Long-Term Performance of 

Epoxy-Coated Reinforcing Steel in 

Heavy Salt-Contaminated Concrete

PUBLICATION NO. FHWA-HRT-04-090 JUNE 2004

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

1. Report No. 

 FHWA-HRT-04-090 

2. Government Accession No.

 

3. Recipient’s Catalog No. 

 

4. Title and Subtitle 

Long-Term Performance of Epoxy-Coated Reinforcing Steel in Heavy SaltContaminated Concrete 

5. Report Date 

June 2004 

6. Performing Organization Code 

7. Author(s) 

Seung-Kyoung Lee, Paul D. Krauss

8. Performing Organization Report No. 

 

9. Performing Organization Name and Address 

WISS, Janney, Elstner Associates, Inc. 

330 Pfingsten Road 

Northbrook, IL 60062-2095 

10. Work Unit No. (TRAIS) 

 

11. Contract or Grant No. 

 DTFH61-93-C-00027 

12. Sponsoring Agency Name and Address 

Office of Infrastructure R&D

Federal Highway Administration 

6300 Georgetown Pike 

McLean, VA 22101-2296 

13. Type of Report and Period Covered

Final Report 

September 1998 to December 2002

14. Sponsoring Agency Code 

15. Supplementary Notes 

Contracting Officer’s Technical Representative (COTR): Yash Paul Virmani, HRDI-10 

Acknowledgements: Leo Zegler, John Drakeford, Gregory Hedien, Steve Harris, Steve Zimmerman 

16. Abstract 

This report describes long-term natural weathering exposure testing of the remaining 31 post-Southern Exposure (SE) test slabs that were 

not autopsied during the 1993–1998 Federal Highway Administration (FHWA) research project. The samples were exposed from 

September 1998 to December 2002 at an outdoor test yard in Northbrook, IL. The 1993–1998 research program involved testing more 

than 52 different bar materials and, consequently, 12 different bar types were selected for long-term durability tests in concrete exposed

to the very aggressive SE test, which involved alternating wetting with 15 weight percent NaCl solution and drying cycles for 96 weeks. 

Periodic macrocell corrosion current between top and bottom mats and short-circuit potential data were collected during the exposure test 

program. Upon termination of the test program, autopsy and subsequent laboratory analysis was performed on the test slabs. 

The test results confirmed that the black bars produced the highest mean macrocell current density (least corrosion resistant) among 

various combinations of test variables regardless of slab configuration, and that the stainless steel bars exhibited negligible mean 

macrocell current density. In general, bent epoxy-coated reinforcing bar (ECR) in the top mat, coupled with black bars in the bottom 

mat, performed the worst among all ECR cases. The straight top-mat ECRs’ macrocell current density varied from 7 to 40 percent of the

highest black bar case, depending on the size of initial coating damage and type of bar in the bottom mat. ECR used in the top mat alone 

reduced the corrosion susceptibility to at least 50 percent of the black bar case, even when it contained coating damage and was 

connected to the black bar bottom mat. In contrast, if straight ECRs in the top mat were connected to ECRs in the bottom mat, the mean 

macrocell current density was no greater than 2 percent of the highest black bar case even when rebar coatings had defects, and approach

the corrosion resistant level of stainless steel reinforcement. Such improved corrosion resistance can be attributed to (1) reduction in 

cathodic area; (2) higher electrical resistance; and (3) reduced cathodic reaction. 

Whenever an ECR slab with negligible macrocell current density was autopsied, the appearance of the extracted ECR and concrete/bar 

interface was excellent with no sign of corrosion. However, when ECRs specimens with high macrocell current densities were 

autopsied, they revealed coating deterioration due to corrosion and exhibited numerous hairline cracks and/or blisters in conjunction with 

reduced adhesion, coating disbondment (permanent adhesion loss), and underlying steel corrosion. No consistent trend was found

between the level of macrocell current density and the extent of coating adhesion loss. The present test results and the earlier FHWA

studies indicate that adhesion appeared to be a poor indicator of long-term performance of the coated bars in chloride contaminated 

concrete; it is concluded that there is no direct relationship between loss of adhesion and the effectiveness of ECR to mitigate corrosion. 

Key Words 

concrete, corrosion, durability, electrochemical impedance 

spectroscopy, black bar, stainless steel, epoxy-coated reinforcing 

steel, mat-to-mat resistance, macrocell current, corrosion rate, 

chloride 

18. Distribution Statement 

No restrictions. This document is available to the public through 

the National Information Service, Springfield, VA 22161. 

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified 

21. No. of Pages 

130

22. Price 

 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 
SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm

ft feet 0.305 meters m

yd yards 0.914 meters m

mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha 

mi2 square miles 2.59 square kilometers km2

VOLUME 

fl oz fluid ounces 29.57 milliliters mL

gal gallons 3.785 liters L

ft3 cubic feet 0.028 cubic meters m3 

yd3 cubic yards 0.765 cubic meters m3 

NOTE: volumes greater than 1000 L shall be shown in m3

MASS oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") 

TEMPERATURE (exact degrees) o

F Fahrenheit 5 (F-32)/9 Celsius oC 

or (F-32)/1.8 

ILLUMINATION

fc foot-candles 10.76 lux lx 

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS

lbf poundforce 4.45 newtons N 

lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH mm millimeters 0.039 inches in

m meters 3.28 feet ft

m meters 1.09 yards yd

km kilometers 0.621 miles mi 

AREA mm2 square millimeters 0.0016 square inches in2 

m2 square meters 10.764 square feet ft

2 

m2 square meters 1.195 square yards yd2 

ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi

2 

VOLUME mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft

3 

m3 cubic meters 1.307 cubic yards yd3 

MASS 

g grams 0.035 ounces oz

kg kilograms 2.202 pounds lb

Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) o

C Celsius 1.8C+32 Fahrenheit oF 

ILLUMINATION

lx lux 0.0929 foot-candles fc

cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS

N newtons 0.225 poundforce lbf

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)

ii
TABLE OF CONTENTS 

EXECUTIVE SUMMARY ...........................................................................................................1 

CHAPTER 1. INTRODUCTION AND PROJECT HISTORY ................................................3 

CHAPTER 2. EXPERIMENTAL METHOD...........................................................................11 

Test Specimens ........................................................................................................................11 

Data Collection ........................................................................................................................11 

Autopsy....................................................................................................................................13 

Chloride Analysis.....................................................................................................................14 

CHAPTER 3. RESULTS AND DISCUSSION......................................................................... 15 

Short-Circuit Potential and Macrocell Current Density...........................................................15 

Statistical Analysis of Test Data ..............................................................................................18 

Autopsy Results.......................................................................................................................18 

Chloride Analysis.....................................................................................................................20 

CHAPTER 4. CONCLUSIONS..................................................................................................47 

REFERENCES.............................................................................................................................49 

APPENDIX A. PHOTOGRAPHS OF TEST SLABS AT END OF OUTDOOR 

EXPOSURE AND AUTOPSIED BARS....................................................................................51 

iii
LIST OF FIGURES 

Figure 1. Configuration of test slab .................................................................................................5 

Figure 2. Estimated chloride accumulation at 25.4 mm (1.0 inch) depth with time in the concrete 

 test slab..............................................................................................................................6 

Figure 3. Average macrocell current data of eight reinforcing bar materials for 96-week 

SE tests..............................................................................................................................9 

Figure 4. Average mat-to-mat AC resistance data of eight reinforcing bar materials for 

96-week SE tests...............................................................................................................9 

Figure 5. Short-circuit potential change with time (straight top (black and ECR)-black bottomuncracked concrete) during outdoor exposure................................................................21 

Figure 6. Macrocell current density change with time (straight top (black and ECR)-black 

bottom-uncracked concrete) during outdoor exposure ...................................................21 

Figure 7. Short-circuit potential change with time (straight top (black and ECR)-black bottomcracked concrete) during outdoor exposure....................................................................22 

Figure 8. Macrocell current density change with time (straight top (black and ECR)-black 

bottom-cracked concrete) during outdoor exposure .......................................................22 

Figure 9. Short-circuit potential change with time (bent top (black and ECR)-black bottomuncracked concrete) during outdoor exposure................................................................23 

Figure 10. Macrocell current density change with time (bent top (black and ECR)-black 

bottom-uncracked concrete) during outdoor exposure ................................................23 

Figure 11. Short-circuit potential change with time (stainless steel and ECR in both matsuncracked concrete) .....................................................................................................24 

Figure 12. Macrocell current density change with time (stainless steel and ECR in both mats- 

 uncracked concrete) .....................................................................................................24 

Figure 13. Mean short-circuit potential change with time (uncracked vs. precracked concrete)..25 

Figure 14. Mean macrocell current density change with time (uncracked vs. 

 precracked concrete)....................................................................................................25 

Figure 15. Mean short-circuit potential change with time (straight vs. bent ECRs in uncracked 

concrete).......................................................................................................................26 

Figure 16. Mean macrocell current density change with time (straight vs. bent ECRs in 

 uncracked concrete) .....................................................................................................26 

Figure 17. Mean short-circuit potential data classified by bar type (from table 9) .......................27 

Figure 18. Mean macrocell current density data classified by bar type (from table 9) .................27 

Figure 19. Relative ratio of macrocell current density per slab configuration ..............................28 

Figure 20. Relationship between macrocell current density versus initial artificial 

 coating defects .............................................................................................................28

iv
Figure 21. Short-circuit potential data classified by coating type .................................................29 

Figure 22(a). Macrocell current density data classified by coating type (linear scale) .................30 

Figure 22(b). Macrocell current density data classified by coating type (logarithmic scale)........30 

Figure 23. Ninety-five percent confidence intervals for short-circuit potential data.....................31 

Figure 24. Ninety-five percent confidence intervals for macrocell current density data...............31 

Figure 25. Ninety-five percent confidence intervals for AC resistance data.................................32 

Figure 26. Ninety-five percent confidence intervals for impedance modulus data .......................32 

Figure 27. Cutting a test slab with a gas-powered saw..................................................................33 

Figure 28. Extraction of embedded reinforcing bars.....................................................................33 

Figure 29. Typical condition of ECR with good corrosion resistance (slab #7—top right bar)....34 

Figure 30. Typical condition of ECR with poor performance (slab #30—top right bar)..............34 

Figure 31. Typical condition of a bent ECR with good performance (slab #1—top left bar).......35 

Figure 32. Typical condition of a bent ECR with poor performance ...........................................35 

Figure 33. Closeup views of ECRs exhibiting various conditions: (a) an intact ECR; 

(b) an ECR containing hairline coating cracks; (c) an ECR containing coating 

blisters and hairline coating cracks; and (d) a delaminated ECR revealing severely 

corroded substrate ........................................................................................................36 

Figure 34. Typical condition of black bars in the top mat.............................................................36 

Figure 35. Typical condition of black bent bars in the top mat (slab #23—top right bar) ............37 

Figure 36. Corroded bottom mat (slab #19)...................................................................................37 

Figure 37. Photograph of autopsied bars extracted from slab #18 (ECR top-black bar bottom) ..38 

Figure 38. Photograph of autopsied bars extracted from slab #10 (ECRs in both mats)...............38 

Figure 39. Ninety-five percent confidence intervals for number of final defects..........................39 

Figure 40. Ninety-five percent confidence intervals for ECR rating data .....................................39 

Figure 41. Ninety-five percent confidence intervals for knife adhesion data................................40 

Figure 42. Ninety-five percent confidence intervals for extent of disbondment data ...................40 

Figure 43. Relationship between water-soluble versus acid-soluble chloride data .......................41 

Figure 44. Ninety-five percent confidence intervals for water-soluble chloride data at top bar 

 depth.............................................................................................................................41 

Figure 45. Slab #1 front, rear, and top views with specifications..................................................51 

Figure 46. Slab #1 extracted rebars condition ...............................................................................52 

Figure 47. Slab #1 after autopsy ....................................................................................................53 

v 
Figure 48. Slab #2 front, rear, and top views with specifications..................................................54 

