Advanced Concrete Technology Set (eBook)

B S Choo, John Newman (Herausgeber)

eBook Download: EPUB

2003 | 1. Auflage
1920 Seiten
Elsevier Science (Verlag)
978-0-08-052656-0 (ISBN)

Infos

Based on the Institute of Concrete Technology's advanced course, this new four volume series is a comprehensive educational and reference resource for the concrete materials technologist.

An expert international team of authors from research, academia and industry has been brought together to produce this unique reference source. Each volume deals with different aspects of the properties, composition, uses and testing of concrete. With worked examples, case studies and illustrations throughout, this series will be a key reference for the concrete specialist for years to come.

* Expert international authorship ensures the series is authoritative
* Case studies and worked examples help the reader apply their knowledge to practice
* Comprehensive coverage of the subject gives the reader all the necessary reference material

Inhalt

Front Cover 1
Advanced Concrete Technology: Constituent Materials 4
Copyright Page 5
Contents 6
Preface 14
List of contributors 16
Part 1: Cements 18
Chapter 1. Cements 20
1.1 Introduction 20
1.2 History of Portland cement manufacture 20
1.3 Chemistry of clinker manufacture 22
1.4 Cement grinding 31
1.5 Portland cement hydration 32
1.6 Portland cement types 39
1.7 Cement production quality control 50
1.8 Influence of cement quality control parameters on properties 53
1.9 Relationship between laboratory mortar results and field concrete 59
1.10 Applications for different cement types 59
1.11 Health and safety aspects of cement use 60
References 62
Chapter 2. Calcium aluminate cements 64
2.1 Introduction 64
2.2 Chemistry and mineralogy of CACs 66
2.3 Properties of fresh CAC concrete – setting, workability, heat evolution 75
2.4 Strength development 78
2.5 Other engineering properties 82
2.6 Supplementary cementing materials 82
2.7 Durability/resistance to degradation 82
2.8 Structural collapses associated with CAC concrete 84
2.9 Modern uses of CAC concrete 86
2.10 Use of CACs in mixed binder systems 89
2.11 Summary 92
References 93
Part 2: Cementitious Additions 96
Chapter 3. Cementitious additions 98
3.1 The pozzolanic reaction and concrete 98
3.2 Fly ash as a cementitious addition to concrete 98
3.3 Fly ash in special concretes 112
3.4 Natural pozzolanas 113
3.5 The use of ggbs in concrete 113
3.6 Silica fume for concrete 129
3.7 Metakaolin 144
3.8 Limestone 153
References 154
Part 3: Admixtures 162
Chapter 4. Admixtures for concrete, mortar and grout 164
4.1 Introduction 164
4.2 Dispersing admixtures 170
4.3 Retarding and retarding plasticizers/superplasticizing admixtures 178
4.4 Accelerating admixtures 181
4.5 Air-entraining admixtures 182
4.6 Water resisting (waterproofing) 186
4.7 Corrosion-inhibiting admixtures 187
4.8 Shrinkage-reducing admixtures 189
4.9 Anti-washout/underwater admixtures 190
4.10 Pumping aids 191
4.11 Sprayed concrete admixtures 192
4.12 Foamed concrete and CLSM 192
4.13 Other concrete admixtures 193
4.14 Mortar admixtures 194
4.15 Grout admixtures 195
4.16 Admixture supply 195
4.17 Health and safety 197
Further reading 197
Part 4: Aggregates 198
Chapter 5. Geology, aggregates and classification 200
5.1 Introduction 200
5.2 Fundamentals 201
5.3 Geological classification of rocks 203
5.4 Sources and types of aggregates 209
5.5 Classification of aggregates 218
5.6 Aggregate quarry assessment 220
5.7 Deleterious materials in aggregates 222
References 231
Chapter 6. Aggregate prospecting and processing 234
6.1 Aims and objectives 234
6.2 Introduction 234
6.3 Extraction and processing of sand and gravel 235
6.4 Processing 238
6.5 Extraction and processing of limestone 243
6.6 Summary 244
Further reading 244
Chapter 7. Lightweight aggregate manufacture 246
7.1 Introduction, definitions and limitations 246
7.2 Lightweight aggregates suitable for use in structural concrete 247
