Basic Civil Engineering (RGPV Syllabus) 2010 PDF

This page intentionally left blank S.S. BHAVIKATTI Emeritus Fellow (AICTE) BVB College of Engineering and Technology, Hubli (Formerly Principal, RYMEC, Bellary Professor & Dean SDMCET, Dharwad and NITK, Surathkal) Copyright © 2010, New Age International (P) Ltd., Publishers Published by New Age International (P) Ltd., Publishers All rights reserved. No part of this ebook may be reproduced in any form, by photostat, microfilm, xerography, or any other means, or incorporated into any information retrieval system, electronic or mechanical, without the written permission of the publisher. All inquiries should be emailed to [email protected] ISBN (13) : 978-81-224-2853-7 PUBLISHING FOR ONE WORLD NEW AGE INTERNATIONAL (P) LIMITED, PUBLISHERS 4835/24, Ansari Road, Daryaganj, New Delhi - 110002 Visit us at www.newagepublishers.com Preface All engineering students should know basic civil engineering since they need interaction with civil engineers in their routine works. Hence all important aspects of civil engineering are taught as elements of civil engineering in all over the world. It covers entire syllabus on Basic Civil Engineering. The author has tried to make it students friendly by providing neat sketches and illustrations with practical problems, wherever necessary. Author hopes that students and faculty will receive this book whole-heartedly. Corrections, if any and suggestions for improvement are welcome. S.S. BHAVIKATTI This page intentionally left blank Contents Preface v UNIT - I: CIVIL ENGINEERING MATERIALS 1–70 1 TRADITIONAL MATERIALS 3–32 1.1 Stones 3 1.2 Bricks 11 1.3 Lime 16 1.4 Cement 18 1.5 Timber 23 Questions 31 2 MORTARS 33–38 2.1 Sand 33 2.2 Cement Mortar 34 2.3 Lime Mortar 35 2.4 Mud Mortar 36 2.5 Special Mortar 37 2.6 Tests on Mortar 37 Questions 38 3 CONCRETE 39–54 3.1 Plain Concrete 39 3.2 Reinforced Cement Concrete (R.C.C.) 49 3.3 Reinforced Brick Concrete (RBC) 50 3.4 Prestressed Concrete (PSC) 50 3.5 Fibre-Reinforced Concrete (FRC) 51 CONTENTS 3.6 Cellular Concrete 52 3.7 Ferro-Cement 52 Questions 53 4 METALS AS BUILDING MATERIALS 55–58 4.1 Ferrous Metals 55 4.2 Aluminium 57 4.3. Copper 58 Questions 58 5 MISCELLANEOUS BUILDING MATERIALS 59–69 5.1 Glass 59 5.2 Plastics 60 5.3 Bitumen 62 5.4 Asbestos 62 5.5 Paints 63 5.6 Distempers 65 5.7 Varnishes 65 5.8 Solid and Hollow Concrete Blocks 66 5.9 Roofing and Flooring Tiles 67 Questions 68 UNIT - II: BUILDING CONSTRUCTION 71–136 6 BUILDING PLANNING 73–81 6.1 Elements of a Building 73 6.2 Basic Requirements of a Building 76 6.3 Planning 77 6.4 Planning Suitable Orientation 77 6.5 Planning for Energy Efficiency 78 6.6 Planning for Suitable Utility 78 6.7 Planning for Meeting Other Requirements 79 Questions 81 7 FOUNDATIONS 82–91 7.1 Dimensions of Foundation 82 7.2 Conventional Spread Footings 83 7.3 R.C.C. Footings 84 7.4 Grillage Footing 86 CONTENTS 7.5 Arch Foundation 87 7.6 Pile Foundations 87 7.7 Foundations in Black Cotton Soil 89 Questions 91 8 SUPER STRUCTURES 92–127 8.1 Types of Super Structures Based on the Method of Load Transfer 92 8.2 Walls 93 8.3 Stone Masonry 94 8.4 Brick Masonry 97 8.5 Plastering 100 8.6 Pointing 101 8.7 Flooring 101 8.8 Roof 105 8.9 Doors and Windows 113 8.10 Lintels 122 8.11 Stairs 123 Questions 126 9 DAMPNESS AND ITS PREVENTION 128–132 9.1 Causes of Dampness 128 9.2 Ill-Effects of Dampness 129 9.3 Requirements of an Ideal Material for Damp Proofing 129 9.4 Materials for Damp Proofing 130 9.5 Methods of Damp Proofing 130 Questions 132 10 COST EFFECTIVE CONSTRUCTION TECHNIQUES 133–135 IN MASS HOUSING SCHEMES 10.1 Minimum Standards 133 10.2 Approach to Cost Effective Mass Housing Schemes 134 10.3 Cost Effective Construction Techniques 135 Questions 135 UNIT - III: SURVEYING 137–236 11 INTRODUCTION TO SURVEYING 139–148 11.1 Object and Uses of Surveying 139 11.2 Primary Divisions in Surveying 140 CONTENTS 11.3 Fundamental Principles of Surveying 141 11.4 Classification of Surveying 142 11.5 Plans and Maps 143 11.6 Scales 144 11.7 Types of Graphical Scales 145 11.8 Units of Measurements 148 Questions 148 12 LINEAR MEASUREMENTS AND CHAIN SURVEYING 149–175 12.1 Methods of Linear Measurements 149 12.2 Instruments used in Chaining 154 12.3 Chain Surveying 156 12.4 Ranging 162 12.5 Obstacles in Chaining 163 12.6 Errors in Chaining 167 12.7 Tape Corrections 168 12.8 Conventional Symbols 173 Questions 175 13 COMPASS SURVEYING 176–194 13.1 Types of Compass 176 13.2 Method of Using a Compass 180 13.3 Bearing 180 13.4 Whole Circle Bearing and Reduced Bearing 180 13.5 Computation of Angles 182 13.6 Declination and DIP 184 13.7 Local Attraction 187 13.8 Chain and Compass Surveying Field Work 190 Questions 193 14 PLANE TABLE SURVEYING 195–208 14.1 Plane Table and its Accessories 195 14.2 Working Operations 198 14.3 Methods of Plane Tabling 199 14.4 Errors in Plane Table Surveying 206 14.5 Advantages and Limitations of Plane Table Survey 207 Questions 207 CONTENTS 15 LEVEL AND LEVELLING 209–225 15.1 Object and Uses of Levelling 209 15.2 Terms Used in Levelling 209 15.3 Levelling Instruments 211 15.4 Levelling Staff 213 15.5 Methods of Levelling 214 15.6 Terms Used in Direct Method of Levelling 215 15.7 Temporary Adjustments of a Level 216 15.8 Types of Direct Levelling 217 Questions 225 16 MODERN TOOLS OF SURVEYING 226–236 16.1 Theodolite 226 16.2 Electromagnetic Distance Measuring Instruments 231 16.3 Total Station 233 16.4 Global Positioning System 235 Questions 236 UNIT - IV: MAPPING AND SENSING 237–268 17 MAPPING AND CONTOURING 239–246 17.1 Mapping 239 17.2 Contours 241 17.3 Methods of Contouring 243 Drawing Contours 246 Questions 246 18 AREAS AND VOLUMES 247–265 18.1 Computation of Areas from Field Notes 247 18.2 Computing Areas from Maps 252 18.3 Computation of Volumes 256 Questions 264 19 REMOTE SENSING AND ITS APPLICATIONS 266–268 19.1 Remote sensing 266 19.2 Geographical Information System (GIS) 267 Questions 268 CONTENTS UNIT - V: DISASTER RESISTANT BUILDING 269–287 20 DISASTER RESISTANT BUILDINGS 271–281 20.1 Earthquakes Resistant Buildings 271 20.2 Types of Earthquakes 271 20.3 Terminology 272 20.4 Magnitude and Intensity 273 20.5 Seismograph 273 20.6 I.S: Codes on Earthquake Resistant Building Design 274 20.7 Improving Earthquake Resistance of Small Buildings 274 20.8 Improving Earthquake Resistance of Tall Buildings 276 20.9 Cyclone Resistant Buildings 278 20.10 Fire Resistant Building 279 Questions 281 21 DISASTER MANAGEMENT AND PLANNING 282–285 21.1 Disaster Prevention Strategy 282 21.2 Early Warning System 283 21.3 Disaster Preparedness 283 21.4 Disaster Mitigation 284 21.5 Disaster Rescue and Relief Measures 284 21.6 Disaster Resettlement, Rehabilitation and Reconstruction 285 Questions 285 22 INDIAN STANDARD CODES 286–287 22.1 IS Codes for Building Design 286 22.2 IS Codes for Building Materials and Construction 287 Questions 287 UNIT - I CIVIL ENGINEERING MATERIALS This page intentionally left blank CHAPTER 1 Traditional Materials Stones, bricks, cement, lime and timber are the traditional materials used for civil engineering constructions for several centuries. In this chapter types, properties, tests and uses of these materials is explained. 1.1 STONES Stone is a ‘naturally available building material’ which has been used from the early age of civilization. It is available in the form of rocks, which is cut to required size and shape and used as building block. It has been used to construct small residential buildings to large palaces and temples all over the world. Red Fort, Taj Mahal, Vidhan Sabha at Bangalore and several palaces of medieval age all over India are the famous stone buildings. 1.1.1 Type of Stones Stones used for civil engineering works may be classified in the following three ways: Geological Physical Chemical Geological Classification Based on their origin of formation stones are classified into three main groups—Igneous, sedimentary and metamorphic rocks. (i) Igneous Rocks: These rocks are formed by cooling and solidifying of the rock masses from their molten magmatic condition of the material of the earth. Generally igneous rocks are strong and durable. Granite, trap and basalt are the rocks belonging to this category, Granites are formed by slow cooling of the lava under thick cover on the top. Hence they have crystalline surface. The cooling of lava at the top surface of earth results into non-crystalline and glassy texture. Trap and basalt belong to this category. 3 4 BASIC CIVIL ENGINEERING (ii) Sedimentary Rocks: Due to weathering action of water, wind and frost existing rocks disintegrates. The disintegrated material is carried by wind and water; the water being most powerful medium. Flowing water deposits its suspended materials at some points of obstacles to its flow. These deposited layers of materials get consolidated under pressure and by heat. Chemical agents also contribute to the cementing of the deposits. The rocks thus formed are more uniform, fine grained and compact in their nature. They represent a bedded or stratified structure in general. Sand stones, lime stones, mud stones etc. belong to this class of rock. (iii) Metamorphic Rocks: Previously formed igneous and sedimentary rocks under go changes due to metamorphic action of pressure and internal heat. For example due to metamorphic action granite becomes greisses, trap and basalt change to schist and laterite, lime stone changes to marble, sand stone becomes quartzite and mud stone becomes slate. Physical Classification Based on the structure, the rocks may be classified as: Stratified rocks Unstratified rocks (i) Stratified Rocks: These rocks are having layered structure. They possess planes of stratification or cleavage. They can be easily split along these planes. Sand stones, lime stones, slate etc. are the examples of this class of stones. (ii) Unstratified Rocks: These rocks are not stratified. They possess crystalline and compact grains. They cannot be split in to thin slab. Granite, trap, marble etc. are the examples of this type of rocks. (iii) Foliated Rocks: These rocks have a tendency to split along a definite