Figure 49. Slab #2 extracted rebars condition ...............................................................................55 

Figure 50. Slab #2 after autopsy ....................................................................................................55 

Figure 51. Slab #3 front, rear, and top views with specifications..................................................56 

Figure 52. Slab #3 extracted rebars condition ...............................................................................57 

Figure 53. Slab #3 after autopsy ....................................................................................................57 

Figure 54. Slab #4 front, rear, and top views with specifications..................................................58 

Figure 55. Slab #4 extracted rebars condition ...............................................................................59 

Figure 56. Slab #4 after autopsy ....................................................................................................60 

Figure 57. Slab #5 front, rear, and top views with specifications..................................................61 

Figure 58. Slab #5 extracted rebars condition ...............................................................................62 

Figure 59. Slab #5 after autopsy ....................................................................................................62 

Figure 60. Slab #6 front, rear, and top views with specifications..................................................63 

Figure 61. Slab #6 extracted rebars condition ...............................................................................64 

Figure 62. Slab #6 after autopsy ....................................................................................................64 

Figure 63. Slab #7 front, rear, and top views with specifications..................................................65 

Figure 64. Slab #7 extracted rebars condition ...............................................................................66 

Figure 65. Slab #7 after autopsy ....................................................................................................66 

Figure 66. Slab #8 front, rear, and top views with specifications..................................................67 

Figure 67. Slab #8 extracted rebars condition ...............................................................................68 

Figure 68. Slab #8 after autopsy ....................................................................................................69 

Figure 69. Slab #9 front, rear, and top views with specifications..................................................70 

Figure 70. Slab #9 extracted rebars condition ...............................................................................71 

Figure 71. Slab #9 after autopsy ....................................................................................................71 

Figure 72. Slab #10 front, rear, and top views with specifications................................................72 

Figure 73. Slab #10 extracted rebars condition .............................................................................73 

Figure 74. Slab #10 after autopsy ..................................................................................................73 

Figure 75. Slab #11 front, rear, and top views with specifications................................................74 

Figure 76. Slab #11 extracted rebars condition .............................................................................75 

Figure 77. Slab #11 after autopsy ..................................................................................................76 

vi 
Figure 78. Slab #12 front, rear, and top views with specifications................................................77 

Figure 79. Slab #12 extracted rebars condition .............................................................................78 

Figure 80. Slab #12 after autopsy ..................................................................................................78 

Figure 81. Slab #13 front, rear, and top views with specifications................................................79 

Figure 82. Slab #13 extracted rebars condition .............................................................................80 

Figure 83. Slab #13 after autopsy ..................................................................................................80 

Figure 84. Slab #14 front, rear, and top views with specifications................................................81 

Figure 85. Slab #14 extracted rebars condition .............................................................................82 

Figure 86. Slab #14 after autopsy ..................................................................................................82 

Figure 87. Slab #15 front, rear, and top views with specifications................................................83 

Figure 88. Slab #15 extracted rebars condition .............................................................................84 

Figure 89. Slab #15 after autopsy ..................................................................................................84 

Figure 90. Slab #16 front, rear, and top views with specifications................................................85 

Figure 91. Slab #16 extracted rebars condition .............................................................................86 

Figure 92. Slab #16 after autopsy ..................................................................................................87 

Figure 93. Slab #17 front, rear, and top views with specifications................................................88 

Figure 94. Slab #17 extracted rebars condition .............................................................................89 

Figure 95. Slab #17 after autopsy ..................................................................................................89 

Figure 96. Slab #18 front, rear, and top views with specifications................................................90 

Figure 97. Slab #18 extracted rebars condition .............................................................................91 

Figure 98. Slab #18 after autopsy ..................................................................................................91 

Figure 99. Slab #19 front, rear, and top views with specifications................................................92 

Figure 100. Slab #19 extracted rebars condition ...........................................................................93 

Figure 101. Slab #19 after autopsy ................................................................................................93 

Figure 102. Slab #20 front, rear, and top views with specifications..............................................94 

Figure 103. Slab #20 extracted rebars condition ...........................................................................95 

Figure 104. Slab #20 after autopsy ................................................................................................95 

Figure 105. Slab #21 front, rear, and top views with specifications..............................................96 

Figure 106. Slab #21 extracted rebars condition ...........................................................................97 

Figure 107. Slab #21 after autopsy ................................................................................................97 

vii 
Figure 108. Slab #22 front, rear, and top views with specifications..............................................98 

Figure 109. Slab #22 extracted rebars condition ...........................................................................99 

Figure 110. Slab #22 after autopsy ..............................................................................................100 

Figure 111. Slab #23 front, rear, and top views with specifications............................................101 

Figure 112. Slab #23 extracted rebars condition .........................................................................102 

Figure 113. Slab #23 after autopsy ..............................................................................................103 

Figure 114. Slab #24 front, rear, and top views with specifications............................................104 

Figure 115. Slab #24 extracted rebars condition .........................................................................105 

Figure 116. Slab #24 after autopsy ..............................................................................................105 

Figure 117. Slab #25 front, rear, and top views with specifications............................................106 

Figure 118. Slab #25 extracted rebars condition .........................................................................107 

Figure 119. Slab #25 after autopsy ..............................................................................................107 

Figure 120. Slab #26 front, rear, and top views with specifications............................................108 

Figure 121. Slab #26 extracted rebars condition .........................................................................109 

Figure 122. Slab #26 after autopsy ..............................................................................................109 

Figure 123. Slab #27 front, rear, and top views with specifications............................................110 

Figure 124. Slab #27 extracted rebars condition .........................................................................111 

Figure 125. Slab #27 after autopsy ..............................................................................................111 

Figure 126. Slab #28 front, rear, and top views with specifications............................................112 

Figure 127. Slab #28 extracted rebars condition .........................................................................113 

Figure 128. Slab #28 after autopsy ..............................................................................................113 

Figure 129. Slab #29 front, rear, and top views with specifications............................................114 

Figure 130. Slab #29 extracted rebars condition .........................................................................115 

Figure 131. Slab #29 after autopsy ..............................................................................................115 

Figure 132. Slab #30 front, rear, and top views with specifications............................................116 

Figure 133. Slab #30 extracted rebars condition .........................................................................117 

Figure 134. Slab #30 after autopsy ..............................................................................................117 

Figure 135. Slab #31 front, rear, and top views with specifications............................................118 

Figure 136. Slab #31 extracted rebars condition .........................................................................119 

Figure 137. Slab #31 after autopsy ..............................................................................................120 

viii 
LIST OF TABLES 

Table 1. Mix properties of concrete used.......................................................................................5 

Table 2. Acid-soluble chloride concentrations (percent by weight of sample) .............................6 

Table 3. Summary of corrosion performance of different reinforcing bar materials under 

96-week SE testing[4] ........................................................................................................8 

able 4. Summary of in-concrete test results per coating type[4] T .................................................10 

Table 5. Summary of test slabs exposed to outdoor weathering..................................................12 

Table 6. Electrochemical and chloride data for test slabs containing ECR in top mat only........42 

Table 7. Electrochemical and chloride data for test slabs containing ECR in both mats............43 

Table 8. Electrochemical and chloride data for test slabs containing black and stainless steel 

 bars.................................................................................................................................43 

Table 9. Electrochemical test data classified by bar type ............................................................44 

Table 10. Electrochemical test data classified by coating type .....................................................44 

Table 11. Characterization of autopsied ECRs tested in the top mat.............................................45 

Table 12. Characterization of autopsied ECRs tested in both mats...............................................46 

ix

EXECUTIVE SUMMARY 

In May 1993, the Federal Highway Administration (FHWA) began a 5-year research project, 

Corrosion Resistant Reinforcing for Concrete Components. The objective of the study was to 

develop cost-effective new breeds of organic, inorganic, ceramic, and metallic coatings, as well 

as metallic alloys that could be utilized on or as reinforcement for embedment in portland cement 

concrete and ensure a corrosion-free design life of 75 to 100 years when exposed to adverse 

environments. The 1993–1998 research program involved testing more than 52 different organic, 

inorganic, ceramic, and metallic coatings on steel bars, as well as solid metallic bars. 

Specifically, these included epoxy-coated, other polymer-coated, ceramic-coated, galvanizedclad, epoxy-coated galvanized-clad, stainless steel-clad, nickel-clad, copper-clad, corrosion 

resistance alloy-clad, inorganic silicate-clad, solid corrosion-resistance alloy steel, solid 

aluminum-bronze, solid stainless steels, and solid titanium reinforcing bars. Consequently, 12 

different bar types were selected for long-term durability tests in concrete exposed to the very 

aggressive Southern Exposure (SE) testing, which involved alternating wetting with 15 weight 

percent NaCl solution and drying cycles for 96 weeks. About 150 test slabs were fabricated for 

the selected 12 different bar types. 

After the conclusion of the 96-week SE testing in 1998, 31 post-SE test slabs that were not 

autopsied were then exposed to a long-term natural weathering at an outdoor test yard in 

Northbrook, IL, from September 1998 to December 2002. Periodic macrocell corrosion current

between two mats and short-circuit potential of top mat bars (while they were connected to the 

bottom mat bars) data were collected during the exposure test program. When the test program

ended after about 7 years, autopsy and subsequent laboratory analysis was performed with the 

test slabs, and the results are reported here. The tests include chlorides in the concrete, condition 

evaluation at bar/concrete interface, and visual examination of extracted bars. 

Macrocell current density was a good indicator of corrosion performance of the various 

reinforcements. The black bars produced the highest mean macrocell current density (least 

corrosion resistant) among various combinations of test variables regardless of slab 

configuration. The stainless steel bars exhibited negligible mean macrocell current density. 

Whenever an epoxy-coated reinforcing bar (ECR) slab with negligible macrocell current density 

was autopsied, the appearance of the extracted ECR and concrete/bar interface was excellent 

with no sign of corrosion, and the coating looked new with a glossy texture. However, when 

ECRs slabs with a high macrocell current density were autopsied, they revealed coating 

deterioration due to corrosion and exhibited numerous hairline cracks and/or blisters in 

conjunction with reduction in adhesion, coating disbondment (permanent loss of adhesion), and 

underlying steel corrosion. Generally, the number of final coating defects on the autopsied ECRs 

increased from their initial values determined before embedment in concrete. There was no 

consistent trend found between the level of macrocell current density and the extent of coating 

adhesion loss. The earlier FHWA studies investigated the adhesion of the coatings using 

accelerated solution immersion tests and cathodic disbonding tests. Based on the review of the 

test results, the adhesion, as tested by solution immersion and cathodic disbonding tests, 

appeared to be a poor indicator of long-term performance of the coated bars in chloride 

contaminated concrete after 96-week SE. These findings led researchers to conclude that there is 

1 
no direct relationship between loss of adhesion and the effectiveness of ECR to mitigate 

corrosion. 

In general, bent ECRs in the top mat coupled with black bars in the bottom mat performed the 

worst among all ECR cases. For straight top-mat ECRs, the mean macrocell current density was 

influenced by the size of initial coating damage and type of bar in the bottom mat. Their 

performance varied from 7 to 40 percent of the highest black bar case as measured by macrocell 

current density. However, if straight ECRs in the top mat were connected to ECRs in the bottom 

mat, the mean macrocell current density was no greater than 2 percent of the highest black bar 

case, regardless of the initial coating defect size. Both mat ECR systems behaved comparable to 

stainless steel bars. According to impedance modulus, alternating current (AC) resistance, 

macrocell current density data, and autopsy results, the excellent performance of test slabs 

containing ECRs in both mats should be attributed to the facts that electrical resistance was very 

high between the two mats, and the ECRs in the bottom mat suppressed the corrosion activity by 

minimizing the area for the cathodic reaction (oxygen reduction). 

