Concrete Technology: Theory and Practice PDF

Multicolour Illustrative Edition CONCRETE TECHNOLOGY THEORY AND PRACTICE M.S. SHETTY BE, ME, FICI, FIIBE, FIE, MACCE Technical Advisor, MC Bauchemie (Ind) Pvt. Ltd. Principal Technical Consultant, Grasim...

Multicolour Illustrative Edition CONCRETE TECHNOLOGY THEORY AND PRACTICE M.S. SHETTY BE, ME, FICI, FIIBE, FIE, MACCE Technical Advisor, MC Bauchemie (Ind) Pvt. Ltd. Principal Technical Consultant, Grasim Industries, Ltd. Consultant to IMCC Delhi Metro Corporation Formerly Senior Prof. and Head of Department of Construction Engineering College of Military Engineering (CME), Pune Ministry of Defence S. CHAND & COMPANY LTD. (An ISO 9001 : 2000 Company) Ram Nagar, New Delhi - 110 055 (i)  CONTENTS Chapter No. Page No. 1. CEMENT 1–26 General 1 Early History of Modern Cement 2 Manufacture of Portland Cement 5 Wet Process 6 Dry Process 9 Chemical Composition 14 Hydration of Cement 17 Heat of Hydration 18 Calcium Silicate Hydrates 19 Calcium Hydroxide 20 Calcium Aluminate Hydrates 21 Structure of Hydrated Cement 22 Transition Zone 22 Water Requirements for Hydration 25 2. TYPES OF CEMENT AND TESTING OF CEMENT 27-65 Types of Cement 28 ASTM Classification 28 Ordinary Portland Cement 29 Rapid Hardening Cement 30 Extra Rapid Hardening Cement 30 Sulphate Resisting Cement 31 Portland Slag Cement 31 Application of GGBS Concrete 33 Quick Setting Cement 33 Super Sulphated Cement 34 Low Heat Cement 34 Portland Pozzolana Cement 35 Advantages of PPC 36 Grading of PPC 37 Application 37 Air-Entraining Cement 37 Coloured Cement 38 Hydrophobic Cement 39 Masonry Cement 39 Expansive Cement 40 IRS-T40 Special Grade Cement 40 Oil-Well Cement 41 Rediset Cement 41 (xi)  Properties of Rediset 41 Applications 42 High Alumina Cement 42 Hydration of High Alumina Cement 42 High Alumina Cement Concrete 43 Refractory Concrete 44 Very High Strength Cement 45 Macro-defect free Cement 45 Densely Packed System 45 Pressure Densification and Warm Pressing 45 High Early Strength Cement 46 Pyrament Cement 46 Magnesium Phosphate Cement 46 Testing of Cement 47 Field Testing 47 Fineness Test 48 Sieve Test 49 Air Permeability Method 49 Standard Consistency Test 50 Setting Time Test 50 Initial Setting Time 52 Final Setting Time 53 Strength Test 53 Soundness Test 54 Heat of Hydration 55 Chemical Composition Test 56 Test Certificate 56 3. AGGREGATES AND TESTING OF AGGREGATES 66-118 General 66 Classification 67 Source 67 Aggregates from Igneous Rocks 68 Aggregates from Sedimentary Rocks 68 Aggregates from Metamorphic Rocks 68 Size 69 Shape 70 Texture 73 Measurement of Surface Texture 74 Strength 74 Aggregate Crushing Value 75 Aggregate Impact Value 76 Aggregate Abrasion Value 76 Deval Attrition Test 76 Dorry Abrasion Test 76 Los Angeles Test 77 Modulus of Elasticity 77 Bulk Density 78 (xii)  Specific Gravity 78 Absorption and Moisture Content 78 Bulking of Aggregate 80 Measurement of Moisture Content of Aggregates 81 Drying Method 82 Displacement Method 82 Calcium Carbide Method 82 Electrical Meter Method 82 Automatic Measurement 82 Cleanliness 83 Soundness of Aggregate 85 Alkali-Aggregate Reaction 85 Factors Promoting Alkali-Aggregate Reaction 86 High Alkali Content in Cement 88 Availability of Moisture 89 Temperature Condition 89 Mechanism of Deterioration of Concrete 89 Control of Alkali Aggregate Reaction 89 Thermal Properties 90 Grading of Aggregates 91 Sieve Analysis 93 Combining Aggregates to obtain Specified Gradings 94 Specific Surface and Surface Index 96 Standard Grading Curve 100 Crushed Sand 105 Gap Grading 107 Testing of Aggregates 107 Test for Determination of Flakiness Index 107 Test for Determination of Elongation Index 109 Test for Determination of Clay and Fine Silt 110 Test for Determination of Organic Impurities 111 Test for Determination of Specific Gravity 112 Test for Bulk Density and Voids 112 Mechanical Properties of Aggregates 113 Test for Aggregate Crushing Value 113 Test for “Ten per cent Fines” Value 114 Test for Aggregate Impact Value 114 Test for Aggregate Abrasion Value 115 4. WATER 119-123 Qualities of Water 119 Use of Sea Water for Mixing Concrete 122 5. ADMIXTURES AND CONSTRUCTION CHEMICALS 124-217 General 124 Admimxtures 125 Construction Chemicals 126 Plasticizers (Water Reducers) 126 (xiii)  Action of Plasticizers 128 Dispersion 128 Retarding Effect 128 Superplasticizers (High Range Water Reducers) 129 Classification of Superplasticizer 130 Effect of Superplasticizers on Fresh Concrete 131 Compatibility of Superplasticizers and Cement 131 Factors Effecting Workability 136 Type of Superplasticizers 136 Dosage 136 Mix Composition 137 Variability in Cement Composition 137 Mixing Procedure 137 Equipment 138 Site Problems in the use of Superplasticizers 138 Slump Loss 140 Steps for Reducing Slump Loss 140 Other Potential Problems 142 Effect of Superplasticizers on the Properties of Hardened Concrete 143 New Generation Superplasticizers 144 Carboxylated Acrylic Ester (CAE) 144 Multicarboxylatether (MCE) 147 Retarders 148 Retarding Plasticizers 149 Accelerators 149 Accelerating Plasticizers 158 Air-entraining Admixtures 158 Air-entraining Agents 159 Factors Affecting Amount of Air-entrainment 159 The Effect of Air-entrainment on the Properties of Concrete 160 Resistance to Freezing and Thawing 161 Effect on Workability 162 Effect on Strength 163 Effect on Segregation and Bleeding 166 Effect on Permeability 169 Effect on Chemical Resistance 169 Effect on Sand, Water and Cement Content 169 Unit Weight 170 Alkali Aggregate Reaction 170 Modulus of Elasticity 170 Abrasion Resistance 170 Optimum Air Content in Concrete 171 Measurement of Air Content 171 Gravimetric Method 171 Volumetric Method 173 Pressure Method 173 The Water Type Meter 173 Pozzolanic or Mineral Admixtures 174 (xiv)  Pozzolanic Materials 175 Natural Pozzolans 175 Artificial Pozzolans 175 Fly Ash 176 Effect of Fly Ash on Fresh Concrete 179 Effect of Fly Ash on Hardened Concrete 180 Durability of Concrete 180 High Volume Fly Ash Concrete (HVFA) 180 Properties of (HVFA) Fresh Concrete 181 Bleeding and Setting Time 181 Heat of Hydration 182 Curing of (HVFA) Concrete 182 Mechanical Properties of (HVFA) Concrete 182 Durability of (HVFA) Concrete 182 Use of High Volume Fly Ash 183 Silica Fume 183 Indian Scenario 184 Available Forms 184 Pozzolanic Action 185 Influence on Fresh Concrete 185 Influence on Hardened Concrete 186 Mixing 186 Curing 186 Rice Husk Ash 186 Surkhi 187 Metakaolin 188 Ground Granulated Blast Furnace Slag (GGBS) 189 Performance of GGBS in Concrete 191 Fresh Concrete 191 Hardened Concrete 191 Damp-Proofing and Water-Proofing Admixtures 192 Gas Forming Agents 193 Air-Detraining Agents 194 Alkali Aggregate Expansion Inhibitors 194 Workability Agents 195 Grouting Agents 195 Corrosion Inhibiting Agents 196 Bonding Admixtures 196 Fungicidal, Germicidal and Insecticidal Admixtures 196 Colouring Agents 197 Miscellaneous Admixtures 197 Damp-proofers 197 Construction Chemicals 198 Membrane Forming Curing Compounds 200 Drying Behaviour 201 