direction only. The direction need not be parallel to each other as in case of stratified rocks. This type of structure is very common in case of metamorphic rocks. Chemical Classification On the basis of their chemical composition engineers prefer to classify rocks as: Silicious rocks Argillaceous rocks and Calcareous rocks (i) Silicious rocks: The main content of these rocks is silica. They are hard and durable. Examples of such rocks are granite, trap, sand stones etc. (ii) Argillaceous rocks: The main constituent of these rocks is argil i.e., clay. These stones are hard and durable but they are brittle. They cannot withstand shock. Slates and laterites are examples of this type of rocks. (iii) Calcareous rocks: The main constituent of these rocks is calcium carbonate. Limestone is a calcareous rock of sedimentary origin while marble is a calcareous rock of metamorphic origin. TRADITIONAL MATERIALS 5 1.1.2 Properties of Stones The following properties of the stones should be looked into before selecting them for engineering works: (i) Structure: The structure of the stone may be stratified (layered) or unstratified. Structured stones should be easily dressed and suitable for super structure. Unstratified stones are hard and difficult to dress. They are preferred for the foundation works. (ii) Texture: Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable. (iii) Density: Denser stones are stronger. Light weight stones are weak. Hence stones with specific gravity less than 2.4 are considered unsuitable for buildings. (iv) Appearance: A stone with uniform and attractive colour is durable, if grains are compact. Marble and granite get very good appearance, when polished. Hence they are used for face works in buildings. (v) Strength: Strength is an important property to be looked into before selecting stone as building block. Indian standard code recommends, a minimum crushing strength of 3.5 N/mm2 for any building block. Table 1.1 shows the crushing strength of various stones. Due to non-uniformity of the material, usually a factor of safety of 10 is used to find the permissible stress in a stone. Hence even laterite can be used safely for a single storey building, because in such structures expected load can hardly give a stress of 0.15 N/mm2. However in stone masonry buildings care should be taken to check the stresses when the beams (Concentrated Loads) are placed on laterite wall. Table 1.1. Crushing strength of common building stones Name of Stone Crushing Strength in N/mm2 Trap 300 to 350 Basalt 153 to 189 Granite 104 to 140 Slate 70 to 210 Marble 72 Sand stone 65 Lime stone 55 Laterite 1.8 to 3.2 (vi) Hardness: It is an important property to be considered when stone is used for flooring and pavement. Coefficient of hardness is to be found by conducting test on standard specimen in Dory’s testing machine. For road works coefficient of hardness should be at least 17. For building works stones with coefficient of hardness less than 14 should not be used. (vii) Percentage wear: It is measured by attrition test. It is an important property to be considered in selecting aggregate for road works and railway ballast. A good stone should not show wear of more than 2%. 6 BASIC CIVIL ENGINEERING (viii) Porosity and Absorption: All stones have pores and hence absorb water. The reaction of water with material of stone cause disintegration. Absorption test is specified as percentage of water absorbed by the stone when it is immersed under water for 24 hours. For a good stone it should be as small as possible and in no case more than 5. (ix) Weathering: Rain and wind cause loss of good appearance of stones. Hence stones with good weather resistance should be used for face works. (x) Toughness: The resistance to impact is called toughness. It is determined by impact test. Stones with toughness index more than 19 are preferred for road works. Toughness index 13 to 19 are considered as medium tough and stones with toughness index less than 13 are poor stones. (xi) Resistance to Fire: Sand stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire. (xii) Ease in Dressing: Cost of dressing contributes to cost of stone masonry to a great extent. Dressing is easy in stones with lesser strength. Hence an engineer should look into sufficient strength rather than high strength while selecting stones for building works. (xiii) Seasoning: The stones obtained from quarry contain moisture in the pores. The strength of the stone improves if this moisture is removed before using the stone. The process of removing moisture from pores is called seasoning. The best way of seasoning is to allow it to the action of nature for 6 to 12 months. This is very much required in the case of laterite stones. 1.1.3 Requirements of Good Building Stones The following are the requirements of good building stones: (i) Strength: The stone should be able to resist the load coming on it. Ordinarilly this is not of primary concern since all stones are having good strength. However in case of large structure, it may be necessary to check the strength. (ii) Durability: Stones selected should be capable of resisting adverse effects of natural forces like wind, rain and heat. (iii) Hardness: The stone used in floors and pavements should be able to resist abrasive forces caused by movement of men and materials over them. (iv) Toughness: Building stones should be tough enough to sustain stresses developed due to vibrations. The vibrations may be due to the machinery mounted over them or due to the loads moving over them. The stone aggregates used in the road constructions should be tough. (v) Specific Gravity: Heavier variety of stones should be used for the construction of dams, retaining walls, docks and harbours. The specific gravity of good building stone is between 2.4 and 2.8. (vi) Porosity and Absorption: Building stone should not be porous. If it is porous rain water enters into the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of water in pores takes place and it results into the disintegration of the stone. (vii) Dressing: Giving required shape to the stone is called dressing. It should be easy to dress so that the cost of dressing is reduced. However the care should be taken so that, this is not be at the cost of the required strength and the durability. (viii) Appearance: In case of the stones to be used for face works, where appearance is a primary requirement, its colour and ability to receive polish is an important factor. TRADITIONAL MATERIALS 7 (ix) Seasoning: Good stones should be free from the quarry sap. Laterite stones should not be used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning. (x) Cost: Cost is an important consideration in selecting a building material. Proximity of the quarry to building site brings down the cost of transportation and hence the cost of stones comes down. However it may be noted that not a single stone can satisfy all the requirements of a good building stones, since one requirement may contradict another. For example, strength and durability requirement contradicts ease of dressing requirement. Hence it is necessary that site engineer looks into the properties required for the inteded work and selects the stone. 1.1.4 Tests on Stones To acertain the required properties of stones, the following tests can be conducted: (i) crushing strength test (ii) water absorption test (iii) abrasion test (iv) impact test (v) acid test. (i) Crushing Strength Test: For conducting this test, specimen of size 40 × 40 × 40 mm are prepared from parent stone. Then the sides are finely dressed and placed in water for 3 days. The saturated specimen is provided with a layer of plaster of paris on its top and bottom surfaces to get even surface so that load applied is distributed uniformly. Uniform load distribution can be obtained satisfactorily by providing a pair of 5 mm thick playwood instead of using plaster of paris layer also. The specimen so placed in the compression testing machine is loaded at the rate of 14 N/mm2 per minute. The crushing load is noted. Then crushing strength is equal to the crushing load divided by the area over which the load is applied. At least three specimen should be tested and the average should be taken as crushing strength. (ii) Water Absorption Test: For this test cube specimen weighing about 50 grams are prepared and the test is carried out in the steps given below: (a) Note the weight of dry speciment as W1. (b) Place the specimen in water for 24 hours. (c) Take out the specimen, wipe out the surface with a piece of cloth and weigh the specimen. Let its weight be W2. (d) Suspend the specimen freely in water and weight it. Let its weight be W3. (e) Place the specimen in boiling water for 5 hours. Then take it out, wipe the surface with cloth and weigh it. Let this weight be W4. Then, W2 − W1 Percentage absorption by weight = × 100...(1) W1 W − W1 Percentage absorption by volume = 2 × 100...(2) W2 − W3 8 BASIC CIVIL ENGINEERING W4 − W1 Percentage porosity by volume = × 100...(3) W2 − W3 W1 Density =...(4) W2 − W1 W1 Specific gravity =...