The 2-year saltwater ponding with alternate wetting, heating, and drying, followed by 5-year 

outdoor weathering, confirmed that use of ECRs in the top mat only (uncoated bottom mat) 

reduced the corrosion susceptibility to at least 50 percent of the black bar case, even when the 

coating has damage. Hence, ECR used in the top mat alone would not provide optimum

corrosion protection. If ECRs are used in both mats in uncracked concrete, corrosion resistance 

increases dramatically, even when the rebar coatings have defects. Such improved corrosion 

resistance can be attributed to a (1) reduction in cathodic area; (2) higher electrical resistance; 

and (3) reduced cathodic reaction.

2 
CHAPTER 1. INTRODUCTION AND PROJECT HISTORY 

The Federal Highway Administration (FHWA) research project, Corrosion Resistant Reinforcing

for Concrete Components, began in 1993. The objective of the proposed study was to develop 

cost-effective new breeds of organic, inorganic, ceramic, and metallic coatings, as well as 

metallic alloys that could be utilized on or as reinforcement for embedment in portland cement 

concrete. It was required that new coatings and alloys should provide significantly more 

corrosion-resistant reinforcement than the fusion-bonded epoxy-coated reinforcement that has 

been used in the United States since 1975 and also the corrosion-free design life shall be 75 to 

100 years when exposed to adverse environments. 

The research was aimed at developing new reinforcement materials and systems that minimally 

damage the coating system during (1) coating application, (2) fabrication bending operations, 

and (3) shipment to and installation at the jobsite. It was required that alloys have superior 

characteristics, and that thin-clad conventional steel resist damage. The coating systems had to 

have superior physical and chemical properties that remain undamaged by long-term exposure to 

ultraviolet radiation, high temperatures, salt-laden atmosphere, and other environmental 

conditions during long-term storage before casting them in concrete. 

On March 3, 1993, 3M informed the researchers that Scotchkote 213 (3M 213 TM) would no 

longer be manufactured, because of rulings from the U.S. Environmental Protection Agency 

(EPA). The 3M 213 epoxy-coated bars had been used almost exclusively in the bridges in the 

United States from about 1980 to 1990. Based on this change, it became crucial to secure bars 

coated with the 3M 213 for the in-concrete tests that were to begin in 1995. 

An invitational letter for submitting candidate bars was sent to 46 companies on May 17 and 18, 

1993. It was anticipated that numerous new candidate organic coatings would be submitted for 

testing, because the 3M 213 epoxy coating material was no longer available, and new steel 

surface pretreatments used before coating the bars were being considered. As a result, 

researchers used a 30-day prescreening test program to screen these numerous organic-coated 

candidate bar systems, with and without special steel surface pretreatments. At that time, the 

organic coaters agreed that pretreatment would improve coating adhesion strength and long-term

performance. 

The 1993–1998 research program involved testing more than 52 different organic, inorganic, 

ceramic, and metallic coatings on steel bars, as well as solid metallic bars. Specifically, they 

included epoxy-coated, other polymer-coated, ceramic-coated, galvanized-clad, epoxy-coated 

galvanized-clad, stainless steel-clad, nickel-clad, copper-clad, corrosion resistance alloy-clad, 

inorganic silicate-clad, solid corrosion-resistance alloy steel, solid aluminum-bronze, solid 

stainless steels, and solid titanium reinforcing bars. 

Prescreening tests on organic-coated bars were conducted from 1993 to 1995. These screening 

tests are chronicled in two reports: The Performance of Bendable and Nonbendable Organic 

Coatings for Reinforcing Bars in Solution and Cathodic Disbondment Tests [1] and the related 

phase II screening test report.[2] Screening tests were also conducted from 1993 to 1995 on 

3 
metallic-clad and solid metallic bars. This research studied 10 types of metal clad bars and 

10 types of solid metal bars. The performance of various inorganic-, ceramic-, and metallic-clad 

bars and solid corrosion-resistant bars is discussed in the 1996 FHWA report, The Corrosion 

Performance of Inorganic-, Ceramic-, and Metallic-Clad Reinforcing Bars and Solid Metallic 

Reinforcing Bars in Accelerated Screening Tests.

[3]

 

Based on screening tests as detailed in the three reports mentioned above, 12 bar types were 

selected for the 96-week in-concrete testing. The 141 reinforced concrete slab specimens using 

12 different bar types were made and were exposed to the 96-week SE testing. These tests were 

completed in late 1997, and the final report was published in a 1998 FHWA report, Corrosion 

Evaluation of Epoxy-Coated, Metallic-Clad and Solid Metallic Reinforcing Bars in Concrete.[4] 

The 96-week SE testing involved with the following wetting and drying cycles: 

• Cyclic wetting and drying of 3-day drying at 38 o

C (100 oF) and 60–80 percent relative 

humidity (RH), followed by 4-day ponding under a 15 percent NaCl solution at 16–27 o

C 

(60–80 o

F) for 12 weeks. 

• Continuous ponding under a 15 percent NaCl solution at 16–27 o

C (60–80 oF) and 60–80 

percent RH for another 12 weeks. 

The 15 percent salt solution was chosen to represent the high salt concentrations occurring on 

inland bridge structures from deicing salts. The long ponding period was utilized to simulate a 

sustained period of submersion or long periods of high concrete moisture common in winter 

months or in marine structures. This 24-week cycle was repeated four times for a total test 

period of 96 weeks. 

Configuration of the concrete slabs used in this FHWA study measured 30.5 x 30.5 x 

17.8 centimeters (cm) (12 x 12 x 7 inches) and contained two layers of 29.2-cm (11.5-inch) long 

and 1.6-cm (5/8-inch) diameter reinforcement, as shown in figure 1. The top mat acted as a 

macroanode and contained either two straight or two bent reinforcing bars, while the bottom mat 

was a macrocathode that contained four straight reinforcing bars. The top mat bar was connected 

to two bottom mat bars through a 10 Ω resistor. A clear cover of 25.4 millimeters (mm) (1.0 

inch) was used in all specimens. This cover conforms to either the American Association of 

State Highway and Transportation Officials- (AASHTO) specified bottom-of-slab cover, or 

possible minimum in-place clear cover, allowing for construction tolerances when 3.8- to 5.0-cm

(1.5- to 2.0-inch) cover requirements are specified. While most previous published corrosion 

studies used only crack-free concrete slabs, some of the test slabs used in this project contained 

the cracks directly over a top mat rebar to simulate cracks observed on actual bridge decks. 

Table 1 presents the concrete mix design data for the test slab concrete. 

4 
Figure 1. Configuration of test slab 

1 inch = 25.4 mm

Table 1. Mix properties of concrete used 

Concrete Property Mean Value 

of 30 Batches

Standard 

Deviation 

Cement, kg/m3 (lb/yd3) 370 (623) 3.3 (5.56) 

Air, percent 5.6 0.51 

Slump, mm (inch) 167 (6.58) 31.7 (1.25) 

Unit wt., kg/m3 (lb/yd3) 2315 (144.5) 21.0 (1.31) 

w/c 0.47 0.01

28-day compressive strength, MPa 

(psi) 39.3 (5,700) 2.7 (403) 

5 
Table 2 shows the chloride concentration data collected during the 96-week FHWA study, and 

figure 2 shows the estimated chloride concentration at the top mat depth (2.5 cm or 1.0 inch) 

with time. It is clear that rapid migration of chloride is achieved through the SE testing. At the 

sixth week of testing, chloride concentration at the 2.5 cm (1.0 inch) depth exceeded 2.97 kg/m3

(5 pounds (lb)/yard (yd)3

) (0.137 percent or 1,370 parts per million (ppm)), which was greater 

than 3 times the known chloride threshold (0.71 to 0.89 kg/m3

 (1.2 to1.5 lb/yd3) or 300 to 350 

ppm) for uncoated American Society for Testing and Materials (ASTM) A615 bar. 

Table 2. Acid-soluble chloride concentrations (percent by weight of sample) 

Nominal Sampling Depth (inch) Estimated Chloride at 

Top Mat 

Test 

Period 

(Weeks) 0.5 1.25 2.0 2.5 Percent by

Weight of 

Sample 

lb/yd3

6 0.347 0.032 < 0.007 < 0.007 0.137 5.3

12 0.551 0.048 0.011 < 0.007 0.216 8.4

24 0.562 0.231 0.031 < 0.007 0.314 12.2

48 0.63 0.484 0.152 0.012 0.533 20.8

72 0.86 0.489 0.204 0.04 0.613 23.9

96 0.873 0.721 0.485 0.314 0.772 30.1

1 inch = 25.4 mm 

1 lb/yd3

 = 0.59 kg/m3

y = 0.0456x 0.6186

R2 = 0.9964

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96

Time (Week)

Chloride Concentration (Percent by Weight of Sample)

y = 0.0456x 0.6186

R2 = 0.9964

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96

Time (Week)

Chloride Concentration (Percent by Weight of Sample)

Figure 2. Estimated chloride accumulation at 25.4 mm (1.0 inch) depth with time in the concrete 

test slab 

6 
Table 3 summarizes the performance data of seven different rebar materials tested under the 96-

week FHWA test program. Figures 3 and 4 show average macrocell current and mat-to-mat AC 

resistance data of each type reinforcing bar in table 3. Furthermore, table 4 classifies average 

macrocell current and mat-to-mat AC resistance of the ECR slabs for each coating type. The 96-

week FHWA study concluded that the best ECR performance was obtained when the bars were 

tested in a straight condition, with 0.004 percent damage in uncracked concrete using an ECR 

cathode in the bottom mat. Researchers also found that there was a clear relationship between 

the mat-to-mat resistance values of the ECRs and their corrosion performance. Better corrosion 

protection was provided by those coating systems that had high electrical resistance, that is, the 

corrosion was strongly dependent on the amount of damage in the coating.[4]

7 
Table 3. Summary of corrosion performance of different reinforcing bar materials under 96-week SE 

Bar Type Slab Macrocell Current Mat-to-Mat Resistance 

Configuration Average 

Macrocell 

Current over 96 

Weeks (uA) 

Percentage of

Black Bar 

Average AC 

Current over 96 

Weeks (ohm) 

Percentage o

Black Bar 

Uncracked 352.5 100 243 100 ASTM A615 Black Precracked 405.3 100 263 100 Uncracked 0.2 to 190.7 0.06 to 54.1 704 to 659,069 290 to 271,222

Six Different EpoxyCoated Bar Types Precracked 1.4 to 191.8 0.35 to 47.3 591 to 103,722 225 to 39,438

Uncracked 207.9 59.0 413 170.0 Galvanized Bar Precracked 294.1 72.5 318 120.9 

Zinc Alloy-Clad Bar Uncracked 126.7 35.9 385 158.4 

Precracked 273 67.3 325 123.6 

Uncracked 3.7 1.0 584 240.3 Copper-Clad Bar Precracked 14.2 3.5 491 186.7 Uncracked 0.5 0.1 602 247.7 

304 Stainless Steel Bar Precracked 11.3 2.8 566 215.2 316 Stainless Steel Uncracked 0.5 0.1 476 195.9Bar Precracked 0.5 0.1 429 163.1

8
0.01

0.1

1

10

100

1000

ASTM

A615 Black

Good

Performing

EpoxyCoated Bar

Poor

Performing

EpoxyCoated Bar

Galvanized

Bar

Zinc AlloyClad BarCopperClad Bar304

Stainless

Steel Bar

316

Stainless

Steel Bar

Bar Type

Average Macrocell Current (uA)

Uncracked slabs Precracked slabs

Figure 3. Average macrocell current data of eight reinforcing bar materials for 96-week SE tests 

1

10

100

1000

10000

100000

1000000

ASTM

A615 Black

Good

Performing

EpoxyCoated Bar

Poor

Performing

EpoxyCoated Bar

Galvanized

Bar

Zinc AlloyClad BarCopperClad Bar304

Stainless

Steel Bar

316

Stainless

Steel Bar

Bar Type

Average Mat-to-Mat AC Resistance (ohm)

Uncracked slabs Precracked slabs

?