7.3 Brief history of lightweight aggregate production 248
7.4 Manufacturing considerations for structural grades of lightweight aggregate 249
7.5 Production methods used for various lightweight aggregates 251
7.6 The future 255
7.7 Conclusions 256
References 257
Chapter 8. The effects of natural aggregates on the properties of concrete 258
8.1 Aims and objectives 258
8.2 Brief history 258
8.3 Introduction 259
8.4 Classification 259
8.5 Sampling 259
8.6 Grading 260
8.7 Maximum size of aggregate 263
8.8 Aggregate shape and surface texture 263
8.9 Aggregate strength 265
8.10 Aggregate density 265
8.11 Drying shrinkage 266
8.12 Soundness 267
8.13 Thermal properties 268
8.14 Fines content 268
8.15 Impurities 269
8.16 Summary 270
References 271
Further reading 272
Index 274
Front Cover 283
Advanced Concrete Technology: Concrete Properties 286
Copyright Page 287
Contents 288
Preface 296
List of contributors 298
Part 1: Fresh concrete 300
Chapter 1. Fresh concrete 302
1.1 Introduction 302
1.2 Workability 303
1.3 Loss of workability 322
1.4 Placing and compaction 323
1.5 Segregation and bleed after placing 324
References 325
Further reading 327
Relevant standards 327
Part 2: Setting and hardening of concrete 330
Chapter 2. Plastic and thermal cracking 332
2.1 Introduction 332
2.2 Plastic cracking 334
2.3 Plastic settlement cracks 334
2.4 Plastic shrinkage cracks 338
2.5 Other cracks in plastic concrete 340
2.6 Early thermal contraction cracks 341
2.7 Curling 343
2.8 Crazing 343
2.9 Long-term drying shrinkage cracks 344
References 346
Further reading 346
Chapter 3. Curing 348
3.1 Aims and objectives 348
3.2 What is curing? 348
3.3 Why cure concrete? 348
3.4 How can curing be achieved in practice? 351
3.5 Which curing method is best? 351
3.6 Protection against vibration 354
3.7 Is curing always effective? 355
3.8 How long should curing be applied? 355
3.9 When is curing of particular importance? 356
3.10 Effect of temperature 356
3.11 What happens if concrete is not cured properly? 357
3.12 The effect of curing on strength 357
3.13 The maturity concept for estimation of required curing duration 358
3.14 Some international curing specifications 358
3.15 Some food for thought 360
3.16 Summary and conclusions 360
References 362
Further reading 362
Chapter 4. Concrete properties: setting and hardening 364
4.1 Strength development 364
4.2 Maturity and accelerated curing 385
4.3 Assessment of safe striking times 392
References 394
Further reading 396
Chapter 5. Hot and cold weather concreting 398
5.1 Introduction 398
5.2 Hot weather concreting 398
5.3 Cold weather concreting 408
References 415
Part 3: Properties of hardened concrete 416
Chapter 6. Strength and failure of concrete under short-term, cyclic and sustained loading 418
6.1 Deformation, fracture and failure 418
6.2 Behaviour of concrete under multiaxial stresses 437
References 450
Chapter 7. Elasticity, shrinkage, creep and thermal movement 452
7.1 Learning objectives 452
7.2 Introduction 452
7.3 Elasticity 453
7.4 Shrinkage 454
7.5 Creep 460
7.6 Thermal movement 468
7.7 Summary 468
References 469
Part 4: Durability of concrete and concrete construction 470
Chapter 8. Durability concept: pore structure and transport processes 472
8.1 Introduction 472
8.2 Durability concept 472
8.3 Forms of physical and chemical deterioration 474
8.4 Transport processes 474
8.5 Summary and conclusions 495
References 496
Further reading 497
Chapter 9. Reinforcement corrosion 500
9.1 Introduction 500
9.2 The corrosion process 501
9.3 The concrete environment 503
9.4 Stages in the deterioration process 504
9.5 Carbonation-induced corrosion 505
9.6 Chloride-induced corrosion 509
9.7 Other causes of corrosion 514
9.8 Corrosion rate 515
9.9 Monitoring corrosion 517
9.10 Repair of corrosion-damaged concrete 520
9.11 Summary 524
References 524
Chapter 10. Concrete and fire exposure 528
10.1 Essentials of concrete behaviour 528
10.2 Strength loss in the cement matrix 529