Types of Curing Compounds 201 Application Procedure 201 General Characteristics 202 (xv)  Water Retention Test 203 Polymer Bonding Agents 204 Polymer Modified Mortar for Repair and Maintenance 204 Mould Releasing Agents 205 Installation Aids 205 Floor Hardners and Dust Proofers 206 Non-Shrink High Strength Grout 207 Surface Retarders 207 Bond Aid for Plastering 208 Ready to use Plaster 208 Guniting Aid 208 Construction Chemicals for Waterproofing 209 Integral Waterproofing Compound 210 Acrylic Based Polymer Coatings 210 Mineral Based Polymer Modified Coatings 211 Protective and Decorative Coatings 212 Chemical DPC 212 Waterproofing Adhesives for Tile, Marble and Granite 213 Silicone based Water Repellant Materials 214 Injection Grout for Cracks 214 Joint Sealants 215 Concrete Repair Systems 215 Stages for Repair Works 215 6. FRESH CONCRETE 218-297 Workability 219 Factors Affecting Workability 220 Water Content 220 Mix Proportions 220 Size of Aggregate 221 Shape of Aggregate 221 Surface Texture 221 Grading of Aggregate 221 Use of Admixture 221 Measurement of Workability 222 Slump Test 222 K-Slump Tester 224 Remarks 227 Compacting Factor Test 227 Flow Test 228 Flow Table Apparatus 229 Accessory Procedure 230 Kelly Ball Test 231 Vee Bee Consistometer Test 232 Segregation 233 Bleeding 234 Method of Test for Bleeding 236 (xvi) Setting Time of Concrete 236 Process of Manufacture of Concrete 238 Batching 238 Volume Batching 238 Weigh Batching 240 Measurement of Water 241 Mixing 241 Hand Mixing 242 Machine Mixing 242 Mixing Time 245 Retempering 246 Maintenance of Mixer 247 Transporting 247 Mortar Pan 247 Wheel Barrow 248 Crane Bucket and Ropeway 249 Truck Mixer and Dumper 249 Belt Conveyors 249 Chute 249 Skip and Hoist 249 Transit Mixer 250 Pumps and Pipeline 251 Development of Concrete Pump 251 Concrete Pumps 251 Types of valve 252 Pipeline and Couplings 252 Laying the Pipeline 253 Capabilities of Concrete Pump 253 Pumpable Concrete 254 Design Consideration 255 Choosing Correct Pump 256 Common Problems 258 Clearing Blockages 259 Placing Concrete 259 Form Work 261 Stripping Time 261 Under Water Concreting 262 Compaction of Concrete 265 Hand Compaction 266 Compaction by Vibration 267 Internal Vibrator 268 Formwork Vibrator 268 Table Vibrator 269 Platform Vibrator 269 Surface Vibrator 269 Compaction by Pressure and Jolting 269 Compaction by Spinning 269 Vibratory Roller 269 (xvii)  General Points on Using Vibrators 270 Further Instructions on use of Vibrators 270 Height of Concrete Layer 271 Depth of Immersion of Vibrator 271 Spacing and Number of Insertion Positions 272 Speed of Insertion 272 Duration of Vibration 273 Vibrating Concrete at Junctions 273 Vibrating Reinforced Concrete 273 Vibrating Near the Form Work 273 Vibrating High Walls and Columns 276 Over Vibration 276 Output of Immersion Vibrations 276 Revibration 276 Vibration of Light-weight Concrete 277 Curing of Concrete 277 Curing methods 279 Water curing 279 Membrane curing 280 Application of Heat 281 Steam curing 282 High Pressure Steam curing 287 Curing by Infra-red Radiation 288 Electrical curing 289 Miscellaneous Methods of Curing 289 When to Start Curing 289 Finishing 291 Formwork Finishes 291 Surface Treatment 292 Exposed Aggregate Finish 293 Bush Hammering 293 Applied Finish 293 Miscellaneous Finish 294 Wear Resistant Floor Finish 294 Requirement of a Good Finish 295 Grinding and Polishing 295 Craziness 295 Whisper Concrete Finish 296 7. STRENGTH OF CONCRETE 298-324 General 298 Water / Cement Ratio 299 Gel / Space Ratio 301 Gain of Strength with Age 303 Accelerated Curing Test 306 Maturity Concept of Concrete 306 Effect of Maximum Size of Aggregate 311 (xviii)  Relation between Compressive and Tensile Strength 311 Centre Point and Third Point Loading 314 Bond Strength 315 Aggregate Cement Bond Strength 316 High Strength Concrete 318 Seeding 319 Revibration 319 High Speed Slurry Mixing 319 Use of Admixture 319 Inhibition of Cracks 319 Sulphur Impregnation 319 Use of Cementitious Aggregate 319 Ultra High Strength Concrete 319 Compaction by Pressure 319 Helical Binding 320 Polymer Concrete 320 Reactive Powder Concrete 320 High-Performance Concrete (HPC) 321 Aggregates for HPC 322 8. ELASTICITY, CREEP AND SHRINKAGE 325-348 Elastic Properties of Aggregate 325 Relation between Modulus of Elasticity and Strength 328 Factors Affecting Modulus of Elasticity 329 Dynamic Modulus of Elasticity 331 Poison’s Ratio 332 Creep 332 Rheological Representation of Creep 333 Macroscopic Rheological Approach 333 Microscopic Rheological Approach 334 Hydration under Sustained Load 335 Measurement of Creep 336 Factors Affecting Creep 339 Influence of Aggregate 339 Influence of Mix Proportions 339 Influence of Age 339 Effect of Creep 339 Shrinkage 340 Plastic Shrinkage 341 Drying Shrinkage 343 Factors Affecting Shrinkage 344 Moisture Movement 347 Autogeneous Shrinkage 347 Carbonation Shrinkage 347 9. DURABILITY OF CONCRETE 349-419 General 349 Strength and Durability Relationship 350 (xix) Volume Change in Concrete 352 Definition of Durability 352 Significance of Durability 352 Impact of W/C Ratio on Durability 353 Permeability 354 Permeability of Cement Paste 354 Permeability of Concrete 356 Interaction between Permeability, Volume Change and Cracking 357 Factors Contributing to Cracks in Concrete 361 Plastic Shrinkage Cracks 361 Settlement Cracks 362 Bleeding 362 Delayed Curing 362 Constructional Effects 363 Early Frost Damage 363 Unsound Materials 364 Shrinkage 364 Drying Shrinkage 365 Thermal Shrinkage 365 Thermal Conductivity 367 Thermal Diffusivity 368 Specific Heat 370 Coefficient of Thermal Expansion 370 Mass Concrete 372 Thermal Expansion and Shrinkage 373 Extensibility 375 Joints in Concrete 376 Construction Joints 376 Expansion Joints 376 Contraction Joints 379 Isolation Joints 381 Concrete Subjected to High Temperature 382 Fire Resistance 382 Freezing and Thawing 383 Deicing Effects of Salts 387 Moisture Movements 387 Transition Zone 387 Biological Process 388 Structural Design Defficiencies 388 Chemical Action 389 Sulphate Attack 389 Methods of Controlling Sulphate Attack 390 Use of Sulphate Resisting Cement 390 Quality of Concrete 390 Use of Air-entrainment 390 Use of Pozzolana 390 High Pressure Steam Curing 390 Use of High Alumina Cement 390 (xx)  Alkali-Aggregate Reaction 394 Acid Attack 395 Concrete in Sea Water 396 Carbonation 398 Rate of Carbonation 398 Measurement of Depth of Carbonation 400 Chloride Attack 400 Corrosion of Steel (Chloride Induced) 402 Corrosion Control 404 Metallurgical Methods 405 Corrosion Inhibitors 405 Coatings to Reinforcement 406 Fusion Bonded Epoxy Coating 407 Galvanised Reinforcement 408 Cathodic Protection 408 Coatings to Concrete 408 Design and Detailing 409 Nominal Cover to Reinforcement 409 Crack Width 411 Deterioration of Concrete by Abrasion, Erosion and Cavitation 411 Effects of Some Materials on Durability 412 Action of Mineral Oils 412 Action of Organic Acids 412 Vegetables and Animal Oils and Fats 412 Action of Sugar on Concrete 413 Action of