(5) W2 − W3 Water absorption ∴ Saturation coefficient = Total porosity W2 − W1 =. W4 − W1 (iii) Abrasion Test: This test is carried out on stones which are used as aggregates for road construction. The test result indicate the suitability of stones against the grinding action under traffic. Any one of the following test may be conducted to find out the suitability of aggregates: (i) Los Angeles abrasion test (ii) Deval abrasion test (iii) Dorry’s abrasion test. However Los Angeles abrasion test is preferred since these test results are having good correlation with the performance of the pavements. The Los Angeles apparatus [Fig. 1.1] consists of a hollow cylinder 0.7 m inside diameter and 0.5 m long with both ends closed. It is mounted on a frame so that it can be rotated about horizontal axis. IS code has standardised the test procedure for different gradation of specimen. Along with specified weight of specimen a specified number of cast iron balls of 48 mm diameter are placed in the cylinder. Fig. 1.1. Los Angeles testing machine TRADITIONAL MATERIALS 9 Then the cylinder is rotated at a speed of 30 to 33 rpm for specified number of times (500 to 1000). Then the aggregate is removed and sieved on 1.7 mm. IS sieve. The weight of aggregate passing is found. Then Los Angeles value is found as Weight of aggregate passing through sieve = × 100. Original weight The following values are recommended for road works: For bituminous mixes – 30% For base course – 50% (iv) Impact Test: The resistance of stones to impact is found by conducting tests in impacting testing machine (Fig. 1.2). It consists of a frame with guides in which a metal hammer weighing 13.5 to 15 kg can freely fall from a height of 380 mm. Lifting handle Hammer of weight 132—137 N 100 mm dia Vertical guide 350 mm bar Cup 102 mm Dia and height 50 mm Circular base Fig. 1.2. Aggregate impact testing machine Aggregates of size 10 mm to 12.5 mm are filled in cylinder in 3 equal layers; each layer being tamped 25 times. The same is then transferred to the cup and again tamped 25 times. The hammer is then allowed to fall freely on the specimen 15 times. The specimen is then sieved through 2.36 mm sieve. Then, W2 Impact value = W1 where W2 = weight of fines W1 = original weight. The recommended impact values for various works are: (i) for wearing course >/ 30% 10 BASIC CIVIL ENGINEERING (ii) for bituminous mechadam >/ 35% (iii) for water bound mechadam >/ 40% (v) Acid Test: This test is normally carried out on sand stones to check the presence of calcium carbonate, which weakens the weather resisting quality. In this test, a sample of stone weighing about 50 to 100 gm is taken and kept in a solution of one per cent hydrochloric acid for seven days. The solution is agitated at intervals. A good building stone maintains its sharp edges and keeps its surface intact. If edges are broken and powder is formed on the surface, it indicates the presence of calcium carbonate. Such stones will have poor weather resistance. 1.1.5 Uses of Stones Stones are used in the following civil engineering constructions: (i) Stone masonry is used for the construction of foundations, walls, columns and arches. (ii) Stones are used for flooring. (iii) Stone slabs are used as damp proof courses, lintels and even as roofing materials. (iv) Stones with good appearance are used for the face works of buildings. Polished marbles and granite are commonly used for face works. (v) Stones are used for paving of roads, footpaths and open spaces round the buildings. (vi) Stones are also used in the constructions of piers and abutments of bridges, dams and retaining walls. (vii) Crushed stones with graved are used to provide base course for roads. When mixed with tar they form finishing coat. (viii) Crushed stones are used in the following works also: (a) As a basic inert material in concrete (b) For making artificial stones and building blocks (c) As railway ballast. 1.1.6 Common Building Stones The following are the some of commonly used stones: (i) Basalt and trap (ii) Granite (iii) Sand stone (iv) Slate (v) Laterite (vi) Marble (vii) Gneiss (viii) Quartzite. Their qualities and uses are explained below: (i) Basalt and Trap: The structure is medium to fine grained and compact. Their colour varies from dark gray to black. Fractures and joints are common. Their weight varies from 18 kN/m3 to 29 kN/m3. The compressive strength varies from 200 to 350 N/mm2. These are igneous rocks. They are used as road metals, aggregates for concrete. They are also used for rubble masonry works for bridge piers, river walls and dams. They are used as pavement. TRADITIONAL MATERIALS 11 (ii) Granite: Granites are also igneous rocks. The colour varies from light gray to pink. The structure is crystalline, fine to coarse grained. They take polish well. They are hard durable. Specific gravity is from 2.6 to 2.7 and compressive strength is 100 to 250 N/mm2. They are used primarily for bridge piers, river walls, and for dams. They are used as kerbs and pedestals. The use of granite for monumental and institutional buildings is common. Polished granites are used as table tops, cladding for columns and wall. They are used as coarse aggregates in concrete. (iii) Sand stone: These are sedimentary rocks, and hence stratified. They consist of quartz and feldspar. They are found in various colours like white, grey, red, buff, brown, yellow and even dark gray. The specific gravity varies from 1.85 to 2.7 and compressive strength varies from 20 to 170 N/mm2. Its porosity varies from 5 to 25 per cent. Weathering of rocks renders it unsuitable as building stone. It is desirable to use sand stones with silica cement for heavy structures, if necessary. They are used for masonry work, for dams, bridge piers and river walls. (iv) Slate: These are metamorphic rocks. They are composed of quartz, mica and clay minerals. The structure is fine grained. They split along the planes of original bedding easily. The colour varies from dark gray, greenish gray, purple gray to black. The specific gravity is 2.6 to 2.7. Compressive strength varies from 100 to 200 N/mm2. They are used as roofing tiles, slabs, pavements etc. (v) Laterite: It is a metamorphic rock. It is having porous and sponges structure. It contains high percentage of iron oxide. Its colour may be brownish, red, yellow, brown and grey. Its specific gravity is 1.85 and compressive strength varies from 1.9 to 2.3 N/mm2. It can be easily quarried in blocks. With seasoning it gains strength. When used as building stone, its outer surface should be plastered. (vi) Marble: This is a metamorphic rock. It can take good polish. It is available in different pleasing colours like white and pink. Its specific gravity is 2.65 and compressive strength is 70–75 N/ mm2. It is used for facing and ornamental works. It is used for columns, flooring, steps etc. (vii) Gneiss: It is a metamorphic rock. It is having fine to coarse grains. Alternative dark and white bands are common. Light grey, pink, purple, greenish gray and dark grey coloured varieties are available. These stones are not preferred because of deleterious constituents present in it. They may be used in minor constructions. However hard varieties may be used for buildings. The specific gravity varies from 2.5 to 3.0 and crushing strength varies from 50 to 200 N/mm2. (viii) Quartzite: Quartzites are metamorphic rocks. The structure is fine to coarse grained and often granular and branded. They are available in different colours like white, gray, yellowish. Quartz is the chief constituent with feldspar and mica in small quantities. The specific gravity varies from 2.55 to 2.65. Crushing strength varies from 50 to 300 N/mm2. They are used as building blocks and slabs. They are also used as aggregates for concrete. 1.2 BRICKS Brick is obtained by moulding good clay into a block, which is dried and then burnt. This is the oldest building block to replace stone. Manufacture of brick started with hand moulding, sun drying and burning in clamps. A considerable amount of technological development has taken place with better 12 BASIC CIVIL ENGINEERING knowledge about to properties of raw materials, better machinaries and improved techniques of moulding drying and burning. The size of the bricks are of 90 mm × 90 mm × 90 mm and 190 mm × 90 mm × 40 mm. With mortar joints, the size of these bricks are taken as 200 mm × 100 mm × 100 mm and 200 mm × 100 mm 3′′ 1′′ 5″ 1′′ × 50 mm. However the old size of 8 ×4 ×2 giving a masonary size of 9″ × 4 × 3″ is still 4 2 8 2 commonly used in India. 1.2.1 Types of Bricks Bricks may be broadly classified as: (i) Building bricks (ii) Paving bricks (iii) Fire bricks (iv) Special bricks. (i) Building Bricks: These bricks are used for the construction of walls. (ii) Paving Bricks: These are vitrified bricks and are used as pavers. (iii) Fire Bricks: These bricks are specially made to withstand furnace temperature. Silica bricks belong to this category. (iv) Special Bricks: These bricks are different from the commonly used building bricks with respect to their shape and the purpose for which they are made. Some of such bricks are listed below: (a) Specially shaped bricks (b) Facing bricks (c) Perforated building bricks (d) Burnt clay hollow bricks (e) Sewer bricks ( f ) Acid resistant bricks. (a) Specially Shaped Bricks: Bricks of special shapes are manufactured to meet the requirements of different situations. Some of them are shown in Fig. 1.3. Bull nosed brick Cant brick Plinth brick Channel brick Coping brick Cornice brick Fig. 1.3. Special shaped bricks TRADITIONAL MATERIALS 13 (b) Facing Bricks: These bricks are used in the outer face of masonry. Once these bricks are provided, plastering is not required. The standard size of these bricks are 190 × 90 × 90 mm or 190 × 90 × 40 mm. (c) Perforated Building Bricks: These bricks are manufactured with area of perforation of 30 to 45 per cent. The area of each perforation should not exceed 500 mm2. The perforation should be uniformly distributed over the surface. They are manufactured in the size 190 × 190 × 90 mm and 290 × 90 × 90 mm. (d) Burn’t Clay Hollow Bricks: Figure 1.4 shows a burnt clay hollow brick. They are light in weight. They are used for the construction of partition walls. They provide good thermal insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm, 290 × 90 × 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less than 11 mm and that of any web not less than 8 mm. WEBS 8 mm minimum thick Fig. 1.4. Hollow bricks (e) Sewer Bricks: These bricks are used for the construction of sewage lines. They are manufactured from surface clay, fire clay shale or with the combination of these. They are manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average strength of these bricks should be a minimum of 17.5 N/mm2. The water absorption should not be more than 10 per cent. ( f ) Acid Resistant Bricks: These bricks are used for floorings likely to be subjected to acid attacks, lining of chambers in chemical plants, lining of sewers carrying industrial wastes etc. These bricks are made of clay or shale of suitable composition with low lime and iron content, flint or sand and vitrified at high temperature in a ceramic kiln. 1.2.2 Properties of Bricks The following are the required properties of good bricks: (i) Colour: Colour should be uniform and bright. (ii) Shape: Bricks should have plane faces. They should have sharp and true right angled corners. (iii) Size: Bricks should be of standard sizes as prescribed by codes. 