Corrosion of Steel in Concrete Understanding, investigation and repair

John P. Broomfield ~

E & FN SPON An lmprint of Chapman & Hall

London· Weinheim· New York· Tokyo · Melbourne ·Madras

Contents

Preface xüi Acknowledgements xv Glossary xvii

1 Introduction 1

2 Corrosion of steel in concrete 5 2.1 The corrosion process 6 2.2 Black rust 9 2.3 Pits, stray current and bacterial corrosion 10

2.3.1 Pit formation 10 2.3.2 Bacterial corrosion 10 2.3.3 Stray current induced corrosion 12 2.3.4 Local versus general corrosion (macrocells versus

microcells) 12 2.4 Electrochemistry, cells and half cells 13 2.5 Conclusions 15

3 Causes and mechanisms of corrosion and corrosion damage in concrete 16 3.1 Carbonation 16

3.1.1 Carbonation transport through concrete 19 3.2 Chloride attack 20

3.2.1 Sources of chlorides 20 3.2.2 Chloride transport through concrete 22 3.2.3 Chloride attack mechanism 22 3.2.4 Macrocell formation 25

3.3 Corrosion damage 25 3.4 Vertical cracks, horizontal cracks and corrosion 28 3.5 The synergistic relationship between chloride and

carbonation attack, chloride binding and release 28 References 28

vüi Contents

4 Condition evaluation 4.1 Preliminary survey 4.2 Detailed survey 4.3 Available techniques 4.4 Visual inspection

4.4.1 Property to be measured 4.4.2 Equipment and use 4.4.3 Interpretation 4.4.4 Limitations

4.5 Delamination 4.5.1 Property to be measured 4.5.2 Equipment and use 4.5.3 Interpretation 4.5.4 Limitations

4.6 Cover 4.6.1 Property to be measured 4.6.2 Equipment and use

· 4.6.3 Interpretation 4.6.4 Limitations

4.7 Half cell potential measurements 4.7.1 Equipment and use 4.7.2 Interpretation and the ASTM criteria 4.7.3 Half cell potential mapping 4.7.4 Cell to cell potentials

4.8 Carbonation depth measurement 4.8.1 Equipment and use 4.8.2 Interpretation 4.8.3 Limitations

4.9 Chloride determination 4.9.1 Property tobe measured 4.9.2 Equipment and use 4.9.3 Interpretation

4.10 Resistivity measurement 4.10.1 Property tobe measured 4.10.2 Equipment and use 4.10.3 Interpretation 4.10.4 Limitations

4.11 Corrosion rate measurement 4.11.l Property tobe measured 4.11.2 Equipment and use: linear polarization 4.11.3 Carrying out a corrosion rate survey 4.11.4 Interpretation: linear polarization 4.11.5 Limitations: linear polarization 4.11.6 Equipment and use: macrocell techniques

30 31 31 31 33 34 34 34 34 36 36 36 37 37 38 39 39 39 39 40 41 44 48 48 51 51 51 52 53 54 55 57 57 60 61 62 62 63 64 64 67 68 72 73

Contents

4.11.7 Interpretation: macrocell techniques 4.12 Other useful tests for corrosion assessment

4.12.1 Permeability and absorption tests 4.12.2 Concrete characteristics: cement content,

petrography, W / C ratio 4.12.3 Radar, radiography, PUNDIT, pulse velocity

4.13 Survey and assessment methodology 4.14 Monitoring 4.15 Special conditions: coated rebars and prestressing

4.15.1 Epoxy coated and galvanized reinforcing bars 4.15.2 Intemal prestressing cables in ducts

References

5 Physical and chemical repair and rehabilitation techniques 5.1 Concrete removal and surface preparation

5.1.1 Pneumatic hammers 5.1.2 Hydrojetting 5.1.3 Milling machines 5.1.4 Comparative costing 5.1.5 Concrete damage and surface preparation

5.2 Patches 5.2.1 Incipient anodes 5.2.2 Load transfer and structural issues

5.3 Coatings, sealers, membranes and barriers 5.3.1 Carbonation repairs 5.3.2 Coatings against chlorides, penetrating sealers 5.3.3 Waterproofing membranes 5.3.4 Barriers and deflection systems

5.4 Encasement and overlays 5.5 Sprayed concrete 5.6 Corrosion inhibitors References

6 Electrochemical repair techniques 6.1 Basic principles of electrochemical techniques 6.2 Cathodic protection

6.2.1 Theory and principles of impressed current systems 6.2.2 Theory and principles of sacrificial anode systems 6.2.3 The history of cathodic protection of steel in

concrete 6.3 The components of an impressed current cathodic

protection system 6.3.1 Cathodic protection anode systems 6.3.2 Deck anode systems

ix

73 75 75

76 76 77 78 79 79 80 81

85 86 88 88 90 92 92 93 93 96 96 97 98 99

101 102 103 -104 106

107 107 108 108 111

115

116 120 120

X Contents

6.3.3 Anodes for vertical and soffit surfaces 124 6.3.4 Conductive coatings 128 6.3.5 Thermal sprayed zinc 128 6.3.6 Clamp on systems 133 6.3.7 Sacrificial anode systems 133