Sewage 413 Surface Treatments of Concrete 413 Maximum Cement Content 415 Concluding Remarks on Durability 418 10. TESTING OF HARDENED CONCRETE 420-457 Compression Test 421 Moulds 422 Compacting 422 Compaction by Hand 423 Compaction by Vibration 423 Capping Specimens 424 Neat cement 424 Cement mortar 424 Sulphur 424 Hard plaster 425 Curing 425 Making and Curing Compression Test Specimen in the Field 425 Failure of Compression Specimen 425 Effect of Height / Diameter Ratio on Strength 427 Comparison between Cube and Cylinder Strength 428 Flexural Strength of Concrete 428 Determination of Tensile Strength 429 (xxi)  Procedure 431 Placing of Specimen in the Testing Machine 431 Indirect Tension Test Methods 433 Ring Tension Test 434 Advantage of ring tension test 434 Limitations of ring tension test 434 Double Punch Test 434 Factors Influencing the Strength Results 435 Test Cores 436 Strength of cores 437 Non-Destructive Testing Methods 437 Schmidt’s Rebound Hammer 439 Limitation 439 Rebound number and strength of concrete 440 Penetration Techniques 441 Pullout test 444 Dynamic or Vibration Method 444 Resonant Frequency Method 445 Usefulness of resonant frequency method 445 Pulse Velocity Method 446 Techniques of measuring pulse velocity through concrete 447 Factors affecting the measurement of pulse velocity 447 Smoothness of contact surace under test 447 Influence of path length on pulse velocity 448 Temperature of concrete 448 Moisture condition of concrete 448 Presence of reinforcement 448 Accuracy of measurement 449 Applications 449 Establishing uniformity of Concrete 449 Establishing acceptance criteria 449 Determination of pulse modulus of clasticity 450 Estimation of strength of concrete 450 Determination of setting characteristics of concrete 450 Studies on durability of concrete 450 Measurement of deteriration of concrete due to fire exposure 451 Relationship between Pulse Velocity and Static Young’s Modulus of Elasticity 452 Combined Methods 452 Radioactivity Methods 452 Nuclear Methods 453 Magnetic Methods 454 Electrical Methods 454 Tests on Composition of Hardened Concrete 454 Determination of Cement Content 454 Determination of Original w/c Ratio 455 Physical Method 455 Accelerated Curing Test 456 (xxii) 11. CONCRETE MIX DESIGN 458-503 General 458 Concept of Mix Design 459 Variables in Proportioning 459 Various Methods of Proportioning 460 Statistical Quality Control of Concrete 460 Common Terminologies 461 Calculation of Standard Deviation and Coefficient of Variation 463 Relation between Average Design Strength and Specified Minimum Strength 463 American Concrete Institute Method of Mix Design 466 Data to be Collected 466 Example: ACI Committee 211.1–91 Method 471 Road Note Number 4 Method 473 DOE Method of Concrete Mix Design 474 Example — DOE Method 477 Concrete Mix Design Procedure for Concrete with Fly-Ash 482 Example of Mix Design with Fly-Ash with DOE Method 482 Mix Design for Pumpable Concrete 484 Example: Basic Design Calculations for a Pumpable Concrete Mix 488 Indian Standard Recommended Method of Concrete Mix Design 489 Illustrative Example of Concrete Mix Design 495 Rapid Method 498 Steps of Mix Design based on rapid method 499 Sampling and Acceptance Criteria 500 Frequency of Sampling 500 Test Specimen 501 Test Results 501 Acceptance Criteria 502 Compressive Strength 502 Flexural Strength 502 Inspection and Testing of Structures 502 Core Test 502 Load Test for Flexural Member 502 Non-destructive Test 503 12. SPECIAL CONCRETE AND CONCRETING METHODS 504-607 Special concrete 504 Light-weight concrete 506 Pumice 506 Diatomite 507 Scoria 507 Volcanic Cinders 507 Saw Dust 507 Rice Husk 507 Brick Bats 508 Cinder, Clinker and Breeze 508 Foamed Slag 508 Bloated Clay 509 Sintered Fly Ash 509 (xxiii)  Exfoliated Vermiculite 509 Expanded Perlite 509 Light-weight Aggregate Concrete 510 Structural Light-weight Concrete 513 Workability 513 Design of Light-weight Aggregate Concrete Mix 514 Mixing Procedure 514 Aerated Concrete 514 Proporties 516 No-fines Concrete 517 Mix Proportion 517 Drying Shrinkage 518 Thermal Conductivity 519 Application 519 High Density Concrete 520 Types of Radiation Hazards 521 Shielding Ability of Concrete 521 Concrete for Radiation Shielding 522 Sulphur-Infiltrated Concrete 525 Application 526 Fibre Reinforced Concrete 526 Fibres used 527 Factors Effecting Properties 528 Relative Fibre Matrix Stiffness 528 Volume of Fibres 528 Aspect Ratio of Fibres 529 Orientation of Fibres 529 Workability 530 Size of coarse Aggregate 530 Mixing 530 Application 531 Glass Fibre Reinforced Cement 531 Current Development in (FRC) 532 High Fibre Volume Micro-Fibre System 532 Slurry Infiltrated Fibre Concrete 532 Compact Reinforced Composites 532 Polymer Concrete 532 Type of Polymer Concrete 533 Polymer Impregnated Concrete 533 Polymer Cement Concrete 534 Polymer concrete 534 Partially Impregnated Concrete 535 Properties of Polymer Impregnated Concrete 536 Stress-Strain Relationship 536 Compressive Strength 536 Tensil Strength 537 Creep 539 Shrinkage due to Polymerisation 539 Durability 539 Water Absorption 540 Coefficient of Thermal Expansion 540 (xxiv)  Resistance to Abrasion 540 Wear and Skid Resistance 540 Fracture of Polymer Impregnated Concrete 540 Application of Polymer Impregnated Concrete 541 Cold Weather Concreting 542 Effects of Cold Weather on Concrete 542 Low Temperature but above 0°C 453 Low Temperature but below 0°C after Concreting 543 Temperature Below 0°C at the Time of Concreting 544 Hardened Concrete Subjected to Freezing and Thawing 544 Concreting Methods at Sub-zero Temperature 544 Hot Weather Concreting 552 Precautions Taken 554 Aggregates 554 Water 555 Production and Delivery 556 Prepacked Concrete 556 Vacuum Concrete 558 Rate of Extraction of Water 558 Vacuum Dewatered Concrete 560 Gunite or Shotcrete 562 Dry-Mix Process 562 Wet-Mix Process 563 Advantages of Wet and Dry Process 563 General Use of Shoterete 563 Concluding Remarks on Shotcrete 565 Recent Studies 566 Ferrocement 566 Casting Techniques 568 Hand Plastering 568 Semi-Mechanised Process 568 Centrifuging 569 Guniting 570 Application 570 Roller Compacted Concrete 570 Self compacting Concrete (SCC) 572 Material for SCC 573 Example of SCC Mixes 574 Requirements for self-compacting concrete 575 Workability Requirement for the fresh SCC 576 Production and Placing 577 Mix Design 577 Test Methods 578 Slump flow Test 579 J-ring test 580 V-Funnel Test 581 L-Box test method 582 U-Box Test 583 Full Box Test 584 Orimet test 587 Complexities involved in making SCC 588 New Generation Plasticizers 589 Indian Scenario of SCC 590 (xxv)  Experience of Delhi Metro Project 590 Experience of Mock-up Trials at Tarapur Atomic Power Project 591 Use of SCC Kaiga 592 Trials at SERC Chennai 594 Study at Hong Kong 595 How economical is Self Compacting Concrete 597 Bacterial Concrete 598 Experimental Investigations 598 Zeopolymer Concrete 599 Basalt fibre concrete and concre reinforced with basalt fibre reinforcements 602 General Reference Books 608-611 List of