14 BASIC CIVIL ENGINEERING (iv) Texture: They should possess fine, dense and uniform texture. They should not possess fissures, cavities, loose grit and unburnt lime. (v) Soundness: When struck with hammer or with another brick, it should produce metallic sound. (vi) Hardness: Finger scratching should not produce any impression on the brick. (vii) Strength: Crushing strength of brick should not be less than 3.5 N/mm2. A field test for strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not break into pieces. (viii) Water Absorption: After immercing the brick in water for 24 hours, water absorption should not be more than 20 per cent by weight. For class-I works this limit is 15 per cent. (ix) Efflorescence: Bricks should not show white patches when soaked in water for 24 hours and then allowed to dry in shade. White patches are due to the presence of sulphate of calcium, magnesium and potassium. They keep the masonry permanently in damp and wet conditions. (x) Thermal Conductivity: Bricks should have low thermal conductivity, so that buildings built with them are cool in summer and warm in winter. (xi) Sound Insulation: Heavier bricks are poor insulators of sound while light weight and hollow bricks provide good sound insulation. (xii) Fire Resistance: Fire resistance of bricks is usually good. In fact bricks are used to encase steel columns to protect them from fire. 1.2.3 Tests on Bricks The following laboratory tests may be conducted on the bricks to find their suitability: (i) Crushing strength (ii) Absorption (iii) Shape and size and (iv) Efflorescence. (i) Crushing Strength: The brick specimen are immersed in water for 24 hours. The frog of the brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied axially at a uniform rate of 14 N/mm 2. The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing strength. (ii) Absorption Test: Brick specimen are weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen is taken. This value should not exceed 20 per cent. TRADITIONAL MATERIALS 15 (iii) Shape and Size: Bricks should be of standard size and edges should be truely rectangular with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length, along the width and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm. IS code permits the following limits: Lengthwise: 3680 to 3920 mm Widthwise: 1740 to 1860 mm Heightwise: 1740 to 1860 mm. The following field tests help in acertaining the good quality bricks: (i) uniformity in size (ii) uniformity in colour (iii) structure (iv) hardness test (v) sound test (vi) strength test. (i) Uniformity in Size: A good brick should have rectangular plane surface and uniform in size. This check is made in the field by observation. (ii) Uniformity in Colour: A good brick will be having uniform colour throughout. This observation may be made before purchasing the brick. (iii) Structure: A few bricks may be broken in the field and their cross-section observed. The section should be homogeneous, compact and free from defects such as holes and lumps. (iv) Sound Test: If two bricks are struck with each other they should produce clear ringing sound. The sound should not be dull. (v) Hardness Test: For this a simple field test is scratch the brick with nail. If no impression is marked on the surface, the brick is sufficiently hard (vi) Efflorescense: The presence of alkalies in brick is not desirable because they form patches of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is performed as explained below: Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well ventilated room. After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second evaporation observe the bricks for white/grey patches. The observation is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or serious to mean (a) Nil: No patches (b) Slight: 10% of area covered with deposits (c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface. (d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of the surface. (e) Serious: Heavy deposits of salt accompanied by flaking of the surface. 16 BASIC CIVIL ENGINEERING 1.2.4 Classification of Bricks Based on their Quality The bricks used in construction are classified as: (i) First class bricks (ii) Second class bricks (iii) Third class bricks and (iv) Fourth class bricks (i) First Class Bricks: These bricks are of standard shape and size. They are burnt in kilns. They fulfill all desirable properties of bricks. (ii) Second Class Bricks: These bricks are ground moulded and burnt in kilns. The edges may not be sharp and uniform. The surface may be some what rough. Such bricks are commonly used for the construction of walls which are going to be plastered. (iii) Third Class Bricks: These bricks are ground moulded and burnt in clamps. Their edges are somewhat distorted. They produce dull sound when struck together. They are used for temporary and unimportant structures. (iv) Fourth Class Bricks: These are the over burnt bricks. They are dark in colour. The shape is irregular. They are used as aggregates for concrete in foundations, floors and roads. 1.2.5 Uses of Bricks Bricks are used in the following civil works: (i) As building blocks. (ii) For lining of ovens, furnaces and chimneys. (iii) For protecting steel columns from fire. (iv) As aggregates in providing water proofing to R.C.C. roofs. (v) For pavers for footpaths and cycle tracks. (vi) For lining sewer lines. 1.3 LIME It is an important binding material used in building construction. Lime has been used as the material of construction from ancient time. When it is mixed with sand it provides lime mortar and when mixed with sand and coarse aggregate, it forms lime concrete. 1.3.1 Types of Limes and their Properties The limes are classified as fat lime, hydraulic lime and poor lime: (i) Fat lime: It is composed of 95 percentage of calcium oxide. When water is added, it slakes 1 vigorously and its volume increases to 2 to 2 times. It is white in colour. Its properties are: 2 TRADITIONAL MATERIALS 17 (a) hardens slowly (b) has high degree of plasticity (c) sets slowly in the presence of air (d) white in colour (e) slakes vigorously. (ii) Hydraulic lime: It contains clay and ferrous oxide. Depending upon the percentage of clay present, the hydraulic lime is divided into the following three types: (a) Feebly hydraulic lime (5 to 10% clay content) (b) Moderately hydraulic lime (11 to 20% clay content) (c) Eminently hydraulic lime (21 to 30% clay content) The properties of hydraulic limes are: Sets under water Colour is not perfectly white Forms a thin paste with water and do not dissolve in water. Its binding property improves if its fine powder is mixed with sand and kept in the form of heap for a week, before using. (iii) Poor lime: It contains more than 30% clay. Its colour is muddy. It has poor binding property. The mortar made with such lime is used for inferior works. IS 712-1973 classifies lime as class A, B, C, D and E. Class A Lime: It is predominently hydraulic lime. It is normally supplied as hydrated lime and is commonly used for structural works. Class B Lime: It contains both hydraulic lime and fat lime. It is supplied as hydrated lime or as quick lime. It is used for making mortar for masonry works. Class C Lime: It is predominently fat lime, supplied both as quick lime and fat lime. It is used for finishing coat in plastering and for white washing. Class D Lime: This lime contains large quantity of magnesium oxide and is similar to fat lime. This is also commonly used for white washing and for finishing coat in plastering. Class E Lime: It is an impure lime stone, known as kankar. It is available in modular and block form. It is supplied as hydrated lime. It is commonly used for masonry mortar. 1.3.2 Tests on Limestones The following practical tests are made on limestones to determine their suitability: (i) Physical tests (ii) Heat test (iii) Chemical test (iv) Ball test. 18 BASIC CIVIL ENGINEERING (i) Physical Test: Pure limestone is white in colour. Hydraulic limestones are bluish grey, brown or are having dark colours. The hydraulic lime gives out earthy smell. They are having clayey taste. The presence of lumps give indication of quick lime and unburnt lime stones. (ii) Heat Test: A piece of dry stone weighing W1 is heated in an open fire for few hours. If weight of sample after cooling is W2, the loss of weight is W2 – W1. The loss of weight indicates the amount of carbon dioxide. From this the amount of calcium carbonate in limestone can be worked out. (iii) Chemical Test: A teaspoon full of lime is placed in a test tube and dilute hydrochloric acid is poured in it. The content is stirred and the test tube is kept in the stand for 24 hours. Vigourous effervescence and less residue indicates pure limestone. If effervescence is less and residue is more it indicates impure limestone. If thick gel is formed and after test tube is held upside down it is possible to identify class of lime as indicated below: Class A lime, if gel do not flow. Class B lime, if gel tends to flow down. Class C lime, if there is no gel formation. (iv) Ball Test: This test is conducted to identify whether the lime belongs to class C or to class B. By adding sufficient water about 40 mm size lime balls are made and they are left undisturbed for six hours. Then the balls are placed in a basin of water. If within minutes slow expansion and slow disintegration starts it indicates class C lime. If there is little or no expansion, but only cracks appear it belongs to class B lime. 1.3.3 Uses of Lime The following are the uses of lime in civil works: (i) For white washing. (ii) For making mortar for masonry works and plastering. (iii) To produce lime sand bricks. (iv) For soil stabilization. (v) As a refractory material for lining open hearth furnaces. (vi) For making cement. 