Cracking Behavior of Structural Slab Bridge Decks

Prepared by: Anil Patnaik, Ph.D.

Prince Baah

Prepared for: The Ohio Department of Transportation,

Office of Statewide Planning & Research

State Job Number 134708

January 2015

Final Report

ii

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

FHWA/OH-2015/4 4. Title and Subtitle 5. Report Date

Cracking Behavior of Structural Slab Bridge Decks January 2015 6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No. Dr. Anil Patnaik (PI) Prince Baah (Graduate Student)

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) The University of Akron 302 Buchtel Common Akron, OH 44325

11. Contract or Grant No. SJN 134708

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Ohio Department of Transportation 1980 West Broad Street Columbus, Ohio 43223

Final Report (08/16/2012 – 01/15/2015) 14. Sponsoring Agency Code

15. Supplementary Notes 16. Abstract

Bridge deck cracking is a common problem throughout the United States, and it affects the service life of concrete bridges. Several departments of transportation (DOTs) in the United States prefer using continuous span structural (CSS) slab bridges without stringers over typical four-lane highways or steams. The primary objective of this project is to study the cracking behavior of CSS slab bridges. Recent inspections of such bridges in Ohio revealed permanent cracks as wide as 0.14 in. under dead load alone. These measured crack widths are more than 15 times the maximum limit recommended in ACI 224R-01 for bridge decks exposed to de-icing salts. Measurements using digital image correlation revealed that the cracks widened under truck loading, and in some cases, the cracks did not fully close after unloading. This report also includes details of an experimental investigation. Prism tests revealed that the concrete specimens with epoxy-coated bars (ECB) develop first crack at smaller loads, and develop larger crack widths compared to the corresponding specimens with uncoated (black) bars. Slab tests revealed that the specimens with longitudinal ECB developed first crack at smaller loads, exhibited wider cracks and a larger number of cracks, and failed at smaller ultimate loads compared to the corresponding test specimens with black bars. To investigate a preventive measure, slab specimens with basalt MiniBar or polypropylene fiber reinforced concrete were included in the test program. These specimens exhibited higher cracking loads, smaller crack widths, smaller mid-span deflections and higher ultimate failure loads compared to the slab specimens without fiber. Merely satisfying the reinforcement spacing requirements given in AASHTO or ACI 318-11 is not adequate to limit cracking below the ACI 224R-01 recommended maximum limit, even though all the relevant design requirements are otherwise met. Addition of fiber to concrete without changing any steel reinforcing details is expected to cost-effectively reduce the severity and extent of cracking in reinforced concrete bridge decks.

17. Keywords 18. Distribution Statement Continuous span structural slab bridges, bridge deck cracking, crack widths, epoxy coated bars, load testing, fiber reinforced concrete deck slabs, chloride content.

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161

19. Security Classification (of this report)

20. Security Classification (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 214 $133,062

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized

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Cracking Behavior of Structural Slab Bridge Decks

Prepared by:

Anil Patnaik, Ph.D. (PI) Professor of Structural Engineering

The University of Akron Department of Civil Engineering

302 Buchtel Common, Akron, Ohio 44325

Phone: (330) 972-5226 Fax: (330) 972-6020

Email: Patnaik@uakron.edu

and

Prince Baah (Ph.D. Student) The University of Akron

Department of Civil Engineering Akron, Ohio 44325

January 2015

Sponsored by:

Ohio Department of Transportation 1980 West Broad Street Columbus, Ohio 43223

Prepared in cooperation with the Ohio Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration

The contents of this report reflect the views of the author(s) who is (are) responsible for the facts and the accuracy

of the data presented herein. The contents do not necessarily reflect the official views or policies of the Ohio

Department of Transportation or the Federal Highway Administration. This report does not constitute a standard,

specification, or regulation.

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ACKNOWLEDGMENTS

Ohio Department of Transportation (ODOT) provided funding for this project to the lead author; and he is grateful for this support. The extensive input and feedback provided by Mr. Perry Ricciardi and Dr. Waseem Khalifa, ODOT Subject Matter Experts for this project, is gratefully acknowledged. Their contributions in finalizing this report have been very valuable. Several graduate students of the University of Akron, Prince Baah, Saikrishna Ganapuram, Sunil Gowda, Abdisa Musa, Mohamed Habouh, Srikanth Marchetty, and Mohammed Hafeez provided assistance in the completion of this project as and when needed. Dave McVaney, Dale Ertley, Bill Wenzel and Brett Bell of University of Akron also provided assistance in completing the experimental work of this project. Mr. Steve Porpora (Summit Testing) was instrumental in traffic control during the field measurements of crack widths under truck loading and for cutting cores. Sheila Pearson helped in proofreading the draft final report.

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TABLE OF CONTENTS

ACKNOWLEDGMENTS ............................................................................................................. iv

TABLE OF CONTENTS .................................................................................................................v

LIST OF FIGURES ....................................................................................................................... ix

LIST OF TABLES ....................................................................................................................... xiii

CHAPTER 1: INTRODUCTION ....................................................................................................1 1.1 Statement of the Problem .......................................................................................................1 1.2 Motivation from Previous Work done by Ganapuram et al. ..................................................2 1.3 Research Objectives ...............................................................................................................4 1.4 Report Organization ...............................................................................................................5

CHAPTER 2: LITERATURE REVIEW .........................................................................................6 2.1 Reinforced Concrete Bridge Deck Cracking .........................................................................6 2.2 Allowable Crack Widths ........................................................................................................6 2.3 Classification of Cracks in Reinforced Concrete Members ...................................................6

2.3.1 Cracks Dependent on Applied Loading ..........................................................................7 2.3.2 Cracks Independent of Loading ......................................................................................7

2.3.2.1 Plastic Shrinkage ......................................................................................................7 2.3.2.2 Autogenous Shrinkage .............................................................................................8 2.3.2.3 Drying Shrinkage .....................................................................................................8 2.3.2.4 Thermally Induced Shrinkage ..................................................................................8

2.3.3 Cracks Based on Orientation...........................................................................................8 2.3.3.1 Transverse Cracking ................................................................................................9 2.3.3.2 Longitudinal Cracking .............................................................................................9 2.3.3.3 Diagonal Cracking .................................................................................................10 2.3.3.4 Map or Pattern Cracking ........................................................................................10

2.4 Cracking Behavior of Reinforced Concrete Structures .......................................................10 2.4.1 Shear Cracking ..............................................................................................................12 2.4.2 Flexural Cracking ..........................................................................................................12

2.5 Factors Related to Cracking in Concrete Bridge Decks ......................................................13 2.5.1 Material and Mix Design Factors .................................................................................15

2.5.1.1 Cement Type, Cement Content and Water to Cement Ratio .................................15 2.5.1.2 Concrete Strength and Slump ................................................................................15 2.5.1.3 Air Content and Admixtures ..................................................................................15 2.5.1.4 Concrete Mixes ......................................................................................................15

2.5.2 Construction and Environmental Factors ......................................................................16 2.5.2.1 Weather, Concrete Temperature, and Curing ........................................................16 2.5.2.2 Time of Casting, Placement Length, and Placement Sequence .............................16

2.5.3 Structural Design Factors ..............................................................................................16 2.5.3.1 Other Design Factors .............................................................................................17 2.5.3.2 Span Type and Skew ..............................................................................................18

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2.5.4 Traffic Related Factors..................................................................................................19 2.5.5 Other Factors .................................................................................................................19 2.5.5.1 Section Stiffness .........................................................................................................19

2.5.5.2 Vibration and Impact Characteristics.....................................................................19 2.5.5.3 Boundary Conditions .............................................................................................19

2.6 Control of Crack Width and Spacing ...................................................................................21 2.6.1 American Concrete Institute (ACI) Approach ..............................................................21

2.6.1.1 ACI 318-95 ............................................................................................................21 2.6.1.2 ACI 318-11 ............................................................................................................22

2.6.2 AASHTO Approach ......................................................................................................23 2.6.3 CEB/FIP Approach .......................................................................................................23 2.6.4 Standards Association of Australia Approach ..............................................................24 2.6.5 Eurocode EC2 Approach ..............................................................................................25

2.7 Review of Crack Width and Spacing Equations ..................................................................26 2.7.1 Gergely and Lutz Equation ...........................................................................................30 2.7.2 Chowdhury and Loo Equation ......................................................................................30 2.7.3 Oh and Kang Equation ..................................................................................................30 2.7.4 Patrick and Wheeler Equation.......................................................................................31 2.7.5 Frosch ............................................................................................................................34 2.7.6 Kaar and Mattock ..........................................................................................................34

2.8 Cyclic and Sustained Loading Effect on Bridge Deck Cracks ............................................35 2.9 Effect of Corrosion of Reinforcing Bars on Concrete Bridge Decks ..................................35 2.10 Effect of Epoxy Coating on Bridge Deck Cracks ..............................................................35 2.11 The Effects of Addition of Fiber on Reinforced Concrete ................................................36 2.12 Arching Action in Reinforced Concrete Slabs ..................................................................37 2.13 Chloride Ion Content in Bridge Decks ..............................................................................38 2.14 Digital Image Correlation Application to Bridge Decks ...................................................39 2.15 Summary of Literature Review ..........................................................................................39

CHAPTER 3: SURVEY AND INVENTORY OF CSS SLAB BRIDGES ...................................41

CHAPTER 4: FACTORS INFLUENCING POTENTIAL CRACKING OF CSS SLAB BRIDGE DECKS ..........................................................................................................................................45

CHAPTER 5: FIELD SURVEY AND MEASUREMENTS OF DEAD LOAD CRACK WIDTHS ON CSS SLAB BRIDGE DECKS ................................................................................50

5.1 Introduction ..........................................................................................................................50 5.2 Crack Survey and Crack Maps of Bridges ...........................................................................50

5.2.1 Bridge 1: WAY-30-1039 ..............................................................................................51 5.2.2 Bridge 2: ASD-42-0656 ................................................................................................53 5.2.3 Bridge 3: ASD-250-0377 ..............................................................................................54 5.2.4 Bridge 4: ATB-20-0326 ................................................................................................56 5.2.5 Bridge 5: POR-224-1172 ..............................................................................................57 5.2.6 Bridge 6: STA-225-076 ................................................................................................58 5.2.7 Bridge 7: MAH-62-0207 ...............................................................................................59 5.2.8 Bridge 8: MAH-224-1619 .............................................................................................59

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5.2.9 Bridge 9: POR-88-1250 ................................................................................................60 5.2.10 Bridge 10: TRU-534-1516 ..........................................................................................61 5.2.11 Bridge 11: TRU-45-2018 ............................................................................................62 5.2.12 Bridge 12: MED-162-2031 .........................................................................................62 5.2.13 Bridge 13: ASD-250-1864 ..........................................................................................63

5.3 Observations on Parapet Cracking .......................................................................................64 5.4 Summary ..............................................................................................................................64

CHAPTER 6: PROPERTIES DETERMINED FROM CONCRETE CORES .............................65 6.1 Compressive Strength Determination from Bridge Deck Concrete Cores ..........................65

6.1.1 Results of Concrete Compressive Strength Test and Density of the Cores ..................67 6.2 Crack Width Measurements from Concrete Cores ..............................................................76 6.3 Chloride Ion Content Determination for the Cores .............................................................80

6.3.1 Acid Soluble Chloride Ion Content Analysis Titration Method Used ..........................81 6.3.1.1 Results of Acid Soluble Chloride Ion Content Analysis .......................................81 6.3.1.2 Accuracy of Analytical Results .............................................................................83

6.4 Summary ..............................................................................................................................88

CHAPTER 7: MEASUREMENTS OF CRACK OPENINGS UNDER LIVE LOADS USING DIGITAL IMAGE CORRELATION ............................................................................................89

7.1 Introduction ..........................................................................................................................89 7.2 DIC Set-up for Crack Width Measurements under Truck Loading .....................................89 7.3 Results for Crack Opening on the Deck Due to Static Truck Loading ................................93 7.4 Results for Crack Opening on the Deck due to Loading of a Moving Truck ....................108 7.5 Results for Crack Opening in the Parapet ..........................................................................118 7.6 Summary of Results for Truck Live Load Tests ................................................................119

CHAPTER 8: STRUCTURAL, SECTION, AND CRACK WIDTH ANALYSIS.....................120 8.1 Introduction ........................................................................................................................120 8.2 Determination of Service Load Moments Using SAP 2000 Structural Analysis Software120

8.2.1 Effect of Stiffness on Piers .........................................................................................121 8.3 Review of ODOT Standard Designs for Three-Span Structural Slab Bridges ..................124 8.4 Correlation of Field Measurements to Predicted Crack Widths and Calculated Steel Stresses .....................................................................................................................................126 8.5 Summary of Structural and Crack Width Analyses ...........................................................127

CHAPTER 9: EXPERIMENTAL INVESTIGATION OF ECB BOND TO CONCRETE ........134 9.1 Introduction ........................................................................................................................134 9.2 Making of Test Specimens ................................................................................................137

9.2.1 Steel Reinforcement ....................................................................................................137 9.2.2 Concrete ......................................................................................................................139

9.3 Making of Laboratory Specimens ......................................................................................139 9.3.1 Making of Formwork ..................................................................................................139 9.3.2 Assembly of Reinforcement Cages .............................................................................140 9.3.3 Casting of Concrete .....................................................................................................140

9.4 Instrumentation ..................................................................................................................141

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9.4.1 Strain Gages ................................................................................................................141 9.4.2 Linear Variable Displacement Transducer (LVDT) ...................................................142 9.4.3 MTS Loading System .................................................................................................143

9.5 Digital Image Correlation ..................................................................................................143 9.6 Testing of the Test Specimens ...........................................................................................143 9.7 Results and Discussion of Direct Tension Crack Width Test ............................................146

9.7.1 Cracking Behavior of Direct Tension Prism Specimens ............................................146 9.8 Results and Discussion of Flexural Crack Width Test Slabs.............................................152

9.8.1 Cracking Behavior of Test Slabs ................................................................................152 9.8.2 Comparison between Predicted and Experimental Results for the Test Slabs ...........159 9.8.3 Load versus Mid-span Deflection Response ...............................................................161 9.8.4 Load versus Strain in Top Steel Reinforcement .........................................................164 9.8.5 Summary of Test Results for Flexural Crack Width Test Slabs without Fiber ..........167

9.9 Summary ............................................................................................................................167

CHAPTER 10: CRACK MINIMIZATION STRATEGY ...........................................................168 10.1 Effect of Addition of Fiber to Reinforced Concrete Slabs ..............................................168 10.2 Summary ..........................................................................................................................177

CHAPTER 11: CONCLUSIONS ................................................................................................178

CHAPTER 12: RECOMMENDATIONS FOR IMPLEMENTATION ......................................181

BIBLIOGRAPHY ........................................................................................................................182

APPENDICES .............................................................................................................................187

APPENDIX A: WORKED EXAMPLES ....................................................................................188

APPENDIX B: CTL ENGINEERING REPORT ON CHLORIDE CONCTENT FOR THREE BRIDGE DECK CORE SAMPLES ............................................................................................203

APPENDIX C: ODOT CS 1-08: STANDARD CONTINUOUS SLAB BRIDGES ..................204

APPENDIX D: ODOT CPP-1-08: STANDARD CAPPED PILE PIER FOR CONTINUOUS SLAB BRIDGES .........................................................................................................................205

APPENDIX E: CHLORIDE ION CONTENT CALCULATIONS ............................................206

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LIST OF FIGURES

Figure 1.1 A typical three-span structural slab bridge .....................................................................1 Figure 1.2 Predicted crack widths for ASD–42–0656 using Gergely and Lutz equation ................5 Figure 2.1 Classification of cracks in reinforced concrete members ...............................................7 Figure 2.2 Classification of cracks (NCHRP Synthesis 333, 2004) ................................................9 Figure 2.3 Primary and secondary cracks in a reinforced concrete tension member ....................12 (ACI-224.2R-92) ............................................................................................................................12 Figure 2.4 Types of cracking in reinforced concrete (https://www.google.com/search?q=flexural+cracking+in+reinforced+concrete+images) ..........13 Figure 2.5 Factors related to cracking in concrete bridge decks....................................................14 Figure 2.6 Cracking in tension (Patrick and Wheeler 2000) .........................................................33 Figure 2.7 Fiber reinforced concrete: Concept and mechanics (Adhikari and Patnaik 2012) .......36 Figure 2.8 Arching Action in Concrete Slabs (Foster 2010) .........................................................37 Figure 2.9 Tension Hoop around the Compression Field (Foster 2010) .......................................37 Figure 3.1 Total number of structural slab bridges in each ODOT district ...................................42 Figure 3.2 Number of structural slab bridges in each ODOT district that were built or rehabilitated between 1990 and 2013. ...........................................................................................42 Figure 3.3 Number of structural slab bridges in Ohio that were built or rehabilitated since 1990 43 Figure 3.4 Number of main spans for structural slab bridges in Ohio (1900–2013) .....................43 Figure 3.5 Sufficiency rating for structural slab bridges in Ohio (1900–2013) .............................44 Figure 4.1 Relation between skew angle and crack width .............................................................46 Figure 4.2 Relation between age of slab and crack width .............................................................46 Figure 4.3 Relation between maximum span length and crack width ...........................................47 Figure 4.4 Relation between slab thickness and crack width ........................................................47 Figure 5.1 Cracking observed on bridge WAY-30-1039...............................................................52 Figure 5.2 Crack map for bridge WAY-30-1039...........................................................................53 Figure 5.3 Observed cracks at one of the negative moment regions on March 24, 2014 ..............53 Figure 5.4 Crack maps of bridge ASD-42-0656 based on 2011 and 2013 inspections .................54 Figure 5.5 Crack map of bridge ASD-250-0377 on January 14, 2013 ..........................................55 Figure 5.6 Maximum crack width recorded on bridge ASD-250-0377, with extensive side cracks at the deck edges ............................................................................................................................55 Figure 5.7 Wide cracks over the piers on bridge ASD-250-0377, as observed on July 24, 2014 .56 Figure 5.8 Crack map for bridge ATB-20-0326. ...........................................................................56 Figure 5.9 Inspection of bridge POR-224-1172 ............................................................................57 Figure 5.10 Crack map of bridge POR-224-1172 on the top of the bridge deck ...........................58 Figure 5.11 Crack map for bridge POR-224-1172 at the bottom of the bridge deck. ...................58 Figure 5.12 Crack map of bridge STA-225-076 ............................................................................59 Figure 5.13 Crack map of bridge MAH-62-0207. .........................................................................59 Figure 5.14 Crack map of bridge MAH-224-1619 ........................................................................60 Figure 5.15 Observed wide cracks on bridge POR-88-1250 parallel to the interior piers .............60 Figure 5.16 Crack map at the top of bridge deck of bridge POR-88-1250, based on inspection on July 2, 2013 ....................................................................................................................................61 Figure 5.17 Extensive wide cracks over the piers of bridge TRU-534-1516 ................................61 Figure 5.18 Crack map for bridge TRU-534-1516 ........................................................................62

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Figure 5.19 Crack map for bridge TRU-45-2018. .........................................................................62 Figure 5.20 Side full depth cracks on bridge MED-162-2016.......................................................63 Figure 5.21 Maximum recorded crack width of 0.1 in. on bridge ASD-250-1864. ......................63 Figure 5.22 Typical parapet cracking (i) interior face (left) and (ii) exterior face (right). ............64 Figure 6.1 Concrete cores obtained from bridge deck, ASD-42-0656. .........................................65 Figure 6.2 Measuring the diameter of a typical concrete core. ......................................................65 Figure 6.3 Core samples prior to capping ......................................................................................66 Figure 6.4 Capped concrete core cylinders ....................................................................................66 Figure 6.5 Compressive strength test of a typical core specimen ..................................................66 Figure 6.6 Schematic of Typical Fracture Patterns (ASTM C39/39M).........................................67 Figure 6.7 Average compressive strength of concrete cores obtained from bridge ASD-42-065673 Figure 6.8 Compressive strength of deck cores cut from bridge ASD-42-0656 ...........................74 Figure 6.9 Densities of core specimens obtained from deck of .....................................................76 Figure 6.10 Crack width near the top of a typical core ..................................................................79 Figure 6.11 Crack width at 2 in. depth below the top surface of core C-10 ..................................79 Figure 6.12 Crack widths at various depths of the cores ...............................................................80 Figure 6.13 Acid soluble chloride content determination in the laboratory – titration method .....82 Figure 6.14 Acid-soluble chloride content by weight of cement of core specimens for bridge ASD-42-0656 .................................................................................................................................84 Figure 6.15 Profile of the acid-soluble chloride % content by weight of the cement for core specimens for bridge ASD-42-0656 ..............................................................................................85 Figure 6.16 Profile of the acid-soluble chloride % content by weight of the sample for core specimens for bridge ASD-42-0656 ..............................................................................................86 Figure 6.17 Profile of the acid-soluble chloride content by weight of cement for core specimens for bridge ASD-42-0656. ...............................................................................................................87 Figure 7.1 Axle load determination for the test truck ....................................................................90 Figure 7.2 Resulting axle loads for the test truck ..........................................................................90 Figure 7.3 General layout of crack measurement locations and typical truck positions on the bridge for static loading .................................................................................................................91 Figure 7.4 Typical stop positions for the truck with respect to location S1-3 ...............................92 Figure 7.5. Recording of crack widening on bridge deck under static loading .............................92 Figure 7.6 Sequence of loading for structural analysis (S1-3 region) ...........................................94 Figure 7.7 Bending moment and shear force diagram for load position 1 ....................................95 Figure 7.8 Bending moment and shear force diagram for load position 4 ....................................96 Figure 7.9 Bending moment and shear force diagram for load position 7 ....................................97 Figure 7.10 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#1) ......................................................................................................................................100 Figure 7.11 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#2) ......................................................................................................................................101 Figure 7.12 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#3) ......................................................................................................................................102 Figure 7.13 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#4) ......................................................................................................................................103 Figure 7.14 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#5) ......................................................................................................................................104

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Figure 7.15 Comparison of measured crack widths with predicted crack widths for truck loading S1-1 ..............................................................................................................................................105 Figure 7.16 Comparison of measured crack widths with predicted crack widths for truck loading S1-2 (#1) ......................................................................................................................................106 Figure 7.17 Comparison of measured crack widths with predicted crack widths for truck loading S1-2 (#2) ......................................................................................................................................107 Figure 7.18 Bending moment and shear force envelopes for a load from a moving truck ..........109 Figure 7.19 Measured crack widths for moving truck loading: S1-3 location for 5 mph ............111 Figure 7.20 Measured crack widths for moving truck loading: S1-3 location for 10 mph ..........112 Figure 7.21 Measured crack widths for moving truck loading: S1-3 location for 20 mph ..........113 Figure 7.22 Measured crack widths for moving truck loading: S1-3 location for 30 mph ..........114 Figure 7.23 Measured crack widths for moving truck loading: S1-1 location for 10 mph ..........115 Figure 7.24 Measured crack widths for moving truck loading: S1-2 location for 10 mph ..........116 Figure 7.25 Measured crack widths for moving truck loading: S1-2 location for 40 mph ..........117 Figure 7.26 Measured crack widths for static truck loading: PS1 parapet location ....................118 Figure 7.27 Measured crack widths for moving truck loading: PS1 parapet location for 5 mph.119 Figure 8.1 AASHTO HL93 truck and lane loads ........................................................................121 Figure 8.2 Typical moment diagram for slab dead load ..............................................................121 Figure 8.3 Typical moment envelope for HL 93 truck load ........................................................122 Figure 8.4 Two schemes used for examining the effect of stiffness on piers ..............................123 Figure 8.5 Predicted crack widths for four bridges using three equations ...................................129 Figure 8.6 Steel stress versus predicted crack width for bridge spans 28–35–28 ft. ...................133 Figure 8.7 Steel stress versus predicted crack width for bridge spans 40–50–40 ft. ...................133 Figure 9.1 Experimental program ................................................................................................135 Figure 9.2 Direct tension test specimen .......................................................................................136 Figure 9.3 Typical longitudinal section of the reinforced concrete test slab. ..............................137 Figure 9.4 Cross section details of the reinforced concrete slab ..................................................137 Figure 9.5 Typical epoxy-coated and uncoated steel reinforcements ..........................................138 Figure 9.6 Stress strain curves for steel reinforcement tested in the laboratory ..........................138 Figure 9.7 Formwork for the slabs and direct tension test specimens .........................................140 Figure 9.8 Typical reinforcement cages .......................................................................................140 Figure 9.9 Placement of concrete.................................................................................................141 Figure 9.10 Installation of strain gages on steel reinforcement ...................................................142 Figure 9.11 Typical arrangement of LVDT to measure crack widths .........................................142 Figure 9.12 Typical setup for DIC using high-speed cameras and painted contrasting dots.......143 Figure 9.13 Direct tension crack width test prisms......................................................................144 Figure 9.14 Test setup for a direct tension concrete prism ..........................................................145 Figure 9.15 Typical precut in one of the test slabs ......................................................................145 Figure 9.16 Schematic diagram of flexural crack width test setup. .............................................146 Figure 9.17 Failed direct tension specimens. ...............................................................................147 Figure 9.18 Crack width comparison of specimens U6-#3 to E6-#3 ...........................................147 Figure 9.19 Load versus maximum crack width for specimens E6-#4 and U6-#4. .....................148 Figure 9.20 Load versus maximum crack width for specimens E4-#4 and U4-#4 with ACI 224.2R-92.....................................................................................................................................148 Figure 9.21 Load versus maximum crack width for E6.25-#11 and U6.25-#11 .........................149

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Figure 9.22 Load versus maximum crack width for E6.25-#11 and U6.25-#11 .........................149 Figure 9.23 Load versus maximum crack width for #9 and #11 prisms ......................................150 Figure 9.24 Load versus maximum crack width for all specimens. ............................................150 Figure 9.25 Crack pattern for Slab U for loading/unloading levels and at failure.......................153 Figure 9.26 Crack pattern for Slab E for loading/unloading levels and at failure .......................154 Figure 9.27 Crack pattern for Slab U-P for loading/unloading levels and at failure ...................155 Figure 9.28 Crack pattern for Slab E-P for loading/unloading levels and at failure ...................156 Figure 9.29 Crack pattern for all slabs at failure .........................................................................157 Figure 9.30 Failure mode of Slab U.............................................................................................158 Figure 9.31 Failure mode of Slab E .............................................................................................158 Figure 9.32 Failure mode of Slab U-P .........................................................................................158 Figure 9.33 Failure mode of Slab E-P .........................................................................................159 Figure 9.34 Load versus crack width: experimental and theoretical comparison ........................160 Figure 9.35 Digital image correlation deflection results for Slab E-P .........................................161 Figure 9.36 Load versus midspan deflection for Slab U .............................................................162 Figure 9.37 Load versus midspan deflection for Slab E ..............................................................162 Figure 9.38 Load versus midspan deflection for Slab U-P ..........................................................163 Figure 9.39 Load versus midspan deflection for Slab E-P ..........................................................163 Figure 9.40 Load versus steel strain for Slab U ...........................................................................164 Figure 9.41 Load versus steel strain for Slab U-P .......................................................................165 Figure 9.42 Load versus steel strain for Slab E ...........................................................................165 Figure 9.43 Load versus steel strain for Slab E-P ........................................................................166 Figure 9.44 Load versus steel strain for all slabs at ultimate loading ..........................................166 Figure 10.1 Polypropylene and basalt MiniBar fiber...................................................................168 Figure 10.2 Load versus maximum crack width for #4 prisms with fiber ...................................170 Figure 10.3 Load versus midspan deflection for slabs at ultimate load .......................................172 Figure 10.4 Flexural test slabs after testing to failure ..................................................................173 Figure 10.5 Load versus crack width: experimental and theoretical comparison ........................174 Figure A.1 Longitudinal and cross (only top bars shown) section of typical slab .......................188 Figure A.2 Loading of a slab from the bottom ............................................................................192 Figure A.3 Control cover distance (Frosch 1999) .......................................................................195

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LIST OF TABLES

Table 1.1 List of Surveyed Bridges in an Earlier Study (Ganapuram et al. 2012) ..........................3 Table 2.1 Allowable Crack Widths from ACI 224R-01 (2008) ......................................................6 Table 2.2 Design Factors Affecting Stringer Supported Bridge Deck Cracks ..............................17 (Shing et al.,1999) ..........................................................................................................................17 Table 2.3 Influence of Factors Affecting Concrete Slab Deck Cracking for Stringer-Supported Bridge Decks (Krauss and Rogalla 1996) ......................................................................................20 Table 2.6 Maximum Steel Stress for Flexure in Reinforced Concrete Slabs ................................25 Table 2.7 Maximum Steel Stress for Flexure in Reinforced Concrete Slabs ................................25 Table 2.8 Crack Width Prediction Formulas from Different Codes (Rasidi et al. 2013) ..............27 Table 2.9 Empirical equations proposed by different researchers for the prediction of crack width (Rasidi et al. 2013) .........................................................................................................................28 Table 2.10 Formulas Proposed by Various Authors for Average Crack Spacing of Reinforced Concrete Members (Borosnyoi and Balazs 2005) .........................................................................29 Table 2.11 Qualitative Assessment of the Various Methods of Chloride Extraction and Analysis38 (Hunkeler et al, 2000) ....................................................................................................................38 Table 2.12 Chloride Limits for New Construction (ACI 318-11) .................................................38 Table 2.13 Reported Chloride Threshold Values in Total Chloride Content per Weight of Binder39 (Angst and Vennesland, 2009) .......................................................................................................39 Table 3.1 List of Selected Structural Slab Bridges ........................................................................44 Table 4.1 ODOT Bridge Inspection Condition Rating Guidelines ................................................48 (ODOT Manual of Bridge Inspection 2010) ..................................................................................48 Table 4.2 Deck Summary Condition Rating of Surveyed Bridges ................................................49 Table 5.1 List of Surveyed Structural Slab Bridges and Recorded Maximum Crack Widths .......51 Table 6.1 Compressive Strength Determination for Bridge Deck Cores C – 11, C – 8, and C – 1068 Table 6.2 Compressive Strength Determination for Bridge Deck Cores C – 5 and C – 7 ............69 Table 6.3 Compressive Strength Determination for Bridge Deck Cores C – 12 and C – 3 ..........70 Table 6.4 Compressive Strength Determination for Bridge Deck Core C – 9 ..............................71 Table 6.5 Compressive Strength Determination for Bridge Deck Cores C – 4 and C – 2 ............72 Table 6.6 Summary of Compressive Strength Test Results for Bridge ASD-42-0656 .................75 Table 6.7 Details of Bridge Deck Concrete Cores (Cracked Specimens): ASD–42–0656 ...........77 Table 6.8 Details of Bridge Deck Concrete Cores (Uncracked Specimens): ASD–42–0656 (continued) .....................................................................................................................................78 Table 6.8 Summary of Acid-Soluble Chloride Content of Cores Cut from Bridge ASD-42-065688 Table 7.1 Static Truck Load, Self Weight Moments and Crack Widths at S1-1 Location ............98 Table 7.2 Static Truck Load, Self Weight Moments and Crack Widths at S1-2 Location ............98 Table 7.3 Static Truck Load, Self Weight Moments and Crack Widths at S1-3 Location ............99 Table 7.4 Moving Truck Load, Moments, Steel Stress and Crack Widths at S1-3 Location ......110 Table 8.1 Unfactored and Service I Limit State Moments for Bridge ASD-42-0656 .................122 Table 8.2 Summary of Analysis Results for Bridges with 40'–50'–40' Spans .............................123 (TRU-534-1516, ASD-42-0656)..................................................................................................123 Table 8.3 Summary of Analysis Results for Bridge with 38'–47.5'–38' Spans (POR-224-1172)124 Table 8.4 Summary of Analysis Results for Bridge with 44'–55'–44' Spans (STA-225-076) ....124

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Table 8.5 Comparison of ODOT Moment Capacities of Typical Three-span Slab Bridges to Calculated Values ........................................................................................................................125 Table 8.6 Comparison of Unfactored Moments Given in ODOT Standards with Determined Values – HL93 Truck Load .........................................................................................................125 Table 8.8 Comparison of the Recorded and Predicted Maximum Crack Widths ........................128 Table 8.9 Predicted Crack Widths for Varying Steel Stresses for the Bridges Surveyed ...........130 Table 8.10 Theoretical Crack Widths at 40 ksi Stress Corresponding to Serviceability Limit State per ACI 318-11 ............................................................................................................................132 Table 9.1 Details of Direct Tension Specimens without Fiber ....................................................135 Table 9.2 Details of Flexural Crack Width Test Slabs without Fiber ..........................................136 Table 9.3 Steel Reinforcement Details (Provided by Akron Rebar Company) ...........................138 Table 9.4 Typical Mix Design for 4,500 psi Concrete ................................................................139 Table 9.5 Summary of Direct Tension Crack Width Test Results of Specimens without Fiber .151 Table 9.6 Summary of Results for Flexural Crack Width Test. ..................................................167 Table 10.1 Properties of Polypropylene and Basalt Fiber ...........................................................169 Table 10.2 Details of Direct Tension Crack Width Specimens ...................................................169 Table 10.3 Details of Flexural Crack Width Test Slabs ..............................................................170 Table 10.4 Summary of Direct Tension Crack Width Test Results of Specimens with/without Fiber .............................................................................................................................................171 Table 10.5 Summary of Results for Flexural Crack Width Test with/without Fiber ..................175 Table A.1 Unfactored and Service I limit state moments for bridge ASD-42-0656 ...................199 Table E.1 Results of Acid-Soluble Chloride Content – Cracked Specimen (C1-2) ....................207 Table E.2 Results of Acid-Soluble Chloride Content – Uncracked Specimen (C - 2) ................207 Table E.4 Results of acid-soluble chloride content – Uncracked Specimen (C - 4) ....................208 Table E.6 Results of acid-soluble chloride content – Cracked Specimens (C - 1) ......................209 Table E.7 Results of acid-soluble chloride content – Uncracked Specimen (C - 7) ....................210 Table E.8 Results of acid-soluble chloride content – Cracked Specimens (C - 8) ......................210 Table E.9 Results of acid-soluble chloride content – Uncracked Specimen (C - 9) ....................211 Table E.10 Results of acid-soluble chloride content – Cracked Specimen (C - 10) ....................212 Table E.11 Results of acid-soluble chloride content – Cracked Specimen (C - 11) ....................213 Table E.12 Results of acid-soluble chloride content – Uncracked Specimen (C - 12) ................214

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CHAPTER 1: INTRODUCTION

1.1 Statement of the Problem Non-prestressed steel reinforced concrete solid structural slab bridges are used by several DOTs in the United States. This type of bridge is common for short spans over typical four-lane highways and streams. Structurally, a typical continuous span structural (CSS) bridge spans parallel to the longitudinal axis between the abutments at the ends and intermediate pier supports. Common slab thicknesses can vary between 11 and 27 inches. A typical three-span bridge is shown in Figure 1.1.

Figure 1.1 A typical three-span structural slab bridge

One of the primary factors affecting concrete bridge durability is deck cracking. Despite a significant amount of research conducted by several researchers specifically studying the problem, cracking in reinforced concrete bridge decks is still a widespread problem in both old and newly constructed bridges. Previous research conducted by the lead author focused mainly on the cracking behavior of stringer supported bridge decks attributed to shrinkage of deck concrete (Ganapuram et al. 2012, Patnaik and Wehbe 2013). However, limited research is available on the cracking behavior of CSS slab bridge decks. The research community has yet to develop a consensus regarding a unified approach to address this problem. Cracks may develop in concrete bridge decks for a variety of reasons, but primarily they are caused by low tensile strength of the concrete, volumetric instability, or deleterious chemical reactions. Crack opening and spacing are also affected by the size and spacing of the reinforcing bars and the effective concrete area surrounding the bars (Soltani et al. 2013). Regardless of the causes, cracking is a

Intermediate Pier

2

serious problem for bridge decks, because cracks provide access to harmful, corrosive chemicals that deteriorate the reinforcing steel embedded within the concrete.

Once chloride and other corrosive agents penetrate concrete, corrosion of the embedded steel can initiate, leading to cracking and spalling, with eventual loss of cross-sectional area of the reinforcing steel. Such deterioration can affect the shear and moment capacity of structural concrete. Also, cracks allow water and de-icing salts to flow vertically through the bridge deck damaging the substructure (Krauss and Rogalla, 1996). According to a survey of 52 transportation agencies across North America, more than 100,000 bridges were found to crack early, typically when concrete is one month old (McDonald et al. 1995). Similar observations were recorded by Patnaik and Wehbe (2013).

