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Development of Test Methods for Assessment of

Concrete Durability for Use in

Performance-Based Specifications

By

Ahmad Shahroodi

A thesis submitted in conformity with the requirements for the degree of

Master’s of Applied Science (M.A.Sc.)

Graduate Department of Civil Engineering

University of Toronto

© Copyright by Ahmad Shahroodi (2010)

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ABSTRACT

Development of Test Methods for Assessment of Concrete Durability for

Use in

Performance-Based Specifications

Ahmad Shahroodi

(M.A.Sc., 2010)

Department of Civil Engineering

University of Toronto

Many Ministry of Transportation of Ontario (MTO) projects consist of construction and

maintenance of reinforced concrete structures. Where appropriate test methods exist,

MTO has been moving towards use of performance-based specifications for durability

control of concrete. MTO currently uses ASTM C1202 (RCPT) coulomb values to assess

concrete durability. This test requires taking cores, so replacing this test with a faster non-

destructive technique is important.

The main focus of this program was to study the Wenner probe surface resistivity as a

non-destructive test device and evaluate the potential for replacement of RCPT with the

Wenner resistivity.

This research program consists of the determination of RCPT values, water sorptivity

coefficients and electrical resistivities (bulk and surface) of nine concrete mixtures.

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In addition, the development of the Wenner probe instrument was studied. As well,

correlations between resistivity and ASTM C1202 and C1585 are provided followed by

technical recommendations for improving the Wenner test.

Keywords: Concrete durability; Permeability; Surface electrical resistivity; Water

sorptivity; Wenner probe; DC-cyclic bulk resistivity; RCPT coulombs passed

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ACK/OWLEDGEME/TS

A special note of thanks is extended to Professor R. D. Hooton for his guidance,

inspiration, and support throughout my thesis endeavour. Sincere appreciation is also due

to Ministry of Transportation of Ontario (MTO) for providing a large portion of funding

and supporting throughout the project and in particular Dr. B. Berszakiewicz.

For their help in performing all of the gruelling laboratory work at the University of

Toronto, Department of Civil Engineering, Materials Research section, recognition is also

due to Olga Perebatova and summer student Sean Hutchinson. Their kind help in this

research project is appreciated.

And last, but certainly not the least, the author wishes to thank his parents for their vital

positive energy, financial assistance, and encouragement. Also many thanks to my lovely

brother and sister. Your love and advice helped me survive the lonely life in Canada and

the long hours spent in the laboratory.

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TABLE OF CO/TE/TS

ABSTRACT………………………………………………………………………………ii

ACKNOWLEGDMENTS……………………………………..……………………...….iv

LIST OF TABLES……………………………………….……...……….……….…..….xii

LIST OF FIGURES……………………………………………..……......….…..…...…xiv

1. INTRODUCTION……….………………………..……………………….....….….….1

1.1 Objective and scope of study…………………………………………..….………3

2. LITERATURE REVIEW…………………………...………..……………..…….…....4

2.1 Influencing factors on concrete durability………………………………….……..4

2.1.1 External aggressive factors………………………………...……….……….7

2.1.1.1 Environmental ………………………………………………..……….7

2.1.1.1.1 External chemical attack…………………………………..…….7

2.1.1.1.1.1 Sulphates (sulphate attack)…………..…………….….8

2.1.1.1.1.2 Chloride corrosion……………………..……...……..12

2.1.1.1.1.3 Carbon dioxide and corrosion…………..….………..15

2.1.1.1.1.4 Acid Attack………………………………...…………16

2.1.1.1.2 External physical attack……………………..…………………17

2.1.1.1.2.1 Freezing and thawing damage……………………….17

2.1.1.1.3 Environmental factors damaging internally………….….……..19

2.1.1.1.3.1 Alkali-silica reaction (ASR)…………………..……...19

2.1.1.2 Operation and loading………………………………………………..20

2.1.1.2.1 Abrasion………………………………………………………..20

2.1.1.2.2 Leaching………………………………………………………..21

2.1.2 Internal structure of concrete………………………………………………22

2.1.2.1 Aggregate phase……………………………………………………...22

2.1.2.2 Cement phase………………………………………………………...23

2.1.2.2.1 W/CM ratio…………………………………………………….23

2.1.2.2.2 Degree of hydration……………………………………………24

2.1.2.2.3 Curing…………………………….………………………...….24

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2.1.2.2.4 Admixtures………………………………………………….….24

2.1.2.2.5 Type of cement…………………………………………….…...25

2.1.2.2.6 Supplementary cementing materials (SCMs)………………….25

2.1.3 Design and construction……………………………………………………25

2.1.3.1 Design………………………………………………………………..26

2.1.3.2 Construction………………………………………………………….27

2.2 Concrete durability measurement………………………………………………..28

2.2.1 Compressive strength test …………………………………………….…...28

2.2.2 Rapid chloride permeability test (RCPT) ……………………………........28

2.2.2.1 First 5 minutes RCPT resistivity……………………………………..31

2.2.2.2 Chloride ion penetration (chloride migration coefficient)…………...31

2.2.2.3 Linear extrapolation technique…………………………………….…33

2.2.2.4 Influencing factors on penetration resistance test……………………33

2.2.2.4.1 Admixtures and RCPT values………………………………….33

2.2.2.4.2 Temperature and RCPT values………………………………...34

2.2.2.5 RCPT weak points …………………………………………………..34

2.2.3 Rate of water absorption (Sorptivity)……………………………………....35

2.2.3.1 Calculation …………………………………………………………..35

2.2.3.2 Laboratory sorptivity test ……………………..……………………..36

2.2.3.3 Field sorptivity test…………………………………………………..37

2.2.3.3.1 Field sorptivity apparatus overview……………………………37

2.2.3.3.1.1 Vacuum-attachment base plate………………………38

2.2.3.3.1.2 Disc plate……………………………………….……39

2.2.3.4 Influencing factors on water sorptivity values .…………………...…41

2.2.3.4.1 Aggregate and the rate of water absorption…………………....41

2.2.4 Electrical resistivity test……………………………………………………41

2.2.4.1 Bulk electrical resistivity ……………………………………………44

2.2.4.2 Surface electrical resistivity………………………………………….49

2.2.4.2.1 Surface disc…………………………………………………….49

2.2.4.2.2 Four - probe line array (Wenner probe)………………………..51

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2.2.4.2.3 Four - probe square array………………………………………55

2.2.4.2.4 Application……………………………………………………..57

2.2.4.3 Influencing factors on concrete electrical resistivity………………...58

2.2.4.3.1 Temperature and electrical resistivity………………………….59

2.2.4.3.2 Chemical admixtures and electrical resistivity………………...60

2.2.4.3.3 Aggregate and electrical resistivity…………………………….60

2.2.4.3.4 Cement type and electrical resistivity………………….………61

2.2.5 Influencing factors on durability tests……………………………………...62

2.2.5.1 W/CM ratio ………………………………………………………….62

2.2.5.2 Supplementary cementitious materials………………………………64

2.2.5.3 Curing ……………………………………………………………….66

2.2.5.4 Moisture content……………………………………………………..67

3. EXPERIMENTAL PROGRAM ……………………………………………………...69

3.1 Methodology……………………………………………………………………..69

3.1.1 Compressive strength …………………………………………...…………69

3.1.2 Rapid chloride permeability test …………………………………………..69

3.1.3 Water sorptivity test…………………………………………………...…...70

3.1.3.1 Laboratory sorptivity test ……………………………………………70

3.1.3.2 Field sorptivity test…………………………………………………..71

3.1.3.2.1 Methodology…………………………………………………...71

3.1.4 Electrical resistivity……………………………………………………...…75

3.1.4.1 Methodology…………………………………………………………75

3.2 Experimental project………………………………………………………...…...78

3.2.1 Research project tests…………………………………………………...….78

3.2.1.1 Electrical resistivity of concrete……………………………………...78

3.2.1.1.1 Surface electrical resistivity…………………………………....78

3.2.1.1.1.1 RM MKII technical properties………..……………...79

3.2.1.1.1.2 Surface electrical resistivity measurement…………..80

3.2.1.1.2 Cyclic-DC bulk electrical resistivity …………………….…….85

3.2.1.1.2.1 Cyclic-DC bulk resistivity of full length cylinders.…..85

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3.2.1.1.2.2 Cyclic-DC bulk resistivity of concrete discs………....85

3.2.1.1.3 Rapid Chloride permeability test resistivity (first 5 minutes)….86

3.2.1.2 Rapid chloride permeability test (RCPT)…………………………….86

3.2.1.3 Rate of water absorption (water sorptivity test)……………………...89

3.2.1.3.1 Laboratory sorptivity test………………………………………89

3.2.1.3.2 Field sorptivity…………………………………………………90

3.2.1.4 Compressive strength test (f΄c)………………………………………90

3.2.2 Specimens………………………………………………………………….93

3.2.2.1 Concrete Cylinders…………………………………………………...93

3.2.2.2 Concrete slabs……………………………………………………..…94

3.2.3 Materials………………………………………………………………..….96

3.2.3.1 Cementitious materials …………..………………………………….96

3.2.3.2 Aggregates…………………………………………………………...97

3.2.3.2.1 Sieve analysis of fine and coarse aggregates………………..…97

3.2.3.2.2 Physical properties of fine and coarse aggregates……………..99

3.2.3.3 Chemical admixtures……………………………………….………100

3.2.4 Mix design………………………………………………………..………102

3.2.5 Testing process…………………………………………………….……...104

3.2.5.1 Concrete methodology…………………………………...…………105

3.2.5.1.1 Material preparation…………………………………………..105

3.2.5.1.2 Mixing concrete…………………………………………..…..106

3.2.5.1.3 Fresh concrete properties……………………………………..108

3.2.5.1.4 Casting concrete……………………………………………....108

3.2.5.1.5 Curing ……………………………………………..…………110

4. RESULTS AND DISCUSSION………………………..……………………………111

4.1 Compressive strength……………………………………..………………….....111

4.1.1 Effects of changing W/CM ratio on compressive strength……...………..113

4.1.2 SCMs effects on compressive strength………………………...……........115

4.1.2.1 Comparison between compressive strength of SCMs concretes …..115

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4.2 Rapid chloride permeability test (RCPT)……………………………………….116

4.2.1 Total charge passed…… ……………………………………………....116

4.2.1.1 Effects of changing W/CM ratio on the RCPT coulombs………….119

4.2.1.2 SCMs effects on RCPT values……………………………..……….120

4.2.2 RCPT electrical resistivity (first 5 min)…………………………………..121

4.2.2.1 W/CM ratio effects on concrete resistivity…………………………123

4.2.2.2 Effects of adding SCMs on the RCPT electrical resistivity………...125

4.2.3 Depth of chloride ion penetration (colorimetric method)……………..….127

4.2.3.1 Effects of adding SCMs on the depth of chloride ion penetration….131

4.2.3.2 W/CM ratio effects on chloride ion penetration……………………133

4.2.4 RCPT extrapolation……………………………………………………....135

4.3 Rate of water absorption (sorptivity)…………………………………………...139

4.3.1 Laboratory sorptivity test…………………………………………………139

4.3.1.1 SCMs effects on the lab sorptivity values…………………………..147

4.3.1.2 W/CM ratio effects on the lab sorptivity values …………………...148

4.3.2 Field sorptivity test…………………………………………………....….149

4.3.3 SCMs effects on the rate of water absorption………………………….…155

4.3.4 W/CM ratio influences on the rate of water sorptivity coefficient….........156

4.3.5 Water sorptivity and degree of saturation………….…………………..…158

4.3.6 Calibration curves …………………………………………...……….…..158

4.4 Electrical resistivity……………………………………………………………..164

4.4.1 DC-cyclic bulk resistivity (Monfore resistivity)………………………….165

4.4.1.1 DC-cyclic bulk resistivity of full length concrete cylinders………..166

4.4.1.1.1 SCMs effects on the DC-cyclic bulk resistivity………………168

4.4.1.1.2 W/CM ratio effects on bulk resistivity………………………..169

4.4.1.2 Bulk resistivity as an indicator for chloride penetrability…………..170

4.4.1.3 Bulk resistivity of concrete discs …………………………………..171

4.4.2 Surface electrical resistivity………………………………………...…….173

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4.4.2.1 Surface electrical resistivity of concrete cylinders……………...….173

4.4.2.1.1 Statistical analysis of concrete cylinders surface resistivity….177

4.4.2.2 Surface electrical resistivity of concrete slabs ……………………..179

4.4.2.2.1 Circular slab number 1………………………………………..180

4.4.2.2.2 Circular slab number 2………………………………………..182

4.4.2.2.3 Statistical Analysis of concrete slabs surface resistivity….…..184

4.4.2.3 Unifying the surface resistivity values…………………………...…188

4.4.2.4 W/CM ratio effects on surface electrical resistivity ………..……...196

4.4.2.5 SCMs effects on surface electrical resistivity ………………….......197

4.4.2.6 Effects of specimen geometry on the Wenner probe values……......198

4.4.2.7 Surface electrical resistivity as an indicator for other properties of

concrete………………………………………………………………………………....202

4.4.2.7.1 Surface electrical resistivity and compressive strength……....202

4.4.2.7.2 Surface electrical resistivity and total charge passed…………204

4.4.2.7.3 Surface electrical resistivity and the other types of electrical

resistivity………………………………………………………………………………..206

4.4.2.7.4 Surface resistivity and water sorptivity coefficient…………..209

4.4.2.7.5 Surface electrical resistivity and diffusion of chloride ion through

concrete………………………………………………………………………………....210

4.4.2.8 Wenner probe as a practical instrument…………………………….212

5. CONCLUSIONS AND RECOMMENDATIONS………………..…………………215

5.1 Conclusions………………………………….……………………………….....215

5.2 Recommendations………………………………………………………………219

6. REFERENCES………………………………………………………………………220

APPENDIX A: CONCRETES MIX DESIGN………………….……………………...232

APPENDIX B: COMPRESSIVE STRENGTH TEST...…………….............................241

APPENDIX C: LABORATORY SORPTIVITY TEST RESULTS…………………...249

APPENDIX D: FIELD SORPTIVITY TEST RESULTS……………………………...250

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APPENDIX E: BULK ELECTRICAL RESISTIVITY……………………………..….251

APPENDIX F: SURFACE ELECTRICAL RESISTIVITY……………………………255

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LIST OF TABLES TABLE PAGE

Table 2.1: Adequate air content for different concretes……………………………………...……………..19

Table 2.2: Chloride ion penetrability based on charge passed…………….……………..…………………30

Table 2.3: Electrical resistivity values for rebar corrosion rate……………………………………….…….43

Table 2.4: Electrical resistivity of rocks………………………………………………………………….…60

Table 3.1: Probe spacings used in the research project…………………………………………….…….…85

Table 3.2: List of concrete cylinders for the project tests……………………………………….……….…93

Table 3.3: Durability tests for the concrete slabs……………………………………………………….…..95

Table 3.4: Chemical composition of cementitious materials …………………………………………..…..96

Table 3.5: Sieve analysis of fine aggregate ……………………………………………………………..….97

Table 3.6: Sieve analysis of coarse aggregate …………………………………………………………..…98

Table 3.7: Sand sieve analysis required for the FM calculation…………………………………………...100

Table 3.8: Aggregates physical properties……………………………………...………………………….100

Table 3.9: Basic mix design data…...…………………………………………………………………...…101

Table 3.10: Chemical admixture properties …………………..…………………………………….……..101

Table 3.11: Research program concrete mixes……………………………………………………….……102

Table 3.12: Concrete mixes proportions (mix design)..…………………………………………………...103

Table 3.13: Chemical admixture dosages ………………………………………………………...………104

Table 3.14: Fresh concrete properties…………………………………………………..……………….…108

Table 4.1: Average compressive strength of different mixes at various ages……………………………..112

Table 4.2: Chloride ion penetrability based on charge passed……..………………….…………………..116

Table 4.3: The RCP test results ………………………………………………………...…………………117

Table 4.4: The RCPT electrical resistivity values…………………………………………………………122

Table 4.5: Electrical resistivity values and rebar corrosion rate………………………...…………………122

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Table 4.6: Depth of chloride ion penetrated during the RCP test………………………………………….128

Table 4.7: Non-steady-state migration coefficient of concrete mixes………………………………….….129

Table 4.8: Extrapolated passing charges (coulombs)………………………………...……….……….…..135

Table 4.9: Effects of maximum anodic temperature on the RCPT coulomb values…………….…….......137

Table 4.10: Average water sorptivity values of concrete discs……………………………………………142

Table 4.11: Water sorptivity coefficient of the circular concrete slabs…………………………………....150

Table 4.12: Degree of saturation of the concrete circular slabs…….……………………………………..152

Table 4.13: Bulk resistivity values of concrete cylinders…………………………………………….……166

Table 4.14: The Monfore resistivity of Ø100 x 50 mm concrete discs…………………………………....172

Table 4.15: Concrete cylinders apparent surface electrical resistivity values …………………………….173

Table 4.16: Statistical analysis of resistivity measurement of concrete cylinders (a= 50mm)…….………177

Table 4.17: Average apparent surface electrical resistivity of circular concrete slabs…………….………184

Table 4.18: Statistical analysis of resistivity measurement of concrete slabs (a= 50mm)……………...…186

Table 4.19: Cell constant conversion factors for different probe spacings………………………………..190

Table 4.20: Surface resistivity of concrete cylinders with different probe spacings……………………....191

Table 4.21: True surface electrical resistivity of concrete cylinders…………………………………..…..192

Table 4.22: Surface resistivity of concrete slabs with different probe spacings………………………..…193

Table 4.23: True surface electrical resistivity of concrete slabs………………………………………...…194

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LIST OF FIGURES

FIGURE PAGE

Figure 2.1: Affecting factors on durability of concrete………………………………………………………6

Figure 2.2: Sulfate-attacked fence posts located where a saline water table exists…………………………..9

Figure 2.3: Concrete suffering from thaumasite……………………………………………..………….…..10

Figure 2.4: Physical sulphate attack mechanism……………………………………………………………11

Figure 2.5: Physical sulphate attack disintegrates concrete surface………………………………………...11

Figure 2.6: Schematic description of corrosion process of a reinforcing steel in concrete………………...13

Figure 2.7: Cracking concrete by product of corrosion……………………………………………………..13

Figure 2.8: Rebar corrosion decreases concrete loading capacity and strength………………………….…14

Figure 2.9: Concrete carbonation process ……………………………………………………………….…15

Figure 2.10: Concept of change in quantity of porosity in adequately cured carbonated concretes……..…16

Figure 2.11: Acid attack deteriorates concrete……………………………………………………………...17

Figure 2.12: Freeze-thaw damage in a concrete column caused rebar corrosion and more deterioration….18

Figure 2.13: ASR Mapping cracking and gel leakage……………………………………………………....20

Figure 2.14: Surface abrasion due to the heavy traffic volume………………………………………….….21

Figure 2.15: Leaching and spalling under footway of a bridge…………………………………………..…22

Figure 2.16: ASTM C1202-07 rapid chloride permeability test setup……………………………………...29

Figure 2.17: Whitish chloride front migration in concrete sprayed after the RCP test………………..……32

Figure 2.18: Field sorptivity apparatus (horizontal orientation)…………………………………………….38

Figure 2.19: Vacuum- attachment base plate……………………………………………………………….39

Figure 2.20: Field sorptivity disc plate……………………………………………………………….……..40

Figure 2.21: Schematic view of reinforcing bar corrosion in concrete………………………………..……43

Figure 2.22: Concrete bulk electrical resistivity test with two electrodes …………………………….……45

Figure 2.23: Schematic diagram for the DC test setup ……………………………………………………..46

Figure 2.24: Schematic diagram for the AC test setup ……………………………………………………..48

Figure 2.25: Setup of one electrode (disc) measurement of concrete resistivity……………………...…….50

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Figure 2.26: Concrete cube with embedded electrodes……………………………………………………..51

Figure 2.27: Schematic representation of four-electrode resistivity test……………………………..……..52

Figure 2.28: Cell constant correction factor for the centered end face configuration……………………....54

Figure 2.29: Cell constant correction factor for the centred longitudinal measuring configuration………..55

Figure 2.30: Four-probe square array principle …………………………………………………………….56

Figure 2.31: Four-probe square array schematic representation for studying crack parameters………...….56

Figure 2.32: Surface resistivity as a function of crack depth……………………………………………….58

Figure 2.33: Relationship between measured resistivity and air temperature ……………………..……….59

Figure 2.34: Relation between resistivity and applied voltage of different cement concretes……….……..61

Figure 2.35: Relation between electrical resistivity and W/CM ratio ………………………………...……63

Figure 2.36: Relative reduction in diffusion coefficient with silica fume…………………………………..65

Figure 3.1: Hose barbs attached to inner and outer chambers of a field sorptivity test apparatus………….72

Figure 3.2: Schematic overview of the field sorptivity process…………………………………………….74

Figure 3.3: DC-cyclic bulk electrical resistivity test set up…………………………………………………76

Figure 3.4: Wenner probe being used to measure surface resistivity of a concrete cylinder……………….77

Figure 3.5: RM MKII (surface resistivity-meter)……………………………………………………...……79

Figure 3.6: Schematic representation of four-electrode resistivity test………………………………..…...79

Figure 3.7: Surface electrical resistivity measurement order for concrete cylinders…………………...…..81

Figure 3.8: Influencing factors for probe spacing in the Wenner resistivity……………………………..…81

Figure 3.9: Effect of concrete section dimensions on surface resistivity measurement………………….…82

Figure 3.10: Effect of edge and end proximity on surface resistivity measurement………………...….…..83

Figure 3.11: Effect of maximum aggregate size on surface resistivity measurement………………………84

Figure 3.12: DC-cyclic bulk resistivity of a concrete disc (test setup)……………………………...………86

Figure 3.13: The RCP test setup……………………………………………………………………...……..87

Figure 3.14: Splitting concrete discs after The RCPT………………………………………………...…….88

Figure 3.15: AgNO3 solution appears the depth of chloride penetration…………………………….……..88

Figure 3.16: Laboratory water sorptivity test setup……………………………………………………..…..89

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Figure 3.17: Field sorptivity test setup on a concrete slab………………………………………………….90

Figure 3.18: Research program concrete tests…………………………………………………………..91-92

Figure 3.19: Concrete cylinders testing layouts ……………………………………..………………….….94

Figure 3.20: Fine aggregate grading curve…………………………………………...…………………….98

Figure 3.21: Coarse aggregate grading curve……………………………………………………………….99

Figure 3.22: Materials loading order………………………………………………………………………107

Figure 3.23: Magnesium float for finishing the concrete slabs surface …………………………………...109

Figure 3.24: First 24 h concrete curing under plastic sheets and wet burlaps………………………..……109

Figure 4.1: Crushing a concrete cylinder during compressive strength test…………………………….…111

Figure 4.2: Compressive strength of concrete mixtures at various ages…………………………………..112

Figure 4.3: Compressive strength of SFSL concrete mixes……………………………………………….113

Figure 4.4: Compressive strength of mixes contain slag………………………………………………….114

Figure 4.5: Concrete strength of plain cement concretes………………………………………………….114

Figure 4.6: Comparison between compressive strength of ternary and binary concrete mixes …………..115

Figure 4.7: The RCPT coulomb values with age……………………………………………………..……117

Figure 4.8: Total coulombs passed (silica fume and slag concrete mixes)….…….………………………118

Figure 4.9: Total coulombs passed (slag concrete mixes)………………………………………………....118

Figure 4.10: Total coulombs passed (plain cement concrete mixes) ………….……………………...…...119

Figure 4.11: Comparison between total charge passed through concrete mixes………………..…………120

Figure 4.12: First 5 minutes RCPT electrical resistivity ………………………………………………….123

Figure 4.13: Effect of changing W/CM ratio on the RCPT electrical resistivity of ternary mixes………..124

Figure 4.14: Effect of changing W/CM ratio on the RCPT electrical resistivity of binary mixes……...…125

Figure 4.15: Silica fume effects on the first 5 min. RCPT electrical resistivity……...……………………126

Figure 4.16: The effects of adding slag on the first 5 min. RCPT electrical resistivity…………………...127

Figure 4.17: Splitting a concrete disc after the RCP test…………………………………………………..128

Figure 4.18: Relation between the RCPT passing charges and the chloride migration coefficient…….…131

Figure 4.19: Depth of chloride ion penetrated into concrete specimens during the RCP test………….….132

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Figure 4.20: Zero depth of chloride ion penetration (ternary concrete)…………………………………...133

Figure 4.21: W/CM ratio effects on the depth of chloride ion penetration during the RCP test……...…...134

Figure 4.22: RCPT recorded and extrapolated charges passed (day 7)……………………………………136

Figure 4.23: RCPT recorded and extrapolated charges passed (day 28)………………………………..…136

Figure 4.24: Relation between the extrapolated and recorded passing charges..……………………….…138

Figure 4.25: Rate of water absorption of top slices……………………………………………………..…140

Figure 4.26: Rate of water absorption of middle slices……………………………………………………141

Figure 4.27: Rate of water absorption of bottom slices……………………………………………………142

Figure 4.28: Extracting cores from the concrete rectangular slabs ……………………………………….143

Figure 4.29: Rate of water absorption of concrete discs extracted from slabs……………………..…143-144

Figure 4.30: Comparison between water sorptivity of concrete discs sliced from concrete cylinders and

concrete cores extracted from concrete slabs…………………………………………………………..….145

Figure 4.31: Water sorptivity and chloride migration coefficient…………………………………………146

Figure 4.32: Relation between the lab sorptivity test values and concrete compressive strength…………147

Figure 4.33: Average rate of water absorption of concrete mixes…………………………………………148

Figure 4.34: Field sorptivity apparatus (horizontal orientation)…………………………………………...149

Figure 4.35: Water sorptivity coefficients of concrete circular slabs ……………………………………..150

Figure 4.36: Middle piece taken from a cored rectangular slab for moisture content measurement……...151

Figure 4.37: Degree of saturation of the concrete slabs at different ages…………………………………153

Figure 4.38: Moisture content effects on the rate of water absorption…………………………………….154

Figure 4.39: SCMs effects on the field sorptivity test results………………………………..……………155

Figure 4.40: W/CM ratio effects on the water sorptivity coefficients of plain cement concrete………….156

Figure 4.41: W/CM ratio effects on the sorptivity coefficients of concrete mixes containing slag……….157

Figure 4.42: W/CM ratio effects on the water sorptivity coefficients of the ternary mixes………………157

Figure 4.43: Water sorptivity- saturation calibrating curve for HPC mix ………………….……………..159

Figure 4.44: Water sorptivity- saturation calibrating curve for HPC+ mix ………………….……………159

Figure 4.45: Water sorptivity- saturation calibrating curve for SFSL 0.40 mix …………….…………….160

Figure 4.46: Water sorptivity- saturation calibrating curve for PCSL 0.40 mix …………….……………160

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Figure 4.47: Water sorptivity- saturation calibrating curve for PCSL 0.40+ mix …………….…………..161

Figure 4.48: Water sorptivity- saturation calibrating curve for PCSL 0.45 mix ……………….…………161

Figure 4.49: Water sorptivity- saturation calibrating curve for PCSL 0.45+ mix ……………….………..162

Figure 4.50: Water sorptivity- saturation calibrating curve for PC 0.45 mix …………………….……….162

Figure 4.51: Water sorptivity- saturation calibrating curve for PC 0.45+ mix…………………….……....163

Figure 4.52: Drying circular concrete slabs……………………………………………………….……….164

Figure 4.53: Concrete bulk resistivity test with two steel electrodes……………………………………...165

Figure 4.54: DC-cyclic bulk resistivity of Ø100 x 200 mm concrete cylinders…………………………...167

Figure 4.55: SCMs effects on the DC-cyclic bulk resistivity values………………………………………168

Figure 4.56: W/CM ratio effects on the Monfore resistivity values………………………...………..……170

Figure 4.57: Relation between chloride migration coefficient and the DC-cyclic bulk resistivity with the

RCPT 5 min. resistivity……………………………………………………………………………………171

Figure 4.58: DC-cyclic bulk resistivity of Ø100 x 50 mm concrete discs……………………………...…172

Figure 4.59: Surface electrical resistivity of concrete cylinders (25 mm probe spacing)………………....175

Figure 4.60: Surface electrical resistivity of concrete cylinders (30 mm probe spacing)…………………175

Figure 4.61: Surface electrical resistivity of concrete cylinders (40 mm probe spacing)………………....176

Figure 4.62: Surface electrical resistivity of concrete cylinders (50 mm probe spacing)…………………176

Figure 4.63: Surface resistivity measuring order for concrete circular slabs…………………………...…179

Figure 4.64: Surface electrical resistivity of concrete slabs labelled number 1 (a= 20 mm) ……………..180

Figure 4.65: Surface electrical resistivity of concrete slabs labelled number 1 (a= 30 mm)……………...181

Figure 4.66: Surface electrical resistivity of concrete slabs labelled number 1 (a=40 mm)………………181

Figure 4.67: Surface electrical resistivity of concrete slabs labelled number 1 (a=50 mm)……………....182

Figure 4.68: Surface electrical resistivity of concrete slabs labelled number 2 (a=20 mm)………………182

Figure 4.69: Surface electrical resistivity of concrete slabs labelled number 2 (a=30 mm)……………....183

Figure 4.70: Surface electrical resistivity of concrete slabs labelled number 2 (a=40 mm)………………183

Figure 4.71: Surface electrical resistivity of concrete slabs labelled number 2 (a=50 mm)………..……..184

Figure 4.72: Cell constant correction factor for specimen used ………………………..…………………189

Figure 4.73: Required limitations for calculating the optimum probe spacing…………………………....195

xix

Figure 4.74: W/CM ratio effects on the surface electrical resistivity of concrete cylinders ……..……….196

Figure 4.75: SCMs effects on the surface electrical resistivity of concrete cylinders……………………..197

Figure 4.76: SCMs effects on the surface electrical resistivity of circular slabs………………………..…197

Figure 4.77: Relation between different specimens resistivity with the optimum probe spacing………....199

Figure 4.78: Comparison between specimens resistivity values and different probe spacings...………….200

Figure 4.79: Probe spacings effect on the penetration depth of the Wenner applied current …..…………201

Figure 4.80: Surface resistivity of concrete cylinders versus compressive strength………………..……..203

Figure 4.81: Surface resistivity of concrete slabs versus compressive strength…………………………...203

Figure 4.82: Surface resistivity of concrete cylinders versus the RCPT passing charge………………….204

Figure 4.83: Modified surface resistivity versus the RCPT results based on MTO specification….……..205

Figure 4.84: Surface resistivity of concrete slabs versus the RCPT passing charge………………………206

Figure 4.85: Surface resistivity of concrete cylinders versus the RCPT resistivity…………………….…207

Figure 4.86: Surface resistivity of concrete slabs versus the RCPT resistivity……………………………207

Figure 4.87: Surface resistivity of fully saturated cylinders versus Monfore resistivity…………………..208

Figure 4.88: Surface resistivity of not fully saturated slabs versus Monfore resistivity…………………..208

Figure 4.89: Surface resistivity of concrete cylinders and water sorptivity coefficient…………………...210

Figure 4.90: Surface resistivity of concrete cylinders versus chloride migration coefficient……………..211

Figure 4.91: Surface resistivity of concrete slabs versus chloride migration coefficient……………….…211

Figure 4.92: Practical relation between the surface resistivity values and other tests values…………...…213

Figure 4.93: Regression analysis of compressive strength and surface electrical resistivity……………...214

1

1

CHAPTER 1

I/TRODUCTIO/

Many Ministry of Transportation of Ontario (MTO) projects consist of construction and

maintenance of reinforced concrete bridge structures. Where appropriate test methods

exist, the Ministry has been moving towards use of performance-based specifications for

construction acceptance and durability control of concrete.

Two primary characteristics of concrete, strength and durability, need to be assessed to

obtain performance of concrete structures.

Concrete strength is measured and controlled by standard testing techniques and

guidelines but the lack of durability assessment standards is an issue. A durable concrete

must retain its original form, quality, and serviceability under its working environmental

conditions.

Generally, concrete durability is affected by five factors:

1) Design: type of materials, materials conditions and proportions, concrete mix

design, and thickness of concrete cover over reinforcing steel

2) Construction practices: mixing, delivering, discharging, consolidating, finishing,

and curing conditions

3) Hardened concrete properties: compressive strength, permeability

4) Environmental exposure conditions: sulphate attack, freeze-thaw, alkali-silica

reaction

5) Loading conditions: type of loading, loading duration, crack width and depth.

Concrete design and construction practices are controlled by standard guidelines. Also

the loading conditions are considered during the design process. The major issue needed

to be studied for preparing durable concretes is the hardened concrete durability.

Permeability is the most influencing factor on the durability and service life of reinforced

concrete members because movement of aggressive fluids from the surrounding

environment into concrete is the main cause for most concrete deteriorations. In other

words, developing an impermeable pore system is necessary to produce a durable

concrete.

2

The permeability is currently estimated by the ASTM C1202, permeability index test.

The testing method requires the removal of cores (a destructive technique) and

preparation of samples for testing purposes which is expensive and time consuming.

Therefore providing suitable and time-saving non-destructive testing methods to assess

concrete performance as measured on hardened concrete in place would be important for

the Ministry.

Some non-destructive tests exist for concrete strength (e.g. Schmidt hammer), but there is

not any direct non-destructive test for measuring the permeability of in-place concrete.

Therefore a fast and simple non-destructive test has to be developed to evaluate the

durability of concrete. A geometry-independent test is the electrical resistivity test. The

electrical resistivity test can be used as a non-destructive alternative to the current

permeability index test. Initially the resistivity test was used on concrete cores and

cylinders taken from existing structures (destructive). Later surface electrical resistivity

measurement techniques which had been used by geologist were developed for concrete

structures. Pre-planned embedment electrodes were required for this test method, so the

method was still destructive and time-consuming. Recently surface electrical resistivity is

measured by an instrument called a Wenner probe without embedding any electrode into

concrete. This test can be done quickly on surfaces both “as is” and after saturation with

water, since moisture conditions affect surface resistivity results.

The Wenner probe measures the electrical properties of covercrete concrete which is

different from that of the bulk concrete due to compaction, bleeding, finishing, and

curing.

In general, durability of covercrete is improved by obtaining a discontinuous capillary

pore structure which is caused by using lower water-to-cementitious ratio (W/CM), using

supplementary cementitious materials, and applying adequate moist curing. A durable

covercrete concrete is necessary to achieve a long service life of concrete structures in a

severe environment, so surface properties were studied in this research project.

3

1.2 Objective and scope of study

The objective of this research consists of testing concrete samples with a range of mix

designs to evaluate the surface electrical resistivity test. In addition, the concrete samples

were tested in the rapid chloride permeability test (RCPT), and rate of water absorption

due to capillary suction, referred to as sorptivity (Hooton, Mesic and Beal (1993) in

DeSouza et al., 1996), in order to correlate the results.

Surface electrical resistivity and water absorption tests can be used on cores and cylinders

extracted from structures, but they also have potential as non-destructive tests for use on

constructed surfaces. Laboratory types of electrical resistivity and water absorption are

the Monfore resistivity test and the ASTM C1585 water sorptivity test (named as

laboratory sorptivity test), respectively. Non-destructive types of electrical resistivity and

water absorption are the Wenner probe and field sorptivity testing technique (DeSouza

and Hooton, 1996). Therefore both destructive and non-destructive forms of these two

tests in addition to the RCPT were used in this research program.

The study begins with a literature review considering concrete durability aspects,

concrete deterioration mechanisms, and environmental effects on surface concrete. A

brief description of testing methods, advantages and limitations, and the mechanisms of

the instruments are included. In the next chapter a detailed methodology for all tests

applied in this project followed by in-depth project plan including experimental variables

are described. Data presentation and analyses of nine series of test cores, cylinders, and

slabs are presented to quantify the applicability of the Wenner probe. Finally practical

correlations between the Wenner probe values and the other standard permeability tests,

conclusions from the study, and recommendations are presented.

4

CHAPTER 2

LITERATURE REVIEW

Two major properties of concrete are Strength and Durability.

Strength is the ability of concrete to resist stress (compressive, tensile, shear, or torsion).

Concrete strength is a function of many factors as well as concrete mix design, curing

process, using reinforcing steels, and etc. On the other hand, durability is another

important property of concrete.

In this research, measuring the durability of concrete was the main concern.

The American Concrete Institute in ACI 116 R defines durability of concrete as its ability

to resist weathering action, chemical attack, abrasion, and other conditions of service.

Also durability of concrete is defined as the capability of concrete by itself of keeping the

original properties for a certain period (Collepardi, 2000). Durable concrete may be

defined as concrete that keeps its original quality, form, and serviceability when it is

exposed to its environment (Savas, 1999).

Many factors affect concrete durability either directly or indirectly.

2.1 Influencing factors on concrete durability

“The most important characteristic of concrete that is believed to be affecting its

durability is permeability (better to use “penetrability” as it is not mechanism specific) of

concrete” (Baykal, 2000 in Chini, 2003). There is an approximate inverse relationship

between concrete penetrability and compressive strength as well as durability. But it is

worth noting that durability of concrete is not necessarily related to the compressive

strength of concrete.

Penetrability of concrete can be determined by measuring the rate of fluids (oxygen,

water, and chloride ions) penetration into concrete to reach a certain level, for example

level of steel bars because most of the types of deterioration are influenced by fluid

ingress (or movement) in concrete. It is not just capillary action that causes a given

5

specimen to absorb fluids, as an aggressive fluid can be transported through concrete pore

structure by various mechanisms as mentioned below:

a) Permeability ( due to an external pressure head ∆P, both side of the test are

saturated, so Darcy’s law can be applied)

b) Sorptivity (absorbing fluid by an unsaturated pore system due to the capillary

force, much like a sponge)

c) Vapour diffusion (due to the humidity gradient: an equilibrium state of saturation

causes liquid in a specimen to move from one saturation gradient to another).

d) Ionic diffusion (due to the ionic such as. Cl- ion gradient)

The main purpose of this research was to evaluating and improving concrete durability,

so studying the factors governs concrete durability is necessary. All these factors

(summarized in Figure 2.1) influence concrete durability by affecting concrete

penetrability.

6

Figure 2.1: Affecting factors on durability of concrete

Penetrability is important for the MTO because a) the Ministry builds, manages, and

maintains bridges, pavements, walls, and piers exposed to moisture and chloride, and b)

all forms of deterioration directly or indirectly result from movement of fluids in

concrete.

Affecting

Factors on

Concrete

Durability

External

Aggressive

Factors

Internal

Structure of Concrete

(Physical Properties)

Design

and

Construction

Environmental

Operation

and Loading

Design

Pore structure

of

Cement Paste

Pore

Solution

Construction

Practices

Physical

Characteristic

External

Chemical

Attacks

External

Physical

Attacks

Environmental

Factors Damaging

Internally

Aggregate

Phase

Concrete

Design

Reinforcement

Design

7

Fluid movement can be a result of permeability, sorptivity, ionic or vapour diffusion.

Appearance of any of this penetrability types results in a permeable concrete. In addition,

deteriorating factors influence concrete durability only if concrete is permeable.

Therefore, it is necessary to consider concrete penetrability during studying the effects of

durability influencing factors.

2.1.1 External aggressive factors

External factors influence concrete durability and deteriorate concrete. Generally,

external deteriorative factors may be environmental factors, or results of facility

operation and maintenance.

2.1.1.1 Environmental

When a concrete member is exposed to an environment, the surrounding environmental

factors can affect concrete durability. Environmental factors cause several types of

deterioration which can affect the durability of concrete. In most of the cases, the

concrete degradation process involves the penetration and subsequent movement of

water, air, or other fluids which are transporting aggressive agents into concrete pore

system (Bryant et al., 2009).

Environmental factors must be studied before designing, mixing, casting and operating

any concrete structure.

Environmental damaging factors can be categorized as external factors attacks concrete

chemically (e.g. sulphate), external factors attacks concrete physically (e.g. freeze-thaw

damage), and environmental factors damaging concrete internally.

2.1.1.1.1 External chemical attack

Concrete structures are exposed to many varying chemicals. These environmental

chemicals attack concrete and deteriorate the concrete physically. Common chemicals

which can attack concrete are discussed in the following sections.

8

2.1.1.1.1.1 Sulphates (sulphate attack)

The major source for sulphate is soil, sea water, sewers, and some chemical operations.

The common sulphates forms which attack concrete are calcium sulfate (CaSO4), sodium

sulfate (NaSO4), and magnesium sulfate (MgSO4), and potassium sulfate (KSO4).

In all sulphate attack, formation of large ettringite crystals (because of the large number

of available water molecules) results tensile force because concrete is hardened at the

time of sulphate attack. Concrete cracks and damages when these forces become higher

than concrete tensile strength. Beside losing strength and loading capacity, cracked

concrete is vulnerable to the other aggressive external factors.