Indian Standard Specifications and Code of Pratices, Related to Cement and Concrete 612-616 Subject Index 617-624 (xxvi)  Cement ! XXVII CONCRETE IN THE UNENDING SERVICE OF NATION BUILDING LET US LEARN THIS SUBJECT TO BE A PART OF THE NATION BUILDING TEAM SARDAR SAROVAR DAM : Sardar Sarovar Project is an Inter-State Multi-Purpose project of National importance. It is one of the largest projects under implementation anywhere in the world. (xxvii) XXVIII ! Concrete Technology THE IDUKKI HYDROELECTRIC PROJECT, KERALA : The reservoir covers nearly 60 square kilometres and has a catchment of 649 square km. Water from the reservoir is taken down to the underground power house at Moolamattom through an underground tunnel, yielding an average gross head of 2182 feet (665 metres). The project has an installed capacity of 780 MW with firm power potential of 230 MW at 100 per cent load factor. THE BHAKRA DAM is a majestic monument across river Sutlej. The construction of this project was started in the year 1948 and was completed in 1963. It is 740 ft. high above the deepest foundation as straight concrete dam being more than three times the height of Qutab Minar. Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world. SAI GANGA approach canal for water supply to Chennai Metro. (xxviii)  Cement ! XXIX DELHI METRO Railway Station under construction. THE BAHÁ'Í HOUSE OF WORSHIP known as the Lotus Temple, built near New Delhi. Diamond shaped ‘MANI KANCHAN’ – Gem Unconventional building with pleasing & Jewellery Park at Kolkata. architecture. (xxix) XXX ! Concrete Technology TARAPUR ATOMIC POWER PROJECT : Reactor Fully automatic construction of concrete Building no. 3 & 4. pavement. A view of large oval shaped dome under construction over Connaught Place Metro Railway Station. It is going to be a new landmark over Delhi Metro. It will be a modern version of Palika garden – A pride feature of Delhi Metro Project. Sky Bus Metro, Goa (xxx)  Cement ! XXXI SOME LANDMARK HIGHRISE BUILDINGS IN THE WORLD Figures on the top is the strength of concrete in MPa SOME HIGHRISE BUILDINGS AROUND THE WORLD (xxxi) XXXII ! Concrete Technology CHANNEL TUNNEL RAIL LINK (UK). Tunnel diameter : 6.84 m and 8.15 m. Number of segments 9+key. Segment thickness : 350 mm. Concrete grade : 60 MPa. Dramix steel fibre reinforcement is used for casting segments without conventional steel. PETRONAS TWIN TOWERS in Kuala Lumpur Malaysia : One of the tallest (451m.) buildings in the world..... and many many more to expand and reshape the world we live in, — all in concrete. (xxxii)  Modern Cement Factory Courtesy : Grasim Industries Cement Division 1 C H A P T E R Cement ! General General ! Early History of Modern Cement ! Manufacture of Portland Cement T he history of cementing material is as old as the history of engineering construction. Some kind of cementing materials were used by Egyptians, ! Wet Process Romans and Indians in their ancient constructions. It ! Dry Process is believed that the early Egyptians mostly used ! Chemical Composition cementing materials, obtained by burning gypsum. Not much light has been thrown on cementing ! Hydration of Cement material, used in the construction of the cities of ! Heat of Hydration Harappa and Mohenjadaro. ! Calcium Silicate Hydrates An analysis of mortar from the Great Pyramid showed that it contained 81.5 per cent calcium ! Calcium Hydroxide sulphate and only 9.5 per cent carbonate. The early ! Calcium Aluminate Hydrates Greeks and Romans used cementing materials ! Structure of Hydrated Cement obtained by burning limestones. The remarkable hardness of the mortar used in early Roman ! Transition Zone brickworks, some of which still exist, is presenting ! Water Requirements for Hydration sufficient evidence of the perfection which the art of cementing material had attained in ancient times. The superiority of Roman mortar has been attributed to thoroughness of mixing and long continued ramming. The Greeks and Romans later became aware of the fact that certain volcanic ash and tuff, when 1 2 " Concrete Technology mixed with lime and sand yielded mortar possessing superior strength and better durability in fresh or salt water. Roman builders used volcanic tuff found near Pozzuoli village near Mount Vesuvius in Italy. This volcanic tuff or ash mostly siliceous in nature thus acquired the name Pozzolana. Later on, the name Pozzolana was applied to any other material, natural or artificial, having nearly the same composition as that of volcanic tuff or ash found at Pozzuoli. The Romans, in the absence of natural volcanic ash, used powered tiles or pottery as pozzolana. In India. powered brick named surkhi has been used in mortar. The Indian practice of through mixing and long continued ramming of lime mortar with or without the addition of Surkhi yielded strong and impervious mortar which confirmed the secret of superiority of Roman mortar. It is learnt that the Romans added blood, milk and lard to their mortar and concrete to achieve better workability. Haemoglobin is a powerful air-entraining agent and plasticizer, which perhaps is yet another reason for the durability of Roman structures. Probably they did not know about the durability aspect but used them as workability agents. The cementing material made by Romans using lime and natural or artificial Pozzolana retained its position as the chief building material for all work, particularly, for hydraulic construction. Belidor, a principal authority in hydraulic construction, recommended an initimate mixture of tiles, stone chips, and scales from a black-smith’s forge, carefully ground, washed free from coal and dirt, dried and sifted and then mixed with fresh slaked lime for making good concrete. When we come to more recent times, the most important advance in the knowledge of cements, the forerunner to the discoveries and manufacture of all modern cements is undoubtedly the investigations carried out by John Smeaton. When he was called upon to rebuild the Eddystone Light-house in 1756, he made extensive enquiries into the state of art existing in those days and also conducted experiments with a view to find out the best material to withstand the severe action of sea water. Finally, he concluded that lime-stones which contained considerable proportion of clayey matter yielded better lime possessing superior hydraulic properties. In spite of the success of Smeaton’s experiments, the use of hydraulic lime made little progress, and the old practice of mixture of lime and pozzolana remained popular for a long period. In 1976 hydraulic cement was made by calcining nodules of argillaceous lime-stones. In about 1800 the product thus obtained was called Roman cement. This type of cement was in use till about 1850 after which this was outdated by portland cement. Early History of Modern Cement The investigations of L.J. Vicat led him to prepare an artificial hydraulic lime by calcining an intimate mixture of limestone and clay. This process may be regarded as the leading knowledge to the