In 2002, corrosion of the reinforcing steel in concrete highway bridges was estimated to have an annual direct cost to highway agencies of $8.3 billion. However, the indirect cost to users due to traffic delays and lost productivity was estimated to be ten times as much (Yunovich et al. 2002). Replacement costs for bridge decks are a significant portion of that direct cost (Virmani and Clemena, 1998). Cracks frequently form relatively early in the life of concrete bridge decks. Cracks may form well in advance of a bridge being open to traffic, and sometimes immediately following construction (Patnaik and Wehbe 2013, Schmitt and Darwin 1995). Concrete bridge deck cracking is influenced by several conditions, including construction practices, concrete mix proportions, material properties, structural design, and loading levels (Patnaik and Wehbe 2013, Ramakrishnan and Patnaik 2006). Early-age deck cracking not only reduces the service life of the bridge deck itself, but it also causes durability issues for the bridge as a whole. This report presents the details of a research study on the cracking behavior of continuous reinforced concrete structural slab bridges. Details of inspections of twelve three-span and one two-span continuous reinforced concrete structural slab bridges in Ohio are included. These bridges were carefully selected from the structural slab bridge inventory in the state. The bridges vary in terms of span length, roadway width, thickness of the deck slab, number of lanes, reinforcement ratio, and geographic location within the state. The study focused on the wide cracks, primarily those in the direction parallel and adjacent to the intermediate pier supports. Summaries of measured and predicted crack widths using existing methods are presented. Section and crack width analyses for select bridges were performed to compare the measured crack widths to the corresponding crack widths determined using different prediction equations. An experimental program was designed and tests were conducted to examine the cracking behavior of prism specimens and one-third scale slab specimens. The variables whose effects on crack widths were studied include (i) the use of epoxy-coated and black bars, (ii) reinforcing bar sizes, (iii) cover thickness, and (iv) the addition of basalt MiniBar or synthetic (polypropylene) fiber in concrete mixes. Digital image correlation was used to measure the widening of cracks under truck loading. Cores were cut from the deck of one of the bridges to investigate the depth and width of the cracks, acid-soluble chloride ion contents and compressive strength along the depth of the deck.

1.2 Motivation from Previous Work done by Ganapuram et al. A literature review suggested that few studies focused on cracking behavior of structural slab bridges. Also, there is no general agreement among different investigators on a prediction methodology for calculating crack widths. There is limited data that can explain the influence of

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the different variables on the cracking performance of bridge decks. This investigation addresses the cracking problems of structural slab bridges that were identified in a previous study for ODOT titled “Quantification of Cracks in Concrete Bridge Decks in Ohio District 3” by Ganapuram et al. (2012) with an emphasis on “non-shrinkage” cracks in CSS slab bridges. In this earlier study, twelve bridges were carefully selected from the inventory of bridges for ODOT District Three so that a variety of different reinforced concrete bridge decks would be represented. The survey included only bridges constructed after 2007 because ODOT began to use Quality Control/Quality Assurance (QC/QA) concrete in 2007. Also, due to safety concerns and traffic control issues, bridges located on interstate highways were not selected for the study. Bridges with curved or tangent alignments were also excluded. The selected bridges included both stringer supported bridge decks as well as CSS slab bridges (Table 1.1).

Table 1.1 List of Surveyed Bridges in an Earlier Study (Ganapuram et al. 2012)

County Route SLM Intersection Date Built Rehab Date Project # Concrete Slab Continuous Ashland SR 89 294 Branch Jerome Fork 2009 - 1037(09)

Lorain SR 83 1032 Carpenter Ditch 2009 - 1011(09)

Ashland US 42 656 Over ASD-060-1647 2009 - 8022(08)

Prestressed Concrete Beam Simple Huron US 250 1830 Over Vermilion River 2009 - 449(07)

Huron US 250 1841 Over CSX Railroad 2009 - 449(07)

Medina SR 18 1403 W. BR of Rocky River 2007 - 437(06)

Steel Beam Simple Lorain SR 301 2499 Over French Ditch 2008 - 277(07)

Steel Beam Continuous Wayne US 30 1953 Tracy Bridge Road 2007 - 251(06)

Ashland US 42 359 Claremont Ave (RT lane only) 1955 2009 1021(09)

Ashland SR 604 296 Over ASD-071-1559 1959 2009 522(08)

Crawford SR 602 600 Sandusky River 1960 2008 3000(08)

Erie US 250 1138 Huron River 1956 2008 6004(07)

The problem of cracking, the extent of cracking, and the documentation of the crack

densities along with pattern of cracking for the selected bridges were partially addressed in the previous project. The findings and recommendations from that study were as follows: 1. CSS slab bridges seemed to have a higher tendency to crack than stringer supported bridge

decks. 2. Several “structural” cracks as wide as 0.1 inch developed parallel to the intermediate

supports, and much wider than 0.007 inch limit (ACI-224R-01) as illustrated in Figure 1.2.

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These non-shrinkage cracks were unique to slab bridge decks and should be further investigated.

3. Further crack surveys should be performed on the bridges studied in a few years to determine if the crack densities increase over time.

4. QC/QA bridge decks measured smaller shrinkage crack densities. 5. The shrinkage crack densities of the bridge decks in Ohio were considerably lower than those

of the bridge decks of some other states.

ODOT routinely designs, builds, and maintains a large number of CSS slab bridges. Cracking of such bridges was also known to be a problem in other states. Therefore, it was determined to study the unique cracking developed in CSS slab bridges so that the causes can be understood and countermeasures established to minimize the same. 1.3 Research Objectives The primary objectives of this project are listed below:

• To determine if severe cracking in CSS slab bridges is a state-wide problem that is prevalent in all ODOT Districts and, if so, to determine the severity of the problem;

• To determine the sources and the consequences of the large non-shrinkage cracks commonly found parallel to the intermediate pier supports on CSS slab bridges. Further, to determine if crack densities change with time; and

• To develop minimization strategies for CSS slab bridges to be built in future, with an intent to develop a basis for potential modifications to design specifications.

In order to address the objectives listed above, this research included the following tasks:

1. Conduct a literature search: Literature search was conducted to investigate previous knowledge related to the cracking behavior of CSS slab bridges.

2. Perform a survey and compile an inventory of CSS slab bridges: To establish if the unique structural slab bridge cracking is a common problem within the different ODOT districts. Informal discussions with bridge engineers and inspectors from all 12 ODOT districts regarding CSS slab bridges were held.

3. Identify factors influencing potential cracking performance of structural slab bridges: Structural analysis and design, materials, construction, traffic and corrosion or other related parameters were identified in this task, and the influence of each factor was considered.

4. Conduct field inspections and measurements of crack widths and depths: The main objective of this task was to determine the depths and widths of existing cracks in the selected CSS slab bridge decks and to collect data for a detailed analysis.

5. Perform a detailed analysis of the selected bridges: Structural and crack width analysis were conducted on selected structural slab bridges to aid in developing moment envelopes of the selected bridges to facilitate an understanding of the stresses developed in the steel reinforcing bars under different live loading conditions.

6. Correlate field measurements with theoretical predictions: The field measurements and data collected in Task 4 were correlated with the results of the analyses obtained from Task 5 in order to verify the accuracy of various equations for predicting crack widths.

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7. Develop crack minimization and mitigation strategy for new bridges: Based on the findings from the preceding tasks, a crack minimization and prevention strategy was developed for new bridges.

8. Prepare a final report and documentation for the project: This draft final report provides documentation of the work performed in this study.

DL – dead load; LL – live load

Figure 1.2 Predicted crack widths for ASD–42–0656 using Gergely and Lutz equation 1.4 Report Organization This draft final report comprises twelve chapters. Chapter 1 presents a statement of the problem, provides the research motivation and objectives, and the details of the report organization. Chapter 2 provides a detailed literature review on the cracking behavior of structural slab bridge decks. Chapter 3 presents the results of a survey and inventory of CSS slab bridges in Ohio. Factors influencing the potential cracking performance of CSS slab bridges are presented in Chapter 4. Chapter 5 provides the results of field inspections. Chapter 6 describes the laboratory program for the determination of chloride content and compressive strength of bridge deck cores. The results from the measurements of crack openings using digital image correlation are presented in Chapter 7. Chapter 8 summarizes the results of the structural, section and crack width analyses. A detailed description and results of the experimental program on flexural and direct tension crack width tests are presented in Chapter 9. Chapter 10 describes the development of a potential crack minimization and mitigation method. Conclusions are presented in Chapter 11. Chapter 12 provides recommendations to ODOT for possible implementation of the research findings.

Bridge span lengths (ft.)

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0.12

0.10

0.08

0.06

0.04

0.02

0.0040-50-40

Cra

ck w

idth

(in.

)

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CHAPTER 2: LITERATURE REVIEW

The literature review conducted to understand the problem of CSS slab bridge deck cracking is summarized in this chapter. 2.1 Reinforced Concrete Bridge Deck Cracking Cracking in concrete is unavoidable due to its low tensile strength and low extensibility. Reinforced concrete structures having low steel stresses under service loads undergo very limited cracking, except for the cracks that occur due to shrinkage of concrete and temperature changes, (Piyasena 2002). However, in cases where service loads cause high steel stresses, particularly when using high-strength steel, visible cracking is expected under service loads. Wide and visible cracks affect the aesthetics of the structure and may provoke adverse criticism. They may also result in steel reinforcement being exposed to the environment, resulting in corrosion of the steel. Moreover, cracks may reduce the bending stiffness of reinforced concrete members, which may lead to excessive deflection. Slab systems designed to achieve low steel stresses at service load may serve their intended function with limited cracking. 2.2 Allowable Crack Widths To minimize the adverse effects of cracks on reinforced concrete bridge decks, the design of the same must ensure that the crack widths under normal service conditions are within allowable limits. The cracking of a reinforced concrete slab at service loads should not impact the appearance of the structure or lead to corrosion of the embedded reinforcement. According to ACI Committee report 224 (ACI 224R-01, 2008), crack widths equal to or greater than 0.007 in. can cause deterioration related to durability when bridge decks are exposed de-icing chemicals. According to these guidelines, crack widths in the range 0.01 to 0.015 in. are acceptable from aesthetic considerations. Table 2.1 shows a summary of the maximum allowable crack widths as suggested in the ACI 224 report.

Table 2.1 Allowable Crack Widths from ACI 224R-01 (2008)

Exposure Condition Maximum Allowable Crack Width Dry Air 0.016 in.

Humidity, Moist Air, Soil 0.012 in. Deicing Chemicals 0.007 in.

Sea Water 0.006 in. Water Retaining Structures 0.004 in.

2.3 Classification of Cracks in Reinforced Concrete Members

The literature review showed that reinforced concrete cracks could be classified in three different ways:

• Cracks that are dependent on applied loading, • Cracks independent of loading, and • Cracks based on orientation.

Figure 2.1 shows the classification of reinforced concrete cracks.

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Figure 2.1 Classification of cracks in reinforced concrete members

According to Leonhardt (1977), cracks formed in reinforced concrete members can be

classified into two main categories: (i) cracks caused by externally applied loads and (ii) cracks that occur independent of the loading conditions.

2.3.1 Cracks Dependent on Applied Loading Flexural cracks and inclined shear cracks are the two main types of cracks caused by externally applied loads. 2.3.2 Cracks Independent of Loading Cracks formed as a result of concrete shrinkage or temperature change are independent of applied loading. Cracks in this classification are typically grouped into two main categories: cracks that occur while the concrete is still plastic and cracks that occur after the concrete has hardened. Plastic shrinkage cracking and subsidence cracking have been identified to occur in plastic concrete. Thermal cracking and drying shrinkage cracking, are believed to be the primary causes of cracking in hardened concrete independent of loading conditions. 2.3.2.1 Plastic Shrinkage

Plastic shrinkage occurs in early-age, fresh concrete and results from excessive water loss. When the fresh concrete is placed into the forms, plastic shrinkage occurs when the surface water on the plastic concrete evaporates excessively. As the water in the concrete is removed, the voids that are produced begin to pull the cement particles closer together, which increases the internal pressure in the concrete (Cohen et al. 1990). This pressure continues to rise until it reaches a critical value at which plastic shrinkage cracking occurs. Water loss for concrete not only takes place through surface evaporation, but it also happens through the substructure or formwork for the concrete bridge deck. According to Schaels and Hoover (1988), environmental conditions, such as wind and temperature, have an influence on plastic shrinkage cracking of concrete. In order to reduce plastic shrinkage, the rate of water evaporation should be minimized. During high winds, concrete casting should be avoided, or wind breaks and fogging should be used to prevent water loss. Because water evaporation only occurs at the surface of the concrete, plastic shrinkage cracking only occurs at the surface.

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2.3.2.2 Autogenous Shrinkage Another source of tensile stress that can cause volumetric changes in concrete is due to

autogenous shrinkage in bridge decks, which results when the concrete becomes dehydrated (TRC E-C107, 2006). During construction, autogenous shrinkage occurs when no additional water is supplied to the concrete throughout the curing process, and the concrete begins to chemically consume its water in order to hydrate and meet the long-term chemical reaction demands of its cementatious materials (Brown et al. 2001). Autogenous shrinkage is much more prevalent in concrete mixes with low water-to-cement (w/c) ratios, because water demands often cannot be met by mix water. While autogenous shrinkage is usually small, it may become an important factor leading to shrinkage cracking in concrete where high-range-water-reducing (HRWR) admixture and fine materials, such as silica fume, are used (Paillere et al. 1989).

2.3.2.3 Drying Shrinkage

Drying shrinkage happens when the volume of the concrete changes due to the change in the water content during the time after placement of the concrete, and it can continue for several days to months after placement. The primary cause of drying shrinkage in concrete is the loss of absorbed water in circumstances where the concrete is exposed to an ambient environment with low relative humidity. Under these conditions, the atmosphere absorbs water from the concrete which results in shrinkage induced tensile forces. As water evaporation continues, the tensile stresses that are confined to the surface tension of the water are transferred to the capillary walls. This tension in the capillary walls causes the shrinkage of the concrete (Brown et al. 2001). Normally, a bridge deck will experience relative humidity ranging from 45% to 90%, which is when the capillary stress mechanism plays an important role. Many factors can directly affect the drying shrinkage of concrete, such as paste volume, water-to-cement ratio, aggregate type, environmental conditions, and curing methods. Of these factors, the paste volume is the most important; drying shrinkage will be greatly reduced if the paste volume is reduced (Xi et al. 2003, Tritsh et al. 2005, Darwin et al. 2007, Delatte et al. 2007).

2.3.2.4 Thermally Induced Shrinkage Thermal bridge deck cracking results from thermally-induced shrinkage in combination with restraint provided by girders, deck reinforcement, shear studs, and abutments. As concrete cures, hydration results in increasing concrete temperatures and expansion. As the concrete gains its initial strength through hydration and chemical reactions, the chemical reactions produce heat in the concrete that forces the concrete to set at temperatures well above the temperature of the surrounding steel. The concrete then begins to cool, but the temperature differences between the concrete and steel cause restraint, resulting in residual stresses. The other thermal load on the concrete results from the temperature cycles on a bridge deck. Once the heat of hydration process is complete, the weather and daily temperature can influence the thermal stresses. Temperature gradients can develop between the top of the bridge deck and the substructure of the bridge (Curtis and White 2007). 2.3.3 Cracks Based on Orientation The orientation of bridge deck cracks will vary, depending on the type of stresses that produce the cracks. Tensile stresses due to bending tend to produce cracks that propagate from the edge of the beam or slab in a direction parallel to the supports and perpendicular to the face

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of the beam, or slab. The Portland Cement Association grouped bridge decks cracks into five distinct categories: transverse cracking, longitudinal cracking, diagonal cracking, pattern or map cracking, and random cracking (PCA Durability 1970). Figure 2.2 shows classification of such cracks. The following subsections describe each category in more detail. 2.3.3.1 Transverse Cracking Transverse cracks are the main type of cracking found on reinforced concrete bridge decks. These cracks are fairly straight and are perpendicular to the longitudinal axis of the bridge deck in most cases. Transverse cracks are typically full depth and are spaced 3 to 10 feet apart along the length of the concrete bridge deck (Krauss and Rogalla, 1996). Ramey et al. (1997) found in their research that transverse cracks appear very early in the construction process; typically soon after casting the concrete. The location and positioning of transverse cracks affect the service life and maintenance costs for a reinforced concrete bridge deck.

Figure 2.2 Classification of cracks (NCHRP Synthesis 333, 2004) 2.3.3.2 Longitudinal Cracking Longitudinal cracks are cracks that form above the longitudinal reinforcing steel on top of the bridge deck and that run parallel to the longitudinal axis of the bridge deck, generally following the paths of the steel beams (Curtis and White 2007). Even though longitudinal cracks can appear on several types of bridges, Schmitt and Darwin (1995) observed that longitudinal

Diagonal Map

Transverse Longitudinal

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cracks occur primarily on solid slab decks and hollow slab decks. The researchers discovered that longitudinal cracking is caused by differential movements along the beams, and they believe that the differential movement results from the rotation of the beams about their longitudinal axes (Curtis and White 2007). However, based on his research, Frosch (2007) found that longitudinal deck cracking typically occurs above the edge of the girders. 2.3.3.3 Diagonal Cracking Although diagonal cracks can be found in all types of concrete bridge decks, these cracks are commonly associated with bridge decks having a skew. Through their research, Fu et al. (2007) found that decks with a skew have a greater tendency to exhibit diagonal cracking than their straight counterparts. In bridge decks with a skew, diagonal cracking occurs more in the corner areas as a result of restraint provided by the abutments and piers. These cracks typically start with a right angle to the deck edge that is along the direction of the supports (Fu et al., 2007). 2.3.3.4 Map or Pattern Cracking Pattern or map cracking, a series of random fine cracks, is prevalent on all types of concrete bridge decks and bridges. These cracks initiate at the bottom of the concrete deck and propagate their way up through the deck until they reach the surface (Curtis and White 2007). This type of cracking can occur when wet concrete is placed on dry precast concrete beams. Map or pattern cracks are also the product of improper curing, where the surface moisture on the concrete evaporates too quickly and the volumetric change of the concrete is restrained (Schmitt and Darwin 1995). 2.4 Cracking Behavior of Reinforced Concrete Structures Reinforced concrete members are designed assuming that the concrete has zero tensile strength. Steel reinforcement is provided to carry the tensile stresses needed to resist the applied loads. The ultimate strength design method is based on the concept that the member will reach its ultimate capacity under a loading condition that has a very low probability of being exceeded during the structure’s lifetime. This provides a margin of safety under service loads. It is expected in a properly designed reinforced concrete structure that service loads will produce tensile stresses that exceed the strength of plain concrete and will result in cracking. When a reinforced concrete member is subjected to tension, two types of cracks eventually form, as shown in Figure 2.3. One type is the visible crack that shows at the surface of the concrete, while the other type does not progress to the concrete surface. Broms (1965) called cracks of the first type “primary cracks” and those of the second type “secondary cracks.” Each of these two types of cracks has a different geometry. The primary or external cracks are widest at the surface of the concrete and narrowest at the surface of reinforcing bars (Goto 1971). The difference in crack width between the concrete surface and the reinforcing bar is small at low tension levels (just after crack formation), and this difference increases as the tension level increases; therefore, the crack width at the reinforcing bar increases more slowly than the width at the concrete surface with an increase in load. The deformations on the reinforcing bars tend to control the crack width by limiting the slip between the concrete and the steel (ACI-224.2R-92). The secondary, or internal, cracks increase in width with distance away from the reinforcement before narrowing and closing prior to reaching the surface of the concrete. Because of the

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variability in tensile strength along the length of a tension member, cracks do not all form at the same stress level (ACI-224.2R-92). Clark and Spiers (1978) estimated that the first major crack forms at about 90% of the average concrete tensile strength, and the last major crack forms at about 110% of the average tensile strength. There is a considerable variation in the spacing of external cracks. The variability in the tensile strength of the concrete, the bond integrity of the bar, and the proximity of previous primary cracks, which tend to decrease the local tensile stress in the concrete, are the main causes of this variation in crack spacing. For a normal range of concrete covers (1.25 to 3 in.), the average crack spacing will not reach the limiting value of twice the cover until the reinforcement stress reaches 20 to 30 ksi (Broms and Lutz 1965). The expected value of the maximum crack spacing is about twice that of the average crack spacing (Broms and Lutz 1965). That is, the maximum crack spacing is equal to about four times the concrete cover. This range of crack spacing for direct axial tension members is more than 20% greater than observed for flexural members. The number of visible cracks can be reduced at a given tensile force by simply increasing the concrete cover. With a large cover, a larger percentage of the cracks will remain as internal cracks at a given level of tensile force. However, as discussed in Section 3.5 of ACI-224.2R-92, increased concrete cover does result in wider visible cracks. Due to the larger variability in crack width in tension members, the maximum crack width in direct tension is expected to be larger than the maximum crack width in flexure at the same steel stress (ACI-224.2R-92). The stress gradient in a flexural member causes cracks to initiate at the most highly stressed location and to develop more gradually than in a tensile member that is uniformly stressed.

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Figure 2.3 Primary and secondary cracks in a reinforced concrete tension member (ACI-224.2R-92)

2.4.1 Shear Cracking Two types of inclined cracking occur in concrete structures: web-shear and flexural-shear cracking. Web-shear cracking begins from an interior point in a member (a beam or slab) when the principal tensile stresses exceed the tensile strength of the concrete. Web-shear cracking generally occurs near the supports of deep flexural members with thin webs, or near the inflection point or bar cut-off points of continuous beams, particularly if the beam is subjected to axial tension. Flexural-shear cracking is initiated by flexural cracking. When flexural cracking occurs, the shear stresses in the concrete above the crack are increased. The flexural-shear crack develops when the combined shear and tensile stress exceeds the tensile strength of the concrete. 2.4.2 Flexural Cracking Flexural members, such as beams and slabs, which are subjected to bending moments will develop flexural cracks when the stresses in the tension zone exceed the flexural tensile strength of plain concrete. For practical purposes, it can be assumed that the cracks will extend from the tension face to the location of the neutral axis of the cross section. Control of steel strain is one of the most effective means to limit crack widths in structures where crack widths need to be limited to prescribed maximums to perform the intended function.

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One of the most important factors controlling flexural cracks width under a given load is the magnitude of the tensile strain in the reinforcing steel. Other important factors affecting crack widths are the concrete cover over the reinforcing steel, the size of rebars, and the distribution of the steel in the tension zone. The cracking behavior of reinforced concrete members in axial tension is similar to that of flexural members, except that the maximum crack width is larger than that predicted by the corresponding expression for flexural members (Broms 1965). The lack of strain gradient and restraint imposed by the compression zone of flexural members is probably the reason for the larger tensile crack width (Soltani 2010). It is difficult to predict the number and width of flexural cracks because of the complex processes that are involved. As a result, there is no universal approach for estimating these quantities, and various design codes use different techniques. Some of these techniques are based on regression analyses of test data, while others are based on simplified models of the mechanics of crack formation, and the predictions that result from these models are accompanied by an inherently high uncertainty. Most methods are useful for predicting crack widths under short-term loading. Under sustained loads, however, the crack widths will increase with time. Figure 2.4 shows the types of cracking in reinforced concrete beams.

Figure 2.4 Types of cracking in reinforced concrete (https://www.google.com/search?q=flexural+cracking+in+reinforced+concrete+images)

2.5 Factors Related to Cracking in Concrete Bridge Decks Factors related to cracking in bridge decks mainly belong to one of the following groups:

• Material and mix design factors; • Construction and environmental factors; • Structural and foundation issues; • Traffic related factors; and • Other factors, including age of the bridge.

Figure 2.5 shows the categories of factors related to cracking in bridge decks, and the types of cracks that belong to each category.

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Figure 2.5 Factors related to cracking in concrete bridge decks

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2.5.1 Material and Mix Design Factors Several material and mix design factors are related to cracking in concrete bridges. These factors are discussed in greater detail in the following subsections. 2.5.1.1 Cement Type, Cement Content and Water to Cement Ratio Many researchers have shown that an increase in the cement content has a direct correlation to an increase in deck cracking (Krauss and Rogalla 1996, Kochanski et al. 1990). In general, these studies have shown that the maximum amount of cement used should be limited to 600 lb/yd3, which correlates to a 28-day unconfined compression strength near 4.5 ksi (Krauss and Rogalla 1996, Kochanski et al. 1990). Several researchers have confirmed that Portland cement Type II helps reduce cracking (Krauss and Rogalla 1996), which they attribute to this material’s reduction in early thermal gradient and shrinkage (Saadeghvaziri and Hadidi 2002). Reduced cracking has frequently been linked to a reduction in the water-to-cement (w/c) ratio, and a w/c ratio near 0.4 has been recommended by some researchers as a maximum value (Krauss and Rogalla 1996, Kochanski et al. 1990). 2.5.1.2 Concrete Strength and Slump Saadeghvaziri and Hadidi (2002) have reported that increased concrete compressive strength is commonly suggested to be a major cause of deck cracking. Increased unconfined compressive strength is usually associated with increased cement content, cement paste volume (water and cement), and higher hydration temperatures (Saadeghvaziri and Hadidi 2002, Schmitt and Darwin 1995). Despite significant research into the effects of concrete slump on cracking, researchers have yet to identify any definitive trends (Wan et al. 2010). Some have found that slump is not related to deck cracking, while others have reported that increasing slump actually decreases cracking (Cheng and Johnson 1985). Additionally, in analyzing cracking patterns in existing bridges, it was found that cracking increases with an increase in slump (Schmitt and Darwin 1995, Krauss and Rogalla 1996). 2.5.1.3 Air Content and Admixtures While air content is considered quite important in cooler climates to help with freezing and thawing cycles, it has also been found that increased air content can reduce deck cracking in warmer climates (Cheng and Johnson 1985). More specifically, a large decrease in cracking was found when the air content exceeds 6% (Schmitt and Darwin 1995). The effects of concrete admixtures are still not fully understood (Wan et al. 2010). In the case of set retarders, for example, various researcher groups have reached different conclusions. While some see no relationship between set retarders and cracking, others encourage their use, believing that the reduced rate of early temperature rise and early gain of modulus of elasticity will help prevent deck cracking (Saadeghvaziri and Hadidi 2002). It is generally agreed that the use of silica fume as an admixture can greatly increase the occurrence of cracking (Krauss and Rogalla 1996), and effect that is most likely due to the silica fume’s tendency to reduce bleeding within the concrete (Schmitt and Darwin 1995). 2.5.1.4 Concrete Mixes It is essential to design a concrete mix that balances the need for low permeability with the need to minimize cracking. Concrete mixtures made using higher cement contents are very

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conducive to cracking by producing higher heat of hydration, greater shrinkage, higher modulus of elasticity, and lower creep (TRC E-C107). With proper planning during material selection and mixture proportioning, a crack-resistant concrete having lower cement content, which still meets durability and performance specifications, can be produced. 2.5.2 Construction and Environmental Factors Construction issues can be classified into two types: physical construction issues that are within the control of the contractor, and environmental issues that are not (TRC E-C107). Both categories can be addressed through a combination of specifications, good concrete placement practices, project partnering, inspection, proper planning, and contractor awareness (TRC E-C107). 2.5.2.1 Weather, Concrete Temperature, and Curing For different ambient temperatures, minimum mix temperatures should be required to produce a good quality of concrete in order to reduce the potential for deck cracking (Wan et al. 2010). At least one study has found that adequate and timely curing is a key factor in reducing cracking (Saadeghvaziri and Hadidi 2002). In general, transportation agencies suggest at least 14 days of moist curing is needed (Krauss and Rogalla 1996). Some investigators suggest that there is no relationship between relative humidity and concrete deck cracking (Schmitt and Darwin 1995). However, plastic shrinkage is related to evaporation rates and concrete bleeding; consequently, it is possible that low humidity will increase evaporation rates and thus increase plastic shrinkage (Saadeghvaziri and Hadidi 2002). Wind velocity is very similar to relative humidity as it relates to concrete cracking. In practice, however, temporary wind breaks are typically erected over the surface of poured concrete, and no relationship has been established between wind velocity and deck cracking (Schmitt and Darwin 1995). 2.5.2.2 Time of Casting, Placement Length, and Placement Sequence Time of casting, placement sequence, and placement length can also influence deck cracking. Several investigators have found that casting during mid-evening or nighttime can reduce cracking, which may be due to the cooler temperatures experienced at night (PCA 1970, Krauss and Rogalla 1996). Although placement sequences are specified in bridge plans, contractors nevertheless will often employ their own placement sequence (Schmitt and Darwin 1995) in a given project. Some researchers suggest that deck cracking in continuous superstructure systems is most likely to occur in the positive moment region of the first span placed (Cheng and Johnson 1985). Finite element analysis has shown that increasing the length of the initial concrete placement (in positive moment regions) can reduce the residual dead load deck stresses by up to 70% throughout the deck, and it has been shown to leave a majority of the deck in residual compression, as opposed to tension (Cheng and Johnson 1985). 2.5.3 Structural Design Factors With proper flexural design and suitable detailing, structural issues are not anticipated to govern the cracking performance or maintenance needs of continuous slab bridges. In fact, according to LRFD Section 5.14.4.1, concrete slab bridges design per AASHTO specifications are considered satisfactory for shear, and shear need not be checked for design load and legal load ratings of concrete members. No service limit states are believed to apply to reinforced

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bridge decks for these types of bridges (Khan, 2010). In general, research on design factors as they relate to cracking behavior is limited (Saadeghvaziri and Hadidi, 2005). A few studies that considered these factors have reported the effects of design issues on cracking qualitatively. Table 2.2 shows design factors affecting stringer supported bridge deck cracks.

Table 2.2 Design Factors Affecting Stringer Supported Bridge Deck Cracks (Shing et al.,1999)

Design Factors Influence on Cracking Level of Influence

Recommendations

Continuous/Simple Span

Continuous span bridges are more susceptible to cracking than simple-span bridges.

Moderate

Girder Type Cracking is more severe with steel girders than with concrete girders

Moderate

Girder End Conditions

Restrained ends induce more cracks. Moderate to High

Reduce longitudinal restraints.

Deck Thickness Thinner decks are more susceptible to cracking. However, there is no conclusive evidence to support this.

Moderate Deck thickness should not be less than 8.5 in (215 mm).

Concrete Cover A thicker concrete cover may reduce settlement cracks.

Minor Use concrete cover not less than 2 in.

Girder Size and Spacing

Decks with larger girders at closer spacing are more susceptible to cracking than those with smaller girders at farther spacing.

Moderate

Transverse Reinforcing Bars

Most transverse cracks are right above the top transverse bars. A Minnesota study (reference?) indicates that decks with No. 6 bars have more severe cracks than those with No. 5 bars. They recommend using No. 5 bars at 5.5'' spacing or No. 6 bars at 6.5 to 7.0'' spacing.

Moderate

Avoid alignment of top and bottom transverse bars within the same vertical plane. Place top longitudinal steel above transverse steel. Use smaller bars at closer spacing.

Creep of Prestressed Concrete Girders

Creep of prestressed concrete girders may induce stresses in decks. Not clear Avoid tension in

prestressed concrete girders.

2.5.3.1 Other Design Factors Other design factors have been found to influence deck cracking. An increase in deck thickness was reported to reduce deck cracking (French et al. 1999, Krauss and Rogalla,1996, Kochanski et al. 1990, Ramey et al. 1997, Horn et al. 1972, Meyers, 1982). Meyers (1982) observed that bridge decks with a thickness equal to or greater than 10 in. are less susceptible to cracking. Kochanski et al. (1990) recommend a deck thickness of 8½ to 9 in., while French et al. (1999) recommended constructing decks with a thickness greater than 6¼ in. However, all these recommendations are for stringer-supported bridge decks and are, therefore, not valid for structural slab bridges.

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Based on an experimental study, Dakhil et al. (1975) reported that concrete over reinforcement is the most important factor affecting crack formation for stringer-supported bridge decks. Different values are documented as the optimum value of the cover depth over the top reinforcing bars:

• Minimum of 1.5 in. (PCA, 1970), and 3.5 in. (Bebaei and Hawkins, 1987) • Normally, 2 in. but 2.5 in. where deicing chemicals are used, and maintain 3 in. limit

(Ramey et al., 1997) • 1.5 – 3 in. cover recommended by others

Contrary to these studies, Meyers (1982) found that decks with cover of 3 in. and more seem to be more susceptible to cracking. Reinforcing detail is of paramount importance in controlling cracks in concrete structures. Bar size, type, spacing, and distribution affect cracking tendency of concrete decks greatly. Dakhil et al. (1975) in their experimental study reported that cracking increases with an increase in bar size. Other studies (Babaei and Hawkins, 1987: Schmitt and Darwin, 1999) also observed the same behavior and recommended limiting the bar size for stringer supported bridge decks. Since longitudinal bars control deck stresses and reduce cracking tendency, an increase in the amount of longitudinal reinforcement without increasing bar size is another recommendation proposed in some studies (Krauss and Rogalla, 1996; PCA, 1970; Kochanski et al. 1990; Horn et al., 1972; Frosch et al., 2002). Kochanski et al. (1990) as well as Ramey et al. (1997) recommended the maximum top transverse bar size of No. 5 and an increase in longitudinal reinforcement. Krauss and Rogalla (1996) recommended use of No. 4 bars with maximum spacing of 6 in. It is also suspected that due to subsidence of fresh concrete over reinforcing bars and formation of a weak plane, bridge decks tend to crack over transverse reinforcing bars. So, French et al. (1999) also recommended limiting transverse bar size and/or maximizing transverse bar spacing. Horn et al. (1975) noticed that tightly tied reinforcement develop more small cracks initially than tied reinforcements but ultimately the extent of cracking was the same. Issa (1999) attributed some cracking to insufficient reinforcing detail at joints between new and old decks. Ramey et al. (1997) suggest following recommendation for reducing deck cracking:

• Limiting the size of deck reinforcement to No. 5 • Reversing laying of transverse and longitudinal rebars in the top mat and staggering top

and bottom rebars so as not to create significant plane of weakness and using higher percentage of longitudinal steel

• Providing mat longitudinal steel on top, using steel with ratio greater than 0.002 and using the same for bottom mesh and trying to use No. 4 bars

• Reducing splices, extending deck transverse steel full width.

2.5.3.2 Span Type and Skew No direct relationship between deck skewness and cracking has been established (Wan et al. 2010). However, an increase in cracking has been observed when the transverse steel is placed parallel to the deck skew (Kochanski et al. 1990). There appears to be no relationship between bridge superstructure span length and cracking in bridge decks (Saadeghvaziri and Hadidi 2005, Schmitt and Darwin 1995). Simply supported girder configurations have large positive moments near girder midspan. Theoretically, the bending moment decreases to zero as

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one moves toward the end supports. Continuous superstructure configurations include girders that act as continuous beams over multiple supports. The continuous superstructure configuration includes a reduction in the positive moment near mid-span of the girders when compared to simply supported superstructure configurations. However, there is a large negative moment created in the girders over the intermediate supports. These negative moments cause tensile stresses in the deck, which can cause deck cracking when vehicle loads are present (Wan et al. 2010). Therefore, researchers suggest the use of simple span superstructure configurations as opposed to a continuous bridge design (Krauss and Rogalla 1996, Schmitt and Darwin 1995). A simply supported span bridge configuration allows free rotation against restraint, whereas continuous supported spans retrain the curvature of the deck at the interior supports, inducing more stresses and ultimately resulting in cracking (Brown et al. 2001) 2.5.4 Traffic Related Factors Although some studies (Krauss and Rogalla 1996, Stewart et al. 1969, Cady et al.1971) reported no relationship between daily traffic of a bridge and the tendency for deck cracking, (Mckeel 1985) observed that bridges carrying traffic at lower speeds exhibit less cracking than those that carry a large number of trucks at higher speeds. It is possible that the traffic loading in conjunction with the residual stresses built into the concrete during construction may result in additive tensile stresses that, when combined, exceed the tensile strength of the concrete (Wan et al 2010). 2.5.5 Other Factors Other factors that are considered to influence deck cracking include section stiffness, vibration and impact characteristics, and boundary conditions. 2.5.5.1 Section Stiffness Results of the research studies on the effect of section stiffness on deck cracking are not conclusive. Babaei and Hawkins (1987) suggested minimizing the flexibility of the superstructure. French et al. (1999) and Krauss and Rogalla (1996) reported that reducing deck stiffness reduces cracking. 2.5.5.2 Vibration and Impact Characteristics Perfetti et al. (1985) found no direct relationship between the frequency of vibration of the superstructure, speed and impact parameters, and transverse cracking. However, Babaei and Hawkins (1987) suggested that reducing the amplitude and frequency of structure vibration under live load may aid in preventing cracking. 2.5.5.3 Boundary Conditions Deck and/or girder support and end conditions can have a pronounced effect on deck cracking (French et al.1999). Cracking is more prevalent on continuous spans as compared to simple spans (Krauss and Rogalla 1996, Mayers 1982, Cady et al.1971, Cheng and Johnson 1985). Table 2.3 presents a more complete list of factors affecting cracking.