Generally three types of sulphate attack which can influence the durability of concrete

have been found:

I) Classic sulphate attack (chemical): This type of sulphate attack forms in two steps:

Sulphate attacks calcium hydroxide which is available in concrete as a hydration product

and gypsum is formed:

Ca(OH)2 + SO4= → CaSO4.2H2O (Gypsum)

Gypsum formation is a not deteriorating process; however formation of ettringite crystals

during the second step damages the concrete (Hooton, 2007):

3CaSO4.2H2O + C3A + 25H20 → 3CaSO4.C3A.31H2O

This type of sulphate attack is associated with sea water and sulphate sources such as soil.

9

Figure 2.2: Sulfate-attacked fence posts located where a saline water table exists (St. John, 1998)

(http://filer.case.edu/slr21/Bridge/sulfate.htm)

Using low C3A cements (Types MS and HS), adding supplementary cementing materials

(SCMs) such as slag, fly ash, or silica fume, using air entraining admixture, and low

water-to-cement (W/CM) ratio can help concrete resist sulphate attack.

II) Thaumasite sulphate attack: Sulphate ions, generally from groundwater, react with

calcium silicate hydrate (C-S-H) and carbonate to form thaumasite (Clark, 2007), so

thaumasite is a less common type of sulphate attack. It can be categorized as internal and

external thaumasite. The chemical reaction and required conditions for thaumasite attack

is not fully known however in both types, low temperature (15°C and particularly at

approx. 0-5°C (Bensted, 1999)), presence of moisture, and presence of carbon dioxide are

necessary. In external sulphate attack, these prerequisites are available in the surrounding

environment, while in internal sulfate attack; presence of a source of readily soluble

CaCO3 in cement paste causes thaumasite. In both types, a silica-bearing sulphate

compound attacks the C-S-H matrix of the cement paste (either

CaO.SiO2.CaSO4.CaCO3.15H2O or CaSiO3.CaCO3.CaSO4.15H2O) (Neville, 1995). C-S-

10

H matrix is completely replaced by a white mushy incohesive mass as shown in Figure

2.3.

Figure 2.3: Concrete suffering from thaumasite (Bickley and Hooton, 2001)

Sulphate resisting cement does not prevent thaumasite because in this type of sulphate

attack, C-S-H is attacked, not C3A. Provision of low-permeable concrete (by low W/CM

ratio, SCMs, and adequate curing period) would control thaumasite attack (Hooton, 2007)

because in low permeable concretes, ingress of sulphate and carbonate ions is controlled.

III) Physical sulphate attack: Free water in concrete contains many ions including

sulphates (commonly dissolved Na2SO4). This water is drawn up through a continuous

capillary pores structure by wick action. If drawn water evaporates near a surface due to

arid weather, dissolved salts deposit near drying surface as shown in Figure 2.4.

11

Figure 2.4: Physical sulphate attack mechanism

The most common efflorescent material is anhydrous sodium sulfate (Na2SO4,

Thenardite) and hydrous sodium sulfate (Na2SO4.10H2O, Mirabilite or Glauber's salt)

(Thaulow and Sahu, 2004).

More salt concentration causes surface scaling similar to freezing and thawing damage as

shown in Figure 2.5.

Figure 2.5: Physical sulphate attack disintegrates concrete surface

(http://img638.imageshack.us/i/saltdeposits.jpg/)

12

There are three major explanations for efflorescent damage in concrete:

1) Volume change from Thenardite to Mirabilite may cause pressure (Hime, 2001 in

Thaulow and Sahu, 2004).

2) Mirabilite is unstable and quickly dehydrates to Thenardite in dry air (Thaulow

and Sahu, 2004). Some scientists have believed that even Thenardite hydration

causes damaging pressure (Evans, 1970 in Thaulow and Sahu, 2004).

3) Damage occurs whether or not Thenardite was produced previously by Mirabilite

decomposition. Together with recent results from the literature, these results

indicate that damage occurs because Thenardite dissolution can produce solutions

highly supersaturated with respect to Mirabilite, so that precipitation of this

mineral can lead to large crystallization pressures (Tsui et al., 2003).

It has been reported that the first two hypotheses are rejected while crystallization

pressure created by salts growing from as supersaturate solution is reported as the actual

damaging mechanism (Thaulow and Sahu, 2004).

To control the sulphate attack, lower W/CM ratio, adequate curing, use of pozzolans, and

use of air-entraining admixture (resultant ettringite crystals can grow in air bubbles) are

necessary. Among all this factors, lower W/CM ratio is the most effective item because it

can reduce the rate of moisture movement in concrete.

2.1.1.1.1.2 Chloride corrosion

Although sea water contains sulphates, it is also a source of chlorides as well as saline

groundwater and de-icing salts used on road and bridges in Canada. Due to chloride

penetration into the reinforced concrete, the de-passive layer around the reinforcing bars,

which protects the bars from corrosion, is destroyed. Steel bars are normally corrosion

protected when embedded in high pH concrete.

The area which receives Cl¯ ion becomes an Anode and other area of the bar which

receives oxygen and water becomes a Cathode. Water and oxygen availability is

necessary for corrosion of depassivated bars.

13

Figure 2.6: Schematic description of corrosion process of a reinforcing steel in concrete

(http://www.cement.org/tech/cct_dur_corrosion.asp)

As shown in Figure 2.6, electrical current flows from anode to cathode through the rebar

and transfers electrons from anode to cathode and takes OH¯ from cathode to anode

through the permeable concrete. As a corrosion electrical circuit forms, iron hydroxide,

Fe (OH) 2, will form as the product of corrosion at the anode.

Iron oxide and hydroxide (two major corrosion products) occupy more space as shown in

Figure 2.7. They cause tensile stress and subsequently cracking and spalling of concrete

happens at the level of reinforcement as shown schematically in Figure 2.7.

Figure 2.7: Cracking concrete by product of corrosion

(http://www.corrosion-club.com/concretecorrosion.htm)

14

More chloride, water, and oxygen get into cracked concrete to accelerate the corrosion

process and deteriorate concrete as shown in Figure 2.8.

Figure 2.8: Rebar corrosion decreases concrete loading capacity and strength

(http://www.cp-tech.co.uk/img28.jpg)

Since the hydroxide ion passes through concrete from Cathode to Anode, increasing the

electrical resistivity of concrete can break the corrosion electrical circuit. Concrete

electrical resistivity is a function of concrete moisture content, pore stricture connectivity,

and ionic content of pore solution (Savas 1999, in Chini 2003). Concretes in dry

environment are corrosion resistant because of their high electrical resistivity.

It is worth noting that due to the destructive effects of chloride on reinforced concrete

structures, accelerating admixtures containing calcium chloride (CaCl2) is no longer

allowed in reinforced or pre-stressed concrete structures.

15

2.1.1.1.1.3 Carbon dioxide and corrosion

In normal concrete, steel bars are chemically protected from corrosion by the alkaline

nature of concrete as concrete high alkalinity causes the formation of a passive oxide film

around the steel reinforcement, which is stable in high pH (Neville, 1995). When carbon

dioxide (CO2) of the air penetrates the pore structure of concrete, calcium hydroxide

(common among other hydration products because of its reactivity) carbonates if

moisture is in the pores and carbonic acid forms (Monkman and Shao, 2006). Carbonic

acid reduces the pH of concrete which was initially about 13-14 because of the cement

hydration alkali products. Calcium carbonate is the product of the reaction as shown in

Figure 2.9.

Figure 2.9: Concrete carbonation process

Carbonation reaction reduces the pH of the pore solution to 8-9, at which level the

passive film (oxide film) around the steel bars is not stable. Therefore, corrosion happens

not from chloride ion penetration, but from carbonation. Moisture is necessary to form

carbonation. It is important to mention that carbonation happens in 50% - 70% concrete

relative humidity (Neville, 1995).

16

pH reduction in concrete not only depassivates the reinforcing bars, but also breaks down

the C-S-H matrix into calcite and silica gel (Ishida and Li, 2008). It results in less

porosity (shown schematically in Figure 2.10) and higher electrical resistivity (Polder,

2000).

Figure 2.10: Concept of change in quantity of porosity in adequately cured carbonated concretes

(Ishida and Li, 2008)

Although the concrete porosity reduces by carbonation (Monkman and Shao, 2006),

carbonation major negative effect (rebar corrosion) is more dominant (Bertolini et al.,

2008). Increasing the depth of covercrete, using surface coating and coated rebars,

adequate curing, and casting good quality and low permeability concrete can reduce

chloride and carbon dioxide ingress into concrete (Neville, 1995).

2.1.1.1.1.4 Acid Attack

Acid attack usually happens at the crown of sewers where the hydrogen sulfide, H2S, is

rising from anaerobic bacteria in sewage. Hydrogen sulphide reacts with aerobic bacteria

located on the inner crown surface, so sulphuric acid is produced:

H2S +2 O2 → H2SO4

The produced sulphuric acid dissolves the C-S-H matrix of concrete (Kosmatka et al.,

2002). Concrete is an alkaline substance, so many of its components readily react with

acids.

Ca(OH)2

C-S-H

Gel

Void

CaCO3

CaCO3

Silica Gel

Void

Before Carbonation After Carbonation

17

Figure 2.11: Acid attack deteriorates concrete (http://filer.case.edu/slr21/Bridge/acid1.jpg)

Keeping a low W/CM ratio will increase the resistance of the concrete to deterioration by

acid because low permeability, a result of the low water/cement ratio keeps the acidic

solution out of the concrete pore structure (Kosmatka et al., 2002). Surface coating by an

acid proof layer is a common industrial acid proofing.

2.1.1.1.2 External physical attack

Concrete structures are exposed to many physical deteriorating factors. The most

important physical environmental factors are temperature and humidity. The common

physical damage in concrete is caused by cold temperatures:

2.1.1.1.2.1 Freezing and thawing damage

This type of damage happens all over Ontario because of its cold weather. Upon freezing

of the internal water, it expands by 9% in volume (Neville, 1995) and if there is no room

for the expansion, tensile stress will be applied to the solid surrounding the freezing

water. Therefore, the “critical saturation” level of pores is about 91% if the pores are

equally saturated. The generated stress by ice formation breaks the paste results in

aggregate-paste separation and cracks; then ice melts and contracts as it thaws (Neville,

1995). Many freeze-thaw cycles crack internal concrete and concrete surface resulting in

18

more concrete deterioration. Cracked concrete has lower strength and higher permeability

resulting in more penetration of chloride. Therefore, other deteriorating damages start to

form in concrete as shown in Figure 2.12. This figure was taken from a deteriorated

bridge column located at Finch Ave. East, Toronto, Ontario, Canada.

Figure 2.12: Freeze-thaw damage in a concrete column caused rebar corrosion and more

deterioration

The damaged region is covered by snow shovelled to the road side during the winter.

Permeable concrete froze and deteriorated after several freeze-thaw cycles. Chloride ion

from the melting salt used by the Toronto city penetrated into the cracked concrete and

destroyed the rebar’s passive layer. Steel corrosion started so concrete was more damaged

by the corrosion expanding products.

If there is enough room for ice expansion, tensile forces generated by ice formation are

not applied to the solid body of cement paste. This additional room can be provided by

air-entraining admixture. This admixture creates spherical air bubbles (with diameters

about 50 µm (Neville, 1995)) in concrete during mixing. The air-bubbles should be well

distributed and have a distance between each other of less than 200 µm in the cement

19

paste (Neville, 1995) after the concrete has hardened. During ice passage into the air

bubbles, some stresses are developed, so concrete needs to have a minimum strength

before exposed to the first freeze-thaw cycle. Neville (1995) recommended that “concrete

should not be exposed to the cold weather until its strength has reached 24 MPa”.

The total air content and the spacing factors are important properties of air-entrainment.

Table 2.1 contains the total air content and average spacing factors for different

aggregates (CSA A23.1, 2009).

Table 2.1: Adequate air content for different concretes (CSA A23.1, 2009)

Maximum Aggregate Size (mm) Air Content (%) Spacing Factor, L (µm)

10 6 - 9 <230

14 - 20 5 - 8 <230

Also concretes with low W/CM ratio are more freeze-thaw resistant because of their

lower permeability which is enough to prevent “critical saturation” of the pores, less

internal freezable water, and smaller volume of capillary pores (Neville, 1995).

2.1.1.1.3 Environmental factors damaging internally

In some cases, environmental factors do not attack concrete directly, but their presence in

concrete mixture can cause later physical deterioration caused by internal chemical

reactions. These factors get into concrete during the mixing period. The most common

type of concrete damaging, caused by the presence of reactive environmental factors, is

alkali-silica attack.

2.1.1.1.3.1 Alkali-silica reaction (ASR)

The main alkali sources in cement paste are calcium, sodium, and potassium hydroxide

(from Ca(OH)2, NaOH and KOH). These alkalis (mainly hydroxide ion, OH¯) attack

various types of micro-crystalline and the silica bonds of active aggregates provided that

the required alkali content, 300 mM/L (Hooton, 2007), is available. . Finally alkali-silica

gel forms which invites water and then swells mainly around aggregates. The swelling

gel creates tensile stress to hardened concrete, so concrete cracks. Sign of this type of

deterioration is known as mapping cracks (because the alkalies and reactive silica

20

particles are well distributed through concrete), leaking of the gel from cracks and joints,

and joint closure due to the gel swelling.

Figure 2.13: ASR Mapping cracking and gel leakage

(http://www.todaysconcretetechnology.com/wp-content/uploads/2009/10/ASR1.jpg)

The major solutions for ASR are a) Using low-alkali cement, b) Limit the cement content

to restrict the alkali loading of concrete (Neville, 1995), c) Avoid using of reactive

aggregate (can be recognised by spectrographic analysis or physical long-term and short-

term tests), and d) Since bonding larger quantities of alkalies improves ASR resistance,

using SCMs causing more C-S-H formation is another practical solution (Neville, 1995).

2.1.1.2 Operation and loading

The maintenance loads are considered during designing a structure, so they do not affect

concrete durability unless concrete has deteriorated or cracked. In case of loading,

unexpected impact loads are the most common affecting factor. The latest standards have

considered the loads might be applied during a structure’s service life. Therefore, loading

is not a major factor affecting concrete durability in modern structures. On the other

hand, the most common operational stresses, affecting the durability of concrete are

surface acid attack (Section 2.1.1.1.1.4), abrasion, and leaching.

21

2.1.1.2.1 Abrasion

Generally friction between a substance and concrete surface as well as constant rolling of

machinery and equipment, traffic, or water flow causes surface abrasion and cover loss.

Due to abrasion, concrete cover above the reinforcing bars is reduced, so concrete

durability is reduced as shown in Figure 2.14 taken on the University of Toronto campus.

Figure 2.14: Surface abrasion due to the heavy traffic volume

As cover concrete thickness reduces, aggressive ions can reach the rebar, so concrete

durability decreases. Surface abrasion resistance is directly proportional to the concrete

strength, strength of aggregate, and density of concrete (Forster, 2000), so factor

improving strength and density such as adequate curing, long water curing, and using

SCMs improve abrasion wear resistance.

2.1.1.2.2 Leaching

In case of water leaching from structural joints, or structure exposure to water flow

cement hydration products (Ca(OH)2 and C-S-H) may start to dissolve, so concrete

becomes soft and etched away. In this type of operation deterioration, lime dissolves in

water at the surface exposed to water and in some cases calcium carbonate is seen on the

other side of concrete as shown in Figure 2.15.

22

Figure 2.15: Leaching and spalling under footway of a bridge (water on top of the footway)

(http://www.rta.nsw.gov.au/cgi-bin/index.cgi?action=heritage.show&id=4301049)

Salt crystallization deteriorates concrete due to the crystallization pressure as mentioned

in Section 2.1.1.1.1.1 (part III). Beside adequate water drainage system, reducing the

permeability of concrete protects concrete against leaching.

2.1.2 Internal structure of concrete

Cement paste phase and aggregate phase (fine and coarse aggregates) make the concrete

internal structure. Properties of both aggregate and cement part of concrete affect

concrete durability.

2.1.2.1 Aggregate phase

Aggregate properties are physical (such as density, water absorption, moisture content,

and grading) and chemical (e.g. silica content). These properties which can be measured

by standard tests must be controlled before the designing process. They change concrete

mix design, setting time, packing, and fresh and hardened concrete behaviours.

Therefore, aggregate properties must be measured and controlled in any concrete project.

23

Since aggregates are usually provided by suppliers, its properties have been standardized,

so cement paste properties are the most dominant factors affecting concrete durability.

However some concrete properties such as electrical resistivity may be influenced by

aggregate properties as described in Sections 2.2.3.4.1 and 2.2.4.3.3.

2.1.2.2 Cement phase

The important part of cement paste in durability studies, is the pore system. Pore system

behaviour is defined as the physical characteristics of pore structure (magnitude, size, and

connectivity of pores) and water in pore system (ionic content and concentration in pore

solution) that can influence the fluid transportation properties through concrete (McCarter

et al., 2009). Therefore, both pore structure physical characteristics and pore solution

must be studied in case of concrete durability improvement.

Penetrability of the concrete is affected by both pore structure and voids between

aggregates as described in Section 2.2.5. Pore structure (voids in cement paste) properties

as well as size, distribution, and internal connection of pores can influence the rate of

deterioration of concrete as pores volume increases; the apparent chloride diffusion

coefficient increases (Savas, 1999 in Chini et al., 2003).

The following factors can improve pore structure properties:

2.1.2.2.1 W/CM ratio

The W/CM ratio represents the amount of water in concrete. As this ratio increases,

concrete porosity increases and the pore structure becomes more continuous (Chini,

2003). Therefore, in a low W/CM ratio concrete, penetrability is low while electrical

resistivity is high because of less continuous pore structure (Neville, 1995).

It is worth mentioning that in order to obtain an acceptable workability and surface finish,

mixes with the water-to-cement ratios below 0.45 required relatively higher amount of

cement and/or utilization of chemical admixtures (Al-khaiat and Fatuuhi, 2002).

The W/CM ratio effects on standard durability tests results are described briefly in

Section 2.2.5.1.

24

2.1.2.2.2 Degree of hydration

More hydration (cement hydration or secondary hydration of added SCMs), results in

more produced C-S-H. Therefore, cement paste voids are filled with more hydration

products and porosity and pore connectivity is reduced (Neville, 1995).

Hydration effects on standard durability tests results are described briefly in Section

2.2.5.3.

2.1.2.2.3 Curing

Proper curing of concrete has a very important influence on the final properties of the

concrete. Length of curing period and curing temperature are the most important factors

defining concrete curing procedure.

Since concrete penetrability (and durability) is related to physical characteristics of the

pore system, any action increases cementing materials hydration, reduces concrete

penetrability. Longer curing period improves concrete durability because the volume of

permeable voids is decreases with longer curing while poor curing results in high

absorptivity near the surface (usually the first 30 mm from the surface) (Saricimen et al.,

2000 in Chini et al., 2003).

Higher curing temperature causes continuity pores; this decreases concrete electrical

resistivity and negatively affects concrete durability (Chini et al., 2003) as described in

Section 2.2.5.3. Also curing scenario such as type of curing (steam or moist curing) and

curing temperature affect concrete durability.

2.1.2.2.4 Admixtures

Any admixture causing discontinuous pore system or finer microstructure, improves

concrete durability. Using water reducing admixtures leads in lower required water

content, so free water decreases which results in less and smaller pores, so concrete

becomes more durable. Adding an air-entraining admixture results in millions of small air

bubbles being produced in the concrete, so concrete becomes freeze-thaw resistant. In

spite of the higher setting time, more plastic shrinkage, in case of using retarding

admixtures, later age compressive strength is higher (Neville, 1995).

Admixtures effects on concrete electrical resistivity are described in Section 2.2.4.3.2.

25

2.1.2.2.5 Type of cement

The difference in cement chemical compositions (C3S, C2S, C3A, and C4AF) contents and

cement particles finest are the leading factors in categorizing different cement types.

Cements with low C3S content has lower early age strength and higher early age

penetrability while their later age properties (more than 90 days) are better than high C3S

cements (Neville, 1995). Cement particles size governs cement paste early strength, as

finer cement particles has higher cement paste 28-day strength due to the more surface

area hydrated and more hydrated cement content (Neville, 1995). Also it has been

reported that, using different types of cement results in different electrical resistivity

values as described in Section 2.2.4.3.4.

2.1.2.2.6 Supplementary cementing materials (SCMs)

The use of supplementary cementitious materials has become one of the best solutions to

make durable concrete mixes. These materials are used to replace some cement (or in

some cases in conjunction with the required cement) in concrete to improve concrete

strength and durability. Also using SCMs is an environmentally acceptable course of

action because of the reduced amount of cement used in concrete industry.

By using SCMs into concrete mixture a denser concrete (improved particle packing)

which has finer and discontinuous pore structure is made (Neville, 1995). Therefore, in

concrete containing SCMs, penetrability coefficient is lower and concrete strength and

electrical resistivity is higher than plain cement concrete mixes (Vieira et al., 2000 in

Chini et al., 2003).

Also pore solution in concrete mixes containing SCMs is different than that in plain

cement concretes because of the SCMs secondary hydration which causes reduction in

pore solution alkali content (Neville, 1995).

SCMs effects on standard durability tests results are described briefly in Section 2.2.5.2.

2.1.3 Design and construction

Generally concrete is a porous material and its durability is influenced by its porosity.

Concrete contains two types of pores: voids between aggregates and pores in cement

paste: voids are formed in concrete between aggregates and cement paste while pore

26

structure is formed in cement paste. Both types of porosity must be minimized with

proper designing methods and standard construction practices to make concrete durable.

2.1.3.1 Design

Both components of a reinforced concrete member, concrete and reinforcing bars, must

be designed properly in case of having a durable structure. Reinforcing bars is designed

according to standards such as “CSA A23, Design of concrete structures”. As the steel

component of a concrete structure can be designed properly by following the standards,

designing the concrete components of the structure is the major issue.

Concrete is made of three major components: cementitious materials, aggregate, and

water (mineral admixtures can be categorized as the forth components used in recent

concretes). Durability of concrete is affected by either individual or combination

characteristics of all these components (will be explained briefly in Section 2.2).

The purpose of designing concrete is to establish a proper proportion for each component

but all concrete will experience the following three phases (Savas 1999, in Chini et al.,

2003):

a) Aggregate (macro)

b) Hydrated cement paste (macro)

c) Interfacial transition zone, ITZ (micro)

ITZ is a low density region around the aggregate between aggregate and bulk hydrated

cement paste. Concrete permeability is influenced by this region’s permeability which

contains smaller cement particles.

Since durability of concrete largely depends on the ease with which fluids can enter and

move through (Neville, 1995), concrete durability is more affected by the last two phases

than the aggregate phase. The property or hydrated cement paste and the transition zone

changed with time as such measurements have shown that the higher porosity present

initially in ITZ is significantly diminished by the migration of ions during cement

hydration (Scrivener et al., 2004). Also cementitious materials can improve the durability

of these two phases: adding silica fume improves concrete properties in two ways: (1) by

reducing the ITZ porosity because silica fume is a super fine material. (2) Silica fume

27

generates more C-S-H which results in more discontinuity in pore structure (Neville,

1995).

Finally it can be concluded that high strength concrete may or may not be a durable

concrete (Hooton, 1993 in DeSouza et al., 1998). In general, durability will result if the

concrete has a low W/C ratio, has achieved adequate thermal and moisture curing, and

has achieved a discontinuous capillary pore structure free of micro and micro defects

(DeSouza et al., 1998).

2.1.3.2 Construction

Concrete construction methods and practices influence the final quality of in-place

concrete (Rasheeduzzafar, 1989 in Bryant et al., 2009) although the mix design dictates

the proportion and types of concrete components. These constructional practices which

affect concrete durability, serviceability, and integrity are:

a) Batching materials regarding to the mix design proportions in correct order (ACI

Guide 304R, 2000).

b) Mixing to coat all aggregate particles with cement paste (ASTM C685)

c) Transportation (ACI Guide 304R, 2000)

d) Placement into frameworks without distributing concrete uniformity

e) Consolidation to reduce amount of voids in concrete and achieve the highest

possible density (ACI Guide 309R, 2005)

f) Finishing (ACI Guide 302R, 2004)

g) Curing the surface concrete to protect concrete from drying which has to begin

immediately after finishing (Kosmatka et al., 2002) explained in Section 2.1.2.2.3.

In other words, if the concrete mixture is not batched, mixed, transported placed,

finished, and cured properly, it will not exhibit the desired performance qualities and

concrete does not become durable (Bryant et al., 2009).

28

2.2 Concrete durability measurement

Durability is another factor, besides strength, that defines performance of concrete.

Measuring concrete durability is more difficult and complicated than measuring

compressive strength. As mentioned before, the most important factor affecting concrete

durability is penetrability. Penetrability is defined in general as the ease with which

fluids, both liquids and gases, can enter into or move through the concrete (Savas, 1999).

It is a function of W/CM ratio, aggregate size, pore size, and pore distribution (Savas,

1999). The key to concrete durability and therefore its performance is to enable concrete

to attain a highly impermeable pore structure (Swamy, 1996 in Bryant et al., 2009).

Concrete permeability can be measured by standard testing techniques. These tests are

destructive for concrete strictures and time-consuming. The ultimate goal of this research

project was to provide reliable correlations between standard tests and non-destructive

and fast electrical tests.

Consequently, standard required tests (e.g. chloride migration under electrical gradient)

and electrical tests must be studied.

2.2.1 Compressive strength test

Although compressive strength test was one of the tests done in this research program, it

was not a durability test. Compressive strength test, methodology, and influencing factors

are briefly described in Appendix B.

2.2.2 Rapid chloride permeability test (RCPT)

Since the ability of concrete to resist chloride penetration is an essential factor in

determining concrete performance, chloride permeability of concrete must be measured

in any concrete durability study. This property of concrete can be measured by a standard

test method for electrical indication of concrete’s ability to resist chloride ion penetration

named as the rapid chloride permeability test (RCPT). The test, designated as AASHTO

T277 in 1983 by the American Association of State Highway and Transportation

Officials (AASHTO), was the first-ever test proposed for rapid qualitative assessment of

chloride permeability of concrete (Chini et al., 2003).

29

The RCP test monitors the amount of electrical current passed through a 50 ± 3 mm thick

concrete slice of actual diameter ranging from 95mm to 102 mm nominal diameter core

or cylinder over 6 h. testing period (ASTM C1202, 2007). A potential difference of 60 V

induces a direct current (Elkey, 1995 in Chini et al., 2003: may cause polarization in the

pore water and a transport of ions) between two cells containing sodium chloride (NaCl)

and sodium hydroxide (NaOH) solutions. The setup is shown in Figure 2.16.

Figure 2.16: ASTM C1202-07 rapid chloride permeability test setup (Stanish et al., 1997)

The RCP testing methodology is described in Section 3.1.2.

Electric charges travel a tortuous path because of obstructing particles, so the effective

path length is longer than the dimensional of the concrete in the direction of the current

(Monfore, 1968). Concrete tortuosity is defined as:

T= 2)(L

Le ,

where, Le is the effective path length and L is the apparent path length of specimen.

This test method evaluates the electrical conductance of concrete (by calculating the total

passing charges in coulombs) over 6 h. to provide a rapid indication of its resistance to

chloride ion penetration as the total charge passed (the area under the electrical current

30

versus time curve), in Coulombs, has been found to be related to resistance of specimen

to chloride ion penetration (ASTM C1202, 2007) as shown in Table 2.2

Table 2.2: Chloride ion penetrability based on charge passed (ASTM C1202, 2007)

Charged Passed (Coulombs) Chloride Ion Penetrability

> 4000 High

2000 - 4000 Moderate

1000 - 2000 Low

100 - 1000 Very Low

< 100 Negligible

These values have been shown to be representative of chloride ion permeability which is

an indirect indication of the permeability of concrete (Baykel, 2000 in Chini et al., 2003).

It can be concluded from Table 2.2 that a low passed charge means relatively

impermeable concrete; However, values may be inaccurate if concrete is atypical (Stanish

et al., 1997).

Since slow hydration of some SCMs delay their impacts by about one or two month and

the RCPT results depend on pore solution chemistry and pore structure characteristics,

Table 2.2 limits would be unreasonable to apply on the 28 day concretes but would be

sufficient for 91 days concrete (Shi, 2004).

Since the test result is a function of electrical resistance of the concrete specimen, the

presence of reinforcing steel or other embedded electrically conductive materials may

have a significant effect. Therefore, the test is not valid for specimen with longitudinal

reinforcing bars that can provide continuous electrical path between the two ends of the

specimen (ASTM C1202, 2007).

This testing method can be used in applications such as quality control and acceptance

testing in practice.

In addition, it is known that RCPT data reflects the electrical resistance of concrete rather

than the resistance to chloride penetration (Wee et al., 2000 in Chini, 2003).

31

2.2.2.1 First 5 minutes RCPT resistivity

After the first 5 minutes of testing in the RCPT, electrical resistivity, ρ, can be calculated

from the current using the following equations:

L

AR

A

LR =⇒= ρρ

R=I

V(Ohm’s law)

I

V

L

d×=∴

4

2πρ ,

where, d is the average of four diameters measured on the specimen’s cross-sections, L is

the thickness of the specimen, I is the first 5 min. electrical current passing through the

concrete disc, and V is the applied voltage, which is 60 V.

Since the solution temperatures remain constant during early minutes, the RCPT

electrical resistivity value is independent from heat effects.

Since the durability of salt-exposed concrete structures is influenced by the ability of

concrete to resist the penetration of chloride ion, chloride ion penetration, measured after

the RCP test, is used for a non-steady-state migration similar to Nordtest NT build 492.

2.2.2.2 Chloride ion penetration (chloride migration coefficient)

The ability of concrete to resist chloride ion penetration is a key component for durability

analysis of concrete structures especially in salt-exposed structures. The RCPT results

have been used as an indicator for concrete durability for many years. However, a

number of scientists have criticized this test for its bias to supplementary cementing

materials, especially silica fume, because cement replacement with silica fume can lead

to an order of magnitude reduction in Na+, K+, Ca++

, and OH- ion concentration in pore

solution (Shi et al., 1998 in Ahmed et al., 2009). They have reported that it is not

appropriate to use the RCPT charge passed alone to evaluate chloride ion penetrability in

concretes incorporating materials affecting the ionic concentration of pore solution

especially silica fume (Bassuoni et al., 2006). However, others have found that the effect

is small (Nokken and Hooton, 2006).

32

Therefore, additional property of concrete which is less dependent on the electrical

conductance of concrete and pore solution is requires to be measured. This property

(depth of chloride ion penetration) represents concrete resistance against chloride ion

penetration forced into concrete over 6 h. RCP test (Bassuoni et al., 2006). This property

is mainly related to continuity of the concrete porosity because the ions can not travel

through the solid pore walls and are only free to travel through the liquid-filled pore

structure (Stanish et al., 2004).

Tested samples can be split open after the RCP test. Fracture surfaces of split samples are

sprayed with 0.1 M silver nitrate solution, AgNO3, to determine the depth of chloride

penetration. Fifteen minutes later the area containing chloride remains white, silver

chloride, while the color of the area free of chloride ion remains natural or brown as

shown in Figure 2.17.

Figure 2.17: Whitish chloride front migration in concrete sprayed after the RCP test

(Bassuoni et al. 2006)

The depth of chloride ion penetration is used to calculate a non-steady-state diffusion

coefficient using the equation in Nordtest NT Build 492 (Bassuoni et al., 2006):

D = tV

LT

)2(

)273(0239.0

−

+( dx - 0.0238

2

)273(

−

+

V

LxT d ),

where, D is non-steady-state migration coefficient (x 1210− 2m /s), V is the applied voltage

(V), T is the average value of initial and final temperature in the anolyte solution (ºC), L

33

is the thickness of the specimen (mm), dx is the average depth of chloride penetration

(mm), and t is time (h).

It is important to mention that although the electrical potential gradient remains constant

during the 6 h. test, chloride binding and direction of pores resistance decrease the rate of

chloride ion penetration (Stanish et al., 2004) which has not been considered in the

migration coefficient relation.

2.2.2.3 Linear extrapolation technique

The RCPT test is continued for either 6 h. or until the NaCl solution’s temperature

reaches 80ºC. This temperature is the upper limit to avoid any damage of test cell

components (Bassuoni, 2006). To avoid high temperature effects on the RCPT values, the

total charge passed through concrete discs over 6 h. can be estimated by multiplying the

30-min. values by 12 (Hooton et al., 1997 in Bassuoni et al., 2006).

By calculating the extrapolated charge passed, the heating effects on the RCPT charge

passed and electrical resistivity results are discounted. The extrapolated charge passed is

always lower than the actual passing charged measured by 6 h. standard procedure

(Bassuoni et al., 2006) because the heat effect is eliminated.

2.2.2.4 Influencing factors on penetration resistance test

Electrical conductivity of concrete depends on both its pore structure characteristics

(charges in pore structure) and pore solution chemistry (Monfore, 1968). Both mentioned

factors are functions of the W/CM ratio, admixture, mix design, supplementary

cementing materials, and etc. (Savas, 1999). Most of them such as W/CM ratio, adding

SCMs, and length of curing not only influence the RCPT results but affect other

durability tests results as described briefly in Section 2.2.5.

2.2.2.4.1 Admixtures and RCPT values

Addition of chemical admixtures, such as calcium nitrite ,Ca(NO2)2 , which is found in

corrosion inhibitor admixtures, affects concrete pore solution chemistry (Wee et al., 2000

in Chini et al., 2003). This may have effects on the accuracy of the Coulomb value.

Calcium nitrite (which is found in corrosion inhibitor admixtures) reduces electrical

34

resistivity (increases the RCPT charge passed of a given concrete), but it does not

increase the rate of chloride ingress (Savas, 1999).

Other chemical admixtures may affect results similarly, so electrical properties of mixes

containing chemical admixtures should be compared with control mixes with caution.

2.2.2.4.2 Temperature and RCPT values

Temperature of the solution should be limited between 20 to 25 °C during measurements

according to ASTM C1202-07. As temperature increases, the reported RCPT level of

permeability will be higher than the actual permeability level measured under the normal

temperature (Bassouni et al., 2006). It can be avoided by linear extrapolation estimation

technique. This disadvantage does not affect first 5 min. electrical resistivity.

2.2.2.5 RCPT weak points

As indicated in the literature, there are four main disadvantages for the RCP test:

1) Applied electrical charges are taken by all chemical ions presented in pore

solution, not only the chloride ions. The RCP test does not distinguish between

the current carried by chloride ion and that carried by the other ions available in

pore solution (Suryavanashi et al., 2002 in Ahmed et al., 2009).

2) The heat generated during the RCP test is the other problem which increases the

total reported charge passed in case of high solution temperature (Bassouni et al.,

2006).

3) Pore fluid characteristics and chemical composition can affect the RCPT results

especially in mixes with pozzolanic materials such as silica fume (Hale et al.,

2002 in Ahmed et al., 2009).

4) The RCPT does not measure the permeability of concrete directly, but it measures

the total charge passed through concrete over 6 h. of testing period which is

related to chloride permeability. This relation is criticized in concrete mixture

containing SCMs especially silica fume since it reduces ionic concentration in

pore system. Therefore, some scientist have claimed that the reduction in total

RCPT charge passed was due to the reduced ionic concentration not discontinuous

and small volume of pore system. This claim is rejected in Section 4.2.3.

35

On the other hand, this test can evaluate concrete electrical resistivity. Also its

convenience and short-time duration are other advantages for this standard durability test.

2.2.3 Rate of water absorption (Sorptivity)

As water penetration is the major cause of steel corrosion and freeze-thaw damage, water

absorption into hardened concrete is an important factor in determination of concrete

durability. Moreover, studying the water absorption of concrete surfaces is more essential

than that of the concrete core. Rate of water absorption of a concrete surface is different

from the rate of absorption of a sample taken from the interior because the exterior

surface is often subjected to less curing, and more exposed to potentially adverse

conditions (ASTM C1585, 2004).

Therefore, surface concrete penetrability is studied by measuring the rate of water

penetrability due to the capillary rise (sorptivity).

2.2.3.1 Calculation

The sorptivity test measures the rate of absorption of water when one surface of concrete

specimen is exposed to water. Capillary suction is the reason for water absorption into the

concrete specimen. DeSouza presented the rate of absorption, I, using the sorptivity

relation expressed by Hall (1989) if a specimen is in contact with water from one of its

surfaces (DeSouza et al., 1997):

I = ρ.A

mass∆,

where, I is cumulative water absorption (mm), mass∆ is the change in the mass of the

specimen which is in contact with water (g) , A is the cross-section area of the specimen

(mm2), and ρ is water density (3mm

g).

The mass∆ represents the amount of water absorbed by the specimen.

36

According to the principle of mass conservation:

Q = -t∂

∂θ,

where, q is volume flow rate per unit area (s

m), t is the flow time (s), and θ is degree of

hydration.

This equation can be combined to yield the one-dimensional non-linear diffusion

equation (Nokken et al., 2002):

t∂

∂θ=

z∂

∂[D (θ )

z∂

∂θ],

where, z is elevation head (mm).

Philip (1957) solved the last equation for the boundary conditions θ (0,t)=1 and θ (x,0)=0

(Nokken et al., 2002). Therefore, the sorptivity equation was derived:

I = S t ,

where, S is water sorptivity (s

mm) and t is time of absorption (s).

In other words, if “I” against square root of time data is represented by a straight line,

water sorptivity in mm/min0.5

should be determined as the slope of the least-squares

linear regression line.

The I-t0.5

plot has to be linear with a regression coefficient, r2, of less than an arbitrary

value of 0.98 (ASTM C1585, 2004), otherwise the sorptivity can not be derived

accurately with this linear relationship.

At the beginning of the test, the graph is not linear due to the skin layer of concrete and

saturation of skin concrete, but later, the plot becomes linear (Desouza, 1996).

Water absorption is strongly affected by the moisture condition of the concrete at the time

of testing, so standard amounts of concrete moisture must be assigned for the test.

Previous works (Hall, 1989 in DeSouza et al., 1996 and Parrott, 1994) have indicated that

certain pre-conditioning regime must be applied to obtain a uniform moisture distribution

in specimens (explained briefly in the methodology section, Section 3.1.3.1).

37

Sorptivity is a term used for water ingress into pores of concrete under unsaturated

conditions (50 to 70% internal relative humidity which is similar to the RH found near

the surface in some field structures according to ASTM C1585-04) due to capillary

suction. Rate of water absorption or sorptivity of a concrete mixture at each age can be

measured by both a laboratory sorptivity test and a field sorptivity test.

2.2.3.2 Laboratory sorptivity test

As mentioned in ASTM C1585-04, the average of test results on at least two Ø 100 ± 6

mm diameter with a length of 50 ± 3 mm specimens shall be used as the test results.

Specimens are obtained from either molded cylinders according to practices or drilled

cores according to test method. Concrete top surfaces are in contact with tap water for

eight days and the amount of water absorbed by the specimen is measured at time

intervals specified in the standard (ASTM C1585, 2004).

2.2.3.3 Field sorptivity test

Since concrete deterioration processes (e.g. rebar corrosion) are influenced by the

concrete fluid penetrability especially in covercrete, the ability of concrete to absorb

water on site provides information about its durability. Concrete long term durability in a

severe environment is achieved by the quality of cover concrete between reinforcing bars

and the exterior surface of the member. This cover layer concrete contains three sub-

layers; “cement skin which is about 0.1 mm thick, mortar skin which is about 5 mm thick,

and the concrete skin about 30 mm” (DeSouza, 1998).

For measuring the fluid penetrability of covercrete non-destructively, the field sorptivity

test is used. Capillary rise, or sorptivity, is the case of one-dimensional absorption, in

which flow is normal to the inflow face throughout the wetted region (test methodology

is briefly described in Section 3.1.3.2.1).

2.2.3.3.1 Field sorptivity apparatus overview

The field sorptivity instrument has two major parts; a separate vacuum base plate and

plexiglass test disc which can be easily removed. Figure 2.18 shows the field sorptivity

apparatus in use on a concrete slab.

38

Figure 2.18: Field sorptivity apparatus (horizontal orientation)

This test configuration causes neutral pressure between the test area and the vacuum

region, so water can not wick into the surrounding vacuum under the base plate (DeSouza

et al., 1998).

2.2.3.3.1.1 Vacuum-attachment base plate

The base plate was fabricated from a 6 mm aluminum plate, 300 mm in diameter with a

125mm central hole. It was equipped with three Delta 150 mm vide clamps (Quick

Setting Drill Press Work Hold-Downs), mounted on stainless steel blocks spaced 120º

apart around the diameter of the plate.

To make a proper seal, the aluminum base plate contains a double gasket. These gaskets

were made of a 6 mm square Neoprene, closed-cell gasket within the inner regions and a

10 mm Neoprene sponge gasket around the outer regions. A 3 mm NPT vacuum port was

tapped into the plate in inner vacuum chamber as shown in Figure 2.19.