10.3 Spalling 530
10.4 The influence of aggregate type 531
10.5 High-strength concrete 531
10.6 Essentials of steel behaviour 532
10.7 Fire behaviour and design codes 533
10.8 Fire types and heat exposure 534
10.9 Behaviour of concrete in extreme fires 535
10.10 Improving the fire resistance of concrete 536
10.11 Evaluation of concrete structures exposed to fire 537
References 539
Chapter 11. Freeze/thaw resistance 542
11.1 Introduction 542
11.2 Mechanisms of ice formation in cementitious materials 543
11.3 Mechanisms induced by ice formation 546
11.4 Laboratory testing and influence of various parameters 548
11.5 De-icer salt scaling 550
11.6 Air entrainment 553
11.7 Special concretes 555
11.8 Field performance 556
References 557
Chapter 12. Acid, soft water and sulfate attack 560
12.1 Aqueous solutions 560
12.2 Reactions of water and acids with concrete/lmortar 562
12.3 Factors affecting rate of attack by water and acids 562
12.4 Reactions of sulfate solutions with concrete 563
12.5 Test methods and results 565
12.6 Specifying concrete for acid, soft water and sulfate exposures 568
References 571
Chapter 13. Alkali-aggregate reactivity 572
13.1 Introduction 572
13.2 Reaction mechanisms 574
13.3 Effects of AAR 582
13.4 Cases of AAR 585
13.5 Diagnosis and prognosis 589
13.6 Minimizing risk and prevention 596
13.7 Repairs and remedies 603
References 605
Further reading 608
Chapter 14. Specification and achievement of cover to reinforcement 610
14.1 Aims and objectives 610
14.2 Introduction 610
14.3 Specification of cover 611
14.4 Achievement in practice 612
14.5 Reliability and workmanship 613
14.6 Excessive cover 613
14.7 Future specification of cover 613
14.8 Durability design 614
14.9 Performance testing 614
14.10 Recommendations for achievement of cover 615
14.11 Measurement of cover 616
14.12 Action in the event of non-conformity 616
14.13 Examples of non-compliance 616
14.14 Recent research 617
14.15 Alternative approaches to ensuring durability 617
References 617
Further reading 618
Index 620
Front Cover 631
Advanced Concrete Technology: Processes 634
Copyright Page 635
Contents 636
Preface 654
List of contributors 656
Part 1: Mix design 660
Chapter 1. Concrete mix design 662
1.1 Introduction 662
1.2 Initial laboratory tests of concrete 668
1.3 Comprehensive mix design of ready-mixed concrete based on laboratory trials 671
1.4 Comprehensive mix design of concrete based on materials properties 676
1.5 MixSim – a computerized comprehensive method of mix design 681
1.6 Special concretes 689
1.7 Simplified mix design methods 690
1.8 Ready-to-use mix designs 696
1.9 Summary 697
References 698
Further reading 699
Part 2: Special concretes 700
Chapter 2. Properties of lightweight concrete 702
2.1 Introduction 702
2.2 No-fines concrete (NFC) 703
2.3 Aerated and foamed concrete 706
2.4 Lightweight aggregate concrete 708
References 724
Chapter 3. High strength concrete 730
3.1 Aims and objectives 730
3.2 Introduction 730
3.3 Materials technology of HSC 731
3.4 Materials selection and mix design 733
3.5 Properties of HSC 736
3.6 Production and use of HSC 739
3.7 Examples of use of HSC 741
3.8 Summary 743
References 743
Further reading 745
Chapter 4. Heat-resisting and refractory concretes 746
4.1 Introduction 746
4.2 Calcium aluminate cement (CAC) versus Portland cement (PC) 746
4.3 Refractory limits of calcium aluminate cements 747
4.4 Refractory and heat-resisting aggregates 749
4.5 Heat-resistant concretes 749
4.6 Insulating concretes 751
4.7 Abrasion and heat-resisting concretes 752
4.8 High-temperature refractory concrete 752
4.9 Low- and ultra-low cement castables 753
4.10 Self-flow castables 754
4.11 Installation of heat-resisting and refractory concretes 754
4.12 Applications 757
References 758
Chapter 5. High-density and radiation-shielding concrete and grout 760
5.1 Objectives 760
5.2 Introduction 760
5.3 Uses and applications 761
5.4 Definitions and standards 763
5.5 Aggregates 763