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Table 2.3 Influence of Factors Affecting Concrete Slab Deck Cracking for Stringer-Supported

Bridge Decks (Krauss and Rogalla 1996)

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2.6 Control of Crack Width and Spacing The purposes for crack control in concrete includes maintaining good appearance

(exposed to view), corrosion protection (exposed to aggressive environments), and water tightness (marine/sanitary structures). Since the 1970s, various approaches have been used to control the width and spacing of cracks in concrete. Code provisions to control the crack width and spacing are discussed in the following subsections. 2.6.1 American Concrete Institute (ACI) Approach In this subsection, two approaches for crack control that were recommended by the American Concrete Institute (ACI) are examined. 2.6.1.1 ACI 318-95 From 1971 through 1995, ACI 318 restrictions concerning distribution of tension reinforcement were based on limiting the width of surface cracks. ACI 318-95 code included provisions for crack control based on crack widths of 0.016 in. and 0.013 in. for interior and exterior applications, respectively. ACI 318-95 requirements for flexural crack control in beams and one-way slabs (with a span-to-depth ratio in the range of 15 to 20) at the level of the tensile reinforcement were based on the Gergely–Lutz equation (Gergely and Lutz 1968) which were derived from regression analyses using data from several crack width studies. In their analysis of flexural crack widths at the level of the reinforcement and on the bottom face of the member, Gergely and Lutz found that:

• The steel stress is the most important variable; • The cover thickness is an important variable, but it is not the only consideration; • The bar diameter is not a major variable; • The size of the side crack width is reduced by the proximity of the compression zone in

the flexural members; • The bottom crack width increases with the strain gradient; and • The major variables are the effective area of concrete, the number of bars, the side or

bottom cover, and the steel stress.

The equations that were considered to best predict the probable maximum bottom crack width and side crack width are presented in Equations 2.1 and 2.2, respectively: 𝑤𝑏 = 0.091�𝑡𝑏𝐴

3 𝛽(𝑓𝑠 − 5) 𝑥 10−3 [2.1]

𝑤𝑠 = 0.091 �𝑡𝑏𝐴3

1+𝑡𝑠ℎ(𝑓𝑠 − 5)𝑥 10−3 [2.2]

where wb = most probable maximum crack width at the bottom of beam (in.); ws = most probable maximum crack width at the level of reinforcement (in.); tb = bottom cover to center of bar (in.); ts = side cover to center of bar (in.); β = ratio of the distance between the neutral axis and tension face to the distance between the neutral axis and the reinforcing steel (about 1.20 in beams); fs = reinforcing steel stress (ksi); A = area of concrete symmetric with reinforcing steel divided by number of bars (in.2); h1 = distance from neutral axis to the reinforcing steel (in.).

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A simplification of Equation 2.1 yields the following with (fs - 5) nearly equal to 0.838fs: 𝑤 = 0.076𝛽𝑓𝑠�𝑑𝑐𝐴

3 𝑥 10−3 [2.3] where w= most probable maximum crack width (in.) and dc = thickness of cover from the extreme tension fiber to the closest bar (in.). When the strain εs in the steel reinforcement is used instead of stress fs, Equation 2.3 becomes 𝑤 = 2.2𝛽𝜀𝑠�𝑑𝑐𝐴

3 [2.4] The cracking behavior in thick one-way slabs (with a span-to-depth ratio of 15 to 20) is similar to that in shallow beams. For one-way slabs with a clear concrete cover in excess of 1 in., Equation. 2.4 can be applied if a value of β of 1.25 to 1.35 is used. ACI 318-95 Section 10.6 used Equation 2.4 with β = 1.2 in the following form: 𝑧 = 𝑓𝑠�𝑑𝑐𝐴

3 [2.5] Equation. 2.5 permits the calculation of z with fs equal to 60% of the specified yield strength fy in lieu of an exact calculation. In ACI 318-95 and earlier code versions, the maximum allowable z (175 kips per in.) for interior exposure corresponds to a probable crack width of 0.016 in. This level of crack width may be excessive for aesthetic concerns. ACI 318 has allowed a value of z = 145 kip per in. for exterior exposure based on a crack width value of 0. 013 in. 2.6.1.2 ACI 318-11 Currently, the ACI 318 requirements are based on the belief that it can be misleading to calculate explicit crack widths, given the inherent variability in cracking. The three important parameters in flexural cracking are steel stress, cover, and bar spacing; of these, steel stress is the most important parameter. ACI 318-2011 committee is now of the opinion that crack width is not directly related to long-term durability, with cover depth and concrete quality being of greater importance. It can be misleading to use a design method that purports to effectively calculate crack widths. A re-evaluation of crack width data (Frosch 1999) provided a new equation based on the physical phenomenon for the determination of the flexural crack widths of reinforced concrete members. This study showed that previous crack width equations are valid for a relatively narrow range of covers up to 2.5 in.

ACI 318-11 does not make distinction between interior and exterior exposure. The ACI 318-11 equation for determining the maximum spacing of flexural reinforcement closest to the tension face to affect adequate crack control is given below: 𝑠 = 15 �40,000

𝑓𝑠� − 2.5𝑐𝑐 ≤ 12 �40,000

𝑓𝑠� [2.6]

where fs = calculated stress in reinforcement closest to the tension face at service load, which is computed based on the unfactored moment. It is permitted to take fs as 2/3fy; cc = the least distance from surface of reinforcement to the tension face; and s = center-to-center spacing of flexural tension reinforcement nearest to the surface of the extreme tension face (in.).

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2.6.2 AASHTO Approach The American Association of State Highway and Transportation Officials (AASHTO 2012) equation for determining the maximum spacing of flexural reinforcement in the layer closest to the tension face to affect adequate crack control is given below: 𝑆 ≤ 700𝛾𝑒

𝛽𝑠𝑓𝑠𝑠− 2𝑑𝑐 [2.7]

in which 𝛽𝑠 = 1 + 𝑑𝑐

0.7(ℎ−𝑑𝑐), where γe is an exposure factor (equal to 1.00 for a Class 1 exposure

condition or 0.75 for a Class 2 exposure condition); dc = thickness of concrete cover measured from extreme fiber to the center of the flexural reinforcement located closest thereto (in.); fss = the tensile stress in steel reinforcement at the service limit state (ksi); h = overall thickness or depth of the member (in.); and s = spacing of reinforcement. 2.6.3 CEB/FIP Approach The Comite Euro-International du Beton and Federation Internationale de la Precontrainte (CEB/FIP) approach (CED/FIP 1990) is different from the ACI approach. The characteristic crack width wk in beams is calculated in terms of the length, ls,max, over which slip occurs between the steel reinforcement and the concrete. The CEB-FIP code defines the characteristic crack width as the width that 5% of cracks will exceed, and it is equal to 1.7 times the mean crack spacing. 𝑤𝑘 = 𝑙𝑠,𝑚𝑚𝑚(𝜀𝑠𝑚 − 𝜀𝑐𝑚 − 𝜀𝑐𝑠) [2.8] where εsm = average reinforcement strain within segment length, ls,max; εcm = average concrete strain within segment length, ls,max; εcs = strain of concrete due to shrinkage. The characteristic crack wk cannot exceed the limiting crack width, wlim, that is, wk ≤ wlim, where wlim = nominal limit value of the crack width specified for cases with expected functional consequences of cracking. 𝑙𝑠,𝑚𝑚𝑚 = 2 (𝜎𝑠2−𝜎𝑠1 ) ɸ𝑠

4𝜏𝑏𝑏 [2.9]

where σs2 = reinforcement stress at the crack location (MPa); σs1 = reinforcement stress at point of zero slip (MPa); ɸs= reinforcing bar diameter or equivalent diameter of bundled bars (mm) τbk = lower fractile value of the average bond stress (MPa), which is equal to 1.8 fctm(t); and fctm(t) = the mean value of the concrete tensile strength at the time that the crack forms. For stabilized cracking, the expression can be simplified as follows: 𝑙𝑠,𝑚𝑚𝑚 = ɸ𝑠

3.6𝜌𝑠,𝑒𝑒 [2.10]

where ρs,ef = the effective reinforcement ratio.

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2.6.4 Standards Association of Australia Approach For reinforced concrete beams and slabs, flexural cracking is deemed by the Standards Association of Australia (AS3600-2009) to be controlled (cracks widths will be less than 0.0118 in.) if each of the following is satisfied:

• The quantity of tensile reinforcement in a beam or slab provides an ultimate strength at least 20% higher than the cracking moment calculated, assuming σcs = 0.

• The distance from the side or suffit of the member to the center of the nearest longitudinal bar shall not exceed 4 in.

• The center-to-center spacing of bars near a tension face of a beam or slab shall not exceed 11.81 in. for a beam and the lesser of two times the slab thickness and 11.81 in. for a slab.

• The stress in the tensile steel is less than a limiting value.

For members subject primarily to flexure, the calculated steel stress caused by the serviceability design moment shall not exceed the larger of the maximum steel stresses in Table 2.4 and 2.5 for beams and Tables 2.6 and 2.7 for slabs.

Table 2.4 Maximum Steel Stress for Tension or Flexure in Reinforced Concrete Beams

Nominal bar diameter (in.)

Maximum steel stress (ksi)

0.39 52 0.47 48 0.63 41 0.79 35 0.94 30 1.10 27 1.26 23 1.42 20 1.57 17

Table 2.5 Maximum Steel Stress for Flexure in Reinforced Concrete Beams

Center-to-center spacing (in.)

Maximum steel stress (ksi)

1.97 52 3.94 46 5.91 41 7.87 35 9.84 29 11.81 23

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Table 2.6 Maximum Steel Stress for Flexure in Reinforced Concrete Slabs

Nominal bar diameter (in.)

Maximum steel stress (ksi) for overall depth Ds

Ds ≤ 11.81 in. Ds > 11.81 in. 0.24 54 65 0.31 50 58 0.39 46 52 0.47 44 48 0.63 38 41 0.79 35 0.94 30

Table 2.7 Maximum Steel Stress for Flexure in Reinforced Concrete Slabs

Center-to-center spacing (in.)

Maximum steel stress (ksi)

1.97 52 3.94 46 5.91 41 7.87 35 9.84 29 11.81 23

2.6.5 Eurocode EC2 Approach The Eurocode EC2 (Euro EC2 1997, Nawy 2001) requires that cracking be limited to a level that does not impair the proper functioning of the structure or cause its appearance to be unacceptable. It limits the maximum design crack width to 0.012 in. for sustained load under normal environmental conditions. This ceiling is expected to be satisfactory with respect to appearance and durability. Stricter requirements are stipulated for more severe environmental conditions. The code stipulates that the design crack width be evaluated from the following expression: 𝑤𝑘 = 𝛽𝑠𝑟𝑚𝜀𝑠𝑚 [2.11] where wk = design crack width; srm = average stabilized crack spacing; εsm = mean strain under relevant combination of loads and allowing for the effect such as tension stiffening or shrinkage; and β = coefficient relating the average crack width to the design value, which is equal to 1.7 for load-induced cracking and for restraint cracking in sections with minimum dimension in excess of 800 mm (32 in.).

The strain εsm in the section is obtained from the following expression:

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𝜀𝑠𝑚 = 𝜎𝑠/𝐸𝑠[1 − 𝛽1𝛽2(𝜎𝑠𝑟/𝜎𝑠)2] [2.12] where σs = stress in the tension reinforcement computed on the basis of a cracked section (MPa); σsr = stress in the tension reinforcement computed on the basis of a cracked section under loading conditions that caused the first crack (MPa); β1 = coefficient accounting for bar bond characteristics (1.0 for deformed bars and 0.5 for plain bars); β2 = coefficient accounting for load duration (1.0 or single short-term loading and 0.5 for sustained or cyclic loading); and Es = modulus of elasticity of the reinforcement (MPa).

The average stabilized mean crack spacing srm is evaluated from the following expression: 𝑠𝑟𝑚 = 50 + 0.25𝑘1𝑘2𝑑𝑏

𝜌𝑡 ,𝑚𝑚 [2.13]

where db = bar diameter; ρt = effective reinforcement ratio (As/Act); the effective concrete area in tension Act is generally the concrete area surrounding the tension reinforcement of depth equal to 2.5 times the distance from the tensile face of the concrete section to the centroid of the reinforcement. For slabs where the depth of the tension zone may be small, the height of the effective area should not be taken greater than [(c – db)/3], where c = clear cover to the reinforcement (mm); k1 = 0.8 for deformed bars and 1.6 for plain bars; and k2 = 0.5 for bending and 1.0 for pure tension. 2.7 Review of Crack Width and Spacing Equations Cracking of concrete is a complex phenomenon (Oh and Kang 1987), and several researchers have developed equations for predicting the crack widths in reinforced concrete using different approaches. Some of the findings were based on experiments, while others have used only numerical expressions and values derived from the literature. Some authors used both experimental and analytical methods. Table 2.8 presents the crack width prediction formulas from different codes. Table 2.9 presents the empirical equations proposed by different researchers for the prediction of crack widths. Table 2.10 summaries formulas proposed by various authors for the average crack spacing (srm). Crack width analysis constitutes an essential step in the serviceability design of concrete structures. The tensile resistance of concrete is normally neglected in design. Slab systems designed with low steel stresses at service load may serve their intended function with very limited cracking. Many variables influence the width and spacing of flexural cracks in reinforced concrete beams and one-way slabs. Because of the complexity of the problem, a number of approximate, semi-theoretical, and empirical approaches have been developed for the determination of the width of flexural cracks, each approach containing a selection of variables. In early theories, crack widths were believed to depend largely on the bond between the concrete and steel; the spacing between cracks and crack width were determined from the tensile strength of the concrete and the rate of transfer of steel tension to the concrete by bond. The crack width was generally postulated to be the elongation of the steel between two cracks. The crack width equations developed based on these basic considerations have been modified by many researchers on the basis of experimental results. An alternative early approach was the no-slip theory, in which it was assumed that there was no slip of the steel relative to the

27

concrete. The crack in this approach was therefore assumed to have zero width at the surface of the reinforcing bar and to increase in width in the direction of the surface of the concrete (i.e., the crack was wedge-shaped). A review of the methods for determining the width of flexural cracks in reinforced concrete slab bridges is presented. In the more recent methods, crack widths have been observed to be primarily a function of the stresses in the steel, the thickness of concrete cover, the distribution of the steel reinforcement, and the relative distances from the neutral axis of the reinforcing steel and the extreme concrete tension fiber. However, crack width measurements have large scatter, even in the results derived from careful laboratory work. Crack width is also influenced by shrinkage and other time-dependent effects, as well as by repeated loading. Some of the recent methods for determining the maximum crack width are discussed in the section below.

Table 2.8 Crack Width Prediction Formulas from Different Codes (Rasidi et al. 2013)

28

Table 2.9 Empirical equations proposed by different researchers for the prediction of crack width (Rasidi et al. 2013)

29

Table 2.10 Formulas Proposed by Various Authors for Average Crack Spacing of Reinforced Concrete Members (Borosnyoi and Balazs 2005)

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2.7.1 Gergely and Lutz Equation The method most accepted in the United States for beams and one-way slabs is that developed by Gergely and Lutz (1968), who subjected data from previous investigations to statistical analysis to determine the importance of the variables involved. At extreme tension fiber, the maximum crack width predicted by Gergely and Lutz is

Wmax = 0.076 �tbA3 h2h1

fs X 10−6 in. [2.14] where wmax = crack width on the bottom of the member; tb = concrete cover from bottom of member to center of lowest level of steel; ts = concrete cover from side of member to center of nearest level of steel; R = h2/h1 = ratio between strain at bottom of member and strain at level of reinforcement; fs = steel stress; and A = average effective area of concrete in tension surrounding the reinforcement. 2.7.2 Chowdhury and Loo Equation A new formula for predicting the average crack widths in reinforced and partially prestressed concrete beams was developed through the incorporation of four governing parameters by Chowdhury and Loo (2001). They checked the performance of the proposed formula against their test results, which included crack spacing and crack width measurements from 18 reinforced and 12 partially prestressed concrete beams. Also included in the comparison were published data on 76 beams from other laboratory investigations. The comparative study indicated that the predictions were accurate.

Chowdhury and Loo have proposed two crack width equations. The average crack width equation suggested by them is given below:

Wcr = �fsEs� �0.6(c− s) + 0.1 �ɸ

ρ�� mm. [2.15]

The maximum crack width is calculated by using the equation below:

𝑊𝑚𝑚𝑚 = 1.5𝑊𝑐𝑟 [2.16] where Wcr = average crack width; Wmax = maximum crack width; ɸ = bar diameter; ρ = reinforcement ratio; c = concrete cover; s = average spacing between the reinforcing bars; Es = the modulus of elasticity of steel; and fs = steel stress. 2.7.3 Oh and Kang Equation Prediction formulas for the maximum crack width and average crack spacing in reinforced concrete flexural members were proposed by Oh and Kang (1987). An experimental program was set up and a series of tests on reinforced concrete beams was conducted. The test results from those experiments were compared with the predictions obtained from the proposed equations. The proposed formulas were also compared with other test data on crack widths and crack spacing. In addition to the prediction equation for the actual values of crack widths under specific applied loads, new design formulas for the maximum crack width were also proposed. Their comprehensive comparisons with 747 data points indicated that the proposed formulas for

31

the maximum crack width show better correlation with various test data than the Gergely and Lutz formula (Oh and Kang 1987). They concluded that the crack width design formula of ACI 318 may be conservative in some cases. Five reinforced concrete test beams were designed by Oh and Kang to investigate crack width and crack spacing. They selected influencing design variables that greatly affect crack spacing and width in their design of test beams. Those main design variables included the concrete cover, diameter of steel bars, reinforcement ratios, spacing of steel bars, and steel stress. The equation developed by Oh and Kang for determining the crack width of a reinforced concrete structure is given below:

WmaxD

= ao(εs − 0.0002)R in. [2.17]

ao = 159 �tbh2�4.5

+ 2.83 � A1As1�13 [2.18]

where A1 = average effective area of concrete around each reinforcing bar; As1 = area of each reinforcing bar; ɛs = axial tensile strain of bars; tb = bottom cover measured from the center of lowest bar; h2 = Distance from the extreme tension fiber to the neutral axis; h3 = distance from the centroid of steel to the neutral axis; R = h2/h3 ; and D = bar diameter. 2.7.4 Patrick and Wheeler Equation Patrick and Wheeler (2000) used classical theory as a basis for deriving equations for predicting cracking in tension members. They considered the behavior of a reinforced concrete tension element with a longitudinal reinforcing bar placed concentrically in its cross-section and loaded at each end by a known force. When the bar was loaded in tension, some bond breakdown occurred between the bar and the concrete near the ends of the element. Further in, a uniform strain distribution was assumed to develop, and slip between the steel and concrete remained at zero. The first crack formed at the weakest section somewhere in the region of uniform strain when the tensile strength of the concrete was reached. This assumes that the tensile capacity of the bar exceeds that of the concrete; when they are equal, it is referred to as the “critical steel content.” Otherwise, the bar will fail in tension outside the concrete before the concrete can crack. Just as with the ends of the concrete element, the force in the steel bar at the crack equals the applied load, while the concrete is unstressed at the crack faces. Also, slip occurs and bond stress, τ, develops between the concrete and the steel bar over a transfer length, ltr, of each side of the crack. It is by bond that the stress is transferred into the concrete. Depending on the overall length of the element in relation to the transfer length, other cracks can form at slightly higher loads. They explained that, theoretically, the spacing between cracks that form adjacent to each other cannot be less than ltr, and it cannot exceed 2ltr. Two cracks that formed at cross-sections 1 and 2 were considered, as shown in Figure 2.6. Patrick and Wheeler assumed that a new crack can only form between them if they are at least 2ltr apart. It was observed that if the spacing is just above this limit and another crack forms, then the crack spacing will be close to ltr. Thus is was written as:

Scr.min = ltr [2.19]

32

Scr.max = 2ltr [2.20]

They used equilibrium of longitudinal forces to establish that if τm is the average bond stress over the transfer length ltr, ft is the tensile strength of concrete and ∑o is the bar perimeter, then: 𝑙𝑡𝑟 = 𝐴𝑐𝑓𝑡

𝜏𝑚∑𝑜 [2.21]

Substituting bar perimeter ∑o = 4Ast/db and reinforcement ratio for tension ρs = Ast/Ac, it implied that: 𝑙𝑡𝑟 = 𝑑𝑏𝑓𝑡

4𝜏𝑚𝜌𝑠 [2.22]

From Equations 2 and 4 the maximum crack spacing became: 𝑠𝑐𝑟.𝑚𝑚𝑚 = 𝑑𝑏𝑓𝑡

2𝜏𝑚𝜌𝑠 [2.23]

Finally, they used a crack width equal to the elongation of the steel between two adjacent cracks less the elongation of the concrete, and defined as:

𝑤𝑚𝑚𝑚 = 𝑠𝑐𝑟.𝑚𝑚𝑚(𝜀𝑠𝑚 − 𝜀𝑐𝑚) [2.24] where εsm and εcm are the mean steel and concrete strains over transition length ltr. At the end of the transition length, the steel bar is fully bonded to the concrete, and the tensile force in the steel at this section is given by:

𝑇𝑏′ = 𝑇𝑏𝑛𝜌𝑠

1+𝑛𝜌𝑠 [2.25]

where Tb is the tensile force in the bar at cracked sections. Assuming a uniform bond stress over transition length ltr, the average strain in the bar was derived as:

𝜀𝑠𝑚 = 12𝐸𝑠

�𝑇𝑏𝐴𝑠𝑡

+ 𝑇𝑏′

𝐴𝑠𝑡� [2.26]

From Equation. 7, the average strain was found to be as follows:

𝜀𝑠𝑚 = 𝑓𝑠2𝐸𝑠

�1+2𝑛𝜌𝑠1+𝑛𝜌𝑠

� [2.27] Neglecting the elongation of the concrete, that is εcm = 0 They derived an approximate equation for maximum crack width as given below: 𝑤𝑚𝑚𝑚 = 𝑠𝑐𝑟.𝑚𝑚𝑚

0.65𝑓𝑠𝐸𝑠

[2.28]

33

𝑤𝑚𝑚𝑚 = 𝑑𝑏𝑓𝑡

2𝜏𝑚𝜌𝑠

0.65𝑒𝑠𝐸𝑠

[2.29] Their study proved that the interdependence between crack width, bar diameter and steel stress could be established using classical theory.

Figure 2.6 Cracking in tension (Patrick and Wheeler 2000)

34

2.7.5 Frosch Frosch (1999) observed a significant shortcoming of Gergely-Lutz (1968) and Kaar-Mattock (1963) crack width equations in that they were both developed empirically using statistical analysis of experimental data that was limited in the range of concrete covers investigated. He observed that only three test specimens had concrete covers greater than 2.5 in. A crack width model developed by Frosch illustrates that crack spacing and width are functions of the distance between the reinforcement steel. His study showed that crack control can be achieved by limiting the spacing of the reinforcing steel. Frosch found out that maximum bar spacings can be determined by limiting the crack widths to acceptable limits. Based on his physical model, the equation for the calculation of maximum crack width for uncoated reinforcement is given below:

𝑤𝑐 = 2 𝑓𝑠𝐸𝑠𝛽�𝑑𝑐2 + (𝑠

2 )2 [2.30]

Frosch (1999) recommended the equation be multiplied by a factor of 2 in the case of epoxy-coated reinforcement. The equation was rearranged to solve for the permissible bar spacing.

𝑠 = 2 �(𝑤𝑐𝐸𝑠2𝑓𝑠𝛽

)2 − 𝑑𝑐2 [2.31]

where s = maximum permissible bar spacing (in.); wc = limiting crack width (in.); Es = 29,000 (ksi); fs = 0.6 fy (ksi); β = 1.0 + 0.08dc; and dc = bottom cover measured from center to lowest bar. A reinforcement stress of 60 percent of yield was selected to account for the service load condition. Also, the following design recommendation is presented based on the physical model that addresses the use of both coated and uncoated reinforcement. The maximum spacing of reinforcement was given as follows: 𝑠 = 12𝛼 [2 − 𝑑𝑐

3𝛼𝑠] ≤ 12𝛼𝑠 [2.32]

where 𝛼𝑠 = 36

𝑓𝑠𝛾𝑐 [2.33]

where dc = thickness of concrete cover measured from extreme tension fiber to the center of bar or wire located closest thereto (in.); s = maximum spacing of reinforcement (in.); αs = reinforcement factor; and γc = reinforcement coating factor, which is 1.0 for uncoated reinforcement or 0.5 for epoxy coated reinforcement, unless test data can justify a higher value. 2.7.6 Kaar and Mattock An extensive laboratory investigation of concrete members reinforced with high strength deformed bars was carried out by Kaar and Mattock (1963). The investigation included cracking behavior of three series of flexural members: half-scale highway bridge girders, comparable

35

rectangular and Tee girders, and slab-strip specimens. A method of crack control in design was proposed for members reinforced with deformed bars. The proposed maximum crack width equation is given below: 𝑤𝑚𝑚𝑚 = 0.115√𝐴 4 𝑓𝑠 𝑋 10−6 𝑖𝑖. [2.34] where fs = tensile stress in steel reinforcement, with fs ≤ 70 ksi; and A = area of concrete in tension surrounding each reinforcing bar. 2.8 Cyclic and Sustained Loading Effect on Bridge Deck Cracks Both cyclic and sustained loading account for increasing crack widths (Nilson 2010). While there is large amount of scatter in test data, results of fatigue tests and sustained loading tests indicate that a doubling of crack width can be expected with time (ACI-224R-01). Under most conditions, the spacing of cracks does not change with time at constant levels of sustained stress or cyclic stress range (Nilson 2010). Repeated loading causes existing cracks to widen through progressive slip between the reinforcement (Soltani 2010). At the same time, existing cracks also propagate further towards the compression side of the member. 2.9 Effect of Corrosion of Reinforcing Bars on Concrete Bridge Decks When steel corrodes in the concrete, it causes expansion of the steel reinforcement. The expansion of the steel can cause cracking of the concrete. This will affect the bond strength. Corrosion causes spalling in concrete, which is loss of the concrete around a bar due to its expansion. Spalling creates two difficulties. First, it can lead to a loss of bond. It also results in loss of a section of concrete. This is more critical when the section that is spalling is in the compression region, a situation that can occur if the steel that is rusting is not the primary reinforcement but is included to control other effects, such as shrinkage and thermal movement. Unlike the concrete in the tension region, all the concrete in the compression region is used to resist load. Thus, if concrete is lost, this will have the effect of reducing the capacity of the member. This may not be critical at low levels of concrete section loss, considering the factors of safety incorporated into the design. If allowed to continue, however, a significant weakening can occur, and the member can fail in a brittle manner. 2.10 Effect of Epoxy Coating on Bridge Deck Cracks Epoxy coating is used to help prevent corrosion of reinforcing steel from deicing chemicals. Research has shown that epoxy coating is often damaged when cracks develop over transverse reinforcement (Kochanski et al. 1990). Chloride penetration, however, has a much more significant effect on epoxy coating. Chloride penetration has been shown to deteriorate the adhesion between the bars and the epoxy; therefore, some have suggested that epoxy coating is ineffective, at least as the sole solution for concrete deck cracking (Kochanski et al. 1990). An important design consideration when using epoxy-coated reinforcement is the effect on bond and crack control. The influence of epoxy coating on bond and anchorage behavior of reinforcing bars has been studied by several researchers (Choi et al. 1990 and Treece et al. 1989). One way of accounting for this effect in design is to use longer development lengths as required in the ACI 318 code. However, little research has been done on the influence of epoxy-coated bars on crack control and tension stiffening (Denis et al. 1996). They found out specimens reinforced

36

with epoxy-coated bars showed larger crack widths than specimens reinforced with uncoated bars. Also, they reported an increase in larger crack widths with increased coating thickness of the epoxy. Meyers (1982) found that decks with epoxy bars tend to show more cracking. Similar finding was reported by Krauss and Rogalla (1996). However, a study by Iowa DOT (1986) recommended use of epoxy-coated rebars to control cracking. 2.11 The Effects of Addition of Fiber on Reinforced Concrete

A number of different fiber have been used to improve the properties of reinforced concrete, and the resulting concrete is referred to as fiber-reinforced concrete (FRC). The various types of non-metallic fiber such as basalt MiniBar, polypropylene, glass, aramid, and carbon fiber are available in the market. Compared to steel, these fiber have a higher strength-to-weight ratio, which can be as much as 10 to 15 times that of steel. Fiber is primarily used in concrete to inhibit tensile crack growth thus significantly increasing the post-crack tensile strength of the concrete (Adhikari 2013). The addition of fiber to concrete in large quantities (or volume fractions) alters the mechanical properties of a structural member, increasing its toughness (energy absorption), ductility, tensile strength and flexural strength to some extent (Hamad and Heider 2011). Fiber may be metallic, organic or synthetic, and they may be available in various geometries.

Patnaik (2011) and Patnaik et al. (2013) performed a comprehensive study on the mechanical and structural characterization of concrete reinforced with basalt MiniBars. Bagherzadeh et al. (2012) studied the influence of polypropylene fiber using different proportions and fiber lengths to improve the performance characteristics of the lightweight cement composites. Figure 2.7 shows the concept and mechanics of fiber reinforced concrete (Adhikari and Patnaik 2012). Denis et al. studied the effect of steel fiber and epoxy-coated reinforcement on tension stiffening and cracking of reinforced concrete.

Figure 2.7 Fiber reinforced concrete: Concept and mechanics (Adhikari and Patnaik 2012)

37

2.12 Arching Action in Reinforced Concrete Slabs Arching or compressive membrane action in reinforced concrete slabs occurs as a result of the large difference between the tensile and compressive strength of the concrete. Cracking of the concrete causes shifting of the neutral axis, which is accompanied by in-plane expansion of the slab at its boundaries. If this natural tendency to expand is restrained, the development of arching action enhances the strength of the slab. The term arching action is normally used to describe the arching phenomenon in one-way spanning slabs, and compressive membrane action is normally used to describe the arching phenomenon in two-way spanning slabs. The extent of strength enhancement caused by arching action was revealed through the full-scale destructive load tests by Ockleston (1958). Several researchers, including Brotchie and Holly (1971) and Black (1975), have since confirmed the effect of arching action in reinforced concrete slabs. The ultimate strengths of lightly reinforced slabs were found to be six times greater than the design strength. Once flexural cracking occurs, a compression field originating from the load point spreads to the restraining supports as shown in Figure 2.8. Foster (2010) explained that section equilibrium is maintained by a tension hoop around the compression field as shown in Figure 2.9.

Figure 2.8 Arching Action in Concrete Slabs (Foster 2010)

Figure 2.9 Tension Hoop around the Compression Field (Foster 2010)

38

2.13 Chloride Ion Content in Bridge Decks The principal cause of corrosion of steel reinforcement in bridge decks is due to chloride

in the concrete. The chloride originates in the concrete ingredients and from de-icing chemicals applied to the bridge deck. Corrosion causes expansion of steel that leads to spalling of the concrete. Several methods are used by different researchers in the determination of acid soluble chloride ion content and water soluble chloride ion content. Table 2.11 shows various methods of chloride extraction and analysis. As can be noticed from this figure, there is a wide variation in recommended chloride limits in different national codes. Acid soluble chloride ion content of 0.35% for 95% of the test results with no result greater than 0.50% is recommended by the British code, CP 110. ACI 318-11 permits a maximum acid soluble chloride ion content by weight of binder (cement) of 0.10% for reinforced concrete wet in service, and 0.20% for reinforced concrete dry in service (Table 2.12). Some researchers have reported corrosion has occurred at values less than 0.4% (Pfeifer et al. 1987, Hope and Ip 1987), particularly in cases where the chloride content was not uniform. The Norwegian code, NS 3420-L, allows an acid soluble chloride content of 0.6% for reinforced concrete made with normal Portland cement, but only 0.002% chloride ion content for prestressed concrete. It is stated in ACI 318-11 that when epoxy- or zinc-coated bars are used, the limits in Table 2.12 may be more restrictive than necessary. Table 2.13 shows reported chloride threshold values in total chloride content per weight of binder by Angst and Vennesland (2009).

Table 2.11 Qualitative Assessment of the Various Methods of Chloride Extraction and Analysis

(Hunkeler et al, 2000)

Method of analysis

Method of extraction Remarks Hot water

extraction Acid-extraction

Titration appropriate appropriate Photometry appropriate sensitive calibration curve, susceptibility to

errors, experience Ion sensitive electrode sensitive sensitive calibration curve, experience, cross

sensibility Ion chromatography - inappropriate cross sensibility X-ray fluorescence (no extraction necessary) appropriate appropriate calibration curve

Table 2.12 Chloride Limits for New Construction (ACI 318-11)

Construction type and condition

Chloride limit for new construction (% by mass of cement)

Test method Acid-soluble Water-soluble

ASTM C 1152 ASTM C 1218 Soxhlet* Prestressed concrete 0.08 0.06 0.06 Reinforced concrete wet in service

0.10 0.08 0.08

Reinforced concrete dry in service 0.20 0.15 0.15

*The Soxhlet test method is described in ACI 222.1

39

Table 2.13 Reported Chloride Threshold Values in Total Chloride Content per Weight of Binder (Angst and Vennesland, 2009)

Reference Cl- Cement Type Reported Value Richartz 1969 A OPC 0.4 Gouda et al. 1970 A OPC, GGBS 1.0 – 3.0 Stratfull et al. 1975 D Various 0.2 – 1.4 Locke et al. 1980 A OPC 0.4 – 0.8 Elsener et al. 1986 A OPC 0.25 – 0.5 Hope et al. 1987 A OPC 0.1 – 0.19 Hasson et al. 1990 D Various cements 0.4 –1.37 Schiessl et al. 1990 A/D Various cements 0.5 – 2.0 Lambert et al. 1991 A/D OPC, SRPC 1.5 – 2.5* Thomas 1996 D OPC, FA 0.2 – 0.7 Alonso et al. 2000 A OPC 1.24 – 3.08* Alonso et al. 2002 D Various cements 0.73 Castellote et al. 2002 D/M SRPC 0.15 – 0.23 Trejo et al. 2003 M OPC 0.02 – 0.24 Manera et al. 2008 A OPC, SF 0.6 – 2.0 minimum – maximum 0.02 – 3.08 A = chloride added to the mix; D/M = chloride introduced into the hardened samples by diffusion/capillary suction (D) or migration (M). Cement types include fly ash (FA), ground-granulated blast-furnace slag (GGBS), ordinary Portland cement (OPC), Portland silica fume (SF), and sulfate-resisting Portland cement (SRPC).*Steel potential below -200 mV with respect to the Standard Calomel Electrode.

2.14 Digital Image Correlation Application to Bridge Decks Digital image correlation (DIC) is a stereoscopic photometric methodology that tracks and measures deformation and movement of the surface of an object using two digital cameras that are mounted at a specific distance from one another on a horizontal support bar. DIC techniques have been used in various civil engineering applications including monitoring of bridges, nuclear reactors, and buildings. The monitoring of civil engineering structures is an important issue due to rapid development of modern building techniques and growing fatigue wear of large-span roof structures and bridges. Malesa et al. (2010) adapted the DIC technique for monitoring of civil engineering structures. Their DIC measurements of a railway bridge were found to be in close agreement with the results obtained from finite element method modeling. 2.15 Summary of Literature Review Limited research is available relevant to the cracking behavior of structural slab bridge decks, and most of the studies in the literature focused on stringer-supported reinforced concrete bridge decks. The literature search is summarized by these main points:

• Reinforced concrete bridge deck cracking is a well-documented problem, nationwide. • Many departments of transportation in the United States provide strict specifications

regarding mix design, construction, placement, and curing procedures, but bridge deck cracking remains a problem.

40

• Numerous cracks greater than 0.12 in. have been reported on stringer supported bridge deck cracking, such as those on the Keenville Viaduct in Johnstown, Pennsylvania.

• Literature review also suggests that there is no general agreement among various investigators on the relative significance of different factors affecting crack widths. Taking all the parameters into account in a single experimental program is not normally feasible due to the large number of variables involved and the interdependency of some of these factors.

• Cracking in bridge decks increases the maintenance cost, reduces the service life, and may result in disruptive and costly repairs.

• Research has shown that epoxy coating is often damaged when cracks develop over transverse reinforcement.

• Chloride penetration has been shown to deteriorate the adhesion between the reinforcing bars and the epoxy coating; therefore, researchers have suggested that epoxy coating is ineffective, at least as the sole solution to concrete deck cracking.

• While there is large amount of scatter in test data, results of fatigue tests and sustained loading tests indicate that a doubling of crack width can be expected with time.

• Repeated loading causes existing cracks to widen through progressive slip between the reinforcement and the concrete.

• Due to the large variability in crack width in tension members, the maximum crack width in direct tension is expected to be larger than the maximum crack width in flexure at the same steel stress.

• Most cracking occurs early in the life of a bridge deck, but it continues to increase over time. • Current design specification (AASHTO 2012 and ACI 318-11) provisions for flexural crack

control have been established with maximum bar spacing specified to limit crack width. • Parametric studies of direct tension members revealed that there is a specific tension load at

which a third series cracks are formed. Further increase of the tension load beyond this load does not result in formation of additional cracks, but only increases the width of existing cracks.

41

CHAPTER 3: SURVEY AND INVENTORY OF CSS SLAB BRIDGES

Typical CSS slab bridges are a popular choice of several DOTs in the United States for short span bridges over typical four-lane highways and streams. ODOT has a total of 2757 structural slab bridges ranging from a single span up to 34 spans. ODOT District 6 has the highest number of structural slab bridges (a total of 325) and District 12 has the fewest, with a total of 47 (Figure 3.1). Figure 3.2 shows the number of structural slab bridges in each ODOT district that was either built or underwent a major rehabilitation between 1990 and 2013. The number of bridges built or rehabilitated since 1990 are presented in Figures 3.3. Three-span continuous bridges constitute 62% of the structural slab bridges in ODOT’s bridge inventory (Figure 3.4). More than half of these bridges (52%) have a sufficiency rating of 90–100%. However, 3.4% of the structural slab bridges have a sufficiency rating that is less than 50% (Figure 3.5).