manufacture of Portland cement. James Frost also patented a cement of this kind Joseph Aspdin’s first cement works, around 1823, at Kirkgate in in 1811 and established a Wakefield, UK. factory in London district. Courtesy : Ambuja Technical Literature  Cement " 3 The story of the invention of Portland cement is, however, attributed to Joseph Aspdin, a Leeds builder and bricklayer, even though similar procedures had been adopted by other inventors. Joseph Aspdin took the patent of portland cement on 21st October 1824. The fancy name of portland was given owing to the resemblance of this hardened cement to the natural stone occurring at Portland in England. In his process Aspdin mixed and ground hard limestones and finely divided clay into the form of slurry and calcined it in a furnace similar to a lime kiln till the CO2 was expelled. The mixture so calcined was then ground to a fine powder. Perhaps, a temperature lower than the clinkering temperature was used by Aspdin. Later in 1845 Isaac Charles Johnson burnt a mixture of clay and chalk till the clinkering stage to make better cement and established factories in 1851. In the early period, cement was used for making mortar only. Later the use of cement was extended for making concrete. As the use of Portland cement was increased for making concrete, engineers called for consistently higher Oldest surviving kiln, northeast Kent, UK, standard material for use in major works. (1847AD). Association of Engineers, Consumers and Cement Courtesy : Ambuja Technical Literature Manufacturers have been established to specify standards for cement. The German standard specification for Portland cement was drawn in 1877. The British standard specification was first drawn up in 1904. The first ASTM specification was issued in 1904. In India, Portland cement was first manufactured in 1904 near Madras, by the South India Industrial Ltd. But this venture failed. Between 1912 and 1913, the Indian Cement Co. Ltd., was established at Porbander (Gujarat) and by 1914 this Company was able to deliver about 1000 tons of Portland cement. By 1918 three factories were established. Together they were able to produce about 85000 tons of cement per year. During the First Five-Year Plan (1951- 1956) cement production in India rose from 2.69 million tons to 4.60 million tons. By 1969 the total production of cement in India was 13.2 million tons and India was then occupying the 9th place in the world, with the USSR producing 89.4 million tonnes and the USA producing 70.5 million tonnes1.1. Table 1.1 shows the Growth of Cement Industry through Plans. Prior to the manufacture of Portland cement in India, it was imported from UK and only a few reinforced concrete structures were built with imported cement. A three storeyed structure built at Byculla, Bombay is one of the oldest RCC structures using Portland cement in India. A concrete masonry building on Mount Road at Madras (1903), the har-ki-pahari bridge at Haridwar (1908) and the Cotton Depot Bombay, then one of the largest of its kind in the world (1922) are some of the oldest concrete structures in India.1.2 4 " Concrete Technology Table 1.1. Growth of Cement Industry through Plans Five Year At the Capacity %age Production %age GDP Plan end of (*) Growth (*) Growth Growth the Year Cement Pre Plan 50-51 3.28 2.20 I Plan 55-56 5.02 4.60 II Plan 60-61 9.30 13.12 7.97 11.62 7.1 III Plan 65-66 12.00 5.23 10.97 6.60 3.4 There were Annual Plans for 1966-67, 67-68 and 68-69 IV Plan 73.74 19.76 10.49 14.66 5.97 4.6 V Plan 78-79 22.58 2.70 19.42 5.78 5.5 VI Plan 84-85 42.00 13.22 30.13 9.18 3.8 VII Plan 89-90 61.55 7.94 45.41 8.55 6.9 Annual 90-91 64.36 0.90 48.90 1.49 5.4 Plans 91-92 66.56 3.42 53.61 9.63 5.3 VIII Plan 92-93 70.19 5.45 54.08 0.88 4.1 93-94 76.88 9.53 57.96 7.17 6.0 94-95 83.69 8.86 62.35 7.57 7.2 95-96 97.25 16.20 69.57 11.58 7.1 96-97 105.25 8.23 76.22 9.56 6.8 IX Plan 97-98 109.30 3.85 83.16 9.10 5.2 (*) Includes mini cement plants Source: Indian Cement Industry Emerging Trends — P. Parthsarathy and S.M. Chakravarthy Table 1.2. Per Capita Cement Consumption of Selected Countries of the World (1982, 1994 and 1997) Country Per Capita Cement Consumption (Kg.) 1982 1994 1997 USA 256 328 347 China 92 333 388 Taiwan 590 1285 966 Japan 617 642 622 Malaysia 290 512 831 Thailand 132 491 595 Argentina 198 184 145 (1996) Brazil 201 165 240 Venezuela 356 222 169 (1996) Turkey 251 436 511 Wo r l d 188 241 252 (1995) India 78 kg (1996), 82 kg (1997)  Cement " 5 The perusal of table 1.2 shows that per capita cement consumption in India is much less than world average. Considerable infrastructural development is needed to build modern India. Production of more cement, knowledge and economical utilisation of cement is the need of the day. The early scientific study of cements did not reveal much about the chemical reactions that take place at the time burning. A deeper study of the fact that the clayey constituents of limestone are responsible for the hydraulic properties in lime (as established by John Smeaton) was not taken for further research. It may be mentioned that among the earlier cement technologists, Vicat, Le Chatelier and Michaelis were the pioneers in the theoretical and practical field. Systematic work on the composition and chemical reaction of Portland cement was first begun in the United States. The study on setting was undertaken by the Bureau of Standards and since 1926 much work on the study of Portland cement was also conducted by the Portland Cement Association, U.K. By this time, the manufacture and use of Portland cement had spread to many countries. Scientific work on cements and fundamental contributions to the chemistry of Portland cements were carried out in Germany, Italy, France, Sweden, Canada and USSR, in addition to Britain and USA. In Great Britain with the establishment of Building Research Station in 1921 a systematic research programme was undertaken and many major contributions have been made. Early literatures on the development and use of Portland cements may be found in the Building Science Abstracts published by Building Research Station U.K. since 1928, “Documentation Bibliographique” issued quarterly since 1948 in France and “Handbuch der Zement Literature” in Germany. Manufacture of Portland Cement The raw materials required for manufacture of Portland cement are calcareous materials, such as limestone or chalk, and argillaceous material such as shale or clay. Cement factories are established where these raw materials are available in plenty. Cement factories have come up in many regions in India, eliminating the inconvenience of long distance transportation of raw and finished materials. The process of manufacture of cement consists of grinding the raw materials, mixing them intimately in certain proportions depending upon their purity and composition and burning them in a kiln at a temperature of about 1300 to 1500°C, at which temperature, the material sinters and partially fuses to form nodular shaped clinker. The clinker is