Contents Foreword xi Preface xiii Acknowledgments xv List of Figures xvii List of Tablesxxici 1. Introduction 1 1.1 Background1 1.2 Empirical Models2 1.2.1 Critical Steel Corrosion at Surface Cracking 2 1.2.2 Crack Width at tHe Concrete Su rface 4 1.2.3 Discussion on tHe Empirical Models 6 1.3 Analytical Models 7 1.3.1 Three-Stage Corrosion-Induced Cracking Mode 17 1.3.2 Corrosion Products Filling Stage 8 1.3.3 Concrete Cover Stressing and Cracking 10 1.3.4 Rust Filling in Corrosion-Induced Cracks 13 1.4 Contents of This Book 13 References 15 2. Steel Corrosion in Concrete 19 2.1 Introduction 19 2.2 Mechanisms of Steel Corrosion in Concrete 20 2.2.1 Corrosion Process 20 2.2.2 Corrosion Rate21 2.2.3 Passivation 21 2.3 Steel Corrosion Induced by Carbonation or Chloride Attack 22 2.3.1 Carbonation-lnduced Corrosion 23 2.3.2 Chloride-lnduced Corrosion 23 2.4 Corrosion Products 25 2.5 Steel Corrosion-Induced Concrete Damage 27 2.6 Conclusions 28 References 29 3. The Expansion Coefficients and Modulus of Steel Corrosion Products 31 3.1 Introduction 31 3.2 Expansion Coefficient of Steel Corrosion Products 33 3.2.1 Experimental Program 33 3.2.2 Tested Results 33 3.2.3 Composition of Rust Samples 39 3.2.4 Expansion Coefficient of Rust Samples 42 3.3 Modulus of Steel Corrosion Products in Concrete 46 3.3.1 Experimental Program 46 3.3.2 Loading and Unloading Stress-Strain Curve 48 3.3.3 Tested Data of Cyclic Low-Compression Test 49 3.3.4 Modulus of Rust 49 3.4 Conclusions 51 References 52 4. Damage Analysis and Cracking Model of Reinforced Concrete Structures with Rebar Corrosion 55 4.1 Introduction 55 4.2 Basic Concrete Cracking Model Due to Steel Corrosion 56 4.3 Noncracking Stage of Corrosion-Induced Concrete Cracking Process 57 4.4 Partial Cracking Stage of Corrosion-Induced Concrete Cracking Process 60 4.4.1 Intact Part 60 4.4.2 Cracked Part 61 4.5 Corrosion-Induced Expansive Pressure 66 4.5.1 Relation Between Expansive Pressure and Steel Corrosion 67 4.5.2 Variation of Expansive Pressure 67 4.5.3 Effect of Concrete Cover THickness 68 4.5.4 Effect of Steel Bar Diameter 70 4.5.5 Effect of Concrete Quality 71 4.6 Discussion on the Radial Loss of Steel Bar 72 4.6.1 Steel Loss Varying with tHe Crack Length 72 4.6.2 Effect of Concrete Cover THickness 73 4.6.3 Effect of Steel Bar Diameter 73 4.6.4 Effect of Rust Expansion Coefficient75 4.6.5 Effect of Concrete Quality 75 4.7 Conclusions 75 References 76 5. Mill Scale and Corrosion Layer at Concrete Surface Cracking 79 5.1 Introduction 79 5.2 Experimental Program 80 5.2.1 Reinforced Concrete Specimens 80 5.2 .2Accelerated Steel Corrosion 81 5.2.3 Sample Preparation 81 5.2.4 0bservation and Measurement 83 5.3 Rust Distributions in the Cracking Sample 84 5.4 Mill Scale 86 5.5 Corrosion Layer Thickness at Surface Cracking of Concrete Cover 87 5.5.1 At Outer Surface Cracking 87 5.5.2 At Inner Surface Cracking 89 5.6 Conclusions 91 References 92 6. Rust Distribution in Corrosion-Induced Cracking Concrete 93 6.1 Introduction 93 6.2 Experimental Program 94 6.2.1 Reinforced Concrete Specimen 94 6.2.2 Curing and Exposure History 94 6.2.3 Sample Preparation 95 6.2.4 0bservation and Measurements 96 6.3 Rust Distributions at the Steel-Concrete Interfaces 97 6.4 Distribution of the Corrosion Products-Filled Paste 100 6.5 Rust Distribution in Corrosion-Induced Cracks 101 6.5.1 Rust Distribution in Cracks by Digital Microscope 101 6.5.2 Rust Filling in Cracks by SEM 104 6.5.3 Discussion of Rust Filling Corrosion-Induced Cracks 107 6.6 Rust Development in Concrete Cracks 107 6.7 Conclusions 108 References 109 7. Nonuniform Distribution of Rust Layer Around Steel Bar in Concrete 111 7.1 Introduction111 