Several bridges from ODOT’s inventory of structural slab bridges were considered as candidates for inclusion in this investigation. In consultation with the subject matter experts (SMEs) at ODOT, 13 of these bridges were selected. Among the factors considered in the bridge selection were the number of main spans, span lengths, roadway width, thickness of the deck slab, number of lanes, reinforcement ratio, concrete strength, and type, age of the bridge deck, skew effects, traffic conditions, and geographic location within the state. Table 3.1 presents the list of the 13 selected bridges.

The decks of the selected bridges were all constructed between 1995 and 2012. The bridges have varying span lengths, from as short as 24–30–24 ft. to a maximum length of 44–55–44 ft. The deck thickness of the selected bridges ranges from 16 to 26 in. Different concrete mix designs were used in the construction of these bridge decks: high performance concrete class HP, Class S, and QC/QA concrete. The study did not consider all cracks on the decks of the selected bridges; rather, it focused on the wide cracks, primarily those in the direction parallel to the intermediate pier supports.

42

Figure 3.1 Total number of structural slab bridges in each ODOT district

Figure 3.2 Number of structural slab bridges in each ODOT district that were built or

rehabilitated between 1990 and 2013.

0

50

100

150

200

250

300

350

No. o

f brid

ges

District

0

10

20

30

40

50

60

70

80

No.

of b

ridge

s

District

43

Figure 3.3 Number of structural slab bridges in Ohio that were built or rehabilitated since 1990

Figure 3.4 Number of main spans for structural slab bridges in Ohio (1900–2013)

0

5

10

15

20

25

30

35

40

45

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

No.

of b

ridge

s

Year

0

200

400

600

800

1000

1200

1400

1600

1800

1 2 3 4 5 6 7 9 10 11 12 13 16 18 19 21 25 31 33 34

No.

of b

ridge

s

Main spans

44

Figure 3.5 Sufficiency rating for structural slab bridges in Ohio (1900–2013)

Table 3.1 List of Selected Structural Slab Bridges

Bridge No. SFN No.

Year Built/

Rebuilt

Spans (ft.)

Deck Thickness

(in.) ASD-42-0656 0301159 2009 40–50–40 24 ASD-250-0377 0304697 2012 37–46.25–37 22.5 WAY-30-1039 8501815 2006 44–55–44 26 POR-224-1172 6703900 2001 38–47.5–38 23 STA-225-076 7605943 2006 44–55–44 26 MAH-62-0207 5001846 2008 28–35–28 18 MAH-224-1619 5004837 2009 28–35–28 18 POR-88-1250 6703607 2006 30–37.5–30 19

TRU-534-1516 7807457 2006 40–50–40 24 TRU-45-2018 7802285 2003 40–50–40 24 ATB-020-0326 0402087 2005 24.2–24.2 20 ASD-250-1864 305006 1998 24.5–35–24.5 18 MED-162-2016 5206251 1995 24–30–24 16

0

200

400

600

800

1000

1200

1400

0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100

No.

of b

ridge

s

Suffiency rating (%)

45

CHAPTER 4: FACTORS INFLUENCING POTENTIAL CRACKING OF CSS SLAB BRIDGE DECKS

Data regarding the design, materials, construction, and traffic for each of the selected

structural slab bridges were collected to establish any potential correlation between these factors and bridge deck cracking. Relationships between crack width and possible factors that cause cracking including skew angle, age of the concrete, maximum span lengths, and slab thickness are shown in Figures 4.1 to 4.4. As can be noticed from these figures, no statistical correlation was found between crack widths at the negative moment region and skew angle, maximum span length, and slab thickness. No matter what type of concrete mixes was used, and what skew angle the bridges had, the amount of cracking seems to be about the same. There seems to be nearly a linear relationship between the crack widths and age.

Factors other than deck geometry and age that could potentially influence the deck cracking were also evaluated and discussed in greater detail in later chapters in this report. Some of the primary factors and their potential influences on deck cracking are summarized below.

A review of construction/inspection diaries for the selected bridges revealed that ODOT’s curing procedure for concrete bridge decks (as specified in CMS 511.14-A) were not fully followed at all times. However, compressive strengths of field cores taken from one bridge deck compared very favorably with both the lab cured cylinder compressive strengths and the required design strength. It is inconclusive if the amount and extent of cracking and the crack widths had any direct relationship with the curing conditions.

A review of structural calculations for all ODOT standard three-span structural slab bridge configurations determined that reinforcing steel provided in CS1-08 was sufficient to meet AASHTO and ACI 318-11 crack control requirements.

The reinforcement details for the selected bridges were scrutinized to determine if the reinforcement used for each bridge met the requirements. Larger rebar sizes, including #9, #10, and #11, were used as main longitudinal bars in the selected bridges. It was determined that the reinforcing steel provided in ODOT standard drawings was sufficient to meet the strength and serviceability requirements given in ACI 318-11 and AASHTO specifications.

Traffic data from the bridge plans for the selected bridges were considered in the investigation. These data included current average daily traffic, design year average daily traffic, design speed, and legal speed. In addition, a review of truck overloading weigh-in-motion data obtained from ODOT’s Office of Technical Services determined that structural impact from overloads was likely insignificant as a causative factor for the wide structural cracks noted on the selected bridges.

ODOT’s current procedure for bridge inspection requires an annual inspection of the entire bridge by trained inspectors. However, this inspection procedure only offers a descriptive assessment of the bridge decks inspected. ODOT’s condition rating for deck summary is shown in Table 4.1. Condition rating includes 0 through 9, with 9 rated as excellent and 0 rated as failed. The data in Table 4.2 reveals that the bridge inspections rated the condition of the 13 selected bridge decks considered in this study mostly as 7 or 8.

46

Figure 4.1 Relation between skew angle and crack width

Figure 4.2 Relation between age of slab and crack width

0

5

10

15

20

25

30

35

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Skew

angl

e (O )

Crack width (in.)

0

2

4

6

8

10

12

14

16

18

20

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Age o

f slab

(yea

rs)

Crack width (in.)

47

Figure 4.3 Relation between maximum span length and crack width

Figure 4.4 Relation between slab thickness and crack width

0

10

20

30

40

50

60

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Max

imum

span

leng

th (f

t)

Crack width (in.)

0

5

10

15

20

25

30

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Slab

thic

knes

s (in

.)

Crack width (in.)

48

Table 4.1 ODOT Bridge Inspection Condition Rating Guidelines (ODOT Manual of Bridge Inspection 2010)

49

Table 4.2 Deck Summary Condition Rating of Surveyed Bridges

Bridge No. SFN Year Built/Rebuilt

Deck Summary Condition Rating

2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003

ASD-42-0656 0301159 2009 8 9 9 9 9 - - - - - -

ASD-250-0377 0304697 2012 9 9 - - - - - - - - -

WAY-30-1039 8501815 2006 7 7 7 7 7 7 8 8 - - -

POR-224-1172 6703900 2001 7 7 7 7 7 7 7 7 7 8 8

STA-225-076 7605943 2006 7 7 7 8 8 8 8 9 - - -

MAH-62-0207 5001846 2008 9 9 9 9 9 - - - - - -

MAH-224-1619 5004837 2009 9 9 9 9 9 - - - - - -

POR-88-1250 6703607 2006 8 8 9 9 9 9 9 9 - - -

TRU-534-1516 7807457 2006 8 8 8 8 9 9 9 9

TRU-45-2018 7802285 2003 7 7 7 7 7 6 6 6 8 8 9

ATB-020-0326 0402087 2005 6 6 7 7 7 7 7 7 9

ASD-250-1864 305006 1998 8 8 8 8 8 8 8 8 8 8 8

MED-162-2016 5206251 1995 7 7 7 7 7 7 7 7 7 8 8

SFN: Structural File Number

50

CHAPTER 5: FIELD SURVEY AND MEASUREMENTS OF DEAD LOAD CRACK WIDTHS ON CSS SLAB BRIDGE DECKS

Field surveys were conducted of CSS slab bridges to determine if the very unique wide

non-shrinkage permanent cracks adjacent to the pier supports were common or limited to CSS slab bridges with certain characteristics. The details of those field surveys and physical inspections are presented in this chapter. 5.1 Introduction Thirteen structural slab bridges were selected for field investigation: twelve were three-span bridges and one was a two-span bridge. The bridges surveyed consisted of both skewed and non-skewed decks. These decks were constructed using different concrete mix designs. The bridges, which were located in nine counties in Ohio, were inspected between December 2012 and July 2014.

During the field investigation, all cracks on the bridge decks near the pier caps (top surface) were marked using colored chalk for easy identification and mapping. Crack lengths were measured using a tape measure, and the crack widths were measured using a crack width gage. The crack patterns and maximum crack widths for dead load only were recorded for all the surveyed bridges. With regard to the cracks on the tops of the bridge decks, this study focused on the negative moment regions where wide flexural cracks were observed in the direction parallel to the intermediate pier supports. However, cracks on the bottom of the decks were also noted to determine if any of the cracks were full-depth cracks.

Table 5.1 presents a list of bridges studied and the maximum recorded crack widths on each bridge. The maximum recorded crack widths over the intermediate pier supports for some of the bridges were over 0.1 in. These crack width measurements are over ten times the limit recommended in ACI 224 report (see Table 2.1). Transverse and longitudinal cracks were also observed at the bottom of the bridge deck close to the middle of the spans for some of the bridges surveyed. In addition to the cracks observed at the top and bottom of the decks, side cracks that were predominantly full-depth cracks confirmed that the cracks extended deep into the deck thickness.

The cracks on the decks of the selected bridges appeared to progress with time. One of the bridges, bridge ASD 250-0377, was opened to traffic for just three months at the time of the first inspection, but it had already developed cracks as wide as 0.03 in. on the top of the deck. Eighteen months later, a second survey was conducted and the maximum crack width was 0.08 inch, more than double the previous maximum crack width. Further, the extent of cracking also progressed. Three crack surveys of bridge ASD-42-0656, which were conducted over 36 months, also verified that the crack widths and the extent of cracking were progressing with time.

5.2 Crack Survey and Crack Maps of Bridges Bridge deck crack surveys were conducted on 13 structural slab bridges in Ohio. Twelve of the bridges inspected were three-span continuous structural slab bridges and one was a two-span continuous structural slab bridge. The crack surveys were focused on the top of the bridge deck in the region parallel to the intermediate supports (piers). Wide transverse flexural cracks were mostly observed in this region of negative moments. Flexural cracks at the bottom of the slabs and full depth side cracks in the deck edges were observed in many of the bridge surveys.

51

Spalling of concrete, crack repairs, parapet cracks and other observed features were documented as well. This study focused on considering the causes, effects, and mitigation of structural (wide) cracks in structural slab bridges.

Table 5.1 List of Surveyed Structural Slab Bridges

Bridge No. SFN No. Year Built/ Rebuilt

Spans (ft.)

Deck Thickness (in.)

Skew Angle of Bridge Deck

Max. Recorded Crack Width Dead Load Only (in.)

ASD-42-0656 0301159 2009 40–50–40 24 12o10' 0.10 ASD-250-0377 0304697 2012 37–46.25–37 22.5 25o 0.03 WAY-30-1039 8501815 2006 44–55–44 26 30o 0.10 POR-224-1172 6703900 2001 38–47.5–38 23 NONE 0.13 STA-225-076 7605943 2006 44–55–44 26 15o 0.10 MAH-62-0207 5001846 2008 28–35–28 18 10o 0.04 MAH-224-1619 5004837 2009 28–35–28 18 20o 0.05 POR-88-1250 6703607 2006 30–37.5–30 19 NONE 0.08

TRU-534-1516 7807457 2006 40–50–40 24 12o 0.10 TRU-45-2018 7802285 2003 40–50–40 24 10o 0.08

ATB-020-0326 0402087 2005 24.2–24.2 20 28o 0.08 ASD-250-1864 305006 1998 24.5–35–24.5 18 NONE 0.10 MED-162-2016 5206251 1995 24–30–24 16 30o 0.10

Table 5.1 List of Surveyed Structural Slab Bridges (Continued)

Bridge Number Type of Substructure ODOT Standard Bridge

Drawings

Does Reinforcement Satisfy ODOT Std

Drg Design Loading

ASD-42-0656 Cap and Column Piers CS-1-03

Dated 4-18-03 Yes HS20 and Alt Military Loading with FWS = 60 psf

ASD-250-0377 Capped Pile Piers CS-1-08

Dated 7-18-08 Yes HL93 and FWS = 60 psf

WAY-30-1039 Capped Pile Piers CS-1-03 Dated 4-18-03 Yes HS25 and Alternate Military Loading

POR-224-1172 Cap and Column Piers CS-1-93; with revisions 06-

30-95 and 07-19-02 Yes HS-20-44 Case II and Alternate Military Loading

STA-225-076 Wall Type Piers CS-1-03 Dated 4-18-03 Yes HS25 and Alternate Military Loading

FWS = 60 psf MAH-62-

0207 Cap and Column Piers CS-1-03 Dated 4-18-03 Yes HS25 and Alternate Military Loading FWS = 60 psf

MAH-224-1619 Capped Pile Piers CS-1-03

Dated 4-18-03 Yes HS25 and Alternate Military Loading FWS = 60 psf

POR-88-1250 Cap and Column Piers CS-1-03

Dated 4-18-03 Yes HS25 and Alternate Military Loading FWS = 60 psf

TRU-534-1516 Capped Pile Piers

CS-1-93 dated 05-11-93; with revisions 06-30-95 and 07-19-02

Yes HS25-44 and Alt Military Loading Superimposed Dead Load = 75 psf including 60 psf for wearing surface – one inch monolithic

TRU-45-2018

Wall Type Piers (ends of piers cut and recast)

CS-1-03 Dated/ Revised 06-30-95 Yes HS25 and Alternate Military Loading

FWS = 60 psf ATB-020-

0326 Wall Type Pier Two-span bridge Unsure N/A HS25 and Alternate Military Loading

FWS = 60 psf

ASD-250-1864 Capped Pile Piers CS-1-93M Revision

06/30/95 Yes MS18 and the Alternate Military Loading; Superimposed Dead Load = 366.93 kg/m2 Monolithic wearing surface assumed 25 mm thick.

MED-162-2016 Capped Pile Piers CS-2-73 dated 04/10/73 Yes HS 20-44 and the alternate military loading

5.2.1 Bridge 1: WAY-30-1039 Details of this bridge are presented in Table 5.1. The entire bridge deck was not reviewed in the crack survey. The only portions inspected were the driving lanes in both directions. Cracks were most prominent in the direction transverse to the bridge axis, parallel and next to the piers.

52

Some instances of epoxy sealing of cracks were documented. Two epoxy-coated reinforcement bars were exposed at the bottom, and some rust stains were observed (did not appear too critical). Longitudinal cracks were also observed at the bottom of the concrete slab parallel to the construction phase joints. Extensive cracking was observed in the middle of the concrete parapet. Measured crack widths on the bridge deck were between 0.04 in and 0.1 in. (Figure 5.1). The crack map for bridge WAY-30-1039 is shown in Figure 5.2.

Figure 5.1 Cracking observed on bridge WAY-30-1039

Longitudinal cracks at the bottom of the deck

53

*Only the portion between the two phase joints were inspected

Figure 5.2 Crack map for bridge WAY-30-1039 5.2.2 Bridge 2: ASD-42-0656

Details of this bridge are presented in Table 5.1. Cracks were mapped and measured on the top of the deck, as shown in Figure 5.3. Cracks were most prominent in the direction transverse to the bridge axis, parallel and next to the piers. Measured crack widths were between 0.04 in. and 0.1 in. When the March 2014 crack survey results for bridge ASD-42-0656 were compared to the crack survey performed on the bridge in March 2011, it was found that the crack widths and the extent of cracking appear to be progressing with time. In addition to the observed wide cracks on the deck, extensive cracks were seen in the concrete parapet at both sides of the bridge. Figure 5.4 shows the crack maps developed from the earlier and current crack surveys.

Figure 5.3 Observed cracks at one of the negative moment regions on March 24, 2014

44′ 55′ 44′

East Bound

West Bound

Phase JointNot Inspected

Not Inspected

Parapet

Phase Joint

Rear Pier Brgs. Pier Line Pier Line Fwd. Pier Brgs.

54

Figure 5.4 Crack maps of bridge ASD-42-0656 based on 2011 and 2013 inspections 5.2.3 Bridge 3: ASD-250-0377 Details of this bridge are presented in Table 5.1. In the first field survey, a few cracks were observed on the top deck surface over the piers (negative moment regions). The maximum recorded crack width was 0.03 in. A crack map for the bridge is shown in Figure 5.5. Increasing levels of deck cracking (Figure 5.6 and Figure 5.7) were observed during a second crack survey, which was conducted on July 24, 2014. The maximum recorded crack width was 0.08, which is more than twice the maximum crack width recorded eighteen months earlier. Cracks were observed to have progressed with time, and several full depth cracks spaced less than 18 in. along the deck edges were also observed about 8 ft. on either side of the pier supports.

50 ft. 40 ft.40 ft.

50 ft. 40 ft.40 ft.

Crack survey on January 14, 2013

Crack survey on March 22, 2011 Ganapuram et al. (2012)

55

Figure 5.5 Crack map of bridge ASD-250-0377 on January 14, 2013

Figure 5.6 Maximum crack width recorded on bridge ASD-250-0377, with extensive side cracks at the deck edges

37′ 43′ 37′

Several through depth cracks spaced less than 18 in.

56

Figure 5.7 Wide cracks over the piers on bridge ASD-250-0377, as observed on July 24, 2014 5.2.4 Bridge 4: ATB-20-0326 Details of this bridge are presented in Table5.1. The maximum recorded crack width was 0.08 in. Some longitudinal cracks were observed at the bottom of the bridge deck. Full-depth side cracks as well as extensive cracking in the concrete parapets were also documented during the field investigation. A crack map for bridge ATB-20-0326 is shown in Figure 5.8.

Figure 5.8 Crack map for bridge ATB-20-0326.

24′-10′′ 24′-10′′

57

5.2.5 Bridge 5: POR-224-1172 Details of this bridge are presented in Table 5.1. A crack survey performed on June 12, 2013, showed wide cracks over the piers. In addition, transverse and longitudinal cracks were observed and documented at the bottom of the deck. The maximum recorded crack width was 0.125 in. Almost full-depth cracks were also documented on the sides of the deck as well as extensive spalling of the abutment concrete. The observed abutment spalling and crack maps are shown in Figures 5.9 - 5.11.

Figure 5.9 Inspection of bridge POR-224-1172

Cracks on the deck, max. width = 0.125 in. Longitudinal cracks at the bottom

Almost full-depth cracks on the side of slab Extensive spalling of abutment concrete

58

Figure 5.10 Crack map of bridge POR-224-1172 on the top of the bridge deck

Figure 5.11 Crack map for bridge POR-224-1172 at the bottom of the bridge deck. 5.2.6 Bridge 6: STA-225-076 Details of this bridge are presented in Table 5.1. The crack survey performed on 06/12/2013 showed some longitudinal cracks as well as cracks over the piers (negative moment regions). The maximum recorded crack width was 0.1 in., and some longitudinal cracks were observed at the bottom of the bridge deck as well. Full-depth cracks were also documented on the sides of the deck. A crack map for bridge STA-225-076 is shown in Figure 5.12.

38′ 47′ 38′

38′ 47′ 38′

59

Figure 5.12 Crack map of bridge STA-225-076 5.2.7 Bridge 7: MAH-62-0207 Details of this bridge are presented in Table 5.1. The survey revealed that cracks were most prominent in the direction transverse to the bridge axis, parallel and next to the piers. The maximum recorded crack width was 0.04 in. Figure 5.13 shows the crack map for the bridge.

Figure 5.13 Crack map of bridge MAH-62-0207. 5.2.8 Bridge 8: MAH-224-1619 Details of this bridge are presented in Table 5.1. A crack survey was performed on the bridge on June 12, 2013. The entire bridge was not inpsected in the crack survey, due to traffic conditions. The survey revealed some longitudinal cracks on the bridge deck as well as cracks over the piers (negative moment regions). The maximum recorded crack width on the bridge deck was 0.05 in. A crack map for this bridge is shown in Figure 5.14.

44′ 55′ 44′

28′ 35′ 28′

60

Figure 5.14 Crack map of bridge MAH-224-1619 5.2.9 Bridge 9: POR-88-1250 Details of this bridge are presented in Table 5.1. The crack survey for this bridge was performed on July 2, 2013. Extensive transverse and longitudinal cracks were observed on this bridge deck as shown in Figure 5.15, and the maximum recorded crack width was 0.08 in. The wide cracks were most prominent in the direction transverse to the bridge axis, parallel and next to the piers. Figure 5.16 shows the crack map of bridge POR-88-1250.

Figure 5.15 Observed wide cracks on bridge POR-88-1250 parallel to the interior piers

*Entire bridge was not covered in the crack survey due to traffic conditions

28′ 35′ 28′

61

Figure 5.16 Crack map at the top of bridge deck of bridge POR-88-1250, based on inspection on

July 2, 2013 5.2.10 Bridge 10: TRU-534-1516 Details of this bridge are presented in Table 5.1. A crack survey performed on July 2, 2013, revealed several wide cracks on the bridge deck and wide cracks over the piers in the negative moment region, as shown in Figure 5.17. Previous sealing of cracks was observed on some portions of the deck, as well as spalling on the abutment concrete. Transverse and longitudinal cracks were also observed at the bottom of the deck. The maximum recorded crack width in the field inspection of bridge TRU-534-1516 was 0.1 in. Figure 5.18 presents the crack map for the top of the bridge deck.

Figure 5.17 Extensive wide cracks over the piers of bridge TRU-534-1516

30′ 37′-5′′ 30′

62

Figure 5.18 Crack map for bridge TRU-534-1516 5.2.11 Bridge 11: TRU-45-2018 Details of this bridge are presented in Table 5.1. A crack survey performed on July 2, 2013, revealed full-depth cracks on the sides of bridge deck as well as transverse cracks at the bottom of the deck near the middle of spans. The maximum recorded crack width for this bridge was 0.08 in., and the crack map is shown in Figure 5.19.

Figure 5.19 Crack map for bridge TRU-45-2018. 5.2.12 Bridge 12: MED-162-2031

Details of this bridge are presented in Table 5.1. A crack survey performed on July 24, 2014, revealed wide cracks over the piers in the negative moment regions, with a maximum recorded crack width of 0.1 in. In addition, nearly full-depth cracks were observed on the side of the bridge deck (Figure 5.20); and transverse and longitudinal cracks were observed at the bottom of the deck.

40′ 50′ 40′

40′ 50′ 40′

63

Figure 5.20 Side full depth cracks on bridge MED-162-2016.

5.2.13 Bridge 13: ASD-250-1864

Details of this bridge are presented in Table5.1. A crack survey performed on July 24, 2014, revealed wide cracks over the piers in the negative moment region, with a maximum recorded crack width of 0.1 in. as shown in Figure 5.21. Full-depth cracks were noted on the sides of the deck, and transverse cracks were observed at the bottom of the deck near the mid-span locations. Several full-depth cracks spaced less than 18 in. along the deck edges were also observed near the pier support region. Cracks appeared to have progressed with time.

Figure 5.21 Maximum recorded crack width of 0.1 in. on bridge ASD-250-1864.

64

5.3 Observations on Parapet Cracking Even though cracking behavior of parapets was not the focus of this study, some

observations recorded from bridge inspections are worth documenting. Significant vertical permanent cracking was observed on parapets on both vertical faces of the parapets (Figure 5.22), demonstrating that the cracks extended through the full thickness of these parapets. Most cracks were concentrated near the intermediate pier supports, and seemingly perpetuated from the structural cracks in the deck and propagated all the way to the top of the parapets. Crack widths were as large as those at the deck surface (0.12 inch) or larger, in some cases, than those at the deck surface adjacent to the corresponding parapet cracks. Extensive parapet cracking was observed for all the inspected bridges that had parapets.

Figure 5.22 Typical parapet cracking (i) interior face (left) and (ii) exterior face (right). 5.4 Summary

Regardless of deck thickness, skewness, and span configurations, CSS slab bridges exhibited excessive cracking with permanent crack widths in the range of 0.1 inch to 0.14 inch under dead load condition alone. These cracks extended over full thickness of the deck near the pier supports as evidenced from the cracks recorded on the exposed vertical sides (edges) of the deck. The crack survey results were similar for several bridges that were inspected in this project. It was confirmed that this problem is a statewide problem. It was also verified that the permanent crack widths and the extent of cracking increased with time (over a duration of less than three years in some of the selected bridges. Permanent cracks in parapets were recorded to be as severe as those on the deck they are supported on, and these cracks perpetuated from the deck cracks suggesting that parapet cracking and deck cracking are related problems.

65

CHAPTER 6: PROPERTIES DETERMINED FROM CONCRETE CORES

Cores were cut from a three-span structural slab bridge, ASD-42-0656, in August 2014 to determine (i) depths and widths of cracks in the negative moment regions (ii) verify compressive strengths along the depth of the deck, and (iii) chloride content profiles along the depth of the deck. This chapter documents the details of these properties determined from these cores. 6.1 Compressive Strength Determination from Bridge Deck Concrete Cores

A total of 12 concrete cores of average diameter of 2.72 in. were cut from both cracked and uncracked portions of the deck. Figure 6.1 and 6.2 show the cores and the measurement of the diameter of a typical core, respectively. Prior to the coring, a ground-penetration radar system was used to locate embedded reinforcing bars so as to avoid cutting them during coring. The total depth of the slab is 24 in., and the lengths of the cores varied from 15.4 to 18.9 in.

Compressive strength tests were conducted in September 2014. For compressive strength testing, each specimen was loaded in a 300 kip capacity testing machine at a loading rate of 10,000–15,000 lb/min which is the required ASTM C39 rate of loading corresponding to 2.75-in. diameter cores. Correction factors based on the various aspect ratios of the cores were applied to obtain the final compressive strength values. Based on the aspect ratios specified in ASTM C39 and the lengths of cored specimens, the individual cores were cut into varying lengths (Figure 6.3) and capped with sulphur mortar (Figure 6.4) prior to testing (Figure 6.5). ASTM C617/C617M specifications were followed for capping the specimens. As the concrete strengths were expected to exceed 5,000 psi, the sulphur mortar caps were allowed to harden for at least 16 hours prior to testing.

Figure 6.1 Concrete cores obtained from bridge deck, ASD-42-0656.

Figure 6.2 Measuring the diameter of a typical concrete core.

66

Figure 6.3 Core samples prior to capping

Figure 6.4 Capped concrete core cylinders

Figure 6.5 Compressive strength test of a typical core specimen

67

6.1.1 Results of Concrete Compressive Strength Test and Density of the Cores Concrete compressive strength tests and density tests were performed on the bridge deck

cores. Fracture patterns for each sample were determined by comparing each sample to typical fracture patterns described by ASTM C39/39M, as presented in Figure 6.6. The compressive strength results obtained for the individual cores are presented in Tables 6.1 – 6.5. The average compressive strength for the individual concrete cores is presented in Figure 6.7. A summary of the compressive strength results for all the concrete cores is shown in Figure 6.8 as well as Table 6.6. Most of the compressive strengths obtained from the cylinders cut from the cores were over 6,000 psi. The densities determined from the concrete cores revealed values ranging from 130 to 134 lb/ft3 (Figure 6.9).

The core test results revealed that the compressive strengths of the cores cut from in-situ concrete meets the required design strength requirement of bridge deck concrete. The compressive strengths obtained from core tests also compared well with the cylinder breaks recorded in the project records. The compressive strengths recorded in the project records are based on compressive strength of cylinders that are cured under laboratory conditions which are more ideal than those encountered during field curing of bridge decks. However, the strength obtained from the cores cut from the selected bridge deck validated the strengths determined under ODOT laboratory conditions. The compressive strengths obtained from the tests on core specimens indicate that the compressive strength increased along the depth of the deck section for most cores.

Figure 6.6 Schematic of Typical Fracture Patterns (ASTM C39/39M)

68

Table 6.1 Compressive Strength Determination for Bridge Deck Cores C – 11, C – 8, and C – 10

C –11 C – 8 C – 10 C–11CM C–11CB C–8CM C–8CB C–10CM C–10CB

Diameter 2.72 2.72 2.72 2.72 2.72 2.72 Cross-sectional area, in.2 5.81 5.81 5.81 5.81 5.81 5.81 Length before capping, in. 4.41 4.41 4.41 4.41 5.13 5.13 Length capped, in. 4.76 4.76 4.76 4.76 5.44 5.44 Mass of core, lb 2.0 2.0 2.0 2.0 2.2 2.2 Volume of core, ft3 0.0148 0.0148 0.0148 0.0148 0.0172 0.0172 Density of core, lb/ft3 135.15 135.15 135.15 135.15 127.91 127.91 Maximum load, lb 39200 34290 43800 44840 27180 34390 Uncorrected compressive strength, psi 6746 5901 7540 7705 4677 5918 Ratio of capped length to diameter 1.75 1.75 1.75 1.75 2.0 2.0 Strength reduction factor 0.98 0.98 0.98 0.98 1.0 1.0 Corrected compressive strength, psi 6611 5783 7389 7551 4677 5918 Fracture pattern Type 3 Type 3 Type 3 Type 3 Type 3 Type 3

Note: Cores were obtained on August 26, 2014, and tested on September 24, 2014.

69

Table 6.2 Compressive Strength Determination for Bridge Deck Cores C – 5 and C – 7

Core C – 5 Core C – 7 C–5CT C–5CM C–5CB C–7CT C–7CM C–7CB

Diameter 2.74 2.74 2.74 2.72 2.72 2.72 Cross-sectional area, in.2 5.90 5.90 5.90 5.81 5.81 5.81 Length before capping, in. 5.13 4.41 4.41 3.75 3.75 3.75 Length capped, in. 5.48 4.80 4.80 4.08 4.08 4.08 Mass of core, lb 2.2 1.9 1.9 1.6 1.6 1.6 Volume of core, ft3 0.0175 0.0151 0.0151 0.0126 0.0126 0.0126 Density of core, lb/ft3 125.7 125.8 125.8 127.0 127.0 127.0 Maximum load, lb 33070 36250 44420 38470 37670 45750 Uncorrected compressive strength, psi 5608 6147 7533 6620 6482 7873 Ratio of capped length to diameter 2.0 1.75 1.75 1.5 1.5 1.5 Strength reduction factor 1.0 0.98 0.98 0.96 0.96 0.96 Corrected compressive strength, psi 5608 6024 7382 6355 6223 7558 Fracture pattern Type 3 Type 3 Type 3 Type 3 Type 3 Type 3

Note: Cores were obtained on August 26, 2014, and tested on September 24, 2014.

70

Table 6.3 Compressive Strength Determination for Bridge Deck Cores C – 12 and C – 3

Core C – 12 Core C – 3

C–12CT C–12CMT C–12CMB C–12CB C–3CB Diameter 2.71 2.71 2.71 2.71 2.72 Cross-sectional area, in.2 5.77 5.77 5.77 5.77 5.81 Length before capping, in. 3.75 3.75 3.75 3.75 5.13 Length capped, in. 4.07 4.07 4.07 4.07 5.44 Mass of core, lb 1.6 1.7 1.6 1.6 2.2 Volume of core, ft3 0.0125 0.0125 0.0125 0.0125 0.0172 Density of core, lb/ft3 128.0 136.0 128.0 128.0 127.9 Maximum load, lb 44010 40280 43210 45590 40020 Uncorrected compressive strength, psi 7629 6983 7491 7903 6887 Ratio of capped length to diameter 1.5 1.5 1.5 1.5 2.0 Strength reduction factor 0.96 0.96 0.96 0.96 1.0 Corrected compressive strength, psi 7324 6704 7191 7587 6887 Fracture pattern Type 3 Type 2 Type 2 Type 3 Type 3

Note: Cores were obtained on August 26, 2014, and tested on September 24, 2014.

71

Table 6.4 Compressive Strength Determination for Bridge Deck Core C – 9

Core C – 9 C–9CT C–9CMT C–9CMB C–9CB

Diameter 2.71 2.71 2.71 2.71 Cross-sectional area, in.2 5.77 5.77 5.77 5.77 Length before capping, in. 3.75 3.75 3.75 3.75 Length capped, in. 4.07 4.07 4.07 4.07 Mass of core, lb 1.6 1.6 1.6 1.6 Volume of core, ft3 0.0125 0.0125 0.0125 0.0125 Density of core, lb/ft3 128.0 128.0 128.0 128.0 Maximum load, lb 37490 41000 45240 42040 Uncorrected compressive strength, psi 6499 7108 7843 7288 Ratio of capped length to diameter 1.5 1.5 1.5 1.5 Strength reduction factor 0.96 0.96 0.96 0.96 Corrected compressive strength, psi 6239 6824 7529 6996 Fracture pattern Type 3 Type 2 Type 3 Type 3

Note: Core was obtained on August 26, 2014, and tested on September 24, 2014.

72

Table 6.5 Compressive Strength Determination for Bridge Deck Cores C – 4 and C – 2

Core C – 4 Core C – 2 C–4CT C–4CM C–4CB C–2CT C–2CM C–2CB

Diameter 2.73 2.73 2.73 2.73 2.73 2.73 Cross-sectional area, in.2 5.85 5.85 5.85 5.85 5.85 5.85 Length before capping, in. 4.41 4.41 5.13 4.41 5.13 3.75 Length capped, in. 4.78 4.78 5.46 4.78 5.46 4.10 Mass of core, lb 1.9 2.0 2.2 1.9 2.3 1.6 Volume of core, ft3 0.0149 0.0149 0.0149 0.0149 0.0174 0.0127 Density of core, lb/ft3 127.5 134.2 147.7 127.5 132.2 126.0 Maximum load, lb 42940 44430 45390 40970 34890 29620 Uncorrected compressive strength, psi 7335 7590 7754 6999 5960 5060 Ratio of capped length to diameter 1.75 1.75 2.0 1.75 2.0 1.5 Strength reduction factor 0.98 0.98 1.0 0.98 1.0 0.96 Corrected compressive strength, psi 7188 7438 7754 6859 5960 4858 Fracture pattern Type 2 Type 3 Type 3 Type 3 Type 3 Type 3

Note: Cores were obtained on August 26, 2014, and tested on September 24, 2014.

73

Figure 6.7 Average compressive strength of concrete cores obtained from bridge ASD-42-0656

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1 2 3 4 5 6 7 8 9 10 11

Aver

age

com

pres

sive

stre

ngth

of c

oncr

ete

core

s (ps

i)

Concrete cores

C-2 C-3 C-4 C-5 C-7 C-8 C-9 C-10 C-11 C-12

74

*Units are in psi

Figure 6.8 Compressive strength of deck cores cut from bridge ASD-42-0656

C - 3 C - 11 C - 8 C - 10 C - 5

C - 7 C - 4 C - 12 C - 9 C - 2

6887

6611

5783

7389

7551

4677

5918

6024

7382

6355

6223

7188

7438

7324

6704

7191

7587

6239

6824

7529

6996

6859

5960

5608

4858

7558

7754

17.6

"

18.4

6"

18.1

8"

17.9

7"

18.0

"

18.9

4"

18.4

4"

17.9

"

17.7

1"15

.44"

75

Table 6.6 Summary of Compressive Strength Test Results for Bridge ASD-42-0656

Specimen Compressive

Strength (psi)

Average Compressive

Strength (psi)

Date Core was Cut and Placed

in Bag Date of Test

C–3CB 6887 6887 08/26/2014 09/24/2014

C–11 C–11CM 6611

6197 08/26/2014 09/24/2014 C–11CB 5783

C–8 C–8CM 7389

7470 08/26/2014 09/24/2014 C–8CB 7551

C–10 C–10CM 4677

5298 08/26/2014 09/24/2014 C–10CB 5918

C–5

C–5CT 5608 6338 08/26/2014 09/24/2014 C–5CM 6024

C–5CB 7382

C–7

C–7CT 6355 6712 08/26/2014 09/24/2014 C–7CM 6223

C–7CB 7558

C–4

C–4CT 7188 7460 08/26/2014 09/24/2014 C–4CM 7438

C–4CB 7754

C–12

C–12CT 7324

7202 08/26/2014 09/24/2014 C–12CMT 6704 C–12CMB 7191 C–12CB 7587

C–9

C–9CT 6239

6897 08/26/2014 09/24/2014 C–9CMT 6824 C–9CMB 7529 C–9CB 6996

C–2

C–2CT 6859 5892 08/26/2014 09/24/2014 C–2CM 5960

C–2CB 4858

Mean Compressive Strength = 6635 psi

76

Figure 6.9 Densities of core specimens obtained from deck of bridge ASD-42-0656

6.2 Crack Width Measurements from Concrete Cores

Six of the 12 cores obtained from bridge ASD–42–0656 were cracked. Details of the cracked and uncracked specimens are shown in Tables 6.6 and 6.7, respectively. Two of the six cracked specimens had full-depth cracks. The crack widths at different depths of the core from the top were measured and recorded. Measured crack widths for the core specimens range from 0.006 to 0.125 in. In general, the crack widths were wider at the top of the core and narrower towards the bottom of the core length. Figures 6.10 and 6.11 show the measured crack widths for a typical core specimen. Crack widths at various depths of the all the cores are shown in Figure 6.12.