5.6 Mix design 767
5.7 Production, transporting and placing 768
5.8 Concrete properties 770
5.9 High-density grouts 771
5.10 Quality management 771
5.11 Specifications 773
5.12 Summary 773
References 773
Chapter 6. Fibre-reinforced concrete 776
6.1 Introduction 776
6.2 Properties of fibres and matrices 777
6.3 Post-cracking composite theory 777
6.4 Theoretical stress–strain curves in uniaxial tension 777
6.5 Principles of fibre reinforcement in flexure 781
6.6 Steel fibre concrete 784
6.7 Mix design and composite manufacture 784
6.8 Properties 786
6.9 Testing 787
6.10 Applications 788
6.11 Polypropylene fibre-reinforced concrete 789
6.12 Mix design and manufacture 790
6.13 Properties of fresh concrete 790
6.14 Properties of hardened concrete 791
6.15 Applications 791
6.16 Glass fibre-reinforced concrete 792
References 792
Further reading 792
Chapter 7. Masonry mortars 794
7.1 Aims and objectives 794
7.2 Historical background 794
7.3 The requirements of mortar 795
7.4 Properties of mortar 798
7.5 Constituents of mortar 801
7.6 Mortar standards and application documents 810
7.7 Mortar mix design 811
7.8 Basic masonry design for durability 812
7.9 Site problems 813
7.10 Summary 815
References 815
Chapter 8. Recycled concrete 818
8.1 Introduction 818
8.2 BRE Digest 433 and the properties of recycled aggregate 818
8.3 Methods of recycling and quality 822
8.4 Recipe and performance specifications 823
8.5 Applications – demonstration projects 824
References 829
Further reading 830
Chapter 9. Self-compacting concrete 832
9.1 Introduction 832
9.2 Materials 833
9.3 Mix design 837
9.4 Plastic concrete 842
9.5 Hardened concrete 845
9.6 Production and transportation 846
9.7 Placement 846
9.8 Formwork 847
9.9 Surface finish 847
9.10 Mix design optimization – moving SCC to mainstream construction 849
9.11 SCC applications 850
References 851
Further reading 853
Part 3: Special processes and technology for particular types of structure 856
Chapter 10. Sprayed concrete 858
10.1 Introduction 858
10.2 History 858
10.3 Definition of sprayed concrete 859
10.4 The wet process 860
10.5 Dry process 861
10.6 Constituent materials 863
10.7 Spraying procedures 865
10.8 Quality assurance 866
10.9 Quality control 867
10.10 Applications of sprayed concrete 869
Further reading 873
Chapter 11. Underwater concrete 874
11.1 Introduction 874
11.2 Conventional methods of placing 874
11.3 Concrete properties 880
11.4 Non-dispersible concrete 882
11.5 Formwork 884
11.6 Reinforcement 884
11.7 Conclusion 885
Further reading 885
Chapter 12. Grouts and grouting 886
12.1 Introduction 886
12.2 Health and safety 887
12.3 The void to be grouted 887
12.4 Grouting theory and standards 888
12.5 Cement grouts 888
12.6 Cementitious grout testing concepts 892
12.7 Grout properties 895
12.8 Grout injection 910
12.9 Volume change 914
12.10 The hardened state of cementitious grouts 917
12.11 Durability 918
12.12 Chemical grout systems – materials issues 918
12.13 Volume change in chemical grouts 922
12.14 The hardened state for chemical grouts 924
12.15 Chemical and geotechnical grout materials 927
12.16 Conclusions 930
References 930
Chapter 13. Concreting large-volume (mass) pours 934
13.1 Introduction 934
13.2 The designer’s role 936
13.3 Planning 946
13.4 Concrete mix design 952
13.5 Construction of large-volume pours 966
13.6 Review 977
References 978
Chapter 14. Slipform 982
14.1 Vertical slipforming 982
14.2 Design of the slipform 987
14.3 Concrete mix 988
14.4 Horizontal slipforming 1002
Chapter 15. Pumped concrete 1006
15.1 Liquids 1006
15.2 Suspensions 1007
15.3 Rheology 1009
15.4 Pressure gradients 1011
15.5 Types of concrete pump 1012
15.6 Requirements of a concrete for pumping 1018
15.7 Effects of aggregates, cement and admixtures on the pumpability of concrete 1022
15.8 Modifications to the concrete mix design to ensure pumpability 1027
15.9 Void content of aggregate and procedures for measuring void content in combined aggregate grading 1028