7.2 Steel Corrosion and Corrosion-Induced Cracks 112 7.3 Gaussian Model to Describe the Nonuniform Rust Layer 113 7.4 Comparing the Proposed Gaussian Model With Other Models 117 7.5 Parameters in Caussian Model 118 7.5.1 λ3: Uniform Coefficient of the Rust Layer 118 7.5.2 λ1:Nouniform Coefficient of the Rust L120 7.5.3 λ2: Spread Coefficient of Rust Layer 122 7.5.4 Relationships Among Parameters Before Concrete Surface Cracking 123 7.6 Conclusions 126 References 126 8. Crack Shape of Corrosion-Induced Cracking in the Concrete Cover 129 8.1 Introduction 129 8.2 Experimental Program 130 8.2.1 Reinforced Concrete Specimens 130 8.2.2 Accelerated Corrosion History 131 8.2.3 Sample Preparation 132 8.2 .40bservation and Measu rement 132 8.3 Crack Shape134 8.3.1 Crack WidtH Model 134 8.3.2 a1: Crack Width Variation Coefficient 134 8.3.3 a2: Crack Width Coefficient at the Surface of tHe Steel Bar 138 8.4 Crack Width and Corrosion Layer Thickness 138 8.4.1 Relationship Between Crack WidtH, wi, and Corrosion Layer Thickness, TCL 138 8.4.2 Wc: Critical Crack WidtH at Concrete Outer Surface Cracking 140 8.4.3 Ws: Crack Width on the Surface of Concrete Cover140 8.5 Relationship of Corrosion Layer Thickness TCL and Crack Width Variation Coefficient ai 141 8.6 Crack Shape in Different Types of Concrete 143 8.7 Conclusions 145 References 145 9. Development of Corrosion Products-Filled Paste at the Steel-Concrete Interface 147 9.1 Introduction 147 9.2 Influence of Cracks on CP Thickness 148 9.3 Relation Between TCP and TCL Excluding the Effect of Inner Cracks 149 9.4 Relation Between TCP and TCL Including the Inner Cracks 153 9.5 Conclusions157 Referencesl 57 10. Steel Corrosion-Induced Concrete Cracking Model 159 10.1 Introduction 159 10.2 Corrosion-Induced Concrete Surface Cracking Model Considering CP 160 10.2.1 Cracking Process Description 160 10.2.2 TCP - TCL Model 161 10.2.3 Nominal Ratio Between the Corrosion Products Volume and the Basic Steel Volume 162 10.3 Time From Corrosion Initiation to Concrete Surface Cracking 164 10.3.1 Faraday's Law164 10.3.2 Corrosion Rate165 10.4 Discussion of Nonuniform Corrosion Situation 167 10.5 Discussion of Influence of Loading on the Cracking Model 168 10.5.1 Force Contributed by tHe MecHanical Interlocking 168 10.5.2 Intersecting Cracks and Localized Corrosion 169 10.6 Conclusions 170 References 170 Notations 171 Cndex 175 List of Figures Figure 1.1 Comparison of steel corrosion at concrete surface cracking between the empirical model-predicted results and the experimental results. 6 Figure 1.2 Comparison of concrete surface crack width propagation between the model-predicted results and the experimental results.7 Figure 1 .3 Three-stage corrosion-induced cracking process. (a) Corrosion initiated. (b) Stage 1: filling.(c) Stage 2: stressing. (d) Stage 3: cracking.8 Figure 1 .4 BSE images showing accumulation of corrosion products at the steel-concrete interface (S, steel;CL, corrosion layer; CP, corrosion products-filled paste;P, unaltered paste; A, air void).9 Figure 1.5 Corrosion-induced concrete cracking model. (a) Thick-walled cylinder model. (b) Double-Iayer thick-walled cylinder model.12 Figure 2.1 The anodic and cathodic reactions. 20 Figure 2.2 Initiation and propagation periods for steel corrosion in concrete.23 Figure 2.3 Pitting attack in a steel bar. 24 Figure 2.4 Transformation of iron oxides.27 Figure 2.5 Stages in corrosion-induced damage. (a) Passive rebar. (b) Corrosion initiation and growth.(c) Further corrosion and cracking propagation.