C B A Water absorption = – 100 A B A Apparent Porosity = – 100 1000 C The true porosity shall be calculated from the following formula: True Porosity = True specific gravity – Apparent specific gravity True Specific gravity Where A = Weight of oven-dry test piece (g) B = Weight of saturated surface-dry test piece (g) C = Quantity of water added in 1000 ml jar containing the test piece (g) Hardness: This test is performed by scratching a stone with knife on Mohs scale. Toughness: This test is performed by breaking the stone with a hammer. Toughness is indicated by resistance to hammering. SCE 7 Dept of CivilCE 6401 Construction Materials 1.3 Deterioration Of Stones The various natural agents such as rain, heat, etc. and chemicals deteriorate the stones with time. Rain Rain water acts both physically and chemically on stones. The physical action is due to the erosive and transportation powers and the latter due to the decomposition, oxidation and hydration of the minerals present in the stones. Physical Action: Alternate wetting by rain and drying by sun causes internal stresses in the stones and consequent disintegration. Chemical Action: In industrial areas the acidic rain water reacts with the constituents of stones leading to its deterioration. Decomposition: The disintegration of alkaline silicate of alumina in stones is mainly because of the action of chemically active water. The hydrated silicate and the carbonate forms of the alkaline materials are very soluble in water and are removed in solution leaving behind a hydrated silicate of alumina ( K aolinite) . T he decomposition of felspar is represented as K Al O .6H O + CO + nH O = K CO + Al O .2SiO .2H O + 4SiO .nH O 2 2 3 2 2 2 2 3 2 3 2 2 2 2 (O rthoclase) ( A lkaline carbonate) (K aolinite) (H ydrated silicate) Oxidation and Hydration: Rock containing iron compounds in the forms of peroxide, sulphide and carbonate are oxidised and hydrated when acted upon by aciduated rain water. As an example the peroxide—FeO is converted into ferric oxide—Fe O which combines with water to form FeO.nH O. 2 3 2 This chemical change is accompanied by an increase in volume and results in a physical change manifested by the liberation of the neighbouring minerals composing the rocks. As another example iron sulphide and siderite readily oxidize to limonite and liberates sulphur, which combines with water and oxygen to form sulphuric acid and finally to sulphates. Frost In cold places frost pierces the pores of the stones where it freezes, expands and creates cracks. Wind Since wind carries dust particles, the abrasion caused by these deteriorates the stones. Temperature Changes Expansion and contraction due to frequent temperature changes cause stone to deteriorate especially if a rock is composed of several minerals with different coefficients of linear expansion. Vegetable Growth Roots of trees and weeds that grow in the masonry joints keep the stones damp and also secrete organic and acidic matters which cause the stones to deteriorate. Dust particles of organic or nonorganic origin may also settle on the surface and penetrate into the pores of stones. When these come in contact with moisture or rain water, bacteriological process starts and the resultant micro-organism producing acids attack stones which cause decay. Mutual Decay When different types of stones are used together mutual decay takes place. For example when sandstone is used under limestone, the chemicals brought down from limestone by rain water to the sandstone will deteriorate it. Chemical Agents Smokes, fumes, acids and acid fumes present in the atmosphere deteriorate the stones. Stones containing CaCO , MgCO are affected badly. 3 3 Lichens These destroy limestone but act as protective coats for other stones. Molluses gradually weaken and ultimately destroy the stone by making a series of parallel vertical holes in limestones and sandstones. SCE 8 Dept of CivilCE 6401 Construction Materials 1.4 Durability Of Stones Quarrying and cutting have a great bearing on the weathering properties of stones. Stone from top ledges of limestone, granite, and slate and from the exposed faces of the rock bed is likely to be less hard and durable. Highly absorbent stone should not be quarried in freezing weather since the rock is likely to split. The method of blasting and cutting also influences the strength of the stone and its resistance to freezing and temperature changes. Small, uniformly distributed charge of blasting powder has a lesser weakening effect than large concentrations of explosives. A porous stone is less durable than a dense stone, since the former is less resistant to freezing. Also, rocks with tortuous pores and tubes are more apt to be injured by freezing than those of equal porosity having straight pores and tubes. Repeated hammering in cutting is likely to injure the stone. Polished stone is more enduring than rough surfaced work, since the rain slides off the former more easily. Stones from stratified rocks should be placed along the natural bed in order to secure maximum weathering resistance. Pyrite, magnetite and iron carbonate oxidize in weathering and cause discolouration of the stone in which they are present. Since oxidation is accompanied by a change in volume, the surrounding structure is weakened. 