The crack width measurements on the cores cut through the deck at the negative moment regions of the selected CSS slab bridge revealed that the very wide cracking is not limited to just the surface of the deck but the cracks are very wide most of the depth of the deck all the way to the level of the bottom reinforcement. The maximum predicted crack width using Gergely and Lutz equation and the allowable crack width recommended in ACI 224R-01 are also shown in Figure 6.12. A comparison of measured crack widths along the depth of the core reveals that the crack widths exceed the allowable maximum in the top 6 to 8 inches for most of the cores. For two cores, the crack widths exceed the allowable limit for top 14 to 17 inches. The measured crack widths are also much greater than the predicted crack width for most of the cores for about 5 inches from the top surface (for about 12 inches for two of the cores).

129.5

130

130.5

131

131.5

132

132.5

133

133.5

134D

ensi

ty o

f brid

ge d

eck

core

(lb/

ft3 )

Core specimen

C-1 C1-2 C-2 C-3 C-4 C-5 C-7 C-8 C-9 C-10 C-11 C-12

77

Table 6.7 Details of Bridge Deck Concrete Cores (Cracked Specimens): ASD–42–0656 Cracked Core Specimens

C1-2 C-3 C-1 C-8 C-10 C-11

Average diameter of core, in.

2.73 2.74

2.72 2.72

2.67 2.71

2.72 2.72

2.72 2.72

2.74 2.72 2.75 2.73 2.72 2.73 2.72 2.73

2.74 2.71 2.73 2.71 2.73 2.69 Cross-sectional area of core, in.2 5.90 5.81 5.77 5.81 5.81 5.81 Average length of core, in.

14.0 14.0

17.69 17.71

17.5 17.35

18.56 18.46

18.25 18.18

17.5 17.6 13.75 17.81 17.25 18.44 18.0 17.75

14.25 17.63 17.3 18.38 18.3 17.56 Crack widths at various depths from the top, in.

At 0 in.: 0.125 At 1 in.: 0.1 At 3.5 in.: 0.06 At 7.0 in.: 0.05 At 10.5 in.: 0.04 At 14 in.: 0.04

At 0 in.: 0.08 At 1 in.: 0.06 At 2 in.: 0.04 At 4 in.: 0.016 At 6 in.: 0.010 At 8 in.: 0.006

At 0 in.: 0.1 At 2 in.: 0.06 At 4 in.: 0.05 At 6 in.: 0.04 At 8 in.: 0.03 At 10 in.: 0.02 At 12 in.: 0.014 At 14 in.: 0.012 At 17 in.: 0.010

At 0 in.: 0.06 At 1 in.: 0.04 At 2 in.: 0.025 At 3 in.: 0.02 At 4 in.: 0.016 At 5 in.: 0.012 At 6.5 in.: 0.010

At 0 in.: 0.06 At 1 in.: 0.04 At 2 in.: 0.03 At 3 in.: 0.02 At 4 in.: 0.016 At 5.5 in.: 0.008

At 0 in.: 0.08 At 1 in.: 0.04 At 2 in.: 0.03 At 3 in.: 0.025 At 4 in.: 0.02 At 5 in.: 0.012 At 6 in.: 0.008

Mass of core, lb 6.2 7.8 7.6 8.3 8.1 7.8 Volume of core, ft3 0.0478 0.0595 0.0579 0.0621 0.0611 0.0592 Density of core, lb/ft3 130 131 131 134 133 132 Remarks

Through depth crack

Depth of crack is 8.0 in.

Through depth crack.

Depth of crack is 6.5 in.

Depth of crack is 5.5 in.

Depth of crack is 6.25 in.

Note: Cores were cut on August 26, 2014, and tested on September 24, 2014.

78

Table 6.8 Details of Bridge Deck Concrete Cores (Uncracked Specimens): ASD–42–0656 (continued) Uncracked Core Specimens

C-2 C-4 C-5 C-7 C-9 C-12

Average diameter of core, in.

2.72 2.73

2.72 2.73

2.73 2.74

2.72 2.72

2.73 2.71

2.72 2.71 2.75 2.74 2.75 2.72 2.72 2.72

2.72 2.74 2.74 2.73 2.69 2.68 Cross-sectional area of core, in.2 5.85 5.85 5.90 5.81 5.77 5.77 Average length of core, in.

17.94 17.90

18.1 18.0

18.25 17.97

16.13 15.44

18.5 18.44

19.0 18.94 18.0 17.9 17.75 15.44 18.44 18.88

17.75 18.0 17.90 14.75 18.38 18.94 Mass of core, lb 8.1 8.0 8.1 6.9 8.2 8.4 Volume of core, ft3 0.0606 0.0609 0.0614 0.0519 0.0616 0.0632 Density of core, lb/ft3 134 131 132 133 133 133

Note: Cores were obtained on August 26, 2014, and tested on September 24, 2014.

79

Figure 6.10 Crack width near the top of a typical core

Figure 6.11 Crack width at 2 in. depth below the top surface of core C-10

80

Figure 6.12 Crack widths at various depths of the cores

6.3 Chloride Ion Content Determination for the Cores

Corrosion-induced deterioration of reinforced concrete bridge superstructure elements is a common and recurring problem for bridges in the United States. The primary cause of reinforcing steel corrosion is chloride ions. The main sources of chloride ions are chloride bearing admixtures used during construction, de-icing salts applied to the surface of concrete deck during the winter season, airborne chlorides, and direct exposure to sea water in marine environments. It is generally accepted by the research community that corrosion of reinforcing steel will occur once a threshold value of chloride ion content adjacent to the bars is reached. This threshold value is approximately 0.025% to 0.033% by weight of the concrete for black bars (NCHRP Project 18-6A). Corrosion causes expansion of steel that leads to spalling of the concrete. Epoxy coated bars are assumed to be better protected against corrosion because of the polymer coating on these bars. However, the corrosion problem is accelerated locally (like a battery effect) where there is damage caused due to shipping and handling, and if that damage is not properly repaired. There is no significant research on the effectiveness of epoxy coating on corrosion in high chloride concentration environment. Limited research by Kochanski (1990) suggested that chloride exposure to epoxy coating can deteriorate adhesion between the steel bars and the epoxy coating making it ineffective for corrosion protection of steel reinforcement.

The concrete cores obtained from bridge ASD-42-0656 were sliced, powdered, and analyzed for chloride ion content as described in the following sections. Both cracked and uncracked sections of the bridge deck were cut and analyzed for chloride ion content. The

0

2

4

6

8

10

12

14

16

18

20

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16D

epth

from

top

surf

ace

of b

ridge

dec

k (in

.)Crack width (in.)

C1-2 C-3 C-1

C-8 C-10 C-11

Allowable Crack Width - ACI 224R-01(for exposure to de-icing chemicals)

Max. Predicted Crack Width – Gergely & Lutz

81

chloride profiles (graphs showing chloride concentration versus depth from the surface) obtained for the cores provide information on the rate of diffusion of the chloride ions in the concrete. The following subsections discuss the procedures for measuring chloride in the core samples, the calculation of the chloride ion content, and a summary of the results for the concrete cores obtained in this study.

6.3.1 Acid Soluble Chloride Ion Content Analysis Titration Method Used

A number of well-established methods are available for determining chloride ion concentrations in concrete, including ASTM C1152-04 (2012) and AASHTO T 260-97 (2005). However, these methods are complex and expensive. The mercuric nitrate method (adopted from Standard Methods for the Examination of Water and Wastewater), is applicable to a chemical solution and can be used to determine the acid digestion of the powdered concrete extracted from sliced core samples. This method was used to determine the chloride ion content in the core specimens.

Preparation of the concrete samples for the chemical titration method involved acid digestion of powder samples extracted from concrete cores. Initially, the top 0.25 in. of each 2.75 in.-diameter core specimen was cut and discarded in order to prevent contamination from any foreign materials, and 0.5-in. slices of concrete at various depths from the top surface were cut with a saw and pulverized so that all the material passes through a 850-µm (No. 20) sieve. Ten grams of sample was measured and transfered to a 250-mL beaker, which was then dispersed with 75 ml of water. Dilute (1+1) nitric acid was used to digest the sample. The beaker was covered with a watch glass and allowed to stand for 1 to 2 minutes. The solution was heated for a few seconds and the sample was filtered through a 12.5 cm filter paper in a Buchner funnel. The filtrate was diluted with deionized water into a 200-ml volumetric flask, and 25 ml of the sample solution was transferred into 100-ml beaker using a pipette. The contents of one part of diphenylcarbazone reagent Powder Pillow indicator were then added to the sample. Using mercuric nitrate standard solution, the sample is titrated under acidic conditions in the presence of the diphenylcarbazone indicator. Upon addition of mercuric ion, a pink-purple complex was formed with the indicator, signaling the end point of the chemical reaction. Figure 6.13 shows the acid-soluble chloride content determination in the laboratory titration method.

6.3.1.1 Results of Acid Soluble Chloride Ion Content Analysis

The methods for the calculation of the chloride ion content as a percent of the concrete sample and as a percent of the cement in the sample are given in Appendix E. The results indicate that the chloride ion content determined at 0.5 in. below the surface was very high. The chloride ion content determined by the weight of the sample ranged from 0.05% to 0.56%. Also, the chloride ion content determined by the weight of cement ranged from 0.47% to 4.8%. Acid soluble chloride content percent by weight of cement for bridge ASD-42-0656 exceeded ACI 318-11 limit for reinforced concrete wet in service of 0.1% (when in direct contact with de-icing chemical, salt water, seawater, etc.) by more than 20 times. The density of the concrete used in the analysis was 3,784 lbs/yd3 (140 lbs/ft3), and the cement content in the concrete mix was 440 lbs/yd3 respectively. Tables in Appendix E show chloride ion content results for all the core samples.

82

Figure 6.13 Acid soluble chloride content determination in the laboratory – titration method

83

Table 6.9 presents a summary of the acid-soluble chloride content of all cases. Figure 6.14 shows acid soluble chloride content by weight of cement of core specimens. Figure 6.15 shows the profiles of acid soluble chloride % content by weight of the cement along the depth of core specimens. Figure 6.16 presents similar profiles of acid soluble chloride % content by weight of the sample. Figure 6.17 shows a summary of the acid-soluble chloride content profile of bridge deck core specimens. Table 6.20 presents the summary of results of acid-soluble chloride content for the core specimens.

The chloride content of the cores within 0.5 inch from the surface of the deck was nearly 3 to 4% by weight of cement, which is about 0.56% by weight of concrete. The corresponding concentrations at about 17 to 18 inches depth were about 0.7% by weight of cement or 0.05% by weight of concrete regardless of whether the core was cut through a crack or through the solid deck portion. The chloride concentrations at the level of the primary reinforcement, which is close to the top surface in the negative moment regions, is on average 2% by weight of cement. There seems to be no significant differences between chloride concentrations along the depth of concrete at uncracked locations and those at cracked locations. The threshold value for black bars recommended in ACI 318-11 is 0.1% by weight of cement for reinforced concrete wet in service. Similar threshold suggested by NCHRP report 18-6A is 0.025% to 0.033% by weight of concrete. By both counts, the threshold values were exceeded by a factor of about 20. The embedded bars in the selected bridge deck are epoxy-coated bars. Therefore the threshold values of such bars are likely to be somewhat higher than those for black bars. However, the corrosion threat from high chloride concentrations on epoxy-coated bars and the protection provided by epoxy-coating on steel bars is not well known, and therefore additional judgment is needed.

6.3.1.2 Accuracy of Analytical Results

Various researchers have used different methods to determine the chloride ion content of concrete samples. In order to validate the chloride concentrations obtained in this project, three of the powdered concrete core specimens were sent to CTL Engineering Inc. for analysis (see Appendix C for the complete test results). Their results, based on ASTM C1152-04 (ASTM 2012) were in close agreement with the results obtained from the mercuric nitrate method that was used in this project.

84

*ACI-318-11 Limit for reinforced concrete wet in service is 0.1% Core specimens through cracks: C1-2, C-1, C-3, C-8, C-10, C-11

Other core specimens: C-2, C-4, C-5, C-7, C-9, C-12

Figure 6.14 Acid-soluble chloride content by weight of cement of core specimens for bridge ASD-42-0656

C 1- 2 C - 3 C - 11 C - 10 C - 5

C - 1 C - 4 C - 12 C - 9 C - 2

3.8%

3.6%

0.8%0.7%

0.6%

17.7

1"

17.6

"

18.4

6"

17.9

7"

15.4

4"

18.0

"

18.9

4"

17.9

"

14.0

"17

.35"

1.1%

0.9%

0.8%

18.1

8"18

.44"

3.6%

0.6%

0.6%

0.5%

4.8%

0.8%

0.7%

0.7%

2.5%

0.8%

0.7%

0.6%

2.3%

0.8%

0.7%

0.6%

3.3%

0.5%

0.5%

3.9%

1.5%

1.0%

0.8%

4.0%

1.3%

0.8%

3.6%

0.8%

0.7%

0.6%

4.2%

0.8%

0.7%

0.7%

3.4%

0.9%

0.8%

0.7%

C - 8

C - 7

0.7%

0.7%

0.6%

85

Figure 6.15 Profile of the acid-soluble chloride % content by weight of the cement for core specimens for bridge ASD-42-0656

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5D

epth

bel

ow d

eck

surf

ace

(in.)

Chloride % weight of cement

C1-2 C - 2 C - 3

C - 4 C - 5 C - 1

C - 7 C - 8 C - 9

C - 10 C - 11 C - 12

ACI-318-11 Limit forReinforced concrete wet in service = 0.1%

86

Figure 6.16 Profile of the acid-soluble chloride % content by weight of the sample for core specimens for bridge ASD-42-0656

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4 0.5 0.6D

epth

bel

ow d

eck

surf

ace

(in.)

Chloride % weight of sample

C1-2 C - 2 C - 3

C - 4 C - 5 C - 1

C - 7 C - 8 C - 9

C - 10 C - 11 C - 12

87

Figure 6.17 Profile of the acid-soluble chloride content by weight of cement for core specimens for bridge ASD-42-0656.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Aver

age

chlo

ride

% w

eigh

t of

cem

ent

Specimen

C1-2 C-2 C-3 C-4 C-5 C-1 C-7 C-8 C-9 C-10 C-11 C-12

Cracked specimens

Uncracked specimens

88

Table 6.8 Summary of Acid-Soluble Chloride Content of Cores Cut from Bridge ASD-42-0656

Date of Test Specimen Average weight % of sample ppm %bwoc

9/16/14 C 1–2 0.19 1900 1.64 9/22/14 C – 2 0.17 1700 1.44 9/17/14 C – 3 0.15 1500 1.32 9/19/14 C – 4 0.17 1700 1.44 9/17/14 C – 5 0.17 1700 1.45 9/15/14 C – 1 0.21 2100 1.81 9/18/14 C – 7 0.19 1900 1.65 9/19/14 C – 8 0.13 1300 1.14 9/19/14 C – 9 0.15 1500 1.27 9/16/14 C – 10 0.13 1300 1.12 9/18/14 C – 11 0.20 2000 1.75 9/19/14 C – 12 0.17 1700 1.44

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

6.4 Summary The permanent crack widths and depths measured from the cores cut on ASD-42-0656

confirmed that very wide cracks are not just confined to the surface of the deck. These permanent cracks penetrate deep into the deck slab with widths exceeding the relevant ACI 224R-01 recommended limit of 0.007″ within at least the top 50% of the depth of the deck near the negative moment regions. Chloride ion contents determined from core concrete revealed that the chloride concentrations are 2% by weight of cement, which is about 20 times the recommended maximum value for black bars in ACI 318-11 at the level of the top bars in the negative moment regions. The compressive strengths determined from the cores demonstrated that these are comparable to those recorded from laboratory cured cylinders.

89

CHAPTER 7: MEASUREMENTS OF CRACK OPENINGS UNDER LIVE LOADS USING DIGITAL IMAGE CORRELATION

After understanding the unique and very wide permanent dead load cracking in CSS slab

bridge decks, attention was turned to the cracking during live load conditions. The permanent dead load cracks were much wider than those predicted using the most commonly used crack width equations. Therefore, it was needed to verify if the cracks from live loads likewise were larger than predicted or as expected from commonly used equations. The results of the truck live load tests on a three-span CSS slab bridge, ASD-42-0656, are presented in this chapter. 7.1 Introduction

Deck crack widening due to live loading was determined by field load tests for a three-span continuous structural slab bridge under static and moving truck loads using an Aramis based digital image correlation (DIC) system. DIC is a stereoscopic photometric methodology that tracks and measures deformation and movement of different points on the surface of an object using two digital cameras mounted at a finite distance from one another. These actual field test results were compared to the theoretical results derived based on the Gergely and Lutz equation.

The deck surface preparation for DIC consisted of applying a regular high-contrast dot pattern of black dots painted on white background to the top surface of the bridge deck. The measurement points can be considered as an extensometers, and strain gages. Photographic images are captured using the two high speed digital cameras. Using the principles of photogrammetry, the three-dimensional (3D) coordinates of each surface point are determined. The DIC results include a 3D shape of the component, 3D displacements, and the in-plane strains. The resulting data can be presented as color plots, video files, or section line diagrams, and it can be exported in ASCII format for further analysis. The bridge selected for these measurements was ASD-42-0656, a three-lane structural slab bridge rebuilt in 2009 in Ashland County in ODOT District 3. A six-axle dump truck loaded with gravel with a gross weight of 66,400 lbs was used to load the bridge in a controlled manner. Before loading, the axle weights and spacing were measured and recorded, as shown in Figure 7.1. The dimensions and axle loads of the test truck are shown in Figure 7.2. 7.2 DIC Set-up for Crack Width Measurements under Truck Loading The transverse flexural cracks monitored for this study were located over and/or adjacent to the piers. These cracks were monitored within the shoulder portion of the deck to keep traffic disruption to a minimum. The test truck was driven close to the crack measurement location, as shown on the layout in Figure 7.3. Typical stop positions for the truck with respect to crack location S1-3 are shown in Figure 7.4. Figure 7.5 shows a test setup for recording crack openings under static truck loading.

90

Figure 7.1 Axle load determination for the test truck

Total weight of the truck = 66.4 kips

Figure 7.2 Resulting axle loads for the test truck

8.3 kips 12.7 kips 12 kips 4.4 kips 14.4 kips 14.6 kips

8.3 kips 24.7 kips 33.4 kips

15'-4" 4'-4" 5'-6" 4'-1" 4'-1"

38'-10"

5'-6"

Truck Stop Position Ref. Point

91

Figure 7.3 General layout of crack measurement locations and typical truck positions on the bridge for static loading

40' 50' 40'

Shoulder

9'

12'

12'

12'

9'

SouthEdge of Shoulder

A B C D

Crack locations on deck slab

N2

S2-1S1-3 S1-1

S1-2

N1-1

N1-3N1-2

S2

Truck stop position spaced at 7'-6" o/c

1

Parapet2'

Typical edge of the truck path

A B C D

7.5'7.5'

234567

North

Turning Lane

PS2 PS1

PN2 PN1

Crack locations on parapet

92

Figure 7.4 Typical stop positions for the truck with respect to location S1-3

Figure 7.5. Recording of crack widening on bridge deck under static loading

76

54

32

1

Truck stop position spaced at 7'-6'' o/cS1-3 crack location

A & D = Abutments

B & C = Piers

93

7.3 Results for Crack Opening on the Deck Due to Static Truck Loading For the static load tests, the test truck was made to stop at specific pre-identified locations

to maximize the bending moment in the deck. The truck was stopped at intervals of 7.5 ft., and the crack opening readings were recorded at the selected location. Once the truck was stopped at all the defined locations, the location selected for crack measurement was changed and the truck stopped at the defined locations again to record the crack width measurements at the new location. This way, crack width measurements were taken at four locations of the bridge identified as S1, S2, N1, and N2 (Figure 7.3) corresponding to the southbound and northbound driving lanes of the bridge. SAP 2000 structural analysis software was used to determine the live load moments at various stop positions of the truck to calculate the theoretical crack widths form the truck loading. Figure 7.6 shows all seven stop positions where the moments and theoretical crack widths were determined. Typical bending moments and shear force diagrams with respect to the S1-3 crack location and for truck stop positions 1, 4 and 7 are shown in Figures 7.7, 7.8, and 7.9, respectively. Crack widths were determined using the equation developed by Gergely and Lutz (1968) for crack locations S1-1, S1-2, and S1-3; these crack widths are presented in Tables 7.1, 7.2, and 7.3, respectively. During this study, the measurements demonstrated that cracks widened and closed with truck loading. A maximum crack widening of up to 0.004 in. (Figure 7.12) was recorded for a typical crack location, S1-3, under static loading.

Graphs showing the corresponding peak crack widening for each time the truck was stopped for static loading were plotted for each run. Figures 7.10 to 7.17 show the comparison of the measured crack widths for crack locations S1-1, S1-2, and S1-3 to the crack widths predicted using the Gergely and Lutz equation. As can be seen from the measured values, the cracks on the bridge deck did not completely close after the removal of the truck from the bridge. Numerous indications of crack opening and closing were observed. The plots in Figures 7.10 through 7.17 show that the crack openings for the static loading condition were generally similar but not too accurate when compared to the crack widths predicted by the Gergely and Lutz equation. Any difference may be due to the assumptions involved in the theoretical calculations of the crack widths.

94

Figure 7.6 Sequence of loading for structural analysis (S1-3 region)

Position #1

Position #2

Position #3

Position #4

Position #5

Position #6

Position #740' 50' 40'

95

Figure 7.7 Bending moment and shear force diagram for load position 1

Bending Moment Diagram

Shear Force Diagram

Truck load reference point

All loads are in kipsAll moments are in kip-ft

40' 50' 40'

Position #1

96

Figure 7.8 Bending moment and shear force diagram for load position 4

Position #4

40' 50' 40'

Bending Moment Diagram

Shear Force Diagram

Truck load reference point

All loads are in kipsAll moments are in kip-ft

97

Figure 7.9 Bending moment and shear force diagram for load position 7

40' 50' 40'

Bending Moment Diagram

Shear Force Diagram

Truck load reference point

All loads are in kipsAll moments are in kip-ft

Position #7

98

Table 7.1 Static Truck Load, Self Weight Moments and Crack Widths at S1-1 Location

Truck Location

Truck Ref. Point

to S1-1 Location

(ft)

Negative Moment at

S1-1 (Slab DL)

(kip-ft)

Negative Moment at

S1-1 (Truck Load)

(kip-ft)

Negative Moment at

S1-1 (Truck +Slab DL)

(kip-ft)

Steel Stress Corresponding to (Truck +Slab DL)

(ksi)

Maximum Crack Width Predicted by Gergely & Lutz (1968)

Truck Load (in.)

Dead Load (in.)

Truck + Slab DL (in.)

1 22.5

54.37 (*fs = 14.2

ksi)

12.54 66.91 17.50 0.0016 0.0069 0.0085 2 15 15.28 69.65 18.22 0.0019 0.0069 0.0088 3 7.5 14.70 69.07 18.06 0.0019 0.0068 0.0087 4 0 18.22 72.59 18.98 0.0023 0.0069 0.0092 5 -7.5 14.93 69.30 18.12 0.0019 0.0069 0.0088 6 -15 17.13 71.50 18.70 0.0022 0.0069 0.0091 7 -22.5 20.59 74.96 19.60 0.0026 0.0069 0.0095

Table 7.2 Static Truck Load, Self Weight Moments and Crack Widths at S1-2 Location

Truck Location

Truck Reference Point to

S1-2 Location

(ft)

Negative Moment at

S1-2 (Slab DL)

(kip-ft)

Negative Moment at

S1-2 (Truck Load)

(kip-ft)

Negative Moment at

S1-2 (Truck +Slab DL)

(kip-ft)

Steel Stress Corresponding to (Truck +Slab DL)

(ksi )

Maximum Crack Width Predicted by Gergely & Lutz (1968)

Truck Load (in.)

Dead Load (in.)

Truck + Slab DL (in.)

1 22.5

61.57 (*fs = 16.1

ksi)

15.03 69.4 18.15 0.0019 0.0069 0.0088

2 15 18.96 73.33 19.18 0.0024 0.0069 0.0093

3 7.5 18.10 72.47 18.95 0.0023 0.0069 0.0092

4 0 21.18 75.55 19.76 0.0027 0.0069 0.0096

5 -7.5 17.98 72.35 18.92 0.0023 0.0069 0.0092

6 -15 17.57 71.94 18.81 0.0022 0.0069 0.0091

7 -22.5 21.12 75.49 19.74 0.0027 0.0069 0.0096

99

Table 7.3 Static Truck Load, Self Weight Moments and Crack Widths at S1-3 Location

Truck Location

Truck Reference Point to

S1-3 Location

(ft)

Negative Moment at

S1-3 (Slab DL)

(kip-ft)

Negative Moment at

S1-3 (Truck Load)

(kip-ft)

Negative Moment at

S1-3 (Truck +Slab DL)

(kip-ft)

Steel Stress Corresponding to (Truck +Slab DL)

(ksi)

Maximum Crack Width Predicted by Gergely & Lutz (1968)

Truck Load (in.)

Dead Load (in.)

Truck + Slab DL (in.)

1 22.5

54.37 (*fs = 14.2

ksi)

13.87 68.24 17.84 0.0018 0.0068 0.0086

2 15 17.86 72.23 18.90 0.0023 0.0068 0.0091

3 7.5 15.98 70.35 18.40 0.0020 0.0069 0.0089

4 0 18.33 72.6 18.99 0.0023 0.0069 0.0092

5 -7.5 15.38 69.75 18.25 0.0019 0.0069 0.0088

6 -15 12.94 67.31 17.62 0.0016 0.0069 0.0085

7 -22.5 17.49 71.86 18.79 0.0022 0.0069 0.0091

100

Figure 7.10 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#1)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

Cra

ck w

iden

ing

(in.)

76

54

32

1

1

23 4

56

7

Truck stop position

101

Figure 7.11 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#2)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)Theoretical

76

54

32

1

1

23

4

56

7

Truck stop position

102

Figure 7.12 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#3)

0 7.5 15 22.5 30 37.5 45 52.5 60

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)

Theoretical

DIC: S1-3 - #3

1

23

4

56

7

Truck stop position

103

Figure 7.13 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#4)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)TheoreticalDIC: S1-3 - #4

76

54

32

1

1

23

4

56

7

Truck stop position

104

Figure 7.14 Comparison of measured crack widths with predicted crack widths for truck loading S1-3 (#5)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)TheoreticalDIC: S1-3 - #5

76

54

32

1

1

23

4

56

7

Truck stop position

105

Figure 7.15 Comparison of measured crack widths with predicted crack widths for truck loading S1-1

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)TheoreticalDIC: S1-1

12

34

5

6

7

Truck stop position

106

Figure 7.16 Comparison of measured crack widths with predicted crack widths for truck loading S1-2 (#1)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

Crac

k w

iden

ing

(in.)

TheoreticalDIC: S1-2 - #1

1 23

4

5 6

7

Truck stop position

107

Figure 7.17 Comparison of measured crack widths with predicted crack widths for truck loading S1-2 (#2)

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005Cr

ack

wid

enin

g (in

.)TheoreticalDIC: S1-2 - #2

1

2 3 4 5 6

7

Truck stop position

108

7.4 Results for Crack Opening on the Deck due to Loading of a Moving Truck For the moving load tests, the truck was driven at 5, 10, 20, 30, 40, 50, and 60 mph. Frame rates ranging from 7 to 29 frames per second were used to capture the data during the moving truck load test runs. The camera readings were started before the truck entered the bridge and continued until it left the bridge. Graphs showing the corresponding peak crack widening were plotted for each truck run for typical crack locations. During this study, the measurements demonstrated that cracks widened and closed with truck loading; however, the cracks did not always completely close immediately after the removal of the truck from the bridge. The theoretical crack widths predicted using the Gergely and Lutz equation for typical crack location S1-3 are represented in Table 7.4. The bending moment and shear force envelopes for the moving truck load used to calculate the theoretical crack widths are shown in Figure 7.18. Once again, SAP 2000 was used to calculate the bending moment and shear force envelopes. Figures 7.19 to 7.25 present a comparison of the measured crack widths to the crack widths predicted using the Gergely and Lutz equation for typical crack locations S1-1, S1-2, and S1-3. The recorded live load crack widths for the moving load condition were somewhat less than what was expected from Gergely and Lutz equation (0.0015 in. versus 0.002 in.). The structure generally behaved as expected or better than expected under truck loading condition in regards to crack widening under moving truck loads. The crack widths measured for slower speeds of the truck movement were found to be larger than those at higher speeds, but were mostly inconclusive. It is reasonable to conclude that individual applications of live loads from traffic do not seem to be the source of the wide cracking. Furthermore, the measured crack widths due to live loads were significantly smaller in comparison to the corresponding permanent cracking due to dead load condition.

109

Figure 7.18 Bending moment and shear force envelopes for a load from a moving truck

40' 50' 40'

Shear force envelope

Bending moment envelope

*Moments are in kip-ft; Shears are in kips

110

Table 7.4 Moving Truck Load, Moments, Steel Stress and Crack Widths at S1-3 Location

Negative Moment

Truck Load

Moment Per 12" width

(kip-ft) Moment + IM

(kip-ft)

Steel Stress (ksi)

Max. Crack Width: Truck Load Only Gergely & Lutz (1968)

Max. Crack Width: Truck Load Only Chowdhury & Loo (2001)

For Static (in.)

For Static + Impact (in.)

For Static (in.)

For Static + Impact (in.)

Negative Moment 15.4 20.5 4.9 0.0020 0.0027 0.0021 0.0028 Positive Moment 3.5 4.6 1.1 0.0004 0.0006 0.0005 0.0007

IM = Impact factor applied on the axles only.

111

Figure 7.19 Measured crack widths for moving truck loading: S1-3 location for 5 mph

-0.0020

-0.0010

0.0000

0.0010

0.0020

0.0030

0.0040

0.0050

0 2 4 6 8 10 12 14 16 18 20 22 24

Crac

k wi

deni

ng (i

n.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

112

Figure 7.20 Measured crack widths for moving truck loading: S1-3 location for 10 mph

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0 2 4 6 8 10 12 14 16

Crac

k w

iden

ing

(in.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

113

Figure 7.21 Measured crack widths for moving truck loading: S1-3 location for 20 mph

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

40 41 42 43 44 45 46 47 48 49 50

Crac

k w

iden

ing

(in.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

114

Figure 7.22 Measured crack widths for moving truck loading: S1-3 location for 30 mph

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0.001

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0.003

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0.005

0 1 2 3 4 5 6

Crac

k w

iden

ing

(in.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

115

Figure 7.23 Measured crack widths for moving truck loading: S1-1 location for 10 mph

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Crac

k w

iden

ing

(in.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

116

Figure 7.24 Measured crack widths for moving truck loading: S1-2 location for 10 mph

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0.005

0 1 2 3 4 5 6 7 8

Crac

k wi

deni

ng (i

n.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

117

Figure 7.25 Measured crack widths for moving truck loading: S1-2 location for 40 mph

-0.0020

-0.0010

0.0000

0.0010

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0.0030

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0.0050

0 1 2 3 4 5 6

Crac

k w

iden

ing

(in.)

Time (s)

Max. Crack Width for Static (Neg. Moment)

Max. Crack Width for Static (Pos. Moment)Max. Crack Width for Static + Impact (Pos. Moment)

Max. Crack Width for Static + Impact (Neg. Moment)

118

7.5 Results for Crack Opening in the Parapet Crack openings were also recorded for the concrete parapets of ASD-42-0656 for both

static and moving truck loads. As mentioned in Section 5.3, the permanent crack widths on parapet surfaces under sustained dead load were found to be about 0.1 to 0.13 inch. Figures 7.26 and 7.27 show plots for crack widening for a typical parapet location (PS1) for both static and moving truck load conditions. The crack widening under truck loading on the inner face of the parapets at locations near the piers was recorded to be about 0.001 inch revealing that the parapets are participating actively as integral part of the deck under live load conditions. Therefore, the deck cracking and the corresponding parapet cracking seem to be related problems.

Figure 7.26 Measured crack widths for static truck loading: PS1 parapet location

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0 25 50 75 100 125 150

Crac

k wid

enin

g (in

.)

Strain stage

119

Figure 7.27 Measured crack widths for moving truck loading: PS1 parapet location for 5 mph.

7.6 Summary of Results for Truck Live Load Tests Based on the truck live load test results, the following observations can be made:

• The recorded live load crack widths for the static loading condition were generally similar to but not too accurate compared with the predicted crack openings based on the equation developed by Gergely and Lutz (1968).

• The recorded live load crack widths for the moving load condition were somewhat less than expected (0.0015 in. for DIC versus 0.002 in.) when compared to the corresponding predictions made by using Gergely and Lutz equation.

• Crack widths measured from the live load condition are small in comparison to the crack widths due to the dead load condition.

• In some cases, live load cracks did not fully close once the truck load was removed. • The bridge deck generally behaved as expected or better than expected in terms of crack

widening under moving truck loading condition. Single applications of live loads do not seem to be the source of the wide cracking in bridge deck.

• From the measurements obtained from crack widening under live load conditions, it appears that the parapet is participating in carrying the truck live load applied on the bridge deck through the reinforcing bars provided at the connection between the deck slab and the parapets. The deck to parapet connection seems to make this load transfer possible. Therefore, parapet cracking and deck cracking in CSS slab bridges are closely related problems.

-0.002

-0.001

0.000

0.001

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0.003

0.004

0.005

0 25 50 75 100 125 150

Crac

k wi

deni

ng (i

n.)

Strain stage

120

CHAPTER 8: STRUCTURAL, SECTION, AND CRACK WIDTH ANALYSIS

ODOT historically designs and constructs many CSS slab bridges every year and currently has over 2,200 structural slab bridges in service. To eliminate redundant design, ODOT developed standard construction drawings for designers for the most common span configurations. The analyses used to develop all multiple span configurations assumed pin connections at the intermediate pier supports. The structural analysis and design data for each of the three-span slab configurations were reviewed to validate that the unique cracking in CSS slab bridge decks could not be attributed to the structural reinforcing. Most CSS slab bridges in Ohio are designed using standard construction drawings provided by ODOT. This chapter presents the results of the structural, section and crack width analyses of the selected structural slab bridges. 8.1 Introduction

The structural analysis involved examining the effect of pier/slab connections assuming both simple and rigid conditions. ODOT standard drawing CS1-08 was reviewed to understand how closely the reinforcing details met AASHTO specifications and ACI 318-11 requirements.

ODOT office of Structural Engineering provided detailed spreadsheet calculations for all the standard bridge span configurations provided in the ODOT standard drawings. The flexural moment capacities as well as unfactored moments were independently determined for each standard three-span reinforced concrete structural slab bridge detailed in ODOT’s standard bridge drawings. These values were compared with the values given in the ODOT design spread sheets. Also, crack widths due to service dead load and live load moments were determined for the same standard three-span structural slab bridges. Finally, the truck overload data that was provided by ODOT’s Office of Technical Services was studied to determine the likelihood of truck overloads influencing the crack widths.

8.2 Determination of Service Load Moments Using SAP 2000 Structural Analysis Software Structural analysis using SAP 2000 software was performed on all standard ODOT three-

span structural slab bridges to determine moments, rotations, deflections and reactions. The unfactored moments developed from the analyses were used to determine Service I moments for the section and crack width analyses. The results of a typical three-span bridge, ASD-42-0656, is presented in this section as an example. This bridge has a depth of 24 in. and spans of 40, 50, and 40 ft. The different load cases considered in the analysis included dead load (DL), future wearing surface (FWS), and AASHTO HL93 truck and lane loads.

HL93 truck loading has a leading axle load of 8 kips, followed by an axle load of 32 kip at a fixed distance of 14 ft., and trailed by another axle load of 32 kip at a distance varying between 14 ft. and 30 ft (Figure 8.1). The HL 93 lane load is a uniformly distributed load with a magnitude of 640 plf. A load of 60 pounds per square foot is considered for the FWS load as specified in the AASHTO Bridge Design Manual. A typical slab dead load moment diagram and HL93 truck load moment envelope are shown in Figures 8.2 and Figure 8.3, respectively. In calculating the Service I moments, distribution factors (DF) based on span length and bridge width were calculated for each span, and the governing DF was applied to the unfactored moments of the HL93 truck and lane loads. In addition, an impact factor of 1.33 was applied to the HL93 truck load.