6.4 Cathodic protection system design 136 6.4.1 Choosing the anode 136 6.4.2 Transformer / rectifiers and control systems 139 6.4.3 Monitoring probes 141 6.4.4 Zone design 143

6.5 Control criteria 143 6.6 Systeminstallation 147

6.6.1 Patching for cathodic protection 147 6.6.2 Rebar connections and continuity 148 6.6.3 Monitoring probe installation 149 6.6.4 Anode installation 149 6.6.5 Transformer/rectifier and control system installation 150 6.6.6 Initial energizing 150

"'6.6.7 Commissioning 150 6.6.8 Operation and maintenance 151

6.7 Cathodic protection of prestressed concrete 151 6.8 Cathodic protection of epoxy coated reinforcing steel 152 6.9 Cathodic protection of structures with ASR 153 6.10 Chloride removal 154

6.10.1 Anode types 154 6.10.2 Electrolytes 154 6.10.3 Operating conditions 155 6.10.4 End point determination 157 6.10.5 Possible effects 159 6.10.6 Alkali-silica reactivity 159 6.10.7 Bond strength 159 6.10.8 Results after treatment: beneficial effects of passing

currents through concrete 161 6.11 Realkalization 161

6.11.1 Anode types 162 6.11.2 Electrolytes 162 6.11.3 Operating conditions 162 6.11.4 End point determination 163 6.11.5 Possible effects 163

6.12 Comparison of techniques 163 6.12.1 Advantages of all electrochemical techniques 163 6.12.2 Disadvantages of all electrochemical techniques 164 6.12.3 Cathodic protection 164 6.12.4 Electrochemical chloride extraction 164

Contents xi

6.12.5 Realkalization 164 6.12.6 Costs 164

References 165

7 Rehabilitation methodology 169 7.1 Technical differences between repair options 171 7.2 Repair costs 171 7.3 Carbonation options 174

7.3.1 Patching_and coating 176 7.3.2 Why choose real.kalization? 177 7.3.3 Why choose corrosion inhibitors? 179

7.4 Summary of options for carbonation repairs 180 7.5 Chloride options 181

7.5.1 Patching and sealing 181 7.5.2 Why choose cathodic protection? 182 7.5.3 Why choose chloride extraction? 183 7.5.4 Other chloride repair options 184

7.6 Summary 185 References 186

8 Understanding and calculating the corrosion of steel in concrete 187 8.1 Initiation time T0, carbonation induced corrosion 188

8.1.1 Parrott's determination of carbonation rat~s from permeability 189

8.2 Chloride ingress rates (initiation) 189 8.2.1 The parabolic approximation 190 8.2.2 Sampling variability for chlorides 191 8.2.3 Mechanisms other than diffusion 191

8.3 Rate of depassivation (activation) 192 8.4 Deterioration and corrosion rates, T1 192

8.4.1 The Clear/Stratfull empirical calculation 194 8.5 Corrosion without spalling 195 8.6 Pitting corrosion 195 8.7 Cracking and spalling rates, condition indices and end

of functional service life 195 8.8 Summary of methodology to determine service life 197 References 197

9 Building for durability 199 9.1 Cover, concrete and design 199 9.2 Fusion bonded epoxy coated rebars 201

9.2.1 How does epoxy coating work? 203 9.2.2 Problems with epoxy coating 206

xii Contents

9.2.3 Advantages and disadvantages of fusion bonded epoxy eoated rebars 207

9.3 Waterproofing membranes 208 9.3.1 Advantages and disadvantages of waterproofing

membranes 210 9.4 Penetrating sealers 210 9.5 Galvanized rebar 211 9.6 Stainless steel reinforcement 211 9.7 Corrosion inhibitors 212 9.8 Installing eathodic protection in new structures 212 9.9 Durable buildings 213 9.10 Conclusions 214 Referenees 215

10 Future developments 216

Appendix A Bodies involved in eorrosion and repair of reinforeed eoncrete 220

Appendix B Strategie Highway Research Program: published reports on eoncrete and structures (eoncrete and the eorrosion of steel in atmospherieaHy exposed reinforced eoncrete bridge eomponents suffering from chloride induced eorrosion) 222

Appendix C Strategie Highway Research Program: unpublished reports on eoncrete and struetures (eoncrete and the eorrosion of steel in atmospherieally exposed reinforeed eonerete bridge eomponents suffering from chloride induced eorrosion) 231

Index 239