1.4 CEMENT Cement is a commonly used binding material in the construction. The cement is obtained by burning a mixture of calcarious (calcium) and argillaceous (clay) material at a very high temperature and then grinding the clinker so produced to a fine powder. It was first produced by a mason Joseph Aspdin in England in 1924. He patented it as portland cement. TRADITIONAL MATERIALS 19 1.4.1 Types of Cement In addition to ordinary portland cement there are many varieties of cement. Important varieties are briefly explained below: (i) White Cement: The cement when made free from colouring oxides of iron, maganese and chlorium results into white cement. In the manufacture of this cement, the oil fuel is used instead of coal for burning. White cement is used for the floor finishes, plastering, ornamental works etc. In swimming pools white cement is used to replace glazed tiles. It is used for fixing marbles and glazed tiles. (ii) Coloured Cement: The cements of desired colours are produced by intimately mixing pigments with ordinary cement. The chlorium oxide gives green colour. Cobalt produce blue colour. Iron oxide with different proportion produce brown, red or yellow colour. Addition of manganese dioxide gives black or brown coloured cement. These cements are used for giving finishing touches to floors, walls, window sills, roofs etc. (iii) Quick Setting Cement: Quick setting cement is produced by reducing the percentage of gypsum and adding a small amount of aluminium sulphate during the manufacture of cement. Finer grinding also adds to quick setting property. This cement starts setting within 5 minutes after adding water and becomes hard mass within 30 minutes. This cement is used to lay concrete under static or slowly running water. (iv) Rapid Hardening Cement: This cement can be produced by increasing lime content and burning at high temperature while manufacturing cement. Grinding to very fine is also necessary. Though the initial and final setting time of this cement is the same as that of portland cement, it gains strength in early days. This property helps in earlier removal of form works and speed in construction activity. (v) Low Heat Cement: In mass concrete works like construction of dams, heat produced due to hydration of cement will not get dispersed easily. This may give rise to cracks. Hence in such constructions it is preferable to use low heat cement. This cement contains low percentage (5%) of tricalcium aluminate (C3A) and higher percentage (46%) of dicalcium silicate (C2S). (vi) Pozzulana Cement: Pozzulana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzulana material is 10 to 30 per cent. It can resist action of sulphate. It releases less heat during setting. It imparts higher degree of water tightness. Its tensile strength is high but compressive strength is low. It is used for mass concrete works. It is also used in sewage line works. (vii) Expanding Cement: This cement expands as it sets. This property is achieved by adding expanding medium like sulpho aluminate and a stabilizing agent to ordinary cement. This is used for filling the cracks in concrete structures. (viii) High Alumina Cement: It is manufactured by calcining a mixture of lime and bauxite. It is more resistant to sulphate and acid attack. It develops almost full strength within 24 hours of adding water. It is used for under water works. (ix) Blast Furnace Cement: In the manufacture of pig iron, slag comes out as a waste product. By grinding clinkers of cement with about 60 to 65 per cent of slag, this cement is produced. The properties of this cement are more or less same as ordinary cement, but it is cheap, since it utilise waste product. This cement is durable but it gains the strength slowly and hence needs longer period of curing. 20 BASIC CIVIL ENGINEERING (x) Acid Resistant Cement: This cement is produced by adding acid resistant aggregated such as quartz, quartzite, sodium silicate or soluble glass. This cement has good resistance to action of acid and water. It is commonly used in the construction of chemical factories. (xi) Sulphate Resistant Cement: By keeping the percentage of tricalcium aluminate C3A below five per cent in ordinary cement this cement is produced. It is used in the construction of structures which are likely to be damaged by alkaline conditions. Examples of such structures are canals, culverts etc. (xii) Fly Ash Blended Cement: Fly ash is a byproduct in thermal stations. The particles of fly ash are very minute and they fly in the air, creating air pollution problems. Thermal power stations have to spend lot of money to arrest fly ash and dispose safely. It is found that one of the best way to dispose fly ash is to mix it with cement in controlled condition and derive some of the beneficiary effects on cement. Now-a-days cement factories produce the fly ash in their own thermal stations or borrow it from other thermal stations and further process it to make it suitable to blend with cement. 20 to 30% fly ash is used for blending. Fly ash blended cements have superior quality of resistance to weathering action. The ultimate strength gained is the same as that with ordinary portland cement. However strength gained in the initial stage is slow. Birla plus, Birla star, A.C.C. Suraksha are some of the brand mame of blended cement. 1.4.2 Properties of Ordinary Portland Cement (i) Chemical properties: Portland cement consists of the following chemical compounds: (a) Tricalcium silicate 3 CaO.SiO2 (C3S) 40% (b) Dicalcium silicate 2CaO.SiO2 (C2S) 30% (c) Tricalcium aluminate 3CaO.Al2O3 (C3A) 11% (d) Tetracalcium aluminate 4CaO.Al2O3.Fe2O3 (C3AF) 11% There may be small quantities of impurifies present such as calcium oxide (CaO) and magnesium oxide (MgO). When water is added to cement, C3A is the first to react and cause initial set. It generates great amount of heat. C3S hydrates early and develops strength in the first 28 days. It also generates heat. C2S is the next to hydrate. It hydrates slowly and is responsible for increase in ultimate strength. C4AF is comparatively inactive compound. (ii) Physical properties: The following physical properties should be checked before selecting a portland cement for the civil engineering works. IS 269–1967 specifies the method of testing and prescribes the limits: (a) Fineness (b) Setting time (c) Soundness (d) Crushing strength. (a) Fineness: It is measured in terms of percentage of weight retained after sieving the cement through 90 micron sieve or by surface area of cement in square centimeters per gramme of cement. According to IS code specification weight retained on the sieve should not be more than 10 per cent. In terms of specific surface should not be less than 2250 cm2/gm. TRADITIONAL MATERIALS 21 (b) Setting time: A period of 30 minutes as minimum setting time for initial setting and a maximum period of 600 minutes as maximum setting time is specified by IS code, provided the tests are conducted as per the procedure prescribed by IS 269-1967. (c) Soundness: Once the concrete has hardened it is necessary to ensure that no volumetric changes takes place. The cement is said to be unsound, if it exhibits volumetric instability after hardening. IS code recommends test with Le Chatelier mould for testing this property. At the end of the test, the indicator of Le Chatelier mould should not expand by more than 10 mm. (a) Crushing strength: For this mortar cubes are made with standard sand and tested in compression testing machine as per the specification of IS code. The minimum strength specified is 16 N/mm2 after 3 days and 22 N/mm2 after 7 days of curing. 1.4.3 Physical Tests on Cement (a) Soundness Test: It is conducted by sieve analysis. 100 gms of cement is taken and sieved through IS sieve No. 9 for fifteen minutes. Residue on the sieve is weighed. This should not exceed 10 per cent by weight of sample taken. (b) Setting Time: Initial setting time and final setting time are the two important physical properties of cement. Initial setting time is the time taken by the cement from adding of water to the starting of losing its plasticity. Final setting time is the time lapsed from adding of the water to complete loss of plasticity. Vicat apparatus is used for finding the setting times [Ref. Fig. 1.5]. Vicat apparatus consists of a movable rod to which any one of the three needles shown in figure can be attached. An indicator is attached to the movable rod. A vicat mould is associated with this apparatus which is in the form of split cylinder. Cap Movable rod weight 300 g Release 60 pin 40 Indicator 20 10 0 Frame 1 mm sq needle C 1 mm sq 50 80 mm Split ring Air E Non porous 40 vent 6.4 plate 0.3 10f 5 Front view Side view Plunger for Enlarged view Vical apparatus with needle standard of needle for initial section time test consistency test Fig. 1.5. Vicat apparatus 22 BASIC CIVIL ENGINEERING Before finding initial and final setting time it is necessary to determine water to be added to get standard consistency. For this 300 gms of cement is mixed with about 30% water and cement paste prepared is filled in the mould which rests on non porous plate. The plunger is attached to the movable rod of vicat apparatus and gently lowered to touch the paste in the mould. Then the plunger is allowed to move freely. If the penetration is 5 mm to 7 mm from the bottom of the mould, then cement is having standard consistency. If not, experiment is repeated with different proportion of water fill water required for standard consistency is found. Then the tests for initial and final setting times can be carried out as explained below: Initial Setting Time: 300 gms of cement is thoroughly mixed with 0.85 times the water for standard consistency and vicat mould is completely filled and top surface is levelled. 