121

(a) HL 93 truck load (b) HL 93 Lane Load

Figure 8.1 AASHTO HL93 truck and lane loads

Figure 8.2 Typical moment diagram for slab dead load

The Service I limit state moments for the bridge were calculated using Mu = 1.0 (DC) +

1.0 (DW) + 1.0 (IM + LL), where IM = impact factor, DC = slab dead load, DW = future wearing surface load, and LL = HL93 truck and lane loads. The unfactored and Service I limit state moments that were determined for bridge ASD-42-0656 are presented in Table 8.1. 8.2.1 Effect of Stiffness on Piers The effect of stiffness on piers was investigated by analyzing four typical three-span structural slab bridge configurations. SAP 2000 structural analysis software was used to examine the pier/slab connection for four of the selected bridges assuming both simple and rigid conditions and to evaluate the effects of pier stiffness on the moment distributions under both conditions (Figure 8.4). The Service I moments based on slab dead load, FWS, HL 93 truck and lane loads for each scheme for the selected bridges are presented in Tables 8.2 to 8.4.

In Figure 8.4 (a) called Scheme A, the supports were idealized as pinned supports, while in Figure 8.1 (b) called Scheme B, the rigidity of the joint between the deck slab and the pier cap (and the piers) was included in the structural analysis model. Pier lengths of 15 ft. were assumed in the model in Scheme B. The negative moments due to live loads on the bridges increased by

640 plf

122

10 to 15% when the rigidity of the connection of the slab with pier cap is considered compared to the corresponding moments obtained with pin supports at the four reaction points (this is the common design assumption generally used by many design engineers and also by ODOT).

Figure 8.3 Typical moment envelope for HL 93 truck load

Table 8.1 Unfactored and Service I Limit State Moments for Bridge ASD-42-0656

Unfactored Moments

Load cases

Moments (kip-ft) Max. positive moment Max. negative

moment Exterior spans

Interior span

Dead Load 33 32.2 61.6

FWS Load 6.6 6.4 12.3

HL 93 Lane Load 106 114 146

HL 93 Truck Load 360 379 270

HL 93 Lane Load including D.F. 10.6 11.4 14.6

HL 93 Truck Load including IM + D.F. 47.9 50.4 35.9 Service I Limit State Moments

[Mu = 1.0 (DC) + 1.0 (DW) + 1.0 (IM + LL)] Max. positive moment (kip-ft) Max. negative moment

(kip-ft) Exterior spans Interior span 98.1 100.4 124.4

Note: D.F. is distribution factor

123

Figure 8.4 Two schemes used for examining the effect of stiffness on piers

Table 8.2 Summary of Analysis Results for Bridges with 40'–50'–40' Spans (TRU-534-1516, ASD-42-0656)

No. of Lanes/ Scheme Type

Service I Limit State Ext. Positive

Moment (kip-ft)

Int. Positive Moment (kip-ft)

Negative Moment (kip-ft)

1 Lane Analysis

Scheme A 88 85 117 Scheme B 78 71 130

2 Lane Analysis

Scheme A 98 100 126 Scheme B 86 82 141

(a) Scheme A

(a) Scheme B

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Table 8.3 Summary of Analysis Results for Bridge with 38'–47.5'–38' Spans (POR-224-1172)

No. of Lanes/ Scheme Type

Service I Limit State

Ext. Positive Moment (kip-ft)

Int. Positive Moment (kip-ft)

Negative Moment (kip-ft)

1 Lane Analysis

Scheme A 80 77 106 Scheme B 71 64 118

2 Lane Analysis

Scheme A 88 91 113 Scheme B 78 74 127

Table 8.4 Summary of Analysis Results for Bridge with 44'–55'–44' Spans (STA-225-076)

No. of Lanes/ Scheme Type

Service I Limit State

Ext. Positive Moment (kip-ft)

Int. Positive Moment (kip-ft)

Negative Moment (kip-ft)

1 Lane Analysis

Scheme A 106 102 143 Scheme B 92 90 159

2 Lane Analysis

Scheme A 120 122 155 Scheme B 103 105 174

8.3 Review of ODOT Standard Designs for Three-Span Structural Slab Bridges

The ODOT standard design calculations (including review of all reinforcing steel details and moment capacities) for three-span structural slab bridges were reviewed. The flexural moment capacities and the factored bending moments were determined for all three-span structural slab bridges and compared with the values provided in the ODOT standard bridge calculations. The calculations that were developed and the values determined in this project compared very favorably with those provided by ODOT. The differences were minimal, if any. Thus the analysis and design of the standard slab bridges are not the source of the extreme cracking. Unfactored moments are needed for crack width calculations. Those were determined for all standard three-span structural slab bridges and compared with the values provided in the ODOT standard bridge calculations. The comparison proved that the values determined in this project matched very well with those given in the ODOT calculations.

Table 8.5 presents results of flexural moment capacities of the top steel reinforcement for the relevant three-span structural slab bridges. Table 8.6 presents typical results of unfactored moments due to HL 93 truck loading for the relevant three-span structural slab bridges. Typical unfactored moments due to HL 93 lane loading for all the relevant three-span structural slab bridges are shown in Table 8.7.

125

Table 8.5 Comparison of ODOT Moment Capacities of Typical Three-span Slab Bridges to Calculated Values

Bridge Spans

(ft)

Moment Capacity (ɸMn) Top Steel Reinforcement – Interior

Span ODOT

(ft-kips)

Moment Capacity (ɸMn) Top Steel Reinforcement – Interior

Span Calculated Values

(ft-kips)

24–30.0–24 79.1 79.1

28–35.0–28 99.3 99.3

30–37.5–30 122.6 122.6

37–46.25–37 182.7 182.0

38–47.25–38 194.6 193.9

40–50–40 212.4 211.7

44–55–44 272.9 271.3

Table 8.6 Comparison of Unfactored Moments Given in ODOT Standards with Determined Values – HL93 Truck Load

Bridge Spans (ft) Loadings

Max. Positive Moment (ft-kips) Max. Negative Moment

(ft-kips) Mab (exterior span) Mab (interior span)

ODOT SAP ODOT SAP ODOT SAP

24–30–24 HL93 TRUCK 205.70 165.25 207.00 172.54 162.50 159.93

28–35–28 HL93 TRUCK 246.9 209.72 248.20 218.01 192.90 190.45

30–37.5–30 HL93 TRUCK 268.20 233.82 269.50 244.41 208.34 205.54

37–46.25–37 HL93 TRUCK 340.30 318.17 342.60 336.83 260.53 258.31

38–47.5–38 HL93 TRUCK 351.00 331.68 352.00 350.69 267.32 265.76

40–50–40 HL93 TRUCK 371.00 360.22 377.00 379.04 280.00 280.57

44–55–44 HL93 TRUCK 412.00 417.30 435.00 435.80 302.00 300.50

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Table 8.7 Comparison of Unfactored Moments of Slab Bridges Given in ODOT Standards with Determined Values; HL93 Lane Load

Bridge Spans (ft) Loadings

Max. Positive Moment (Ft-kips) Max. Negative Moment

(Ft-kips) Mab (exterior span) Mab (interior span)

ODOT SAP ODOT SAP ODOT SAP

24–30–24 HL93 LANE 38.07 38.23 40.70 41.12 53.50 52.46

28–35–28 HL93 LANE 52.30 52.02 55.39 55.93 72.82 71.54

30–37.5–30 HL93 LANE 59.48 59.70 63.59 64.19 83.59 82.18

37–46.25–37 HL93 LANE 90.47 90.80 96.72 97.58 127.15 125.21

38–47.5–38 HL93 LANE 95.43 95.77 100.00 102.92 134.11 132.09

40–50–40 HL93 LANE 106.00 106.12 114.00 114.03 149.00 146.40

44–55–44 HL93 LANE 129.00 128.50 137.00 137.95 180.00 177.20

8.4 Correlation of Field Measurements to Predicted Crack Widths and Calculated Steel Stresses Different investigators have used either experimental and/or analytical methods to develop crack width prediction equations. Some of the available studies include Lan and Ding (1992), Chowdhury and Loo (2001), Rao and Dilger (1992), Beeby (1979), Frosch (1999), Gergely and Lutz (1968), Oh and Kang (1987), and Rasidi et al. (2013). Three of the most common methods were selected from this list to predict crack widths at service load moments over the piers. The different load cases considered in the analysis included dead load, and AASHTO HL93 truck and lane loads. The crack widths predicted using Chowdhury and Loo (2001), Gergely and Lutz (1968), and Oh and Kang (1987) for the three-span bridges surveyed are presented in Table 8.8. Crack widths predicted using the three selected equations are shown in Figure 8.5. The figure shows the predicted crack widths for three three-span structural slab bridges with different sets of spans (on the horizontal axis). For each bridge, three sets of crack widths are also shown. Each set of bars represents the predicted crack widths under theoretical dead load or dead load plus live load condition for black steel. The figure shows that the crack widths under dead load plus live load condition are theoretically larger than the allowable crack width of 0.007 inch recommended in ACI 224R-01 for decks exposed to de-icing chemicals. The figure also shows the maximum permanent crack widths measured at site for some of the bridges under dead load alone. The difference between the theoretical crack widths predicted for the dead load or dead load plus live load conditions and the measured permanent crack widths is significant and; the two values differ by a factor of 10 to 15.

Table 8.9 shows the predicted crack widths for the selected CSS slab bridges at different levels of steel stresses. Table 8.10 summarizes the predicted crack widths corresponding to the maximum allowable steel stress of 40 ksi. ACI 318-11 recommends checking of serviceability limit state at 66.7% of the specified yield strength of the reinforcing steel. In the selected bridges, the yield strength of steel is 60 ksi and therefore, 40 ksi represents the 66.7% of 60 ksi. The

127

values given in Table 8.10 show that the crack widths obtained from the three selected equations are nearly equal to each other.

Steel stress versus predicted crack width for bridge spans 28–35–28 ft. and 40–50–40 ft. are shown in Figures 8.6 and 8.7, respectively. The relationship between the steel stresses and the corresponding crack widths plotted in these figures shows almost a linear relationship between the two.

8.5 Summary of Structural and Crack Width Analyses

The following observations were made based on the structural, section, and crack width analyses of the structural slab bridges that were studied in this project:

• The structural analysis including the rigidity due to the connection between the slab and the pier cap revealed that including the stiffness due to the rigid connection and the flexibility due to the height of piers results in live load moments that are larger by about 10 to 15% in the negative moment region than the corresponding moments determined with pin supports. However, this increase is considered only marginal because it does not explain the difference between the predicted and measured crack widths which is different by a factor of 10 to 15.

• A review of truck overload data determined that structural impacts from overloads were likely insignificant.

• The structural analysis and design checks performed in this project determined that the reinforcing steel provided in CS1-108 was more than sufficient to meet the relevant AASHTO and ACI 318-11 requirements. The design calculations and details developed in this project mostly matched the corresponding design calculations and details adopted in ODOT standards; and were generally found to satisfy all other relevant requirements of AASHTO and ACI 318-11.

• Three most common crack width equations used in this project predict crack widths that are nearly equal under identical loading conditions. However, these equations were not able to predict the permanent crack width measured on CSS slab bridge decks under dead load condition alone.

• The source of the unique cracking in the CSS slab bridge decks was not due to a lack of steel reinforcement or inadequate design.

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Table 8.8 Comparison of the Recorded and Predicted Maximum Crack Widths

Bridge Number (SFN No.)

Spans (ft)

Max. Recorded

crack width (in.)

Maximum Crack Width using Gergely & Lutz (1968)

Maximum Crack Width Chowdhury & Loo (2001)

Maximum Crack Width Oh & Kang (1987)

DL (in.)

DL+LL (in.)

DL (in.)

DL+LL (in.)

DL (in.)

DL+LL (in.)

ASD-42-0656 (0301159) 40–50–40 0.100 0.0078 0.0144 0.0081 0.0149 0.0051 0.0122

ASD-250-0377 (0304697) 37–46.25–37 0.030 0.0073 0.0143 0.0073 0.0142 0.0044 0.0118

WAY-250-1039 (8501815) 44–55–44 0.100 0.0081 0.0138 0.0084 0.0144 0.0056 0.0121

POR-224-1172 (6703900) 38–47.5–38 0.125 0.0074 0.0142 0.0074 0.0142 0.0046 0.0118

STA-225-076 (7605943) 44–55–44 0.100 0.0081 0.0138 0.0084 0.0144 0.0056 0.0121

MAH-62-0207 (5001846) 28–35–28 0.040 0.0062 0.0152 0.0056 0.0136 0.0029 0.0112

MAH-224-1619 (5004837) 28–35–28 0.050 0.0062 0.0152 0.0056 0.0136 0.0029 0.0112

POR-88-1250 (6703607) 30–37.5–30 0.080 0.0061 0.0141 0.0054 0.0124 0.0029 0.0107

TRU-534-1516 (7807457) 40–50–40 0.100 0.0078 0.0144 0.0081 0.0149 0.0051 0.0122

TRU-45-2018 (7802285) 40–50–40 0.080 0.0078 0.0144 0.0081 0.0149 0.0051 0.0122

129

Figure 8.5 Predicted crack widths for four bridges using three equations

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

38-47.5-38 40-50-40 44-55-44

Max

imum

cra

ck w

idth

(in.

)

Bridge span lengths (ft.)

Allowable Crack Width - ACI 224R-01(for exposure to de-icing chemicals)

Maximum recorded crack width for STA-225-076, TRU-534-1516, ASD-42-0656

Maximum recorded crack width for POR-224-1172

Gergely & Lutz Eq. (DL, DL+LL)

Chowdhury & Loo Eq. (DL, DL+LL)

Oh & Kang Equation (DL, DL+LL)

130

Table 8.9 Predicted Crack Widths for Varying Steel Stresses for the Bridges Surveyed

Bridge Number (SFN No.) Bridge Spans (ft.)

Steel Stress (ksi)

Crack Width Gergely & Lutz (1968)

(in.) Chowdury & Loo (2001)

(in.) Oh & Kang (1987)

(in.)

MAH-62-0207 (5001846) MAH-224-1619 (5004837)

28–35–28

10 0.0054 0.0048 0.0021 20 0.0107 0.0096 0.0071 30 0.061 0.0144 0.0121 40 0.0214 0.0192 0.0171 50 0.0268 0.0240 0.0221 60 0.0321 0.0288 0.0271

POR-88-1250 (6703607)

30–37.5–30

10 0.0054 0.0048 0.0022 20 0.0108 0.0095 0.0075 30 0.0163 0.0143 0.0127 40 0.0217 0.0191 0.0180 50 0.0271 0.0239 0.0233 60 0.0325 0.0286 0.0180

ASD-250-0377 (0304697)

37–46.25–37

10 0.0053 0.0053 0.0024 20 0.0107 0.0107 0.0080 30 0.0160 0.0160 0.0136 40 0.0214 0.0213 0.0192 50 0.0267 0.0266 0.0248 60 0.0321 0.0320 0.0305

131

Table 8.9 Predicted Crack Widths for Varying Steel Stresses for the Bridges Surveyed (continued)

Bridge No. (SFN No.) Bridge Spans

(ft)

Steel Stress (ksi)

Crack Width Gergely & Lutz (1968)

(in.) Chowdury & Loo (2001)

(in.) Oh & Kang (1987)

(in.) POR-224-1172 (6703900)

38–47.5–38

10 0.0053 0.0053 0.0024 20 0.0107 0.0106 0.0080 30 0.0160 0.0160 0.0137 40 0.0213 0.0213 0.0193 50 0.0266 0.0266 0.0250 60 0.0320 0.0319 0.0306

ASD-42-0656 (0301159) TRU-534-1516 (7807457) TRU-45-2018 (7802285)

40–50–40

10 0.0053 0.0055 0.0024 20 0.0106 0.0109 0.0081 30 0.0159 0.0164 0.0138 40 0.0212 0.0219 0.0195 50 0.0265 0.0274 0.0252 60 0.0318 0.0328 0.0309

WAY-250-1039 (8501815) STA-225-076 (7605943)

44–55–44

10 0.0053 0.0055 0.0025 20 0.0106 0.0110 0.0085 30 0.0159 0.0165 0.0145 40 0.0213 0.0221 0.0204 50 0.0266 0.0276 0.0264 60 0.0319 0.0331 0.0324

132

Table 8.10 Theoretical Crack Widths at 40 ksi Stress Corresponding to Serviceability Limit State per ACI 318-11

Bridge Number (SFN No.)

Spans (ft)

Max. Recorded Crack Width

(in.)

Crack Width Corresponding to Max. Allowable Steel Stress (40 ksi) at Service Limit State by ACI 318-11

Gergely & Lutz (1968) (in.)

Chowdhury & Loo (2001) (in.)

Oh & Kang (1987) (in.)

ASD-42-0656 (0301159) 40–50–40 0.100 0.0212 0.0219 0.0195

ASD-250-0377 (0304697) 37–46.25–37 0.030 0.0214 0.0213 0.0192

WAY-250-1039 (8501815) 44–55–44 0.100 0.0213 0.0221 0.0204

POR-224-1172 (6703900) 38–47.5–38 0.125 0.0213 0.0213 0.0193

STA-225-076 (7605943) 44–55–44 0.100 0.0213 0.0221 0.0204

MAH-62-0207 (5001846) 28–35–28 0.040 0.0214 0.0192 0.0171

MAH-224-1619 (5004837) 28–35–28 0.050 0.0214 0.0192 0.0171

POR-88-1250 (6703607) 30–37.5–30 0.080 0.0217 0.0191 0.0180

TRU-534-1516 (7807457) 40–50–40 0.100 0.0212 0.0219 0.0195

TRU-45-2018 (7802285) 40–50–40 0.080 0.0212 0.0219 0.0195

133

Figure 8.6 Steel stress versus predicted crack width for bridge spans 28–35–28 ft.

Figure 8.7 Steel stress versus predicted crack width for bridge spans 40–50–40 ft.

0

10

20

30

40

50

60

70

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Stee

l Stre

ss (k

si)

Crack Width (in.)

Gergely & Lutz (1968)

Chowdury & Loo (2001)

Oh & Kang (1987)

Max. Allowable Steel Stress at Service Limit State: ACI 318-11

0

10

20

30

40

50

60

70

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Stee

l Stre

ss (k

si)

Crack Width (in.)

Gergely & Lutz (1968)Chowdury & Loo (2001)Oh & Kang (1987)

Max. Allowable Steel Stress at Service Limit State: ACI 318-11

134

CHAPTER 9: EXPERIMENTAL INVESTIGATION OF ECB BOND TO CONCRETE Many DOTs use epoxy-coated bars (ECBs) in place of black bars in the construction of structural slab bridges to provide protection against corrosion of the embedded reinforcing steel. An important unknown when using epoxy-coated reinforcement is the effect of the epoxy coating on bond development and crack control. The effects of epoxy coating on bond and anchorage behavior of reinforcing bars were studied by several investigators (e.g., Treece and Jirsa, 1989). However, little research has been done on the influence of ECB on crack control (Mitchell et al. 1996). This chapter presents the results of a test program designed specifically to study the cracking behavior of epoxy-coated steel reinforced concrete specimens. 9.1 Introduction

A series of tests were conducted to investigate the effect of epoxy coating on the crack width development in reinforced concrete. The first phase of the experimental program was comprised of making prisms for direct tension tests to evaluate cracking behavior of concrete. A flow chart outlining the experimental investigation plan is presented in Figure 9.1. A total of thirty two prisms were made: sixteen of the specimens contained a single epoxy-coated steel bar in each specimen, and the other sixteen had a single black bar. The effect of the addition of fiber was also evaluated, and the corresponding results are presented in Chapter 10. Four different concrete sections were used, but all concrete prisms were 30 inch long. The sections used include 4×4, 5×5, 6×6, and 6.25×6.25 in. resulting in cover thicknesses to the center of the bar of 2, 2.5, 3, and 3.1 in., respectively. Four different sizes of reinforcement were used, namely #3, #4, #9 and #11 rebars. Each prism had a single rebar embedded in the concrete. Details of direct tension test specimens without fiber are shown in Table 9.1. Typical details for a direct tension prism specimen are shown in Figure 9.2. The second phase of the experimental program constituted the construction of eight reinforced concrete slab elements that were instrumented and tested in a flexural configuration. These slabs represent a standard ODOT 40–50–40 ft. structural slab bridge to one-third scale in the negative moment region over an intermediate pier. All the test slabs had the same cross section and reinforcement configuration with an effective span of 10 ft. and an overall depth of 8 in. The main top reinforcement comprised two #6 bars at 6.6 in. on-center and bottom reinforcement of two #5 bars at a spacing of 6.4 in. Four slab specimens were reinforced with epoxy-coated steel bars, whereas the remaining four slab specimens were reinforced with black bars. Two of the test slabs had two precut grooves (with a width of 0.125 in. and depth of 0.5 in.) near the midspan section with a distance of 7¼ in. between them. The grooves were made in the slabs to try to initiate the cracks from those locations. The precut locations were used as the locations where crack width development can be monitored with LVDTs (linear variable displacement transducers). The slabs were evaluated over the entire range of service, post-cracked and ultimate limit states. The slabs were subjected to varying levels of loading/unloading until failure. Details of four of the test slabs are shown in Table 9.2. The details of the remaining four test slabs are presented in chapter 10. A typical slab longitudinal section and cross-section are shown in Figure 9.3 and Figure 9.4, respectively.

135

Figure 9.1 Experimental program

Table 9.1 Details of Direct Tension Specimens without Fiber

Specimen Rebar Type Rebar Size Cross Section

(in.) Reinforcement Ratio U4-#3 Uncoated #3 4×4 in. 0.007 U4-#4 Uncoated #4 4×4 in. 0.013 E4-#3 Epoxy coated #3 4×4 in. 0.007 E4-#4 Epoxy coated #4 4×4 in. 0.013 U6-#3 Uncoated #3 6×6 in. 0.003 U6-#4 Uncoated #4 6×6 in. 0.006 E6-#3 Epoxy coated #3 6×6 in. 0.003 E6-#4 Epoxy coated #4 6×6 in. 0.006

U6.25A-#9 Uncoated #9 6.25×6.25 in. 0.026 U6.25B-#9 Uncoated #9 6.25×6.25 in. 0.026

U6.25A-#11 Uncoated #11 6.25×6.25 in. 0.040 U6.25B-#11 Uncoated #11 6.25×6.25 in. 0.040 E6.25A-#9 Epoxy coated #9 6.25×6.25 in. 0.026 E6.25B-#9 Epoxy coated #9 6.25×6.25 in. 0.026

E6.25A-#11 Epoxy coated #11 6.25×6.25 in. 0.040 E6.25B-#11 Epoxy coated #11 6.25×6.25 in. 0.040

Experimental Program

Flexural Crack Width Tests Direct Tension Crack Width Tests

8 Slab Specimens

Variables include: cover thickness, rebar size, effect of

epoxy coating , effect of addition of fibers

Variables include:effect of epoxy coating,

effect of addition of fibers

32 Prism Specimens

Compare experimental results to predicted values

Determine cracking load, steel strains, crack widths, crack spacing, crack patterns,

Phase II Phase I

failure load

Determine cracking load, steel strains, crack widths, crack spacing, crack patterns, failure load

136

Figure 9.2 Direct tension test specimen

Table 9.2 Details of Flexural Crack Width Test Slabs without Fiber

Specimen Rebar Type Precut

(⅛" thick; ½" deep)

SLAB U Uncoated No

SLAB E Epoxy-coated No

SLAB U-P Uncoated Yes

SLAB E-P Epoxy-coated Yes

#3 / #4 /#9 /#11; epoxy/uncoated rebar

30 in.

7 in.

4×4/5×5/6×6/6.25×6.25 in. section

7 in.

137

Figure 9.3 Typical longitudinal section of the reinforced concrete test slab.

Figure 9.4 Cross section details of the reinforced concrete slab

9.2 Making of Test Specimens The preparation of the test specimens is discussed in the following subsections. 9.2.1 Steel Reinforcement Each of the direct tension test specimens had either a single #3, #4, #9 or #11 uncoated or epoxy-coated rebar. For the test slabs, the main top reinforcement comprised two #6 bars at 6.6 in. center-to-center and bottom reinforcement of two #5 bars at a spacing of 6.4 in. Two of the slabs were reinforced with epoxy-coated bars, whereas the remaining two of the four specimens were reinforced with black bars. In addition, #3 bars were used as distribution steel in the transverse direction in the test slabs. The steel reinforcement was supplied by the Akron Rebar Company (Akron, Ohio). Figure 9.5 shows typical black bars and epoxy-coated bars. The yield strength values guaranteed by the supplier for #3 and #4 bars were 69.6 ksi and 66.9 ksi, respectively (Table 9.3). However, the measured yield strengths were 80.6 and 78 ksi for the #3 and #4 bars, respectively. Figure 9.6 shows typical stress-strain curves for steel reinforcement tested in the laboratory for this study.

8"

#6 rebar @ 6.6" c/c

#5 rebar @ 6.4" c/c

#3 rebar @ 6" c/c

Top cover = 0.75"Bottom cover = 0.75"

13.2"

138

Figure 9.5 Typical epoxy-coated and uncoated steel reinforcements

Table 9.3 Steel Reinforcement Details (Provided by Akron Rebar Company)

Property #3 #4 #5 #6 Diameter (in.) 0.375 0.5 0.625 0.75

Area (in.2) 0.11 0.20 0.31 0.44 Yield strength (psi) 69,600 66,900 64,300 67,500

Ultimate strength (psi) 110,100 106,200 102,500 104,500 Tensile modulus (ksi) 29000 29000 29000 29000

Elongation (%) 13.4 14.6 12.9 12.6

Figure 9.6 Stress strain curves for steel reinforcement tested in the laboratory

0

20

40

60

80

100

120

140

160

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Stre

ss (k

si)

Strain (in/in)

Epoxy #3 Bar Epoxy #4 BarUncoated #3 Bar Uncoated #4 Bar

139

9.2.2 Concrete A concrete mix designed to achieve a minimum of 4,500 psi (as required by SCD-108) was used for the construction of all direct tension specimens as well as the one-third scale slabs. Ready-mix concrete was provided by a local supplier (Associated Associate Inc., Mantua, Ohio) and the mix design used for the present investigation is presented in the Table 9.4. Concrete cylinders (4 in. diameter and 8 in. long) were also cast and tested at 28 days of age, and on the day of testing to determine the compressive strength of the concrete. The concrete compressive strength testing was conducted for the cylinders according to ASTM C39/C39M. The average compressive strengths determined for the concrete were 4,600 psi on 28 days and 5,100 psi on the day of testing.

Table 9.4 Typical Mix Design for 4,500 psi Concrete

Material Design Quantity Batched Quantity

Coarse Aggregates; No. 57 1,710 lb 3,420 lb

Sand 1,311 lb 2,740 lb

Cement (Type I), 564 lb 1,125 lb

Admixture ( SIKA 200) 5 oz/100 lb of Cement 56 oz

Air 6% 9 oz

Water 30.0 gal 6 gal

Water/Cement Ratio 0.443 0.444

9.3 Making of Laboratory Specimens The construction process included preparation of formwork, assembly of reinforcement cages, concrete casting, and curing of specimens. 9.3.1 Making of Formwork Plywood formwork was made in the materials laboratory of the University of Akron to cast the test specimens (Figure 9.7).

140

Figure 9.7 Formwork for the slabs and direct tension test specimens

9.3.2 Assembly of Reinforcement Cages Figure 9.8 shows the reinforcement cages placed in the formwork for slab specimens (on

left and for prism specimens (on right).

Figure 9.8 Typical reinforcement cages 9.3.3 Casting of Concrete Concrete mix from the same concrete batch was used in making eight direct tension specimens and four slab specimens. The slump of the concrete was 7 in. The concrete was placed in the formwork and compacted using needle vibrators. In addition, concrete was also placed in plastic molds to make cylinders for compressive strength testing. Figure 9.9 shows the placement of the concrete, the preparation of the test cylinders, and curing of the specimens for 7 days with wet burlap and plastic sheets.

141

Figure 9.9 Placement of concrete 9.4 Instrumentation Several sensors were installed at various stages of the experimental program to record strains, deflections, crack widths and forces. These sensors included strain gages, LVDTs, and load cells. A computer with a data acquisition (DAQ) interface system was used to monitor and record strain and LVDT data. 9.4.1 Strain Gages Two types of strain gages were used to measure strains in the flexural reinforcement and on the surface of concrete. Installation of the strain gages is shown in Figure 9.10.

Preparation of test cylinders Curing of concrete

Slump test Casting of concrete

142

Figure 9.10 Installation of strain gages on steel reinforcement

9.4.2 Linear Variable Displacement Transducer (LVDT) LVDTs were installed on the top of each slab and were used to record the crack widths. In addition, an LVDT was installed at the bottom of each test slab to measure the midspan deflection. Figure 9.11 shows a typical LVDT used for recording the crack width.

Figure 9.11 Typical arrangement of LVDT to measure crack widths

(a) Surface preparation for strain gages (b) Installed strain gages

(c) Strain gages on slab reinforcement (d) Strain gages on direct tension specimens

143

9.4.3 MTS Loading System Load tests of the slab specimens were conducted using an MTS hydraulic actuator at The University of Akron. This actuator has a capacity of 55 kips in both tension and compression with a stroke or travel length of 12 in. The ultimate load test for each slab specimen was performed in a force control mode with a uniform loading/unloading rate of 0.25 kip per minute. The test setup is shown in Figure 9.12. 9.5 Digital Image Correlation Contrasting dots were painted onto the surfaces of the test slabs to allow digital image correlation (DIC) to be used for recording concrete strains and deflection at midspan. The displacement results were compared to the LVDT recordings at the midspan section. Figure 9.12 shows a typical DIC setup.

Figure 9.12 Typical setup for DIC using high-speed cameras and painted contrasting dots

9.6 Testing of the Test Specimens Direct tension tests on prisms were conducted to determine the cracking load, steel strains, concrete strains and crack widths at various load levels. For each specimen, two strain gages were installed on the steel reinforcing bar embedded in the concrete. Figure 9.13 shows the direct tension test prisms. The test setup for a typical prism is shown in Figure 9.14. The displacement control mode was used in loading the prism. The cracking load for each specimen was recorded, and the corresponding crack width was measured using a crack gage. At each load level, the maximum crack widths were recorded. The flexural crack width test of the slabs was conducted to determine the cracking load, failure load, midspan deflection, steel strains, concrete strains and crack widths at various load levels. The simply supported slab with an effective span of 10 ft. was tested under a four-point-loading setup. The two loading points of the steel spreader were 7.25 in. apart. The slabs were loaded from the bottom of the slabs. The main longitudinal reinforcement was placed at the top.

144

A service limit state test was performed first, where each slab was loaded until the first crack was observed. Several flexural cracks developed at the top of the slabs as the load was increased beyond the cracking load. Consequently, the slabs experienced a further reduction in their flexural stiffness with each successive loading/unloading cycle.

The crack width and crack pattern were recorded and plotted at each loading level until failure. Figure 9.15 shows two typical precuts in one of the test slabs with spacing between the two cuts being 7.25 in. A schematic of the test setup for a typical slab specimen is shown in Figure 9.16. Each slab was subjected to incremental loading/unloading of 4, 6, 8, and 10 kips. The same slab was then loaded to failure after the incremental loading/unloading stages were completed.

Figure 9.13 Direct tension crack width test prisms

145

Figure 9.14 Test setup for a direct tension concrete prism

Figure 9.15 Typical precut in one of the test slabs

Digital Image Correlation Camera

Typical specimen

146

Figure 9.16 Schematic diagram of flexural crack width test setup.

9.7 Results and Discussion of Direct Tension Crack Width Test The results of the direct tension and flexural crack width tests are discussed in the

following sections.

9.7.1 Cracking Behavior of Direct Tension Prism Specimens The cracking loads recorded for specimens U6-#4, E6-#4, U4-#3, and E4-#3 were 7.0, 6.0, 4.2, and 3.8 kips, respectively as summarized in Table 9.5. Specimens with ECBs cracked at about 85 to 90% of the load of the corresponding specimens with black bars. The specimens with ECBs showed about 37% greater crack widths than the corresponding uncoated black bar specimens at failure. The crack patterns for the prisms without fiber are shown in Figure 9.17. Figure 9.18 shows a comparison of crack widths of specimen U6-#3 with those of E6-#3 at different loadings. The applied loads versus maximum recorded crack widths for E6-#4 and U6-#4 are shown in Figure 9.19. The average crack spacing measured for specimens U4-#4, U4-#3, E4-#4, and E4-#3 were 5.2, 4.4, 5.2, and 6.2 in., respectively. The maximum recorded crack widths at 18 kips for specimens U6-#4, E6-#4, U4-#4, and E4-#4 were 0.05, 0.08, 0.08, and 0.1 in., respectively. Also, the maximum recorded crack widths at 11 kips for specimens U6-#3, E6-#3, U4-#3, and E4-#3 were 0.06, 0.08, 0.09, and 0.13 in., respectively.

The observed cracking loads for U4-#4 and U4-#3 with uncoated bars were in close agreement with the theoretical cracking loads predicted using ACI 224.2R-92 and those predicted using equations from Rizkalla and Hwang (1984). There are currently no equations available for similar predictions for prism specimens with ECB. Figures 9.20 to 9.23 show a

147

comparison of experimental load versus maximum crack width predicted with ACI 224.2R-92 for selected prisms. Load versus crack width for all prisms are shown in Figure 9.24. Table 9.5 presents a summary of results of the direct tension tests.

Generally, in comparison with prisms with black bars, the prisms with epoxy-coated bars cracked at a lower cracking load, and exhibited significantly wider cracks at any load level. Similar difference between the crack widths for the larger diameter bars does not seem as severe as is was for smaller diameter bars. Uncoated (black) bars generally had smaller crack widths compared with those for the corresponding test specimens with epoxy-coated bars.

Figure 9.17 Failed direct tension specimens.

Figure 9.18 Crack width comparison of specimens U6-#3 to E6-#3

148

Figure 9.19 Load versus maximum crack width for specimens E6-#4 and U6-#4.

Figure 9.20 Load versus maximum crack width for specimens E4-#4 and U4-#4

with ACI 224.2R-92.

0

2

4

6

8

10

12

14

16

18

20

22

24

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Load

(kip

s)

Maximum crack width (in)

ACI

E6 - #4

U6 - #4

0

2

4

6

8

10

12

14

16

18

20

22

24

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Load

(kip

s)

Maximum crack width (in)

E4 - #4

U4 - #4

ACI

149

Figure 9.21 Load versus maximum crack width for E6.25-#11 and U6.25-#11

Figure 9.22 Load versus maximum crack width for E6.25-#11 and U6.25-#11

0

10

20

30

40

50

60

70

80

90

100

110

120

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Load

(kip

s)

Crack width (in.)

U6.25-#11

E6.25-#11

ACI-224-2R-92

0

10

20

30

40

50

60

70

80

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Load

(kip

s)

Crack width (in.)

U6.25-#9

E6.25-#9

ACI-224-2R-92

150

Figure 9.23 Load versus maximum crack width for #9 and #11 prisms

Figure 9.24 Load versus maximum crack width for all specimens.

0

10

20

30

40

50

60

70

80

90

100

110

120

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Load

(kip

s)

Crack width (in.)

U6.25-#9

U6.25-#11

E6.25-#9

E6.25-#11

0

2

4

6

8

10

12

14

16

18

20

22

24

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Load

(kip

s)

Maximum crack width (in)

U4 - #3

E4 - #4

E6 - #3

E6 - #4

U6 - #3

U6 - #4

U4 - #4

E4 - #3

151

Table 9.5 Summary of Direct Tension Crack Width Test Results of Specimens without Fiber

Specimen Rebar Type

Rebar Size

Cross Section

(in.)

Reinforcement Ratio

Maximum Applied

Load (kips)

Experimental Cracking

Load (kips)

ACI 224.2R-92 Cracking

Load (kips)

Experimental Max. Crack

Width (in.)

ACI224.2R-92 Max. Crack

Width (in.)

Average Crack Spacing

(in.)

U4-#3 Uncoated #3 4×4 0.0069 11 4.2 4.6 0.090 0.028 4.4 E4-#3 Epoxy

coated #3 4×4 0.0069 11 3.8 - 0.130 - 6.2

U4-#4 Uncoated #4 4×4 0.0125 18 4.5 4.8 0.080 0.025 5.2 E4-#4 Epoxy

coated #4 4×4 0.0125 18 4.0 - 0.100 - 5.2

U6-#3 Uncoated #3 6×6 0.0031 11 6.7 10.2 0.060 0.041 -

E6-#3 Epoxy coated

#3 6×6 0.0031 11 6.5 - 0.080 - -

U6-#4 Uncoated #4 6×6 0.0056 18 7.0 10.3 0.050 0.037 -

E6-#4 Epoxy coated

#4 6×6 0.0056 18 6.0 - 0.080 - -

U6.25-#9 Uncoated #9 6.25×6.25 0.0256 70 15.0 13.5 0.085 0.030 2.75 E6.25-#9 Epoxy

coated #9 6.25×6.25 0.0256 70 13.4 - 0.092 - 3.75

U6.25-#11 Uncoated #11 6.25×6.25 0.0399 110 14.2 14.6 0.120 0.030 3.5 E6.25-#11 Epoxy

coated #11 6.25×6.25 0.0399 110 13.1 - 0.130 - 5.2

152

9.8 Results and Discussion of Flexural Crack Width Test Slabs In this section, the experimental results obtained from the slab tests are compared with

theoretical predictions obtained by using the equations suggested by Gergely and Lutz (1968), Chowdhury and Loo (2001), and Oh and Kang (1987). They are also compared to each other. 9.8.1 Cracking Behavior of Test Slabs During flexural crack tests, the load was applied incrementally to the bottom of each test slab until the first flexural crack was observed at the top. The first crack was generally detected at a load level between 1.8 kips and 3.0 kips in all slabs without fiber. The propagation of cracks as the test progressed was also monitored, and a crack gage was used to measure the observed cracks. The first crack was detected for Slab U, Slab E, Slab U-P, and Slab E-P at loads of 3.0, 2.0, 2.8, and 1.8 kips, respectively, and the corresponding measured crack widths were 0.008, 0.01, 0.006, and 0.008 in., respectively. The slabs with epoxy-coated bars withstood lower cracking loads compared to the corresponding test slabs with black bars. All the cracks were observed near the midspan section of the slabs. The cracked stage began with the initiation of the first flexural crack.