39

Figure 2.19: Vacuum- attachment base plate (DeSouza et al., 1996)

All gaskets were glued in place with contact cement (DeSouza et al., 1996)

2.2.3.3.1.2 Disc plate

The sorptivity disc plate consists of a 150 mm diameter; 25 mm thick cast Acrylic plate

which is sealed to the base plate using three bench clamps as shown in Figure 2.20.

40

Figure 2.20: Field sorptivity disc plate (DeSouza et al., 1996)

The plexiglass has two chambers. The chambers were sealed with 12mm thick room-

temperature-vulcanized (RTV) silicone rings to utilize lateral confining forces to properly

seal the test surface. To maintain a high point, the inner 91 mm diameter region was

machined to have a concave domed interior profile as shown in Figure 2.23. Therefore,

air can get out.

By placing the instrument on a concrete surface, water in the domed part of the sorptivity

disc is absorbed due to the capillary pore suction. The volume of water absorbed by the

cover layer concrete over 16 minutes can be read from the graduated pipette connected to

the top part of the instrument. The water absorption is the volume of absorbed water

41

divided by the affected area. The slope of the water absorption versus square root of time

plot is the water sorptivity.

This type of water sorptivity test is inexpensive, quick (about 20 minutes), and

nondestructive.

2.2.3.4 Influencing factors on water sorptivity values

The water penetrability of concrete only depends on the pore structure of concrete (Shi,

2004). Water permeability of concrete is not only a function of porosity, but also size,

distribution, shape, tortuosity, and continuity of the pores (Neville, 1995). Therefore, any

factors influencing the physical characteristic of the pore system, affects the rate of water

absorption of concrete. Most of these factors (e.g. W/CM ratio, adding SCMs, curing

period, and moisture content) influence other durability test results which are described in

Section 2.2.5.

2.2.3.4.1 Aggregate and the rate of water absorption

Because the flow path has to circumvent the aggregate particles, the effective path

becomes longer so that the effect of aggregate in reducing the permeability may be

considerable (Neville, 1995). Presence of aggregate in concrete mixtures influence the

permeability coefficient of concrete if aggregate is low-permeable. On the other hand, if

aggregate is more permeable than cement paste, aggregate introduce will increase the

permeability of concrete (Shi, 2004). However, for a given W/CM ratio and degree of

hydration, sorptivity of concrete made with low-permeability aggregate is about one to

two orders lower than that of cement paste due to the ITZ between aggregate and cement

paste (Neville, 1995 in Shi, 2004).

2.2.4 Electrical resistivity test

In addition to ASTM C1202-07, electrical resistivity has been used to characterize the

electrical properties of concrete. Electrical resistivity of concrete is a measurement of its

ability to resist electron transfer. This electrical property (ionic transport property) of

concrete has become an indicator for assessment the physical properties of the pore

42

structure and microstructure and the chemistry of pore solution for more than forty years

(Monfore, 1968).

Electrical resistivity is a geometry-independent material property that describes the

electrical resistance of concrete (Gowers and Millard, 1999). Resistance is the ratio

between applied voltage and resulting current in a unit cell according to Ohm’s law. The

dimension of resistivity is resistance multiplied by length, so the unit is usually Ω.m or

KΩ.cm. This physical parameter is different for every material and can be found from

electro-magnetism tables. On the other hand, it is difficult to find a unique number as

resistivity for composite materials because of different properties of their components.

Concrete is a composite material whose compounds can be described as: (a) a solid phase

purely resistive (aggregates), (b) a solid phase which participates to conduction through

its porous structure (cement matrix) and being the source of ions found in the third phase,

(c) the liquid phase, i.e. interstitial solution (Lastaste, 2003). Therefore, an electrical

circuit can be created in this composite material, which can be linked to the circulation of

fluids through the pore network. Generally, the current flows through the pore liquid in

the cement paste and aggregate can be considered inert (Ferreira and Jalali, 2010).

Electrical resistivity of concrete varies over very broad ranges: from 1011

Ω.cm for oven-

dried concretes to less than 103 Ω.cm for saturated concretes (Lopez and Gonzalez,

1993).

Electrical property of concrete is important for civil engineers because of two reasons:

1) Since the major types of fluid transportation through concrete (permeability and

diffusion) are analogous to the flow a current under a potential difference (hence,

electrical resistance), electrical properties of concrete can serve as a simple and

effective assessing indicator of fluid transport processes and hence, durability

(McCarter et al., 2009).

2) During rebar corrosion in concrete (one of the main causes of deterioration of

reinforced concrete), an electrical circuit is formed as shown in Figure 2.21;

corrosion current passes thought concrete from cathode to anode. Therefore, to

make a corrosion resistant concrete, electrical resistivity of concrete must be

increased. Increasing the electrical resistivity of concrete breaks the electrical

43

circuit which is required for the steel corrosion. Therefore, the concrete electrical

property can control the magnitude of the corrosion current.

Figure 2.21: Schematic view of reinforcing bar corrosion in concrete (Millard and Gowers, 1991)

The steel corrosion is inversely proportional over a wide electrical resistivity range, so an

important application for the electrical resistivity values is to indicate the corrosion rate

of steel bars in concrete (Lopez and Gonzalez, 1993).

There is not a general agreement about the resistivity level above which corrosion risks

will be negligible, but a relation between resistivity and rate of steel corrosion is shown in

Table 2.3. In general, a low resistivity is related to a high risk of corrosion (Ferreira and

Jalali, 2010).

Table 2.3: Electrical resistivity values for rebar corrosion rate (Millard and Gowers, 1991)

Electrical Resistivity (KΩ. Cm) Corrosion Risk Level

> 20 Low Rate

10 - 20 Moderate Rate

5 -10 High Rate

< 5 Very High Rate

44

These levels have been confirmed from correlations with linear polarisation an AC

impedance corrosion measurements (Millard et al., 1989).

The electrical resistivity of concrete is dependent on the degree of pore saturation

(humidity), pore structure continuity, ionic concentration in pore solution, and to a lesser

extent, on the degree of paste hydration (Lopez and Gonzalez, 1993).

The resistivity of a concrete specimen can be measured non-destructively using

electrodes placed on a specimen surface. This requires at least two electrodes, one of

which may be a reinforcing bar in case of in-situ measurements (Polder, 2000). A voltage

is applied between the electrodes and the resulting current is measured or vice versa

(Morris et al., 1996). From Ohm’s law, the ratio of voltage to electrical current results in

resistance of the sample (R=V/I). The resistivity is obtained by multiplying the measured

resistance by a conversion factor, called the cell constant, m (Polder, 2000). For a given

cell arrangement, the cell constant can be obtained either from theoretical considerations

or from calibration using standard concrete samples or electrolytes of known resistivity

(Polder, 2000). In order to have the cell constant, different cell arrangements must be

studied.

Generally, electrical resistivity tests can be categorized as test measuring the bulk

resistivity of concrete and tests measuring the surface electrical resistibility of concrete.

2.2.4.1 Bulk electrical resistivity

In principle, the bulk electrical resistivity of concrete can be measured using two

electrodes placed on concrete opposite surfaces (Morris et al., 1996).

One electrode induces the electrical current and the other electrode receives the current.

Voltmeter can calculate the potential drop, P, during this electric circuit or the external

plate-electrodes provide a uniform electrical field within concrete specimen and the

voltage drop is measured by the instrument (McCarter et al., 2009) as shown in Figure

2.22.

45

Figure 2.22: Concrete bulk electrical resistivity test with two electrodes

The ratio of the potential drop to the current is the member electrical resistance according

to the Ohm’s law. Electrical resistivity, ρ, can be calculated from the following equations:

P=RI (Ohm’s Law)

R= ρ (L/A) ⇒ ρ =P/I (A/L)

I

P

L

d×=∴

4

2πρ

,

where, d is the section diameter (mm), L is the length of the cylinder (mm), I is the

current passed through the specimen (A), and P is the voltage drop (V).

This measuring technique can be complicated by the need for effective and uniform

contacts between the end electrodes and concrete specimen end surfaces, so flat cylinder

end surface, flexible electrodes, and resistance free connections between electrodes and

concrete are required (Morris et al., 1996).

Depending on the type of applied electrical current, this type of resistivity measurement

can be classified into two methods: DC method (using cyclic direct current, Monfore) and

AC method (using alternating current).

A schematic view of a DC resistivity meter is shown in Figure 2.23.

46

Figure 2.23: Schematic diagram for the DC test setup (El-Dieb et al., unpublished)

The DC measurement is carried out using a cyclic DC potential similar to that of the

Monfore. The resistivity meter used at the University of Toronto applies a cyclic voltage

across the specimen between 3 and 5 volts every 5 seconds, so the derived resistivity

equation is modified into:

Resistivity = LII

AVV

×−

×−

)(

)(

35

35 (KΩ.cm),

where, V3 and V5 are average applied voltage for 3 and 5 volts respectively, I3 and I5 are

average applied electrical current for 3 and 5 volts in Amperes respectively, A is the area

47

of the core face (cm2) and L is specimen’s thickness (cm). In DC resistivity-meters, high

contact-persistence between the current electrodes and the concrete surface desensitize a

resistivity measuring instrument by reducing the amount of applied current flowing for a

fixed voltage drive (Ewins, 1990). In other words, if the conductor is an electrolyte (e.g.

cement paste) the passage of direct current will cause polarization and the establishment

of a potential at the electrodes that opposes the applied potential (Monfore, 1968). In this

case the polarization potential reduces the current passed through the specimen:

I=R

EE pa −,

where, Ea is the applied potential (V) and Ep is the polarization potential (or back emf)

(V).

Polarization potential which depends on the ions present and the materials of the

electrodes results from reactions that take place at the electrodes. During this reaction,

thin films of oxygen, hydrogen, or other gases may be formed on the electrodes resulting

lower potential created (Monfore, 1968).

On the other hand, resistivity-meter used in this research program worked with the cyclic

direct current. The cyclic DC avoids polarization effects.

In AC resistivity-meters, electrode/concrete interface polarization and capacitive effects

(formation of a thin gas film between electrodes and electrolyte) are not seen, resulting in

real (and lower than DC instrument) resistivity values (El- Dieb et al., unpublished).

Schematic diagram of an AC resistivity-meter is similar to a DC resistivity meter as

shown in Figure 2.24.

48

Figure 2.24: Schematic diagram for the AC test setup (El-Dieb et al., unpublished)

The DC method overestimated by about 58% the concrete resistivity than the AC method

due to the electrode polarization potential or back emf at the electrode surfaces (El-Dieb

et al., unpublished). This polarization effect can be avoided at 50 Hz frequency and more,

as Hammond and Robson interpreted this to mean that the capacitative reactance of

concrete is much larger than its electrical resistivity (Neville, 1995). On the other hand,

El-Dieb et al. reported that the AC resistivity values are similar to the RCPT resistivity

values measured by direct current (instantaneous measurement of the resistivity (first 5

min.) under the application of a direct current).

Electrical resistivity of stainless steel electrodes is near zero, but in case of using

saturated sponge as a connection between electrode and specimen; concrete resistance is

calculated as (McCarter et al., 2009):

Rconc.= R measured - Rspone ,

where, Rspone is the electrical resistance of the saturated sponge (Ω). To obtain the true

resistivity, the use of a high frequency instrument is necessary, so the sponge-specimen

interface region is “short-circuited” and not considered as measurement (McCarter et al.,

2009).

49

In conclusion, DC measurements are more appropriate than AC if the current (or

potential required to overcome polarization) due to polarization is subtracted from the

total value of current or potential, respectively (Monfore, 1968 and Hausmann, 1964 in

Hansson, 1983). This potential drop due to polarization effects is the intercept on the

voltage axis of the linear portion of the Vcell vs. I curve (Hansson, 1983).

Bulk resistivity measurement techniques are useful for cast specimens or cores taken

from an existing structure. To apply this testing method to a concrete member on site;

both electrodes should be installed on un-sealed surface(s) of the member, if installing in

two opposite surfaces is possible.

In practice, this method is expected to be less accurate and poorly reproducible because

the electrode size has an important effect on the measured values (Polder, 2000).

2.2.4.2 Surface electrical resistivity

There are two major reasons for evaluating the surface electrical resistivity of concrete:

1) Concrete long term durability in a severe environment is achieved by the quality

of concrete between reinforcing bars and the exterior surface of the member

because all deteriorating factors attack concrete and rebar from covercrete.

Therefore, studying the covercrete electrical resistivity (and its correlation with

penetrability) is necessary in case of durability assessment.

2) Bulk electrical resistivity tests are destructive (cores must be taken from an

existing structure), while surface electrical resistivity tests are non-destructively

(can be performed on as constructed surface). Non-destructive evaluations appear

more and more important in civil engineering projects especially in high sensitive

structures such as nuclear plants where coring is not allowed.

The surface electrical resistivity of concrete can be measured non-destructively by several

techniques:

2.2.4.2.1 Surface disc

One of surface electrical assessment testing methods is a disc-electrode method. This

method involves an electrode-disc placed on concrete surface over a rebar and measures

50

the resistance between the disc and the rebar. This method requires a connection to the

reinforcement cage and full steel continuity (Polder, 2000) as shown in Figure 2.25.

Figure 2.25: Setup of one electrode (disc) measurement of concrete resistivity (Polder, 2000)

By applying this test method to several concrete slabs of known resistivity, the cell

constant can be determined. For cover depths, disc and bar diameters being 10-50 mm,

the cell constant is approximately 0.1 m (Polder, 2000). Therefore, the resistivity

measured using a disc electrode is approximately:

p(disc)= 0.1*R(disc –bar) = 0.1V / I ,

where, V (or ∆V is used sometimes) is the potential drop (V), I is the current passed

through covercrete (A), and ρ is surface electrical resistivity (Ω.cm).

The other type of surface resistivity measurement technique for measuring resistivity

which was first used by geologists for investing soil strata (Wenner, 1980 in Millard et

al., 1989) is a four-probe technique. In this technique four electrodes are located on

concrete surface. Two electrodes are for current insertion and the other two are the

potential measurement points (Morris et al., 1996). Primary measurements have shown

that direct current can not be used to measure the resistivity of concrete because of the

polarization effect on electrode/concrete interface (Millard et al., 1989). If a sine-wave

current source is used, impedance is likely to be measured between the voltage probes

rebar

V

disc

51

(probe/concrete interface problems) rather than a resistance, and this may vary with

frequency, so the results are doubtful (Ewins, 1990).

Two common types of four-probe array technique are different due to their electrode

configuration.

2.2.4.2.2 Four - probe line array (Wenner probe)

This convenient technique measures the in-place surface electrical resistivity of concrete

non- destructively. Four equi-spaced, a, electrodes, placed on the surface of concrete in a

linear array were used in Wenner probe.

In this method a low-frequency alternating current (AC) passes between the two outer

probes. The two inner electrodes serve as the potential drop electrodes. Electrodes can be

embedded in concrete during casting as shown in Figure 2.26.

Figure 2.26: Concrete cube with embedded electrodes (McCarter et al., 2009)

If the concrete specimen be approximated as a semi-infinite medium, resistivity of

concrete is given as (Tagg, 1964 in McCarter et al., 2009):

ρ =

2222 44

2

4

21

4

da

a

da

a

aRc

+−

++

Π,

a

d

52

where, a is the electrode spacing, d is the depth of embedment of the electrode tip, and Rc

is the concrete resistance which is V/I according to the Ohm’s law.

In another type of surface electrical resistivity measurement, electrodes are pressed

against constructed surfaces of concrete (Wenner probe). Alternating current (AC) is

passing between two other electrodes while the voltage drop is measured by two inner

electrodes as shown in Figure 2.27.

Figure 2.27 Schematic representation of four-electrode resistivity test (Gowers and Millard, 1999)

Probe spacing, a, must be determined carefully. If the probe spacing is too small, the

presence or absence of aggregate particles (very high resistivity) will lead to a high

degree of scatter while in case of too large spacing, inaccuracies due to the current field

being constricted by the specimen’s edges is seen (Millard et al., 1989).

53

The Wenner resistivity can be calculated from the previous equation, but the depth of

embedment of the electrode tip (d) is zero:

ρ=

2222 44

2

4

21

4

da

a

da

a

aRc

+−

++

Π

d=0 (electrodes on located on the surface) and

∴ ρ= 2ΠaI

V,

where, a is the probe spacing (mm), V is the voltage drop measured by two inner probes

(V), and I is the applied current by the two outer probe (A). 2πa is the cell constant for

four linear probe array.

Four major difficulties must be overcome when the four electrode method is applied to

concrete (Millard et al., 1989):

a) Steel bars must be kept away from the depth affected by the applied electrical

current flow (see Figure 2.27), otherwise the apparent resistivity is being recorded

significantly lower than the true resistivity of concrete (Millard and Gowers,

1991).

b) Probe spacing must be chosen as specimen becomes semi-infinite (will be

explained in Section 3.2.1.1.1.2).

c) When measuring the resistivity it is important to eliminate any resistance between

the probes and the body of concrete. High probe resistance causes significant

errors especially in high frequency instruments (Ewins, 1990). This resistance can

be avoided by using saturated wooden bars (or sponges) or contact gel as the

connection between the electrodes and concrete surface.

d) Dramatic error occurs when there are two surface layers with different resistivities

such as might be caused by a recent wetting of concrete already having surface

carbonation which causes a increase in the apparent resistivity but also salt ingress

into the surface zone (Millard and Gowers, 1991).

54

All surface electrical resistivity relations are based on the assumption that the probe is in

contact with the face of a semi-infinite uniform body (Morris et al., 1996). In practice, the

electrodes are in contact with a body of finite dimensions unless the optimum probe

spacing is figured out based on the specimen’s geometry, aggregate size, and rebar

location (Section 3.2.1.1.1.2).

Therefore, concrete resistivity is calculated from a relation between apparent resistivity

measured by the resistivity-meter and the cell constant correction, K, a function of inter-

probe distance, a, and the geometry of concrete body (Morris et al., 1996):

K

appρρ =

Generally, two types of Wenner probe configuration for concrete cylinders (specimens

used in this research program) are common:

Probe configuration type 1) The first configuration is considered the metallic electrodes

centre on one of the end faces of a concrete cylinder.

Figure 2.28 presents appropriate cell constant correction, K, for this type of Wenner

probe configuration.

Figure 2.28: Cell constant correction factor for the centered end face configuration

(Morris et al., 1996)

55

Usually for the case that removing the sample from its mould is not wanted or enough

room is not available to install the probes on the side of the cylinder (Morris et al., 1996).

Probe configuration type 2) The second situation is consisted in placing the resistivity-

meter electrodes longitudinally on the side of a concrete cylinder. This is the most

common type of electrode configuration for Wenner probe technique in civil engineering

projects. By using the graph shown in Figure 2.29, the cell constant correction for this

type of probe installation can be found.

Figure 2.29: Cell constant correction factor for the centred longitudinal measuring configuration

(Morris et al., 1996)

The cell constant correction factors found for concrete cylinders based on Figures 2.28

and 2.29 can be used for other types of specimen if the geometrical dimensions, required

in those graphs, are adapted.

2.2.4.2.3 Four - probe square array

This convenient testing technique measures the in-place electrical resistivity of concrete

non-destructively. In this type of surface electrical resistivity measurement, four

electrodes spaced out 5 or 10 cm arranged in a square (Lataste et al., 2003) is used as

shown in Figure 2.30.

56

Figure 2.30: Four-probe square array principle (Lataste et al., 2003)

Two neighboring electrodes (A and B) inject a known electrical intensity while the

potential difference, ∆V created by the passage of the current in the material is measured

between the two remaining electrodes (M and N) (Lataste et al., 2003). 3D current and

voltage flow pattern for four-probe square array is shown in Figure 2.31.

Figure 2.31: Four-probe square array schematic representation for studying crack parameters

(Lataste et al., 2003)

57

The equation presented on Figure 2.30 is the apparent resistivity of concrete sample and

22

2

−

aπ is the cell constant for four-probe square array instrument.

To calculate the resistivity of concrete, the following equation should be followed:

K

appρρ =

Cell constant correction, K, is a function of the probe distance, a, and the geometry of

concrete body test as described in Section 2.2.4.2.2. In this type of the surface resistivity

measurement, both sides length of concrete member should be considered to find the

correct cell constant correction (Lataste et al., 2003). This is the main strategy to find the

correct cell constant correction, in four-probe square array.

2.2.4.2.4 Application

Electrical resistivity measured by the Wenner probe can be related to permeability

properties and moisture content of concrete, which is the ultimate goal of this project. As

well, the Wenner probe can be used for resistivity mapping (Polder, 2001). Resistivity

mapping is useful in case of actively corroding steel. In resistivity mapping, surface

electrical resistivity values of each electrical zone can distinguish the high corrosion risk

locations by the corrosion prediction levels as shown in Table 2.3 (Millard and Gowers,

1991). This potential mapping technique identifies regions where corrosion in occurring,

but does not give any information about the rate of corrosion activity. But the corrosion

rate of steel rebar can be estimated by electrical resistivity when concrete resistivity

exceeds 70 Ω.m (Lopez and Gonzalez, 1993):

RC = concreteρ

1000,

where, RC is corrosion rate (µm Fe/yr) and concreteρ is concrete electrical resistivity

(Ω.m).

Nevertheless, in some cases steel corrosion can not be truly detected by electrical

resistivity; saturated carbonated concretes (supports high corrosion rate once the steel has

lost the passivity layer) have been found 3 to 4 times more resistant than saturated un-

carbonated concretes (Millard and Gowers, 1991).

58

Resistivity mapping by surface electrical resistivity is also beneficial for local

electrochemical repair methods which are based on the locations with different corrosion

rates (Polder, 2001).

Also the Wenner probe can be used as a crack detector within concrete members.

Average resistivity value of an un-cracked concrete is around 800 ± 10% Ω.m while the

average resistivity in the delamination zones is between 1700 and 3000 Ω.m (Lataste et

al., 2003). In addition, depth of cracks can be estimated by the apparent resistivity values

as shown in Figure 2.32.

Figure 2.32: Surface resistivity as a function of crack depth (Lataste et al., 2003)

It can be concluded from Figure 2.32 that the resistivity value increases if the applied

electrical current is perpendicular to the crack. If cracks are conductive (i.e. full of water)

the top line in Figure 2.32 remains relatively 800 Ω.m constant (un-cracked concrete).

2.2.4.3 Influencing factors on concrete electrical resistivity

The electrical resistivity of a concrete can be defined as the resistance of concrete for

flow of electrical current through concrete, so any factor affecting passing electrical

current, influences concrete electrical resistivity (Sengul and Jjorv, 2009).

As conduction of electricity through moist concrete is visualized as the ion movement in

the evaporable water (in paste matrix and in some cases in aggregates pores), any factors

affects amount of liquid (moisture content), pore solution ionic concentration, or

59

continuity of pores will influence the resistivity of concrete (Monfore, 1968). Electrical

conductivity of concrete depends on its pore structure (volume of porosity and porous

connectivity) and pore solution chemistry (Lataste et al., 2003 and Savas, 1999).

Therefore, factors influencing physical characteristic of pore system (e.g. porosity and

pore-size distribution), pore solution chemistry, and ionic mobility in the pore solution

must affect electrical resistivity values of concrete. Among of all these influencing

factors, W/CM ratio, adding SCMs, moisture content, and curing affect other durability

tests as described in Section 2.2.5.

2.2.4.3.1 Temperature and electrical resistivity

Temperature has an important effect on concrete electrical resistivity. Overall, a

temperature increase causes a decrease of electrical resistivity and vice versa because

concrete has electrolytic properties and temperature influences ion mobility, ion-ion and

ion-solid interactions (Millard et al., 1989) as shown in Figure 2.33.

Figure 2.33: Relationship between measured resistivity and air temperature

(Gowers and Millard, 1999)

60

From laboratory work, it appears that the temperature effect may vary with moisture

content; electrical resistivity changes with 3% for saturated and 5% for dry concrete for

each degree K temperature change (Bertolini and Polder, 1997, Polder, 2000, and Elkey,

1995 in Chini, 2003).

However, temperature effects are far more significant than small changes in moisture

content; from site experience, electrical resistivity is significantly higher during the

winter (although the moisture content is high) than the summer period (Millard et al.,

1989).

2.2.4.3.2 Chemical admixtures and electrical resistivity

As mentioned before, electrical properties of concrete are influenced by the ionic

concentration and mobility in pore solution. Therefore, any chemical admixture affecting

pore solution chemical composition will influence concrete electrical resistivity:

1) The use of ammonium phosphate in concrete has been reported to increase the

electrical resistance of concrete (Freitag, 1961 in Monfore 1968).

2) Also it has been reported that concretes with nitrate based corrosion inhibiting

admixtures, such as calcium nitrite, Ca(NO2)2, would not be reflected properly using

a resistivity test (Stanish et al., 2004).

2.2.4.3.3 Aggregate and electrical resistivity

Electrical resistivity of aggregates is larger than resistivity of the other components of

concrete (Neville, 1995). Table 2.4 contains electrical resistivity of common aggregates

used in concrete industry.

Table 2.4: Electrical resistivity of rocks (Monfore, 1968)

Type of Aggregate Resistivity

(Ω.cm)

Sandstone 18,000

Limestone 30,000

Marble 290,000

Granite 880,000

61

In contrast with the numbers presented in Table 2.4, resistivity of rocks embedded in

concrete (exposed to alkalies) is lower, hence resistivity of concrete is considerably

dependant upon the resistivity of its cement paste matrix (Monfore, 1968).

In addition, it has been derived that the electrical conductivity of concrete at a certain

degree of hydration is inversely proportional to the volume fraction of aggregate in

concrete (Xie et al., 1991 in Shi, 2004).

Some aggregates may release alkalis into the pore solution (reported for limestone

aggregate) which will have a significant effect on electrical resistivity and the RCPT

results of concrete (Grattan, 1994 in Shi, 2004)

2.2.4.3.4 Cement type and electrical resistivity

As the chemical composition of cement controls the quantity of ions present in the

evaporable water, electrical resistivity becomes more dependent on the cement used

(Neville, 1995). Figure 2.34 has shown that concretes made of different types of cement

have shown different resistivity values.

Figure 2.34: Relation between resistivity and applied voltage of different cement concretes with

W/CM= 0.49 (/eville, 1995)

62

Also is can be seen that electrical resistivity values and applied voltages are directly

proportional.

2.2.5 Influencing factors on durability tests

Among all affecting factors on durability test results, four of them are common for all

tests.

2.2.5.1 W/CM ratio

W/CM ratio represents the evaporable water and gel porosity in concrete (Neville, 1995).

Higher W/CM ratio concretes have more continuous pore systems and larger pore size

distributions resulting in higher total charge passed (Ahmed et al., 2009).

In the case of depth of chloride penetration, the apparent chloride diffusion coefficient

increases, as the pore volume increases. The transport of chloride ions has little to do with

the chemistry of pore solution, but it is influenced by pore structure characteristics (Shi,

2004) as there is an inverse relationship between penetrability and diffusion coefficients

as well (Savas, 1999).

Bassouni et al., (2006) have concluded that since chloride migration coefficient is only

influenced by the physical characteristics of the pore system, W/CM ratio is the most

governing factor for chloride ion penetration.

Since W/CM ratio represents the porosity and pore size distribution of concrete as higher

the ratio, higher the amount of porosity in concrete (Neville, 1995) water sorptivity of

concrete mixes with higher W/CM ratio is higher than that in mixes with lower ratio

(Nokken et al., 2002). In addition, for cement pastes hydrated to the same degree, the

permeability is lower the higher the cement content, i.e. the lower the W/CM ratio

(Neville, 1995).

It has been reported that the concrete resistivity trend over time is similar to that of

mechanical strength of concrete (significantly influenced by the W/CM ratio), so W/CM

ratio is an influencing factor on concrete electrical resistivity (Hansson, 1983). It affects

the electrical resistivity value of concrete in two ways:

63

a) Higher W/CM results in increases in the volume of evaporable water (conductive

material) in concrete. Therefore resistivity of cement paste decreases (Neville,

1995).

b) Electrical resistivity of hardened concrete is sensitive to the volume of porosity

and to the porous connectivity degree which are increased in higher W/CM ratio

concretes (Andrade, 2010).

These effects can be seen in Figure 2.35.

Figure 2.35: Relation between electrical resistivity and W/CM ratio at 28 days with different cement

contents (/eville, 1995)

64

Therefore, to provide a high electrical resistivity concrete, the W/CM ratio must be

minimized.

Also it can be concluded from Figure 2.35 that at a constant W/CM ratio, concrete with

lower cement content has higher electrical resistivity because of the less available

electrolyte for the current to pass. In case of cement content, for a constant W/C ratio,

increasing the paste volume creates more channels, pore water, for electrolytic

movement, so electrical resistivity is decreased (Elkey et al., 1995).

2.2.5.2 Supplementary cementitious materials

By adding SCMs to the concrete mixture, a denser concrete (improved particle packing)

which has finer and discontinuous pore structure is made (Neville, 1995) due to SCMs

secondary hydration products which blocks the pore system and makes it discontinuous.

It results in lower total charge passed and the level of permeability of concrete (Chini et

al., 2003).

The dependence of RCPT results on pore fluid conductivity has little relevance to the

chloride permeability of the concrete; therefore, for concrete contains SCMs, the

interpretation of chloride permeability based on the RCPT results becomes unrealistic

(Wee et al., 2000 in Chini et al., 2003). Concrete with ground granulated blast furnace

slag (GGBFS) as well as all SCMs has significantly lower coulomb values than a plain

concrete without SCMs because SCMs refines pore size; it also decreases alkali of the

concrete by decreasing the Na+ and OH¯ ion from the solution (Ahmed et al., 2009).

Among all SCMs, applying the RCPT to concretes containing silica fume has been

criticized. The replacement of Portland cement with silica fume can reduce the electrical

conductivity of concrete more than 90% due to the changes in the chemical composition

of pore solution, which have little to do with the transport of chloride ions in concrete

(Shi, 2004). On the other hand, Pun et al. (1997) showed that using silica fume in

concrete mixes did not have any significant effect on ASTM C1202 chloride penetration

resistance results since there was not any significant difference between the concrete

behaviour from the RCP test and other standard tests measuring chloride diffusion

coefficient as shown in Figure 2.36.

65

Figure 2.36: Relative reduction in diffusion coefficient with silica fume (W/CM= 0.35)

(Pun et al., 1997)

Therefore, it has been recommended to measure the chloride migration coefficient similar

to Nordtest NT build 492 beside the total charge passed at the end of the RCPT in cases

of binary or ternary mixes containing silica fume (Bassouni et al., 2006).

Using SCMs results in lower pores tortuosity and sorptivity value (Neville, 1995). Silica

fume concretes has a much more substantial effect on permeability than normal Portland

cement (Johnston, 1992 in DeSouza, 2996).

Electrical resistivity of concretes containing SCMs is higher than for plain cement

concretes because the pore system becomes discontinuous and blocked as results

secondary hydration of SCMs (Chini et al., 2003). Discontinuity of the pore system

blocks the ionic movement in pore water, so electrons can not easily pass through pores

and must transfer across the high resistivity parts of concrete such as hydrated cement gel

(Hansson, 1983).

Electrical charges applied by the resistivity-meter’s electrodes must be taken by the ions

presented in pore solution, so concrete electrical resistivity decreases with increasing the

alkalinity of pore solution (Monfore, 1968). Therefore, adding SCMs results in a lower

alkali concentration or lower pH value in the pore solution because SCMs incorporate

more alkali into hydration products than they release (Shehata et al., 1999), so electrical

resistivity increases due to the lower ionic concentration (Elkey et al., 1995).

66

In analysing electrical resistivity, knowledge of pore solution is necessary because if a

concrete exhibits a high resistivity value, this may be due to a reduction in ionic

concentration rather than fine, tortuous pore structure (McCarter et al., 2009). This debate

is common especially when silica fume is used within the pore fluid compared to

Portland cement. a replacement of 5% Portland cement with silica fume decreases the

specific conductivity of pore solution to approximately 75% of that of Portland cement at

day 7 (Shi, 2004). Silica fume can reduce the ITZ porosity because silica fume is a super

fine material witch results in higher electrical resistivity (Neville, 1995).

2.2.5.3 Curing

Sarkar (1987) in Ahmed et al. (2009) reported that, “normal concrete is characterized by

more open microstructure, increased presence and well crystallized formation Ca(OH)2,

and higher Ca/Si ratio compared to high performance concrete mixes. These

characteristics of C-S-H and CH in normal concrete result in very high charge passed”.

As cement hydrates, gel porosity decreases in addition to lowering continuity of the pore

system due to cement hydration (Neville, 1995), resulting in lower charge passed, higher

electrical resistivity, and lower water sorptivity values. Mature concrete has more filled

pores which results in lower coulombs at later ages than early ages. In addition, the

reduced charge in later age can be attributed to the finer pore-size distribution which is

affected by the more cement hydration products (Bassouni et al., 2006).

Therefore, any action that increases cement hydration is beneficial; the longer the moist

curing period, the higher the degree of hydration, so the lower chloride permeability level

and higher electrical resistivity (Savas, 1999). Curing temperature is another influencing

factor on pore system. Standard cured concrete has lower 91 day coulomb values than

accelerated cured specimens (Savas, 1999). Normally cured concrete has lower chloride

ion diffusion than the high-temperature cured concrete at later ages (Stanish et al., 1997).

With the progress of cement hydration, water permeability values decrease rapidly

because the gross volume of gel increases, so the gel gradually fills some of the original

water-filled spaces (Neville, 1995). Therefore, longer curing period will reduce concrete

capillary pores water sorptivity.

67

In case of fixed water saturation level, electrical conductivity (inverse of resistivity)

changes as the solution in the pores changes (Kessler et al., 2004), so any factors

affecting the pore solution and pore system such as curing condition and type of

cementing materials change electrical resistivity values.

Although electrical resistivity of concrete increases with age due to more cement

hydration, the rate of resistivity increase is proportional to the length of curing period

(Monfore, 1968). In other words, for constant moisture content, electrical resistivity

increases with longer curing and more hydration.

2.2.5.4 Moisture content

Although the specimens are vacuum saturated prior to the RCP test according to ASTM

C1202-07, some scientists have tested semi-dry specimens. Moisture content between 40-

60% saturation (that pore water begins to gain or lose continuity) results in a 3%

fluctuation in the RCPT values per each 1% change in degree of saturation (Elkey, 1995

in Chini et al., 2003).

Concrete moisture content influences its water permeability: the higher the moisture

content of the concrete, the lower the measured sorptivity values (Neville, 1995). This

conclusion is seen in both types of sorptivity test results:

1) Filed water sorptivity values increase with decreasing level of concrete saturation

(DeSouza, 1996).

2) Although the relative humidity of the specimens used for laboratory sorptivity test

was constant, the same conclusion has been discussed by other researchers:

Nokken et al. (2002) have shown that the sorptivity decreases with increasing

degree of saturation and also decreasing W/CM ratio.

Concrete resistivity is sensitive to moisture content of concrete; a value of less than 1

KΩ.cm for water-saturated concrete can increase to over 100 KΩ.cm for the same

concrete when oven dried (Millard et al., 1989).

68

There are two main reasons for high electrical resistivity in dry concretes:

1) Water is conductive: Electrical resistivity increases when concrete dries out.

Generally, dried materials have more resistivity than wet materials, because of the

electrical conductivity of water filled the pore system (Monfore, 1968).

2) Discontinuity of Pore water system: Pore water begins to be discontinuous, at

moisture contents less than 80% which causes an increase in electrical resistivity

values (Neville, 1995).

It is recommended that for on-site measurements, a quick study of moisture effects is

performed before proper measurements (Lataste et al., 2003).

69

CHAPTER 3

EXPERIME/TAL PROGRAM

The main focus of this study was to develop non-destructive testing methods to evaluate

the durability of covercrete. Most of the report is discussing concrete surface electrical

resistivity measured by four-electrode instrument (Wenner probe). To improve reliability

of data measured by Wenner probe, it was crucial to calibrate the testing device with

other standard laboratory testing methods. In addition, standard time-consuming

durability tests such as ASTM C1202-07 were evaluated for comparison.

Therefore, testing methodology must be studied at the beginning point of the project.

3.1 Methodology

This methodology is to read as a narrative. The reason is to describe the testing methods,

required in this research program, in detail to maintain the consistency of the testing

procedures.

The testing methodology is based on available standard testing methods (e.g. ASTM

C1202, 2007). In case of the field sorptivity test and electrical resistivity test which have

not been standardized, the testing methodology is based on previous works presented in

the literature.

3.1.1 Compressive strength (ASTM C39, 2005)

The compressive strength test of moist cured concrete cylinders was done in accordance

to ASTM C39-05. The detailed methodology is described in Appendix B.

3.1.2 Rapid chloride permeability test (ASTM C1202, 2007)

According to ASTM C1202-07 the following steps should be taken during the rapid

chloride permeability test:

a) Sample preparation

b) The RCP test

Both sample preparation and the RCPT process were done according to ASTM C1202-

07.

70

3.1.3 Water sorptivity test

Sorptivity test measures the rate of water absorption when only one surface of concrete

specimen is exposed to water. Capillary suction under unsaturated conditions is the

reasons for water absorption of concrete specimens.

Rate of water absorption or sorptivity of a concrete mixture at each age can be measured

by two types of sorptivity test; laboratory sorptivity test (destructive) and field sorptivity

test (non-destructive).

3.1.3.1 Laboratory sorptivity test (ASTM C1585, 2004)

As mentioned in ASTM C1585-04, the average of test results on at least two Ø 100 ± 6

mm diameter with a length of 50 ± 3 mm specimens were used.

Specimens are obtained from either molded cylinders according to practices or drilled

cores according to test method. The cross sectional area of a specimen should not vary

more than 1 % from the top to the bottom of the specimen (ASTM C1585, 2004).

Laboratory sorptivity test was done according to ASTM C1585-04. The only difference

was sample conditioning procedure.

Since the amount of water absorbed is affected by the amount of water present in

concrete, the most important part of the lab sorptivity test is to find a best way for

conditioning concrete discs. There are two types of sample conditioning (to reach 50 to

70% internal relative humidity which is similar to the RH found near the surface in some

field structures according to ASTM C1585-04) recommended by the standard and other

researchers:

1) As standard mentioned test specimens should be placed in the environmental

chamber at a temperature of 50 ± 2°C and RH of 80 ± 3 % for three days.

Alternatively, test specimens can be placed in a dessicator inside an oven at a

temperature of 50 ± 2°C for three days. The relative humidity in the dessicator is

controlled with a saturated solution of potassium bromide (KBr). The solution

should be placed in the bottom of the dessicator to ensure the largest surface of

evaporation possible, so specimen is not in contact with the solution. After 3

days, each specimen must be placed inside a sealable container. Precautions must

71

be taken to allow free flow of air around the specimen by ensuring minimal

contact of the specimen with the walls of the container. The container is stored at

23 ± 2°C for at least 15 days before the start of the absorption procedure. At the

time of testing, internal relative humidity is about 50 to 70% which is similar to

the relative humidity found near the surface in the some field structures (ASTM

C1585, 2004).

2) Previous works have found that “three days oven drying at 50ºC followed by

sealed drying for four days at 50ºC provides a rapid and convenient method of

obtaining a uniform moisture distribution and a surface relative humidity of 50 to

60% and moisture contents above 1.0%” (Parrott, 1994). This amount of relative

humidity represents in-situ concrete condition. It is worth mentioning that

ettringite destroys at 70ºC (Neville, 1995), so 50ºC is the best conditioning

temperature because micro-structural cracking is minimized in this temperature.

The second type of sample conditioning was used in this research program.

The testing process and calculation were done according to ASTM C1585-04.

3.1.3.2 Field sorptivity test

The permeability of outer zone of concrete can be different from that of the bulk concrete

due to compaction, bleeding, finishing and curing, as well as the choice of constituent

materials (DeSouza et al., 1997), so studying the outer layer of skin penetrability is

necessary to analyse the durability of concrete. An updated and non-destructive sorptivity

testing technique was created at the University of Toronto for measuring the water

penetrability of concrete surface. The apparatus used during this sorptivity measurement

was described in Section 2.2.3.3.1.

3.1.3.2.1 Methodology

There was not any standard methodology for the field sorptivity test. The main concept

beyond this measuring technique was to attain the best approximation of unidirectional

flow within the inner chamber. Therefore, the outer chamber needed to be full off water

before the inner domed area. The outer chamber saturated the concrete beneath, so the

72

water penetrating into the concrete under inner chamber flowed uni-directionally. Two 6

mm hose barbs were housed on both the interior and outer chamber as shown in Figure

3.1.

Figure 3.1: Hose barbs attached to inner and outer chambers of a field sorptivity test apparatus

The hose barb at the higher point of the dome was attached to the water column

(graduated pipette), while the lower hose barb was attached to the water reservoir to fill

the domed area. The lower hose barb in the outer chamber was attached to the water

reservoir, while the upper hose barb was open to the atmosphere (air vent). All

connections were made of 6 mm Quick Disconnect Shutoff valves, to allow for easy

connection and removal.