1.5 Preservation Of Stones Preservation of stone is essential to prevent its decay. Different types of stones require different treatments. But in general stones should be made dry with the help of blow lamp and then a coating of paraffin, linseed oil, light paint, etc. is applied over the surface. This makes a protective coating over the stone. However, this treatment is periodic and not permanent. When treatment is done with the linseed oil, it is boiled and applied in three coats over the stone. Thereafter, a coat of dilute ammonia in warm water is applied. The structure to be preserved should be maintained by washing stones frequently with water and steam so that dirt and salts deposited are removed from time to time. However, the best way is to apply preservatives. Stones are washed with thin solution of silicate of soda or potash. Then, on drying a solution of CaCl is applied over it. These two solutions called Szerelmy’s liquid, combine to form 2 silicate of lime which fills the pores in stones. The common salt formed in this process is washed afterwards. The silicate of lime forms an insoluble film which helps to protect the stones. Sometimes lead paint is also used to preserve the stones, but the natural colour of the stone is spoilt. Painting stone with coal tar also helps in the preservation but it spoils the beauty of the stone. Use of chemicals should be avoided as far as possible, especially the caustic alkalis. Although cleaning is easy with chemicals, there is the risk of introducing salts which may subsequently cause damage to the stone. In industrial towns, stones are preserved by application of solution of baryta, Ba( O H) — Barium 2 hydrate. The sulphur dioxide present in acid reacts on the calcium contents of stones to form calcium sulphate. Soot and dust present in the atmosphere adhere to the calcium sulphate and form a hard skin. In due course of time, the calcium sulphate so formed flakes off and exposes fresh stone surface for further attack. This is known as sulphate attack. Baryta reacts with calcium sulphate deposited on the stones and forms insoluble barium sulphate and calcium hydroxide. The calcium hydroxide absorbs carbon dioxide from the air to form calcium carbonate. Ba (OH) + CaSO ¾¾¾® BaSO + Ca(O H) 2 4 4 2 (B arium sulphate)( C alcium hydroxide) Ca( O H) + CO ¾¾¾® CaCO + H O 2 2 3 2 (Calcium carbonate) The question whether or not stone preservatives should be used on old and decayed stone is a difficult one. Real evidence of the value of various treatments is most difficult to assess. The treatments, if carefully applied under favourable circumstances, may result in an apparent slowing down of the rate of decay. However, the rate of decay of stone is so slow that a short period experience is of very little value in establishing the effectiveness of the treatment. Also, there is some evidence that treatments which appear to be successful for few years, fail to maintain the improvement. In fact, the value of preservatives is not yet proved, and they may actually be detrimental if judged over a long period. SCE 9 Dept of CivilCE 6401 Construction Materials 1.6 Selection Of Stones The conditions which govern the selection of stone for structural purposes are cost, fashion, ornamental value and durability, although the latter property is frequently overlooked or disregarded. Cost is largely influenced by transportation charges, difficulties in quarrying and cutting, the ornamental features, and the durability of stone. The type of dressing of stone may make a difference to the cost, particularly with the stones derived from igneous rocks. When the cost of quarried stone to cost of finished stone is considered, it will be found that the labour cost is far greater than the price of the stone. Thus, a difference in the price between two alternative stones is unimportant and it would be unwise to reject a more durable stone on the grounds that it was costly. Another factor which should be considered is the suitability of the stone for the type of design, for example, for a highly carved design if, by mistake, a harder stone such as granite is selected the cost will be affected. Colour, arrangement and shape of mineral constituents greatly influence fashion and ornamental value. One of the first factors influencing the selection of stone for a particular work will be