The slabs were subjected to incremental loading/unloading of 4, 6, 8, 10 kips, and the loading/unloading continued until each slab failed. LVDTs were installed to monitor cracks on the top of the slabs. The crack width and crack pattern were recorded and plotted for each slab. More cracks developed progressively farther from the midspan as the load was increased. For Slab E, the maximum recorded crack widths at 4, 6, 8, 10, and at failure were 0.016, 0.02, 0.03, 0.04, and 0.125 in., respectively. Similarly, for Slab U, the maximum recorded crack widths at 4, 6, 8, 10 kips and at failure were 0.01, 0.012, 0.016, 0.02, and 0.08 in., respectively. Under various load levels, the two similar slabs (with and without precut grooves) with uncoated bars (Slab U and Slab U-P) experienced similar crack widths and overall flexural crack patterns. The same was observed for the two slabs with epoxy-coated bars (Slab E and Slab E-P). However, the recorded difference in crack widths for Slab U and Slab E were quite significant. For example, at load level of 10 kips, the maximum observed crack widths were 0.02 and 0.04 in. in Slab U and Slab E, respectively. A similar trend was observed in Slab E-P and Slab U-P. At a load level of 10 kips, the maximum observed crack widths were 0.025, and 0.05 in. for Slab U-P and Slab E-P, respectively. Slab E-P exhibited the largest crack width, followed by Slab E, Slab U-P, and Slab U. These test results indicate that the crack widths for slabs with epoxy-coated bars were twice as much as those with black bars. The wider crack widths may be attributed to inferior bonds between the epoxy-coated bars and the surrounding concrete. Slab U, Slab E, Slab U-P, and Slab E-P failed at loads of 14.4, 12.4, 13.8, and 12.6 kips, respectively, and the corresponding crack widths measured at failure using a crack gage were 0.08, 0.125, 0.08, and 0.16 in., respectively. In addition, the measured crack widths using LVDTs at failure were 0.078, 0.149, 0.060, and 0.199 in. for Slab U, Slab E, Slab U-P, and Slab E-P, respectively. Fewer cracks were observed for the uncoated slab specimens when compared to the corresponding epoxy-coated specimens at various loading/unloading stages. The experimental average crack spacing observed for Slab U, Slab E, Slab U-P, and Slab E-P were 5.4, 4.8, 5.5, and 4.6 in., respectively. Figures 9.25 to 9.29 show the crack patterns for the test slabs for the various loading/unloading stages and at failure. The recorded maximum crack widths and failed test slabs are shown in Figure 9.30 to 9.33.

153

Figure 9.25 Crack pattern for Slab U for loading/unloading levels and at failure

4 kip loading & unloading

6 kip loading & unloading

8 kip loading & unloading

10 kip loading & unloading

Ultimate loading

154

Figure 9.26 Crack pattern for Slab E for loading/unloading levels and at failure

4 kip loading & unloading

6 kip loading & unloading

8 kip loading & unloading

10 kip loading & unloading

Ultimate loading

155

Figure 9.27 Crack pattern for Slab U-P for loading/unloading levels and at failure

4 kip loading & unloading

6 kip loading & unloading

8 kip loading & unloading

10 kip loading & unloading

Ultimate loading

156

Figure 9.28 Crack pattern for Slab E-P for loading/unloading levels and at failure

4 kip loading & unloading

6 kip loading & unloading

8 kip loading & unloading

10 kip loading & unloading

Ultimate loading

157

Figure 9.29 Crack pattern for all slabs at failure

SLAB U

SLAB E

SLAB U-P

SLAB E-P

158

Figure 9.30 Failure mode of Slab U

Figure 9.31 Failure mode of Slab E

Figure 9.32 Failure mode of Slab U-P

*Crack width = 0.125"

*Crack width = 0.08"

159

Figure 9.33 Failure mode of Slab E-P

9.8.2 Comparison between Predicted and Experimental Results for the Test Slabs In general, the experimental failure load, cracking load, and average crack spacing in the slabs were found to match the values predicted using various equations. The results of the theoretical crack widths determined from Gergely and Lutz (1968), Chowdhury and Loo (2001), and Oh and Kang (1987) were close until approximately a load of 10 kips, beyond which a sharp increase was observed in measured crack widths that lead to a significant difference between the experimental and theoretical values. This could be attributed to the loading/unloading patterns for which the slabs were subjected to until ultimate loading. The experimental average crack spacings of 5.4, 4.8, 5.5, and 4.6 in. for Slab U, Slab E, Slab U-P, and Slab E-P, respectively are similar to the theoretical average crack spacings of 4.9 in. and 5.1 in. using the Chowdhury and Loo (2001) and the Frosch (1999) equations, respectively. The determined theoretical cracking load was 2.7 kips compared to experimental cracking loads of 3.0, 2.0, 2.8, and 1.8 kips for Slab U, Slab E, Slab U-P, and Slab E-P, respectively. The predicted failure load was 14 kips compared to the experimental failure load of 14.4, 12.4, 13.8, and 12.6 kips, for Slab U, Slab E, Slab U-P, and Slab E-P, respectively. All the test slabs with epoxy-coated bars cracked and failed at loads lower than their corresponding predicted values. The maximum load carrying capacities of the uncoated slab specimens were about 12% higher than the corresponding epoxy-coated specimens. Figure 9.34 shows load versus crack widths for the test slabs without fiber. These test results seem to be the most notable findings in terms of explaining larger crack widths and greater extent of cracking observed on the CSS slab bridge decks with epoxy-coated bars.

a

*mm scale; Crack width =4 mm=0.16 in.

160

Figure 9.34 Load versus crack width: experimental and theoretical comparison

0

2

4

6

8

10

12

14

16

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Load

(kip

s)

Crack width (in.)

Slab USlab ESlab U-PSlab E-PGergely & Lutz (1968)Chowdhury & Loo (2001)Oh & Kang (1987)

161

9.8.3 Load versus Mid-span Deflection Response LVDTs installed at the midspan of each slab were used to record the deflections. In addition, DIC was used to measure the displacement of the slab at the midspan sections. The initiation of the first flexural crack was marked by an obvious change in the slope in the load deflection curves. Several flexural cracks developed in the slabs after the load was increased beyond the cracking load. The residual deflection was recorded for each loading/unloading deflection. All slabs exhibited similar load deflection response until failure. The load deflection response for all the slabs was nearly linear until approximately 10 kips. At the yielding of steel bars in the slabs, the flexural cracks seem to progressively widen, and the slabs exhibited a rapid increase in the midspan deflection. The maximum observed deflection was 1.84, 1.87, 1.81 and 1.80 in. in Slab U, Slab E, Slab U-P and Slab E-P, respectively. These deflections are reasonably close to each other.

The DIC displacement results were compared to the LVDT recordings at the mid-span section, and the resulting values were found to be reasonably close. Figure 9.35 shows typical DIC displacement results for Slab E-P. The load deflection response until failure for all slabs is presented in Figures 9.36 to 9.39.

Figure 9.35 Digital image correlation deflection results for Slab E-P

Stage

1.501.251.000.7500.500.2500.00

1.98

Disp

lace

men

t (in

.)

Max. Displacement of 1.9 in.Displacement

1.9[in.]

1.8

1.9

1.7

1.4

1.3

1.2

1.1

0.9

0.8

162

Figure 9.36 Load versus midspan deflection for Slab U

Figure 9.37 Load versus midspan deflection for Slab E

0

2

4

6

8

10

12

14

16

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kip

)

Midspan deflection (in.)

4 kip load & unload

6 kip load & unload

8 kip load & unload

10 kip load & unload

Ultimate load

Ultimate load=14.4 kip

0

2

4

6

8

10

12

14

16

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kip

)

Midspan deflection (in.)

4 kip load & unload

6 kip load & unload

8 kip load & unload

10 kip load & unload

Ultimate load

Ultimate load=12.4 kip

163

Figure 9.38 Load versus midspan deflection for Slab U-P

Figure 9.39 Load versus midspan deflection for Slab E-P

0

2

4

6

8

10

12

14

16

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kip

)

Midspan deflection (in.)

4 kip load & unload

6 kip load & unload

8 kip load & unload

10 kip load & unload

Ultimate load

Ultimate load=13.8 kip

0

2

4

6

8

10

12

14

16

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Load

(kip

)

Midspan deflection (in.)

4 kip load & unload

6 kip load & unload

8 kip load & unload

10 kip load & unload

Ultimate load

Ultimate load=12.6 kip

164

9.8.4 Load versus Strain in Top Steel Reinforcement Two strain gages were installed on each of the two top steel reinforcing bars at the midspan of each slab specimen. All slabs exhibited similar load versus steel strain response. For example, at a load level of 6 kips, the recorded steel strains for Slab E-P, Slab U, Slab E, and Slab U-P are 0.00125, 0.00127, 0.00129, and 0.00133 in./in., respectively. Figures 9.40 to 9.43 show the load versus strain plots for the top reinforcement for the individual test slabs. Figure 9.44 shows the load versus strain in the top steel reinforcement at ultimate loading for all test slabs without fiber.

Figure 9.40 Load versus steel strain for Slab U

0

2

4

6

8

10

12

14

16

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

Load

(kip

)

Steel strain (in./in.)

Strain Gage R1a

Strain Gage R1b

Strain Gage R2a

R2a R2b

R1a R1b

R2a R2bStrain gages arrangement on top rebars

165

Figure 9.41 Load versus steel strain for Slab U-P

Figure 9.42 Load versus steel strain for Slab E

0

2

4

6

8

10

12

14

16

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

Load

(kip

)

Strain (in./in.)

Strain Gage R1a

Strain Gage R1b

Strain Gage R2a

Strain Gage R2b

R2a R2b

R1a R1b

R2a R2bStrain gages arrangement on top rebars

0

2

4

6

8

10

12

14

16

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

Load

(kip

)

Strain (in./in.)

Strain Gage R1a

Strain Gage R1b

Strain Gage R2a

R2a R2b

R1a R1b

R2a R2bStrain gages arrangement on top rebars

166

Figure 9.43 Load versus steel strain for Slab E-P

Figure 9.44 Load versus steel strain for all slabs at ultimate loading

0

2

4

6

8

10

12

14

16

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

Load

(kip

)

Steel strain (in./in.)

Strain Gage R1a

Strain Gage R1b

Strain Gage R2a

0

2

4

6

8

10

12

14

16

0.0000 0.0025 0.0050 0.0075 0.0100 0.0125 0.0150 0.0175 0.0200

Load

(kip

)

Steel strain (in./in.)

Slab U

Slab U-P

Slab E

Slab E-P

167

9.8.5 Summary of Test Results for Flexural Crack Width Test Slabs without Fiber Table 9.6 presents a summary of results for flexural crack width testing in slabs without fiber. In comparison to slabs with black bars, the slabs with epoxy-coated bars experienced (i) larger crack widths, (ii) lower cracking loads, (iii) lower ultimate loads, (iv) similar mid-span deflections and (iv) smaller average crack spacing.

Table 9.6 Summary of Results for Flexural Crack Width Test.

Parameter SLAB U

SLAB E

SLAB U-P

SLAB E-P

Experimental cracking load (kips) 3.0 2.0 2.8 1.8

Predicted cracking load (kips) 2.7 2.7 2.7 2.7

Average crack spacing (in.) 5.4 4.8 5.5 4.6

Predicted average crack spacing – Chowdhury & Loo, 2001(in.) 4.9 4.9 4.9 4.9

Experimental ultimate load (kips) 14.4 12.4 13.8 12.6

Predicted ultimate load (kips) 14.0 14.0 14.0 14.0

Experimental max. midspan deflection (in.) 1.84 1.87 1.81 1.87

9.9 Summary It is reiterated and established in this chapter that the results of the prism and slab tests are

the first indication of a possible cause for the extensive deck cracking. From the prism tests, it is evident that the prism specimens with epoxy-coated bars exhibited smaller cracking loads (when the first crack develops) and much larger crack widths compared to those for prism specimens with black bars. From the slab specimen tests, it was recorded that in comparison with slab specimens with black bars, the slab specimens with epoxy-coated bars exhibited smaller cracking load, much larger crack widths during the entire loading duration, smaller ultimate failure loads, and much larger mid-span deflections.

168

CHAPTER 10: CRACK MINIMIZATION STRATEGY

The effect of the addition of polypropylene or basalt MiniBar fiber to the concrete was evaluated in this chapter, and the results are presented. Slab and prism specimens made from concrete with fiber and reinforced with steel reinforcement with and without epoxy coating were tested, and their performance was captured during these tests. 10.1 Effect of Addition of Fiber to Reinforced Concrete Slabs

One of the important features of fiber reinforced concrete is the ability of the fiber to bridge across cracks. Fiber when added to concrete modify the cracking mechanism from macro cracking to micro cracking. The results are that crack widths are reduced, and the ultimate tensile cracking strain capacity of the concrete is increased. The mechanical bond between the embedded fiber and binder matrix redistributes the stresses. Additionally, the ability to modify the cracking mode results in quantifiable benefits. Reduced micro cracking leads to reduced permeability and increased surface abrasion resistance, impact resistance and fatigue strength (Patnaik et al. 2014). There are many different metallic and non-metallic micro or macro fiber available for use in fiber reinforced concrete. A new type of macro fiber known as MiniBars was recently made from basalt fiber and is gaining acceptance in the industry. The addition of fiber to concrete will also improve the bond strength between the reinforcing bar and the surrounding concrete. This is particularly useful for ECB because they are demonstrated in this study to have larger cracking potential, maybe due to inferior bond strength.

The effect of the addition of polypropylene and basalt MiniBar fiber to the concrete was evaluated with one-third scale slab test specimens. The slabs and prisms made from concrete with fiber had the same sectional properties as the specimens without fiber. An equivalent dosage based on 10 lbs/yd3 of fiber was used to make the test specimens in this study. Figure 10.1 shows polypropylene fiber and basalt MiniBar fiber used in this study, and Table 10.1 provides information regarding the properties of these fiber. Details of the direct tension test prism specimens and flexural crack width test slabs containing fiber are shown in Tables 10.2 and 10.3, respectively.

Figure 10.2 shows loads versus maximum crack widths for typical prisms with #4 bars with fiber. A summary of results of the direct tension crack width tests for specimens with and without fiber is presented in Table 10.4. Figure 10.3 shows the load versus midspan deflection for the slabs at ultimate load.

(a) Polypropylene fiber (b) Basalt MiniBar fiber

Figure 10.1 Polypropylene and basalt MiniBar fiber

169

Flexural test slabs after testing to failure are shown in Figure 10.4. Figure 10.5 shows loads versus crack widths in comparing experimental to predicted results. A summary of results for flexural crack width tests with/without fiber are presented in Table 10.5, and Table 10.6 presents the summary of the percentage improvement with the use of fiber.

Table 10.1 Properties of Polypropylene and Basalt Fiber

Properties Polypropylene Fiber Basalt MiniBar Fiber

Length (mm) 38–54 42–45 Diameter (mm) -- 0.66 Density(gm/cc) 0.91 1.8

Strain at Rupture -- 0.023 Tensile Strength (ksi) 83–96 157

Table 10.2 Details of Direct Tension Crack Width Specimens

With/without fiber Specimen Rebar Type Rebar Size

Cross Section (in.)

Reinforcement Ratio

WITH BASALT MINIBAR FIBER

U4-#3-BF Uncoated #3 4×4 in. 0.007 U4-#4 BF Uncoated #4 4×4 in. 0.013 E4-#3 BF Epoxy coated #3 4×4 in. 0.007 E4-#4 BF Epoxy coated #4 4×4 in. 0.013 U5-#3 BF Uncoated #3 5×5 in. 0.004 U5-#4 BF Uncoated #4 5×5 in. 0.008 E5-#3 BF Epoxy coated #3 5×5 in. 0.004 E5-#4 BF Epoxy coated #4 5×5 in. 0.008

WITH POLYPROPYLENE

FIBER

U4-#3-PF Uncoated #3 4×4 in. 0.007 U4-#4 PF Uncoated #4 4×4 in. 0.013 E4-#3 PF Epoxy coated #3 4×4 in. 0.007 E4-#4 PF Epoxy coated #4 4×4 in. 0.013 U5-#3 PF Uncoated #3 5×5 in. 0.004 U5-#4 PF Uncoated #4 5×5 in. 0.008 E5-#3 PF Epoxy coated #3 5×5 in. 0.004 E5-#4 PF Epoxy coated #4 5×5 in. 0.008

170

Table 10.3 Details of Flexural Crack Width Test Slabs

Specimen Rebar Type

WITH BASALT MINIBAR FIBER

SLAB U-BF Uncoated

SLAB E-BF Epoxy-coated

WITH POLYPROPYLENE

FIBER

SLAB U-PF Uncoated

SLAB E-PF Epoxy-coated

Figure 10.2 Load versus maximum crack width for #4 prisms with fiber

0

2

4

6

8

10

12

14

16

18

20

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Load

(kip

s)

Maximum crack width (in)

E4 - #4U4 - #4U4 - #4BFU4 - #4PFE4 - #4BFE4 - #4PFACI 224.2R-92

171

Table 10.4 Summary of Direct Tension Crack Width Test Results of Specimens with/without Fiber

With/ without fiber Specimen Rebar Type Rebar Size Cross Section

(in.) Reinforcement

Ratio Max. Applied Load

(kips)

Experimental Cracking Load

(kips)

ACI 224.2R-92 Cracking

Load (kips)

Experimental Max. Crack

Width (in.)

ACI224.2R-92 Max. Crack

Width (in.)

Average Crack Spacing (in.)

WITHOUT FIBER

U4-#3 Uncoated #3 4×4 0.0069 11 4.2 4.6 0.090 0.0276 4.4 U4-#4 Uncoated #4 4×4 0.0125 18 4.5 4.8 0.080 0.0248 5.2

E4-#3 Epoxy coated #3 4×4 0.0069 11 3.8 - 0.130 - 6.2

E4-#4 Epoxy coated #4 4×4 0.0125 18 4.0 - 0.100 - 5.2

U6-#3 Uncoated #3 6×6 0.0031 11 6.7 10.2 0.060 0.0414 -

U6-#4 Uncoated #4 6×6 0.0056 18 7.0 10.3 0.050 0.0373 -

E6-#3 Epoxy coated #3 6×6 0.0031 11 6.5 - 0.080 - - E6-#4 Epoxy coated #4 6×6 0.0056 18 6.0 - 0.080 - -

U6.25-#9 Uncoated #9 6.25×6.25 0.0256 70 15.0 13.5 0.085 0.0300 2.75 U6.25-#11 Uncoated #11 6.25×6.25 0.0399 110 14.2 14.6 0.120 0.0304 3.5 E6.25-#9 Epoxy coated #9 6.25×6.25 0.0256 70 13.4 - 0.092 - 3.75 E6.25-#11 Epoxy coated #11 6.25×6.25 0.0399 110 13.1 - 0.130 - 5.2

WITH BASALT FIBER

U4-#3-BF Uncoated #3 4×4 0.0069 11 4.4 - 0.086 - 6.0

U4-#4 BF Uncoated #4 4×4 0.0125 18 4.8 - 0.077 - 5.75

E4-#3 BF Epoxy coated #3 4×4 0.0069 11 4.3 - 0.096 - 11.0

E4-#4 BF Epoxy coated #4 4×4 0.0125 18 4.2 - 0.090 - 5.38

U5-#3 BF Uncoated #3 5×5 0.0044 11 6.5 - 0.081 - 8.5

U5-#4 BF Uncoated #4 5×5 0.0080 18 6.9 - 0.074 - 10.0

E5-#3 BF Epoxy coated #3 5×5 0.0044 11 6.2 - 0.084 - 8.5 E5-#4 BF Epoxy coated #4 5×5 0.0080 18 5.9 - 0.082 - 2.5

WITH POLYPROPYLENE

FIBER

U4-#3-PF Uncoated #3 4×4 0.0069 11 4.7 - 0.088 - 6.0 U4-#4 PF Uncoated #4 4×4 0.0125 18 4.6 - 0.078 - 4.5 E4-#3 PF Epoxy coated #3 4×4 0.0069 11 4.2 - 0.114 - 4.75 E4-#4 PF Epoxy coated #4 4×4 0.0125 18 4.1 - 0.095 - 5.75

U5-#3 PF Uncoated #3 5×5 0.0044 11 6.4 - 0.081 - 7.25

U5-#4 PF Uncoated #4 5×5 0.0080 18 6.7 - 0.076 - 8.0 E5-#3 PF Epoxy coated #3 5×5 0.0044 11 6.1 - 0.084 - - E5-#4 PF Epoxy coated #4 5×5 0.0080 18 5.8 - 0.084 - 6.5

172

Figure 10.3 Load versus midspan deflection for slabs at ultimate load

0

2

4

6

8

10

12

14

16

18

20

0 1 2 3 4 5 6 7

Load

(kip

s)

Midspan deflection (in.)

Slab U-PFSlab U-BFSlab E-PFSlab E-BFSlab USlab U-PSlab ESlab E-P

173

Figure 10.4 Flexural test slabs after testing to failure

B BF

FF

Slabs with Fiber Slabs without Fiber

174

Figure 10.5 Load versus crack width: experimental and theoretical comparison

0

2

4

6

8

10

12

14

16

18

0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40

Load

(kip

s)

Crack width (in.)

Slab USlab U-PSlab ESlab E-PSlab U-BFSlab E-BFSlab U-PFSlab E-PFGergely & Lutz (1968)Chowdhury & Loo (2001)Oh & Kang (1987)

175

Table 10.5 Summary of Results for Flexural Crack Width Test with/without Fiber

SLAB

U SLAB U-P

SLAB E

SLAB E-P

SLAB U-BF

SLAB E-BF

SLAB U-PF

SLAB E-PF

Experimental cracking load (kips) 3.0 2.8 2.0 1.8 3.6 3.3 3.4 3.2

Predicted cracking load (kips) 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7

Average crack spacing (in.) 5.4 5.5 4.8 4.6 4.6 5.1 4.5 4.8

Predicted average crack spacing – Chowdhury & Loo, 2001(in.) 4.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9

Experimental ultimate load (kips) 14.4 13.8 12.4 12.6 17.9 16.2 16.3 15.9

Predicted ultimate load (kips) 13.99 13.99 13.99 13.99 13.99 13.99 13.99 13.99

Experimental max. midspan deflection (in.) 1.84 1.81 1.87 1.8 5.79 4.79 4.83 4.98

176

Table 10.6 Summary of the Effect of Addition of Fiber

Crack Widths at specific applied loads for the test slabs

SLAB U

SLAB U-BF SLAB U-PF SLAB

E

SLAB E-BF SLAB E-PF

Applied load

(kips)

% improvement

Applied load

(kips)

% improvement

Applied load

(kips)

% improvement

Applied load

(kips)

% improvement

Cracking load (kips)

3.0 3.6 20 3.4 13 2.0 3.3 65 3.2 60

6 0.012 0.0085 29 0.009 25 0.02 0.015 25 0.016 20

7 0.014 0.0072 49 0.01 29 0.025 0.0165 34 0.018 28

8 0.016 0.0082 49 0.011 31 0.03 0.018 40 0.02 33

9 0.018 0.0093 48 0.0125 31 0.035 0.02 43 0.0225 36

10 0.02 0.012 40 0.015 25 0.04 0.022 45 0.025 38

Ave. crack width

improvement (%)

43 28 37 31

177

10.2 Summary Addition of fiber to the concrete that was used to make the test slab specimens

significantly reduced the crack widths. In comparison to slabs without fiber, slabs with basalt MiniBar or polypropylene fiber experienced (i) smaller crack widths over the entire loading range, (ii) higher cracking loads, (iii) higher ultimate failure loads, and (iv) maximum mid-span deflections at failure (better ductility). Consequently, the addition of fiber to the concrete mix used for making reinforced concrete decks is expected to improve cracking behavior of reinforced concrete bridge decks.

However, further evaluation is needed to find an optimum dosage of fiber to be added to concrete to achieve improved performance of concrete bridge decks. A few new bridge decks need to be constructed with fiber reinforced concrete and monitored for a few years to demonstrate the expected benefits and to address the related constructability issues, if any.

178

CHAPTER 11: CONCLUSIONS

Based on the results of this study, the following primary conclusions can be drawn:

Dead Load Condition 1. Structural slab bridge decks surveyed in 8 counties from D-3 and D-4 exhibited similar type

of non-shrinkage cracking. This problem was confirmed to be a statewide problem unique to CSS slab bridges.

2. The crack widths measured on representative bridges are as large as eight to ten times the

allowable maximum crack widths recommended in ACI 224R-01 for bridge decks exposed to de-icing chemicals. The crack widths and the extent of cracking of such decks increased with time.

3. Crack widths and depths measured on the concrete cores cut from one of the bridge decks confirmed that the crack widths were excessive as determined from the measurements taken on the deck surface; and the cracks extended almost the entire depth of some of the cores.

4. The current maximum spacing limits specified for longitudinal steel reinforcement given in

AASHTO-2012 and ACI 318-2011 are not adequate to control this type of cracking even for dead load condition. The current specifications were developed in the 1960s, before the use of epoxy-coated bars was adopted and therefore, are inaccurate by a large margin when applied to bridge decks reinforced with epoxy-coated bars.

5. Parapet cracking is a very significant issue for ODOT and its causes are largely unknown.

The crack width measurements recorded in this project suggest that the parapet cracking in CSS slab bridges is closely related to the deck cracking.

Live Load Condition 1. The recorded live load crack widths for the static loading condition was similar to the

predicted crack openings based on Gergely and Lutz Equation. Live load induced cracking is small in comparison to the cracking due to dead load condition. In some cases, these cracks do not close fully once the live load was removed.

2. The recorded live load crack widths for the moving load condition were somewhat less than

expected but yet reasonably close (0.0015″ vs 0.002″). 3. The deck structure generally behaved as expected or better than expected under truck loading

condition. Single application of live loads is not the source of wide cracking.

179

Structural Analysis and Overload Data 1. Several three-span continuous structural slab bridges were analyzed using SAP 2000

computer program to determine the design bending moments and shear forces under strength limit states and serviceability limit states. The results obtained from the SAP 2000 analysis were similar to those used by ODOT O.S.E to develop SD CS1-08. It was also determined that the reinforcing steel provided in CS1 was sufficient to meet the current AASHTO-2012 and ACI 318-11 requirements.

2. Analyses were also performed considering the effects of the pier/slab connections for both

simple condition, and rigid condition that included the pier cap and 15 feet of piers (similar to frame action) to determine the effects of joint stiffness on the moment distributions in either case. Live load moments were found to increase by 10 to 15% in the negative moment region when the effects of the pier/slab connection are considered compared to the simply supported condition which is a common design practice.

3. Truck overload data for the last one year as provided by the Office of Technical Services was

reviewed leading to the conclusion that structural impacts from overloads were likely insignificant.

Construction Issues 1. Based on a review of construction documentation, it was found that the specifications were

reasonably closely followed. No apparent construction reasons were found that would justify wide cracking in structural bridge decks.

2. The densities determined from the concrete cores revealed values ranging from 130 to 134 lb/ft3. Most of the compressive strengths obtained from the cylinders cut from the cores were over 6,000 psi.

3. The compressive strength tests of cores cut from the selected bridge deck demonstrated that

the field cores cut from the deck have compressive strengths comparable to those recorded on laboratory cured cylinders; i.e., the curing done on site is sufficient to develop the required compressive strength.

Acid Soluble Chloride Ion Content Chloride ion content determined at 0.5 in. below the surface was very high with chloride ion content by weight of the concrete was 0.56%. The chloride ion content determined by the weight of cement ranged from 0.47% to 4.8%. Acid soluble chloride content percent by weight of cement for bridge ASD-42-0656 exceeded ACI 318-11 limit for reinforced concrete wet-in-service of 0.1% (for direct contact with de-icing chemical, salt water, seawater, etc.) by a large margin. At the level of primary top reinforcement near the pier supports, the chloride concentrations are about 2% by weight of cement which is exceeding the limit recommended by ACI 318-11 by a factor of 20.

180

Evaluation of Bond Between Epoxy Coated Bars and the Surrounding Concrete

1. In comparison with prisms with black bars, the prisms with epoxy-coated bars cracked at a lower cracking load, and exhibited significantly wider cracks at any load level.

2. Similar difference between the crack widths for the larger diameter bars does not seem as

severe as is was for smaller diameter bars. 3. Uncoated (black) bars generally had smaller crack widths than those for the corresponding

test specimens with epoxy-coated bars.

Slab Flexural Tests 1. Laboratory-scale slab flexural tests representing the intermediate support region of typical

bridge decks revealed that maximum recorded crack widths of slabs with epoxy-coated bars can be as much as twice the crack widths of similar slabs that are reinforced with uncoated (black) bars.

2. In comparison to slabs with black bars, the slabs with epoxy-coated bars experienced (i)

larger crack widths, (ii) lower cracking loads, (iii) lower ultimate loads, (iv) smaller average crack spacing and (v) similar mid-span deflections.

3. The inferior cracking performance of slab specimens reinforced with epoxy-coated bars

compared to those reinforced with black bars is identified as an issue that must be evaluated more closely.

Effects of Addition of Fiber to Concrete

Adding fiber to concrete significantly reduces the crack widths in concrete. In comparison to slabs without fiber, slabs with basalt MiniBar or polypropylene fiber experienced (i) smaller crack widths in the entire loading range, (ii) higher cracking loads, (iii) higher ultimate loads, and (iv) maximum mid-span deflections at failure (better ductility). Consequently, the addition of fiber to the concrete mix used for making a reinforced concrete decks is expected to improve cracking behavior of reinforced concrete deck.

181

CHAPTER 12: RECOMMENDATIONS FOR IMPLEMENTATION

This study revealed that the problem of very wide permanent structural cracking near the intermediate pier supports is a statewide problem. A systematic study of various factors that were expected to cause this excessive cracking in CSS slab bridge decks did not support some of the factors to be contributing to the problem. The factors that were not found to be affecting the cracking behavior in any significant manner were: (i) design and detailing methodology used by ODOT in developing the standard designs and drawings (ii) deck plan geometry or location (iii) construction issues (iv) live load conditions and/or (v) occasional overloading of bridge decks.

The laboratory tests conducted in this study suggest that the use of epoxy-coated bars (ECB) may be contributing to the problem of excessive permanent CSS slab bridge deck cracking, even though it may not be the sole cause of the problem. The inferior bond between ECB and the surrounding concrete may also be a factor in cracking behavior of deck slabs. It was demonstrated in this study through laboratory scale tests that reinforced concrete slabs with basalt MiniBar or polypropylene fiber will improve the performance by reducing crack widths over the entire loading range, marginally increasing moment strength, and improving ductility through large deflections at failure. Consequently, the addition of fiber to the concrete mix used for making reinforced concrete decks is expected to substantially improve the cracking behavior of reinforced concrete bridge decks and is believed to be an implementable finding from this study.

However, further evaluation is needed to find an optimum dosage of fiber to be added to concrete to achieve improved performance of concrete bridge decks under practical site conditions. It is recommended that a few new bridge decks be constructed with fiber reinforced concrete and monitored for a few years to demonstrate the expected benefits and to address the related constructability issues, if any. With the implementation of fiber reinforced concrete in bridge decks, it is expected that the cracking problem will be minimized, maintenance cost minimized, and the service life of reinforced concrete structural slab bridge decks extended.

182

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187

APPENDICES

188

APPENDIX A: WORKED EXAMPLES A1: Flexural Crack Width Calculations for Slabs

In this section, the cracking load, moment capacity, average crack spacing and maximum crack width are calculated for Slab U. A1.1: Section Properties for a Typical Slab

All slabs were loaded from the bottom, and the top of the slab was in tension. Figure A.1 shows the cross section and longitudinal and section of a typical slab. The two loading points were 7.25 in. apart.

Figure A.1 Longitudinal and cross (only top bars shown) section of typical slab

Section properties of a typical slab:

Cross-section area, A = 105.6 in.2 Effective span = 10 ft. Distance from load to support, a = 56.375 in. Distance between the two loading points, z = 7.25 in. Concrete compressive strength on day of test, fc' = 5,150 psi Specified tensile strength of steel reinforcement, fy = 65.9 ksi Width, b = 13.2 in. Effective depth, d = 7.25 in.

8"

13.2"

0.75"

3.3"

8"

10'6" 6"

#5bottom longitudinal rebar @ 6.4" c/c

#6 top longitudinal rebar @ 6.6" c/c

#3transverserebar @ 6" c/c

P2

P2

189

Overall depth, h = 8 in Area of steel for 2 Nos. of #6 bars, As = 0.88 in.2

A1.2: Cracking and Yielding and Ultimate Load Calculations for Slabs

Modulus of rupture, fr, = '5.7 cf = 51505.7 × = 538.2 psi

Moment of inertia of gross area, Ig = 12

3bh =

1282.13 3×

= 563.2 in.4

Distance from the section centroid to the extreme tension fiber, yt =

2h =

28 = 4 in.

Cracking moment, t

grcr y

IfM =

42.5632.538 ×

=crM = 75.78 kip-in. = 6.31 kip-ft

Cracking load, 375.56

78.7522 ×==

aM

P crcr = 2.7 kip

The experimental yield loads for Slab U, Slab E, Slab U-P, and Slab E-P are 3.0, 2.0, 2.8, and 1.8 kip, respectively.

After Cracking

Modulus of elasticity of concrete, '57000 cc fE = = 515057000× = 4090519.5 psi

Section curvature at cracking, gc

crcr IE

M=ϕ =

2.5635195.409078.75×

= 0.00003289/in.

Strain in Concrete, C

rcr E

f=ε 0001316.0

5.40905192.538

== in./in.

Using cr

crcϕε

= = 00003289.00001316.0 = 4.0012 in.

From strain compatibility, strain in steel,

−−

×=chcd

crs εε =

−−

×0012.48

0012.425.70001316.0

= 0.0001069 in./in.

190

At Yielding

Strain in steel, 29000

9.65===

Esf y

ys εε = 0.002272 in./in.

Using strain compatibility, cdc

yc

−=

εε

Rearranging, cy

cdc

εεε+

= = c

c

εε+002272.0

25.7 [Eqn. A1]

Assuming a linear stress – strain relationship before yield Compression Force in Concrete, bcfC c2

1=

Where, fc = compressive stress in concrete = Eccε Therefore, ccccc ccbcEbcfC εεε 4287.269972.135195.4090

21

21

21

=××××===

Tension in Top Steel Reinforcement, T = Asfy = 0.88 × 65.9 = 57.992 kip Assuming equilibrium, Tension force = Compressive force 57.992 = 26997.4287cεc [Eqn. A2] Determining c and εc by solving Eqn. A1 and Eqn. A2 simultaneously, gives Strain in concrete, εc = 0.000982 in./in. Depth to neutral axis, c = 2.1875 in. Moment at Yield, ( )3

cdfAM ysy −= = ( )31875.225.7992.57 − = 378.1562 kip-in.

Load at Yield, 375.56

1562.37822 ×==

aM

P yy = 13.4157 kip

The experimental yield loads for Slab U, Slab E, Slab U-P, and Slab E-P are 13.8, 11.0, 13.4, and 11.8 kip, respectively. Ultimate Load

Assuming concrete crushing strain, ε = 0.003 in./in. Concrete strain at peak compressive stress, εo = 0.002 Compression in Concrete, bcfC c

'α= Using parabolic stress strain curve of concrete

191

The stress intensity coefficient,

+

= 1ln

2

o

o

εε

εε

α =

+

1

002.0003.0ln

003.0002.0 2

= 0.7858 Assumed depth of neutral axis, c = 1.0856 in. (determined from trial and error using excel program) Therefore, C 0856.12.13150.57858.0 ×××= = 57.992 kips

Steel strain,

−−

×=chcd

cs εε

−−

×=0856.18

0856.125.7003.0 = 0.002675 > εy = 0.002272 in/in

Therefore, use fs = fy = 65.9 ksi Tension in Steel, T = As × fs = 0.88 x 75 = 57.992 kip Therefore, equilibrium has been established, C = T = 57.992 kip Location of resultant coefficient, β

+

−

−=

−

1ln

tan121

2

1

o

o

o

εε

εε

εε

β

+

−

−=

−

1002.0003.0ln

002.0003.0tan

003.0002.012

12

1

= 0.4149

Ultimate Moment Capacity, Mu = T (d – βc) = 57.992 (7.25 – 0.4149 × 1.0856) = 394.322 kip-in = 32.86 kip-ft.