cooled and ground to fine powder with addition of about 3 to 5% of gypsum. The product formed by using this procedure is Portland cement. There are two processes known as “wet” and “dry” processes depending upon whether the mixing and grinding of raw materials is done in wet or dry conditions. With a little change in the above process we have the semi-dry process also where the raw materials are ground dry and then mixed with about 10-14 per cent of water and further burnt to clinkering temperature. For many years the wet process remained popular because of the possibility of more accurate control in the mixing of raw materials. The techniques of intimate mixing of raw materials in powder form was not available then. Later, the dry process gained momentum with the modern development of the technique of dry mixing of powdered materials using compressed air. The dry process requires much less fuel as the materials are already in a dry state, whereas in the wet process the slurry contains about 35 to 50 per cent water. To dry 6 " Concrete Technology the slurry we thus require more fuel. In India most of the cement factories used the wet process. Recently a number of factories have been commissioned to employ the dry process method. Within next few years most of the cement factories will adopt dry process system. In the wet process, the limestone brought from the quarries is first crushed to smaller fragments. Then it is taken to a ball or tube mill where it is mixed with clay or shale as the case may be and ground to a fine consistency of slurry with the addition of water. The slurry is a liquid of creamy consistency with water content of about 35 to 50 per cent, wherein particles, crushed to the fineness of Indian Standard Sieve number 9, are held in suspension. The slurry is pumped to slurry tanks or basins where it is kept in an agitated condition by means of rotating arms with chains or blowing compressed air from the bottom to prevent settling of limestone and clay particles. The composition of the slurry is tested to give the required chemical composition and corrected periodically in the tube mill and also in the slurry tank by blending slurry from different storage tanks. Finally, the corrected slurry is stored in the final storage tanks and kept in a homogeneous condition by the agitation of slurry. The corrected slurry is sprayed on to the upper end of a rotary kiln against hot heavy hanging chains. The rotary kiln is an important component of a cement factory. It is a thick steel cylinder of diameter anything from 3 metres to 8 metres, lined with refractory materials, mounted on roller bearings and capable of rotating about its own axis at a specified speed. The length of the rotary kiln may vary anything from 30 metres to 200 metres. The slurry on being sprayed against a hot surface of flexible chain loses moisture and becomes flakes. These flakes peel off and fall on the floor. The rotation of the rotary kiln causes the flakes to move from the upper end towards the lower end of the kiln subjecting itself to higher and higher temperature. The kiln is fired from the lower end. The fuel is either powered coal, oil or natural gass. By the time the material rolls down to the lower end of the rotary kiln, the dry material  Cement " 7 Fig. 1.1. Diagrammatic representation of the dry process of manufacure of cement. (Courtesy : Grasim Industries Cement Division) 8 " Concrete Technology A view of Limestone quarry, raw material preparation : The prime raw material limestone after blasting in mines is broken into big boulders. Then it is transported by dumpers, tippers to limestone crusher where it is crushed to 15 to 20 mm size. STACKER FOR CRUSHED LIMESTONE RECLAIMER FOR CRUSHED LIMESTONE After crushing, the crushed limestone is piled longitudinally by an equipment called stacker. The stacker deposits limestone longitudinally in the form of a pile. The pile is normally 250 to 300 m long and 8-10 m height. The reclaimer cuts the pile vertically, simultaneously from top to bottom to ensure homogenization of limestone. Reclaimer for homogenization of crushed limestone.  Cement " 9 undergoes a series of chemical reactions until finally, in the hottest part of the kiln, where the temperature is in the order of 1500°C, about 20 to 30 per cent of the materials get fused. Lime, silica and alumina get recombined. The fused mass turns into nodular form of size 3 mm to 20 mm known as clinker. The clinker drops into a rotary cooler where it is cooled under controlled conditions The clinker is stored in silos or bins. The clinker weighs about 1100 to 1300 gms per litre. The litre weight of clinker indicates the quality of clinker. The cooled clinker is then ground in a ball mill with the addition of 3 to 5 per cent of gypsum in order to prevent flash-setting of the cement. A ball mill consists of several compartments charged with progressively smaller hardened steel balls. The particles crushed to the required fineness are separated by currents of air and taken to storage silos from where the cement is bagged or filled into barrels for bulk supply to dams or other large work sites. In the modern process of grinding, the particle size distribution of cement particles are maintained in such a way as to give desirable grading pattern. Just as the good grading of aggregates is essential for making good concrete, it is now recognised that good grading pattern of the cement particles is also important. The Fig. 1.1 shows the flow diagram of dry process of manufacture of cement. Dry Process In the dry and semi-dry process the raw materials are crushed dry and fed in correct proportions into a grinding mill where they are dried and reduced to a very fine powder. The dry powder called the raw meal is then further blended and corrected for its right composition and mixed by means of compressed air. The aerated powder tends to behave almost like liquid and in about one hour of aeration a uniform mixture is obtained. The blended meal is further sieved and fed into a rotating disc called granulator. A quantity of water about 12 per cent by wright is added to make the blended meal into pellets. This is done to permit air flow for exchange of heat for further chemical reactions and conversion of the same into clinker further in the rotary kiln. The equipments used in the dry process kiln is comparatively smaller. The process is quite economical. The total consumption of coal in this method is only about 100 kg when compared to the requirement of about 350 kg for producing a ton of cement in the wet process. During March 1998, in India, there were 173 large plants operating, out of which 49 plants used wet process, 115 plants used dry process and 9 plants used semi-dry process. Since the time of partial liberalisation of cement industry in India (1982), there has been an upgradation in the quality of cement. Many cement companies upgraded their plants both in respect of capacity and quality. Many of the recent plants employed the best equipments, such as cross