15.10 Suitable combinations of aggregates for pumpable concrete 1031
15.11 Recognizing pumpable concrete 1034
15.12 Pressure bleed test apparatus 1035
15.13 Conclusion 1036
References 1037
Chapter 16. Concrete construction for liquid-retaining structures 1040
16.1 Introduction 1040
16.2 Permeability and durability 1041
16.3 Constituent materials 1042
16.4 Cracking and autogenous healing 1044
16.5 Cracking due to temperature and moisture effects 1046
16.6 Workmanship 1055
16.7 Summary 1056
References 1056
Chapter 17. Coatings 1058
17.1 Introduction 1058
17.2 Reasons for use 1059
17.3 Materials for surface coating/treatment 1063
17.4 Surface preparation and application 1066
References 1071
Further reading 1071
Part 4: Readymixed concrete 1072
Chapter 18. Production of readymixed concrete 1074
18.1 Development of readymixed concrete 1074
18.2 Effects of transportation on concrete properties 1075
18.3 Production methods 1078
References 1085
Part 5: Exposed concrete finishes 1086
Chapter 19. Weathering of concrete 1088
19.1 Introduction 1088
19.2 The inevitability of weathering 1088
19.3 Alternative approaches 1090
19.4 Weathering on old buildings 1090
19.5 The weathering system 1092
19.6 Characteristics of concrete 1093
19.7 External factors 1098
19.8 The visible effects of weathering 1105
19.9 Control of weathering 1110
References 1116
Part 6: Formwork 1118
Chapter 20. Formwork and falsework 1120
20.1 Introduction 1120
20.2 Definitions 1120
20.3 Formwork 1121
20.4 Falsework 1135
20.5 Striking formwork and falsework 1140
References 1143
Part 7: Precast concrete 1146
Chapter 21. Precast concrete structural elements 1148
21.1 Summary 1148
21.2 Structural precast concrete 1149
21.3 The advantages to be achieved by employing precast concrete 1149
21.4 Principles of precasting 1152
21.5 Moulds for precast concrete 1159
21.6 Casting techniques 1160
21.7 Curing 1166
21.8 Testing and controls 1167
21.9 Frame components 1168
21.10 Cladding 1172
21.11 Bridge beams 1178
21.12 Double-tee beams 1178
21.13 Sea-defence units 1179
21.14 Piles 1179
21.15 Sleepers 1180
21.16 Structural elements for groundwork and support 1180
21.17 Erection at site 1182
21.18 Segmental casting 1183
21.19 Troubleshooting precast concrete 1184
21.20 Conclusions 1189
Case studies 1190
References 1191
Part 8: Concrete roads 1192
Chapter 22. Concrete roads and pavements 1194
22.1 Introduction 1194
22.2 Typical concrete pavement types 1195
22.3 Manner of pavement failure 1201
22.4 Design methods 1204
22.5 Joint design and detailing 1207
22.6 Materials and concrete properties 1210
22.7 Construction methods 1213
22.8 Maintenance issues and repair of pavements 1214
22.9 New techniques 1216
22.10 Conclusions 1217
Reference 1217
Chapter 23. Cement-bound materials (CBM) 1218
23.1 Introduction 1218
23.2 Methods of specifying CBM 1221
23.3 Summary 1229
References 1229
Part 9: Industrial floors 1230
Chapter 24. Concrete floors 1232
24.1 Introduction 1232
24.2 Concrete for industrial floors 1233
24.3 Production issues: consistency 1241
24.4 Floor construction 1243
24.5 Design and loading 1246
24.6 Floor toppings 1259
24.7 Floor specification 1259
24.8 Defect identification and remedial measures 1263
Part 10 Reinforced and prestressed concrete 1268
Chapter 25. Reinforced and prestressed concrete 1270
25.1 Objectives 1270
25.2 Principles of limit state design 1271
25.3 Structural elements 1273
25.4 Design values 1274
25.5 Load testing of simple structures 1277
25.6 Behaviour of reinforced concrete beams 1277
25.7 Behaviour of prestressed concrete beams 1281
25.8 Summary 1283
References 1283
Part 11: Alternative reinforcement for concrete 1286
Chapter 26. Alternative reinforcement for concrete 1288
26.1 Aims and objectives 1288
26.2 Other types of reinforcement 1289
26.3 General introduction to fibre composites 1293
26.4 FRP internal reinforcement 1296
26.5 FRP prestressing strand 1301
26.6 Summary 1304
References 1305
Further reading 1306