73

In order to produce accurate and reliable results, the following procedures were

implemented (DeSouza et al., 1996):

Step I) Specimen preparation: Specimens preparation for the filed sorptivity test had

two major parts:

1) If it is not possible to pre-condition concrete in situ to standard moisture content,

moisture effect on the rate of absorption must be considered. In this project concrete

samples were weighed each time prior to testing. At the end of the test the moisture

content was calculated from the fully dried mass of the specimens.

2) In order to achieve a maximum vacuum pressure, the section of the specimen

underneath the outer guard ring had a smooth flat finished surface, without cracks.

This surface area could be either ground or epoxy.

Step II) The sorptivity base plate was placed on the specimen surface with the smooth

surfaces of the specimen between two circular Neoprene sponge gaskets. To ensure the

gasket did not traverse any large voids or cracks, the base plate was pressed manually

against the surface.

Step III) The vacuum pump was engaged while the sorptivity base plate was pushed

downward to obtain a vacuum between two the circular neoprene sponge gaskets. The

vacuum pump had to be adjusted to approximately 380 mm HG (DeSouza et al., 1996).

The pump should reach a steady-state condition in approximately 30-60 s (vacuum was

applied during the full test duration).

Step IV) After 2 minutes vacuuming, the water reservoir (tap water 23 ± 2ºC) was

attached to the lower hose bard of the outer chamber. Outer chamber was filled while the

other outer hose barb acted as an air vent. The timer was started with the first contact of

water to concrete surface. Now the area underneath the outer chamber was going to be

saturated which caused unidirectional flow in the inner chamber as shown in Figure 3.2.

74

Figure 3.2: Schematic overview of the field sorptivity process

Step V) After 2 minutes and 30 seconds, saturation period of the outer ring, water

reservoir was connected to the lower hose barb of the inner domed area until water came

up the full length of graduated pipette tube and started dripping from it. After removing

all air bubbles from the tube, the hose was detached from the water reservoir.

Step VI) A volume of water was placed in the apparatus. The initial height off the water

above the concrete slab was recorded immediately after the last air bubble was removed.

Concrete started to absorb water. The height of water was being measured as water was

absorbed into the surface of the concrete and drawn along the measuring pipette.

Readings were taken every minute (after initial contact of water with the test surface) for

the first 10 minutes, then at 12 and 16 minutes (the tail sorptivity curve). During all

readings, vacuum pump needed to be monitored to ensure that it remained constant.

Step VII) After the 16 minute reading, the vacuum pump was turn off, remained water

was drain from the system, and the apparatus was removed from concrete surface.

75

Step VIII) Calculation

The rate of absorption, I (mm), was more generally calculated using the following

relationship as expressed by Hall (1989) in DeSouza et al. (1998):

I=ρ×

∆

Area

mass,

where, ∆mass is the change in mass of the sample (g), Area is the cross sectional area of

test specimen (mm²), and ρ is fluid density (g/mm3). If the relationship between I and the

square root of time is well represented by a straight line, the sorptivity, S (mm/min½

)

should be determined by the slope of the least-squares linear regression line of I against

t½

.

As discussed before, it was not possible to condition concrete in-situ to standard moisture

content, so it was necessary to correlate the effect of moisture content on the rate of

absorption. Moisture content ([test mass- dry mass at 110˚c] / dry mass at 110˚c) of a

concrete sample was important to calibrate the instrument and crate a calibration curve

for the sorptivity test. Therefore, every time concrete specimens w weighed before the

field sorptivity test.

3.1.4 Electrical resistivity

Three types of electrical resistivity were measured in this research program: the RCPT

resistivity (explained in Section 2.2.2.1), DC-cyclic bulk resistivity (Monfore resistivity),

and surface electrical resistivity (Wenner probe). There was no any standard test

methodology for electrical resistivity, so the testing method (surface and bulk electrical

resistivity) is briefly explained.

3.1.4.1 Methodology

DC-cyclic resistivity of concrete specimens was measured by taking the following steps:

Step I) Concrete specimen end faces were ground flat prior to the test.

76

Step II) Concrete specimen was placed between two stainless steel electrodes. Since

electrode/concrete interface resistance was the major cause of data scatter, salt free water

based contact gel named as “Spectra 360” was used as shown in Figure 3.3.

Figure 3.3: DC-cyclic bulk electrical resistivity test set up (concrete disc between electrodes)

Step III) By turning on the instrument, a cyclic voltage was applied across the specimen

between 3 and 5 volts every 5 seconds. Electrical current passed trough specimen was

measured and reported by the instrument.

Step IV) Based on the voltage and current reported by the instrument after 15 min.,

electrical resistivity was calculated by the following equation:

ρ = LII

AVV

×−

×−

)(

)(

35

35 (KΩ.cm),

where, V3 and V5 are average applied voltage for 3 and 5 volts respectively, I3 and I5 are

average applied electrical current (A) for 3 and 5 volts respectively, A is specimen’s

cross-section area (cm2) and L is specimen’s thickness (cm).

77

For measuring surface electrical resistivity, a four-probe line array (Wenner probe) was

used in all testes presented and analysed in this report.

Following steps were taken during surface electrical resistivity measurement of a

concrete specimen during this research project:

Step I) The equally spaced probes was adjusted to that required spacing by sliding the

probes along the guide rails and connect the probe to the instrument using the cable

provided.

Step II) The spacing control value (cm) was set to that of the probe spacing from step I.

Step III) The plastic covers was removed from the four electrodes tips (All wooden

electrodes should have been wet at the time of testing as well as during the measurement;

otherwise measured data were not reliable).

Step IV) Any surface water was removed by a damp rag from concrete sample surface to

avoid any short connection.

Step V) Probes were placed in contact with the surface of the concrete specimen and a

firm steady pressure downwards was maintained on the probes as shown in Figure 3.4.

Figure 3.4: Wenner probe being used to measure surface resistivity of a concrete cylinder

78

Step VI) The surface electrical resistivity of the concrete sample displayed on the meter

screen in KΩ.cm was recorded.

Step VII) The probes were left off the surface of the concrete and moved them to the

next position.

If the screen reading was unsteady of drifting slowly there would be a contact problem.

For bulk resistivity test, more contact gel must be used and specimen end faces must be

completely ground. In case of the Wenner resistivity the probe tips should be soaked in

water for a few more minutes. Contact problems will be prevented by using fully water

saturated probe tips.

Concrete electrical resistivity which is required to limit the rate of steel corrosion remains

virtually unchanged in a saturated pore network (Lopez and Gonzalez, 1993). In this

situation, resistivity values represent pore system continuity and ionic concentration in

pore solution, so corrosion rate decreases as a result of chloride diffusion control

(Monfore, 1968). All concrete specimens tested for electrical resistivity were fully

saturated in this research program.

3.2 Experimental project

Before starting the project, different concrete mix design specimens were used in order to

understand the operation of the instrument and to make modification to it.

All required tests, required materials, mix design, curing regime, and testing schedule for

this research program are presented in this chapter.

3.2.1 Research project tests

Three durability tests were conducted in this research project: Wenner probe and bulk

electrical resistivity, rapid chloride permeability, and rate of water absorption.

Besides, compressive strength of concrete cylinders was measured.

3.2.1.1 Electrical resistivity of concrete

Three types of electrical resistivity were measured at each age in this research program:

79

3.2.1.1.1 Surface electrical resistivity

The CNS Farnell “RM MKII”, shown in Figure 3.5, made by CNS FARNELL Ltd.,

England, was used in this research project for measuring concrete electrical surface

resistivity. The resistivity meter was developed by engineers from Taylor Woodrow.

Figure 3.5: RM MKII (surface resistivity-meter)

By using a standard Wenner linear four- probe array, water-saturated wood contact

points, a flat-topped AC wave form for the current source and sophisticated electronic

circuity, a true measure of the DC component of resistivity is measured.

3.2.1.1.1.1 RM MKII technical properties

Two outer probes apply low-frequency alternating current to concrete while the

instrument measures voltage drop between its two inner probes as shown in Figure 3.6.

Figure 3.6: Schematic representation of four-electrode resistivity test (Wenner method)

(http://www.canin-concrete-corrosion.com/analyzing-methods.html)

80

Probe spacing can be adjusted between 0-100 mm. Spacing between probes can be

influenced by several factors as well as the thickness of concrete member, location of the

probe array from edges of concrete specimen, and the thickness of concrete cover.

Sinusoidal electrical current applied can be adjusted from 20µA to 2mA. Alternating with

a flat topped, trapezoidal waveform at a frequency of about 13 Hz. A low frequency

should be used to eliminate capacitive effects (Millard et al., 1989). The amount of

electrical current passed through concrete remains constant and limited to a certain value

recommended by the manufacturer. If the electrical current showed by the instrument was

less than the recommended amount in the manual, the electrical current had to be changed

to an acceptable range. By adjusting the applied electrical current, sufficient current flows

between the outer probes, so the concrete surface electrical resistivity measured is

reliable.

There were four possible basic ranges of full-scale resistivity measurement: 0-2 KΩ.cm,

0-20 KΩ.cm, 0-200 KΩ.cm, and 0-2 MΩ.cm.

The basic accuracy was reported to be ± 2% of reading, + 3 digits, for current drives

down to 1/20th

of the nominal ‘constant’ value assuming equal contact resistances on the

current probe. The Wenner probe was calibrated, so it was not necessary to calibrate the

instrument by a metal sheet before the project.

3.2.1.1.1.2 Surface electrical resistivity measurement

Three Ø100 x 200 mm water saturated concrete cylinders were tested at each age. Four

longitudinal readings (90 degrees apart) along the cylinder height from each concrete

cylinder were measured as shown in Figure 3.7.

Hence, reported surface resistivity at each time was an average of twelve readings (4 x 3

cylinders).

81

Figure 3.7: Surface electrical resistivity measurement order for concrete cylinders

Eight measurements on the finished surface of each concrete slab were read. Therefore,

reported surface resistivity at each time was an average of sixteen readings (8 x 2 slabs).

Data from previously studies were used to find the optimum probe spacing in the first

trial. Previous work has shown that the factors shown in Figure 3.8, scattering the

resistivity values measured by the Wenner probe, were needed to be considered in order

to find the optimum probe spacing.

Figure 3.8: Influencing factors for probe spacing in the Wenner resistivity

Influencing

Factors on

Probe Spacing

Specimen

Concrete

Specimen

Thickness

Edge Effects

Rebar Locations (Covercrete Thickness)

Maximum

Aggregate Size

82

To have a homogeneous current flow, electrodes must be far from the reinforcing bars.

All concrete samples used in this project were non-reinforced specimens, so steel location

was not an affecting factor on determining the probe spacing.

In practice it has been found that “a significant error occurs if resistivity measurements

are taken on a thin concrete section or near to an edge” (Gowers and Millard, 1999). To

avoid this problem, Figure 3.9 provides a relation between probe spacing and resistivity.

Figure 3.9: Effect of concrete section dimensions on surface resistivity measurement

(Gowers and Millard, 1999)

If the dimensions of a concrete element are relatively small, the current is constricted to

flow into a different field pattern to that shown in Figure 3.6. This will result in an over-

estimation of the evaluation of surface electrical resistivity of concrete (Gowers and

Millard, 1999). The optimum probe spacing used in this research project was selected

with regard to the specimens geometry.

83

As mentioned before, all resistivity equations had been derived from semi-infinite

samples. In case of infinite specimens either a constant correction, K, should be

considered or geometrical effects should be eliminated. Therefore, the edge effect must

be considered. Figure 3.10 provides a correlation between electrode distance from the

specimen edges and concrete surface electrical resistivity.

Figure 3.10: Effect of edge and end proximity on surface resistivity measurement

(Gowers and Millard, 1999)

It can be concluded from Figure 3.10 that the distance of probe contact from any element

edge should be at least twice the probe spacing.

Maximum aggregate size can also influence the space between electrodes. The influence

of individual aggregate particles on resistivity measurements is not significant if particle

the size is smaller than the Wenner contact spacing (Gowers and Millard, 1999).

84

Figure 3.11 illustrates the effect of maximum aggregate size on concrete surface electrical

resistivity.

Figure 3.11: Effect of maximum aggregate size on surface resistivity measurement

(Gowers and Millard, 1999)

It can be concluded from Figure 3.11 that contact spacing is 1.5 times (or greater) as large

as the maximum size of the aggregate, 10 mm in this research program, to obtain a

standard deviation less than 5%.

Regarding to the last three correlations, the optimum probe spacing for the

Ø100 x 200 mm concrete cylinders was 25 mm and for the Ø406 x 75 mm concrete slabs

was 15 mm. Due to the Wenner probe’s instrumental limitations, the optimum probe

spacing for circular slabs was changed to 20 mm because it was the minimum probe

spacing for Wenner probe.

For all surface resistivity measurements, a 50 mm probe spacing was necessary because

of the MTO instrument probe spacing. Besides, different probe spacing between the

85

optimum spacing and the common spacing, 50 mm, were chosen to study different probe

spacing effects on electrical resistivity.

Probe spacings used in this research program are summarized in Table 3.1.

Table 3.1: Probe spacings used in the research project

Types of Specimen Probe Spacing (mm)*

Concrete Cylinders

(Ø100 x 200 mm)

(4 readings at each age on each

concrete cylinder)

25

(optimum) 30 40

50

(MTO)

Concrete Circular Slabs

(Thickness = 75 mm)

(8 readings :Diagonally + Horizontally +

Vertically readings)

20

(optimum) 30 40

50

(MTO)

*Probe spacing should be more than 15.9 mm according to the Farnell probe’s manual

3.2.1.1.2 Cyclic-DC bulk electrical resistivity (Monfore resistivity)

Two bulk resistivity tests were performed in this program:

3.2.1.1.2.1 Cyclic-DC bulk electrical resistivity of full length cylinders

Three Ø100 x 200 mm water saturated concrete cylinders, used for surface electrical

resistivity measurement, were tested at each age. The average of three Cyclic-DC

resistivity readings was measured for calculating the electrical resistivity of concrete.

3.2.1.1.2.2 Cyclic-DC bulk electrical resistivity of concrete discs

A saturated concrete cylinder was sliced into three discs with thicknesses of 50 ± 3 mm.

The bottom and middle slices were tested for the cyclic-DC bulk resistivity at each age

as shown in Figure 3.12.

86

Figure 3.12: DC-cyclic bulk resistivity of a concrete disc (test setup)

This test takes 15 minutes for each specimen.

3.2.1.1.3 Rapid Chloride permeability test resistivity (first 5 minutes)

This type of resistivity will be explained in Section 3.2.1.2.

3.2.1.2 Rapid chloride permeability test (RCPT)

In this test, chloride ions are forced into concrete by an external DC voltage on concrete

surface. For a concrete mix at each age, two 50 ± 3 mm thick concrete discs sliced from

the bottom and middle part of a concrete cylinder were tested (Ø100 x 50mm). The discs

were sliced by a water-cooled diamond saw and conditioned one day prior to the test time

under vacuum tap water for 3 hours according to ASTM C1202-07. After 18 ± 2h, the

soaked specimens under water were removed, surface dried, measured for the average

section diameter and thickness, and tightly edges-sealed with vinyl electrical tape. The

sealed specimens were placed between two half cells. The half cell contacting the top

surface of the specimen was filled out with 3.0% NaCl (the catholyte) and the other cell

87

was filled out with 0.3N NaOH. Temperature of the cell contained NaCl was monitored

during the test. This temperature has to be less than 90ºC to avoid boiling of the solution

and damaging the cell.

Figure 3.13: The RCP test setup

(the black wire connected the /aCl cell to the negative terminal of the power supply while the other

wire was connected between the /aOH cell and the positive terminal)

The purpose of this test was not only to measure the total charge passed in coulombs but

also to measure the RCPT first 5 min. electrical resistivity (explained in Section 2.2.2.1).

As chloride ingress can be the most dominant factor that affects the rebar corrosion

process concrete, the depth of chloride ion penetration over 6 h. RCP test was measured.

At the end of the RCP test, samples were split open as shown in Figure 3.14.

88

Figure 3.14: Splitting concrete discs after The RCPT

Split samples were then sprayed with a 0.01 M silver nitrate, Ag/O3, solution to

determine the depth of the chloride penetration (colorimetric method).

Figure 3.15: Ag/O3 solution appears the depth of chloride penetration (AgCl2 white color)

This was used to calculate a non-steady-state diffusion coefficient using the equation in

Nordtest NT Build 492:

89

D = tV

LT

)2(

)273(0239.0

−

+( dx - 0.0238

2

)273(

−

+

V

LxT d ),

where, D is non-steady-state migration coefficient (x 1210− 2m /s), V is applied voltage

(V), T is average value of initial and final temperature in the anolyte solution (ºC), L is

thickness of the specimen (mm), dx is average depth of chloride penetration (mm), t is

time (h).

3.2.1.3 Rate of water absorption (water sorptivity test)

Generally two types of water sorptivity test are common: laboratory and field sorptivity

test.

3.2.1.3.1 Laboratory sorptivity test

In addition to a disc extracted from a rectangular slab, top, middle, and bottom slices of a

concrete cylinder were tested according to ASTM C1585-04. Samples were conditioned

for seven days, three days oven dry 50ºC followed by sealed storage for four days at 50ºC

to obtain a uniform moisture distribution and obtain a relative humidity of 50-70%

(suggested by Parrott ,1994).

Figure 3.16: Laboratory water sorptivity test setup

(Exposed faces were covered with plastic sheets)

90

According to ASTM C1585-04, the maximum water level was 5 mm from the plastic

mesh located under concrete discs.

3.2.1.3.2 Field sorptivity

Lab sorptivity results were compared to the surface sorptivity test performed on two

Ø406 x 75 mm circular concrete slabs at each time.

Figure 3.17: Field sorptivity test setup on a concrete slab

The average of two measurements was used to calculate the water sorptivity of concrete.

3.2.1.4 Compressive strength test (f΄c)

Three Ø100 x 200 mm concrete cylinders removed from the moist room prior to the test,

were used to obtain the compressive strength at each age: 3, 7, 28, 56, 91 days according

to ASTM C39-05. The concrete cylinders were end ground.

91

It is important to mention that concrete temperature effect was not studied in this research

program and all concrete specimens were tested in the room temperature, 23 ± 2°C.

All tests required in this research program are summarized in Figure 3.18.

Figure 3.18 (a): Research program concrete tests

Tests

Electrical

Resistivity

Surface

Electrical

Resistivity

(Wenner Probe)

Bulk

Electrical

Resistivity

(Monfore

Cyclic DC)

Concrete

cylinders

Ø100 x 200

mm

Full length

specimens

Ø100 x 200

mm

Concrete

circular

slabs

Ø406 x 75

mm

Concrete

discs

Ø100 x 50

mm

Rate of

Water

Absorption (Sorptivity)

Field

Sorptivity Concrete

slabs

Ø406 x 75

mm

Lab.

Sorptivity Concrete discs

Ø100 x 50mm

ASTM C1585

92

Figure 3.18 (b): Research program concrete tests

Tests

Rapid Chloride

Penetrability

Test (RCPT)

Extrapolated

RCPT

Coulombs

(30 min. x 12)

RCPT

(6 hours) Ø100 x 50 mm

ASTM C1202

Depth of Cl‾ ion

penetration

with spraying

AgNO3

RCPT

Electrical

Resistivity

Compressive

Strength ASTM C39

Total charged

passed trough

concrete discs over 6

hours

(Coulombs)

93

3.2.2 Specimens

The sample types for this project include Ø100 x 200 mm concrete cylinders, Ø406 x

75mm circular concrete slabs, and 300 x 400 x 75 mm rectangular concrete slabs.

3.2.2.1 Concrete Cylinders

According to Table 3.2, thirty one cylinders were required for each concrete mixture.

Table 3.2: List of concrete cylinders for the project tests

Concrete Cylinders (Ø100 x 200 mm)

TEST 3 day 7 day 28 day 56 day 91 day Total

Compressive

Strength

and

Surface

Resistivity

3 3 3 3 3 15

RCPT

and

Bulk

Resistivity

and

Sorptivity

2

2(Continuously

Cured)

3 3 3 3 16

Total 7 6 6 6 6 31

The testing layouts for the concrete cylinder tests are shown in Figure 3.19.

94

Figure 3.19: Concrete cylinders testing layouts

3.2.2.2 Concrete slabs

Two Ø406 x 75 mm circular slabs and one 300 x 400 x 75 mm rectangular slab were cast

for each concrete mix. The concrete slabs were de-moulded after 24 h of casting and

cured for a further period of seven days. After seven days, slab’s edge was sealed with

electrical tape and exposed in an environmental room at 23ºC and 50% relative humidity.

95

The circular slabs were used for field sorptivity tests at 14, 28, 56, 91 days and surface

electrical resistivity tests at 3, 7, 14, 28, 56, 91 days. Since a slab’s moisture content was

an influencing factor on surface electrical resistivity (explained in Section 2.2.5), each

circular slab was weighed before the resistivity measurement (scale maximum capacity

was 30,000 ±5 g). After 91 days, the mass of all concrete slabs did not change which

means the moisture content of the slabs were in equal condition with the 50% RH room.

Moisture content at each age was calculated by the following equation

Moisture content at each age (%) = 91day at Mass

91day at Mass -ageeach at Mass x100

At 28, 56, and 91 days, a core was extracted from the rectangular slab for the laboratory

sorptivity test.

Table 3.3 summarizes all the durability tests for the concrete slabs required in the

research program.

Table 3.3: Durability tests for the concrete slabs

Type of the concrete

slab Size Durability Tests

Circular Ø406 x 75 mm I) Surface electrical resistivity

II) Field sorptivity test

Rectangular 300 x 400x75mm Laboratory sorptivity test on extracted

cores

According to Tables 3.2 and 3.3, the amount of concrete required for each concrete

mixture was

Concrete Cylinders: 31 x (0.100 x 0.100 x 3.14/4) x (0.200) = 0.04867 m³ = 48.67 L.

Concrete Circular Slabs: 2 x (0.406 x 0.406 x 3.14/4) x 0.075= 0.01940 m³ = 19.40 L.

Concert Rectangular Slabs: 1 x 0.35 x 0.25 x 0.075= 0.009 m³ = 6.50 L.

∴Total Volume= 74.57 x 1.1 (allowing for waste) ≈ 82 L.

96

3.2.3 Materials

Concrete contains cementitious materials, aggregate, chemical admixtures, water, and air.

Now that physical and chemical properties or concrete components affect fresh and

hardened concrete properties, they must be measured before designing the mix design.

3.2.3.1 Cementitious materials

The main cementing material included an ordinary Portland cement (GU) meeting CSA

A3001. Supplementary cementitious materials included the ground granulated blast

furnace slag (GGBFS), and blended silica fume cement meeting CSA A3001.

Two types of cement were used as concrete paste; Ordinary Portland cement (OPC) and

silica fume blended Cement (Type GUb-8SF). 7-8 % silica fume provides a dramatic

improvement in chloride penetration resistance regardless of the test procedure used (Pun

et al., 1997). Silica fume made up of free silica has a large specific surface area, so it is a

fast in reacting material. Silica fume has two major limitations: it has a big demand of

water which causes a viscous or even dry concrete and silica fume is expensive.

The chemical composition (oxide analysis) and physical properties of cementitious

materials as measured by Holcim Canada Inc. are given in Table 3.4.

Table 3.4: Chemical composition of cementitious materials

Holcim

GU

Cement

(OPC)

Blended

silica fume

cement

GUb-8SF

Ground

granulated

blast

furnace slag

SiO2 19.24 25.28 34.1

Al2O3 5.43

5.02 13.2

Fe2O3 2.36 1.98 0.7

CaO 60.94 55.97 41.8

MgO 2.34 2.30 6.3

SO3 4.11 3.71 2.4 Ch

em

ica

l C

om

po

sit

ion

(%

)

K2O 1.11 1.10 0.34

Density (kg/m3) 3134 3080 2854

Blaine Fineness (m2/kg) 350 337 425

97

3.2.3.2 Aggregates

Crushed lime stone with a maximum nominal size of 10 mm meeting ASTM C33-07

were used as coarse aggregate. Washed natural siliceous river bed sand was used as fine

aggregate meeting ASTM C33-07. Coarse and fine aggregates used in this research

program were supplied by Dufferin Concrete.

3.2.3.2.1 Sieve analysis of fine and coarse aggregates

Sieve analysis of aggregates is necessary for control of the production of concrete. Sieve

analysis data is useful in developing relationships concerning concrete porosity and

packing.

Sieve analysis of fine aggregate was measured according to ASTM C136-06 as reported

in Table 3.5.

Table 3.5: Sieve analysis of fine aggregate

Mass Retained (g) Percent Retained OPSS 1002 Sieve Size Sieve Cumulative Sieve Cumulative

Percent Passing Minimum Maximum

9.50 mm 0 0 0% 0% 100% 100%

4.75 mm 1.90 1.90 0% 0% 100% 95% 100%

2.36 mm 49.47 51.37 10% 10% 90% 80% 100%

1.18 mm 119.28 170.65 24% 35% 65% 50% 85%

600 µm 123.18 293.83 25% 59% 41% 25% 60%

300 µm 123.35 417.18 25% 84% 16% 10% 30%

150 µm 55.29 472.47 11% 96% 4% 0% 10%

75 µm 15.76 488.23 3% 99% 1% 0% 3%

Pan 5.80 494.03 1% 100% 0% 0%

To compare the results to the grading requirements of CSA A23.1, data have been plotted

in Figure 3.20.

98

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.01 0.1 1 10

Sieve Size (mm)

Pe

rce

nt

Pa

ss

ing

(%

)

Figure 3.20: Fine aggregate grading curve

Sieve analysis of coarse aggregates was measured according ASTM C136-06 as shown in

Table 3.6.

Table 3.6: Sieve analysis of coarse aggregate

Mass Retained (g) Percent Retained ASTM C33-07 Sieve Size

Sieve Cumulative Sieve Cumulative

Percent Passing Minimum Maximum

19.00 mm 0 0 0% 0% 100% 100%

12.50 mm 421.0 421.0 8% 8% 92% 90% 100%

9.50 mm 1525.4 1946.4 30% 38% 62% 40% 70%

4.75 mm 2937.0 4883.5 58% 97% 3% 0% 15%

2.36 mm 125.7 5009.2 2% 99% 1% 0% 5%

Pan 47.6 5056.8 1% 100% 0% 0%

99

Data have been plotted along with CSA A23.1 grading requirements in Figure 3.21.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 10 100

Sieve Size (mm)

Pe

rce

nt

Pa

ss

ing

(%

)

Figure 3.21: Coarse aggregate grading curve

Both fine and coarse aggregates grading graphs are within the standard grading limits.

3.2.3.2.2 Physical properties of fine and coarse aggregates

Coarse and fine aggregate properties such as density, sieve analysis, water absorption and

the fineness modulus were measured according to ASTM C127-07 and ASTM C128-04,

respectively.

100

The fineness modulus (FM) of sand was calculated from the sieve analysis of 160µm,

315 µm, 630 µm, 1.25mm, 2.5mm, and 10 mm sieves.

Table 3.7: Sand sieve analysis required for the FM calculation

Mass Retained (g) Percent Retained Sieve Size Sieve Cumulative Sieve Cumulative

9.50 mm 0 0 0% 0%

4.75 mm 1.90 1.90 0% 0%

2.36 mm 49.47 51.37 10% 10%

1.18 mm 119.28 170.65 24% 35%

600 µm 123.18 293.83 25% 59%

300 µm 123.35 417.18 25% 84%

150 µm 55.29 472.47 11% 96%

75 µm 15.76 488.23 3% -------

Pan 5.80 494.03 1% --------- Total ≈285

F.M= (Total cumulative mass retained) / 100 = 285 / 100 = 2.85

In addition, aggregates physical properties were measured as tabulated in Table 3.8.

Table 3.8: Aggregates physical properties

Aggregate

SSD

Density

(3m

Kg)

Fineness

Modulus

Dry-Rodded

Density

(3m

Kg)

Water

Absorption

(%)

Fine Aggregate 2720 2.85 ----------- 1.16

Coarse Aggregate 2702 ---------- 1582 1.38

3.2.3.3 Chemical admixtures

Water reducing admixture (WR) and Superplasticizer (SP), high range water reducer,

were added to fresh concrete to maintain its fresh properties such as workability

especially in low W/CM mixes. Also air entraining admixture (AE) was required. In

mixes containing water reducing admixture, water content was limited to 160 kg/m3

while in mixes with superplasticizer this limitation was 140~150 kg/m3. The water

101

content and the W/CM ratio were used to calculate the required cement content, as shown

in Table 3.9.

Table 3.9: Basic mix design basic data

W/CM Cement Content (Kg/m³)

Water (Kg/m³)

Admixture Target Air Volume (m³/1 m³)

0.35 410 143.5 SP-AE 0.06-0.08

0.40 375 150 WR/SP-AE 0.06-0.08

0.45 355 160 WR-AE 0.06-0.08

All chemical admixtures were produced by BASF Construction Chemicals LLC. The

admixtures properties reported by the supplier are listed in Table 3.10.

Table 3.10: Chemical admixture properties

Chemical

Admixture

Commercial

Name

Density

(3cm

gr)

pH Colour Odour

Required

Standard

Recommended

Dosage by BASF

Co.

(Kg

mL

100)

Water Reducing

Admixture

(WR)

POZZOLITH

210 1.138 ≈7 Dark Brown Odourless

ASTM

C494-08 130-390

Air-Entraining

Admixture

Vinsol-Resin

(AE)

MB-VR 1.030

11.8

-

12.8

Dark Brown Soapy ASTM

C260-06 16-260

Superplasticizer

Based on

Polycarboxylate

(SP)

GLENIUM

7700 1.064 5

Purple

Brown Mild

ASTM

C494-08 260-975

102

3.2.4 Mix design

The concretes cast in this research program represented a wide range of concrete

mixtures covering those typically used by Ministry of Transportation of Ontario. The

number of concrete mixtures was a combination of five mix designs and four re-tempered

mixes. For four of the mixes, additional batches were cast and left in the mixer for

approximately one hour, and then water was added to maintain the original slump. In this

way, the sensitivity of electrical resistivity and sorptivity values to re-tempering could be

assessed.

It is important to mention that concrete slump, set at 90 ± 25 mm, was measured

according to ASTM C143-08 at the end of the mixing period.

The concrete mix variables for the project are presented in Table 3.11.

Table 3.11: Research program concrete mixes

Cement w/cm

Cementitious content

0.35

410 kg/m3

0.40

375 kg/m3

0.45

355 kg/m3

Portland cement X+

25% slag X+ X+

Silica fume cement and 25% slag X+ X

+ Additional samples were cast with re-tempering water added after a delay period (one hour)

Nine concrete mixtures were cast according to concrete mixes proposed in Table 3.11.

The required volume for each mixture was about 82 L which was enough for casting all

specimens. The W/CM ratios of 0.35, 0.40, and 0.45 were selected. The W/CM ratios and

aggregate content were corrected to SSD conditions. All cement used in this program

was normal Portland cement (GU) while for two mixes named high performance concrete

103

(HPC) and one water-to-cement ratio of 0.40, silica fume-cement (Type GUb-8SF) was

used.

Concrete mix design and other pertinent information used in this program are presented

in Table 3.12. Concrete mixtures labelled “+” were re-tempered. Detailed mix design is

presented in Appendix A.

Table 3.12: Concrete mixes proportions for 82 litre concrete (mix design)

Concrete

Mixture

Cement

(GU)

(kg)

Silica

fume

Cement

(kg)

Sand

(kg)

Stone

10 mm

(kg)

Water

(kg)

Slag

(kg)

Added Water

re-tempering

(L)

HPC

(SFSL 0.35) ------- 24.6 57.9 87.2 9.6 8.2

HPC+

(SFSL 0.35+)

------- 25.2 59.3 89.1 10.1 8.4 1

SFSL 0.40 ------- 22.5 59.2 87.5 9.7 7.5

PCSL 0.40 23.1 ------- 60.6 89.3 10.7 7.7

PCSL 0.40+ 23.1 ------- 61.2 89.7 9.7 7.7 0.95

PCSL 0.45 21.8 ------- 60.0 88.8 11.9 7.3

PCSL 0.45+ 21.8 ------- 60.3 88.8 11.5 7.3 0.71

PC 0.45 29.1 ------- 60.6 88.7 12.0 ------- PC 0.45+ 29.1 ------- 60.4 89.9 11.0 ------- 2

The mixtures were selected to characterize a wide range of concrete mixtures from high-

performance concrete (HPC) used in Ontario bridges to concrete that similar to mixtures

used in a residential application.

For each concrete mixture, a 10 L trial mix was used to find the optimal admixture

dosage. The optimum dosage is the admixture content which added to the concrete

mixture to maintain the expected fresh properties such as slump and air content.

The finalized admixtures dosages (mL per100 kg cement) are provided in Table 3.13.

104

Table 3.13: Chemical admixture dosages (mL/ 100 kg cement)

Concrete

Mixture

Air

Entraining

Admixture

Water

Reducing

Admixture

Superplasticizer

HPC

(SFSL 0.35) 510 -------------- 600

HPC+

(SFSL0.35+) 510 -------------- 600

SFSL 0.40 400 -------------- 450

PCSL 0.40 105 -------------- 375

PCSL 0.40+ 90 340 146

PCSL 0.45 75 340 --------------

PCSL 0.45+ 75 340 --------------

PC 0.45 70 315 --------------

PC 0.45+ 70 315 --------------

3.2.5 Testing process

The testing process in this program depends on concrete age and type of concrete

specimens.

Concrete cylinders: Concrete cylinders were cast for the compressive strength, the DC-

Cyclic bulk resistivity, and the surface electrical resistivity measurements. Besides, the

total charge passed through the concrete samples was measured by the RCPT method at

each age except day 3. Therefore, two concrete cylinders were sliced and conditioned

according to ASTM C1202-07 a day prior to testing.

At 28, 56 and 91 days one concrete cylinder was sliced into three Ø100 x 50 mm discs in

addition to a core extracted from the rectangular slab for the laboratory water sorptivity

test. All concrete slices were prepared according to the method described before (three

days oven drying at 50°C following by four days sealed in 50°C). It was assumed that

cement hydration slowed to near zero during the seven days conditioning period.

105

Therefore, the laboratory sorptivity was measured seven days from the day that cylinders

were removed from the fog room.

Circular slabs: Circular slabs were cast for two tests: surface electrical resistivity and

field water sorptivity.

The surface electrical resistivity was the average of two measurements on both circular

slabs at 3, 7, 14, 28, 56, and 91 days by the 4-electrode Wenner probe.

Since a saturated concrete slab did not absorb water, the field sorptivity test was

performed on the concrete slab aged more than 7 days (removing day from the moist

room). Therefore, the testing time for the field sorptivity test was 14, 28, 56, 91 days.

3.2.5.1 Concrete methodology

In order to have consistency in all concrete mixes to allow comparison of results, all

material preparation, mixing, casting, and curing steps were performed in the exact same

manner meeting ASTM C192-07, as described in the following steps.

3.2.5.1.1 Material preparation

Two days prior casting, coarse aggregate, twice as needed ,was washed to remove dust

and excessive fines, and to avoid the intrusion of chloride in the ingredients of the mixes.

The coarse aggregate was placed on a big pan over night to drain. A day later, the fine

aggregate was placed on a pan and mixed to maintain constant moisture content. The

washed coarse aggregate was mixed to maintain constant moisture content. Finally the

aggregates were sealed in pails to prevent any moisture changes. Two samples were taken

from coarse and fine aggregate containers.

After weighing the samples, they were dried in 110° C for 24 hour; moisture content was

calculated as:

Moisture content (%) = C110at Mass Dried

C110at Mass Dried -Mass Initial

°

° x100

106

3.2.5.1.2 Mixing concrete

Immediately prior to the mixing, the masses of coarse aggregate, fine aggregate, and

water were adjusted to compensate for the respective moisture content.

A horizontal rotating cum flow-pan type 150 litres capacity EIRICH model EAG21 mixer

was used for preparing concrete mixes. All materials were mixed in the EIRICH

mechanical mixer in accordance with the ASTM C192-07 standard procedure.

To minimize the water absorption by the mixer, the inner wall and blades were damped

with wet burlap. The weighed materials were added in the mixer drum in the following

order:

I- Coarse aggregate (stone)

II- Cement + SCMs

III- Fine aggregate (sand)

IV-Air entraining admixture (placed on top of the fine aggregate prior to mixing to avoid

absorption by the stone) as shown in Figure 3.22.

107

Figure 3.22: Materials loading order

According to the ASTM C192-07, alternating periods of mixing and rest were used:

(a) Mixing dry materials for 30 seconds prior to adding water and the water reducing

admixture (or superplasticizer).

(b) Mixer was turned off after 3 minutes mixing, 3 minutes rest and 2 more minutes

mixing.

Total mixing period = 3 minutes mixing (30 seconds dry materials, then add water and

mix for 2.5 minutes) + 3 minutes waiting + 2 minutes mixing.

Water reducing admixture was combined with the mix water prior to application into the

mixer. On the other hand, the optimum superplasticizer effect is generally obtained with a

delayed addition (Neville, 1995), so the superplasticizer was added to the mixer, 30

seconds after adding water.

108

3.2.5.1.3 Fresh concrete properties

At the end of the mixing period, fresh concrete properties were measured as shown in

Table 3.14. Fresh properties of re-tempered concrete mixes were changed after adding

water as shown in the table.

Table 3.14: Fresh concrete properties

Concrete

Mixture

Design

W/CM

Ratio

Actual

W/CM

Ratio

SCMs

Air

Content

(ASTM C173-10)

(%)

Slump

(ASTM C143-08)

(mm)

Concrete

Temperature

(°C)

Density

( 3m

Kg)

HPC

(SFSL 0.35) 0.35 0.35 SF-SL 7.4 95 25 2349

HPC+

(SFSL 0.35+) 0.35 0.38 SF-SL 7.8 → 8.0 85 → 100 26 → 26 2390 →2277

SFSL 0.40 0.40 0.40 SF-SL 5.8 85 25 2410

PCSL 0.40 0.40 0.40 SL 5.9 85 24.5 2405

PCSL 0.40+ 0.40 0.43 SL 8.4 → 8.0 85 → 105 24 → 24 2424 →2324

PCSL 0.45 0.45 0.45 SL 6.9 105 25 2313

PCSL 0.45+ 0.45 0.47 SL 8.2 → 8.0 115 → 110 24 → 23.5 2291→ 2272

PC 0.45 0.45 0.45 ------- 6.1 80 23.5 2410

PC 0.45+ 0.45 0.52 ------- 6.0 → 5.8 85 → 110 23 → 23 2403→2359

3.2.5.1.4 Casting concrete

After measuring the fresh concrete properties, concrete was cast into polyethylene

cylindrical and steel rectangular and circular moulds.

Concrete slabs were cast in two layers. Each layer was consolidated by placing the slab

on the vibrating table for up to 10 seconds.

After casting all specimens, cylindrical moulds were capped with polyethylene caps and

covered by wet burlap. Concrete slabs were finished with a magnesium float after initial

set of the concrete as shown in Figure 3.23.

109

Figure 3.23: Magnesium float for finishing the concrete slabs surface

All three (two circular and one rectangular) concrete slabs, were covered with plastic

sheets followed by wet burlap for 24 hours. The temperature in the laboratory varied

from 21 to 26ºC.

Figure 3.24: First 24 h concrete curing under plastic sheets and wet burlaps

110

24 hours later, all specimens were demolded and labelled.

3.2.5.1.5 Curing

The curing regime in this research program had three parts:

1- First 24 hours before demolding: Concrete samples were sealed or covered to

prevent moisture loss during the first 24 hours.

2- First seven days: Since cement hydrates at a much reduced rate when the internal

relative humidity drops below 100% and ceases at approximately 80% (Neville, 1995),

initial curing is important. Therefore, concrete specimens were kept in the moist room for

seven days. It was recommended not to use saturated lime water for the following reason:

“The specimens should not be cured in a saturated lime water tank, as this curing

condition decreases the resistivity of the concrete” (Florida Method of Test for Concrete

Resistivity, FM 5-578).

3- After day seven: After seven days moist curing, concrete slabs were removed from

the moist room. The edges were sealed, so they dry from the top and the bottom surfaces.

Concrete slabs were exposed in an environmental room at 50 ± 4 % relative humidity and

23 ± 1 ºC according to ASTM C157-08. Concrete cylinders were kept in the fog room

until the test time. Therefore, concrete cylinders were fully saturated while concrete slabs

were partially dried.

All the slabs were weighed after sealing the edges. These masses, masses of the fully

saturated concrete, were required for calculating the moisture content of the specimens at

different ages.

111

CHAPTER 4

RESULTS A/D DISCUSSIO/

Tables of results included in this chapter depict final results or averages from testing

procedures.