Figure 4. Average mat-to-mat AC resistance data of eight reinforcing bar materials for 96-week 

SE tests 

9 
Table 4. Summary of in-concrete test results per coating type[4]

Slab Configuration ECR Coating Type 

Data Presence of Crack Top Mat Bottom Mat Initial Defect Size

(Percent) 

A B C D 

Straight 0.5 2.5 24.6 53.8 4.8 black 0.004 0.3 0.2 4.3 1.2 

0.5 0.3 0.4 1.2 1.4 

Straight ECR 

Straight ECR 0.004 0.2 0.3 0.3 1.3 

0.5 38.8 30.8 80.3 30.2 

Uncracked 

Bent ECR Straight 

black 0.004 0.5 0.4 7.9 1.9 

0.5 59.6 65.4 103.7 11.3 

Average Macrocell Current (uA) 

Precracked Straight ECR Straight black 0.004 7.8 60.0 24.8 1.4 

Straight 0.5 3,239 3,359 1,671 3,514 black 0.004 361,707 543,182 511,331 659,069 

0.5 5,941 9,255 7,147 6,914 

Straight ECR 

Straight ECR 0.004 488,452 561,286 528,333 941,250 

0.5 1,349 1,943 1,393 2,738 

Uncracked 

Bent ECR Straight 

black 0.004 13,561 97,752 171,951 68,950 

0.5 1,281 2,918 831 1,715 

Average Mat-toMat Resistance (ohm) 

Precracked Straight ECR Straight black 0.004 14,653 4,005 21,406 103,722 

10
CHAPTER 2. EXPERIMENTAL METHOD 

Test Specimens 

Table 5 describes the test slabs employed in this study. The ECR specimens from the 96-week 

SE test that remained for extended outdoor exposure were coated with six different powder 

coating products, which were manufactured by Akzo, O’Brian, 3M, and Ajikawa (Japanese). 

Individual coatings were identified as Akzo-GreyTM, Akzo-GreenTM, Akzo-OliveTM, O’Brian 

GoldTM, 3M 213, and Ajikawa.TM They are randomly designated as coatings A through F in this 

report. This nomenclature is identical to that in Report No. FHWA-RD-98-153.[4] As 

summarized in table 5, the slabs were classified into four configuration groups. These were (1) 

slabs containing ECR in the top mat and black bar in the bottom mat (ECR top-black bottom, 19 

slabs); (2) slabs containing ECRs in both mats (ECR top-ECR bottom, 6 slabs); (3) control slabs 

containing black bars in both mats (black top-black bottom, 3 slabs); and (4) slabs containing 

straight stainless steel bars coupled with either black or stainless steel bottom bars (stainless 

steel, 3 slabs). Among the 19 ECR top-black bottom slabs, 6 had two 180-degree bent ECRs in 

the top mat, and the concrete cover of another 7 slabs was precracked over the straight bars. One 

specimen of each black top-black bottom and stainless top-black bottom slabs contained 180-

degree bent bars in the top mat. In addition, one black and stainless slab had precracks over the 

top mat bars. None of the ECR top-ECR bottom slabs contained bent bars or precracks. 

Every ECR bar was intentionally damaged by drilling holes through the coating to represent 

either 0.004 or 0.5 percent artificial coating defect using two different drill bit sizes. In every 

ECR top-ECR bottom slab, the two top mat ECRs contained different defect sizes, and a top mat 

ECR was paired with two bottom mat ECRs containing the same size of defect. 

Data Collection 

Corrosion progress of the top bar was monitored by both short-circuit potential (SCP) and 

macrocell current. SCP was measured when top and bottom bars were electrically connected. 

On the other hand, macrocell current was measured as the voltage drop across a 10-Ω resistor 

connected between the top and bottom bar mats. The current data then were converted into 

macrocell current density according to Ohm’s law and a known surface area of 145.7 cm2

 (22.6 

inch2

) for the anode (top bar). The same area was used for both coated and uncoated steel. Test 

data was collected periodically. During the last data measurements, additional data were 

collected, including the open-circuit potential (OCP) of top mat bars after the top and bottom mat 

bars were disconnected, the AC resistance between the top and bottom mats, and the impedance 

modulus ( Z ) at 0.1 Hertz (Hz) of top mat bars using Electrochemical Impedance Spectroscopy 

(EIS). Before autopsy, researchers documented the exterior condition of the test slabs using a 

digital camera. Photographs of the test slabs are provided in appendix A. 

11 
12 

Table 5. Summary of test slabs exposed to outdoor weathering

Slab Configuration 

Test Group Slab ID Top Mat Bar ID Bar Type Bent or Straight Bottom Mat Precracked 

(Yes/No) 

3A S N 3 3B Coating C1

S Black N 

6A S N 6 6B Coating B1

S Black N 

15A S N 15 15B Coating D1

S Black N 

18A S N 18 18B Coating F2

S Black N 

24A S N 24 24B Coating A1

S Black N 

28A S N 28 28B Coating E2

S Black N 

7A S Y 7 7B Coating A S Black Y 

13A S Y 13 13B Coating C S Black Y 

14A S Y 14 14B Coating E S Black Y 

19A S Y 19 19B Coating F S Black Y 

21A S Y 21 21B Coating D S Black Y 

25A S Y 25 25B Coating B S Black Y 

30A S Y 30 30B Coating C S Black Y 

1A B N 1 1B Coating D B Black N 

4A B N 4 4B Coating C B Black N 

8A B N 8 8B Coating F B Black N 

11A B N 11 11B Coating B B Black N 

22A B N 22 22B Coating A B Black N 

31A B N 

ECR Top and Black Bottom 

31 31B Coating E B Black N 

2A S N 2 2B Coating F S Coating F N 

9A S N 9 9B Coating B S Coating B N 

10A S N 10 10B Coating A S Coating A N 

12A S N 12 12B Coating C S Coating C N 

17A S N 17 17B Coating D S Coating D N 

ECR Top and ECR Bottom 

29A S N 29 29B Coating E S Coating E N 

5A S N 5 5B Black S Black N 

23A B N 23 23B Black B Black N 

Black Top 

and Black 

20A S Y 

Bottom 

20 20B Black S Black Y 

16A B N 16 16B Stainless steel B Black N 

26A S N 26 26B Stainless steel S Black Y 

27A S Y 

Stainless 

Steel 

27 27B Stainless steel S Stainless steel N 

1. Bendable coating 

2. Nonbendable coating and bent bars were coated after bending 
Autopsy 

Autopsies were conducted in groups of four or five test slabs. A detailed autopsy of each slab 

was performed according to the following procedures: 

Autopsy procedure for ECR 

1. Rebar identification tags were attached to each test bar. 

2. Digital photographs were taken to record final physical condition of the test slabs before

demolition. 

3. The slabs were broken open using a gas-powered saw with a diamond blade, and the bars were

extracted carefully. 

4. The bar surface facing the top side of the slab was marked with an arrow at one end of the bar. 

5. The concrete/rebar interface was examined for corrosion products and photographed. 

6. Coating defects were identified visually and with an holiday detector. 

7. Using a magnifier, researchers identified coating defects, characterized these by type of defect 

(bare area, mashed area, crack, or holiday), and marked them with a permanent marker. 

Photographs were taken of both sides of each ECR to document the defects. 

8. Deteriorated coating was removed with a utility knife. A knife adhesion test also was 

performed at six spots of undamaged coating areas to determine qualitative adhesion strength. 

9. Photographs were taken of both sides of each ECR after loose (disbonded) coating was

removed to document its extent of coating disbondment and assess the condition of the steel 

substrate beneath the removed coating. 

10. The extent of removed coating was measured quantitatively. 

11. Coating thickness was measured using a digital coating thickness gage. 

The elapsed time between steps 6 and 11 did not exceed 1 week. 

Autopsy procedure for black bars and stainless steel bars 

1. Rebar identification tags were attached to each bar. 

2. Photographs were taken to record final physical condition of the test slabs before demolition. 

3. The slabs were broken open using a gas-powered saw with a diamond blade, and the bars were

extracted carefully. 

4. The bar surface facing the top of the slabs was marked with an arrow at one end of the bars. 

5. The concrete/rebar interface was examined for corrosion products and photographed. 

6. Photographs were taken of both sides of each bar to document the condition of the bar. 

7. The bars were cleaned using chemicals and a wire brush to remove corrosion products, and 

corrosion damage was assessed. 

8. Photographs were taken of both sides of the cleaned bars. 

The elapsed time between steps 6 and 8 did not exceed 1 week. 
Chloride Analysis 

Concrete powder samples were taken by drilling with a 9.5-mm (3/8-inch) diameter masonry drill 

bit along the reinforcing steel imprints in the top mat of every slab. In addition, 14 powder 

samples were also collected from the selected bar imprints in the bottom mat. These powder 

samples were analyzed for water-soluble chloride concentration according to ASTM C1218 to 

determine the chloride content readily available at the bar depth. Based on the water-soluble 

chloride concentration analysis results, 23 samples (15 from top mat and 8 from bottom mat) were 

further selected and analyzed for acid-soluble chloride concentration according to ASTM C1152 to 

determine a relationship of water-soluble versus acid-soluble chloride concentrations. 

14 
CHAPTER 3. RESULTS AND DISCUSSION 

Short-Circuit Potential and Macrocell Current Density 

Tables 6 through 8 summarize the last electrochemical test data, grouped by type of test slab, that 

were collected in December 2002 just before the autopsy of the slabs. The data include SCP, 

OCP, macrocell current, AC resistance, and impedance modulus at 0.1 Hz. Figures 5 through 16 

summarize the changes of mean SCP and mean macrocell current density with time for the slabs

having different configurations. The elapsed time in the figures was calculated from the day 

when the slabs were placed in the outdoor test yard. It was noted that when test slabs had 

suffered from corrosion-induced physical damage, the data listed in tables 6, 7, and 8 did not 

represent actual condition of the reinforcing bars in those slabs. 

Test slabs containing black bars in both mats 

Each of the black bar test samples had cracking and delamination of the concrete cover after 96-

week SE testing and before placing the slabs outdoors. Therefore, the SCP and microcell 

currents measured after cracking are not indicative of the true difference in performance, because 

the corrosion rate and potentials (SCP) drop after cracking and delamination of the concrete 

cover occurs. The straight, non-bent black bars had an average corrosion current density of 

about 2.4 μA/cm2

 (15.5 μA/inch2) during the 96-week SE testing. Upon outdoor exposure, the 

black bar samples averaged somewhat less than 1.5 μA/cm2 (9.7 μA/inch2

). This same effect 

may be present for some of the other poorly performing ECR samples with large damaged areas, 

precracks, and bending damage. 

Test slabs containing ECRs in the top mat and black bars in the bottom mat 

Test slabs containing ECRs performed better, especially the ones with smaller initial defect size

(0.004 percent), than the black bar control slabs because ECRs exhibited lower macrocell current 

and more positive SCP over the test period than those of the black bar counterparts. Macrocell 

current density of the black bars became negative in every category after 1,600 days (see figures 

6, 8, and 10). Negative current readings indicated reversal of macrocell current between original 

anode (top mat) and original cathode (bottom mat) at the time of measurement. Such current 

reversal was caused by corroding bottom mat cathode steel first instead of usual corrosion 

initiation at the top mat bars. This situation was possible when chloride reached the black bars in 

the bottom mat and subsequently initiated the active corrosion there, while top mat ECRs were 

able to suppress corrosion. As discussed later, chloride concentration at some bottom bar depths 

was found to far exceed the chloride threshold for corrosion initiation of black bars (250 to 300 

ppm). 

Test slabs containing ECRs in both mats and stainless steel 

Figures 11 and 12 show variations of mean SCP and macrocell current density with time for the 

slabs containing either ECRs in both mats or stainless steel. There were three test slabs 

containing stainless steel bars in the top mat or in both mats, and two of them were precracked. 