Index 1308
Front Cover 1330
Advanced Concrete Technology: Testing and Quality 1333
Copyright Page 1334
Contents 1335
Preface 1343
List ofcontributors 1345
Part 1: Testing 1347
Chapter 1. Analysis of fresh concrete 1349
1.1 Introduction 1349
1.2 British Standards covering flesh analysis 1350
1.3 Tests for cement content 1350
1.4 Tests for pfa content 1360
1.5 Tests for ggbs content 1363
1.6 Tests for water content 1365
1.7 Aggregate grading 1367
1.8 Summary 1368
Reference 1368
Chapter 2. Strength-testing machines for concrete 1369
2.1 Introduction 1369
2.2 Uniaxial compression testing 1369
2.3 Specification for compression testing machines 1373
2.4 Verification procedures 1374
2.5 Tensile strength testing 1376
2.6 Flexural strength testing 1378
References 1379
Chapter 3. Accelerated strength testing 1381
3.1 Aims of accelerated and early-age testing 1381
3.2 Principles 1382
3.3 British Standards procedures 1383
3.4 American Society for Testing and Materials (ASTM) procedures 1385
3.5 Other national standards 1387
3.6 Other research 1387
3.7 Applications of accelerated and early-age testing 1388
3.8 Conclusion 1395
References 1396
Chapter 4. Analysis of hardened concrete and mortar 1399
4.1 Aims and objectives 1399
4.2 Brief history 1399
4.3 Introduction 1400
4.4 Reasons for analysis 1400
4.5 Information that can be obtained by analysis 1400
4.6 Sampling procedures 1401
4.7 Determination of cement content of concrete 1404
4.8 Analysis of mortar to determine mix proportions 1406
4.9 Other determinations 1408
4.10 Accuracy and precision of determined cement content of concrete 1411
4.11 Accuracy and precision of determined mix proportions of mortar 1411
4.12 Summary 1412
Acknowledgements 1412
References 1412
Further reading 1413
Chapter 5. Core sampling and testing 1415
5.1 Introduction 1415
5.2 The current situation regarding standards and guidance 1415
5.3 Current core sampling, planning and interpretation procedures 1416
5.4 Worked examples 1426
5.5 Updating CSTR No. 11 1429
References 1435
Chapter 6. Diagnosis, inspection, testing and repair of reinforced concrete structures 1437
6.1 Introduction 1437
6.2 What is concrete? 1438
6.3 Recognizing concrete defects 1440
6.4 Investigation of reinforced concrete deterioration 1448
6.5 Testing for reinforcement corrosion 1479
References 1487
Part 2: Repair 1491
Chapter 7. Concrete Repair 1493
7.1 Patch repairs 1493
7.2 Cathodic protection 1496
7.3 Electrochemical chloride extraction (desalination) and realkalization 1499
7.4 Corrosion inhibitors 1508
Acknowledgements 1509
References 1509
Part 3: Quality and standards 1511
Chapter 8. Quality concepts 1513
8.1 Introduction 1513
8.2 Definitions 1513
8.3 Systems management standards 1515
8.4 Third-party registration and sector schemes 1526
8.5 Self-certification and quality control 1530
8.6 Details of ISO 9001 1532
8.7 Laboratory management 1539
References 1540
Chapter 9. Quality control 1541
9.1 Introduction 1541
9.2 Control charts 1542
9.3 Shewhart charts 1543
9.4 Cusum charts 1548
9.5 Compliance or acceptance testing 1557
9.6 Operating-Characteristic (O-C) curves 1558
9.7 Producer's and consumer's risk 1559
9.8 Experimental design 1560
References 1563
Further reading 1564
Chapter 10. Statistical analysis techniques in ACT 1566
10.1 Introduction 1566
10.2 Overview and objectives 1567
10.3 Sample data and probability measures 1567
10.4 Sampling and estimation 1578
10.5 Significance tests 1586
10.6 Regression models 1591
10.7 Statistical formulae and tables 1598
Further reading 1605
Chapter 11. Standards, specifications and codes of practice 1606
11.1 Aims and objectives 1606
11.2 Introduction 1606
11.3 Standards, specifications and codes of practice 1607
11.4 Prescription-based standards and performance-based standards 1613
11.5 The treatment of durability in standards, codes of practice and standard specifications 1615
11.6 Specifications 1632
References 1634
Further reading 1636
Index 1638