4.1 Compressive strength

The average compressive strength of three Ø100 x 200 mm water saturated concrete

cylinders is shown in Table 4.1. The rate of loading was recommended to be within the

range of 1.14-2.76 KN/S. The rate of loading applied during this research project was

1.9-2.1 KN/S. Most of the types of fracture were cone while the rest was shear. If a

crushed cylinder had an unusual type of fracture, the results would be ignored according

to ASTM C39-05.

Figure 4.1: Crushing a concrete cylinder during compressive strength test (shear fracture)

The compressive strengths of concrete mixes at different ages are tabulated in Table 4.1.

It is important to mention that each value presented in Table 4.1 is the average of three

strengths obtained from three cylinders.

112

Table 4.1: Average compressive strength of different mixes at various ages

Compressive Strength (MPa)

Concrete Mixtures

Actual W/CM

SCMS Day 3 Day 7 Day 28 Day 56 Day 91

HPC 0.35 SF, SL 45.67 57.41 68.58 73.73 76.46

HPC + 0.38 SF, SL 44.57 54.02 61.87 65.72 68.22

SFSL 0.40 0.40 SF, SL 42.84 52.97 59.84 61.89 63.28

PCSL 0.40 0.40 SL 35.79 39.18 49.34 52.02 55.49

PCSL 0.40+ 0.43 SL 32.48 34.87 44.43 47.32 49.38

PCSL 0.45 0.45 SL 30.26 31.54 40.28 44.22 45.82

PCSL 0.45+ 0.47 SL 27.00 29.84 38.08 41.73 44.41

PC 0.45 0.45 - 31.54 33.87 37.28 39.18 43.13

PC 0.45+ 0.52 - 30.45 31.94 34.11 37.43 40.13

The compressive strength test results of all concrete mixes are plotted in Figure 4.2.

0 3 7 28 56 91

W/C

M+

<=

==

==

==

==

==

==

==

==

==

Sil

ica

fu

me

+ S

lag

Sla

g

No SCMs

20

30

40

50

60

70

80

Age (day)

Co

mp

res

siv

e S

tre

ng

th (

MP

a)

HPC (SFSL 0.35)

HPC+ (SFSL 0.38)

SFSL 0.40

PCSL 0.40

PCSL 0.40+(PCSL 0.43)

PCSL 0.45

PCSL 0.45+(PCSL 0.47)

PC 0.45

PC 0.45+ (PC 0.52)

Figure 4.2: Compressive strength of concrete mixtures at various ages

As shown in Figure 4.2, compressive strength increased rapidly during the first 28 days.

In concrete mixes with silica fume (HPC, HPC+, and SFSL 0.40 which are three top

graphs in Figure 4.2) rate of strength gain was significantly high within concrete early-

113

ages even in the first 7 days because silica fume made a significant contribution to early-

age strength. In concrete mixes without any supplementary cementitious material (PC

0.45 and PC 0.45+) compressive strength increased but not so much at later ages. In early

ages, compressive strengths of 25% slag replacement mixes were lower than plain

cement concretes (similar W/CM ratio) since slag contributed in later ages. Rate of

strength gain reduced after 28 days in all mixes especially in mixes without slag because

slag reacted later.

Factors affecting compressive strength are W/CM ratio, the presence of SCMs, concrete

age, degree of consolidation, air-void system and type of curing.

4.1.1 Effects of changing W/CM ratio on compressive strength

Changing W/CM ratio influences concrete porosity. Figures 4.3, 4.4, and 4.5 present

compressive strength of concrete mixes at different ages.

0 3 7 28 56 91

W/CM=0.35

W/CM=0.38

W/CM=0.40

20253035404550556065707580

Age (day)

Co

mp

res

siv

e S

tre

ng

th (

MP

a)

HPC (SFSL 0.35)

HPC+

(SFSL 0.38)

SFSL 0.40

Figure 4.3: Compressive strength of SFSL concrete mixes

114

0 3 7 28 56 91

W/CM=0.40

W/CM=0.43

W/CM=0.45

W/CM=0.47

20

25

30

35

40

45

50

55

60

Age (day)

Co

mp

res

siv

e S

tre

ng

th (

MP

a)

PCSL 0.40

PCSL 0.40+

(PCSL 0.43)

PCSL 0.45

PCSL 0.45+ (PCSL 0.47)

Figure 4.4: Compressive strength of mixes contain slag

0 3 7 28 56 91

W/CM=0.45

W/CM=0.52

20

25

30

35

40

45

50

Age (day)

Co

mp

res

siv

e S

tre

ng

th (

MP

a)

PC 0.45

PC 0.45+

(PC 0.52)

Figure 4.5: Concrete strength of plain cement concretes

It can be concluded from the figures that in all concrete mixes, higher W/CM ratio results

in less compressive strength. More water in concrete mix causes more porosity and

lowers compressive strength.

115

4.1.2 SCMs effects on compressive strength

Three different types of concrete mixture were cast in this research project: Plain cement

concrete mixes, concrete mixes with 25% slag replacement, and concrete mixes with

25% slag and 8% silica fume replacement.

It is concluded from Figure 4.2 that concrete mixes with slag and silica fume had higher

early and later age compressive strength. As the PCSL 0.45 mix had less Portland cement

content than the PC 0.45 mix, its 7 days compressive strength is lower while its strength

is higher at later ages as seen in Figure 4.2. It can be explained as “the pozzolanic

reaction between the SiO2 in slag and the Ca(OH)2 is a slower reaction than the clinker

hydration reaction” (Hansson, 1983).

The addition of silica fume may accelerate the growth of compressive strength compared

with addition of slag.

4.1.2.1 Comparison between compressive strength of SCMs concretes

Both silica fume and slag improve concrete strength because of their secondary

hydration. Figure 4.6 compares compressive strength of two concrete mixes with the

same W/CM ratio.

0 3 7 28 56 9120

30

40

50

60

70

Age (day)

Co

mp

res

siv

e S

tre

ng

th (M

Pa

)

SFSL 0.40

PCSL 0.40

Figure 4.6: Comparison between compressive strength of ternary and binary concrete mixes

(W/CM= 0.40)

116

Since silica fume is finer than slag, it hydrates earlier and makes a significant

contribution to early-age strength of concrete while slag affects later-age strength. In

conclusion a concrete mixture containing silica fume and slag shows higher strength than

a concrete mixture with slag and both concrete mixes are stronger than a plain cement

concrete mix.

4.2 Rapid chloride permeability test (RCPT)

Three different properties were measured from the ASTM C1202-07, RCP testing: (a)

total charged passed through concrete over 6 hours, (b) the RCPT first 5 minutes

electrical resistivity, and (c) chloride migration coefficient from depth of chloride

penetrated during the test.

4.2.1 Total charge passed

The RCPT methodology was briefly described in Section 3.1.2. The ASTM C1202-07

standard presents a table to guide the interpretation of results. This table is presented here

as Table 4.2.

Table 4.2: Chloride ion penetrability based on charge passed (ASTM C1202, 2007)

Charged Passed (Coulombs) Chloride Ion Penetrability

> 4000 High

2000 - 4000 Moderate

1000 - 2000 Low

100 - 1000 Very Low

< 100 Negligible

Total charged passed through two Ø100 x 50 mm concrete discs, simulating concrete

above the rebar level are presented in Table 4.3. Three 50 mm thick discs were cut from a

Ø100 x 200 mm cylinder. The middle and bottom discs were used for the RCP test. The

total charge of each mixture at each age is the average of charge passed through middle

disc and bottom disc.

117

Table 4.3: The RCP test results

Age (day)

7 28 56 91 Mix

Design

Charged

Passed

(Coulombs)

Penetrability

Level

Charged

Passed

(Coulombs)

Penetrability

Level

Charged

Passed

(Coulombs)

Penetrability

Level

Charged

Passed

(Coulombs)

Penetrability

Level

HPC 754 Very Low 231 Very Low 219 Very Low 125 Very Low

HPC+ 822 Very Low 241 Very Low 229 Very Low 165 Very Low

SFSL 0.40 914 Very Low 292 Very Low 247 Very Low 186 Very Low

PCSL 0.40 1621 Low 847 Very Low 640 Very Low 403 Very Low

PCSL 0.40+ 2585 Moderate 1044 Low 808 Very Low 636 Very Low

PCSL 0.45 2938 Moderate 1272 Low 810 Very Low 705 Very Low

PCSL 0.45+ 3256 Moderate 1258 Low 1004 Low 744 Very Low

PC 0.45 5154 High 2665 Moderate 1906 Low 1565 Low

PC 0.45+ 6014 High 3922 Moderate 2423 Moderate 1918 Low

RCPT results are plotted in Figure 4.7. The bottom three lines represent the total charge

passed through specimens which contained silica fume. The two top lines represent

specimens without any SCMs and with the highest W/CM ratio.

0 7 28 56 91

W/C

M

<=

==

==

==

==

==

==

==

=

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

Age (day)

Av

era

ge

Pa

ss

ed

Ch

arg

es

(C

ou

lom

bs)

PC 0.45+

(PC 0.52)

PC 0.45

PCSL 0.45+

(PCSL 0.47)

PCSL 0.45

PCSL 0.40+

(PCSL 0.43)

PCSL 0.40

SFSL 0.40

HPC+

(SFSL 0.38)

HPC

(SFSL 0.35)

Figure 4.7: The RCPT coulomb values with age

118

RCPT results for different types of mix design are shown in Figures 4.8, 4.9, and 4.10.

Figure 4.8: Total coulombs passed (silica fume and slag concrete mixes)

Figure 4.9: Total coulombs passed (slag concrete mixes)

119

Figure 4.10: Total coulombs passed (plain cement concrete mixes)

A comparison of the charge passed for different mixtures in Figures 4.8, 4.9, and 4.10 has

shown that all ternary mixes (8% silica fume and 25% slag replacement) were ranked

very low with a total passed charges less than 1000 coulombs. Binary mixes were ranked

moderate at 7 days (except W/CM= 0.40 mix). The reduction in coulombs passed is

significant for the slag mixes from approximately 2700 at 7 days to less than 700 at 91

days. Plain cement concrete mixes (GU cement concretes without any SCMs) were

ranked high at 7 days, but this rank is improved over 91 days.

The mobility of pore water ions through the cement paste porosity influences the total

charge passed, so any factors affecting the ionic quantity and ionic mobility, influences

the RCPT coulombs.

4.2.1.1 Effects of changing W/CM ratio on the RCPT coulombs

As mention in Section 2.2.5, higher W/CM ratio results in higher porosity, so the total

charge passed is higher in lower W/CM ratio concrete as shown in Figure 4.7. In high

W/CM ratio concrete mixes, the pore structure is more connected than the pore structure

120

in low W/CM ratio concretes (Neville, 1995) which results in higher electrical charge

passed over the 6 h test. Also Table 4.3 indicates that as W/CM ratio increases, chloride

ion penetrability ranking increases from very low to high.

4.2.1.2 SCMs effects on RCPT values

It can be seen in Figure 4.8 that the ternary silica fume blend with 25% slag (three lower

graphs) had shown lower charge passed when compared with the PC 0.45 control or

binary blend of Portland cement and slag (PCSL 0.45).

Figure 4.11 indicates that concrete mixes containing slag has lower penetrability level

than plain cement concrete mixes.

0

1000

2000

3000

4000

5000

6000

7000

7 28 56 91

Age (Day)

To

tal C

ha

rge

Pa

ss

ed

(C

ou

lom

bs)

PCSL 0.40

PCSL 0.40+ (PCSL 0.43)

PCSL 0.45

PCSL 0.45+ (PCSL 0.47)

PC 0.45

PC 0.45+ (PC 0.52)

Figure 4.11: Comparison between total charge passed through concrete mixes containing slag and

plain cement concrete mixes

As mentioned in the literature review, researchers have believed that because of the

discontinuous pore structure in concrete mixes containing silica fume and slag, the total

charged passed through SFSL mixes is lower than SL mixes and plain cement mixes at

121

all ages (Section 2.2.2.4.2). Silica fume which is significantly fine reduces concrete

porosity which results in lower ion penetrability.

In addition the RCPT passing charge is sensitive to the pore solution chemistry since

electrons are transported by ions through the specimen pore system. Cement replacement

with silica fume can lead to an order of magnitude reduction in Na+, K+, Ca++

, and OH-

ion concentration in pore solution (Shi et al., 1998 in Ahmed et al., 2009), so lower

coulombs in silica fume concretes can be a result of either discontinuous pore system or

reduced ionic concentration. In other words, in concrete mixes containing silica fume

ASTM C1202 is not an appropriate method to evaluate chloride ion penetrability since

the results are affected by ionic concentration in pore solution (explained in Section

2.2.2.2). To make this standard test appropriate, Section 4.2.3 provides an additional

testing method to modify ASTM C1202-07.

4.2.2 RCPT electrical resistivity (first 5 min)

Another use for the RCP test is the measurement of bulk electrical resistivity. Bulk

electrical resistivity of a Ø100 x 50 mm concrete disc was calculated as,

L

AR

A

LR =⇒= ρρ

R=I

V(Ohm’s law)

I

V

L

d×=∴

4

2πρ

,

where, d is taken as the average of four diameters measured on the specimen cross-

sections; L is the thickness of the specimen; I is the electrical current passed through the

specimen over the first 5 minutes; and V is the applied voltage which is 60 Volts.

The RCPT electrical resistivity values for concrete mixes cast in this research program

are presented in Table 4.4. Electrical resistivity of a concrete mixture at each age was

taken as the average of resistivity of two tests.

122

Table 4.4: The RCPT electrical resistivity values (KΩ. cm)

Age (days) Mix Design W/CM

7 28 56 91

HPC 0.35 23.4 71.6 76.8 83.9 HPC+ 0.38 20.9 66.9 73.5 80.7

SFSL 0.40 0.40 18.9 58.7 70.3 77.5

PCSL 0.40 0.40 10.5 19.3 26.5 36.7 PCSL 0.40+ 0.43 7.6 15.7 20.2 26.7 PCSL 0.45 0.45 6.4 13.0 20.1 24.5

PCSL 0.45+ 0.47 6.1 13.8 18.7 23.6

PC 0.45 0.45 4.2 7.5 9.6 11.4 PC 0.45+ 0.52 3.7 5.5 8.1 10.2

In general, a low electrical resistivity is related to a high level of rebar corrosion risk.

Previous research has related the bulk electrical resistivity and severity of rebar corrosion

as indicated in Table 4.5.

Table 4.5: Electrical resistivity values and rebar corrosion rate (Feliu et al., 1996)

Electrical Resistivity (KΩ. Cm) Corrosion Risk Level

> 20 Low Rate

10-20 Moderate Rate

5-10 High Rate

< 5 Very High Rate

The levels shown in Table 4.5 will be changed in presence of de-icing salts. The RCPT

electrical resistivity of concrete mixtures is shown in Figure 4.12. Now that the main

cause for deterioration in reinforced concrete structures is rebar corrosion, the RCPT

resistivity, which is related to the rebar corrosion risk level, can be a reliable indicator for

concrete durability.

123

7 28 56 910

0

10

20

30

40

50

60

70

80

90

Age (day)

Fir

st 5 m

in. R

esis

tivity (K

Ω.c

m)

HPC (SFSL 0.35)

HPC+ (SFSL 0.38)

SFSL 0.40

PCSL 0.40

PCSL 0.40+ (PCSL 0.43)

PCSL 0.45

PCSL 0.45+(PCSL 0.47)

PC 0.45

PC 0.45+ (PC 0.52)

Figure 4.12: First 5 minutes RCPT electrical resistivity

It can be seen that adding silica fume to the concrete mixture influences the early age

electrical resistivity (three top lines in Figure 4.12).

Changing the W/CM ratio and adding SCMs affect the RCPT electrical resistivity as

described with following:

4.2.2.1 W/CM ratio effects on concrete resistivity

W/CM ratio influences concrete porosity. The RCPT electrical resistivity values of

different W/CM ratio mixes, shown in Table 4.4, have shown that higher W/CM ratio

concrete has lower electrical resistivity.

Relations presented in Figures 4.13 and 4.14 have shown that reducing the W/CM ratio

increases electrical resistivity of concrete. The difference between electrical resistivity of

higher and lower W/CM ratio concrete remains constant in plain cement concrete and

124

25% slag replacement cement concrete. In concrete mixes containing silica fume and

slag, this difference amount is significant between days 7 and 28.

8% Silica Fume and 25% Slag Replacement

0.35

0.35

W/CM = 0.35

0.35

0.38

0.38

0.38

0.38

0.40

0.40

0.40

0.40

0

10

20

30

40

50

60

70

80

90

7 28 56 91

Age (Day)

Fir

st

5 m

in. R

CP

T E

lec

tric

al R

es

isti

vit

y (

KΩ

.cm

)

HPC

(SFSL 0.35)

HPC+

(SFSL 0.38)

SFSL 0.40

Figure 4.13: Effect of changing W/CM ratio on the RCPT electrical resistivity of ternary mixes

125

25% Slag Replacement

0.40

0.40

W/CM =0.40

0.40

0.43

0.43

0.43

0.43

0.45

0.45

0.45

0.45

0.47

0.47

0.47

0.47

0

5

10

15

20

25

30

35

40

7 28 56 91

Age (Day)

Fir

st

5 m

in. R

CP

T E

lectr

ical R

esis

tivit

y (

KΩ

.cm

)

PCSL 0.40

PCSL 0.40+

(PCSL 0.43)

PCSL 0.45

PCSL 0.45+

(PCSL 0.47)

Figure 4.14: Effect of changing W/CM ratio on the RCPT electrical resistivity of binary mixes

Increasing the W/CM ratio from 0.40 to 0.47 reduced the RCPT electrical resistivity at 7,

28, and 56 days by 42 %, 28%, and 29%, respectively. In concrete mixes with silica fume

and slag, increasing the W/CM ratio from 0.35 to 0.40 reduced the RCPT electrical

resistivity at 7, 28, and 56 days by 19 %, 18%, and 9%, respectively.

It is worth mentioning that the difference between the RCPT resistivity values of all

mixes decreased with concrete age.

4.2.2.2 Effects of adding SCMs on the RCPT electrical resistivity

The RCPT electrical resistivity of a binary (25 % slag replacement and GU cement) and a

ternary (8%silica fume, 25% slag, and GU cement) concrete mixes, W/CM ratio is 0.40,

are shown in Figure 4.15.

126

RCPT Electrical Resistivity (W/CM= 0.40)

18.9

58.7

70.3

77.5

10.5

19.3

26.5

36.7

0

10

20

30

40

50

60

70

80

90

7 28 56 91

Age (Day)

Fir

st

5 m

in.

RC

PT

Ele

ctr

ica

l R

es

isti

vit

y

(KΩ

.cm

) SFSL 0.40

PCSL 0.40

Figure 4.15: Silica fume effects on the first 5 min. RCPT electrical resistivity

As shown Figure 4.15, concrete mixes with silica fume have higher resistivity than

concrete mixes without silica fume, so adding SCMs increases the first 5 min. RCPT

electrical resistivity of concrete significantly. Silica fume improves electrical resistivity

of concrete by factor of 3 at early ages (e.g. at 28 days) in comparison with similar mixes

not containing silica fume.

Although slag contributes to later age properties of concrete, the difference between the

RCPT resistivity of mixes with silica fume and without silica fume remains constant from

day 7 to day 56 because the mixes with silica fume, contain slag as well. In other words,

the ternary blends of slag and silica fume behave much better than binary slag mixes.

Figure 4.16 illustrates that concrete mixes containing slag as a SCM have higher

electrical resistivity than plain cement concrete mixes (the W/CM ratio was the same in

both mixes).

127

RCPT: Electrical Resistivity (W/CM= 0.45)

20.1

6.4

13.0

24.5

9.6

7.5

11.4

4.2

0

5

10

15

20

25

30

35

40

7 28 56 91

Age (Day)

Fir

st

5 m

in. R

CP

T E

lec

tric

al R

es

isti

vit

y

(KΩ

.cm

)

PCSL 0.45

PC 0.45

Figure 4.16: The effects of adding slag on the first 5 min. RCPT electrical resistivity

As slag improves later age properties of concrete, the difference between resistivity of

Portland cement concrete and 25% slag concrete, is higher at later age.

4.2.3 Depth of chloride ion penetration (colorimetric method)

Concrete discs used for the RCP test were split open along the central line by Carver

manual hydraulic pump at the end of the RCP testing as shown in Figure 4.17.

128

Figure 4.17: Splitting a concrete disc after the RCP test

The fracture surfaces of split samples were sprayed with 0.1 M silver nitrate solution,

AgNO3, to illustrate the depth of the chloride penetration.

From these, the average depth of chloride ion penetration at eight different locations

across the width of the specimens is tabulated in Table 4.6.

Table 4.6: Depth of chloride ion penetrated during the RCP test

Depth of Chloride Ion Penetration (mm)

Concrete Age MIXTURE

Day 7 Day 28 Day 56 Day 91

HPC 5.5 1.5 0.50 0.0** HPC+ 4.0 1.5 1.0 0.0*

SFSL 0.40 8.0 2 1.5 0.0*

PCSL 0.40 10.5 5.5 5.0 3.5 PCSL 0.40+ 16.0 6.0 6.0 5.5 PCSL 0.45 17.0 7.5 7.0 6.0

PCSL 0.45+ 19.5 9.0 7.5 6.5

PC 0.45 32.0 16.0 14.0 10.5 PC 0.45+ 34.0 21.5 17.0 16.0

* The depth of chloride penetration was not visible and uniform enough to be measured

** /o chloride penetration as shown in Figure 4.20

129

The values presented in Table 4.6 were used to calculate a non-steady-state diffusion

coefficient using the equation in Nordtest NT Build 492:

D = tV

LT

)2(

)273(0239.0

−

+( dx - 0.0238

2

)273(

−

+

V

LxT d ),

where, D is the non-steady-state migration coefficient (x 1210− 2m /s), V is the applied

voltage (60 Volts), T is the average value of initial and final temperature in the anolyte

solution (ºC), L is the thickness of the specimen (mm), dx is the average depth of

chloride penetration (mm), and t is time (6 h).

The non-steady-state migration coefficients calculated based on the chloride ion

penetration values, presented in Table 4.6, are tabulated in Table 4.7.

Table 4.7: /on-steady-state migration coefficient of concrete mixes

Age

MIXTURE

Day 7 Day 28 Day 56 Day 91

5.53 1.66 0.50 0.00 Cl‾ Penetration (mm)

26.75 24.25 24.5 23.1 Temperature (ºC)

52.94 51.12 50.81 50.69 Thickness (mm) HPC

5.0 1.2 0.2 0.0 Migration coefficient

(10-12 m2/s)

3.69 1.63 1.13 0.00 Cl‾ Penetration (mm)

25.75 24.5 24.75 23.5 Temperature (ºC)

53.13 51.07 50.15 50.27 Thickness (mm) HPC+

3.2 1.2 0.7 0.0 Migration coefficient

(10-12 m2/s)

8.24 1.85 1.23 0.00 Cl‾ Penetration (mm)

25.5 24.75 24.5 24 Temperature (ºC)

53.08 51.17 50.73 50.12 Thickness (mm) SFSL 0.40

7.7 1.4 0.8 0.0 Migration coefficient

(10-12 m2/s)

130

10.56 5.51 4.97 3.50 Cl‾ Penetration (mm)

28 26.25 27 24.25 Temperature (ºC)

53.06 51.2 50.89 49.86 Thickness (mm) PCSL 0.40

10.2 4.8 4.3 2.8 Migration coefficient

(10-12 m2/s)

16.19

6.29

5.81

5.60

Cl‾ Penetration (mm)

42.75 27 26 24.5 Temperature (ºC)

52.33 52.95 52.8 50.82 Thickness (mm) PCSL 0.40+

16.5 5.8 5.3 4.9 Migration coefficient

(10-12 m2/s)

17.13 7.31 6.91 6.05 Cl‾ Penetration (mm)

32 27 26.5 25 Temperature (ºC)

52.36 53.04 50.91 49.66 Thickness (mm) PCSL 0.45

17.0 6.8 6.2 5.2 Migration coefficient

(10-12 m2/s)

19.45 8.69 7.50 6.42 Cl‾ Penetration (mm)

41.75 27.25 26.5 26 Temperature (ºC)

53.07 53 51.34 48.92 Thickness (mm) PCSL 0.45+

20.3 8.2 6.8 5.5 Migration coefficient

(10-12 m2/s)

31.75 15.94 13.75 10.50 Cl‾ Penetration (mm)

39.5 33 31 27.75 Temperature (ºC)

52.6 52.72 52.6 52.6 Thickness (mm) PC 0.45

33.3 15.9 13.5 10.0 Migration coefficient

(10-12 m2/s)

34.25 21.40 17.03 16.05 Cl‾ Penetration (mm)

42 35.25 30.75 30 Temperature (ºC)

53.25 53.01 52.3 52.99 Thickness (mm) PC 0.45+

36.7 21.9 16.8 15.9 Migration coefficient

(10-12 m2/s)

As expected, the migration coefficient decreased with a reduction of the W/CM ratio and

adding SCMs. The addition of SCMs had a significant effect on reducing the migration

coefficient by approximately 48% at 28 days of age due to the pozzolanic and micro-filler

(silica fume) effects.

131

A linear relation represents the correlation between the total charge passed and the RCPT

migration coefficient as shown in Figure 4.18.

D = 0.006 q- 0.004

R2 = 0.98

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0 1000 2000 3000 4000 5000 6000 7000

RCPT Charge (Coulombs)

RC

PT

Ch

lori

de

Mig

rati

on

Co

eff

icie

nt

(10

-12 m

2/s

)

Figure 4.18: Relation between the RCPT passing charges and the chloride migration coefficient

The coefficient of determination (R2) between the total charge and the migration

coefficient data is 0.98. It reflects a significant association between these two datasets.

Consequently, it can be concluded that diffusion migration coefficient is marginally

affected by conductivity of pore solution which is in agreement with previous research

done by Stanish et al., 2004.

4.2.3.1 Effects of adding SCMs on the depth of chloride ion penetration

Figure 4.19 illustrates the depth of chloride penetration based on the values presented in

Table 4.6.

132

Rapid Chloride Permability Test

(Chloride Ion Penetration)

7 28 56 91

No SCM

Slag

Silica fume + Slag0

5

10

15

20

25

30

35

Age (day)

Cl ⁻⁻ ⁻⁻

Depth

of P

enetr

ation (m

m)

PC 0.45

PCSL 0.45

PCSL 0.40

SFSL 0.40

Figure 4.19: Depth of chloride ion penetrated into concrete specimens during the RCP test

Concrete mixes containing SCMs had lower penetrability levels and lower chloride

penetration depths. Adding silica fume reduced concrete penetrability especially in early

ages in comparison with the other mixes. The depth of chloride ion penetrated into silica

fume specimens over 6 hours RCP test is the lowest. This value became zero at 91 days.

These results have proved that the RCPT is a reliable technique for concretes with SCMs

because concretes containing silica fume had the lowest (and zero at 91 days) depths of

chloride penetration in addition to their low passing coulombs.

Adding silica fume decreased concrete penetrability level as shown in Table 4.3. Also

depth of chloride ion penetration is affected by addition of silica fume as the depth of

chloride penetration is zero at 91 days (Figure 4.20).

133

Figure 4.20: Zero depth of chloride ion penetration from the top surface during the RCP test

(silica fume and slag concrete)

Therefore, the criticizes of some scientist (explained in Section 2.2.2.5) have be rejected

as silica fume mixes showed less chloride penetration coefficient which is independent

from ionic concentration and connectivity than mixes not containing silica fume.

4.2.3.2 W/CM ratio effects on chloride ion penetration

As mentioned in the literature, the W/CM ratio is the governing factor for chloride ion

penetration because the chloride diffusion is mostly dependent on concrete pore structure

than pore solution.

Figure 4.21 shows that by increasing the W/CM ratio, the depth of chloride ion

penetration is increased because higher W/CM ratio results in more porosity and higher

pore size distribution. Therefore, the pore structure is more connected in high W/CM

ratio concretes.

134

Figure 4.21: W/CM ratio effects on the depth of chloride ion penetration during the RCP test

In conclusion, the chloride penetrability depth is more sensitive to the W/CM ratio than

by adding SCMs because the migration coefficient is sensitive to the physical

characteristics of the pore structure. Therefore, it is not appropriate to use the RCPT

passing charge alone to evaluate chloride penetrability because it is more sensitive to the

pore solution chemistry while chloride penetrability is more affected by the pore structure

which is influenced by the W/CM ratio and the degree of hydration. Therefore, another

property which is related to the physical characteristics of pore system must be

investigated. A relation between the RCP test’s Dcl and coulombs has to be used to

modify the ASTM C1202.

135

4.2.4 RCPT extrapolation

High current flow can generate heat in solutions which results in higher reported

coulombs. Therefore, the RCPT test continued for either 6 hours or until NaCl solution’s

temperature reaches 80ºC. To discount heat effects, the extrapolated RCPT values are

calculated. As described by Hooton et al. (1997) in Bassuoni et al., 2006, linear

extrapolation to 6 h was done by multiplying the first 30 minutes coulombs by 12. In

such cases, extrapolated data may provide better estimation than the ultimate recorded

charge.

The calculated extrapolated data for concrete mixes are shown in Table 4.8.

Table 4.8: Extrapolated passing charges (Coulombs)

Concrete

Mixtures Day 7 Day 28 Day 56 Day 91

HPC 734 232 233 143

HPC+ 796 237 239 179

SFSL 0.35 884 285 255 198

PCSL 0.40 1593 821 631 434 PCSL 0.40+ 2314 1011 778 674

PCSL 0.45 2627 1221 779 776 PCSL 0.45+ 2885 1204 951 755

PC 0.45 4264 2398 1764 1469 PC 0.45+ 4859 3269 2104 1724

The extrapolated charges were compared with the recorded values as shown in Figures

4.22 and 4.23.

136

Figure 4.22: RCPT recorded and extrapolated charges passed (day 7)

The extrapolated passing charges were lower than the recorded charges because of the

heat effect which increased the total charges passed over 6 hours.

Replacing Portland cement with silica fume by 8% led to 43% reduction in both the

extrapolated and recorded passing charge at 7 days of age.

Figure 4.23: RCPT recorded and extrapolated charges passed (day 28)

137

As the total charge increased, the difference between the extrapolated and recorded

values (∆q) increased due to the heat effect during the standard RCP test; e.g. from 2.7%

in HPC to 19% in PC 0.45+ at day 7 and from 0% in HPC to 17% in PC 0.45+ at day 28

.

Heat generated during the RCP testing increased the recorded coulombs. This increase is

significant in concrete mixes with a high level of penetrability. Also there is a relation

between the maximum anode temperature and the difference between the extrapolated

and recorded passing charge as shown in Table 4.9.

Table 4.9: Effects of maximum anodic temperature on the RCPT coulomb values

Day 7 Day 28 Day 56

Mixtures Tmax

(°c)

∆q

(Coulombs)

Tmax

(°c)

∆q

(Coulombs)

Tmax

(°c)

∆q

(Coulombs)

HPC 28 2.7 25 0.0 25 -6.0

HPC+ 28 3.3 26 1.9 25 -4.1

SFSL 0.40 28.5 3.4 26 2.5 25 -3.2

PCSL 0.40 33 1.6 29 2.7 28 1.6

PCSL 0.40+ 49.5 10.5 29 3.2 28 3.8

PCSL 0.45 41 10.6 31 4.0 29 3.9

PCSL 0.45+ 50 11.4 32 4.3 30 5.3

PC 0.45 54.5 17.3 40 10.0 37 7.5

PC 0.45+ 59 19.2 47 16.6 39 13.2

Since there is a linear relation between extrapolated and recorded values (Figure 4.24),

the extrapolating passing charge values are reliable indicators for chloride penetrability in

highly permeable concrete mixtures. Also the linear extrapolation results are not

influenced by conductivity biases caused by SCMs especially silica fume.

138

y = 0.82 x + 118.76

R2 = 0.99

0

1000

2000

3000

4000

5000

6000

7000

0 1000 2000 3000 4000 5000 6000 7000

Recorded Charge (Coulombs)

Ex

tra

po

late

d C

ha

rge

(C

oulo

mbs)

Figure 4.24: Relation between the extrapolated and recorded passing charges

The generated heat during the test is directly proportional to the amount of passing

charge which is affected by the level; of penetrability. High performance concretes at 91

days, had the lowest level of penetrability, so the heat generated during the test is the

least.

In conclusion, extrapolating the 6 h. coulombs from 30 minute readings is a reliable

technique to avoid the heat effects on the values, but just for concretes with level of

penetrability higher than “very low”, 1000 coulombs, according to ASTM C1202-07.

Concretes with the total charge passed lower than 1000 coulombs showed higher 6 h.

charges than calculated extrapolated charges.

As a practical recommendation, extrapolated values can be replaced with the recorded

values if the extrapolated passing charge is less than 800 coulombs (or the maximum

anodic temperature is less than 26° C. This conclusion is based on data presented in

Tables 4.8 and 4.9.

139

4.3 Rate of water absorption (sorptivity)

Water sorptivity is a term used to describe water ingress into pores of unsaturated

concrete due to capillary suction.

Two types of water sorptivity were studied in this research program:

a) Laboratory water sorptivity

b) Field water sorptivity

In both types of sorptivity test capillary sorptivity is the case of one-dimensional

absorption. The rate of absorption, I, is calculated using sorptivity relation:

I = ρ.A

mass∆,

where, I is cumulative water absorption (mm), A is cross-section area of the specimen

which is in contact with water (mm2), and ρ is density of water (3mm

g).

The rate of water absorption, sorptivity (S), is the slope of I- t graph (mm/sec1/2

).

4.3.1 Laboratory sorptivity test

The rate of water absorption was measured according to ASTM C1585-04 as described

briefly in Section 3.1.3. Four types of concrete discs (ASTM C1585-04: 100 ± 6 mm

diameter with a length of 50 ± 3 mm) were tested at any age: a bottom disc, a middle

disc, and a top disc sliced from a concrete cylinder in addition to a disc cored from the

rectangular concrete slabs.

Three days oven drying at 50ºC followed by sealed drying for four days at 50ºC was the

conditioning regime to obtain a uniform moisture distribution and a surface relative

humidity of 50 to 60% as described by Parrott (1994) and DeSouza et al. (1997).

After 7 days conditioning, the side of the specimens were sealed with electrical tape to

simulate one-dimensional flow. The laboratory sorptivity test was done according to

methodology described in Section 3.1.3.1.

140

The initial and secondary water sorptivity values of concrete specimens are shown in

Figures 4.25, 4.26, 4.27, and 4.29.

Since the water absorption is the slope of the I- t graph with a correlation of coefficient

more than 0.98 (ASTM C1585, 2004), the initial rate of absorption (1 min to the first 6

hours) of some mixes with correlation of coefficient less than 0.98 were calculated based

on data measured from1 to 60 min or 2h to 6h.

Figure 4.25: Rate of water absorption of top slices

The amount of water absorption is reduced as concrete ages. Since mature concrete has a

more discontinuous pore system, water absorption due to the capillary pores suction is

reduced. Concrete mixes containing silica fume (three bottom lines in Figure 4.25) had

lower initial water sorptivity values because of the silica fume effects on concrete pose

structure (described in the literature review, Section 2.2.3.4.2).

141

Figure 4.26: Rate of water absorption of middle slices

Since higher W/CM ratios result in higher porosity and high continuity of the pore

structure, the water sorptivity of PCSL 0.45 mix is higher than water sorptivity value of

PCSL 0.40+ (0.43) and PCSL 0.40 mixes. But the secondary rate of water absorption of

the middle disc from PCSL0.45 mix at 56 days is lower than the same mix with the lower

W/CM ratio (as shown in Figure 4.26). This anomalous result happened only at 56 days

for PCSL 0.45 mixture.

142

Figure 4.27: Rate of water absorption of bottom slices

In most cases, the rate of water absorption of the bottom discs is the lower than that of the

middle and the top discs because the bottom slices were denser due to the gravity.

The average rate of water absorption (initial and secondary absorption values) of three

slices cut from a concrete cylinder was calculated to the nearest 0.1 x 10-4 mm/sec½ as

tabulated in Table 4.10.

Table 4.10: Average water sorptivity values of concrete discs (x 10-4

mm/sec½)

Age

Day 28 Day 56 Day 91 Mixtures

Initial Secondary Initial Secondary Initial Secondary

HPC 17.0 3.4 13.1 2.6 11.2 1.2

HPC+ 19.5 3.9 16.0 3.2 12.6 2.0

SFSL 0.40 21.8 4.9 17.1 3.6 14.8 2.8

PCSL 0.40 25.3 6.1 20.1 5.1 16.2 3.7 PCSL 0.40+ 27.5 6.8 24.1 5.6 19.1 4.2

PCSL 0.45 31.6 8.0 26.4 5.6 20.9 4.7 PCSL 0.45+ 34.9 8.9 30.6 6.6 25.2 5.5

PC 0.45 39.5 12.6 32.6 8.0 31.6 6.9 PC 0.45+ 43.3 16.1 37.3 12.0 35.8 10.1

143

In addition, a Ø100 ± 6 mm diameter and 50 ± 3 mm thick core was taken at each age

from the concrete rectangular slabs as shown in Figure 4.28.

Figure 4.28: Extracting cores from the concrete rectangular slabs

After conditioning, the finished surface of the concrete core was tested by water

sorptivity test to simulate the situation on site.

The secondary water absorption values of concrete cores taken at 28, 56, and 91 days are

shown in Figure 4.29.

0 28 56 91

No SCM

Slag

W/C

M

=============>+Silica fume + Slag

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Age (day)

Wate

r S

orp

tivity (x10

-4 m

m/s

ec

½)

PC 0.45+

PC 0.45

PCSL 0.45+

PCSL 0.45

PCSL 0.40+

PCSL 0.40

SFSL 0.40

HPC+ (SFSL 0.37)

HPC (SFSL 0.35)

Figure 4.29 (a): Initial rate of water absorption of the finished surface of concrete discs extracted

from rectangular concrete slabs

144

0 28 56 91

No SCM

Slag

Silica fume + Slag

W/C

M

==

==

==

==

==

==

=>

+

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Age (day)

Wate

r S

orp

tivity (

x10

-4 m

m/s

ec

½)

PC 0.45+

PC 0.45

PCSL 0.45+

PCSL 0.45

PCSL 0.40+

PCSL 0.40

SFSL 0.40

HPC+ (SFSL 0.37)

HPC (SFSL 0.35)

Figure 4.29 (b): Secondary rate of water absorption of the finished surface of concrete discs extracted

from rectangular concrete slabs

The only differences between concrete discs sliced from a concrete cylinder and a

concrete disc extracted from the rectangular slabs were the edge effect, curing regime,

and the finished surface. Concrete cylinders were kept in the fog room till the testing time

while concrete slabs were kept in the 50% RH room after first seven days moist curing.

To study the effects of curing regime on the rate of water absorption, the average

secondary water sorptivity of concrete cylinders (average values for the top, middle, and

bottom slices) were compared with the secondary water sorptivity values of concrete

cores as shown in Figure 4.30.

145

y = 0.98 x

R2 = 0.98

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

Water Sorptivity of Extracted Cores (x10-4 mm/sec½)

Wa

ter

So

rpti

vity

of

Slice

d D

iscs

(x1

0-4 m

m/s

ec½

)

Figure 4.30: Comparison between the secondary water sorptivity values of concrete discs sliced from

concrete cylinders and concrete cores extracted from concrete slabs

The secondary rate of water absorption of concrete discs and cores are almost identical,

but concrete cores absorbed more water. Water sorptivity values of concrete cores were

higher than that in concrete slices by an average of 5% at 91 days. Since the moisture

content of concrete slabs kept in 50% RH room reduced after they had been removed

from the moist room, the degree of hydration was reduced. Consequently, at later ages

the tortuosity of cores was higher than concrete cylinders resulted in higher rate of water

absorption. It resulted in higher water sorptivity coefficients although the differences

between sorptivity values of cores and slices were not significant since mid-depth of

slabs, where represented by cores, had more than 70% RH during most of the time as

presented in Table 4.12. Therefore hydration did not stop. Also paste skin of the cylinders

may influence the rate of absorption.

146

As mentioned, volume and tortuosity of the pore system which affects the rate of water

absorption can be represented by the RCPT chloride migration coefficient (Table 4.7),

the RCPT results and water sorptivity can be related as shown in Figure 4.31.

y = 1.64 x - 3.82

R2 = 0.92

0

5

10

15

20

25

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

Water Sorptivity of Sliced Discs (x10-4

mm/sec½

)

RC

PT

Ch

lori

de M

igra

tio

n C

oeff

icie

nt (x

10-1

2 m

2/s

)

Figure 4.31: Water sorptivity and chloride migration coefficient

The linear relation indicates that both water sorptivity coefficient and chloride ion

penetration coefficient are influenced by similar factors.

There is a relation (non-linear) between the water sorptivity and compressive strength

(Figure 4.32).