(d) Spalling/delamination.28 Figure 3.1 XRD pattern of eight different rust samples.36 Figure 3.2 TG curves of all rust samples.37 Figure 3.3 DTA curves of all rust samples.38 Figure 3.4 XRD patterns of the original and heated sample l. 40 Figure 3.5 improved XRD patterns of eight rust samples. 41 Figure 3.6 The concrete port and the steel corrosion products. (a) The concrete port in Yokosuka. (b) The corroded steel bar in the concrete beam. (c) The corrosion roduct peeled from the corroded steel bar.(d) Flaky rust samples.47 Figure 3.7 Typical loading and unloading stress-strain curve. 48 Figure 4.1 Deformations of the rust layer and surrounding concrete under expansive pressure.(a) Noncracking. (b) Partial cracking.57 Figure 4.2 Partitions of the cracking part.63 Figure 4.3 Expansive pressure against steel corrosion.67 Figure 4.4 Variation of expansive pressure after initiation of racks in concrete cover. (a) Expansive pressure gainst crack length. (b) Expansive pressure in cracked concrete.68 Figure 4.5 ffect of concrete cover thickness on expansive pressure.69 Figure 4.6 ak value of expansive pressure against concrete cover thickness.69 Figure 4.7 rmalized expansive pressure as a function of normalized crack length.70 Figure 4.8 fect of steel bar diameter on expansive pressure.71 Figure 4.9 ffect of tensile strength on expansive pressure. 72 Figure 4.10 adial loss of steel bar as a function of crack length.73 Figure 4.11 ffect of concrete cover thickness on steel loss uring surface cracking.74 Figure 4.12 Effect of steel bar diameter on steel loss during surface cracking.74 Figure 4.13 Effect of rust expansion coefficient on steel loss during surface cracking.75 Figure 4.14 Effect of compressive strength on steel loss during surface cracking.76 Figure 5.1 yout details of the concrete specimens (dimensions are in mm).80 Figure 5.2 Cracking parts of specimens were cast into a ow-viscosity epoxy resin.81 Figure 5.3 Schematic diagrams of the specimens and the location of the slices.82 Figure 5.4 Sample (slice l -1) for digital microscope observation.82 Figure 5.5 Sample trimmed from slice 2-2 for SEM observation.83 Figure 5.6 Rust distributions at the steel-concrete interface and n the corrosion-induced cracks (CP, corrosion roducts-filled paste; CL, corrosion layer).84 Figure 5.7 EDS analysis across a corrosion-induced crack. (a) Corrosion-induced crack and an analytical line across the crack. (b) Distribution of Fe across the orrosion-induced crack analyzed by EDS along the nalytical line.85 Figure 5.8 EDS analysis across the steel-concrete interface. (a) BSE image at the steel-concrete interface (MS, mill scale) and an analytical line across the interface. (b) The distribution of Fe and O across the steel-concrete interface analyzed by EDS along the analytical line.86 Figure 5.9 Mill scale distribution at the steel-concrete interface.87 Figure 5.10 Crack pattern of slice 1-1.88 Figure 5.11 Crack pattern of slice 2-1 . 89 Figure 5.12 The crack patterns on the cross-section of the measured slices. The longest radial crack length and the corrosion layer thickness are listed below each slice.90 Figure 5.13 Relation between corrosion layer thickness and crack length.91 Figure 6.1 Schematic of the reinforced concrete specimen (dimensions are in mm).94 Figure 6.2 Schematic diagrams of the cut specimen. (a) Specimen. (b) The cut panels and slices.95 Figure 6.3 Sample preparation for SEM. (a) Slice L-9.(b) Sample for SEM.96 Figure 6.4 Measurement of the thickness of the rust layer accum u I ated at the rebar-concrete interface.