15 
Because of the small number of slabs, the stainless steel slabs were treated as one variable, even 

though some contained cracks and/or black bottom bars. Each pair of ECRs in the top and 

bottom mats contained the same coating damage (0.004 or 0.5 percent), and every slab contained 

two pairs of ECRs with each of the two coating defect areas. While the 0.5 percent damaged 

ECRs exhibited more negative potentials compared to the others (ECRs with 0.004 percent 

coating defect and stainless steel) during most of the exposure time, all of the mean macrocell 

current density data remained very small throughout the test period. Mean macrocell current 

density of stainless steel bars with black bottom steel became negative at around 1,600 days due 

to active corrosion in the bottom black mat. Furthermore, when ECR was used in both mats, the 

coating defect size did not make a noticeable difference in macrocell current density output, 

which approached that of stainless steel bars. This observation suggests that using ECRs in both 

mats in northern bridge decks is likely to give very high corrosion resistance in corrosive 

environments under deicing salt applications, and may approach an equivalent corrosion 

resistance to that offered by stainless steel bars. 

Effect of precrack 

The effect of having precracks on SCP and macrocell current density can be seen in figures 13 

and 14, which show the change of mean SCP and mean macrocell current density with time for 

the slabs containing straight black bars and straight ECRs, respectively. All the top bars were 

connected to black bottom bars. In general, mean SCP and macrocell current density data for 

black bars and top mat ECRs behaved similarly in precracked and uncracked concrete during the 

outdoor weathering test period. The presence of the precrack influenced the time-to-corrosion 

initiation during the initial 96 weeks of SE testing more than after long-term outdoor exposure. 

Effect of bent ECR 

Figures 15 and 16 show the change of mean SCP and mean macrocell current density with time 

for straight and bent ECRs in uncracked concrete, respectively. Test slabs containing ECRs in 

both mats exhibited the most negative mean SCP among three groups, however, the performance 

between the groups was not largely different. When bent ECRs were connected to the black 

bottom bars, they produced the highest mean macrocell current density and were followed 

closely by the straight ECRs coupled with black bottom bars. In contrast, test slabs containing 

straight ECRs in both mats exhibited insignificant mean macrocell current density throughout the 

entire exposure period. 

Further data analysis related to slab configuration and bar type 

Table 9 summarizes the mean values of the test data presented in figures 5 through 12 according 

to four bar types (black, stainless steel, ECR with 0.5 percent initial coating damage, and ECR 

with 0.004 percent initial coating damage) and five slab configurations (straight top-black 

bottom-uncracked, straight top-ECR bottom-uncracked, straight top-black bottom-precracked, 

bent top-black bottom-uncracked, and stainless steel bars in uncracked). 

The SCP and macrocell current density data listed in table 9 also are presented in figures 17 and 

18, respectively. As shown in figure 17, black and stainless steel bars exhibited the most 

16 
negative and positive mean SCP, respectively. Mean SCP of the black bars moved in the 

negative direction when slabs contained precracks and bent bars. When coating defect size 

decreased from 0.5 to 0.004 percent, the mean SCP became more positive (lower corrosion 

tendency). As observed in figures 5 through 16, mean macrocell current density varied 

significantly depending on slab configuration and bar type. This trend is summarized in figure 

18. The black bars produced the highest mean macrocell current density among various 

combinations of test variables regardless of slab configuration, i.e., presence of crack and bar 

shape (bent vs. straight). 

To illustrate relative significance of slab configuration and bar type on the mean macrocell 

current density, figure 19 presents the ratios of macrocell current density data shown in table 9 

and figure 18 by dividing them by the highest average value (1.3 μA/cm2 (8.4 μA/inch2

)) of the 

black bent bar-black bottom-uncracked concrete slabs. The stainless steel bars exhibited 

negligible mean macrocell current density which was only 1 percent of the highest black bar 

case. For straight ECRs, the mean macrocell current density was influenced by the size of the 

initial coating damage and whether the bottom mat bar was coated or uncoated. When straight 

ECRs in the top mat were coupled with black bars in the bottom mat, the size of coating defect 

became a factor for controlling macrocell current density. In the case of straight top ECRs 

containing 0.004 percent of initial coating defect coupled with black bottom bars, mean 

macrocell current density was 7 to 21 percent of the highest black bar case, depending on the 

presence of precracks. If straight top ECRs contained 0.5 percent initial coating defect, the 

current values increased to more than 40 percent of the highest black bar case, regardless of 

whether the slab had a precrack. For bent ECRs, even ones containing 0.004 percent coating 

damage produced noticeable macrocell current density when they were connected to black 

bottom bars, such that mean macrocell current density increased to 38 and 49 percent of the 

highest black bar case, regardless of initial coating defect size. If top mat ECRs were connected 

to ECRs in the bottom mats in uncracked concrete, the effect of coating damage on macrocell 

current density was minor, and the ratio decreased to no greater than 2 percent of the highest 

black bar data. They behaved similarly to stainless steel bars. 

Figure 20 shows the effect of coating defect size on macrocell current density for ECRs in top 

mat only and ECRs in both mats cases. A regression analysis shows a well-defined relationship, 

indicating that defect size makes a significant influence on the ECRs coupled with black bottom

bars, but the coating size effect is diminished when ECRs are used in both mats. 

Effect of coating type 

Table 10 lists mean SCP and mean macrocell current density data per coating type. The same

data are presented in figures 21 and 22. Because of a large variation among different coating 

types, mean macrocell current density is presented in two scales: a linear scale in figure 22(a) 

and a logarithmic scale in figure 22(b). Performance differences are difficult to interpret from

the SCP data in figure 21. Generally, coatings C and F had the worst SCP data, while coatings 

A, D, and E had the best SCP data. It can be seen in figure 22 that mean macrocell current 

density varied significantly by coating type, which could be related to coating quality, but such 

variation disappeared when ECRs were used in both mats. Coatings A and D performed well in 

17 
all configurations, while coatings C and F had generally poor performance (except for the case of 

ECRs in both mats). 

Statistical Analysis of Test Data 

A statistical analysis was conducted to calculate sample mean ( x ) and sample standard deviation 

(s) for SCP, macrocell current density, AC resistance, and impedance modulus at 0.1 Hz data. 

Then, the results were used to determine the 95 percent confidence interval for the unknown 

population mean (μ). The 95 percent confidence interval for μ means that researchers are 95 

percent confident that the unknown μ is within this interval for a variable. Statistical analysis 

was performed for the variables classified by combinations of slab configuration and bar type, 

and the final results are provided in figures 23 through 26. 

Figure 23 shows the distribution of μ for the SCP data categorized by 12 combinations of test 

variables. The μ’s are evenly distributed among different variables. The stainless steel bars and 

bent black bars exhibited the most positive and most negative SCP mean values, respectively. 

Figure 24 shows distribution of μ’s for the macrocell current density data categorized by 12 

combinations of test variables. As noted in earlier sections, use of stainless steel bars and ECRs 

containing 0.004 percent initial coating damage produced the least current density. When ECRs 

having 0.5 percent initial coating defect are used in both mats, the macrocell current density 

slightly increased from zero. These are followed by straight ECRs containing 0.004 percent 

coating defects in the top mat only and other top mat only ECR cases. The black bar cases 

yielded the highest mean values. 

High coating resistance and impedance is characteristic of a quality, corrosion-resistant coating. 

Figures 25 and 26 show distribution of μ’s for AC resistance measured between the two mats 

and impedance modulus at 0.1 Hz of top mat bar, respectively. Impedance modulus data 

exhibited larger variations and higher absolute values than did the AC resistance test data. The 

four highest upper limits of μ’s were achieved by ECRs containing 0.004 percent coating defect. 

However, the lowest limit of μ’s was near zero resistance for most combinations of test 

variables. 

Autopsy Results 

Researchers began test slab autopsies by making a 1.3-cm (0.5-inch) deep groove along the 

bottom side of the slabs at two locations (figure 27) using a gas-powered saw. A test slab was 

split into several fragments by using a chisel and hammer. Embedded bars were then carefully 

extracted using a small chisel and hammer (figure 28). Researchers exercised caution when 

removing ECRs to avoid coating damage. 

Figure 29 shows a photograph of a top mat straight ECR that performed well throughout the 

severe testing regime. The ECR and concrete/bar interface appearance was excellent, with no 

sign of corrosion. Figure 30 shows a severely corroded, straight, top mat ECR. Figures 31 and 

32 show photographs of well and poorly performing bent ECRs, respectively, both from the top 

mat. 

18 
Closeup examination of the extracted ECRs revealed four different coating conditions, which are 

shown in figure 33. When the ECR performed well, the exposed coating looked new with a 

glossy texture (figure 33(a)). It was observed that when the epoxy coating reaches the advanced 

stage of deterioration due to corrosion, the coating exhibits numerous hairline cracks (figure 

33(b)) and then blisters (figure 33(c)). Accumulation of multiple rust layers beneath disbonded 

coating was also a common corrosion morphology observed on severely corroded ECRs (figure 

33(d)). The disbonded coating mentioned above was defined as a permanently separated coating 

from substrate upon knife adhesion test performed several days after the ECRs were excavated. 

Therefore, it was different from temporary adhesion loss, which can recover fully or partially 

with time. 

Figures 34 and 35 show photographs of a severely corroded straight black bar and a poorly 

performed bent black, respectively. Figure 36 shows a photograph of a broken test slab 

fragment, which exhibited active corrosion in the bottom black bar mat. 

All of the extracted bars, including those in the bottom mat, were carefully documented, cleaned, 

and examined according to the autopsy procedure described. Figures 37 and 38 show 

photographs of autopsied bars taken after they were cleaned. The bars shown in figure 37 were 

removed from slab #18, which contained ECRs in the top mat only. While one top ECR (the 

second bar from the top in the photograph) exhibited localized coating disbondment originated 

from corrosion at the smaller artificial coating defects (0.004 percent), the other top ECR (the 

first bar from the top in the photograph) experienced severe corrosion, again initiated at the 

larger artificial coating defects (0.5 percent), such that the epoxy coating could be peeled off 

completely. 

The bars shown in figure 38 were removed from slab #10, which contained ECRs in both mats. 

While one top ECR (the second bar from top in the photograph) exhibited virtually no reduction 

in adhesion even at the smaller artificial coating defects (0.004 percent), the other top mat ECR 

(the first bar from top in the photograph) experienced moderate corrosion that initiated at the 

larger artificial coating defects (0.5 percent), such that epoxy coating could be peeled off locally 

around the initial defects. The ECRs extracted from the bottom mat were corrosion-free and had 

minimal adhesion loss. The photographs of individual autopsied bars are included in appendix 

A. 

Tables 11 and 12 summarize the findings of the autopsied ECRs in terms of the number of final 

defects, coating thickness, exterior physical appearance, knife adhesion, and degree of adhesion 

loss. Final defects were classified as bare area, mashed area (mechanical damage), coating 

crack, and holiday. The number of final coating defects on the autopsied ECRs was very large 

on some poorly performing bars, while others maintained good coating continuity. The coating 

cracks as shown in figure 33 were the most frequent form of coating deterioration. When the 

coating defects were too excessive to count individual defects, an arbitrary number of 100 was 

assigned to quantify the worst condition in the subsequent data analysis. 

Figures 39 through 42 present the 95 percent confidence intervals for μ of the data provided in 

tables 11 and 12. Each plot was constructed for 10 combinations of test variables. It is 

19 
statistically significant that the ECRs removed from the bottom mat of the ECR top-ECR bottom

slabs exhibited the least number of final defects (figure 39) and the best appearance (figure 40). 

The bottom mat ECRs extracted from these slabs also exhibited the strongest knife adhesion 

(figure 41) and the least amount of coating disbondment (figure 42). Their performance was 

followed by the top mat straight ECRs containing 0.004 and 0.5 percent coating defects, 

respectively. Conditions of top mat ECRs that were removed from the ECR top-ECR bottom

slabs were not particularly different from those of the top mat only cases. Based on macrocell 

current density data and autopsy results, the excellent performance of test slabs containing ECRs 

in both mats should be attributed to the fact that the presence of ECR in the bottom mat 

suppresses the corrosion activity by minimizing the cathodic reaction (oxygen reduction through 

consuming electrons). In general, bent ECRs, when coupled with black bottom bars, performed 

the worst of all materials tested. 