147

y = 49030 x-2

R2 = 0.89

0

2

4

6

8

10

12

14

16

30 35 40 45 50 55 60 65 70 75 80

Compressive Strength (MPa)

Wa

ter

So

rpti

vit

y

(x1

0-4

mm

/se

c½

)

Figure 4.32: Relation between the lab sorptivity test values and concrete compressive strength

It can be concluded that the water sorptivity is influenced by factors affecting capillary

pore system and its continuity such as the W/CM ratio, the addition of SCMs and the

degree of hydration.

Although the relative humidity of the specimens used for laboratory sorptivity test was

constant, it has been discussed by other researchers (Nokken et al., 2002) that concrete

sorptivity decreases with increasing degree of saturation and also decreasing W/CM ratio.

4.3.1.1 SCMs effects on the lab sorptivity values

Silica fume, an ultrafine material, strengthens interfacial transition zone (ITZ) by better

particle packing and providing nucleation by its pozzolanic reaction with portlandite.

Therefore, the microstructure of concrete becomes denser resulting in lower water

permeability. As shown in Figure 4.33, concrete mixes containing slag had lower water

sorptivity values than plain cement concrete mixes at all ages.

148

0 28 56 91

No SCMs

Slag

Silica fume +

Slag

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Age (day)

Wate

r S

orp

tivit

y (x

10

-4 m

m/s

ec

½)

PC 0.45+

PC 0.45

PCSL 0.45+

PCSL 0.45

PCSL 0.40+

PCSL 0.40

SFSL 0.40

HPC+ (SFSL 0.37)

HPC (SFSL 0.35)

Figure 4.33: Average rate of water absorption of concrete mixes

Although not measured, it can be predicted that at 7 days water sorptivity of plain cement

concretes would lower than slag concrete mixes with similar W/CM ratio because of

slag’s later age contribution to concrete properties. In contrast, it can be anticipated that

at later ages, ternary mixes have lower sorptivity coefficients than any other mixes.

4.3.1.2 W/CM ratio effects on the lab sorptivity values

Since the ability of concrete to resist water penetration is influenced by the connectivity

of its capillary pore structure (explained in Section 2.2.5), lower W/CM ratio mixes had

lower sorptivity values as shown in Figures 4.29 and 4.33. Concrete mixes with low

W/CM ratio have lower porosity and the pore system is less continuous. They result in

lower amount of water absorbed by the capillary suction.

It is important to mention that the HPC mixes containing silica fume and slag had fast

initial sorptivity due to their finer pore structure, but sorptivity decreased rapidly due to

discontinuity.

149

4.3.2 Field sorptivity test

Since concrete deterioration processes (e.g. rebar corrosion) are influenced by fluid

penetrability especially of covercrete, the ability of concrete to absorb water on site can

provide information about its durability.

For each concrete mixture, two Ø406 x 75 mm circular slabs were tested at ages 14, 28,

56, and 91 days as described briefly in Section 3.1.3.2.

Figure 4.34: Field sorptivity apparatus (horizontal orientation)

The water sorptivity was measured in naturally occurring conditions (concrete slabs were

tested as they removed from the 50% RH room) and moisture content of slabs were

measured by weighting slabs. Therefore, no pre-conditioning regime was applied to the

concrete slabs. The rate of water absorption is calculated as shown in Table 4.11.

150

Table 4.11: Water sorptivity coefficient of the circular concrete slabs (mm/min1/2

)

Day 14 Day 28 Day 56 Day 91 Mixture

CS1 CS2 Ave. CS1 CS2 Ave. CS1 CS2 Ave. CS1 CS2 Ave.

HPC 0.009 0.006 0.008 0.009 0.012 0.010 0.020 0.013 0.017 0.022 0.019 0.020

HPC + 0.010 0.008 0.009 0.015 0.008 0.011 0.022 0.019 0.021 0.028 0.024 0.026

SFSL 0.40 0.010 0.009 0.009 0.015 0.012 0.013 0.027 0.023 0.025 0.030 0.026 0.028

PCSL 0.40 0.012 0.013 0.013 0.017 0.019 0.018 0.031 0.032 0.031 0.049 0.050 0.049

PCSL 0.40+ 0.015 0.016 0.016 0.032 0.031 0.031 0.047 0.052 0.050 0.071 0.072 0.072

PCSL 0.45 0.028 0.029 0.028 0.042 0.053 0.047 0.060 0.057 0.058 0.089 0.100 0.094

PCSL 0.45+ 0.030 0.029 0.029 0.054 0.060 0.057 0.074 0.063 0.068 0.115 0.116 0.115

PC 0.45 0.006 0.016 0.011 0.017 0.018 0.018 0.031 0.030 0.030 0.044 0.048 0.046

PC 0.45+ 0.025 0.030 0.028 0.025 0.037 0.031 0.038 0.046 0.042 0.057 0.078 0.067

It is seen that the amount of water absorption is increased with a decrease in the relative

humidity in the pore system of the concrete specimens due to continued drying with age

as shown in Figure 4.35.

0 14 28 56 910.000

0.020

0.040

0.060

0.080

0.100

0.120

Age (day)

Wate

r S

orp

tivity (m

m/m

in 0

.5)

PCSL 0.45+

(PCSL 0.47)PCSL 0.45

PCSL 0.40+

(PCSL 0.43)PC 0.45+

(PC 0.52)PC 0.45

PCSL 0.40

SFSL 0.40

HPC+

(SFSL 0.38)HPC

(SFSL 0.35)

Figure 4.35: Water sorptivity coefficients of circular concrete slabs

151

Since day 14 is important for the Ministry of Transportation of Ontario (bridge joints

installation), the field sorptivity test was started at this day. As shown in Figure 4.35, rate

of water absorption increased as concrete becomes more mature. This unusual finding

was caused by the reduction in the concrete moisture level. Concrete slabs were not pre-

conditioned before the test, so moisture content at each testing time was less than that in

the previous time. Therefore, drier concrete absorbed more water although the pores

tortuosity was reduced due to the cement hydration and SCMs secondary hydrations.

Despite the test results can not provide useful data about the physical characteristics of

the pore structure and the degree of hydration, it can be a useful technique measuring the

moisture content of in situ concretes.

It was not possible to precondition concrete slabs to a standard relative humidity prior to

testing as can be done in the laboratory sorptivity test. Therefore, the rate of water

absorption must be correlated with the slab’s moisture content. Since it was not possible

to place a Ø406 x 75 mm circular slab in an oven to dry, a concrete piece was taken from

the cored rectangular slabs (Figure 4.36), which were kept in the same condition as the

circular slabs, weighed, and dried at 110°C.

Figure 4.36: Middle piece taken from a cored rectangular slab for moisture content measurement

152

It is important to mention that these concrete pieces were taken approximately seven

months from the casting time. At this time the weight of slabs remained constant, so there

was a humidity balance between the room conditions and the concrete (50% RH). The

amount of water (a percentage of the dry mass) in 50% RH concrete pieces was used to

calculate the dry mass of circular slabs.

Table 4.12: Degree of saturation of circular concrete slabs

Concrete Age Mixture

7 days 14 days 28 days 56 days 91 days 7 months

HPC 100% 92% 89% 86% 84% 50%

HPC + 100% 90% 85% 80% 77% 50%

SFSL 0.40 100% 90% 86% 81% 77% 50%

PCSL 0.40 100% 91% 84% 78% 73% 50%

PCSL 0.40+ 100% 88% 81% 74% 69% 50%

PCSL 0.45 100% 82% 77% 72% 64% 50%

PCSL 0.45+ 100% 83% 78% 71% 64% 50%

PC 0.45 100% 83% 77% 70% 64% 50%

PC 0.45+ 100% 85% 78% 71% 63% 50%

Data presented in Table 4.12 are visualized in Figure 4.37.

153

0 7 14 28 56 91

RCPT Chloride Penetration Depth

60

65

70

75

80

85

90

95

100

Drying Time (day)

De

gre

e o

f S

atu

rati

on

(%

) HPC

HPC +

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.37: Degree of saturation of the concrete slabs at different ages

It can be seen that the physical characteristic of concrete which affects the depth of

chloride ion penetrated into concrete can be considered as an influencing factor for the

rate of moisture loss and degree of saturation. Concrete mixes with higher volume and

connectivity of pores, so higher chloride penetration coefficient (e.g. PC 0.45+) lost their

moisture more and faster than concretes with less porosity and pore system continuity

such as HPC. In other words, moisture evaporation is less and slower in concretes with

less porosity and pore continuity.

If water sorptivity test results are calibrated, the field sorptivity test can be used as a rapid

quality assurance procedure. The calibration curve is plotted as shown in Figure 4.38

based on data presented in Tables 4.11 and 4.12.

154

0.000

0.020

0.040

0.060

0.080

0.100

0.120

60 65 70 75 80 85 90 95 100

Degree of Saturation (%)

Wa

ter

So

rpti

vit

y C

oe

ffic

ien

t (m

m/m

in0.5

)

PCSL 0.45+

PCSL 0.45

PCSL 0.40+

PCSL 0.40

PC 0.45+

SFSL 0.40

HPC

HPC+

PC 0.45

Figure 4.38: Moisture content effects on the rate of water absorption

The need to adjust the sorptivity values for moisture content can be minimized if all tests

were performed after the same conditioning procedure (e.g. ASTM C 1202-07).

The rate of absorption increased as the moisture content decreased with the smallest rate

of absorption occurring at 14 days with degrees of saturation close to 100%. The largest

rate of water absorption occurs at the lowest moisture content and zero rate at the

saturated condition (after removing from the fog room after 7 days moist curing).

Water sorptivity is influenced by many factors. Among these factors, cementitious

materials ratio, the water-to-cement ratio, and concrete moisture content are the most

important factors.

To plot the calibration curves for each concrete mix (Figures 4.43-4.51), water sorptivity

coefficient at 50% RH (when slabs’ weight located in 50% RH room became constant

155

which meant slabs were in humidity equilibrium condition with the room) were

measured.

4.3.3 SCMs effects on the rate of water absorption

Both laboratory and field sorptivity test data have shown that adding SCMs to a concrete

mixture, results in less water absorption, but it depends on the age of the concrete. As

shown in Figure 4.39, concrete mixes containing silica fume and slag had the lowest

early age sorptivity coefficient because of silica fume rapid pozzolanic reactivity.

0 14 28 56 910.000

0.020

0.040

0.060

0.080

0.100

Age (day)

Wate

r Sorp

tivity (m

m/m

in 0

.5)

PCSL 0.45

PCSL 0.40

PC 0.45

SFSL 0.40

Figure 4.39: SCMs effects on the field sorptivity test results

The ternary mix with both silica fume and slag had shown a low rate of water absorption

in later ages because of the secondary hydration products of silica fume and mostly slag.

Cementing materials hydration reduced the moisture content of the concrete slabs in

addition to decreasing the tortuosity of pores. Concrete mix containing GGFS absorbed

more water than plain cement concrete with similar W/CM ratio because slag effects are

significant in concrete later ages. At later ages, binary mixes (slag and Portland cement)

156

had even higher sorptivity coefficients than plain cement concrete mixes because slag

absorbed more water during its secondary hydration to form more C-S-H. Therefore, the

moisture content of concrete slab containing slag (PCSL 0.45) is lower than plain cement

concrete (PC 0.45) which results in higher water sorptivity coefficients.

In other words, the field sorptivity test with the procedure applied during this research

program is not an applicable test to analyse the characteristics of the pore structure while

it can be a useful non-destructive technique to distinguish between different mix designs

especially in mixes containing silica fume.

4.3.4 W/CM ratio influences on the rate of water sorptivity coefficient

Since pore size and pore connectivity decreased with decreasing the W/CM ratio (Ahmed

et al., 2009), an increase of water sorptivity is observed with an increase of water-to-

cementitious materials ratio. In other words, high W/CM concretes have greater pore

volume with connected pores which results in faster water absorption. It can be seen in

all concrete mixes as shown in Figures 4.40, 4.41, and 4.42.

0 14 28 56 91

W/C

M

==========>

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

Age (day)

Sorp

tivity C

oeffic

ient (m

m/m

in 0

.5)

PC 0.45+ (PC 0.52)

PC 0.45

Figure 4.40: W/CM ratio effects on the water sorptivity coefficients of plain cement concrete

157

0 14 28 56 91

W/C

M

==========>

0.000

0.020

0.040

0.060

0.080

0.100

0.120

Age (day)

Sorp

tivity C

oeffic

ient (m

m/m

in 0

.5)

PCSL 0.45+(PCSL 0.47)

PCSL 0.45

PCSL 0.40+(PCSL 0.43)

PCSL 0.40

Figure 4.41: W/CM ratio effects on the sorptivity coefficients of concrete mixes containing slag

(25 % replacement)

0 14 28 56 91

W/C

M

==========>

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Age (day)

Sorp

tivity C

oeffic

ient (m

m/m

in 0

.5)

SFSL 0.40

HPC+ (SFSL 0.38)

HPC (SFSL 0.35)

Figure 4.42: W/CM ratio effects on the water sorptivity coefficients of the ternary mixes

158

In all concrete mixes, higher W/CM ratio mixes had higher water sorptivity coefficient.

But the amount of increase in water sorptivity coefficient is dependant to the concrete

mix design. It is seen that increasing the W/CM ratio for 0.05, increased the water

permeability values by 26 % in ternary mixes and 38% in binary and 32% in plain

cement mixes at 91 days. It can be concluded that the binary mixes absorbed more water

because of their lower moisture content in contrast with their lower porosity than plain

cement mixes.

4.3.5 Water sorptivity and degree of saturation

Relative humidity of concrete specimens used for laboratory sorptivity test was about

80% while concrete slabs used for field sorptivity test had different moisture contents

because of the slow conditioning process of Ø406 x 75 mm circular slabs. Field sorptivity

test results have supported DeSouza’s results (DeSouza, 1998) which showed that water

sorptivity increases with decreasing levels of concrete saturation.

In conclusion, the field sorptivity test can be a useful test for similar mix design concretes

with different W/CM ratios. To compare the change in physical characteristics of the

pore system of different mix designs, the field sorptivity test can be applicable provided

that all specimens are conditioned to a similar level of relative humidity.

It is recommended for future works to pre-condition the slabs to a fully dried level by

vacuum and silica gel. In this case, the effects of the change in physical properties of the

pore structure will be studied by the water absorption values regardless of the moisture

history of concrete.

4.3.6 Calibration curves and prediction of the later age sorptivity coefficient

Since each concrete has a unique calibration curve, it is necessary to plot it as shown in

Figures 4.43 to 4.51 based on water sorptivity coefficient at first 91 days and at 50% RH.

It is important to mention that the water sorptivity coefficients after 50% RH can be

calculated regarding to the best fit representing the measured values. 50% RH point

represented the day when the weight of concrete slabs remained constant in 50% RH

curing room. The days when the slabs weight became constant, were varied in mixes as

rates of absorption and evaporation of mixes were different.

159

HPC (SFSL 0.35)

day 91

day 56

day 28day 14

day 7

y = 102.3 e-12x

R2 = 0.98

50

60

70

80

90

100

0.0

0

0.0

2

0.0

4

0.0

6

0.0

8

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f Satu

ration

(%

)

Figure 4.43: Water sorptivity- saturation calibrating curve for HPC mix

HPC+ (SFSL 0.38)

y = 100.0 e-11.3 x

R2 = 0.99

50

60

70

80

90

100

0.0

0

0.0

2

0.0

4

0.0

6

0.0

8

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f S

atu

ration

(%

)

Figure 4.44: Water sorptivity- saturation calibrating curve for HPC+ mix

160

SFSL 0.40

y = 102.0 e-11.4 x

R2 = 0.98

50

60

70

80

90

100

0.00 0.02 0.04 0.06 0.08

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f Satu

ration

(%

)

Figure 4.45: Water sorptivity- saturation calibrating curve for SFSL 0.40 mix

PCSL 0.40

y = 95.0 e-5.07 x

R2 = 0.98

50

60

70

80

90

100

0.0

0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f S

atu

ration

(%

)

Figure 4.46: Water sorptivity- saturation calibrating curve for PCSL 0.40 mix

161

PCSL 0.40+ (PCSL 0.43)

y = 99.1 e-5.9 x

R2 = 0.97

50

60

70

80

90

100

0.0

0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f Satu

ration

(%

)

Figure 4.47: Water sorptivity- saturation calibrating curve for PCSL 0.40+ mix

PCSL 0.45

y = 96.7 e-4.7 x

R2 = 0.98

50

60

70

80

90

100

0.0

0

0.0

3

0.0

6

0.1

0

0.1

3

0.1

6

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f S

atu

ration

(%

)

Figure 4.48: Water sorptivity- saturation calibrating curve for PCSL 0.45 mix

162

PCSL 0.45+ (PCSL 0.47)

y = 98.5 e-4.5 x

R2 = 0.95

50

60

70

80

90

100

0.0

0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f Satu

ration

(%

)

Figure 4.49: Water sorptivity- saturation calibrating curve for PCSL 0.45+ mix

PC 0.45

y = 93.1 e-8.3 x

R2 = 0.97

50

60

70

80

90

100

0.00 0.02 0.04 0.06 0.08 0.10

Water Sorptivity Coefficient (mm/min0.5)

Degre

e o

f S

atu

ration

(%

)

Figure 4.50: Water sorptivity- saturation calibrating curve for PC 0.45 mix

163

PC 0.45+ (PC 0.52)

y = 95.4 e-5.7 x

R2 = 0.96

50

60

70

80

90

100

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

Water Sorptivityy Coefficient (mm/min0.5)

Degre

e o

f S

atu

ration

(%

)

Figure 4.51: Water sorptivity- saturation calibrating curve for PC 0.45+ mix

As the rest of the calibration curves can be plotted (not measured) based on the first 91

days water sorptivity values and sorptivity coefficient at 50% RH, some water sorptivity

coefficients of dry samples were against the basic concepts of the concrete technology;

for example, although the PCSL 0.45 mix had 25% slag replaced with the Portland

cement (higher electrical resistivity), its permeability coefficient at 0% degree of

saturation was higher than that in PC 0.45 (lower resistivity). In case of W/CM ratio

effects, the water sorptivity coefficient at 0% RH of higher a W/CM ratio concrete was

higher than that in a lower W/CM ratio specimen (similar mix design) which proved that

this procedure can be useful for analysing the W/CM ratio effects on the pore system (as

concluded in Section 4.3.4).

If a similar pre-conditioning regime was applied to all concrete specimens and specimens

were in a similar RH at the time of testing, the later age (0% moisture content) sorptivity

coefficients would represent the change in the physical characteristics of the pore system

caused by cementing materials hydration and the W/CM ratio.

164

To check the calculated sorptivity coefficient at 0% MC, one concrete slab from every

mix designed was fully dried as shown in Figure 4.52.

Figure 4.52: Drying circular concrete slabs

Water sorptivity of fully dried (0% MC) circular concrete slabs were measured and

compared with the calculated coefficients (not shown in Figures 4.43-4.51). The

difference between the measured sorptivity coefficients and calculated coefficients was

not significant (except in PC 0.45 mix), so estimating 0% MC sorptivity values based on

the calibration curves is a reliable method. In this case, it can be predicted that, the water

sorptivity coefficient of higher resistivity concrete is lower and vice versa.

4.4 Electrical resistivity

Measurement of concrete electrical resistivity has been proposed as a possible method for

assessment of the physical characteristics of pore structure and microstructure and pore

solution chemistry. Electrical current passes through the pore structure because saturated

pores in the porous cement paste contain ions although cement hydrates in solutions.

Beside the RCPT resistivity (Section 4.2.2), DC-cyclic bulk resistivity and surface

electrical resistivity were measured in this research program.

Measuring the electrical bulk resistivity is the most common and reliable method for

measuring electrical resistivity. The measurement of surface electrical resistivity by the

165

Wenner technique is a time saving, but less reliable method if adequate technical

recommendations have not been considered as critics believed: Millard and Gowers

(1991) and Morris et al. (1996). But this research has indicated that the Wenner technique

is a reliable test method.

As mentioned in the literature, electrical resistivity of concrete is a function of the pore

solution chemistry, the pore volume, its connectivity, and the degree of saturation of

concrete (moisture content). All the specimens tested for electrical resistivity were fully

water saturated, so the effect of moisture content on concrete conductivity was not

studied in this research program.

4.4.1 DC-cyclic bulk resistivity (Monfore resistivity)

The bulk electrical resistivity of a concrete cylinder was measured using two stainless

steel electrodes placed on opposite surfaces of a specimen as shown in Figure 4.53.

Figure 4.53: Concrete bulk resistivity test with two steel electrodes (DC-cyclic bulk resistivity)

166

One electrode induced the cyclic direct current and the other electrode received the

current. The DC measurement was carried out using a cyclic DC potential similar to that

of Monfore (Monfore, 1968 and Polder, 2001) but switching between 3 volts and 5 volts

every 5 seconds. The bulk electrical resistivity in this research program was calculated as:

ρ = LII

dVV

×−

Π×−

)(

)(

35

2

35 (KΩ.cm),

where, V5 is 5 volts, V3 is 3 volts, I5 is current at V5 (A), I3 is current at V3, d is specimen

section diameter (mm), and L is the length of specimen (mm).

In this research program, the Monfore resistivity of three Ø100 x 200 mm saturated

cylinders and two Ø100 x 50 mm discs sliced from middle and bottom parts of concrete

cylinders were measured at each age. In all specimens, the top faces were in contact with

the negative electrode while the bottom surfaces were in contact with the positive

electrodes.

4.4.1.1 DC-cyclic bulk resistivity of full length concrete cylinders

According to the last equation, the DC-cyclic resistivity of three water saturated Ø100 x

200 mm concrete cylinders, was measured in 15 minutes at each age. Table 4.13 presents

the average of three resistivity values.

Table 4.13: Bulk resistivity values of concrete cylinders

DC-Cyclic Bulk Resistivity (KΩ.cm) Mixture

Day 3 Day 7 Day 28 Day 56 Day 91 HPC 17.5 26.3 82.4 94.5 102.4

HPC + 16.9 24.8 79.2 88.1 92.7 SFSL 0.40 9.1 20.5 72.5 78.2 82.3

PCSL 0.40 6.3 9.8 23.3 29.4 42.0 PCSL 0.40+ 3.8 5.7 18.1 25.0 32.6 PCSL 0.45 3.5 3.8 15.7 22.1 29.8

PCSL 0.45+ 3.7 3.8 15.1 19.7 28.8

PC 0.45 3.4 4.9 6.8 9.8 12.6 PC 0.45+ 3.5 4.6 8.2 8.6 10.4

167

Figure 4.54 in plotted based on the average electrical resistivity presented in Table 4.13.

0 3 7 28 56 91

Sili

ce f

um

e +

Sla

gS

lag

No S

CM

0

10

20

30

40

50

60

70

80

90

100

110

Age (day)

DC

Cyclic B

ulk

Resis

tivit

y (

KΩ

.cm

) HPC (SFSL0.35)

HPC+ (SFSL0.38)

SFSL 0.40

PCSL 0.40

PCSL 0.40+(PCSL 0.43)

PCSL 0.45

PCSL 0.45+(PCSL 0.47)

PC 0.45

PC 0.45+(PC 0.52)

Figure 4.54: DC-cyclic bulk resistivity of Ø100 x 200 mm concrete cylinders

It can be seen that the addition of slag and silica fume to concrete mixtures, affects the

electrical resistivity significantly. Also any change in W/CM ratio influences electrical

resistivity of concrete.

The ionic concentration in pore solution increases with age because of the dissolution of

calcium and alkali ions (Nokken et al., 2006). It causes higher electrical conductivity

(lower resistivity). On the other hand, the connectivity of the pore structure and pore size

distribution decrease as concrete ages.

As shown in Figure 4.54, the Monfore resistivity of all concrete mixes increased as

concrete aged. It shows that the change in the physical characteristics of the pore system

is more dominant than the change in pore solution. Mature concrete has less connected

pores which results in higher electrical resistance.

168

Electrical properties of concrete are dependant on the amount of free water (moisture

content which was always 100% in this study), the type of supplementary cementitious

materials, the W/CM ratio, and the degree of hydration.

4.4.1.1.1 SCMs effects on the DC-cyclic bulk resistivity

The influence of adding silica fume to concrete mixes can be appreciated by comparing

data for mixes with 8% silica fume and without silica fume (with similar W/CM ratio) as

shown in Figure 4.55.

0 3 7 28 56 91

Silica fume +Slag

W/CM

0.40

Slag

Slag0.40

0.45

No SCM

0.45

0

10

20

30

40

50

60

70

80

90

100

110

Age (day)

DC

Cy

clic

Bu

lk R

es

isti

vit

y (

KΩ

.cm

)

SFSL 0.40

PCSL 0.40

PCSL 0.45

PC 0.45

Figure 4.55: SCMs effects on the DC-cyclic bulk resistivity values

The W/CM ratio in the two lower lines is 0.45. The only difference in their mix design is

the presence of slag. Concrete mixtures containing slag had higher electrical resistivity

after 10 days than plain cement concrete. This difference is more significant in later ages

because of the later age contribution of slag. In contrast, electrical resistivity of plain

cement concretes is higher than that in similar concrete mixes with 25% slag replacement

169

during the first 10 days although no one is interested in 10 days resistivity (Figure 4.55).

All these facts have proved that concrete mixes containing GGBS have lower durability

than plain cement concrete in early ages and higher durability in later ages significantly

after 28 days.

It is known that silica fume will increase the bulk resistivity of concrete in three ways:

1) Silica fume reacts with calcium hydroxides, Ca(OH)2, in the pore solution to form

secondary hydrates. Silica fume reduces the ionic concentration of the pore

solution resulting in less electrical charge passing trough the pore system

(Bassuoni et al., 2006), so this is a critic for the bulk resistivity measurements of

silica fume concretes,

2) Silica fume is a super fine material, so it increases the density of cement paste.

The ITZ penetrability is decreased significantly by adding silica fume to the

mixture (Neville, 1995).

3) Because of the silica fume secondary hydrates (C-S-H), the volume and

connectivity of the pore structure is decreased significantly which results in less

pores tortuosity (Hansson, 1983).

Concrete mixes with 8% silica fume and 25 % slag replaced with cement had the highest

electrical resistivity in comparison with the other mixes. Silica fume mostly affects early

age properties of concrete and the difference between early age resistivity of ternary

mixes and other mixes is significantly higher than that in later ages.

4.4.1.1.2 W/CM ratio effects on bulk resistivity

W/CM ratio fundamentally affects concrete porosity. More porosity and connected pores,

caused by higher W/CM ratio, results in lower electrical resistivity because the applied

electrical current can easily pass through the pore structure. It can be concluded from

Figure 4.56 that concrete mixes with similar mix design but different W/CM ratio had

different electrical properties.

170

0 3 7 28 56 91

0.35

0.38

W/CM

0.40

0.40

0.47

0.45

0.43

0.52

0.45

0

10

20

30

40

50

60

70

80

90

100

110

Age (day)

DC

Cy

clic B

ulk

Re

sis

tiv

ity

(K

Ω.c

m)

HPC(SFSL0.35)

HPC+(SFSL 0.38)

SFSL 0.40

PCSL 0.40

PCSL 0.40+(PCSL 0.43)

PCSL 0.45

PCSL 0.45+(PCSL 0.47)

PC 0.45

PC 0.45+(PC 0.52)

Figure 4.56: W/CM ratio effects on the Monfore resistivity values

In all mixes tested in the research program, as W/CM ratio increased, the Monfore

resistivity decreased. On the other hand, low W/CM ratio specimens had higher electrical

resistivity.

The W/CM ratio effects were significant in concrete specimen containing both slag and

silica fume (top three lines in Figure 4.56). In contrast, the W/CM ratio did not

significantly affect electrical properties of plain cement concrete mixtures (two lower

lines). Also it can be seen that effects of any charge in the W/CM ratio is significant in

lower W/CM ratios.

4.4.1.2 Bulk resistivity as an indicator for chloride penetrability

The diffusion of chloride ion through concrete can be correlated with the DC-cyclic bulk

resistivity. Also the total RCPT passing charge represents the ranking of the concrete

with respect to its chloride permeability. Consequently, the Monfore resistivity can be

used as an indicator for chloride ion penetrability (Section 4.2.3) as shown in Figure 4.57.

171

Figure 4.57: Relation between chloride migration coefficient and the DC-cyclic bulk resistivity with

the RCPT 5 min. resistivity

4.4.1.3 Bulk resistivity of concrete discs

Two Ø100 x 50 mm concrete discs were sliced from a concrete cylinder at each age. All

specimens were vacuum-saturated one day prior to the testing time according to the

process recommended in ASTM C1202-07. The DC-cyclic bulk resistivity of concrete

mixtures (average of electrical resistivity of the bottom and middle slices) were measured

as shown in Table 4.14.

172

Table 4.14: The Monfore resistivity of Ø100 x 50 mm concrete discs

DC-Cyclic Bulk Resistivity (KΩ.cm) Mixture

Day 3 Day 7 Day 28 Day 56 Day 91

HPC 4.9 22.6 77.4 91.3 99.6 HPC + 4.5 24.8 74.9 89.6 96.8

SFSL 0.40 4.5 24.3 64.3 78.3 84.5

PCSL 0.40 4.0 6.6 17.3 30.1 42.6 PCSL 0.40+ 4.3 5.3 15.3 24.4 32.1 PCSL 0.45 3.9 4.6 13.3 21.6 29.1

PCSL 0.45+ 3.6 4.6 11.6 22.4 27.4

PC 0.45 4.2 4.2 6.6 10.9 13.0 PC 0.45+ 4.1 3.8 6.4 9.8 11.3

Figure 4.58 is based on data presented in Table 4.14.

0 3 7 28 56 910

10

20

30

40

50

60

70

80

90

100

110

Age (day)

DC

Cyclic B

ulk

Resis

tivit

y

(KΩ

.cm

)

HPC (SFSL 0.35)

HPC+ (SFSL 0.35+)

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.58: DC-cyclic bulk resistivity of Ø100 x 50 mm concrete discs

It can be seen that there is a logical relation between the Monfore resistivity and concrete

age for all mixes; as concrete ages, electrical resistivity increases. It is important to

mention that electrical resistivities of bottom slices, more compacted, were usually higher

than middle slices resistivity due to gravity effects on aggregates.

In most of the cases, the difference between the bulk resistivity of concrete slices and

resistivity of full length cylinders from a similar mix was less than 20%. In other words,

173

DC-cyclic bulk resistivity test was independent from geometry of specimens. Therefore,

the Monfore resistivity test values represent the resistivity of concrete.

4.4.2 Surface electrical resistivity

Surface electrical resistivity was measured by four-electrode, Wenner, method. In this

method a low-frequency alternating current (AC) passes between the two outer probes.

The two inner probes measure the voltage drop (V). As explained in Section 2.2.4.2.2,

surface electrical resistivity was calculated as:

ρ =2πaI

V,

where, a is the probe spacing (mm) which can be adjusted in this research program, I is

the electrical current (mA) and V is the voltage drop (V). The probe spacings used in this

research program were 20, 30, 40 and 50mm for concrete slabs and 25, 30, 40, and 50mm

for concrete cylinders.

4.4.2.1 Surface electrical resistivity of concrete cylinders

Despite the fact that the Wenner method is a simple and convenient test method, probe

spacing should be adjusted carefully. Surface electrical resistivity is directly proportional

to the probe spacing (a).

Three water saturated Ø100 x 200 mm concrete cylinders were tested at each age.

Surface electrical resistivity of a concrete cylinder was the average of four measurements

done longitudinally on the cylinder surface along its length as shown in Figure 3.7.

The average of twelve resistivity values at each time is reported in Table 4.15.

Table 4.15: Concrete cylinders apparent surface electrical resistivity values

Surface Electrical Resistivity

(KΩ.cm) Mixture

Probe

Spacing

(mm) Day 3 Day 7 Day 28 Day 56 Day 91

25 15.5 36.1 106.7 112.8 121.7

30 17.1 42.9 125.7 133.8 144.4

40 24.5 54.2 163.7 167.8 174.7 HPC

50 28.1 71.5 207.3 211.9 220.6

174

25 12.3 37.0 105.7 109.3 114.7

30 13.5 40.7 121.7 125.7 132.3

40 17.7 51.8 153.1 156.0 160.3 HPC+

50 22.0 66.7 198.8 200.7 208.3

25 17.8 26.0 88.3 97.6 109.6

30 19.8 37.3 108.5 113.3 122.0

40 24.6 46.6 137.8 146.7 156.4 SFSL 0.40

50 32.5 60.6 180.4 189.3 196.3

25 8.4 17.4 31.0 33.9 48.3

30 9.0 17.5 37.4 41.3 57.3

40 12.4 22.6 47.0 51.7 65.3 PCSL 0.40

50 16.1 29.6 61.4 69.2 88.6

25 8.2 10.6 21.2 27.8 40.1

30 9.2 11.5 23.7 35.0 45.7

40 11.6 15.2 29.5 43.9 58.1 PCSL 0.40+

50 15.3 20.1 39.3 57.3 79.7

25 6.0 8.4 21.0 21.6 40.1

30 6.6 10.0 23.4 24.5 45.0

40 8.3 12.7 28.8 32.5 56.7 PCSL 0.45

50 11.8 16.8 39.3 47.4 74.2

25 4.7 8.2 19.3 27.1 30.3

30 5.0 9.0 21.1 29.3 35.4

40 6.6 11.3 27.4 35.9 45.8 PCSL 0.45+

50 9.0 15.2 36.6 46.3 60.9

25 4.0 5.0 9.9 12.3 15.3

30 4.4 5.8 10.5 13.4 17.4

40 5.6 6.9 14.3 17.0 21.9 PC 0.45

50 7.2 9.4 19.1 22.8 28.4

25 4.1 4.8 7.8 10.2 11.7

30 4.5 5.3 8.7 11.5 13.3

40 5.9 6.7 10.5 14.6 17.1 PC 0.45+

50 7.7 8.6 13.2 19.7 23.2

175

Figures 4.59- 4.62 represent the average electrical resistivity of concrete mixtures (three

cylinders) with different probe spacings. These graphs are plotted based on the values

presented in Table 4.15.

a= 25 mm

0 3 7 28 56 91

0

50

100

150

200

250

Age (day)

Su

rfa

ce

Re

sis

tiv

ity

(K

Ω.c

m)

HPC

HPC+

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.59: Surface electrical resistivity of concrete cylinders (25 mm probe spacing)

a= 30 mm

0 3 7 28 56 91

0

50

100

150

200

250

Age (day)

Su

rfa

ce

Re

sis

tiv

ity

(K

Ω.c

m)

HPC

HPC+

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.60: Surface electrical resistivity of concrete cylinders (30 mm probe spacing)

176

a= 40 mm

0 3 7 28 56 91

0

50

100

150

200

250

Age (day)

Su

rfa

ce

Re

sis

tiv

ity

(K

Ω.c

m)

HPC

HPC+

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.61: Surface electrical resistivity of concrete cylinders (40 mm probe spacing)

a= 50 mm

0 3 7 28 56 91

0

50

100

150

200

250

Age (day)

Su

rfa

ce

Re

sis

tiv

ity

(K

Ω.c

m)

HPC

HPC+

SFSL 0.40

PCSL 0.40

PCSL 0.40+

PCSL 0.45

PCSL 0.45+

PC 0.45

PC 0.45+

Figure 4.62: Surface electrical resistivity of concrete cylinders (50 mm probe spacing)

In all cases, surface electrical resistivity increased with concrete age because of the

continued hydration. This improvement of surface resistivity was rapid at early ages of

the silica fume mixes. Slag increased the resistivity values significantly at later ages.

177

It is important to mention that three cylinders were tested each time (four measurements

on each cylinder). Therefore, the values presented in Figures 4.59, 4.60, 4.61, and 4.62

were the average of twelve measurements at each time.

4.4.2.1.1 Statistical analysis of concrete cylinders surface resistivity

Twelve measurements were taken for each concrete mixture at each time throughout the

cylinders surfaces. Table 4.16 presents the resistivity measurement results for the

concrete cylinders for the standard probe spacing (50 mm). Similar data can be presented

for the other probe spacings.

Table 4.16: Statistical analysis of resistivity measurement of concrete cylinders (a= 50mm)

Statistical Summary Mixture Statistics

Day 3 Day 7 Day 28 Day 56 Day 91

n 12 12 12 12 12

Mean

(KΩ.cm) 28.17 71.53 207.28 211.91 220.58

б* 5.06 12.10 6.50 8.10 8.65

HPC

COV (%) 17.96 16.92 3.14 3.82 3.92

n 12 12 12 12 12

Mean

(KΩ.cm) 21.98 66.69 198.75 200.67 208.26

б 2.30 8.97 5.97 7.55 7.89

HPC+

COV (%) 10.48 13.45 3.00 3.76 3.79

n 12 12 12 12 12

Mean

(KΩ.cm) 32.50 60.62 180.41 189.27 196.25

б 2.27 2.95 5.28 7.53 6.89

SFSL 0.40

COV (%) 6.99 4.87 2.93 3.98 3.51

n 12 12 12 12 12

Mean

(KΩ.cm) 16.11 29.57 61.37 69.22 88.58

б 0.96 1.05 4.58 2.07 2.15

PCSL 0.40

COV (%) 5.94 3.54 7.46 2.99 2.43

178

n 12 12 12 12 12

Mean

(KΩ.cm) 15.33 20.13 39.29 57.28 79.70

б 0.47 0.88 2.11 1.92 4.08

PCSL 0.40+

COV (%) 3.09 4.38 5.37 3.35 5.12

n 12 12 12 12 12

Mean

(KΩ.cm) 11.77 16.83 39.25 47.43 74.17

б 0.79 1.23 1.94 2.32 2.94

PCSL 0.45

COV (%) 6.74 7.32 4.94 4.88 3.97

n 12 12 12 12 12

Mean

(KΩ.cm) 8.97 15.23 36.60 46.32 60.88

б 0.52 0.59 0.94 3.19 3.32

PCSL 0.45+

COV (%) 5.82 3.90 2.57 6.89 5.46

n 12 12 12 12 12

Mean

(KΩ.cm) 7.20 9.40 19.15 22.78 28.37

б 0.64 0.87 1.05 0.99 1.38

PC 0.45

COV (%) 8.91 9.20 5.46 4.35 4.86

n 12 12 12 12 12

Mean

(KΩ.cm) 7.67 8.63 13.20 19.68 23.22

б 0.75 0.77 0.62 1.54 1.41

PC 0.45+

COV (%) 9.76 8.91 4.67 7.81 6.09

* 1

)( 2

−

−=∑

n

xi µσ (sample standard deviation)

Coefficient of variation ( %100×µ

σ ) represents the variability of a set of numbers. The

variability of a set of resistivity measurements is low (lower than 10%) in most of the

mixtures. Both high performance concretes had a COV higher than 10 % at 3 and 7 days.

Therefore, there was not a notable difference between the twelve measurements in all

mixes and the average resistivity was confidentially the electrical resistivity of the

mixture.

179

4.4.2.2 Surface electrical resistivity of concrete slabs

Two Ø406 x 75 mm circular slabs were used for surface electrical resistivity at each age.

The moisture content of concrete slabs was an affecting factor on resistivity values, so

electrical resistivity was measured after the field sorptivity test. Hence, the slab top

surface was wetted for ~20 minutes prior to the surface electrical resistivity test. The

amount of water absorbed during the sorptivity test was enough to make the pore

structure of the affected depth by the resistivity equi-potential lines saturated. This

assumption is acceptable because in some slabs, electrical resistivity was re-measured

after 10 more minutes water contact and the re-measured resistivity values was not

statistically different from the initial resistivity values.

The average of eight measurements on each concrete slab, measuring pattern is shown in

Figure 4.63, was used.

Figure 4.63: Surface resistivity measuring order for circular concrete slabs (top view)

180

Five different probes spacing (20, 30, 40, and 50 mm) were used. The electrical

resistivity of each slab with different probe spacings is presented in Figures 70 to 78.

4.4.2.2.1 Circular slab number 1

Surface electrical resistivity of concrete slabs which is the average of eight measurements

at each time is graphed in Figures 4.64, 4.65, 4.66, and 4.67.

Sign “a” represents the resistivity meter’s probe spacing.

Figure 4.64: Surface electrical resistivity of concrete slabs labelled number 1 (20 mm probe spacing)

181

Figure 4.65: Surface electrical resistivity of concrete slabs labelled number 1 (30 mm probe spacing)

Figure 4.66: Surface electrical resistivity of concrete slabs labelled number 1 (40 mm probe spacing)

182

Figure 4.67: Surface electrical resistivity of concrete slabs labelled number 1 (50 mm probe spacing)

4.4.2.2.2 Circular slab number 2

Surface electrical resistivity of concrete slabs which is the average of eight measurements

at each time is graphed in Figures 4.68, 4.69, 4.70, and 4.71.

Sign “a” represents the resistivity meter’s probe spacing.