1 mm square needle is fixed to the rod and gently placed over the paste. Then it is freely allowed to penetrate. In the beginning the needle penetrates the paste completely. As time lapses the paste start losing its plasticity and offers resistance to penetration. When needle can penetrate up to 5 to 7 mm above bottom of the paste experiment is stopped and time lapsed between the addition of water and end if the experiment is noted as initial setting time. Final Setting Time. The square needle is replaced with annular collar. Experiment is continued by allowing this needle to freely move after gently touching the surface of the paste. Time lapsed between the addition of water and the mark of needle but not of annular ring is found on the paste. This time is noted as final setting time. (c) Soundness Test: This test is conducted to find free lime in cement, which is not desirable. Le Chatelier apparatus shown in Fig. 1.6 is used for conducting this test. It consists of a split brass mould of diameter 30 mm and height 30 mm. On either side of the split, there are two indicators, with pointed ends. The ends of indicators are 165 mm from the centre of the mould. Glass plate 30 mm Glass plate Elevation Brass mould Thickness 0.50 mm Indicators with pointed ends m Split not more than 0.50 mm m 30 165 mm Plan Fig. 1.6. Le Chatelier’s apparatus Properly oiled Le Chatelier mould is placed on a glass plate and is filled completely with a cement paste having 0.78 times the water required for standard consistency. It is then covered with TRADITIONAL MATERIALS 23 another glass plate and a small weight is placed over it. Then the whole assembly is kept under water for 24 hours. The temperature of water should be between 24°C and 50°C. Note the distance between the indicator. Then place the mould again in the water and heat the assembly such that water reaches the boiling point in 30 minutes. Boil the water for one hour. The mould is removed from water and allowed to cool. The distance between the two pointers is measured. The difference between the two readings indicate the expansion of the cement due to the presence of unburnt lime. This value should not exceed 10 mm. (d) Crushing Strength Test: For this 200 gm of cement is mixed with 600 gm of standard sand confirming to IS 650–1966. After mixing thoroughly in dry condition for a minute distilled potable P water + 3 percentage is added where P is the water required for the standard consistency. They are 4 mixed with trowel for 3 to 4 minutes to get uniform mixture. The mix is placed in a cube mould of 70.6 mm size (Area 5000 mm2) kept on a steel plate and prodded with 25 mm standard steel rod 20 times within 8 seconds. Then the mould is placed on a standard vibrating table that vibrates at a speed of 12000 ± 400 vibration per minute. A hopper is secured at the top and the remaining mortar is filled. The mould is vibrated for two minutes and hopper removed. The top is finished with a knife or with a trowel and levelled. After 24 ± 1 hour mould is removed and cube is placed under clean water for curing. After specified period cubes are tested in compression testing machine, keeping the specimen on its level edges. Average of three cubes is reported as crushing strength. The compressive strength at the end of 3 days should not be less than 11.5 N/mm2 and that at the end of 7 days not less than 17.5 N/mm2. 1.4.4 Uses of Cement Cement is used widely for the construction of various structures. Some of them are listed below: (i) Cement slurry is used for filling cracks in concrete structures. (ii) Cement mortar is used for masonry work, plastering and pointing. (iii) Cement concrete is used for the construction of various structures like buildings, bridges. water tanks, tunnels, docks, harhours etc. (iv) Cement is used to manufacture lamp posts, telephone posts, railway sleepers, piles etc. (v) For manufacturing cement pipes, garden seats, dust bins, flower pots etc. cement is commonly used. (vi) It is useful for the construction of roads, footpaths, courts for various sports etc. 1.5 TIMBER Timber refers to wood used for construction works. In fact the word timber is derived from an old English word ‘Timbrian’ which means ‘to build’. A tree that yields good wood for construction is called ‘Standing Timber.’ After felling a tree, its branches are cut and its stem is roughly converted into pieces of suitable length, so that it can be transported to timber yard. This form of timber is known as rough timber. By sawing, rough timber is converted into various commercial sizes like planks, battens, posts, beams etc. Such form of timber is known as converted timber. 24 BASIC CIVIL ENGINEERING Timber was used as building material even by primitive man. Many ancient temples, palaces and bridges built with timber can be seen even today. 1.5.1 Classification of Timber Various bases are considered for the classification of timbers. The following are the important basis: (i) Mode of growth (ii) Modulus of elasticity (iii) Durability (iv) Grading (v) Availability. (i) Classification Based on Mode of Growth: On the basis of mode of growth trees are classified as (a) Exogeneous and (b) Endogeneous (a) Exogeneous Trees: These trees grow outward by adding distinct consecutive ring every year. These rings are known as annual rings. Hence it is possible to find the age of timber by counting these annual rings. These trees may be further divided into (1) coniferrous and (2) deciduous. Coniferrous trees are having cone shaped leaves and fruits. The leaves do not fall till new ones are grown. They yield soft wood. Deciduous trees are having broad leaves. These leaves fall in autumn and new ones appear in springs. They yield strong wood and hence they are commonly used in building construction. The classification as soft wood and hard wood have commercial importance. The difference between soft wood and hard wood is given below: 1. In soft wood annual rings are seen distinctly whereas in hard wood they are indistinct. 2. The colour of soft wood is light whereas the colour of hard wood is dark. 3. Soft woods have lesser strength in compression and shear compared to hard woods. 4. Soft woods are light and hard woods are heavy. 5. Fire resistance of soft wood is poor compared to that of hard wood. 6. The structure of soft wood is resinous while structure of hard wood is close grained. The cross-section of a exogeneous tree is as shown in the Fig. 1.7. The following components are visible to the naked eye: Outer Heart bark wood Pith Sap wood Inner bark Medullary rays Cambium layer Fig. 1.7. Cross-section of exogeneous tree TRADITIONAL MATERIALS 25 1. Pith: It is the inner most part of the tree and hence the oldest part of exogeneous tree when the plant becomes old, the pith dies and becomes fibrous and dark. It varies in size and shape. 2. Heart Wood: This is the portion surrounding pith. It is dark in colour and strong. This portion is useful for various engineering purpose. This is the dead part of wood. It consists of several annular rings. 3. Sap Wood: It is the layer next to heart wood. It denotes recent growth and contains sap. It takes active part in the growth of trees by allowing sap to move in upward direction. The annual rings of sap wood are less sharply divided and are light in colour. The sap wood is also known as alburnum. 4. Cambium Layer: It is a thin layer of fresh sap lying between sap wood and the inner bark. It contains sap which is not yet converted into sap wood. If the bark is removed and cambium layer is exposed to atmosphere, cells cease to be active and tree dies. 5. Inner Bark: It is a inner skin of tree protecting the cambium layer. It gives protection to cambium layer. 6. Outer Bark: It is the outer skin of the tree and consists of wood fibres. Sometimes it contains fissures and cracks. 7. Medullary Rags: These are thin radial fibres extending from pith to cambium layer. They hold annular rings together. In some of trees they are broken and some other they may not be prominent. (b) Endogeneous Trees: These trees grow inwards. Fresh fibrous mass is in the inner most portion. Examples of endogenous trees are bamboo and cane. They are not useful for structural works. (ii) Classification Based on Modulus of Elasticity: Young’s modulus is determined by conducting bending test. On this basis timber is classified as: Group A: E = 12.5 kN/mm2 Group B: E = 9.8 kN/mm2 to 12.5 kN/mm2 Group C: E = 5.6 kN/mm2 to 9.8 kN/mm2. (iii) Classification Based on Durability: Durability tests are conducted by the forest research establishment. They bury test specimen of size 600 × 50 × 50 mm in the ground to half their length and observe their conditions regularly over several years. Then timbers are classified as: High durability: If average life is more than 10 years. Moderate durability: Average life between 5 to 10 years. Low durability: Average life less than 5 years. (iv) Classification Based on Grading: IS 883-1970 classifies the structural timber into three grades-select grade, grade I and grade II. The classification is based on permissible stresses, defects etc. (v) Classification Based on Availability: Forest departments classify timbers based on the availability as X—Most common. 1415 m3 or more per year Y—Common. 355 m3 to 1415 m3 per year Z—Less common. Less than 355 m3 per year. 26 BASIC CIVIL ENGINEERING 1.5.2 Properties of Timber Properties of good timbers are: Colour: It should be uniform. Odour: It should be pleasant when cut freshly. Soundness: A clear ringing sound when struck indicates the timber is good. Texture: Texture of good timber is fine and even. Grains: In good timber grains are close. Density: Higher the density stronger is the timber. Hardness: Harder timbers are strong and durable. Warping: Good timber do not warp under changing environmental conditions. Toughness: Timber should be capable of resisting shock loads. Abrasion: Good timber do not deteriorate due to wear. This property should be looked into, if timber is to be used for flooring. Strength: Timber should have high strength in bending, shear and direct compression. Modulus of Elasticity: Timber with higher modulus of elasticity are preferred in construction. Fire resistance: A good timber should have high resistance to fire. Permeability: Good timber has low water permeability. Workability: Timber should be easily workable. It should not clog the saw. Durability: Good timber is one which is capable of resisting the action of fungi and insects attack Defects: Good timber is free from defects like dead knots, shakes and cracks. 