Ultimate Load, 375.56

322.39422 ×==

aM

P uu = 13.989 kip

The experimental ultimate loads for Slab U, Slab E, Slab U-P, and Slab E-P are 14.4, 12.4, 13.8, and 12.6 kip, respectively. A1.3: Calculation of Deflection for Slabs Using Moment Curvature Relation Midspan deflection was calculated from bending moment and radius of curvature relation 1𝑅

= 𝑀𝐸𝐸

; 1𝑅

= 𝑑2𝑚𝑑𝑑2

; 𝑀 = 𝐸𝐸 𝑑2𝑚

𝑑𝑑2

192

Where, M is the bending moment; I is the second moment of area about the centroid; E is the modulus of elasticity; dy/dx is the slope, y represents deflection, R is the radius of curvature, and EI is the flexural stiffness. Figure A.2 shows the details of the loading of a slab from the bottom

Figure A.2 Loading of a slab from the bottom

PL/2 = 6.7 kip; a = 56.375 in.; Z = 7.25 in. The bending moment at position X including the midspan section is given by: 𝐸𝐸 𝑑

2𝑑𝑑𝑚2

= 6.7(𝑥 − 56.375) + 6.7(𝑥 − 63.625) − 6.7𝑥 = 6.7𝑥 − 804 Integrate with respect to x once; 𝐸𝐸 𝑑𝑑

𝑑𝑚= 6.7𝑚2

2− 804𝑥 + 𝐴 [A.1]

Integrate with respect to x again; 𝐸𝐸𝐸 = 6.7𝑚3

6− 402𝑥2 + 𝐴𝑥 + 𝐵 [A.2]

A and B are constants of integration and must be found from the boundary conditions. These are at x = 0, y = 0 (no deflection at left support point) at x =120, y = 0 (no deflection at right support point) putting x = 0 and y =0 in Eqn. B1 results in B = 0 Substitute B = 0, x = 120, and y = 0 in Eqn. B2 and we get A = 32160 Substitute A = 32160 and B = 0 into Eqn. B2 and the complete equation is 𝐸𝐸𝐸 = 1.117𝑥3 − 402𝑥2 + 32160𝑥 Eqn. A.3 Substitute x = 60 in Eqn. A.3 and solving for y gives the midspan deflection EI = EIe = 4090.52 × 208.95 = 854714.154

PL2

PL2

y

PL2

PL2

x

a

L

z

193

Midspan deflection, 𝐸 = 1.117(60)3−402(60)2+32160(60)854714.154

= 0.85 𝑖𝑖. A1.4: Calculation of Deflection for Slabs Using Elastic Equation

The slab deflection was calculated based on elastic principles of mechanics.

Moment capacity of slab, MN = 30.1 kip-ft. = 361.2 kip-in. Since loading was applied to the bottom of the slabs MN = ML – MD MD = Dead load moment = 16.5 kip-in. ML = Live load moment = MN + MD = 361.2 – 16.5 = 377.7 kip-in.

𝑀𝐿 =𝑃𝐿𝑎

2

Applied load, 𝑃𝐿 = 2𝑀𝐿

𝑚= 2×377.7

56.375= 13.4 𝑘𝑖𝑘

Cracked moment of inertia was determined using the transformed section 𝐸𝑐𝑟 = 𝑏𝑘2𝑗𝑑3/2 Where kd = distance from the bottom of the slab to the neutral axis jd = moment arm for the equivalent compression and tension forces Top reinforcement ration, ρ = 𝐴𝑠

𝑏𝑑= 0.88

13.2×7.25= 0.0092

Modular ratio, n = 7.09 𝑘 = �(𝜌𝑖)2 + 2𝜌𝑖 − 𝜌𝑖 = �(0.0092 × 7.09)2 + 2 × 0.0092 × 7.09 − (0.0092 × 7.09) k = 0.3018 j = 1-k/3 = 1 – 0.3018/3 = 0.8994

𝐸𝑐𝑟 = 13.2 × (0.3018)2(0.8994)(7.25)3

2= 206.04 𝑖𝑖.4

194

Effective moment of inertia, 𝐸𝑒 = {�𝑀𝑐𝑐𝑀𝑎�3𝐸𝑔 + �1 − �𝑀𝑐𝑐

𝑀𝑎�3� 𝐸𝑐𝑟} ≤ 𝐸𝑔

Where Gross moment of inertia, Ig = 563.2 in.4 Maximum applied moment, Ma = 377.7 kip-in.

𝐸𝑒 = ��75.78377

�3

563.2 + �1 − �75.78377

�3

�206.04� = 208.95 𝑖𝑖.4 ≤ 𝐸𝑔

Deflection at midspan is given by ∆ =

𝑤𝑎24𝐸𝐸𝑒

(3𝑙2 − 4𝑎2)

Where E = 4090.52 ksi; effective span, l = 10 ft. = 120 in. Applied load, w = PL/2

∆ = 13.4

2 (56.375)24(4090.52)(208.95) [3(120)2 − 4(56.375)2] = 0.56 𝑖𝑖.

A1.5: Calculation of Crack Spacing for Slabs

Crack spacing was calculated using Frosch (1999) and Chowdhury and Loo (2001) equations.

A1.5.1: Using Frosch (1999) Approach

Frosch noted that spacing of cracks depends on the concrete cover, and calculates the crack spacing as follows:

Sc = φsd* Where Sc = crack spacing d* = controlling cover distance (Figure B.3) = �𝑑𝑐2 + 𝑑𝑠2 =√0.752 + 3.32 = 3.38 𝑖𝑖. φs = crack spacing factor = 1.0 for minimum crack spacing = 1.5 for average crack spacing = 2.0 for maximum crack spacing Minimum crack spacing, Sc(min) = 1.0 × 3.38 = 3.38 in. Average crack spacing, Sc(avg) = 1.5 × 3.38 = 5.07 in. Maximum crack spacing, Sc(max) = 2.0 × 3.38 = 6.76 in.

195

Figure A.3 Control cover distance (Frosch 1999)

A1.5.2: Using Chowdhury and Loo (2001) Approach

The average crack spacing equation given by Chowdhury and Loo (2001) is

+−=

ρDSClcr 1.0)(6.0

Where lcr = average crack spacing C = top reinforcement cover = 0.75 in. S = Average spacing between top reinforcement bars = 6.25 in. ρ = reinforcement ratio for top reinforcement bars = 0.0092 D = Diameter of top reinforcement = 0.75 in.

Average crack spacing, .9.40097.0

75.01.0)25.675.0(6.01.0)(6.0 inDSClcr =

+−=

+−=

ρ

A1.6: Theoretical Calculation of Crack Width for Slabs

Maximum crack width at extreme top tension fiber of the slabs corresponding to a load of 10 kip and service moment of 23.49 kip-ft was determined using Gergely and Lutz (1968), Chowdhury and Loo (2001), and Oh and Kang (1987) equations.

8"

13.2"

dc=0.75"

ds=3.3"

196

A1.6.1: Crack Width Prediction for a Typical Laboratory Slab using Gergely and Lutz (1968) Equation

.

CRACK WIDTH CALCULATION - USING GERGELY-LUTZ (1968) APPROACH

CRACK WIDTH CORRESPONDING TO LOAD =10 KIP, SERVICE MOMENT = 23.49 KIP-FT

Service I Limit State Max. Negative Moments Mb = Mc Mb = Mc 23.49 kip-ftSection Properties Top Steel Area Ast 0.88 in.2

Bottom Steel Area Asc 0.62 in.2

Deck Thickness h 8.00 in.Diameter of Top Reinforcement Dt 0.75 in.Diameter of Bottom Reinforcement Db 0.625 in.Top Cover Ct 0.75 in.Bottom Cover Cb 0.75 in.Modulus of Elasticity of Concrete Ec 4090520 psiModulus of Elasticity of Steel Es 2.90E+07 psiModular Ratio n 7.09Effective Depth of Bottom Reinforcement d 7.25 in.Compressive Strength of Concrete f'c 5150 psiWidth of Slab b 13.2 in.

Crack Width at Top Extreme Fiber - Negative Moment RegionEffective Depth of Top Reinforcement d1 7.25 in.Reinforcement Ratio (top reinf) 𝜌t 0.0092Reinforcement Ratio (bottom reinf) 𝜌b 0.0065

tt 0.75 in.

Average Effecfive Area of Concrete in Tension A 19.80 in.2

X 0.07341Y 0.14467K 0.26491

Depth of Neutral Axis kd 1.9206 in.h1 5.33 in.h2 6.0794 in.K1 0.52195 psi

Moment of Inertia of Cracked Section Icr 218.793 in.4

Calculation of Steel Tensile Stress at Cracking fS 48677.6 psi

Max. Crack Width in Extreme Top Tension Fiber Wmax 0.01036 in.

b

hdNeutral axis

h2

dn=kd

tt

h1

tb

d1

ℎ1 = ℎ2 -𝑡𝑡

ℎ2 = ℎ -𝑘𝑑

197

A2: Direct Tension Crack Width Calculations for Prisms ACI 224.2R-92 and Rizkalla and Hwang (1993) equations were used to determine

cracking load and maximum crack widths of the prisms. Section and material properties of U4-#3 prism #3 rebar area As = 0.11 in.2 Gross concrete area of U4-#3 prism, Ag = 4 × 4 = 16 in.2 Concrete compressive strength on day of test (66 days), fc' = 5,100 psi Tensile strength of steel reinforcement, fy = 75 ksi Modulus of elasticity of concrete, '57000 cc fE = = 5100 57000 × = 4030.51 ksi Modulus of elasticity of steel, Es = 29,000 ksi Modular ratio, n = Es/Ec = 7.2 Effective concrete cover for U4-#3, te = 2 in. Tensile strength of concrete (from Rizkalla & Hwang, 1993),

psiff ct 3.296)5100()( 3/23/2'' ===

Reinforcement ratio for U4-#3 prism, 00687557.01611.0

===g

s

AA

ρ

A2.1: Calculation of Cracking Load for Specimen U4-#3 using ACI-224.2R-92

The cracking load of a U4-#3 prism is given by

kipfAnP tgcr 9.4)3.29616)(00687557.02.700687557.01()1( ' =××+−=+−= ρρ B2.2: Calculation of Cracking Load for Specimen U4-#3 by Rizkalla and Hwang (1983)

The cracking load of a U4-#3 prism is given by

crccr fAnP )1( ρ+= Where: Ac = Ag = 16 in.2; fcr = ft' = 296.3 psi

198

kipcrfcAncrP 9.4)3.29616)(00687557.02.71()1( =××+=+= ρ A2.2: Calculation of Maximum Crack Width for Specimen U4-#3 by ACI-224.2R-92

The expression for maximum tensile crack width is given by

3max 10138.0 −×= estfW

Where te = concrete cover; fs = tensile strength of steel reinforcement for U3-#4 prism at load of 11 kip, ksif s 100

11.011

==

.0276.0102100138.0 3

max inW =×××= − A3: Flexural Crack Width Calculations for ODOT Bridge ASD-42-0656

Section and material properties of a typical slab: This is a three span bridge with length of spans: Span #1 = 40 ft.; Span #1 = 50 ft.; Span #1 = 40 ft. Deck thickness = 24 in. Concrete compressive strength, fc' = 4,500 psi Specified tensile strength of steel reinforcement, fy = 60 ksi Bottom steel in the positive flexure per 1 ft. strip, #9 bars @ 6.5 in., Asc = 1.85 in.2 Top steel over the support per 1 ft. strip, #10 bars @ 6.25 in., Ast = 1.85 in.2 Impact factor for truck = 1.33; Impact factor for lane = 1.00 Calculation of strip widths and distribution factors: For multiple lane loading, the strip width, 𝐸 = 84 + 1.44�𝐿1𝑊1 ≤ 12 × (𝑊

𝑁𝐿)

Where, L1 = modified span length, take as the lesser of (a) the actual span length in ft. or (b) 60 ft. W = Width of the bridge = 20 ft.; NL = Number of lanes used = 2 W = actual edge-to-edge bridge width used = 20 ft. W1 = modified edge-to-edge width of bridge, taken as the lesser of (a) the actual edge to edge width W (ft.), or (b) 60 ft. for multiple-lane loading, 30 ft. for single-lane loading Span #1, 𝐸 = 84 + 1.44�𝐿1𝑊1 = 84 + 1.44√40 × 20 = 124.7 𝑖𝑖. = 10.39 𝑓𝑡. Span #2, 𝐸 = 84 + 1.44�𝐿1𝑊1 = 84 + 1.44√50 × 20 = 129.54 𝑖𝑖. = 10.79 𝑓𝑡. Span #3, 𝐸 = 84 + 1.44�𝐿1𝑊1 = 84 + 1.44√40 × 20 = 124.7 𝑖𝑖. = 10.39 𝑓𝑡.

199

12 × �𝑊𝑁𝐿� = 12 × �20

2� = 120 𝑖𝑖. = 10 𝑓𝑡.

Therefore E = 10 ft. governs for all the spans Live load distribution factor (D.F.) for slab bridge = 1/E =1/10 The determined unfactored and Service I Limit State moments for ASD-42-0656 bridge are shown in Table 4.1 The Service I Limit State moments are calculated using, Mu = 1.0 (DC) + 1.0 (DW) + 1.0 (IM + LL). Where IM = Impact factor; DC = Slab dead load; DW = Future wearing surface load; LL = HL93 truck and lane loads

Table A.1 Unfactored and Service I limit state moments for bridge ASD-42-0656

Unfactored Moments

Load cases

Moments (kip-ft.) Max. positive moment Max. negative

moment Exterior spans

Interior span

Dead Load 33 32.2 61.6

FWS Load 6.6 6.4 12.3

HL 93 Lane Load 106 114 146

HL 93 Truck Load 360 379 281

HL 93 Lane Load including D.F. 10.6 11.4 14.6

HL 93 Truck Load including IM+D.F. 47.9 50.4 37.4

Service I Limit State Moments Mu = 1.0 (DC) + 1.0 (DW) + 1.0 (IM + LL)

Max. positive moment (kip-ft.) Max. negative moment (kip-ft) Exterior spans Interior span 98.1 100.4 125.9

A3.1: Calculation of Maximum Crack Width at Service Limit State

Maximum crack width at extreme top tension fiber of the bridge deck using Service I Limit State moments [1.0 (DC) + 1.0 (DW) + 1.0 (IM + LL)] was calculated using Gergely and Lutz (1968), Chowdhury and Loo (2001, and Oh and Kang (1987) equations.

200

A3.1.1: Crack Width Prediction for a Typical Slab using Gergely and Lutz (1968) Equation

No. of Lanes = 2; BRIDGE SPANS: 40-50-40 ft.

Service I Limit State Max. Negative Moments Mb = Mc Mb = Mc 125 kip-ftSection Properties Top Steel Area per 1' Strip Ast 2.44 in.2

Bottom Steel Area per 1' Strip Asc 1.85 in.2

Deck Thickness h 24.00 in.Diameter of Top Reinforcement Dt 1.25 in.Diameter of Bottom Reinforcement Db 1.125 in.Top Cover Ct 2.5 in.Bottom Cover Cb 1.5 in.Modulus of Elasticity of Concrete Ec 3823676 psiModulus of Elasticity of Steel Es 2.90E+07 psiModular Ratio n 8Effective Depth of Bottom Reinforcement d 21.94 in.Compressive Strength of Concrete f'c 4500 psiWidth of Slab ( 1 ft. strip ) b 12 in.

Crack Width at Top Extreme Fiber - Negative Moment RegionEffective Depth of Top Reinforcement d1 20.88 in.Reinforcement Ratio (top reinf) 𝜌t 0.0097Reinforcement Ratio (bottom reinf) 𝜌b 0.0070

tt 3.125 in.

Average Effecfive Area of Concrete in Tension A 75.00 in.2

X 0.09073Y 0.16785K 0.29002

Depth of Neutral Axis kd 6.36222 in.h1 15.58 in.h2 17.6378 in.K1 0.59243 psi

Moment of Inertia of Cracked Section Icr 6254.57 in.4

Calculation of Steel Tensile Stress at Cracking fS 29882.7 psi

Max. Crack Width in Extreme Top Tension Fiber Wmax 0.016 in.

b

hdNeutral axis

h2

dn=kd

tt

h1

tb

d1

201

A3.1.2: Crack Width Prediction for a Typical Bridge using Chowdhury and Loo (2001) Equation

No. of Lanes = 2; BRIDGE SPANS: 40 ft.- 50 ft.-40 ft.

Service I Limit State Max. Negative Moments Max. Negative MomentMb = Mc Mb = Mc 125 kip-ftSection Properties Top Steel Area per 1 ft. Strip Ast 2.44 in.2

Bottom Steel Area per 1' Strip Asc 1.85 in.2

Deck Thickness h 24.00 in.Diameter of Top Reinforcement Dt 1.25 in. 31.75 mmDiameter of Bottom Reinforcement Db 1.125 in.Top Cover Ct 2.5 in. 63.5 mmBottom Cover Cb 1.5 in.Modulus of Elasticity of Concrete Ec 3823676 psi

Modulus of Elasticity of Steel Es 2.90E+07 psi 199947 N/mm2

Modular Ratio n 8Effective Depth of Bottom Reinforcement d 21.94 in.Compressive Strength of Concrete f'c 4500 psiWidth of Slab ( 1 foot strip ) b 12 in.Effective Depth of Top Reinforcement d1 20.88 in.Reinforcement Ratio (top reinf) 𝜌t 0.0097Reinforcement Ratio (bottom reinf) 𝜌b 0.0070Average Spacing Between Top Reinforcement Bars S 6.25 in. 158.75 mmYield Strength of Steel Reinforcement fy 60000.00 psiDepth of Neutral Axis Determined kd 6.36222 in.Moment of Inertia of Cracked Section Icr 6254.57136 in.4Steel Tensile Stress at Cracking fs 29882.7 psi 205.8917 N/mm2

Crack Width at Top Extreme Fiber - Negative Moment RegionAverage Crack Spacing lcr 10.5830 in. 268.8080 mm

Average Crack Width Wcr 0.0109 in. 0.28 mm

Max. Crack Width in Extreme Top Tension Fiber Wmax 0.016 in. 0.415 mm

202

A3.1.3: Crack Width Prediction for a Typical Bridge using Oh and Kang (1987) Equation

No. of Lanes = 2; BRIDGE SPANS: 40-50-40 ft.

Service I Limit State Max. Negative Moments Max. Negative MomentMb = Mc Mb = Mc 125 kip-ftSection Properties Top Steel Area per 1 ft. Strip Ast 2.44 in.2

Bottom Steel Area per 1' Strip Asc 1.85 in.2

Deck Thickness h 24.00 in.Diameter of Top Reinforcement Dt 1.25 in.Diameter of Bottom Reinforcement Db 1.125 in.Top Cover Ct 2.5 in.Bottom Cover Cb 1.5 in.Modulus of Elasticity of Concrete Ec 3823676 psiModulus of Elasticity of Steel Es 2.90E+07 psiModular Ratio n 8Effective Depth of Bottom Reinforcement d 21.94 in.Compressive Strength of Concrete f'c 4500 psiWidth of Slab ( 1 foot strip ) b 12 in.

Effective Depth of Top Reinforcement d1 20.88 in.Reinforcement Ratio (top reinf) 𝜌t 0.0097Reinforcement Ratio (bottom reinf) 𝜌b 0.0070

tt 3.125 in.

Average Effecfive Area of Concrete in Tension A 75.00 in2

Depth of Neutral Axis Determined kd 6.36222 in.Moment of Inertia of Cracked Section Icr 6254.57136 in.4

Calculation of Steel Tensile Stress at Cracking fS 29882.7 psiAxial Strain of bars ɛS 0.001030Distance from the Centroid os Steel to the Neutral Axis h3 14.51 in.Distance from the Extreme Tension Fiber to Neutral Axis h2 17.6377808 in.Depth of Equivalent Area h1 8.68 in.

R 1.21532744tb 1.5 in.

Number of reinforcing bars in tension (1 foot strip) m 2Area of each reinforcing bar As1 1.27 in.2

Effective Area of Concrete Surrounding Reinforcing Bar A1 52.1027382 in.2

a0 9.70635445

Max. Crack Width in Extreme Top Tension Fiber Wmax 0.013 in.

203

APPENDIX B: CTL ENGINEERING REPORT ON CHLORIDE CONCTENT FOR THREE BRIDGE DECK CORE SAMPLES

204

APPENDIX C: ODOT CS 1-08: STANDARD CONTINUOUS SLAB BRIDGES

205

APPENDIX D: ODOT CPP-1-08: STANDARD CAPPED PILE PIER FOR CONTINUOUS SLAB BRIDGES

206

APPENDIX E: CHLORIDE ION CONTENT CALCULATIONS E.1 Calculation of Chloride Ion Content as weight % of Sample

The steps used in calculating the chloride ion content as weight % of sample is presented below. First, the concentration of chloride is determined:

C = VF [E.1] where C = concentration of chloride (Cl) in mg/L, V = titrant volume of mercuric nitrate solution in mL, F = aliquot factor = 5 × 100 mL / 25 mL = 20 The mass (M) of chloride (in g) in an equivalent 200 mL volumetric flask is given by M = 0.2C/1000. The percentage of chloride by mass of the concrete sample (Cl%) is given by 𝑀𝑊

(100), where W = mass of concrete sample (g). E.2 Calculation of Chloride Content in Parts Per Million (ppm)

To express the chloride content in parts per million (ppm) by weight of concrete, 1000 ppm was used to be equal to 0.1% chloride by weight of concrete. Calculation of Chloride Content as Percentage by Weight of the Cement (Binder)

The chloride content could also be expressed as a percentage by weight of the cement, %bwoc. %bwoc = 𝐶𝐶𝑝𝑝𝑚

𝐶𝑐 ×100 [E.2]

where Clppm = chloride content in concrete sample in ppm. The percentage of cement content in concrete, Cc is given by

𝐶𝐷𝑐

, where C = cement content in concrete in lb/yd3 and Dc = density of concrete in lb/yd3. E.4 Calculation of Pounds of Chloride Per Cubic Yard of Concrete The calculation of pounds of chloride per cubic yard of concrete is given by 𝑃 = 𝐶𝐶 ×𝐷𝑐

1000000 [E.3]

where P = pounds of chloride per cubic yard of concrete Cl = chloride content in concrete sample in ppm Dc = density of concrete in lb/yd3

E.5 Results of Acid-Soluble Chloride Content for Core Specimens

207

Table E.1 Results of Acid-Soluble Chloride Content – Cracked Specimen (C1-2)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/16/14 0.5

C1- 2T

C1- 2T-#1 24.77 35.80 11.03 11.03

0.4412

4412

3.7943 9/16/14 C1- 2T-#2 33.47 44.32 10.85

9/16/14 C1- 2T-#3 21.60 32.80 11.20 9/16/14

4.75

C1- 2MT C1- 2MT-#1 35.8 38.70 2.90

3.09

0.1236

1236

1.0630 9/16/14 C1- 2MT-#2 18.52 21.60 3.08 9/16/14 C1- 2MT-#3 32.80 36.10 3.30 9/16/14

9.31

C1- 2MB C1- 2MB-#1 41.50 44.30 2.80

2.73

0.1092

1092

0.9391 9/16/14 C1- 2MB-#2 36.10 38.65 2.55 9/16/14 C1- 2MB-#3 38.65 41.50 2.85 9/17/14

13.5

C1- 2B C1- 2B-#1 2.20 4.40 2.20

2.20

0.0880

880

0.7568 9/17/14 C1- 2B-#2 43.05 45.41 2.36 9/17/14 C1- 2B-#3 20.26 22.30 2.04

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

Table E.2 Results of Acid-Soluble Chloride Content – Uncracked Specimen (C - 2)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/22/14 0.5

C - 2T

C - 2T-#1 17.10 27.20 10.10 9.98

0.3992

3992

3.4331 9/22/14 C - 2T-#2 15.71 25.40 9.69

9/22/14 C - 2T-#3 1.87 12.02 10.15 9/22/14

5.97

C - 2MT C - 2MT-#1 12.02 14.50 2.48

2.50

0.1000

1000

0.8600 9/22/14 C - 2MT-#2 14.50 17.10 2.60 9/22/14 C - 2MT-#3 27.20 29.61 2.41 9/22/14

10.93

C- 2MB C- 2MB-#1 1.48 3.73 2.25

2.29

0.0916

916

0.7878 9/22/14 C- 2MB-#2 3.73 5.98 2.25 9/22/14 C- 2MB-#3 5.98 8.36 2.38 9/22/14

17.4

C - 2B C - 2B-#1 8.36 10.46 2.10

2.01

0.0804

804

0.6914 9/22/14 C - 2B-#2 10.46 12.48 2.02 9/22/14 C - 2B-#3 12.48 14.39 1.91

*ppm = part per million; %bwoc = percentage by weight of the cement (binder).

208

Table E.3 Results of Acid-Soluble Chloride Content – Cracked Specimen (C - 3)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/17/14 0.5

C - 3T

C - 3T-#1 22.3 32.65 10.35 10.32

0.4128

4128

3.5501 9/17/14 C - 3T-#2 32.65 43.05 10.40

9/17/14 C - 3T-#3 4.40 14.61 10.21 9/17/14

5.88

C - 3MT C - 3MT-#1 16.85 18.70 1.85

1.88

0.0752

752

0.6467 9/17/14 C - 3MT-#2 14.61 16.85 2.24 9/17/14 C - 3MT-#3 18.70 20.26 1.56 9/17/14

12.27

C - 3MB C - 3MB-#1 0.14 2.20 2.06

1.77

0.0708

708

0.6089 9/17/14 C - 3MB-#2 15.72 17.03 1.31 9/17/14 C - 3MB-#3 1.42 3.35 1.93 9/17/14

17.21

C - 3B C - 3B-#1 1.87 20.08 1.38

1.41

0.0564

564

0.4850 9/17/14 C - 3B-#2 14.55 15.72 1.17 9/17/14 C - 3B-#3 17.03 18.70 1.67

*ppm = part per million; %bwoc = percentage by weight of the cement (binder).

Table E.4 Results of acid-soluble chloride content – Uncracked Specimen (C - 4)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/19/14 0.5

C - 4T

C - 4T-#1 9.60 20.17 10.57 10.59

0.4236

4236

3.643 9/19/14 C - 4T-#2 20.17 30.62 10.45

9/19/14 C - 4T-#3 10.81 21.56 10.75 9/19/14

5.44

C - 4MT C - 4MT-#1 32.90 35.12 2.22

2.22

0.0888

888

0.7637 9/19/14 C - 4MT-#2 33.50 35.67 2.17 9/19/14 C - 4MT-#3 30.62 32.90 2.28 9/19/14

10.38

C- 4MB C- 4MB-#1 32.15 34.20 2.05

2.09

0.0836

836

0.7189 9/19/14 C- 4MB-#2 6.50 8.67 2.17 9/19/14 C- 4MB-#3 10.20 12.24 2.04 9/19/14

17.5

C - 4B C - 4B-#1 0.00 1.75 1.75

1.82

0.0728

728

0.6261 9/19/14 C - 4B-#2 2.20 3.90 1.70 9/19/14 C - 4B-#3 4.50 6.50 20.00

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

209

Table E.5 Results of acid-soluble chloride content – Uncracked Specimen (C - 5)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/17/14 0.5

C - 5T

C - 5T-#1 4.93 14.55 9.62 9.70

0.3880

3880

3.3368 9/17/14 C - 5T-#2 23.12 32.82 9.70

9/17/14 C - 5T-#3 32.82 42.60 9.78 9/17/14

6.13

C - 5M C - 5M-#1 8.86 10.72 1.86

1.54

0.0616

616

0.5298 9/17/14 C - 5M-#2 21.42 23.12 1.70 9/17/14 C - 5M-#3 7.08 8.86 1.78 9/17/14

19.47

C- 5B C- 5B-#1 3.35 4.93 1.58

1.37

0.0548

548

0.4713 9/17/14 C- 5B-#2 20.08 21.42 1.34 9/17/14 C- 5B-#3 5.90 7.08 1.18

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

Table E.6 Results of acid-soluble chloride content – Cracked Specimens (C - 1)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/15/14 0.5

C - 1T

C - 1T-#1 24.83 36.20 11.37 11.30

0.4520

4520

3.8872 9/15/14 C - 1T-#2 36.20 47.50 11.30

9/15/14 C - 1T-#3 4.00 15.24 11.24 9/15/14

5.75

C - 1MT C - 1MT-#1 0.00 4.00 4.00

4.40 0.1760

1760

1.5136 9/15/14 C - 1MT-#2 21.60 26.08 4.48

9/15/14 C - 1MT-#3 26.08 30.80 4.72 9/15/14

11.56

C - 1MB C - 1MB-#1 18.47 21.60 3.13

3.02 0.1208

1208

1.0389 9/15/14 C - 1MB-#2 15.24 18.47 3.23

9/15/14 C - 1MB-#3 30.80 33.50 2.70 9/15/14

16.85

C - 1B C - 1B-#1 38.40 40.60 2.20

2.37 0.0948

948

0.8153 9/15/14 C - 1B-#2 33.50 35.90 2.40

9/15/14 C - 1B-#3 35.90 38.40 2.50

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

210

Table E.7 Results of acid-soluble chloride content – Uncracked Specimen (C - 7)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/17/14 0.5

C - 7T

C - 7T-#1 44.73 56.24 11.51 11.50

0.4600

4600

3.956 9/17/14 C - 7T-#2 22.12 33.71 11.59

9/17/14 C - 7T-#3 10.72 22.12 11.40 9/17/14

4.75

C - 7MT C - 7MT-#1 33.71 37.21 3.50

3.70

0.1480

1480

1.2728 9/17/14 C - 7MT-#2 42.60 45.80 3.20 9/17/14 C - 7MT-#3 36.20 40.60 4.40 9/18/14

9.0

C- 7MB C- 7MB-#1 1.00 3.20 2.20

2.19

0.0876

876

0.7534 9/18/14 C- 7MB-#2 11.10 13.28 2.18 9/18/14 C- 7MB-#3 5.00 7.20 2.20 9/18/14

14.94

C - 7B C - 7B-#1 26.75 28.60 1.85

1.79

0.0716

716

0.6158 9/18/14 C - 7B-#2 3.20 5.00 1.80 9/18/14 C - 7B-#3 7.20 8.92 1.72

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

Table E.8 Results of acid-soluble chloride content – Cracked Specimens (C - 8)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/18/14 0.5

C - 8T

C - 8T-#1 23.60 31.18 7.58 7.37

0.2948

2948

2.5353 9/18/14 C - 8T-#2 31.18 38.40 7.22

9/18/14 C - 8T-#3 38.40 45.70 7.30 9/18/14

6.13

C - 8MT C - 8MT-#1 1.70 4.00 2.30

2.28

0.0912

912

0.7843 9/18/14 C - 8MT-#2 16.57 19.04 2.47 9/18/14 C - 8MT-#3 14.50 16.57 2.07 9/19/14

13.02

C - 8MB C - 8MB-#1 29.60 31.57 1.97

1.93

0.0772

772

0.6639 9/19/14 C - 8MB-#2 1.50 3.40 1.90 9/19/14 C - 8MB-#3 31.57 33.50 1.93 9/19/14

17.96

C - 8B C - 8B-#1 8.67 10.20 1.53

1.64

0.0656

656

0.5642 9/19/14 C - 8B-#2 0.00 1.75 1.75 9/19/14 C - 8B-#3 1.75 3.40 1.65 *ppm = part per million; %bwoc = percentage by weight of the cement (binder)

211

Table E.9 Results of acid-soluble chloride content – Uncracked Specimen (C - 9)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm

% bwoc

9/19/14 0.50

C - 9T

C - 9T-#1 21.56 31.62 10.06 10.34

0.4136

4136

3.5569 9/19/14 C - 9T-#2 31.62 41.9 10.28

9/19/14 C - 9T-#3 36.75 47.42 10.67 9/19/14

4.75

C - 9MT C - 9MT-#1 29.85 32.15 2.3

2.28

0.0912

912

0.7843 9/19/14 C - 9MT-#2 7.30 9.45 2.15 9/19/14 C - 9MT-#3 8.41 10.81 2.4 9/19/14

9.00

C- 9M C- 9M-#1 3.4 15.8 2.1

2.00

0.0800

800

0.6880 9/19/14 C- 9M-#2 2.65 5.36 1.96 9/19/14 C- 9M-#3 4.6 4.6 1.95 9/19/14

13.25

C – 9MB C – 9MB-#1 4.6 6.54 1.94

1.93

0.0772

772

0.6639 9/19/14 C – 9MB-#2 26.0 27.92 1.92 9/19/14 C – 9MB-#3 27.92 29.85 1.93 9/19/14

17.94

C- 9B C- 9B-#1 0.75 2.65 1.9

1.88

0.0752

752

0.6467 9/19/14 C- 9B-#2 6.54 8.41 1.87 9/19/14 C- 9B-#3 19.72 21.6 1.88

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

212

Table E.10 Results of acid-soluble chloride content – Cracked Specimen (C - 10)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/16/14 0.5

C - 10T

C - 10T-#1 22.2 29.22 7.02 6.81

0.2724

2724

2.3426 9/16/14 C - 10T-#2 9.90 16.70 6.80

9/16/14 C - 10T-#3 3.30 9.90 6.60 9/16/14

6.06 C - 10MT

C - 10MT-#1 1.00 3.30 2.30 2.43

0.0972

972

0.8359 9/16/14 C - 10MT-#2 21.82 24.50 2.68

9/16/14 C - 10MT-#3 31.15 33.47 2.32 9/16/14

12.06 C - 10MB

C - 10MB-#1 18.40 20.55 2.15 2.10

0.0840

840

0.7224 9/16/14 C - 10MB-#2 46.20 48.41 2.21

9/16/14 C - 10MB-#3 29.22 31.15 1.95 9/16/14

17.68

C - 10B C - 10B-#1 16.70 18.40 1.70

1.74

0.0696

696

0.5986 9/16/14 C - 10B-#2 44.32 46.20 1.88 9/16/14 C - 10B-#3 20.55 22.20 1.65

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

213

Table E.11 Results of acid-soluble chloride content – Cracked Specimen (C - 11)

Date of Test

Depth to which

sample was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/18/14

0.50

C - 11T

C - 11T-#1 14.62 28.81 14.19

13.97

0.5588

5588

4.8057 9/18/14 C - 11T-#2 13.28 26.75 13.47

9/18/14 C - 11T-#3 28.81 43.05 14.24

9/18/14

5.88

C - 11MT

C - 11MT-#1 8.92 11.1 2.18

2.25

0.0900

900

0.7740 9/18/14 C - 11MT-#2 21.4 23.6 2.20

9/18/14 C - 11MT-#3 19.04 21.40 2.36

9/18/14

12.16

C - 11MB

C - 11MB-#1 10.42 12.54 2.12

2.12

0.0848

848

0.7293 9/18/14 C - 11MB-#2 1.75 3.85 2.10

9/18/14 C - 11MB-#3 3.85 6.00 2.15

9/18/14

17.10

C - 11B

C - 11B-#1 12.54 14.50 1.96

2.01

0.0804

804

0.6914 9/18/14 C - 11B-#2 6.35 8.33 1.98

9/18/14 C - 11B-#3 8.33 10.42 2.09

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)

214

Table E.12 Results of acid-soluble chloride content – Uncracked Specimen (C - 12)

Date of Test

Depth to which sample

was taken

Sample Names at Various Depths

Sample Triplicates

Initial Burette Reading

(mL)

Final Burette Reading

(mL)

Titrant Volume

(mL)

Average Titrant Volume

(mL)

Chloride Content

wt. % of sample ppm %bwoc

9/19/14 0.50

C - 12T

C - 12T-#1 35.67 48.17 12.50 12.55

0.5020

5020

4.3172 9/19/14 C - 12T-#2 12.24 25.10 12.86

9/19/14 C - 12T-#3 0.20 12.50 12.30 9/19/14

4.75 C - 12MT

C - 12MT-#1 21.60 23.80 2.20 2.28

0.0912

912

0.7843 9/19/14 C - 12MT-#2 7.37 9.60 2.23

9/19/14 C - 12MT-#3 25.10 27.50 2.40 9/19/14

9.00

C- 12M C- 12M-#1 23.80 26.00 2.20

2.15

0.0860

860

0.7396 9/19/14 C- 12M-#2 9.45 11.60 2.15 9/19/14 C- 12M-#3 25.50 29.60 2.10 9/19/14

13.25 C – 12MB

C – 12MB-#1 11.60 13.70 2.10 2.08

0.0832

832

0.7155 9/19/14 C – 12MB-#2 15.80 17.90 2.10

9/19/14 C – 12MB-#3 5.34 7.34 2.03 9/19/14

18.44

C- 12B C- 12B-#1 3.40 5.34 1.94

1.90

0.0760

760

0.6536 9/19/14 C- 12B-#2 5.36 7.30 1.94 9/19/14 C- 12B-#3 17.90 19.72 1.82

*ppm = part per million; %bwoc = percentage by weight of the cement (binder)