Figure 4.68: Surface electrical resistivity of concrete slabs labelled number 2 (20 mm probe spacing)

183

Figure 4.69: Surface electrical resistivity of concrete slabs labelled number 2 (30 mm probe spacing)

Figure 4.70: Surface electrical resistivity of concrete slabs labelled number 2 (40 mm probe spacing)

184

Figure 4.71: Surface electrical resistivity of concrete slabs labelled number 2 (50 mm probe spacing)

In can be seen that electrical resistivity were influenced by the addition of the

supplementary cementing materials, the W/CM ratio, and age of concrete. Due to less

connected pores and smaller pore size distribution caused by cement and SCMs

secondary hydration, electrical resistivity was attributed to increasing age of the concrete.

4.4.2.2.3 Statistical Analysis of concrete slabs surface resistivity

Two concrete slabs were tested at each age; the average surface electrical resistivities are

shown in Table 4.17.

Table 4.17: Average apparent surface electrical resistivity of circular concrete slabs

Surface Electrical Resistivity (KΩ.cm)

Mixture

Probe

Spacing/

Age a= 20 mm a= 30 mm a= 40 mm a= 50 mm

Day 3 7.0 8.9 9.8 11.3

Day 7 21.8 24.0 26.7 29.6

Day 14 71.2 83.3 88.0 98.1

Day 28 109.8 153.1 151.1 166.5

Day 56 197.7 250.5 261.2 264.9

HPC

Day 91 230.4 295.3 300.2 311.3

185

Day 3 5.5 6.9 7.3 8.5

Day 7 17.0 21.1 22.9 26.3

Day 14 66.4 77.5 80.5 89.9

Day 28 99.6 135.5 135.9 157.7

Day 56 142.6 182.8 199.4 226.4

HPC+

Day 91 154.3 194.3 230.7 254.6

Day 3 10.0 12.7 14.1 15.2

Day 7 16.3 19.5 21.8 25.2

Day 14 50.9 58.5 61.5 70.6

Day 28 90.1 120.7 120.4 134.2

Day 56 122.5 166.8 181.1 183.6

SFSL 0.40

Day 91 134.9 180.4 194.8 215.0

Day 3 3.4 4.5 5.1 6.0

Day 7 8.3 10.3 11.0 12.5

Day 14 17.2 20.7 22.5 26.0

Day 28 28.3 31.7 33.9 35.8

Day 56 43.5 47.0 49.3 52.4

PCSL 0.40

Day 91 54.8 75.0 81.4 99.0

Day 3 3.4 4.5 5.1 6.0

Day 7 5.9 7.9 9.0 10.6

Day 14 16.1 18.1 19.2 22.6

Day 28 22.7 28.1 30.3 33.0

Day 56 31.0 35.6 41.7 49.8

PCSL 0.40+

Day 91 46.3 57.2 76.4 90.5

Day 3 3.0 3.9 4.4 5.1

Day 7 4.5 6.0 6.9 7.9

Day 14 13.6 17.5 17.7 20.1

Day 28 17.7 22.4 24.8 28.6

Day 56 22.0 30.6 35.1 40.1

PCSL 0.45

Day 91 33.2 49.6 60.1 77.9

Day 3 2.2 3.0 3.3 3.8

Day 7 4.5 5.5 6.2 7.3

Day 14 11.6 14.5 15.7 17.6

Day 28 14.5 20.2 22.0 24.6

Day 56 20.4 31.1 34.9 43.4

PCSL 0.45+

Day 91 28.4 43.1 54.6 65.9

186

Day 3 2.8 3.2 3.7 4.2

Day 7 3.5 4.0 4.5 5.0

Day 14 6.7 7.7 8.2 8.7

Day 28 9.5 11.2 11.2 12.4

Day 56 13.4 16.8 16.9 18.4

PC 0.45

Day 91 22.5 31.5 33.4 34.6

Day 3 2.3 2.8 2.9 3.7

Day 7 3.2 3.5 4.0 4.6

Day 14 6.4 8.0 7.8 8.4

Day 28 8.6 10.2 9.9 10.7

Day 56 11.5 15.0 14.5 15.8

PC 0.45+

Day 91 19.7 25.3 27.9 26.7

Sixteen measurements were taken for each concrete mixture at each time throughout the

circular slabs finished surfaces (eight measurements on each pair of slab). Table 4.18

presents the statistical analysis for resistivity measurement values obtained from the

concrete slabs for the standard probe spacing (50 mm).

Table 4.18: Statistical analysis of resistivity measurement of concrete slabs (a= 50mm)

Statistical Summary Mixture Statistics

Day 3 Day 7 Day 14 Day 28 Day 56 Day 91

n 16 16 16 16 16 16

Mean

(KΩ.cm) 11.28 29.61 98.07 166.53 264.88 311.26

б 1.40 2.53 7.23 8.22 10.86 9.99

HPC

COV (%) 12.45 8.56 7.38 4.94 4.10 3.21

n 16 16 16 16 16 16

Mean

(KΩ.cm) 8.49 26.30 89.85 157.71 226.38 254.61

б 0.79 2.78 7.84 6.25 6.00 4.86

HPC+

COV (%) 9.30 10.58 8.72 3.96 2.65 1.91

n 16 16 16 16 16 16

Mean

(KΩ.cm) 15.16 25.19 70.63 134.20 183.57 214.97

б 1.39 2.77 6.29 6.51 7.54 7.98

SFSL 0.40

COV (%) 9.20 11.00 8.90 4.85 4.11 3.71

187

n 16 16 16 16 16 16

Mean

(KΩ.cm) 5.98 12.53 25.96 35.84 52.39 99.04

б 0.88 1.77 4.09 2.37 3.43 6.06

PCSL 0.40

COV (%) 14.70 14.15 15.76 6.60 6.54 6.12

n 16 16 16 16 16 16

Mean

(KΩ.cm) 6.08 10.56 22.64 32.96 49.76 90.53

б 0.98 1.64 3.63 0.70 2.16 3.76

PCSL 0.40+

COV (%) 16.08 15.51 16.03 2.12 4.35 4.15

n 16 16 16 16 16 16

Mean

(KΩ.cm) 5.06 7.93 20.10 28.60 40.11 77.87

б 0.52 1.03 3.16 2.09 3.12 5.13

PCSL 0.45

COV (%) 10.20 13.01 15.74 7.31 7.78 6.59

n 16 16 16 16 16 16

Mean

(KΩ.cm) 3.84 7.25 17.63 24.59 43.44 65.86

б 0.53 0.85 2.03 1.32 1.77 2.56

PCSL 0.45+

COV (%) 13.82 11.71 11.52 5.38 4.08 3.89

n 16 16 16 16 16 16

Mean

(KΩ.cm) 4.23 4.99 8.66 12.36 18.35 34.56

б 0.25 0.45 0.74 0.82 1.09 17.87

PC 0.45

COV (%) 6.02 9.08 8.51 6.61 5.95 5.17

n 16 16 16 16 16 16

Mean

(KΩ.cm) 3.65 4.56 8.43 10.65 15.84 26.74

б 0.44 0.42 1.12 0.66 0.46 0.91

PC 0.45+

COV (%) 11.96 9.17 13.34 6.17 2.90 3.42

The coefficient of a set of resistivity measurements is low (less than 20%) in most of the

mixtures. Binary mixes (25% slag replacement) had higher COV in early ages (between

10% and 20%).

188

Now that all coefficients of variations were generally low, the average resistivity of two

slabs was confidentially the electrical resistivity of the mixture.

4.4.2.3 Unifying the surface resistivity values

The electrical resistivity is a number for each material (at a given age, temperature and

moisture content) while the Wenner resistivity values are influenced by the probe spacing

as shown in Tables 4.15 and 4.17. In other words, different resistivity values were

obtained by using different probe spacings.

The Wenner probe has been design based on an assumption that the electrodes are in

contact with the face of a semi-infinite uniform body which can be approximated by

using the optimum probe spacing (Gowers and Millard, 1999). Therefore, using any other

probe spacing higher than the optimum probe spacing (25 mm for cylinders and 20 mm

for slabs as calculated in Section 3.2.1.1.1.2) must be calibrated. As explained in Section

2.2.4.2.2, concrete resistivity is calculated from a relation between apparent resistivity

measured by the resistivity-meter with probe spacings other than the optimum spacing

and the cell constant correction factor, K, a function of inter-probe distance, a, and the

geometry of concrete body (Morris et al., 1996). The cell constant correction factor can

be calculated based on the graph recommended by Morris et al. (1996) as shown in

Figures 2.28 and 2.29.

In contrast, the concept of optimum probe spacing for achieving the semi-infinite body

assumption was not considered in the relations shown in Figures 2.28 and 2.29. Electrical

resistivity values measured by the optimum probe spacing are the actual resistivity of

concrete and do not have to be reduced by the correction factor (K must be 1), while the

cell constant correction factor obtained from those figures for the optimum probe spacing

was more than 1. Therefore, the cell constant factors recommended by Morris et al.

(1996) must be modified.

The optimum cell constant factor (KOptimum) obtained for the optimum probe spacing can

be divided by the cell constant correction factor (Kprobe) to obtain the actual resistivity. It

results in a cell constant conversion factor, φ.

189

Hence,

φ = obe

Optimum

K

K

Pr

ρactual = φ ρapp.

The cell constant conversion factor not only unifies the electrical resistivity values

obtained from different probe spacings, but also converts the apparent resistivity into the

actual electrical resistivity representing the resistivity of a semi-infinite concrete body. In

this research program, Figure 2.28 was used for calculating the cell constant correction

factor for both cylindrical and slab specimens. This Figure was originally designed for

concrete cylinders, but it has been modified for concrete slabs as shown in Figure 4.72.

In this research program, the relation between the length and diameter of cylinders (L/d)

is 2 and Figure 2.28 was designed based on this relation. The L/d ratio in circular

concrete slabs used in this project was 5. Therefore, for calculating the cell constant

factor, a factor of 2

5must be multiplied by the thickness of the concrete slabs as shown in

Figure 4.72.

Figure 4.72: Cell constant correction factor for specimen used

(Modified for circular concrete slabs after Morris et al., 1996)

190

The cell constant conversion factors for the probe spacings used in this research program

are tabulated in Table 4.19. These numbers are based on relations presented in Figure

4.72.

Table 4.19: Cell constant conversion factors for different probe spacings

Specimen Probe Spacing

(mm)

Cell Constant

Conversion Factor

(φ)

a=25

(Optimum) 40.1

40.1 = 1.00

a=30 60.1

40.1 = 0.88

a=40 05.2

40.1 = 0.69

Ø100 x 200 mm

Cylinders

(The optimum Cell

Constant factor = 1.40

based on relations on

Figure 4.72) a=50

65.2

40.1 = 0.53

a= 20

(Optimum) 00.1

00.1 = 1.00

a= 30 25.1

00.1 = 0.80

a= 40 35.1

00.1 = 0.74

Ø 406 x 75 mm

Circular Slabs

(The optimum Cell

Constant factor = 1.00

based on relations on

Figure 4.72) a= 50

55.1

00.1= 0.65

Therefore, the electrical resistivity values of concrete cylinders were recalculated based

on the measured apparent resistivity values presented in Table 4.15 and the cell constant

conversion factors from Table 4.19 as shown in Table 4.20.

191

Table 4.20: Surface resistivity of concrete cylinders with different probe spacings

Surface Electrical Resistivity (ρactual = φ ρapp.)

(KΩ.cm) Mixture

Probe

Spacing

(mm)

φ

Day 3 Day 7 Day 28 Day 56 Day 91

25 1 15.5 36.1 106.7 112.8 121.7

30 0.88 15.1 37.7 110.6 117.8 127.1

40 0.69 16.9 37.4 112.9 115.7 120.5 HPC

50 0.53 14.9 37.9 109.9 112.3 116.9

25 1 12.3 37.0 105.7 109.3 114.7

30 0.88 11.9 35.8 107.1 110.6 116.4

40 0.69 12.2 35.7 105.7 107.6 110.6 HPC+

50 0.53 11.7 35.3 105.3 106.4 110.4

25 1 17.8 26.0 88.3 97.6 109.6

30 0.88 17.4 32.8 95.5 99.7 107.4

40 0.69 17.0 32.2 95.1 101.2 107.9 SFSL 0.40

50 0.53 17.2 32.1 95.6 100.3 104.0

25 1 8.4 17.4 31.0 33.9 48.3

30 0.88 7.9 15.4 32.9 36.3 50.4

40 0.69 8.5 15.6 32.4 35.7 45.0 PCSL 0.40

50 0.53 8.5 15.7 32.5 36.7 46.9

25 1 8.2 10.6 21.2 27.8 40.1

30 0.88 8.1 10.1 20.8 30.8 40.2

40 0.69 8.0 10.5 20.4 30.3 40.1 PCSL 0.40+

50 0.53 8.1 10.7 20.8 30.4 42.2

25 1 6.0 8.4 21.0 21.6 40.1

30 0.88 5.8 8.8 20.6 21.6 39.6

40 0.69 5.7 8.8 19.9 22.4 39.1 PCSL 0.45

50 0.53 6.2 8.9 20.8 25.1 39.3

25 1 4.7 8.2 19.3 27.1 30.3

30 0.88 4.4 7.9 18.6 25.8 31.2

40 0.69 4.6 7.8 18.9 24.8 31.6 PCSL 0.45+

50 0.53 4.8 8.1 19.4 24.6 32.3

25 1 4.0 5.0 9.9 12.3 15.3 PC 0.45

30 0.88 3.8 5.1 9.2 11.8 15.3

192

40 0.69 3.9 4.7 9.8 11.7 15.1

50 0.53 3.8 5.0 10.1 12.1 15.0

25 1 4.1 4.8 7.8 10.2 11.7

30 0.88 4.0 4.7 7.7 10.1 11.7

40 0.69 4.1 4.6 7.2 10.1 11.8 PC 0.45+

50 0.53 4.1 4.6 7.0 10.4 12.3

The corrected surface electrical resistivity values of concrete which were the average of

four united and modified resistivity values obtained by different probe spacings was

independent of the Wenner probe electrode spacings as shown in Table 4.21.

Table 4.21: True surface electrical resistivity of concrete cylinders

Surface Electrical Resistivity

(KΩ.cm) Mixture

Day 3 Day 7 Day 28 Day 56 Day 91

HPC 15.6 37.3 110.0 114.7 121.6

HPC+ 12.0 36.0 106.0 108.5 113.0

SFSL 0.40 17.4 30.8 93.6 99.7 107.2

PCSL 0.40 8.3 16.0 32.2 35.7 47.7

PCSL 0.40+ 8.1 10.5 20.8 29.8 40.7

PCSL 0.45 5.9 8.7 20.6 22.7 39.5

PCSL 0.45+ 4.6 8.0 19.1 25.6 31.3

PC 0.45 3.9 5.0 9.8 12.0 15.2

PC 0.45+ 4.1 4.7 7.4 10.2 11.9

It can be seen that the average resistivity values unified by the cell constant conversion

factor were approximately the same as the resistivity values obtained by using the

optimum probe spacing. In other words, the surface resistivity values presented in Table

4.21 can be taken as the surface electrical resistivities of semi-infinite bodies of concrete

at different ages.

Surface electrical resistivity values of circular concrete slabs can be unified based on the

calculated cell constant conversion factors presented in Table 4.19. The converted surface

electrical resistivities of concrete slabs which represent the resistivity of a semi-infinite

concrete body are tabulated in Table 4.22.

193

Table 4.22: Surface resistivity of concrete slabs with different probe spacings

Surface Electrical Resistivity (ρactual = φ ρapp.)

(KΩ.cm)

Mixture

Probe

Spacing

(mm)

φ

Day 3 Day 7 Day 14 Day 28 Day 56 Day 91

20 1 7.0 21.8 71.2 109.8 197.7 230.4

30 0.80 7.1 19.2 66.6 122.5 200.4 236.2

40 0.74 7.3 19.7 65.1 111.9 193.3 222.1 HPC

50 0.65 7.3 19.2 63.7 108.2 172.2 202.3

20 1 5.5 17.0 66.4 99.6 142.6 154.3

30 0.80 5.5 16.9 62.0 108.4 146.2 155.4

40 0.74 5.4 16.9 59.5 100.5 147.6 170.7 HPC+

50 0.65 5.5 17.1 58.4 102.5 147.1 165.5

20 1 10.0 16.3 50.9 90.1 122.5 134.9

30 0.80 10.2 15.6 46.8 96.6 133.4 144.3

40 0.74 10.4 16.1 45.5 89.1 134.0 144.1 SFSL 0.40

50 0.65 9.9 16.4 45.9 87.2 119.3 139.7

20 1 3.4 8.3 17.2 28.3 43.5 54.8

30 0.80 3.6 8.2 16.5 25.4 37.6 60.0

40 0.74 3.8 8.1 16.6 25.1 36.5 60.2

PCSL 0.40

50 0.65 3.9 8.1 16.9 23.3 34.1 64.4

20 1 4.1 5.9 16.1 22.7 31.0 46.3

30 0.80 4.0 6.3 14.5 22.5 28.5 45.8

40 0.74 3.8 6.7 14.2 22.4 30.8 56.5 PCSL 0.40+

50 0.65 3.9 6.9 14.7 21.4 32.3 58.8

20 1 3.0 4.5 13.6 17.7 22.0 33.2

30 0.80 3.1 4.8 14.0 17.9 24.5 39.7

40 0.74 3.3 5.1 13.1 18.3 26.0 44.5 PCSL 0.45

50 0.65 3.3 5.2 13.1 18.6 26.1 50.6

20 1 2.2 4.5 11.6 14.5 20.4 28.4

30 0.80 2.4 4.4 11.6 16.1 24.9 34.4

40 0.74 2.4 4.6 11.6 16.3 25.8 40.4 PCSL 0.45+

50 0.65 2.5 4.7 11.5 16.0 28.2 42.8

20 1 2.8 3.5 6.7 9.5 13.4 22.4 PC 0.45

30 0.80 2.6 3.2 6.2 9.0 13.4 25.2

194

40 0.74 2.7 3.3 6.1 8.3 12.5 24.7

50 0.65 2.8 3.2 5.6 8.0 11.9 22.5

20 1 2.3 3.2 6.4 8.6 11.5 19.7

30 0.80 2.2 2.8 6.4 8.2 12.0 20.3

40 0.74 2.1 2.9 5.8 7.3 10.8 20.6 PC 0.45+

50 0.65 2.4 3.0 5.5 6.9 10.3 17.4

Surface electrical resistivity of concrete which is the average of four united and modified

resistivity values obtained by different probe spacings is independent from the Wenner

probe electrode spacing as shown in Table 4.23.

Table 4.23: True surface electrical resistivity of concrete slabs

Surface Electrical Resistivity

(KΩ.cm) Mixture

Day 3 Day 7 Day 14 Day 28 Day 56 Day 91

HPC 7.2 20.0 66.7 113.1 190.9 222.8

HPC+ 5.5 17.0 61.6 102.8 145.9 161.5

SFSL 0.40 10.1 16.1 47.3 90.8 127.3 140.8

PCSL 0.40 3.7 8.2 16.8 25.5 37.9 59.8

PCSL 0.40+ 4.0 6.4 14.9 22.3 30.7 51.9

PCSL 0.45 3.2 4.9 13.4 18.1 24.6 42.0

PCSL 0.45+ 2.4 4.5 11.6 15.7 24.8 36.5

PC 0.45 2.7 3.3 6.1 8.7 12.8 23.7

PC 0.45+ 2.3 3.0 6.0 7.7 11.1 19.5

Since the true surface resistivity values for specimens is the average of unified resistivity

values obtained by different probe spacings, true resistivity of slabs and cylinders are not

exactly equal. The reasons will be explained briefly in Section 4.4.2.6.

Five practical steps are recommended for use of the Wenner probe for measuring the

surface electrical resistivity of a concrete structure:

195

Step I) Surface electrical resistivity is measured by the Wenner probe on site without

limiting the probe spacing (any probe spacing can be used). The cell constant

correction factor (Kprobe) for the applied probe spacing is found based on Figure 4.72.

Step II) The “optimum probe spacing” which represents the electrical resistivity of a

semi-infinite body is calculated based on the technical graphs presented in Section

3.2.1.1.1.2 or from Figure 4.73.

Figure 4.73: Required limitations for calculating the optimum probe spacing

(Gowers and Millard, 1999)

MTO bridge decks are typically 225 mm thick with 70 ± 20 mm cover above rebars

and maximum aggregate size of 19 mm, so the optimum probe spacing for most of

the MTO projects is 50 mm.

Step III) The optimum cell constant correction factor (KOptimum) is calculated based

on the optimum probe spacing (Step II) and the relations illustrated in Figure 4.72.

196

Step IV) The cell constant conversion factor (φ) is calculated as:

φ = obe

Optimum

K

K

Pr

Step V) The actual electrical resistivity of concrete which is independent from the

probe spacing and a unique number for a mix design is calculated by multiplying the

conversion factor and apparent resistivity measured in Step I.

ρactual = φ ρapp.

4.4.2.4 W/CM ratio effects on surface electrical resistivity

As Figure 4.74 shows, the lower the W/CM ratio, the higher the surface electrical

resistivity. This statement is true for concrete cylinders and slabs, as a similar order was

seen for the concrete slab’s electrical resistivity (Sections 4.4.2.2.1 and 4.4.2.2.2).

0 3 7 28 56 91

<=

==

==

=In

cre

asi

ng

Silica fume + slag<

==

==

==

Incr

ea

sin

g

W/CM

<=

==

==

=In

cre

asi

ng

Slag

No SCM0

20

40

60

80

100

120

140

Age (day)

Su

rfa

ce

Re

sis

tiv

ity

(K

Ω.c

m)

HPC

HPC+

SFSL 0.40

PCSL 0.40

PCSL0.40+PCSL 0.45

PCSL0.45+PC 0.45

PC 0.45+

Figure 4.74: W/CM ratio effects on the surface electrical resistivity of concrete cylinders

Lower W/CM ratio resulted in lower porosity and connected pores. In this case, the

induced electrical current by the two outer electrodes could not pass through concrete

pores system easily, so higher electrical resistivity was measured. Discontinuous pore

structure results in high resistivity paths available for ion movement.

197

4.4.2.5 SCMs effects on surface electrical resistivity

Figures 4.75 and 4.76 show the slag and silica fume effects on the surface electrical

resistivity of concrete cylinders and slabs.

0 3 7 28 56 91

0.40

Silica fume + Slag

0.40Slag

W/CM

0.45Slag

0.45No SCM

0

20

40

60

80

100

120

Age (day)

Su

rfa

ce

Res

istiv

ity

(K

Ω.c

m)

SFSL 0.40

PCSL 0.40

PCSL 0.45

PC 0.45

Figure 4.75: SCMs effects on the surface electrical resistivity of concrete cylinders

03 7 14 28 56 91

50

100

150 W/CM

0.45

0.40

0.40Silica fume +

Slag

Slag

Slag

0.45

No SCM

Age (day)

Su

rface R

esis

tivity (K

Ω .cm

)

SFSL 0.40

PCSL 0.40

PCSL 0.45

PC 0.45

Figure 4.76: SCMs effects on the surface electrical resistivity of circular slabs

198

As mentioned in the literature, adding silica fume decreases the ionic concentration of the

pore solution because of its secondary hydration process which reduces the free alkalis

(Na+, K

+ and mostly OH

-) content in cement paste. The significant influence of adding

silica fume to concrete mixes can be appreciated by comparing data for mixes with 8%

silica fume and without silica fume (the two upper line in Figures 4.75 and 4.76). 8%

silica fume replacement increased the electrical resistivity of concrete significantly, but

not because of the reduced ionic concentration. Used SCMs reduced the pore system

connectivity. Also using silica fume resulted in smaller pore size distribution. In addition,

concrete mix which contained slag had higher surface electrical resistivity than plain

cement concrete mix (W/CM= 0.45 in Figures 4.75 and 4.76).

At later ages, hydration of slag made the pore system denser and less porous.

Consequently, the electrical resistivity of concrete ternary mixes containing silica fume

and slag were higher than binary mixes. Plain cement concrete mixes had the lowest

resistivity at both early and later ages.

4.4.2.6 Effects of specimen geometry on the Wenner probe values

Two types of concrete specimens were tested in this research program: Ø200 x 100 mm

concrete cylinders and Ø406 x 75 mm circular concrete slabs. It was expected that the

surface electrical resistivity values measured by the Wenner probe were geometry-

independent because the electrical resistivity is influenced only by the pore system

properties and the specimen’s moisture content. Both types of specimens were water

saturated during the test. Figure 4.77 compares the surface resistivity of the specimens

with the optimum probe spacing calculated in Section 3.2.1.1.1.2 according to the

technical relations recommended by Gowers and Millar (1999).

199

y = 0.97 x - 2.33

R2 = 0.98

0

25

50

75

100

125

150

0 25 50 75 100 125 150

Concrete Cylinder (a= 25 mm)

Co

ncre

te S

lab

(a

= 2

0 m

m)

Figure 4.77: Relation between different specimens resistivity with the optimum probe spacing

Previous work has concluded that surface resistivity values are dependent to specimen

geometry as larger concrete volume of a specimen results in lower resistivity value

(Sengul and Gjorv, 2008). However it has been found that geometry effects can be

neglected by applying the “optimum probe spacing” as shown in Figure 4.77. Hence, the

Wenner probe can measure the actual resistivity of concrete independent of the specimen

geometry if the optimum probe spacing is applied. Surface resistivity values of concrete

cylinders were al little higher than that in slabs since cylinders were kept in the fog room

prior to the testing time. Therefore, cementing materials were fully hydrated in cylinders

while the rate of hydration in slabs (kept in 50% RH room) were lower which resulted in

less discontinuous pore system and lower Wenner resistivity values (the moisture

contents of the influenced depths were the same since the least probe spacings were used

and cylinders and slabs surfaces were saturated).

200

In contrast, the other probe spacings give scattered resistivity values as shown in Figure

4.78.

Figure 4.78: Comparison between specimens resistivity values and different probe spacings

It can be seen in Figure 4.78 that as probe spacing increased, surface resistivity measured

by the Wenner probe became more independent from specimen geometry (difference

between slabs and cylinders became near zero).

Two conclusions can be derived based on the last two figures:

a) If the optimum probe spacing, which can be found based on the specimen’s

thickness, maximum aggregate size, rebars location, and distance between the

probe array and specimen edges is applied, the measured resistivity values are

independent from the specimen’s geometry. Electrical resistivity measured by the

optimum probe spacing represents resistivity of a semi-infinite concrete body

(Figure 4.77).

201

b) Resistivity measurement tends to be representative of the concrete region located

between the electrodes current density distribution. Concrete slabs were removed

from the moist room after seven days wet curing. Prior to the Wenner test, slabs

were soaked for approximately 16 minutes (because of the field sorptivity test)

and then kept soaked till concrete surface became saturated. The surface layers of

concrete slabs were saturated, so the applied current between two outer probes of

the optimum probe spacing (a= 20 mm) passed thought the saturated volume. In

this case, the situation in concrete slabs was the same as in saturated concrete

cylinders which was proved in Figure 4.77. As the probe spacing increased, the

penetration depth of the applied current was increased, so current may have

passed through a partially wet concrete volume which resulted in higher apparent

resistivity (Figure 4.78). A probe spacing of 50 mm resulted in the highest current

penetration through the specimen’s depth. In this case applied current path may

pass through the core of the circular slab where the last drying level was, as

shown schematically in Figure 4.79.

Figure 4.79: Probe spacings effect on the penetration depth of the Wenner applied current

Therefore, the applied current passed through a saturated (or near saturation) volume, so

the measured resistivity was the same as the resistivity measured for a saturated concrete

cylinder (the line on the right in Figure 4.78).

202

The second explanation is just an assumption. The affected pore structure was almost

saturated prior to the resistivity test because in some cases more water saturation did not

change the measured resistivity values.

It is important to mention that in neither of the cases, the current flow was not restricted

by the concrete edges since the probe spacings were less than specimen thickness.

As a practical conclusion, the optimum probe spacing must be calculated and applied to

the Wenner probe. In this case, the measured values represent the changes in the concrete

micro structure. In case of different probe spacings, it is recommended to fully saturate

the concrete depth which is affected by the applied current path. Since the Wenner

current penetration depth is approximately equal to the probe spacing, water sorptivity

coefficient which was calculated in Section 4.3, is useful for saturating the required

depth.

4.4.2.7 Surface electrical resistivity as an indicator for other properties of concrete

It was found that the surface electrical resistivity of concrete can be well correlated with

the other properties of concrete measured by the other tests in this research program.

Some destructive tests must be used for measurement of these physical properties of

concrete while measuring the surface electrical resistivity of as-constructed concrete by

the Wenner probe is non-destructive and time saving. Hence, the electrical resistivity of

concrete can be used to estimate the other properties of concrete provided that the

correlation between the resistivity and those properties are available.

4.4.2.7.1 Surface electrical resistivity and compressive strength

Both electrical resistivity and compressive strength are influenced by the concrete

porosity, as shown in Figures 4.80 and 4.81. Although higher resistivity concrete had

higher compressive strength, compressive strength is not the reason for this.

203

y = 0.62 e0.08 x

R2 = 0.91

0

50

100

150

200

250

20 30 40 50 60 70 80

Compressive Strength (MPa)

Su

rface E

lectr

ical R

esis

tivit

y

(K

Ω.c

m)

Figure 4.80: Surface resistivity of concrete cylinders versus compressive strength

y = 0.23 e0.1x

R2 = 0.85

0

50

100

150

200

250

300

20 30 40 50 60 70 80

Compressive Strength (MPa)

Su

rface E

lectr

ical R

esis

tivity (K

Ω .c

m)

Figure 4.81: Surface resistivity of concrete slabs versus compressive strength

204

It can be seen that the relations were not linear because the surface resistivity is more

influenced by the factors affecting the pore system than compressive strength. For

example, in one mix design, lowering the W/CM ratio (or adding SCMs) increases the

compressive strength by 16% where as the surface electrical resistivity was increased by

up to 60% at the same age.

Different moisture distribution in circular concrete slabs resulted in a lower R-square

coefficient in Figure 4.81 than Figure 4.80.

4.4.2.7.2 Surface electrical resistivity and total charge passed

The electrical current reported by the RCPT is not only the charge taken by the dissolved

ions in the pore system, but also the charge carried by the penetrating chloride ion. This

is one of the major disadvantages of the RCPT. On the other hand, during the surface

electrical test the induced current is carried by only chemical ion available in the pore

system. Now that there is a relation between the RCPT and surface resistivity values with

high R-square values (Figures 4.82, 4.83, and 4.84) the RCPT results can be replaced

with the surface electrical values to avoid chloride ion effects on the total charge passed.

y = 15954 x-0.94

R2 = 0.98

0

20

40

60

80

100

120

140

160

180

200

0 1000 2000 3000 4000 5000 6000 7000

RCPT Passing Charge (Coulombs)

Su

rface E

lectr

ical R

esis

tivit

y

(KΩ

.cm

)

Figure 4.82: Surface resistivity of concrete cylinders versus the RCPT passing charge

205

Since MTO level of concrete acceptance according to the RCPT is 1000 coulombs,

modified correlation between the Wenner probe resistivity and the RCPT charge passed

in useful as shown in Figure 4.83.

y = 13632x-0.91

R2 = 0.96

0

20

40

60

80

100

120

140

160

180

0 100 200 300 400 500 600 700 800 900 1000

RCPT Passing Charge (Coulombs)

Su

rfa

ce

Ele

ctr

ica

l R

es

isti

vit

y

(KΩ

.cm

)

Figure 4.83: Modified surface resistivity versus the RCPT results based on MTO specification

In addition, surface electrical resistivity of concrete slabs (tested in fully saturated

condition) can be correlated wit the RCPT results as shown in Figure 4.84.

206

y = 54692x-1.1

R2 = 0.95

0

20

40

60

80

100

120

140

160

180

200

220

240

260

0 1000 2000 3000 4000 5000 6000 7000

RCPT Passing Charge (coulombs)

Su

rface E

lectr

ical R

esis

tivit

y (

KΩ

.cm

)

Figure 4.84: Surface resistivity of concrete slabs versus the RCPT passing charge

4.4.2.7.3 Surface electrical resistivity and the other types of electrical resistivity

A well-defined correlation was observed between the surface electrical resistivity and the

first 5 min. RCPT resistivity as shown in Figures 4.85 and 4.86.

207

y = 1.48 x - 0.60

R2 = 0.99

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70 80 90

RCPT First 5 min. Electrical Resistivity (KΩ.cm)

Surf

ace E

lectr

ical R

esis

tivity (

KΩ

.cm

)

Figure 4.85: Surface resistivity of concrete cylinders versus the RCPT resistivity

y = 1.82 x - 7.04

R2 = 0.97

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70 80 90

RCPT First 5 min. Electrical Resistivity (KΩ .cm)

Su

rface E

lectr

ical R

esis

tivity (K

Ω .c

m)

Figure 4.86: Surface resistivity of concrete slabs versus the RCPT resistivity

208

In the application of the four-electrode method, a good correlation between surface

electrical resistivity and Monfore bulk resistivity was obtained as shown in Figures 4.87

and 4.88.

y = 1.24 x + 0.79

R2 = 0.99

0

25

50

75

100

125

150

0 20 40 60 80 100

DC-Cyclic Bulk Resistivity (KΩ .cm)

Su

rface E

lectr

ical R

esis

tivity (K

Ω .cm

)

Figure 4.87: Surface resistivity of fully saturated cylinders versus Monfore resistivity

y = 1.60 x - 6.63

R2 = 0.96

0

25

50

75

100

125

150

175

0 20 40 60 80 100

DC-Cyclic Bulk Resistivity (KΩ .cm)

Su

rfa

ce

Ele

ctr

ica

l R

es

isti

vit

y (

KΩ

.cm

)

Figure 4.88: Surface resistivity of not fully saturated slabs versus Monfore resistivity

209

Surface electrical resistivity of concrete cylinders was better correlated to the Monfore

resistivity (higher R-square values) than surface electrical resistivity of concrete slabs

since surface resistivities of slabs cured at 50% RH room were higher than that in fully

saturated cylinders. These test results demonstrate that the curing conditions of concrete

are very important for measuring electrical resistivity of concrete. Therefore, multiplying

surface resistivity values of concrete by 1.24 will result in DC-cyclic bulk resistivity

value of same concrete provided (Figure 4.87).

In all cases, surface electrical resistivity was higher than any other type of electrical

resistivity because of the wall effects of cylindrical moulds and surface drying. Wall

effect causes finer aggregate and more cement paste distribution on specimen’s surface

(boundary effect). Also concrete surface dries before concrete core.

The little difference between the correlation coefficients in Figures 4.87 and 4.88 was

caused by the different moisture content of concrete slabs from cylinders. Figures 4.85

and 4.87 were plotted based on the values measured on fully saturated cylinders, so both

axes were based on saturated values.

The resistivity of surface concrete can be affected by wall effects, moisture content, water

bleeding, and aggregate segregation. Higher segregation, lower moisture content, and

presence of more cement paste on the surface layer of the concrete specimens resulted in

higher surface electrical resistivity.

4.4.2.7.4 Surface electrical resistivity and water sorptivity coefficient

Both pore structure connectivity and the quantity and mobility of the pore water are

affected the surface electrical resistivity. Also capillary pore tortuosity is affected by the

physical characteristics of the pore system and influences the water sorptivity results.

Therefore, surface electrical resistivity and water sorptivity results can be correlated as

shown in Figure 4.89.

210

y = 446.3 x-1.55

R2 = 0.95

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18

Water Sorptivity Coefficient (x10-4 mm/sec½)

Su

rface E

lectr

ical R

esis

tivit

y (

KΩ

.cm

)

Figure 4.89: Surface resistivity of concrete cylinders and water sorptivity coefficient

In as much as the water sorptivity coefficients of concrete slabs were influenced by the

different moisture contents at the time of testing, the relation between the filed sorptivity

values and surface resistivity is not reliable.

4.4.2.7.5 Surface electrical resistivity and diffusion of chloride ion through concrete

Rebar corrosion initiation depends on chloride ion penetration. On the other hand,

concrete surface electrical resistivity can be related to the susceptibility for chloride ion

penetration (as shown in Figures 4.90 and 4.91).

211

y = 279.8 x-1.21

R2 = 0.92

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120 140

Surface Electrical Resistivity (KΩ .cm)

RC

PT

Ch

lori

de M

igra

tio

n C

oeff

icie

nt

(10

-12 m

2/s

)

Figure 4.90: Surface resistivity of concrete cylinders versus chloride migration coefficient

y = 126.2 x-0.98

R2 = 0.88

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250

Surface Electrical Resistivity (KΩ .cm)

RC

PT

Ch

lori

de M

igra

tio

n C

oeff

icie

nt

(10

-12 m

2/s

)

Figure 4.91: Surface resistivity of concrete slabs versus chloride migration coefficient

212

Higher chloride migration coefficient is caused by the bigger pore size distribution and

more pores connectivity. Higher chloride migration coefficient, lower surface electrical

resistivity. Different moisture distribution in circular concrete slabs resulted in lower R-

square coefficient in Figure 4.91 than that in Figure 4.90.

4.4.2.8 Wenner probe as a practical instrument

Although some critics have reported that the Wenner probe is not an accurate instrument

because of the different measured values at different locations of a concrete member,

statistical analyses summarized in Tables 4.16 and 4.18 have rejected this statement. As

shown before, the coefficient of variation (COV) of surface electrical resistivity

measurements were very low (fewer than 20% in all mixes) independent from the type of

the specimen and mix design. The values measured by the four-electrode resistivity-

meter represent the surface resistivity of concrete with a low COV provided that enough

measurements have been done.

The Wenner probe values can be used for many applications, but among of them, one

application is the most practical. The surface electrical resistivity of concrete can be

measured non-destructively in less than three seconds. This value can be related to the

other properties of concrete which are time-consuming and destructive to be measured.

Figure 4.92 shows a practical relation between the surface electrical resistivity and other

properties of concrete (e.g. the RCPT coulombs and resistivity, water sorptivity, and etc.)

measured by the standard tests in this research program.

213

Figure 4.92: Practical relation between the surface resistivity values and other tests values

214

In addition, early age surface electrical resistivity (prior to formwork removal) can be

used for the prediction of 28 day compressive strength. The quality control of the

compressive strength of concrete is typically performed on standardized specimens such

as Ø100 x 200 mm cylinders used in Section 4.1 at the age of 28 days. However

construction process is continuous because of the cost and deadline issues after formwork

removal. Ferreira and Jalali (2010) have shown that the 7 day Wenner resistivity can be

used for the prediction for 28 day compressive strength since this argument has been

proved by both experimental and theoretical approaches (Ferreira and Jalali, 2010).

The prediction graphs based on 7 day Wenner resistivity values and 28 day compressive

strengths are shown in Figure 4.93.

(Cylinders) y = 0.91 x + 32.35

R2 = 0.97

(Slabs) y = 1.87x + 30.85

R2 = 0.98

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35 40

7-day Surface Electrical Resistivity (KΩ .cm)

28-d

ay C

om

pre

ssiv

e S

tren

gth

(M

Pa)

Figure 4.93: Regression analysis of compressive strength and surface electrical resistivity

215

CHAPTER 5

CO/CLUSIO/S A/D RECOMME/DATIO/S

A durable concrete is not necessarily a high strength concrete, but rather it is an

impermeable concrete. The ability of aggressive fluids to penetrate into concrete is

influenced by concrete porosity and connectivity of the capillary pore structure. Concrete

penetrability can be measured by standard tests which are time-consuming and

destructive. However, electrical resistivity tests of concrete can also be used as indicator

of concrete penetrability. A series of experiments (compressive strength, RCP, first 5

minute RCPT resistivity, depth of chloride ion penetration by silver nitrate spraying (NT

492) using the modified ASTM C1202, Monfore DC-cyclic bulk resistivity, and surface

electrical resistivity) were performed in this research project. Based on data from this

research program, the following conclusions and recommendations have been made.

5.1 Conclusions

1- Reducing W/CM ratio, adding SCMs to mixtures, and increasing the length of

moist curing improved concrete durability. This finding was established from the results

of the RCP test, bulk resistivity, initial and secondary water sorptivity, and the surface

electrical resistivity test. Also the depth of chloride penetration (NT 492) increased as the

W/CM ratio increased, while adding SCMs and increasing the length of moist curing

decreased the depth of chloride ion penetrated.

2- Silica fume improved concrete properties at early ages and slag contributed at

later ages. Early age concrete resistivity was significantly higher in ternary mixes

contained silica fume and slag than binary mixes contained slag, while at later ages the

resistivity binary mixes contained slag was higher than that in similar W/CM ratio plain

cement concrete mixes.

3- The RCPT charge passed and the calculated first 5 min. RCPT resistivity were

influenced by pore solution conductivity, while depth of chloride ion penetrated into

concrete was only dependant on the physical characteristics of pore structure. For

example, at 91 days of age, electrical conductivity was low while chloride penetration

216

coefficient was zero (in concrete mixes containing 8% silica fume and 25% slag with

W/CM ratio 0.35, 0.38, and 0.40).