1.5.3 Seasoning of Timber This is a process by which moisture content in a freshly cut tree is reduced to a suitable level. By doing so the durability of timber is increased. The various methods of seasoning used may be classified into: (i) Natural seasoning (ii) Artificial seasoning. (i) Natural Seasoning: It may be air seasoning or water seasoning. Air seasoning is carried out in a shed with a platform. On about 300 mm high platform timber balks are stacked as shown in Fig. 1.8. Care is taken to see that there is proper air circulation around each timber balk. Over a period, in a natural process moisture content reduces. A well seasoned timber contains only 15% moisture. This is a slow but a good process of seasoning. Water seasoning is carried out on the banks of rivers. The thicker end of the timber is kept pointing upstream side. After a period of 2 to 4 weeks the timber is taken out. During this period sap contained in the timber is washed out to a great extent. Then timber is stalked in a shed with free air circulation. TRADITIONAL MATERIALS 27 A Roof Roof Timber Members 300 cm Spacers Platform B 150 cm 30 cm Pillars Elevation Section on AB Fig. 1.8. Air seasoning (ii) Artificial Seasoning: In this method timber is seasoned in a chamber with regulated heat, controlled humidity and proper air circulation. Seasoning can be completed in 4 to 5 days only. The different methods of seasoning are: (a) Boiling (b) Kiln seasoning (c) Chemical seasoning (d) Electrical seasoning. (a) Boiling: In this method timber is immersed in water and then water is boiled for 3 to 4 hours. Then it is dried slowly. Instead of boiling water hot steam may be circulated on timber. The process of seasoning is fast, but costly. (b) Kiln Seasoning: Kiln is an airtight chamber. Timber to be seasoned is placed inside it. Then fully saturated air with a temperature 35°C to 38°C is forced in the kiln. The heat gradually reaches inside timber. Then relative humidity is gradually reduced and temperature is increased, and maintained till desired degree of moisture content is achieved. The kiln used may be stationary or progressive. In progressive kiln the carriages carrying timber travel from one end of kiln to other end gradually. The hot air is supplied from the discharging end so that temperature increase is gradual from charging end to discharging end. This method is used for seasoning on a larger scale. (c) Chemical Seasoning: In this method, the timber is immersed in a solution of suitable salt. Then the timber is dried in a kiln. The preliminary treatment by chemical seasoning ensures uniform seasoning of outer and inner parts of timber. (d) Electrical Seasoning: In this method high frequency alternate electric current is passed through timber. Resistance to electric current is low when moisture content in timber is high. As moisture content reduces the resistance reduces. Measure of resistance can be used to stop seasoning at appropriate level. 28 BASIC CIVIL ENGINEERING However it is costly process. This technique has been tried in some plywood industries but not in seasoning of timber on mass scale. 1.5.4 Defects in Timber Various defects which are likely to occur in timber may be grouped into the following three: (i) Due to natural forces (ii) Due to defective seasoning and conversions. (iii) Due to attack by fungi and insects. (i) Defects due to Natural Forces: The following defects are caused by natural forces: (a) Knots (b) Shakes (c) Wind cracks (d) Upsets (a) Knots: When a tree grows, many of its branches fall and the stump of these branches in the trunk is covered. In the sawn pieces of timber the stump of fallen branches appear as knots. Knots are dark and hard pieces. Grains are distorted in this portion. Figure 1.9 shows some varieties of knots. If the knot is intact with surrounding wood, it is called live knot. If it is not held firmly it is dead knot. Live knot Decayed knots Fig. 1.9. Knots (b) Shakes: The shakes are cracks in the timber which appear due to excessive heat, frost or twisting due to wind during the growth of a tree. Depending upon the shape and the positions shakes can be classified as star shake, cup shake, ring shakes and heart shakes [Ref. Fig. 1.10] Cup shakes Shakes Star shakes Ring shake Heart Cup shakes Heart shakes Ring shakes Star shakes Fig. 1.10. Shakes TRADITIONAL MATERIALS 29 (c) Wind Cracks: These are the cracks on the outside of a log due to the shrinkage of the exterior surface. They appear as shown in Fig. 1.11. Wind cracks Fig. 1.11. Wind cracks (d) Upsets: Figure 1.12 shows a typical upset in a timber. This type of defect is due to excessive compression in the tree when it was young. Upset is an injury by crushing. This is also known as rupture. Fig. 1.12. Upset (ii) Defects due to Defective Seasoning and Conversion: If seasoning is not uniform, the converted timber may warp and twist in various directions. Sometimes honey combining and even cracks appear. This type of defects are more susceptible in case of kiln seasoning. In the process of converting timber to commercial sizes and shapes the following types of defects are likely to airse: chip marks, torn grain etc. (iii) Defects due to Fungi and Insects Attack: Fungi are minute microscopic plant organism. They grow in wood if moisture content is more than 20°C and exposed to air. Due to fungi attack rotting of wood, takes place. Wood becomes weak and stains appear on it. Beetles, marine borers and termites (white ants) are the insects which eat wood and weaken the timber. Some woods like teak have chemicals in their compositions and resist such attacks. Other woods are to be protected by chemical treatment. 1.5.5 Preservation of Timber Preservation of timber means protecting timber from fungi and insects attack so that its life is increased. Timber is to be seasoned well before application of preservatives. The following are the widely used preservatives: 1. Tar 2. Paints 30 BASIC CIVIL ENGINEERING 3. Chemical salt 4. Creosote 5. ASCO 1. Tar: Hot coal tar is applied to timber with brush. The coating of tar protects the timber from the attack of fungi and insects. It is a cheapest way of protecting timber. Main disadvantage of this method of preservation is that appearance is not good after tar is applied it is not possible to apply other attractive paints. Hence tarring is made only for the unimportant structures like fence poles. 2. Paints: Two to three coats of oil paints are applied on clean surface of wood. The paint protects the timber from moisture. The paint is to be applied from time to time. Paint improves the appearance of the timber. Solignum paint is a special paint which protects the timber from the attack of termites. 3. Chemical salt: These are the preservatives made by dissolving salts in water. The salts used are copper sulphate, masonry chloride, zinc chloride and sodium fluoride. After treating the timber with these chemical salt paints and varnishes can be applied to get good appearance. 4. Creosote: Creosote oil is obtained by distillation of coal tar. The seasoned timber is kept in an air tight chamber and air is exhausted. Then creosote oil is pumped into the chamber at a pressure of 0.8 to 1.0 N/mm2 at a temperature of 50°C. After 1 to 2 hours timber is taken out of the chamber. 5. ASCO: This preservative is developed by the Forest Research Institute, Dehradun. It consists of 1 part by weight of hydrated arsenic pentoxide (As2O5, 2 H2O), 3 parts by weight of copper sulphate (CuSO4⋅5 H2O) and 4 parts by weight of potassium dichromate (K2Cr2O7) or sodium dichromate (Na2Cr2O7⋅2 H2O). This preservative is available in powder form. By mixing six parts of this powder with 100 parts of water, the solution is prepared. The solution is then sprayed over the surface of timber. This treatment prevents attack from termites. The surface may be painted to get desired appearance. 1.5.6 Uses of Timber Timber is used for the following works: 1. For heavy construction works like columns, trusses, piles. 2. For light construction works like doors, windows, flooring and roofing. 3. For other permanent works like for railway sleepers, fencing poles, electric poles and gates. 4. For temporary works in construction like scaffolding, centering, shoring and strutting, packing of materials. 5. For decorative works like showcases and furnitures. 6. For body works of buses, lorries, trains and boats 7. For industrial uses like pulps (used in making papers), card boards, wall papers 8. For making sports goods and musical instruments. TRADITIONAL MATERIALS 31 QUESTIONS 1. Discuss the geological classification of stones. 2. Briefly explain physical and chemical classification of rocks. 3. Discuss the characteristics of good building stones. 4. Explain any three tests performed on stones to find their properties. 5. Write various uses of stones in civil engineering works. 6. Name any four stones along with their characteristics and uses. 7. What do you understand by the term brick? Explain different types of bricks. 8. Describe the properties of good bricks. 9. Explain briefly any four types of tests conducted on bricks in the laboratories to acertain their qualities. 10. What are the field tests carried out to determine the qualities of the brick? 11. Explain classification of bricks based on their quality. 12. What are the different uses of bricks? 13. Differentiate between fat lime and hydraulic lime. 14. Briefly explain IS code classification of lime as class A, B, C, D and E. 15. What are the test carried on lime? Briefly explain. 16. List the various uses of lime. 17. What is cement? How quick setting and rapid hardening cement differs from portland cement? 18. Write short notes on (i) Low heat cement (ii) Pozzulana cement (iii) Coloured cement and (iv) Expanding cement. 19. State chemical and physical properties of portland cement. 