colour. It is important that the designer is aware about how the colour is likely to change after long exposure and in particular how it may vary in polluted atmospheres. As an example limestone, being slightly soluble in water, will remain clean in portions facing rain but retain a film of soot in sheltered areas. This results in strong colour contrast. Resistance to fire and weathering—factors which are largely influenced by the mineral constitution of the rock—are the most important determinators of durability. It is very important to select a stone according to its exposure conditions. Limestones when used in areas not exposed to rain but acted upon by sulphur gases of polluted atmosphere, form a hard and impermeable surface skin which subsequently blisters and flakes off. It must be noted that flaking of this kind occurs mainly on external work only, although the air inside the building is almost equally polluted, probably due to the damper conditions inside. Limestones, sandstones and granites all tend to crack and spall when exposed to fire, and there is really little to choose between them in this respect. 1.7 Bricks One of the oldest building material brick continues to be a most popular and leading construction material because of being cheap, durable and easy to handle and work with. Clay bricks are used for building-up exterior and interior walls, partitions, piers, footings and other load bearing structures. 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: Length of brick = 2 × width of brick + thickness of mortar Height of brick = width of brick Size of a standard brick ( a lso known as modular brick) should be 19 × 9 × 9 cm and 19 × 9 × 4 cm. When placed in masonry the 19 × 9 × 9 cm brick with mortar becomes 20 × 10 × 10 cm. However, the bricks available in most part of the country still are 9" × " × 3" and are known as field bricks. Weight of such a brick is 3.0 kg. An indent called frog, 1–2 cm deep, as shown in Fig. 5, is provided for 9 cm high bricks. The size of frog should be 10 × 4 × 1 cm. 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. SCE 10 Dept of CivilCE 6401 Construction Materials Fig. 5 Bricks with Frog 1.8 Classification Of Bricks On Field Practice Clay bricks are classified as first class, second class, third class and fourth class based on their physical and mechanical properties. First Class Bricks 1. These are thoroughly burnt and are of deep red, cherry or copper colour. 2. The surface should be smooth and rectangular, with parallel, sharp and straight edges and square corners. 3. These should be free from flaws, cracks and stones. 4. These should have uniform texture. 5. No impression should be left on the brick when a scratch is made by a finger nail. 6. The fractured surface of the brick should not show lumps of lime. 7. A metallic or ringing sound should come when two bricks are struck against each other. 9. Water absorption should be 12–15% of its dry weight when immersed in cold water for 24 2 hours. The crushing strength of the brick should not be less than 10 N/mm . This limit varies with different Government organizations around the country. Uses: 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. 2. A little higher water absorption of about 16–20% of its dry weight is allowed. 2 3. The crushing strength should not be less than 7.0 N/mm . Uses: Second class bricks are recommended for all important or unimportant hidden masonry works and centering of reinforced brick and reinforced cement concrete (R CC) st ructures. 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. Uses : It is used for building temporary structures. Fourth Class Bricks are overburnt and badly distorted in shape and size and are brittle in nature. Uses: The ballast of such bricks is used for foundation and floors in lime concrete and road metal. On Strength The Bureau of Indian Standards (B IS) has classified the bricks on the basis of compressive strength and is as given in Table 2 Table 2 Classification of Bricks based on Compressive Strength (IS : 1077) 2 Average compressive strength not less than (N/mm ) Class 35 35.0 30 30.0 25 25.0 SCE 11 Dept of CivilCE 6401 Construction Materials 20 20.0 17.5 17.5 15 15.0 12.5 12.5 10 10.0 7.5 7.5 5 5.0 3.5 3.5 2 Notes: 1. The burnt clay bricks having compressive strength more than 40.0 N/mm are known as heavy duty bricks and are used for heavy duty structures such as bridges, foundations for industrial buildings, multistory buildings, etc. The water absorption of these bricks is limited to 5 per cent. 2. 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. Subclass-A Subclass-B Dimension Tolerance Dimension Tolerance ( cm) (mm) ( cm) ( mm) Length 380 ± 12 380 ± 30 Width 180 ± 6 180 ± 15 Height ( i) 9 cm 180 ± 6 180 ± 15 (ii) 4 cm 80 ± 3 80 ± 6 On the Basis of Use Common Brick is a general multi-purpose unit manufactured economically without special reference to appearance. 