4- Although the total charge passed through concrete in the RCP test was influenced

by physical characteristics of the pore system, it was more sensitive to the change in pore

fluid conductivity resulting from the cementitious materials used in mix design than

W/CM ratio. Replacing 8% Portland cement by silica fume increased the 5 min. RCPT

resistivity by a factor of 3 at 28 days, while a reduction in W/CM ratio from 0.40 to 0.35

increased the 5 min. RCPT resistivity by 18% in concrete mixes contained silica fume

and slag and 28% in a binary mix containing 25% slag.

5- Concrete permeability is directly proportional to the quantity and mobility of the

pore water which are affected by the porosity and the pore structure of the hardened

cement paste. Using SCMs and reducing W/CM ratio decreased sorptivity coefficient and

RCPT charges.

6- Calculating the chloride penetration coefficient by silver nitrate spraying method

(NT 492) proved that RCPT technique is a reliable test for concretes containing SCMs

such as silica fume.

7- Extrapolating the 6 h. coulomb values from 30 minute readings is a reliable

technique to avoid the heat effects on the values, but this is only a concern with concrete

having a level of penetrability higher than “very low”, 1000 coulombs. By dividing

extrapolated charges by 0.82, 6 h RCPT coulombs can be estimated.

8- The internal moisture content of concrete specimens used for the laboratory

sorptivity test (ASTM C1585) was between 50% to 60%, while concrete slabs used for

the field sorptivity test had different moisture contents because of the lengthy period

required to condition the Ø406 x 75 mm circular slabs. Field sorptivity test results proved

that water sorptivity was increased by decreasing levels of concrete saturation through the

time period of the project. Therefore, one problem to be overcome by a field sorptivity

test is the influence of concrete moisture content on test results.

9- The rate of water absorption (initial and secondary) and the amount of water

absorbed by the concrete decreased with increased maturity. Also water sorptivity was

reduced as W/CM ratio decreased and where SCMs were used.

217

10- Three types of resistivity were measured in this research project: surface

resistivity by the Wenner probe, Monfore DC-cyclic bulk resistivity, and the first 5 min.

RCPT resistivity. Surface electrical resistivity was the fastest (less than 5 seconds),

followed by first 5 min. RCPT resistivity, and Monfore resistivity (15 minutes). These

resistivity values were well correlated (the difference between these electrical resistivities

remained constant in each mixture as concrete aged, so linear functions could relate

them) which represented that the influencing factors were similar.

11- Surface resistivity using a Wenner probe can be used as an indicator for in-place

quality of concrete and therefore long-term concrete durability. Electrical resistivity (both

bulk and surface resistivity) is a function of concrete moisture content, the ionic

conductivity of concrete pore water, and physical characteristics of the pore structure:

a. Concrete moisture content significantly affected the surface electrical

resistivity measured by the Wenner probe as concrete slabs had shown high

resistivity values before the field sorptivity test performed (RH was about

50%) while resistivity of fully saturated surfaces (after conducting the field

sorptivity test) was lower.

b. Decreasing W/CM ratio resulted in higher surface electrical resistivity values

because lower W/CM ratio resulted in lower porosity and a more

discontinuous pore structure.

c. A high electrical resistivity was not necessarily due to a fine or discontinuous

pore structure, because ionic concentration within the pore fluid influenced

the magnitude of passing current.

12- Specimen surface properties influenced surface electrical resistivity values

measured by the Wenner probe. Surface electrical resistivity values of concrete cylinders

were higher than Monfore bulk resistivity and RCPT resistivity due to the wall effects of

cylindrical molds and potentially surface drying.

13- Since the RCPT values were well correlated with the Wenner array results, the

surface electrical resistivity could be used as an indicator of the ASTM C1202 resistance

to chloride ion penetration currently used by MTO and CSA A23.1.

14- From these experiments there was an inverse correlation between concrete

resistivity and non-steady-state chloride diffusion coefficients obtained from NT 492.

218

15- The Monfore bulk resistivity test results were independent of specimen geometry

since bulk resistivity values measured by the DC-cyclic resistivity-meter for full length

cylinders and concrete discs were not significantly different.

16- A good correlation between surface electrical resistivity measured by the Wenner

4-probe array and other permeability indicator tests were found in this research.

Therefore, electrical resistivity measured by the Wenner probe can be used as an

indication of concrete permeability although electrical conductivity depends on both pore

structure and chemistry of pore solution.

17- The average surface electrical resistivity-to-bulk resistivity value ratio (bulk

surface

ρ

ρ)

was 1.24. This number is based on resistivity values of concrete specimens at same

moisture content. In addition, the surface electrical resistivity-to- first 5 min. RCPT

resistivity ratio (RCPT

surface

ρ

ρ) was 1.48.

18- Surface electrical resistivity values can be used as indicators for RCPT charge

passed although there was not a linear relation between the Wenner values and RCPT

Coulombs.

19- Measuring both the field water sorptivity and surface electrical resistivity by the

Wenner probe are relatively, quick, simple and non-destructive if used in the field. In

addition, the outer concrete surface is being tested, so covercrete quality and alternative

curing methods can be studied. However, both are influenced by surface moisture

conditions.

20- The 28-day compressive strength of concrete (MPa) can be estimated by

multiplying 7-day Wenner resistivity (KΩ.cm) by 1.87.

219

5.3 Recommendations

The Wenner probe surface resistivity as a technique for in-situ evaluation of durability of

covercrete was studied. It can be used as a regular quality assurance procedure. The

following recommendations are made for use of the Wenner probe technique and for

modifying ASTM C1202:

1- In the lab, the Wenner probe provided meaningful results quickly. However, for

use in the field, these results (as well as field sorptivity test results) must be calibrated

with in-situ moisture contents of concrete surfaces and with laboratory testing

procedures. In the field, powder samples (10 mm deep for the field sorptivity test and up

to the probe spacing for the Wenner probe test) should be collected in order to obtain a

representative measure of the in-situ moisture condition of structure. Finally calibration

curves must be plotted for every mixture.

2- Although the low coefficient of variation (COV) of results indicated that the

different Wenner resistivity values measured on the surface of the Ø406 x 75 mm circular

slabs were not statistically variable, measurement locations should be close together (not

far than 100 mm). For using this non-destructive instrument, the number of

measurements performed on each slab, four diagonal and four orthogonal, can be reduced

to four (diagonal) for a 1300 cm2

area.

3- With the Wenner probe, calculating the optimum probe spacing and the cell

constant conversion factor are necessary for measuring the true surface electrical

resistivity of concrete, which is independent from probe spacing.

4- Moreover effects of changes in physical properties of pore structure, such as

continuity of porous or pore size distribution by the water sorptivity test for different

moisture histories of concrete (in pre-conditioning concrete specimens, fully dried in a

vacuum over silica gel), should be studied.

5- In concrete mixtures containing materials that affect pore solution chemistry (e.g.

silica fume), calculating the migration coefficient by the silver nitrate spraying method

(NT 492) was an indicator of the chloride penetrability of concrete since it eliminated

conductivity biases caused by the pore solution chemistry. It is recommended that ASTM

C1202-07 be modified to incorporate these additional measurements.

220

220

CHAPTER 6

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223

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232

APPE/DIX A

CO/CRETES MIX DESIG/

HPC (SFSL-0.35)

Silica fume cement Slag 25 % W/C=0.35

410 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.35 « Water-cement ratio

80 « Batch Volume, Litres

2.41% « Sand moisture content 1.16% = Abs. Of sand

2.72% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Silica Fume Cement (GUb-8SF) 3080 307.5 0.100 307.5 24.6

Slag 2854 102.5 0.036 102.5 8.2

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 714.3 0.263 723.3 57.9

Coarse Agg. 2702 1075.8 0.398 1090.4 87.2

Water 1000 143.5 0.144 119.8 9.6

Air 0.060 2343.6 1.000 2343.6

233

HPC+ (SFSL-0.35+)

Silica fume cement Slag 25 % W/C=0.35

410 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.35 « Water-cement ratio

82 « Batch Volume, Litres

2.44% « Sand moisture content 1.16% = Abs. Of sand

2.40% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Silica Fume Cement (GUb-8SF) 3080 307.5 0.100 307.5 25.2

Slag 2854 102.5 0.036 102.5 8.4

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 714.3 0.263 723.5 59.3

Coarse Agg. 2702 1075.8 0.398 1086.9 89.1

Water 1000 143.5 0.144 123.2 10.1

Air 0.060

2343.6 1.000 2343.6

234

SFSL-0.40

Silica fume cement Slag 25 % W/C=0.40

375 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.4 « Water-cement ratio

80 « Batch Volume, Litres

2.71% « Sand moisture content 1.16% = Abs. Of sand

3.01% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Silica Fume Cement (GUb-8SF) 3080 281.3 0.091 281.3 22.5

Slag 2854 93.8 0.033 93.8 7.5

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 728.1 0.268 739.6 59.2

Coarse Agg. 2702 1075.8 0.398 1093.6 87.5

Water 1000 150.0 0.150 120.7 9.7

Air 0.060

2328.9 1.000 2328.9

235

PCSL-0.40

PC10 Slag 25 % W/C=0.40

375 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.4 « Water-cement ratio

82 « Batch Volume, Litres

2.13% « Sand moisture content 1.16% = Abs. Of sand

2.54% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3 Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 281.3 0.090 281.3 23.0

Slag 2854 93.8 0.033 93.8 7.7

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 732.4 0.269 739.6 60.6

Coarse Agg. 2702 1075.8 0.398 1088.4 89.3

Water 1000 150.0 0.150 130.2 10.7

Air 0.060

2333.2 1.000 2333.2

236

PCSL-0.40+

PC10 Slag 25 % W/C=0.40

375 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.4 « Water-cement ratio

82 « Batch Volume, Litres

2.98% « Sand moisture content 1.16% = Abs. Of sand

3.01% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 281.3 0.090 281.3 23.1

Slag 2854 93.8 0.033 93.8 7.7

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 732.4 0.269 746.0 61.2

Coarse Agg. 2702 1075.8 0.398 1093.6 89.7

Water 1000 150.0 0.150 118.6 9.7

Air 0.060

2333.2 1.000 2333.2

237

PCSL-0.45

PC10 Slag 25 % W/C=0.45

355 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.45 « Water-cement ratio

82 « Batch Volume, Litres

2.23% « Sand moisture content 1.16% = Abs. Of sand

2.07% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 266.3 0.085 266.3 21.8

Slag 2854 88.8 0.031 88.8 7.3

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 723.7 0.266 731.5 60

Coarse Agg. 2702 1075.8 0.398 1083.3 88.8

Water 1000 159.8 0.160 144.4 11.8

Air 0.060

2314.2 1.000 2314.2

238

PCSL-0.45+

PC10 Slag 25 % W/C=0.45

355 « Cementitious content, kg/m3

25% « % Slag

0% « % Silica Fume

0% « % FA

0.45 « Water-cement ratio

82 « Batch Volume, Litres

2.80% « Sand moisture content 1.16% = Abs. Of sand

2.02% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 266.3 0.085 266.3 21.8

Slag 2854 88.8 0.031 88.8 7.3

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 723.7 0.266 735.7 60.3

Coarse Agg. 2702 1075.8 0.398 1082.7 88.8

Water 1000 159.8 0.160 140.8 11.5

Air 0.060

2314.2 1.000 2314.2

239

PC-0.45

PC 10 Slag 0 % W/C=0.45

355 « Cementitious content, kg/m3

0% « % Slag

0% « % Silica Fume

0% « % FA

0.45 « Water-cement ratio

82 « Batch Volume, Litres

2.25% « Sand moisture content 1.16% = Abs. Of sand

1.90% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 355.0 0.113 355.0 29.1

Slag 2854 0.0 0.000 0.0 0.0

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 731.2 0.269 739.3 60.6

Coarse Agg. 2702 1075.8 0.398 1081.4 88.7

Water 1000 159.8 0.160 146.1 12.0

Air 0.060

2321.8 1.000 2321.8

240

PC-0.45+

PC 10 Slag 0 % W/C=0.45

355 « Cementitious content, kg/m3

0% « % Slag

0% « % Silica Fume

0% « % FA

0.45 « Water-cement ratio

82 « Batch Volume, Litres

1.81% « Sand moisture content 1.16% = Abs. Of sand

3.24% « Coarse Agg. Moisture content 1.38% = Abs. Of Coarse Agg.

Density kg/m3

Design Mass per m3 (kg)

Volume m3

Adjusted Mass per m3 (kg)

Batch Mass (kg)

Portland Cement (GU) 3134 355.0 0.113 355.0 29.1

Slag 2854 0.0 0.000 0.0 0.0

Silica Fume 2300 0.0 0.000 0.0 0.0

FA 2600 0.0 0.000 0.0 0.0

Sand 2720 731.2 0.269 736.0 60.4

Coarse Agg. 2702 1075.8 0.398 1096.2 89.9

Water 1000 159.8 0.160 134.6 11.0

Air 0.060

2321.8 1.000 2321.8

241

APPE/DIX B

COMPRESSIVE STRE/GTH TEST

Compressive strength of concrete cylinders is the most common test of hardened concrete

used as a measure of concrete quality, the most important engineering property.

According to ASTM C39-05 a concrete cylinder is subjected to a compressive axial load

until it becomes crashed. When the limit of compressive strength is reached, the concrete

cylinder is crushed and the strength (ultimate taken load divided by the section area) is

calculated.

Figure B.1: Crushed cylinder in compressive strength test

The results of this test are used as a basis for quality control of concrete proportioning,

mixing, curing, and placing operation (ASTM C39, 2005).

242

B.1 Influencing factors on concrete strength

The compressive strength is inversely proportional to concrete porosity, so any factor

reducing concrete porosity increases compressive strength (Neville, 1995). Three major

factors influence the mechanical strength as concrete is considered fully-compacted:

W/CM ratio, SCMs effects, and cement hydration.

B.1.1 W/CM ratio and concrete strength

When concrete is fully compacted, its strength is taken to be inversely proportional to the

W/CM ratio as shown in the following relation (Abrams, 1919 in Neville, 1995):

CMWcK

Kf

/

2

1= ,

where K1 and K2 are empirical constants.

Since more water results in more porosity, higher W/CM ratio results in lower

compressive strength and higher permeability (MacDonald and Northwood, 2000 in

Chini et al., 2003) as shown in Figure B.2.

Figure B.2: Relation between logarithm of strength and W/CM ratio (/eville, 1995)

243

It can be concluded from previous researches that in practice, the W/CM ratio is the

largest single factor in the strength of fully compacted concretes (Neville, 1995). In

addition, concretes with lower W/CM ratio express a long-term strength more rapidly

than higher W/CM ratio concretes because of the rapid establishment of the

discontinuous system of gel (Neville, 1995).

B.1.2 SCMs and concrete strength

SCMs reduce concrete porosity and discontinue capillary pore structure during their

secondary hydration (Chini, 2003). In other words, SCMs improve concrete properties in

two ways: changing the weak CH into the strong C-S-H during secondary hydration and

also reducing concrete porosity by its micro-filler effect (e.g. silica fume). Since silica

fume, one of the cementitious materials used in this research program, is extremely fine

(approximately 1/100th

the size of an average cement particle), it fills the microscopic

voids between cement particles results in better paste-to-aggregate bond (Kosmatka et

al.,2002). More importantly silica fume reduces ITZ porosity (Neville, 1995).

Therefore, mixes containing SCMs have higher compressive strength (also split tensile

strength and rupture strength) and durability than plain cement concrete mixes (Jianyong

and Pei, 1997).

B.1.3 Cement hydration and concrete strength

Concrete mechanical strength increases as concrete hydrates, due to less total porosity

which is filled by cement hydration product as shown in Figure B.3.

244

Figure B.3: Compressive strength and age of concrete

(http://www.theconstructioncivil.com/2009/09/concrete-curing.html)

In addition, it can be concluded that curing scenario, affecting cement hydration,

influences the rate of strength gain in concrete. Any type of curing accelerating cement

hydration procedure, improves concrete compressive strength (e.g. compressive strength

of moist cured concrete is significantly higher than air cured concrete).

B.2 Methodology

The following steps are needed to be taken according to ASTM C39-05 during the

measurement of compressive strength. It is worth noting that a compression cylinder has

to be kept moist until testing (ASTM C39, 2005).

Step I) Grinding concrete cylinders: Since cylinders ends are in contact with the testing

machine platens, both ends must be flat by either grinding or capping (up to 70 MPa).

Any inclined end results in a compressive load which is not axial. The ends shall not be

out of plane by more than 0.05 mm. Neither end of the specimen shall be depart from

perpendicularity to the axis by more than 0.5º which is 1 mm in 100 mm diameter.

245

Step II) Cross-section area: Cross-section area of a cylinder is π4

2D, where, D is the

average section diameter of the specimen (mm). The diameter of a cylinder is an average

of four measurements at right angles on both ends of the cylinder (two measurements on

each end). The diameter of cylinders is to be determined to the nearest 0.25 mm. The

length shall be measured to the nearest millimetre and shall have length-to-diameter

(L/D) ratio between 1.8 to 2.2. As ASTM C39-05 mentions, an individual diameter shall

not be different from any other diameter of the same cylinder by more than 2%.

Step III) Concrete cylinder is placed between platen plates of the testing machine.

Platen faces have a minimum dimension at least 3% greater than the diameter of the

specimen to be tested (ASTM C39, 2005). The rate of loading shall be applied at a

constant rate within the range of 0.15 to 0.35 MPa/S (Neville, 1995). Therefore, for the

research program the load is applied at a rate of movement corresponding to a loading

rate on the specimen of 2.0 ± 0.1 KN/S. The load is applied until the specimen fails and

the peak load is recorded. Compressive strength is calculated by dividing the maximum

load by section area to the nearest 0.1 MPa and corrected for L/D ratio as shown in Table

B.1.

Table B.1: L/D correction factors for compressive strength test (ASTM C 39, 2005)

L/D 2.0 1.75 1.50 1.25 1.0

Factor 1.0 0.98 0.96 0.93 0.87

The type of failure and appearance of the fracture surface have to be one of the standard

types of fracture. Standard types of fracture for concrete cylinders and cubes are shown in

Figure B.4.

246

Figure B.4: Types of concrete specimen fracture (ASTM C39, 2003)

The type of failure and appearance of the fracture surface is recorded if different from

type (a). The cone failure results when the friction between the specimen and the platens

restrains the lateral force applied to the specimen by its horizontal expansion during

compressive strength test. Compressive strength of unusual types of fracture is not

acceptable.

247

B.3 Compressive strength test results

Day 3 (MPa) Day 7 (MPa)

Mixture CYL.1 CYL.2 CYL.3

f΄c 3day CYL.1 CYL.2 CYL.3

f΄c 7day

HPC 44.92 46.99 45.11 45.67 57.64 57.68 56.9 57.41

HPC+ 43.86 44.87 44.97 44.57 54.76 53.18 54.13 54.02

SFSL-0.40 39.73 43.55 45.23 42.84 53.49 52.11 53.3 52.97

PCSL-0.40 37.26 35.02 35.1 35.79 39.11 40.29 38.13 39.18

PCSL-0.40+ 32.11 33.33 32.01 32.48 34.51 35.2 34.9 34.87

PCSL-0.45 29.81 29.29 31.69 30.26 32.01 31.64 30.96 31.54

PCSL-0.45+ 27.18 28.02 25.81 27.00 29.73 29.26 30.52 29.84

PC-0.45 32.44 32.19 30 31.54 35 33.8 32.8 33.87

PC-0.45+ 28.74 32.5 30.1 30.45 32.1 30.19 33.52 31.94

Day 28 (MPa) Day 56 (MPa)

Mixture CYL.1 CYL.2 CYL.3

f΄c 28day CYL.1 CYL.2 CYL.3

f΄c 56day

HPC 67.28 68.24 70.23 68.58 73.11 75.54 72.54 73.73

HPC+ 63.88 59.2 62.54 61.87 65.81 65.25 66.1 65.72

SFSL-0.40 60.23 59.64 59.65 59.84 62.92 62.24 60.52 61.89

PCSL-0.40 48.14 50.31 49.57 49.34 51.98 52.81 51.28 52.02

PCSL-0.40+ 44.25 43.12 45.91 44.43 48.11 47.45 46.39 47.32

PCSL-0.45 39.74 41.56 39.55 40.28 43.28 44.9 44.48 44.22

PCSL-0.45+ 36.68 37.95 39.6 38.08 41.71 42.36 41.11 41.73

PC-0.45 38.02 38.5 35.32 37.28 37.01 41.84 38.69 39.18

PC-0.45+ 33.45 33.35 35.53 34.11 36.08 38.68 37.52 37.43

248

Day 91 (MPa)

Mixture CYL.1 CYL.2 CYL.3

f΄c 91day

HPC 78.58 74.55 76.25 76.46

HPC+ 70.02 67.53 67.12 68.22

SFSL-0.40 62.58 64.58 62.68 63.28

PCSL-0.40 48.48 58 59.99 55.49

PCSL-0.40+ 47.92 50.83 49.38 49.38

PCSL-0.45 46.85 45.81 44.8 45.82

PCSL-0.45+ 45.8 43.43 44 44.41

PC-0.45 41.1 46.48 41.81 43.13

PC-0.45+ 40.03 41.33 39.04 40.13

249

APPE/DIX C

LABORATORY SORPTIVITY TEST RESULTS

Sorptivity (x10-4 mm/sec½) Day 28 Day 56 Day 91 Mixture

Initial Secondary Initial Secondary Initial Secondary

BOTTOM HPC 16.3 3.9 10.7 2.8 6.9 1.1

HPC+ 17.4 4.3 12.6 3.2 7.8 1.8

SFSL - 0.40 19.8 4.8 13.5 3.2 9.5 2.3

PCSL - 0.40 22.7 5.3 16.0 4.5 12.2 2.8

PCSL - 0.40+ 25.0 5.8 21.5 4.7 13.8 3.5

PCSL - 0.45 28.5 7.2 24.7 5.0 16.9 4.1

PCSL - 0.45+ 31.0 8.4 25.9 5.4 21.2 5.0

PC - 0.45 36.0 11.7 27.0 6.8 26.3 5.7

PC - 0.45+ 39.4 16.5 32.1 11.1 30.5 8.2

MIDDLE HPC 16.0 3.1 13.4 2.4 12.1 1.0

HPC+ 19.5 3.9 16.0 3.2 14.0 2.2

SFSL - 0.40 21.7 4.5 16.7 3.5 16.0 2.8

PCSL - 0.40 25.5 6.8 21.0 5.8 18.5 3.8

PCSL - 0.40+ 27.3 7.3 24.2 6.3 20.9 4.1

PCSL - 0.45 32.9 8.6 25.8 5.4 22.1 4.8

PCSL - 0.45+ 36.2 9.6 33.8 7.7 26.3 5.8

PC - 0.45 40.3 14.0 35.1 9.5 34.1 8.2

PC - 0.45+ 44.4 16.9 39.6 13.3 38.0 11.8

TOP

HPC 18.6 3.2 15.2 2.5 14.6 1.5

HPC+ 21.5 3.6 19.5 3.2 16.0 2.1

SFSL - 0.40 24.0 5.4 21.0 4.1 18.8 3.3

PCSL - 0.40 27.8 6.1 23.3 5.0 17.9 4.4

PCSL - 0.40+ 30.3 7.4 26.5 5.8 22.7 4.9

PCSL - 0.45 33.3 8.2 28.6 6.4 23.7 5.2

PCSL - 0.45+ 37.6 8.5 32.1 6.8 28.2 5.8

PC - 0.45 42.2 11.9 35.9 7.7 34.3 6.6

PC - 0.45+ 46.0 15.0 40.2 11.6 38.9 10.3

CORED HPC 30.1 3.6 25.3 2.0 22.1 1.6

HPC+ 34.1 4.4 28.6 3.0 25.9 2.3

SFSL - 0.40 36.3 5.5 29.9 3.9 25.9 2.7

PCSL - 0.40 41.6 6.0 35.8 5.3 32.7 4.0

PCSL - 0.40+ 44.6 6.8 40.9 5.6 37.8 4.4

PCSL - 0.45 49.7 8.0 42.3 5.9 39.7 5.0

PCSL - 0.45+ 52.8 8.9 50.8 6.6 44.9 5.7

PC - 0.45 61.8 13.0 56.3 9.0 53.8 8.0 PC - 0.45+ 76.8 14.6 63.1 11.3 59.1 10.5

250

APPE/DIX D

FIELD SORPTIVITY TEST RESULTS

MIXTURE CS 1 CS 2 Sorptivity (mm/min0.5)

AGE

HPC 0.009 0.006 0.008 14

HPC + 0.010 0.008 0.009 14

SFSL 0.40 0.010 0.009 0.009 14

PCSL 0.40 0.012 0.013 0.013 14

PCSL 0.40+ 0.015 0.016 0.016 14

PCSL 0.45 0.028 0.029 0.028 14

PCSL 0.45+ 0.030 0.029 0.029 14

PC 0.45 0.006 0.016 0.011 14

PC 0.45+ 0.025 0.030 0.028 14

HPC 0.009 0.012 0.010 28

HPC + 0.015 0.008 0.011 28

SFSL 0.40 0.015 0.012 0.013 28

PCSL 0.40 0.017 0.019 0.018 28

PCSL 0.40+ 0.032 0.031 0.031 28

PCSL 0.45 0.042 0.053 0.047 28

PCSL 0.45+ 0.054 0.060 0.057 28

PC 0.45 0.017 0.018 0.018 28

PC 0.45+ 0.025 0.037 0.031 28

HPC 0.020 0.013 0.017 56

HPC + 0.022 0.019 0.021 56

SFSL 0.40 0.027 0.023 0.025 56

PCSL 0.40 0.031 0.032 0.031 56

PCSL 0.40+ 0.047 0.052 0.050 56

PCSL 0.45 0.060 0.057 0.058 56

PCSL 0.45+ 0.074 0.063 0.068 56

PC 0.45 0.031 0.030 0.030 56

PC 0.45+ 0.038 0.046 0.042 56

HPC 0.022 0.019 0.020 91

HPC + 0.028 0.024 0.026 91

SFSL 0.40 0.030 0.026 0.028 91

PCSL 0.40 0.049 0.050 0.049 91

PCSL 0.40+ 0.071 0.072 0.072 91

PCSL 0.45 0.089 0.100 0.094 91

PCSL 0.45+ 0.115 0.116 0.115 91

PC 0.45 0.044 0.048 0.046 91

PC 0.45+ 0.057 0.078 0.067 91

251

APPE/DIX E

DC-CYCLIC BULK ELECTRICAL RESISTIVITY

E.1 Full length cylinders (Ø100 x 200 mm)

Day 3 Day 7

Mixture CYL.1 CYL.2 CYL.3

ρ3day (KΩ.cm) CYL.1 CYL.2 CYL.3

ρ7day (KΩ.cm)

HPC 29.47 9.52 13.63 17.54 27.97 29.58 21.29 26.28

HPC+ 28.20 9.29 13.28 16.92 27.00 32.01 15.40 24.80

SFSL-0.40 8.15 4.69 14.38 9.07 28.07 9.26 24.23 20.52

PCSL-0.40 8.36 6.32 4.29 6.32 5.82 9.36 14.34 9.84

PCSL-0.40+ 3.37 3.65 4.26 3.76 8.29 4.49 4.23 5.67

PCSL-0.45 3.42 3.60 3.50 3.51 3.39 3.57 4.37 3.78

PCSL-0.45+ 3.36 3.53 4.27 3.72 3.40 3.54 4.30 3.75

PC-0.45 3.35 3.45 3.30 3.37 5.00 4.85 4.94 4.93

PC-0.45+ 3.36 3.68 3.56 3.53 4.81 4.65 4.25 4.57

Day 28 Day 56

Mixture CYL.1 CYL.2 CYL.3

ρ28day (KΩ.cm) CYL.1 CYL.2 CYL.3

ρ56day (KΩ.cm)

HPC 83.08 81.12 82.88 82.36 92.43 94.52 96.66 94.54

HPC+ 82.97 76.78 77.74 79.16 85.89 86.34 91.92 88.05

SFSL-0.40 71.12 72.80 73.63 72.52 77.30 78.11 79.29 78.23

PCSL-0.40 23.48 23.81 22.66 23.32 29.00 28.91 30.38 29.43

PCSL-0.40+ 17.51 17.36 19.36 18.08 24.81 25.91 24.18 24.97

PCSL-0.45 15.51 16.26 15.39 15.72 16.91 30.16 19.23 22.10

PCSL-0.45+ 14.86 15.18 15.27 15.10 19.32 19.72 19.98 19.67

PC-0.45 7.15 8.15 5.12 6.81 9.12 10.68 9.50 9.77

PC-0.45+ 5.90 4.50 14.07 8.16 8.34 9.42 8.15 8.64

252

Day 91

Mixture CYL.1 CYL.2 CYL.3

ρ91day (KΩ.cm)

HPC 105.21 102.00 100.00 102.40

HPC+ 90.56 97.51 90.00 92.69

SFSL-0.40 85.32 80.21 81.25 82.26

PCSL-0.40 40.88 43.80 41.16 41.95

PCSL-0.40+ 36.36 30.08 31.49 32.64

PCSL-0.45 28.72 31.08 29.54 29.78

PCSL-0.45+ 26.44 28.90 30.90 28.75

PC-0.45 11.77 13.55 12.61 12.64

PC-0.45+ 10.69 9.90 10.59 10.39

253

E.2 Concrete cores (Ø100 x 50 mm)

Day 3 Day 7 Mixture

Middle Bottom ρ3day (KΩ.cm)

Middle Bottom ρ7day (KΩ.cm)

HPC 4.39 5.42 4.91 20.13 25.10 22.62

HPC+ 4.62 4.43 4.53 23.73 25.84 24.79

SFSL-0.40 4.93 3.97 4.45 24.33 24.23 24.28

PCSL-0.40 4.95 3.11 4.03 5.90 7.32 6.61

PCSL-0.40+ 4.09 4.56 4.33 4.66 6.00 5.33

PCSL-0.45 4.57 3.16 3.87 4.12 5.13 4.63

PCSL-0.45+ 4.00 3.10 3.55 4.16 5.08 4.62

PC-0.45 5.18 3.20 4.19 5.10 3.20 4.15

PC-0.45+ 3.12 5.02 4.07 3.59 4.00 3.79

Day 28 Day 56

Mixture Middle Bottom

ρ28day (KΩ.cm) Middle Bottom

ρ56day (KΩ.cm)

HPC 80.35 74.34 77.35 91.38 91.26 91.32

HPC+ 73.31 76.40 74.86 90.73 88.52 89.63

SFSL-0.40 64.97 63.67 64.32 82.71 73.93 78.32

PCSL-0.40 15.18 19.36 17.27 29.85 30.28 30.07

PCSL-0.40+ 13.69 16.90 15.30 23.58 25.17 24.38

PCSL-0.45 12.98 13.64 13.31 20.92 22.34 21.63

PCSL-0.45+ 11.53 11.62 11.57 22.34 22.42 22.38

PC-0.45 6.97 6.13 6.55 10.02 11.81 10.92

PC-0.45+ 5.90 6.92 6.41 9.84 9.64 9.74

254

Day 91

Mixture Middle Bottom

ρ91day (KΩ.cm)

HPC 110.00 89.20 99.60

HPC+ 99.00 94.58 96.79

SFSL-0.40 87.00 81.99 84.50

PCSL-0.40 41.83 43.28 42.56

PCSL-0.40+ 30.84 33.31 32.08

PCSL-0.45 28.89 29.34 29.12

PCSL-0.45+ 26.88 27.86 27.37

PC-0.45 12.45 13.49 12.97

PC-0.45+ 11.58 11.10 11.34

255

255

APPE/DIX F

SURFACE ELECTRICAL RESISTIVITY

F.1 Cylinders (Ø100 x 200 mm)

Day 28 Day 56

Wet Cylinders Wet Cylinders Mixture

a =25 mm a =30 mm a =40 mm a =50 mm a =25 mm a =30 mm a =40 mm a =50 mm

HPC 106.73 125.72 163.67 207.28 112.75 133.83 167.75 211.91

HPC+ 105.71 121.73 153.13 198.75 109.33 125.67 156.00 200.67

SFSL-0.40 88.33 108.51 137.82 180.41 97.59 113.29 146.65 189.27

PCSL-0.40 30.96 37.44 46.98 61.37 33.90 41.27 51.72 69.22

PCSL-0.40+ 21.15 23.68 29.53 39.29 27.80 35.01 43.92 57.28

PCSL-0.45 21.03 23.43 28.79 39.25 21.60 24.53 32.45 47.43

PCSL-0.45+ 19.30 21.12 27.44 36.60 27.09 29.30 35.93 46.32

PC-0.45 9.90 10.46 14.27 19.15 12.33 13.41 16.96 22.78

PC-0.45+ 7.78 8.72 10.48 13.20 10.21 11.46 14.59 19.68

Day 3 Day 7

Wet Cylinders Wet Cylinders Mixture

a =25 mm a =30 mm a =40 mm a =50 mm a =25 mm a =30 mm a =40 mm a =50 mm

HPC 15.57 17.13 24.54 28.17 36.13 42.88 54.18 71.53

HPC+ 12.29 13.50 17.65 21.98 36.98 40.70 51.81 66.69

SFSL-0.40 17.81 19.75 24.62 32.50 26.00 37.29 46.63 60.62

PCSL-0.40 8.37 8.98 12.35 16.11 17.41 17.53 22.58 29.57

PCSL-0.40+ 8.20 9.23 11.58 15.33 10.56 11.53 15.18 20.13

PCSL-0.45 6.00 6.63 8.27 11.77 8.37 10.03 12.73 16.83

PCSL-0.45+ 4.70 5.00 6.63 8.97 8.22 9.00 11.28 15.23

PC-0.45 4.00 4.35 5.60 7.20 5.00 5.77 6.87 9.40

PC-0.45+ 4.13 4.50 5.93 7.67 4.80 5.33 6.67 8.63

256

Day 91

Wet Cylinders

Mixture

a =25 mm a =30 mm a =40 mm a =50 mm

HPC 121.69 144.38 174.69 220.58

HPC+ 114.65 132.32 160.25 208.26

SFSL-0.40 109.56 122.02 156.35 196.25

PCSL-0.40 48.28 57.25 65.25 88.58

PCSL-0.40+ 40.10 45.68 58.11 79.70

PCSL-0.45 40.10 45.03 56.70 74.17

PCSL-0.45+ 30.33 35.41 45.77 60.88

PC-0.45 15.30 17.40 21.90 28.37

PC-0.45+ 11.69 13.34 17.08 23.22

257

F.2 Circular slabs (Ø406 x 75 mm)

Mixture Day 3 Day 7

Slab #1 a =20 mm a =30 mm a =40 mm a =50 mm a =20 mm a =30 mm a =40 mm a =50 mm

HPC 7.11 9.03 9.93 11.45 22.25 24.21 26.41 29.63

HPC+ 5.80 7.18 7.88 8.79 17.65 21.61 23.24 27.03

SFSL-0.40 10.11 12.65 14.28 15.38 16.63 19.54 22.43 26.06

PCSL-0.40 3.44 4.55 5.25 6.13 8.49 10.58 11.33 13.18

PCSL-0.40+ 4.25 5.24 5.48 6.46 6.19 8.06 9.14 10.76

PCSL-0.45 2.98 3.96 4.48 5.13 4.33 5.94 6.93 7.95

PCSL-0.45+ 2.21 2.86 3.25 3.76 4.49 5.50 6.18 7.13

PC-0.45 2.78 3.28 3.66 4.19 3.54 3.95 4.66 5.15

PC-0.45+ 2.34 2.79 2.99 3.84 3.13 3.54 4.08 4.70

Slab #2 a =20 mm a =30 mm a =40 mm a =50 mm a =20mm a =30 mm a =40 mm a =50 mm

HPC 6.80 8.78 9.70 11.11 21.30 23.84 26.94 29.59

HPC+ 5.29 6.60 6.73 8.20 16.36 20.53 22.49 25.58

SFSL-0.40 9.83 12.79 13.93 14.94 15.93 19.44 21.16 24.33

PCSL-0.40 3.36 4.40 5.01 5.83 8.01 10.01 10.70 11.89

PCSL-0.40+ 3.90 4.68 4.93 5.69 5.63 7.69 8.95 10.36

PCSL-0.45 3.06 3.84 4.36 5.00 4.63 5.99 6.88 7.91

PCSL-0.45+ 2.25 3.06 3.33 3.91 4.45 5.46 6.23 7.38

PC-0.45 2.85 3.13 3.69 4.28 3.53 4.05 4.29 4.83

PC-0.45+ 2.31 2.75 2.76 3.46 3.35 3.44 3.85 4.41

258

Day 14 Day 28 Mixture

WET WET

Slab #1 a =20 mm a =30 mm a =40 mm a =50 mm a =20 mm a =30 mm a =40 mm a =50 mm

HPC 71.15 84.91 87.75 97.86 120.05 154.10 156.80 170.05

HPC+ 66.88 78.75 81.06 90.09 108.40 141.60 134.93 153.23

SFSL-0.40 50.21 58.36 61.14 70.18 99.50 126.88 119.70 138.55

PCSL-0.40 16.73 20.61 22.54 26.41 28.03 31.13 32.15 34.23

PCSL-0.40+ 16.26 18.85 19.59 23.25 23.88 29.30 31.40 33.35

PCSL-0.45 13.56 18.50 17.93 20.84 18.85 23.48 25.73 30.43

PCSL-0.45+ 13.03 15.01 16.74 17.89 14.40 20.33 21.25 23.45

PC-0.45 6.86 7.64 8.23 8.74 9.60 12.00 12.15 13.03

PC-0.45+ 6.23 7.79 7.81 8.54 8.98 10.78 9.43 10.15

Slab #2 a =20 mm a =30 mm a =40 mm a =50 mm a =20 mm a =30 mm a =40 mm a =50 mm

HPC 71.18 81.65 88.20 98.28 99.53 152.08 145.53 163.00

HPC+ 65.85 76.16 79.88 89.61 90.75 129.38 136.80 162.20

SFSL-0.40 51.53 58.55 61.94 71.08 80.73 114.55 121.15 129.85

PCSL-0.40 17.64 20.71 22.38 25.51 28.53 32.28 35.70 37.45

PCSL-0.40+ 15.93 17.44 18.81 22.03 21.60 26.98 29.15 32.58

PCSL-0.45 13.64 16.41 17.46 19.36 16.53 21.25 23.80 26.78

PCSL-0.45+ 10.09 14.01 14.74 17.36 14.60 20.00 22.78 25.73

PC-0.45 6.53 7.79 8.16 8.59 9.40 10.38 10.33 11.70

PC-0.45+ 6.50 8.20 7.80 8.33 8.30 9.60 10.28 11.15

259

Day 56 Day 91 Mixture

WET WET

Slab #1 a =20 mm a =30 mm a =40 mm a =50 mm a =20 mm a =30 mm a =40 mm a =50 mm

HPC 235.88 251.50 267.50 269.88 260.85 280.35 280.21 300.52

HPC+ 153.50 178.75 197.38 222.63 159.00 190.25 220.25 259.01

SFSL-0.40 135.21 167.30 178.59 181.39 140.20 180.11 188.85 219.68

PCSL-0.40 47.15 49.23 49.20 52.08 67.99 87.56 90.28 109.22

PCSL-0.40+ 33.41 38.60 41.53 49.64 58.57 63.54 83.49 98.90

PCSL-0.45 25.25 34.40 37.60 42.70 35.88 53.40 63.99 82.73

PCSL-0.45+ 22.28 32.18 36.10 44.23 29.76 45.45 55.04 67.00

PC-0.45 13.28 16.53 16.23 17.40 24.56 30.73 31.10 32.48

PC-0.45+ 12.15 15.48 14.28 15.65 21.16 25.29 27.83 27.48

Slab #2 a =20 mm a =30 mm a =40 mm a =50 mm a =20 mm a =30 mm a =40 mm a =50 mm

HPC 159.60 249.50 254.88 259.88 200.00 310.21 320.12 322.00

HPC+ 131.75 186.75 201.50 230.13 149.64 198.25 241.20 250.21

SFSL-0.40 109.77 166.29 183.65 185.75 129.65 180.58 200.69 210.25

PCSL-0.40 39.88 44.70 49.39 52.71 41.69 62.38 72.45 88.85

PCSL-0.40+ 28.53 32.60 41.80 49.89 34.08 50.89 69.25 82.16

PCSL-0.45 18.68 26.83 32.55 37.53 30.53 45.83 56.25 73.01

PCSL-0.45+ 18.45 30.05 33.75 42.65 27.01 40.64 54.24 64.71

PC-0.45 13.43 16.98 17.58 19.30 20.33 32.34 35.69 36.65

PC-0.45+ 10.88 14.53 14.80 16.03 18.29 25.35 27.90 26.00

260

END

SUMMER 2010

FIN