Textauszug

1

Fresh concrete

P.L. Domone

1.1 Introduction

Fresh concrete is a transient material with continuously changing properties. It is, however, essential that these are such that the concrete can be handled, transported, placed, compacted and finished to form a homogenous, usually void-free, solid mass that realizes the full-potential hardened properties. A wide range of techniques and systems are available for these processes, and the concrete technologist, producer and user must ensure that the concrete is suitable for those proposed or favoured.

Fresh concrete technology has advanced at a pace similar to many other aspects of concrete technology over the past three decades, and indeed many of these advances have been inter-dependent. For example, the availability of superplasticizers has enabled workable concrete to be produced at lower water/binder ratios thus increasing the in-situ strength.

In this chapter, we will start by considering the property known as workability*, including its definition and common methods of measurement. We will point out the limitations of these, and show how this leads to the need for a more fundamental scientific description of the behaviour of fresh cement pastes and concrete. We will then describe how this has been achieved by applying the principles of rheology, and explain the development and use of test methods which give a more complete understanding of the behaviour. We will then discuss the effect on the rheological properties of a range of constituent materials, including admixtures and cement replacement materials, and how a knowledge of these properties can be used to advantage. The factors that influence the loss of workability before setting are then briefly considered.

We will not discuss the specific properties required for particular handling or placing techniques such as pumping, slipform construction, underwater concreting etc. These are covered in various chapters in Volume 3 of this series, but hopefully the more general description given in this chapter will be of value when reading these. We will, however, describe the principles of ensuring that the concrete is correctly placed and compacted to give a uniform, homogenous result. Finally, we will discuss the behaviour of the concrete after placing but before setting, with particular reference to segregation and bleed.

1.2 Workability

1.2.1 Terminology and definitions

Problems of terminology and definition are immediately encountered in any discussion of the fresh properties of concrete. Every experienced concrete technologist, producer and handler has an understanding of the nature and properties of the material, and can choose from a wide variety of terms and expressions to describe it; examples include harsh, cohesive, lean, stiff, rich, etc. Unfortunately, all these terms, and many others, are both subjective and qualitative, and even those that purport to be quantitative, e.g. slump, give a very limited and sometimes misleading picture, as we will see. This is not to say that such terms and values should not be used, but that they must be used with caution, particularly when trying to describe or specify the properties unambiguously.

A satisfactory definition of workability is by no means straightforward. Over 50 years ago, Glanville, et al. (1947), after an extensive study of fresh concrete properties, defined workability as ‘the amount of work needed to produce full compaction’, thereby relating it to the placing rather than the handling process. A more recent ACI definition has encompassed other operations; it is ‘that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished’ (ACI, 1990). This makes no attempt to define how the workability can be measured or specified. A similar criticism applies to the ASTM definition of that property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity’ (ASTM, 1993).