Chloride Analysis 

Tables 6 through 8 list the water-soluble chloride data for every bar in the top mat. Based on the 

reversal of macrocell current and the high level of chloride in the top mat, some slabs were 

selected for additional chloride analysis at the bottom mat. To estimate the total chloride, limited 

acid-soluble chloride analysis also was conducted, with the selected powder samples 

representing various concentrations of water-soluble chloride. Figure 43 shows a result of the 

regression analysis demonstrating a relationship between water-soluble vs. acid-soluble chloride 

concentration. Regression analysis of the experimental chloride data indicates that the watersoluble chloride concentration of the concrete is approximately 89 percent of the total (acidsoluble) chloride concentration. Coarse aggregates used in this project came from Eau Claire, WI. 

Because these aggregates did not contain chlorides, the acid-soluble (total chlorides) and watersoluble (free chlorides) test results were similar. 

Figure 44 shows the 95 percent confidence intervals for μ for 10 combinations of test variables. 

It is interesting to note that water-soluble chloride concentration in the top mat containing black 

bars was far lower than the rest. This is likely due to the fact that the slabs containing black bars 

were cracked and delaminated after the 96-week SE testing and before being placed outdoors. 

Rainwater passing through the cracks and delaminations likely dissolved some of the free 

chloride ions in the concrete near the top mat of steel. Compounding of the free chloride in the 

black bar rust products also may have occurred. 

20 
-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Short-Circuit Potential (V vs. CSE)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 5. Short-circuit potential change with time (straight top (black and ECR)-black

bottom-uncracked concrete) during outdoor exposure 

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Macrocell Current Density (u

A/cm2

)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 6. Macrocell current density change with time (straight top (black and ECR)-black 

bottom-uncracked concrete) during outdoor exposure 

21 
-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Short-Circuit Potential (V vs. CSE)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 7. Short-circuit potential change with time (straight top (black and ECR)-black bottomcracked concrete) during outdoor exposure 

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Macrocell Current Density (uA/cm2

)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 8. Macrocell current density change with time (straight top (black and ECR)-black 

bottom-cracked concrete) during outdoor exposure 

22 
-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Short-Circuit Potential (V vs. CSE)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 9. Short-circuit potential change with time (bent top (black and ECR)-black bottomuncracked concrete) during outdoor exposure 

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Macrocell Current Density (uA/cm2

)

Black Mean ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 10. Macrocell current density change with time (bent top (black and ECR)-black bottomuncracked concrete) during outdoor exposure 

23 
-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Short-Circuit Potential (V vs. CSE)

Stainless Steel ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 11. Short-circuit potential change with time (stainless steel and ECR 

 in both mats-uncracked concrete) 

-0.05

0.00

0.05

0.10

0.15

0.20

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Macrocell Current Density (uA/cm2

)

Stainless Steel ECR Mean (0.004% damage) ECR Mean (0.5% damage)

Figure 12. Macrocell current density change with time (stainless steel and ECR 

 in both mats-uncracked concrete) 

24 
Figure 13. Mean short-circuit potential change with time (uncracked vs. precracked concrete) 

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (day)

Macrocell Current Density (uA/cm2

)

Straight Black Top - Black Bottom - Uncracked Straight ECR Top - Black Bottom - Uncracked

Straight Black Top - Black Bottom - Precracked Straight ECR Top - Black Bottom - Precracked

Figure 14. Mean macrocell current density change with time (uncracked vs. precracked concrete) 

25 
-0.600

-0.500

-0.400

-0.300

-0.200

-0.100

0.000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (Day)

Short-Circuit Potential (V vs. CSE)

Straight ECR Top - Black Bottom - Uncracked Straight ECRs in Both Mats - Uncracked

Bent ECR Top - Black Bottom - Uncracked

Figure 15. Mean short-circuit potential change with time (straight vs. bent ECRs in 

uncracked concrete) 

0.0

0.3

0.6

0.9

1.2

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (day)

Macrocell Current Density (uA/cm2

)

Straight ECR Top - Black Bottom - Uncracked Straight ECRs in Both Mats - Uncracked

Bent ECR Top - Black Bottom - Uncracked

Figure 16. Mean macrocell current density change with time (straight vs. bent ECRs in 

 uncracked concrete) 

26 
-0.413

-0.274

-0.341

-0.272

-0.456

-0.447

-0.353

-0.382

-0.469

-0.319

-0.354

-0.196

-0.500

-0.450

-0.400

-0.350

-0.300

-0.250

-0.200

-0.150

-0.100

-0.050

0.000

Black Stainless Steel ECR with 0.004% Initial

Coating Damage

ECR with 0.5% Initial

Coating Damage

Category

Short-Circuit Potential (

V vs. C

SE)

Straight Top - Black Bottom - Uncracked Straight Top - ECR Bottom - Uncracked

Straight Top - Black Bottom - Precracked Bent Top - Black Bottom - Uncracked

Stainless Steel

Figure 17. Mean short-circuit potential data classified by bar type (from table 9) 1.24 0.09 0.60 0.01 0.02 1.24 0.27 0.53 1.30 0.64 0.49 0.01

0.0

0.3

0.6

0.9

1.2

1.5

Black Stainless Steel ECR with 0.004% Initial

Coating Damage

ECR with 0.5% Initial

Coating Damage

Category

Macrocell current density (uA/c

m2

)

Straight Top - Black Bottom - Uncracked Straight Top - ECR Bottom - Uncracked

Straight Top - Black Bottom - Precracked Bent Top - Black Bottom - Uncracked

Stainless Steel

Figure 18. Mean macrocell current density data classified by bar type (from table 9) 

27 
0.95 0.95

1.00

0.07

0.21

0.49

0.01

0.46

0.41 0.38

0.02 0.01

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Straight Top - Black

Bottom - Uncracked

Straight Top - Black

Bottom - Precracked

Bent Top - Black

Bottom - Uncracked

Straight Top - ECR

Bottom - Uncracked

Stainless Steel

Category

Ratio

Black ECR with 0.004% Initial Coating Damage ECR with 0.5% Initial Coating Damage Stainless Steel

Figure 19. Relative ratio of macrocell current density per slab configuration 

y (ECR in top mat only) = -0.1053Ln(x) + 0.7914

R2 = 0.94

y (ECR in both mats) = -0.0055Ln(x) + 0.0376

R2 = 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.01 0.1 1 10 100 1000

Reciprocal of Initial Coating Damage (%)

Macrocell Current Density (uA/cm2

)

ECR in Top Mat Only ECR in Both Mats Log. (ECR in Top Mat Only) Log. (ECR in Both Mats)

Figure 20. Relationship between macrocell current density versus initial artificial coating defects 

28 
-0.291

-0.272

-0.217

-0.450

-0.149

-0.301

-0.387

-0.372

-0.250

-0.415

-0.554

-0.293

-0.303

-0.288

-0.355

-0.303

-0.350

-0.346

-0.209

-0.427

-0.505

-0.328

-0.377

-0.282

-0.430

-0.193

-0.211

-0.452

-0.600

-0.500

-0.400

-0.300

-0.200

-0.100

0.000

All ECRs

Combined

Coating A Coating B Coating C Coating D Coating E Coating F

Category

Short-Circuit Potential (V vs. CSE)

Straight Top - Black bottom - Uncracked Straight Top - ECR bottom - Uncracked

Straight Top - Black Bottom - Precracked Bent Top - Black bottom - Uncracked

Figure 21. Short-circuit potential data classified by coating type 

29 
0.35

0.02

0.25

0.87

0.02

0.28

0.59

0.010.01

0.04

0.010.01

0.40

0.02

0.46

0.77

0.03

0.19

0.57

0.55

0.13

0.28

1.94

0.02

0.03

1.00

0.01

0.0

0.5

1.0

1.5

2.0

All ECRs

Combined

Coating A Coating B Coating C Coating D Coating E Coating F

Category

Macrocell Current Density (uA/cm2

)

Straight Top - Black Bottom - Uncracked Straight Top - ECR Bottom - Uncracked

Straight Top - Black Bottom - Precracked Bent Top - Black Bottom - Uncracked

0.01

Figure 22(a). Macrocell current density data classified by coating type (linear scale) 0.35 0.02 0.25 0.87 0.02 0.28 0.59 0.01 0.010.01 0.04 0.010.01 0.40 0.02 0.460.77 0.03 0.19 0.57 0.55 0.13 0.28 1.94 0.020.03 1.00 0.01

0.001

0.010

0.100

1.000

10.000

All ECRs

Combined

Coating A Coating B Coating C Coating D Coating E Coating F

Category

Macrocell Current Density (uA/cm2

)

Straight Top - Black Bottom - Uncracked Straight Top - ECR Bottom - Uncracked

Straight Top - Black Bottom - Precracked Bent Top - Black Bottom - Uncracked

Figure 22(b). Macrocell current density data classified by coating type (logarithmic scale) 

30 
-0.650 -0.600 -0.550 -0.500 -0.450 -0.400 -0.350 -0.300 -0.250 -0.200

Short-Circuit Potential (V vs. CSE)

ECR Top (0.5% damage)+ECR Bottom (0.5%

damage)

Bent Black Top

Black Top in Precracked Concrete

Black Top

ECR Top (0.5% damage) in Precracked

Concrete

Bent ECR Top (0.5% damage)

ECR Top (0.004% damage) in Precracked

Concrete

ECR Top (0.5% damage)

Bent ECR Top (0.004% damage)

ECR Top (0.004% damage)

ECR Top (0.004% damage)+ECR Bottom

(0.004% damage)

Stainless Steel Top + Stainless Steel Bottom

Category

Figure 23. Ninety-five percent confidence intervals for short-circuit potential data 

0.0 0.3 0.6 0.9 1.2 1.5 1.8

Macrocell Current Density (uA/cm2)

ECR Top (0.004% damage) + ECR Bottom

(0.004% damage)

Stainless Steel

ECR Top (0.5% damage) + ECR Bottom

(0.5% damage)

ECR Top (0.004% damage)

ECR Top (0.004% damage) in

Precracked Concrete

Bent ECR Top (0.5% damage)

ECR Top (0.5% damage) in

Precracked Concrete

ECR Top (0.5% damage)

Bent ECR Top (0.004% damage)

Black Top

Black Top in Precracked Concrete

Bent Black Top

Category

Figure 24. Ninety-five percent confidence intervals for macrocell current density data 

31 
Category 

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

AC Resistance (ohm)

Black Top and Black Bottom

Stainless Steel

ECR Top (0.5% damage)

Bent ECR Top (0.5% damage)

ECR Top (0.5% damage) in

Precracked Concrete

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage)

ECR Top (0.004% damage) in

Precracked Concrete

Bent ECR Top (0.004% damage)

ECR Top (0.004% damage)

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage)

Figure 25. Ninety-five percent confidence intervals for AC resistance data 

Category 

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

Impedance Modulus at 0.1 Hz (ohm)

Black Top and Black Bottom

Stainless Steel

ECR Top (0.5% damage)

Bent ECR Top (0.5% damage)

ECR Top (0.5% damage) in

Precracked Concrete

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage)

ECR Top (0.004% damage) in

Precracked Concrete

Bent ECR Top (0.004% damage)

ECR Top (0.004% damage)

ECR Top (0.004% damage)+ECR Bottom

(0.004% damage)

Figure 26. Ninety-five percent confidence intervals for impedance modulus data 

32 
Figure 27. Cutting a test slab with a gas-powered saw 

Figure 28. Extraction of embedded reinforcing bars 

33 
Figure 29. Typical condition of ECR with good corrosion resistance (slab #7—top right bar) 

Rebar imprint

Rebar imprint

Figure 30. Typical condition of ECR with poor performance (slab #30—top right bar) 

34 
Figure 31. Typical condition of a bent ECR with good performance (slab #1—top left bar) 

Figure 32. Typical condition of a bent ECR with poor performance 

35 
(a) (b)

(c) (d)