belt analyser manufactured by Gamma-Metrics of USA to find the composition of limestone at the conveyor belts, high pressure twin roller press, six stage preheater, precalciner and vertical roller mill. The latest process includes stacker and reclaimer, on-line X- ray analyser, Fuzzy Logic kiln control system and other modern process control. In one of the recently built cement plant at Reddypalayam near Trichy, by Grasim Indistries, employed Robot for automatic collection of hourly samples from 5 different places on the process line and help analyse the ame, throughout 24 hours, untouched by men, to avoid human errors in quality control. With all the above sophisticated equipments and controls, consistent quality of clinker is produced. The methods are commonly employed for direct control of quality of clinker. The first method involves reflected light optical microscopy of polished and etched section of clinker, 10 " Concrete Technology RAW MILL The proportioned raw materials are transported by belt conveyor to Raw Mill for grinding into powder form before burning. RAW MEAL SILO After grinding, the powdered raw mix, is stored in a raw meal-silo where blending takes place. Blending is done by injecting compressed air. Generally blending ratio is 1:10. This powder material (Raw meal) is fed to the kiln for burning.  Cement " 11 ROBO LAB Consists of automatic sampling and sending station located at different locations in the plant. Samples are being sent through pneumatic tubes to Robo lab. This avoids human error in sampling and ensures accurate quality in semi finished and finished products. 1st of its kind in India has been used at Grasim Cement plant at Reddypalayam. Robot receiving samples. 12 " Concrete Technology Close circuit grinding technology is most modern grinding system for raw mix as well as for clinker grinding. The systems are in compound mode and are equipped with high efficiency Roller press and separators. The above mentioned system enables to maintain low power consumption for grinding as well as Electronic packers : it has continuous narrow particle size distribution. With this circuit, it is weighing system and it ensures that the possible to manufacture higher surface area of product bags separating from the nozzles have as per customers, requirement. accurate weight of cement. The weight of filled bag is also displayed on the packer. Multi-compartment silo. Cross section of multi-compartment silo.  Cement " 13 Jumbo bag transportation. followed by point count of areas occupied by various compounds. The second method, which is also applicable to powdered cement, involves X-ray diffraction of powder specimen. Calibration curves based on known mixtures of pure compounds, help to estimate the compound composition. As a rough and ready method, litre weight (bulk density) of clinker is made use of to ascertain the quality. A litre weight of about 1200 gms. is found to be satisfactory. Jumbo bag packing. It is important to note that the strength properties of cement are considerably influenced by the cooling rate of clinker. This fact has of late attracted the attention of both the cement manufacturers and machinery producers. The experimental results reported by Enkegaard are shown in table 1.3. Table 1.3. Influence of Rate of Cooling on Compressive Strength1.3 Type of cement Cooling Compressive Strength MPa conditions 3 days 7 days 28 days Quick 9.9 15.3 26 Moderate 9.7 21.0 27 Normal Cement Slow 9.7 19.3 24 Very slow 8.7 18.7 23 High early Quick 10.2 18.8 29 strength Moderate 14.2 26.7 33 cement Slow 10.2 21.0 29 Very Slow 9.1 18.1 28 14 " Concrete Technology It can be seen from the table that a moderate rate of cooling of clinker in the rotary cooler will result in higher strength. By moderate cooling it is implied that from about 1200°C, the clinker is brought to about 500°C in about 15 minutes and from the 500°C the temperature is brought down to normal atmospheric temperature in about 10 minutes. The rate of cooling influences the degree of crystallisation, the size of the crystal and the amount of amorphous materials present in the clinker. The properties of this amorphous material for similar chemical composition will be different from the one which is crystallined. Chemical Composition The raw materials used for the manufacture of cement consist mainly of lime, silica, alumina and iron oxide. These oxides interact with one another in the kiln at high temperature to form more complex compounds. The relative proportions of these oxide compositions are responsible for influencing the various properties of cement; in addition to rate of cooling and fineness of grinding. Table 1.4 shows the approximate oxide composition limits of ordinary Portland cement. Table 1.4. Approximate Oxide Composition Limits of Ordinary Portland Cement Oxide Per cent content CaO 60–67 SiO2 17–25 Al2O3 3.0–8.0 Fe2O3 0.5–6.0 MgO 0.1–4.0 Alkalies (K2O, Na2O) 0.4–1.3 SO3 1.3–3.0 Indian standard specification for 33 grade cement, IS 269-1989, specifies the following chemical requirements: (a) Ratio of percentage of lime to percentage of silica, alumina and iron oxide; known as Lime Saturation Factor, when calculated by the formula CaO − 0.7 SO 3 Not greater than 1.02 and not less than 0.66 2.8 SiO 2 + 1.2 Al 2 O3 + 0.65 Fe 2 O3 (b) Ratio of percentage of alumina to that of iron oxide Not less tan 0.66 (c ) Weight of insoluble residue Not more than 4 per cent (d ) Weight of magnesia Not more than 6 per cent (e ) Total sulphur content, calculated as sulphuric Not more than 2.5% when anhydride (SO3) C3A is 5% or less. Not more than 3%, when C3A is more than 5% (f ) Total loss on ignition Not more than 5 per cent  Cement " 15 As mentioned earlier the oxides persent in the raw materials when subjected to high clinkering temperature combine with each other to form complex compounds. The identification of the major compounds is largely based on R.H. Bogue’s work and hence it is called “Bogue’s Compounds”. The four compounds usually regarded as major compounds are listed in table 1.5. Table 1.5. Bogue’s Compounds Name of Compound Formula Abbreviated Formula Tricalcium silicate 3 CaO.SiO2 C 3S Dicalcium silicate 2 CaO.Sio2 C 2S Tricalcium aluminate 3 Cao.Al2O3 C 3A Tetracalcium aluminoferrite 4 CaO.Al2O3.Fe2O3 C4AF It is to be noted that for simplicity’s sake abbreviated notations are used. C stands for CaO, S stands for SiO2, A for Al2O3, F for Fe2O3 and H for H2O. The equations suggested by Bogue for calculating the percentages of major compounds are given below. C 3 S = 4.07 (CaO) – 7.60 (SiO 2) – 6.72 (Al 2O 3 ) – 1.43 (Fe 2O 3) – 2.85 (SO 3) C 2S = 2.87 (SiO 2) – 0.754 (3CaO.SiO 2 ) C 3A = 2.65 (Al 2O 3) – 1.69 (Fe 2O 3 ) C 4AF= 3.04 (Fe 2O 3) The oxide shown within the brackets represents the percentage of the same in the raw materials. Table 1.6. The Oxide Composition of a Typical Portland Cement and the Corrosponding Calculated Compound Composition. Oxide composition Calculated compound composition Per cent using Bogue’s equation per cent CaO 63 C 3S 54.1 SiO 2 20 C 2S 16.6 Al 2 O 3 6 C 3A 10.8 Fe 2 O 3 3 C 4AF 9.1 MgO 1.5 SO 2 2 K 2O  1.0  Na 2 O  In addition to the four major compounds, there are many minor compounds formed in the kiln. The influence of these minor compounds on the properties of cement or hydrated compounds is not significant. Two of the minor oxides namely K2O and Na2O referred to as alkalis in cement are of some importance. This aspect will be dealt with later when discussing alkali-aggregate reaction. The oxide composition of typical Portland cement and the corresponding calculated compound composition is shown in table 1.6. 