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. Machine-made: 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. SCE 12 Dept of CivilCE 6401 Construction Materials 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. Perforated: Small holes may exceed 25 per cent of the total volume of the brick. Hollow: The total of holes, which need not be small, may exceed 25 per cent of the volume of the brick. Cellular: Holes closed at one end exceed 20 per cent of the volume. 2 Note: Small holes are less than 20 mm or less than 500 mm in cross section. 1.9 Manufacturing Of Bricks Additives in the Manufacture of Bricks Certain additives such as fly ash, sandy loam, rice husk ash, basalt stone dust, etc. are often required not only to modify the shaping, drying and firing behaviour of clay mass, but also to help conserve agricultural land and utilise waste materials available in large quantities. 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: Fly Ash: A waste 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. and shows a chemical composition similar to brick earths. 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. Sandy Loam: Addition of sandy loam is often found effective in controlling the drying behaviour of highly plastic soil mass containing expanding group of clay minerals. Sandy loam should preferably have a mechanical composition as specified below. The material should, however, meet the other requirement as well. Clay ( 2 micron) 8–10% Silt ( 2 –20 micron) 30–50% Sand ( 20 micron) 40–60% Rice Husk Ash: The ash should preferably have unburnt carbon content in the range of 3–5% and should be free from extraneous material. It can be used with plastic black red soils showing excessive shrinkage. Basalt Stone Dust: Basalt stone occurs underneath the black cotton soil and its dust is a waste product available in large quantity from basalt stone crushing units. The finer fraction from basalt stone units is mixed with soil mass to modify the shaping, drying and firing behaviour of bricks. The dust recommended for use as an additive with brick earth should be fine (pa ssing 1 mm sieve), free from coarse materials or mica flakes and should be of non-calcitic or dolomitic origin. The operations involved in the manufacture of clay bricks are represented diagrammatically in Fig. 5 SCE 13 Dept of CivilCE 6401 Construction Materials Fig. 5 Operations Involved in Manufacturing of Clay Bricks Preparation of Brick Earth It consists of the following operations. Unsoiling: The soil used for making building bricks should be processed so as to be free of gravel, coarse sand ( pr actical size more than 2 mm), lime and kankar particles, organic matter, etc. About 20 cm of the top layer of the earth, normally containing stones, pebbles, gravel, roots, etc., is removed after clearing the trees and vegetation. Digging: After removing the top layer of the earth, proportions of additives such as fly ash, sandy loam, rice husk ash, stone dust, etc. should be spread over the plane ground surface on volume basis. The soil mass is then manually excavated, puddled, watered and left over for weathering and subsequent processing. The digging operation should be done before rains. Weathering: Stones, gravels, pebbles, roots, etc. are removed from the dug earth and the soil is heaped on level ground in layers of 60–120 cm. The soil is left in heaps and exposed to weather for at least one month in cases where such weathering is considered necessary for the soil. This is done to develop homogeneity in the mass of soil, particularly if they are from different sources, and also to eliminate the impurities which get oxidized. Soluble salts in the clay would also be eroded by rain to some extent, which otherwise could have caused scumming at the time of burning of the bricks in the kiln. The soil should be turned over at least twice and it should be ensured that the entire soil is wet throughout the period of weathering. In order to keep it wet, water may be sprayed as often as necessary. The plasticity and strength of the clay are improved by exposing the clay to weather. Blending: The earth is then mixed with sandy-earth and calcareous-earth in suitable proportions to modify the composition of soil. Moderate amount of water is mixed so as to obtain the right consistency for moulding. The mass is then mixed uniformly with spades. Addition of water to the soil at the dumps is necessary for the easy mixing and workability, but the addition of water should be controlled in such a way that it may not create a problem in moulding and drying. Excessive moisture content may effect the size and shape of the finished brick SCE 14 Dept of Civil

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