Figure 33. Closeup views of ECRs exhibiting various conditions: (a) an intact ECR; (b) an ECR 

containing hairline coating cracks; (c) an ECR containing coating blisters and hairline 

coating cracks; and (d) a delaminated ECR revealing severely corroded substrate 

Figure 34. Typical condition of black bars in the top mat 

36 
Figure 35. Typical condition of black bent bars in the top mat (slab #23—top right bar) 

Figure 36. Corroded bottom mat (slab #19) 

37 
Figure 37. Photograph of autopsied bars extracted from slab #18 (ECR top-black bar bottom)

Figure 38. Photograph of autopsied bars extracted from slab #10 (ECRs in both mats) 

38 
Category 

0 10 20 30 40 50 60 70 80 90 100

Number of Defects

ECR Top (0.004% damage)+ECR Bottom

(0.004% damage): Bottom ECR

ECR Top (0.5% damage)+ECR Bottom

(0.5% damage): Bottom ECR

ECR Top (0.004% damage) in

Precracked Concrete

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Top ECR

ECR Top (0.004% damage)

ECR Top (0.5% damage) in

Precracked Concrete

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Top ECR

ECR Top (0.5% damage)

Bent ECR Top (0.004% damage)

Bent ECR Top (0.5% damage)

Figure 39. Ninety-five percent confidence intervals for number of final defects 

Category 

0 1 2 3 4 5

ECR Condition

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Bottom ECR

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Bottom ECR

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Top ECR

ECR Top (0.004% damage) in

Precracked Concrete

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Top ECR

Bent ECR Top (0.004% damage)

ECR Top (0.004% damage)

ECR Top (0.5% damage)

ECR Top (0.5% damage) in

Precracked Concrete

Bent ECR Top (0.5% damage)

Figure 40. Ninety-five percent confidence intervals for ECR rating data 

39 
Category 

0 1 2 3 4 5

Knife Adhesion

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Bottom ECR

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Bottom ECR

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Top ECR

ECR Top (0.004% damage)

ECR Top (0.5% damage)

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Top ECR

ECR Top (0.004% damage) in

Precracked Concrete

ECR Top (0.5% damage) in

Precracked Concrete

Bent ECR Top (0.5% damage)

Bent ECR Top (0.004% damage)

Figure 41. Ninety-five percent confidence intervals for knife adhesion data 

Category 

0 10 20 30 40 50 60 70 80 90 100

Disbondment (Percent)

ECR Top (0.004% damage)+ECR Bottom

(0.004% damage): Bottom ECR

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Bottom ECR

ECR Top (0.004% damage)

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage): Top ECR

ECR Top (0.004% damage) in

Precracked Concrete

Bent ECR Top (0.004% damage)

ECR Top (0.5% damage)

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage): Top ECR

ECR Top (0.5% damage) in

Precracked Concrete

Bent ECR Top (0.5% damage)

Figure 42. Ninety-five percent confidence intervals for extent of disbondment data 

40 
y = 1.1249x + 0.0113

R2 = 0.9176

0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.2 0.4 0.6 0.8 1.0 1.2

Water-Soluble Chloride Content (wt % of Sample)

AcidSoluble Chloride Content (

wt % of Sa

mple)

Line of Equality

Figure 43. Relationship between water-soluble versus acid-soluble chloride data 

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Chloride Concentration (ppm)

Black Top and Black Bottom

Bent ECR Top (0.5% damage)

ECR Top (0.004% damage)+ECR 

Bottom (0.004% damage)

ECR Top (0.5% damage)

ECR Top (0.5% damage)+ECR 

Bottom (0.5% damage)

Bent ECR Top (0.004% damage)

Stainless Steel

ECR Top (0.004% damage) in

Precracked Concrete

ECR Top (0.5% damage) in

Precracked Concrete

ECR Top (0.004% damage)

Category 

Figure 44. Ninety-five percent confidence intervals for water-soluble chloride data at top bar 

 depth 

41 
Table 6. Electrochemical and chloride data for test slabs containing ECR in top m

at only 

Water-Soluble Acid-Soluble Wate

3A 0.5 -0.403 114.1 -0.430 1.6E+02 5.1E+01 1,880

3B 0.004 -0.576 132.8 -0.635 2.8E+02 2.1E+02 4,3006A 0.5 -0.239 67.6 -0.320 4.4E+02 3.0E+02 3,5906B 0.004 -0.125 0.023 -0.308 3.2E+05 1.3E+06 4,880

15A 0.004 -0.064 0.0003 -0.166 2.2E+05 2.1E+06 3,66015B 0.5 -0.136 0.339 -0.155 3.7E+03 1.6E+04 3,80018A 0.5 -0.429 157.4 -0.479 1.8E+02 1.9E+03 5,83018B 0.004 -0.489 26.9 -0.583 1.1E+03 1.0E+02 9,19024A 0.5 -0.228 17.8 -0.396 2.2E+03 4.3E+03 4,100 4,69024B 0.004 -0.161 0.002 -0.140 6.8E+05 1.2E+07 4,81028A 0.004 -0.360 234.8 -0.597 5.2E+02 1.7E+03 8,33028B 0.5 -0.392 8.5 -0.454 7.4E+02 1.9E+03 2,480

7A 0.5 -0.384 -5.6 -0.443 2.1E+03 3.3E+03 4,080 7B 0.004 -0.335 -0.224 -0.399 1.4E+05 2.2E+06 2,570

13A 0.5 -0.174 1.2 -0.240 3.8E+03 2.8E+04 3,90013B 0.004 -0.082 0.003 -0.152 1.9E+05 5.7E+05 2,40014A 0.004 -0.334 0.518 -0.474 3.0E+04 1.4E+05 5,27014B 0.5 -0.337 13.5 -0.396 5.5E+02 6.1E+02 5,35019A 0.004 -0.471 23.8 -0.502 4.6E+02 1.2E+03 8,06019B 0.5 -0.520 350 -0.572 1.6E+02 7.9E+01 9,550 10,610

21A 0.5 -0.152 0.002 -0.233 1.2E+04 6.7E+04 2,520

21B 0.004 -0.140 0.678 -0.173 9.4E+04 4.3E+05 3,50025A 0.004 -0.431 -0.752 -0.383 3.8E+03 4.9E+04 3,650 

25B 0.5 -0.508 122.3 -0.555 2.0E+02 1.6E+02 7,400 9,270

30A 0.004 -0.489 -0.548 -0.512 2.6E+02 1.2E+02 2,740 3,75030B 0.5 -0.613 -100.7 -0.573 1.2E+02 7.4E+01 4,570 

1A 0.5 -0.157 1.3 -0.210 4.6E+03 3.6E+04 3,670 2,620

1B 0.004 -0.115 0.002 -0.106 5.2E+05 1.2E+06 5,090 

4A 0.5 -0.467 246.5 -0.524 2.0E+02 1.0E+02 2,850

4B 0.004 -0.433 320.5 -0.489 1.8E+02 7.5E+01 2,740 8A 0.004 -0.385 248.6 -0.449 2.8E+02 9.7E+01 4,9208B 0.5 -0.235 50.2 -0.297 4.4E+02 2.2E+02 3,590

11A 0.5 -0.312 15.2 -0.403 7.0E+02 1.0E+03 3,64011B 0.004 -0.150 1.0 -0.316 5.2E+03 2.8E+04 5,080 4,72022A 0.004 -0.433 51.4 -0.590 1.0E+03 1.5E+03 5,04022B 0.5 -0.274 18.7 -0.318 5.9E+02 1.2E+03 3,130 3,88031A 0.5 -0.130 2.6 -0.213 4.2E+03 3.2E+04 2,71031B 0.004 -0.146 0.0002 -0.087 > 1100000 5.7E+06 2,450 3,660 E

C

F

BADBCDACE

F

D

F

AE

24

Final Data Upon Termination

I (uA) 

Chloride Concentrat

Top Mat SCP

(V vs. CSE)

OCP

(V vs. CSE)

AC 

Resistance 

(Ohm)

Impedance at

0.1 Hz

(Ohm)

213025

Slab ID

1518191314

7

Test

Group

Slab Configuration

63

Top Bar 

ID

ECR Artificial 

Defect Size

(Percent)

Coating 

Type

CB

Straight ECR Top + Black Bottom in

precracked Concrete

Straight ECR Top + Black Bottom

i Uncracked Concrete

Bent ECR Top + Black Bottom

i Uncracked Concrete

283122

418

11

42
Table 7. Electrochemical and chloride data for test slabs containing ECR in both mats 

Top Mat Bottom Mat Water-Soluble Acid-Soluble 

2A 0.004 0.004 -0.173 0.003 -0.145 8.6E+05 1.7E+06 3,490

2B 0.5 0.5 -0.305 -2.3 -0.264 1.5E+03 1.8E+03 3,430 4,890 9A 0.5 0.5 -0.459 0.134 -0.418 3.8E+03 2.1E+03 4,880 6,2509B 0.004 0.004 -0.459 -0.008 -0.388 3.3E+05 6.5E+04 3,720 

10A 0.5 0.5 -0.181 0.009 -0.186 6.2E+03 4.9E+04 4,520 6,470

10B 0.004 0.004 -0.174 0.000001 -0.165 > 1.1E+06 1.7E+06 4,180 

12A 0.5 0.5 -0.521 1.4 -0.561 2.6E+03 1.8E+02 3,510 12B 0.004 0.004 -0.562 0.013 -0.590 1.5E+05 1.2E+02 4,300

17A 0.004 0.004 -0.262 -0.00004 -0.313 6.4E+05 9.8E+05 5,370 5,720 

17B 0.5 0.5 -0.275 0.008 -0.333 8.4E+03 9.7E+04 5,870

29A 0.004 0.004 -0.060 0.00005 -0.075 5.6E+05 4.9E+07 3,59029B 0.5 0.5 -0.389 0.146 -0.394 3.0E+03 2.7E+03 3,160

D

EFBA

C

Test 

Group Slab ID

ECR Artificial defect size (Percent)

Slab Configuration

Bar ID Coating Type

Final Data Upon Termination

I (uA)

Chloride Concen

Top Mat SCP

(V vs. CSE)

OCP

(V vs. CSE)

AC 

Resistance

(Ohm)

Impedance at 

0.1 Hz (Ohm)

Straight Top ECR + Bottom ECR in

Uncracked Concrete

2

1729

9

1012

43 Table 8. Electrochemical and chloride data for test slabs containing black and stainless steel b

Water-Soluble Acid-Soluble 

5A S N -0.284 -83.6 -0.278 2.5E+02 1.4E+03 1,470

5B S N -0.307 -260.1 -0.320 2.4E+02 7.5E+01 1,290 

23A B N -0.334 -177.2 -0.348 1.9E+02 4.6E+01 1,670

23B B N -0.257 -225.4 -0.235 2.1E+02 6.5E+01 1,190 

20A S Y -0.360 -102.9 -0.324 3.1E+02 1.7E+02 1,210 20B S Y -0.439 0.0002 -0.302 2.5E+02 1.4E+02 1,170 800

16A B N -0.361 -6.8 -0.257 8.7E+02 8.7E+02 5,280 

16B B N -0.446 -7.8 -0.243 3.9E+02 1.2E+03 4,310

26A S N -0.147 0.023 -0.152 5.6E+02 2.7E+01 5,77026B S Y -0.197 0.06 -0.183 5.2E+02 4.9E+03 3,30027A S Y -0.230 -0.005 -0.239 5.4E+02 2.6E+03 3,33027B S N -0.240 0.0003 -0.169 5.4E+02 1.9E+03 5,280

Black Top+ Black 

Bottom

Stainless Steel

BlackBlack 

Stainless Steel

Black

Stainless SteelStainless Steel

5

26

Black Black

Stainless Steel

Black BlackBlack 

27

201623

Final Data Upon Termination

I (uA)

Chloride Conce

Top Mat SCP

(V vs. CSE)

OCP

(V vs. CSE)

AC 

Resistance

(Ohm)

Impedance at 

0.1 Hz (Ohm)

Bent / 

Straight

Slab Configuration

Bottom Mat Precrack

(Yes/ No)

Test 

Group Slab ID Bar ID Top Mat
Table 9. Electrochemical test data classified by bar type 

Slab Configuration 

Data Material Straight TopBlack 

Bottom— 

Uncracked 

Straight TopECR Bottom—

Uncracked 

Straight TopBlack 

Bottom— 

Precracked

Bent TopBlack 

Bottom— 

Uncracked 

Stainless Steel

Black -0.413 -0.447 -0.469 

Stainless Steel -0.196

ECR with 0.004%

Initial Coating

Damage 

-0.274 -0.272 -0.353 -0.319 

ShortCircuit 

Potential 

(V vs. 