20. What is standard consistency of cement? How it is determined in the laboratory? 21. Explain the terms initial setting time and final setting time of cement. How they are determined? 22. Explain the following test procedure on cement: (i) Soundness test (ii) Crushing strength test 23. List various uses of cement. 24. Explain the terms: timber, standing timber, rough timber and converted timber. 25. Draw and explain cross-section of an exogeneous tree. 32 BASIC CIVIL ENGINEERING 26. Differentiate between (i) exogeneous and endogeneous trees (ii) soft wood and hard wood. 27. What are the requirements of good timber? 28. What is meant by seasoning of timber? Distinguish between natural and artificial seasoning. 29. Write short notes on: (i) Air seasoning (ii) Water seasoning (iii) Kiln seasoning and (iv) Chemical seasoning. 30. Explain various defects in timber due to natural forces. 31. Write short notes on defects in timber due to (i) defective seasoning and conversion (ii) attack by fungi and insects. 32. What do you understand by the term preservation of timber? Briefly explain the different methods of preservation adopted. 33. State different uses of timber. CHAPTER 2 Mortars Mortar is an intimate mixture of binding material, fine aggregate and water. When water is added to the dry mixture of binding material and the inert material, binding material develops the property that binds not only the inert material but also the surrounding stones and bricks. If the cement is the binding material, then the mortar is known as cement mortar. Other mortars commonly used are lime mortar and mud mortar. The inert material used is sand. In this chapter, first an introduction is given to the inert material sand and then the proportioning, mixing, curing, properties and uses of different mortars is explained. At the end of the chapter various tests conducted on mortars is presented. 2.1 SAND Sand is a natural product which is obtained as river sand, nalla sand and pit sand. However sea sand should not be used for the following reasons: 1. It contains salt and hence structure will remain damp. The mortar is affected by efflorenscence and blisters appear. 2. It contains shells and other organic matter, which decompose after some time, reducing the life of the mortar. Sand may be obtained artificially by crushing hard stones. Usually artificial sand is obtained as a by-product while crushing stones to get jelly (coarse aggregate). Sand is used in mortar and concrete for the following purpose: 1. It sub-divides the paste of binding material into thin films and allows it to adhere and spread. 2. It fills up the gap between the building blocks and spreads the binding material. 3. It adds to the density of the mortar. 4. It prevents the shrinkage of the cementing material. 5. It allows carbon dioxide from the atmosphere to reach some depth and thereby improve setting power. 6. The cost of cementing material per unit volume is reduced as this low cost material increases the volume of mortar. 33 34 BASIC CIVIL ENGINEERING 7. Silica of sand contributes to formation of silicates resulting into the hardened mass. The properties of good sand are: 1. It should be chemically inert. 2. It should be free from organic or vegetable matter. 3. It should be free from salt. 4. It should contain sharp, angular and coarse grains. 5. It should be well graded. 6. It should be hard. 2.2 CEMENT MORTAR For preparing mortar, first a mixture of cement and sand is made thoroughly mixing them in dry condition. Water is gradually added and mixed with shovels. The cement to sand proportion recommended for various works is as shown is Table 2.1 Table 2.1. Cement to sand proportions for various works S. No. Works Cement: Sand 1 Masonry works 1:6 to 1:8 2 Plastering masonry 1:3 to 1:4 3 Plastering concrete 1:3 4 Pointing 1:2 to 1:3 Curing: Cement gains the strength gradually with hydration. Hence it is necessary to see that mortar is wet till hydration has taken place. The process to ensure sufficient moisture for hydration after laying mortar/concrete is called curing. Curing is ensured by spraying water. Curing normally starts 6–24 hours after mortar is used. It may be noted that in the initial period water requirement is more for hydration and gradually it reduces. Curing is recommended for 28 days. Properties of Cement Mortar: The following are the important properties of cement mortar: 1. When water is added to the dry mixture of cement and sand, hydration of cement starts and it binds sand particles and also the surrounding surfaces of masonry and concrete. 2. A mix richer than 1:3 is prone to shrinkage. 3. Well proportioned mortar provides impervious surface. 4. Leaner mix is not capable of closing the voids in sand and hence the plastered surface is porous. 5. The strength of mortar depends upon the proportion of cement and sand. Strengths obtained with various proportion of cement and sand is shown in Table 2.2. MORTARS 35 Table 2.2 S. No. Cement: Sand Compressive Strength 1 1:3 10 N/mm2 2 1:4 7.5 N/mm2 3 1:5 5.0 N/mm2 4 1:6 3.0 N/mm2 5 1:8 0.7 N/mm2 Uses of Cement Mortar Mortar is used 1. to bind masonry units like stone, bricks, cement blocks. 2. to plaster slab and walls make them impervious. 3. to give neat finishing to walls and concrete works. 4. for pointing masonry joints. 5. for preparing building blocks. 6. as a filler material in ferro cement works. 7. to fill joints and cracks in walls. 8. as a filler material in stone masonry. 2.3 LIME MORTAR Fat lime and hydraulic limes are used for making lime mortar. If fat lime is used sand mixed is normally 2 to 3 times its volume. If hydraulic lime is used sand mixed is only 2 times the volume of lime. Lime is prepared by pounding, if quantity required is small or by grinding, if the required quantity is more. Pounding: For pounding pits are formed in hard grands. The size of pit is usually 1.80 m long, 0.4 m wide and 0.5 m deep. It is provided with lining of bricks or stones. Lime and sand dry mixed with required proportion is placed in the pit. Small quantity of water is added at intervals. In each interval the mix is pounded with wooden pounders and mortar is turned up and down. The process is continued till uniform colour and desired consistancy is achieved. Grinding: This is the better way of getting good mix. The grinding may be carried out in bullock driven grinding mill or in power driven grinding mill. Figure 2.1 shows a typical bullock driven grinding mill. It consists of a circular trench of radius 3 to 4.5 m, 0.3 m wide and 0.4 m deep. A wooden shaft pivoted at centre carries a stone wheel of width just 50 mm to 100 mm less than that of trench. Bullock drive this wheel in the trench for grinding mortar. The dry mix is placed in the trench. Water is added gradually and bullock driven stone wheels grind the mix. A worker turns the mix up and down regularly. This method of preparing mortar needs 6 hours and can produce about 1.7 m3 of mortar. 36 BASIC CIVIL ENGINEERING Bullock to be attached at this end Stone wheel Pivot Shaft Mortar G L Circular trench Fig. 2.1. Bullock driven grinding mill Figure 2.2 shows a typical power driven grinding mill used for preparing lime mortar. Two rollers rotate in a pan of diameter 1.8 to 2.4 m. Either pan or roller is rotated with the help of oil engine or electric power. During mixing required quantity of water is added gradually. Driving Stone Rollers pully Frame Steel pan + + Fig. 2.2. Power driven grinding mill Lime mortar is also having good grinding property. Fat lime mortar is used for plastering while hydraulic lime mortar is used for masonry construction. This mortar was considered cheap in olden days and was commonly used in small towns. However the combersome process of preparation and ease in availibility of cement in market has almost replaced the use of lime mortar. 2.4 MUD MORTAR Clay lumps are collected and are wetted with water and allowed to mature for 1 or 2 days. It is kneeded well until it attains required consistancy. Sometimes fibrous materials like gobber is added in the mix. It prevents cracks in the plaster. If plaster is to be used for outer walls, it is sprayed or painted with bitumen. It is cheap mortar. Its durability is less. It is normally used for the construction of temporary sheds and cheap houses in rural areas. MORTARS 37 2.5 SPECIAL MORTAR The following are some of the special mortars: 1. Cement clay mortar 2. Gauged mortar 3. Decorative mortar. 1. Cement Clay Mortar: Quality of clay mortar can be improved by adding cement to the mix. Normal proportion of clay to cement is 1:1. It maintains the economy to some extent and there is sufficient improvements in the durability of mud-mortar. 2. Gauged Mortar: It is the mortar obtained by adding cement to lime mortar. The usual proportion of cement, lime and sand are 1:1:6, 1:2:9 and 1:3:12. This mortar is to be used within half an hour after mixing cement. Obviously, it is cheaper than cement mortar and its quality is between that of cement mortar and lime mortar. 3. Decorative Mortar: These mortars are obtained by using coloured cement. They are used to give pleasant appearance to outer walls. 2.6 TESTS ON MORTAR The following tests are conducted on the prepared mortars to ensure their quality: 1. Crushing Test 2. Tensile Strength Test 3. Adhesive Test. 1. Crushing Test: This test is carried out on a brick work with the mortar. This brick work is crushed in a compression testing machine and the load is noted down. Then the crushing strength is obtained as load divided by cross-sectional area. 2. Tensile Strength Test: The mortar prepared is placed in a mould of bricket which has central cross-sectional area as 38 mm 38 mm × 38 mm. After curing the briquette [Fig. 2.3] is pulled under the grips of tensile testing machine. The ultimate load Elevation noted. Then the tensile strength of mortar is load divided by the central cross-sectional area. 3. Adhesive Test: Two bricks are joined together with 38 mm 76 mm mortar to be tested as shown in Fig. 2.4. The upper brick is susp

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