16 " Concrete Technology C2S C3A + C4AF C3S Schematic presentation of various compounds in clinker Courtesy : All the photographs on manufacture of cement are by Grasim Industries Cement Division Tricalcium silicate and dicalcium silicate are the most important compounds responsible for strength. Together they constitute 70 to 80 per cent of cement. The average C3S content in modern cement is about 45 per cent and that of C2S is about 25 per cent. The sum of the contents of C3 A and C4 AF has decreased slightly in modern cements. The calculated quantity of the compounds in cement varies greatly even for a relatively small change in the oxide composition of the raw materials. To manufacture a cement of stipulated compound composition, it becomes absolutely necessary to closely control the oxide composition of the raw materials. An increase in lime content beyond a certain value makes it difficult to combine with other compounds and free lime will exist in the clinker which causes unsoundness in cement. An increase in silica content at the expense of the content of alumina and ferric oxide will make the cement difficult to fuse and form clinker. Cements with a high total alumina and high ferric oxide content is favourable to the production of high early strengths in cement. This is perhaps due to the influence of these oxides for the complete combining of the entire quantity of lime present to form tricalcium silicate. The advancement made in the various spheres of science and technology has helped us to recognise and understand the micro structure of the cement compounds before hydration and after hydration. The X-ray powder diffraction method, X-ray fluorescence method and use of powerful electron microscope capable of magnifying 50,000 times or even more has helped to reveal the crystalline or amorphous structure of the unhydrated or hydrated cement. Both Le Chatelier and Tornebohm observed four different kinds of crystals in thin sections of cement clinkers. Tornebohm called these four kinds of crystals as Alite, Belite, Celite and Felite. Tornebohm’s description of the minerals in cement was found to be similar to Bogue’s description of the compounds. Therefore, Bogue’s compounds C3S, C2S, C3A and C4AF are sometimes called in literature as Alite, Belite, Celite and Felite respectively.  Cement " 17 Cement and hydration of Portland cement can be schematically represented as below: Hydration of Cement Anhydrous cement does not bind fine and coarse aggregate. It acquires adhesive property only when mixed with water. The chemical reactions that take place between cement and water is referred as hydration of cement. The chemistry of concrete is essentially the chemistry of the reaction between cement and water.On account of hydration certain products are formed. These products are important because they have cementing or adhesive value. The quality, quantity, continuity, stability and the rate of formation of the hydration products are important. Anhydrous cement compounds when mixed with water, react with each other to form hydrated compounds of very low solubility. The hydration of cement can be visualised in two ways. The first is “through solution” mechanism. In this the cement compounds dissolve to produce a supersaturated solution from which different hydrated products get precipitated. The second possibility is 18 " Concrete Technology that water attacks cement compounds in the solid state converting the compounds into hydrated products starting from the surface and proceeding to the interior of the compounds with time. It is probable that both “through solution” and “solid state” types of mechanism may occur during the course of reactions between cement and water. The former mechanism may predominate in the early stages of hydration in view of large quantities of water being available, and the latter mechanism may operate during the later stages of hydration. Heat of Hydration The reaction of cement with water is exothermic. The reaction liberates a considerable quantity of heat. This liberation of heat is called heat of hydration. This is clearly seen if freshly mixed cement is put in a vaccum flask and the temperature of the mass is read at intervals. The study and control of the heat of hydration becomes important in the construction of concrete dams and other mass concrete constructions. It has been observed that the temperature in the interior of large mass concrete is 50°C above the original temperature of the concrete mass at the time of placing and this high temperature is found to persist for a prolonged period. Fig 1.2 shows the pattern of liberation of heat from setting cement1.4 and during early hardening period. On mixing cement with water, a rapid heat evolution, lasting a few minutes, occurs. This heat evolution is probably due to the reaction of solution of aluminates and sulphates (ascending peak A). This initial heat evolution ceases quickly when the solubility of aluminate is depressed by gypsum. (decending peak A). Next heat evolution is on account of formation of ettringite and also may be due to the reaction of C3S (ascending peak B). Refer Fig. 1.2. Different compounds hydrate at different rates and liberate different quantities of heat. Fig. 1.3 shows the rate of hydration of pure compounds. Since retarders are added to control the flash setting properties of C3 A, actually the early heat of hydration is mainly contributed from the hydration of C3S. Fineness of cement also influences the rate of development of heat but not the total heat. The total quantity of heat generated in the complete hydration will depend upon the relative quantities of the major compounds present in a cement. Analysis of heat of hydration data of large number of cements, Verbec and Foster1.5 computed heat evolution of four major compounds of cement. Table 1.7. shows the heats of hydration of four compounds.  Cement " 19 Table 1.7. Heat of Hydration1.5 Compound Heat of hydration at the given age (cal/g) 3 days 90 days 13 years C3S 58 104 122 C2S 12 42 59 C3A 212 311 324 C4AF 69 98 102 Since the heat of hydration of cement is an additive property, it can be predicted from an expression of the type H = aA + bB + cC + dD Where H represents the heat of hydration, A, B, C, and D are the percentage contents of C3S, C2S, C3 A and C4 AF. and a, b, c and d are coefficients representing the contribution of 1 per cent of the co