(a) Field of view: 50X52 mm. (b) Field of view:3.74 X 3.68 mm.97 Figure 6.5 Rust distributions at the steel-concrete interface in sample R-5. (a) BSE image at the steel-concrete interface (CP, corrosion products-filled paste;MS, mill scale; CL, corrosion layer) and an analytical line across the interface. (b) The distributions of Fe and O across the steel-concrete interface analyzed by EDS along the analytical line.98 Figure 6.6 Schematic of ion migration and reaction during steel corrosion in the presence of chloride ions in concrete.99 Figure 6.7 Average thickness of the corrosion products-filled paste (CP) for different thicknesses of the corrosion layer (CL).100 Figure 6.8 Rust distribution in slice R-6. (a) Slice R-6. (b) Area l. (c) Area 2. (d) Area 3. (e) Area 4.102 Figure 6.9 Crack at the steel-concrete interface of slice M-14 (6897¨m X 6155Um).103 Figure 6.10 Slice L-4 with the more severe corroded steel bar.104 Figure 6.11 Rust distributed in a crack penetrating the concrete cover in sample L-9. (a) BSE image of the corrosion-induced crack and an analytical line across the crack. (b) The distribution of Fe across the crack analyzed by EDS along the analytical line.105 Figure 6.12 Rust distributed in an inner crack in sample R-7. (a) BSE image of the corrosion-induced crack and an analytical line across the crack. (b) The distribution of Fe across the crack analyzed by EDS along the analytical line.106 Figure 6.13 Schematic diagram of crack propagation and rust development. (a) Before surface cracking.(b) Surface cracking. (c) After surface cracking.107 Figure 7.1 Steel corrosion varies with the distance to the front of specimen R.112 Figure 7.2 Typical cracks and rust layer of slices from specimen R.113 Figure 7.3 Measured thickness of the rust layer around the rebar perimeter.114 Figure 7.4 Polar coordinate system defined for the corner andiis middle rebars.115 Figure 7.5 Polar coordinate system for measurement and fitting of the rust layer.117 Figure 7.6 The regression analysis of the proposed models for the tested data.119 Figure 7.7 R2 0f four models.120 Figure 7.8 Physical meaning ofλ3. (a) Partial corrosion (λ3 = 0). (b) Whole cross-section corrosion(λ3 = Tr.min).120 Figure 7.9 Two parts of the rust layer when steel corrosion spreads throughout the entire circumference.122 Figure 7.10 Area of corrosion peaks grow with the increase of Ai. 122 Figure 7.11 Peak area of partial corrosion. 123 Figure 7.12 Relationship between Ai and p. 123 Figure 7.13 Nonuniform corrosion spreading widely with the increase of A2.124 Figure 8.1Layout details of specimens (dimensions are in mm).130 Figure 8.2 Wetting and drying cycles combined with a constant current.131 Figure 8.3Schematic diagram of preparation of samples for digital microscopy observation. (a) Cracked parts of specimens were cast in epoxy resin. (b) A sample prepared for digital microscopy observation.132 Figure 8.4 Measurement and calculation of the crack width,Wi, at radius Ri. (a) Measurement of crack width.(b) Total crack width, wi.133 Figure 8.5 Measured data and the fitting line of the crack width. (a) Slice R000-l-8, representing the inner cracking scenario. (b) Slice R000-2-8, representing the cracks that had penetrated the concrete cover.135 Figure 8.6 Schematic crack shape model. 136 Figure 8.7 Relationship between parameter ai and corrosion layer thickness TCL.137 Figure 8.8 Relationship between parameter a2 and corrosion layer thickness TCL.138 Figure 8.9 Relationship between crack width on concrete surface, Ws, and corrosion layer thickness, TCL.141 Figure 8.10 Schematic diagram of corrosion-induced crack propagation.142 Figure 9.1 Influence of cracks on CP development. (a-c) Inner crack. (d, e) Outer crack. CP, corrosion products-filled paste; CL, corrosion layer; TCP, thickness of CP; TCL, thickness of CL.148 Figure 9.2 Schematic of measured regions at the concrete-steel interface.150 Figure 9.3 Thickness of the corrosion products-filled paste (CP) versus thicknesses of the corrosion layer (CL)excluding the regions of the inner cracks for ROOO. (a) Measured data. (b) A part of the data map after grouping in the range of 20 lLm for R067.150 Figure 9.4 Relationship between TCP and TCL excluding the regions of the inner cracks. (a) ROOO. (b) R033.