Such definitions are clearly inadequate for the description, specification and quality control of fresh concrete, and many attempts have been to provide a more satisfactory definition which includes quantitative measurements. These are sometimes more restrictive, for example the ACI (1990) definition of consistency as ‘the relative mobility or ability of freshly mixed concrete to flow’, which is measured by the slump test. This difficulty illustrates that no single test or measurement can properly describe all of the required properties of the fresh concrete.

(Tattersall 1991) has proposed a division of the terminology relating to workability into three classes:

Class 1: Qualitative, to be used in a general descriptive way without any attempt to quantify, e.g. workability, flowability, compactability, stability, pumpability.

Class 2: Quantitative empirical, to be used as a simple quantitative statement of behaviour in a particular set of circumstances, e.g. slump, flow table spread.

Class 3: Quantitative fundamental, to be used strictly in accordance with the definitions in BS 5168: Glossary of rheological terms, e.g. viscosity, mobility, fluidity, yield value.1

Such a division is helpful in that it clearly exposes the limitations of many of the terms, and it will be useful to keep this in mind when reading this chapter.

1.2.2 Measurement of workability by quantitative empirical methods

Many tests have been devised and used over many years to produce quantitative empirical values in Class 2 above. They give a single measurement, and are therefore often referred to as ‘single-point’ tests, to distinguish them from the ‘two-point tests’ which give two measurements, and which we will describe later.

As long ago as 1947, twenty-nine single-point tests were described as the more important of those developed up to that time (Glanville et al., 1947). A recent compendium of tests has included sixteen single-point tests, and therefore at least this number are likely to be in current use (RILEM, 2002). Few, if any, of the tests described are suitable for the complete range of workabilities used in practice. Indeed, many have been developed in the past two decades in response to the use of increasingly higher workability concrete, including, most recently, self-compacting concrete.

Four tests have a current British Standard: slump, compacting factor, Vebe and flow table (or more simply, flow), and will now be discussed together with the slump flow test, an adaptation of the slump test for self-compacting concrete, and the degree of compactability test, which has replaced the compacting factor test in the recent European Standards. The tests are shown and described in Figures 1.1–1.6. Table 1.1 gives the principles on which they operate, and some comments on their use.

Figure 1.1 The slump test (BS 1881 Part 102: 1983; BS EN 12350-2: 2000; ASTM C 143-90a).

Figure 1.2 The compacting factor test (BS 1881 Part 103: 1993).

Figure 1.3 The Vebe test (BS 1881 Part 104: 1983, BS EN 12350-3: 2000).

Figure 1.4 The flow table test (BS 1881 Part 105: 1984, BS EN 12350-5: 2000).

Figure 1.5 The slump flow test.

Figure 1.6 The degree of compactability test (BS EN 12350-4: 2000).

Table 1.1

Common single-point workability tests

Slump (Figure 1.1)

measures a flow property of concrete under self-weight after standard compaction

• suitable for medium and high workability concrete • sensitive to small changes in water content • very simple suitable for site use • heavily operator dependent

Compacting factor (Figure 1.2)

measures the effect of a standard amount of work (height of fall) on compaction

• suitable for low, medium and high workability mixes • fairly simple, but requires scales • less operator dependent than slump

Vebe (Figure 1.3)

measures the amount of work (time at constant vibration) for full compaction

• suitable for very low and low workability mixes • greater relation to concrete placing conditions than slump • more complex than other methods, requires standard vibrating equipment • sometimes difficult to define end point

Flow table (Figure 1.4)

measures the effect of a standard amount of work (bumps) on spread

• suitable for high and very high workability...

Produkt-Details

• Erscheint lt. Verlag: 6.11.2003
• Sprache: englisch
• Themenwelt: Technik ► Architektur
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Maschinenbau
• Themenwelt: Wirtschaft
• ISBN-10: 0-08-052656-X / 008052656X
• ISBN-13: 978-0-08-052656-0 / 9780080526560