(c) R067. (d) R100.151 Figure 9.5 TCP- Tcu models for four types of concrete (excluding the effect of inner cracks).151 Figure 9.6 Effect of concrete quality on Tcp. 152 Figure 9.7 Thickness of corrosion products-filled paste (CP) versus thickness of corrosion layer (CL) including the regions of the inner crack for ROOOs. (a) AlI measured data. (b) Local magnification.153 Figure 9.8 Tested data of all samples and their average value of tested data.156 Figure 9.9 TCP- TCL models for four types of concrete (including the effect of inner cracks). CP, corrosion products-filled paste; TCP, thickness of CP; TCL,thickness of corrosion layer.156 Figure 10.1 Corrosion-induced concrete cracking model considering corrosion products-filled paste. (a) Steel depassivation. (b) Corrosion-induced crack appears and CP and CL form simultaneously. (c) TCL and TCP increase gradually until the crack reaches the concrete outer surface.160 Figure 10.2 Relationship between TCP and TCL. 161 Figure 10.3 Conversion from the thickness of CP ( TCP) to the thickness of CL ( TCL,pore).162 Figure 10.4 Nonuniform corrosion layer and the corresponding CP thickness. (a) Nonuniform corrosion layer.(b) Corresponding CP thickness.168 Figure 10.5 The mechanical interlocking between the steel ribs and the concrete keys.169 List of Tables Table 1.1 Experimental Study of Corrosion Products-Filled Paste 9 Table 1.2 Corrosion-induced Cracking Model 11 Table 1.3 Rust Filling in Corrosion-Induced Cracks 13 Table 2.1 Different Types of I ron Oxides 25 Table 2.2 Selected Properties of the I ron Oxides 27 Table 3.1 Details of the Rust Samples 34 Table 3.2 The Content of Two Categories: Products for Eight Samples (mg)42 Table 3.3 The Expansion Coefficient of the Main Hydroxy-Oxides and Oxides 43 Table 3.4 The Expansion Coefficients for All Rust Samples 44 Table 3.5 Exposure Classes Related to Environmental Conditions 44 Table 3.6 Environmental Classifications for All Rust Samples 45 Table 3.7 Rust Expansion Coefficients Corresponding to Different Environments 46 Table 3.8 Tested Data from the Cyclic Low-Compression Test 50 Table 4.1 Calculated Mechanical Parameters of the Four Types of Concrete 72 Table 5.1 Mixture Composition of the Concrete Specimens (kg/m3) 80 Table 6.1 Mixture Composition of Concrete Specimens (kg/m3) 94 Table 6.2 Data for Each Group in Fig. 6.7 101 Table 7.1 Values of Ai, A2, A3, and A4 0btained from the Fitting of Experimental Data 115 Table 7.2 Description of Two Nonuniform Corrosion Scenarios 116 Table 7.3 Parametric Regression Value in Model 118 Table 8.1 Compositions of the Concrete Specimen Mixtures 130 Table 8.2 Measurement Results and Parametric Regression Values 136 Table 8.3 Linear Regression Results for ai Compared to TCL 138 Table 8.4 Linear Regression Results for a2 Compared to TCL 139 Table 8.5 Substituting Results of Wi and Critical Crack Width we 139 Table 8.6 Linear Regression Results of Ws Compared to TCL 141 Table 8.7 Comparison of Crack Shapes Between NAC and RAC 144 Table 9.1 Fitting Values of k-r and Tcmpax (μm) 151 Table 9.2 Average TCP and TCL of Each Sample, Mean Values of TCP, and Their Mean Square Deviation of Each Type of Concrete Specimens(μm) 155 Table 9.3 Values of kT Considering the Effect of Inner Cracks 156
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