CSE) ECR with 0.5%

Initial Coating

Damage 

-0.341 -0.456 -0.382 -0.354 

Black 1.239 1.240 1.304 

Stainless Steel 0.009 

ECR with 0.004%

Initial Coating

Damage 

0.085 0.007 0.268 0.644 Macrocell 

Current 

Density 

(uA/cm2

) ECR with 0.5%

Initial Coating

Damage 

0.595 0.021 0.531 0.491 

Table 10. Electrochemical test data classified by coating type 

Data Material Slab Configuration 

Straight TopBlack Bottom— 

Uncracked 

Straight Top-ECR 

Bottom— 

Uncracked 

Straight TopBlack Bottom— 

Precracked

Bent Top-Black 

Bottom— 

Uncracked 

All ECRs 

Combined 

-0.291 -0.372 -0.355 -0.328

Coating A -0.272 -0.250 -0.303 -0.377

Coating B -0.217 -0.415 -0.350 -0.282

Coating C -0.450 -0.554 -0.346 -0.430

Coating D -0.149 -0.293 -0.209 -0.193

Coating E -0.301 -0.303 -0.427 -0.211

Short-Circuit 

Potential 

(V vs. SCE) 

Coating F -0.387 -0.288 -0.505 -0.452

All ECRs 

Combined 

0.350 0.014 0.399 0.568

Coating A 0.023 0.007 0.025 0.133

Coating B 0.253 0.009 0.461 0.279

Coating C 0.871 0.011 0.770 1.940

Coating D 0.016 0.039 0.025 0.024

Coating E 0.279 0.008 0.192 0.033

Macrocell 

Current 

Density 

(uA/cm2

) 

Coating F 0.595 0.011 0.547 0.996

44 
Table 11. Characterization of autopsied ECRs tested in the top m

at 

Bare Area Mashed Area Coating Crack Holiday Total Mean STDEV

3A 0.5 7 0 100 0 100 13.9 3.5 5 

3B 0.004 0 0 100 2 100 8.4 1.8 5 

6A 0.5 2 0 100 0 100 17.4 2.9 5 

6B 0.004 0 1 0 4 5 11.6 1.3 1 

15A 0.004 0 0 0 2 2 11.8 0.5 1 15B 0.5 2 0 0 0 2 13.0 0.8 1 18A 0.5 7 0 100 0 100 14.6 3.1 5 18B 0.004 3 0 16 0 19 9.1 1.4 5 

24A 0.5 2 0 16 1 19 9.4 1.8 4 24B 0.004 4 0 0 0 4 7.6 0.6 2 28A 0.004 0 1 18 0 19 4 

28B 0.5 3 0 100 0 100 4 

7A 0.5 2 2 28 2 34 10.6 2.5 4 

7B 0.004 0 0 3 3 6 9.1 1.2 3 

13A 0.5 2 0 1 1 4 10.4 1.5 3 

13B 0.004 0 2 0 3 5 9.4 1.2 1 

14A 0.004 0 1 0 2 3 9.1 1.1 2 14B 0.5 8 2 26 4 40 12.1 5.3 5 

19A 0.004 1 0 23 2 26 14.7 2.8 5 19B 0.5 17 0 100 0 100 17.5 3.3 5 21A 0.5 2 2 10 0 14 14.1 2.0 4 21B 0.004 0 0 0 1 1 14.6 1.0 2 25A 0.004 2 3 23 4 32 9.1 1.9 4 

25B 0.5 10 7 46 2 65 15.7 3.5 5 

30A 0.004 4 0 100 0 100 18.5 4.7 5 30B 0.5 2 0 100 0 100 18.4 4.9 5 

1A 0.5 3 4 0 0 7 14.3 1.2 3 1B 0.004 1 1 0 0 2 15.4 1.3 3 

4A 0.5 6 0 100 0 100 10.7 3.3 5 

4B 0.004 5 0 100 0 100 13.0 4.3 5 8A 0.004 13 0 100 0 100 15.5 3.5 5 8B 0.5 3 0 100 0 100 19.7 5.6 5 

11A 0.5 4 0 61 0 65 16.0 3.3 5 11B 0.004 0 1 4 6 11 10.9 1.5 3 22A 0.004 0 2 100 0 100 10.3 1.1 4 22B 0.5 5 0 100 0 100 11.4 1.9 5 31A 0.5 11 9 2 2 24 7.1 1.7 5 

31B 0.004 7 5 2 2 16 7.2 1.9 4 

Number of Final Defects Coating Thickness (mils) 

Characterization of Epoxy-Coated Reinforcing Bars

Artificial Defect

Size 

(Percent)

Exterior

Condition 

(1: excellent - 

5: worst)

Knife 

(1: st

5: w

Top Bar ID

Test 

Group Slab ID

24

Straight ECR Top + Black Bottom in

precracked Concrete

Straight Top ECR + Black Bottom in

Uncracked Concrete

63

21302515181314

Bent Top ECR + Black Bottom in

Uncracked Concrete

283122

418

11

7

19

Coating 

Type

C

B

D

FAEA

C

EF

D

B

CDC

FBAE

45
Table 12. Characterization of autopsied ECRs tested in both m

ats 

Bare Area Mashed Area Coating Crack Holiday Total Mean STDEV

2A-Top 0.004 2 0 1 0 3 10.6 1.8 2 2B-Top 0.5 8 0 71 2 81 13.2 2.5 5 

2A-Bottom 1 0.004 3 0 1 2 6 9.2 3.0 1 2A-Bottom 2 0.004 7 1 0 1 9 13.3 2.0 1 2B-Bottom 1 0.5 2 2 1 0 5 9.3 0.6 1 2B-Bottom 2 0.5 8 2 2 0 12 8.2 0.9 2 

9A-Top 0.5 2 0 39 4 45 11.5 1.6 3 9B-Top 0.004 0 0 0 3 3 9.7 1.0 2 

9A-Bottom 1 0.5 2 0 0 0 2 10.9 1.0 1 9A-Bottom 2 0.5 0 0 0 4 4 10.4 0.6 2 9B-Bottom 1 0.004 0 2 1 2 5 10.4 0.7 1 9B-Bottom 2 0.004 2 0 0 0 2 10.7 0.7 1 

10A-Top 0.5 3 0 4 0 7 8.8 1.1 2 10B-Top 0.004 0 4 0 4 8 7.9 0.9 2 

10A-Bottom 1 0.5 2 0 0 0 2 7.5 0.8 1 10A-Bottom 2 0.5 2 0 0 0 2 8.2 1.0 2 10B-Bottom 1 0.004 2 1 0 4 7 8.3 0.8 3 10B-Bottom 2 0.004 0 0 0 4 4 8.2 0.7 2 

12A-Top 0.5 7 3 100 0 100 9.7 2.4 5 12B-Top 0.004 9 0 100 0 100 9.7 2.4 5 

12A-Bottom 1 0.5 2 1 0 0 3 8.3 1.1 1 12A-Bottom 2 0.5 1 6 2 0 9 8.2 1.0 3 12B-Bottom 1 0.004 0 0 0 4 4 8.7 2.4 1 12B-Bottom 2 0.004 0 0 0 3 3 8.5 0.8 2 

17A-Top 0.004 1 0 0 1 2 12.8 0.9 2 17B-Top 0.5 2 0 0 0 2 13.0 0.8 2 

17A-Bottom 1 0.004 0 0 0 4 4 14.5 1.0 2 17A-Bottom 2 0.004 0 0 0 4 4 13.7 0.8 2 17B-Bottom 1 0.5 2 0 0 0 2 14.3 0.9 2 17B-Bottom 2 0.5 2 0 0 1 3 13.1 1.1 2 

29A-Top 0.004 0 0 0 3 3 8.4 1.9 1 29B-Top 0.5 6 2 32 1 41 7.9 0.9 4 

29A-Bottom 1 0.004 1 0 0 4 5 8.1 0.9 2 29A-Bottom 2 0.004 4 0 0 0 4 9.9 1.3 2 29B-Bottom 1 0.5 3 0 0 0 3 8.9 0.8 2 29B-Bottom 2 0.5 2 5 0 0 7 7.9 1.0 2 

2

29

Straight ECR Top + Bottom ECR in Uncracked Concrete

9

121017

Test

Group Slab ID Bar ID

Characterization of Epoxy-Coated Reinforcing Bars

Artificial Defect 

Size

(Percent)

K

(

Number of Final Defects Coating Thickness (mils) Exterior

Condition 

(1: excellent - 

5: worst)

CD

E

Coating 

Type

F

BA

46
CHAPTER 4. CONCLUSIONS 

1. The black bars produced the highest mean macrocell current density among various 

combinations of test variables regardless of slab configuration, i.e., presence of crack and bar 

shape (bent vs. straight). The highest mean macrocell current density (1.3 μA/cm2

 (8.4 

μA/inch2

)) was obtained from the black bent bar coupled with black bottom bars in 

uncracked concrete. In contrast, the stainless steel bars exhibited negligible mean macrocell 

current density, which was only 1 percent of the highest black bar case. Autopsy revealed 

that the corrosion morphology of black and stainless steel bars was consistent with the 

macrocell current density data. Macrocell current density was a good performance indicator 

of test slabs. 

2. For straight top mat ECRs, the mean macrocell current density was influenced by the size of 

initial coating damage and type of bar in the bottom mat. When they were coupled with 

black bars in the bottom mat, the size of the coating defect became a critical factor for 

controlling macrocell current density. In the case of straight top mat ECRs containing 0.004 

percent of initial coating defect coupled with black bottom bars, the mean macrocell current 

density was 7 to 21 percent of the highest black bar case, depending on whether the slab was 

precracked. If straight top mat ECRs containing 0.5 percent coating damage were connected 

to the black bottom bars, the current values increased to more than 40 percent of the black 

bar value, regardless of precracks in the concrete. 

3. However, if straight ECRs in the top mat were connected to ECRs in the bottom mat in 

uncracked concrete, the mean macrocell current density decreased to no greater than 2 

percent of the highest black bar case, regardless of the initial coating defect size. They

behaved comparable to stainless steel bars. 

4. For bent ECRs, even ones containing 0.004 percent coating damage produced noticeable 

macrocell current density when they were connected to black bottom bars, such that mean 

macrocell current density increased to 38 and 49 percent of the highest black bar case, 

regardless of initial coating defect size. In general, bent ECRs coupled with black bottom

bars performed the worst of the ECR cases.

5. Mean macrocell current density varied significantly by coating type; this could be related to 

coating quality. However, when ECRs were used in both mats, such variation disappeared, 

and all bars behaved very well with very low mean macrocell current density.

6. The SCP data obtained during this test program exhibited large data scatter with time, and no 

consistent trends developed that could lead to compare the corrosion performance of different 

bar types and shapes. 

7. Whenever an ECR slab with negligible macrocell current density was autopsied, the 

appearance of the ECR and concrete/bar interface was excellent with no sign of corrosion, 

and the coating looked new with a glossy texture. However, when severely corroded ECRs 

recognized by high macrocell current densities were autopsied, they revealed coating 

47 
deterioration due to corrosion and exhibited numerous hairline cracks and/or blisters in 

conjunction with extensive coating disbondment and underlying steel corrosion. When test 

slabs exhibited severe damage, electrochemical test data collected from those slabs did not 

provide meaningful results.

8. Final defects were classified as bare area, mashed area (mechanical damage), coating crack, 

and holiday. Generally, the number of final coating defects on the autopsied ECRs increased 

from their initial values determined before embedment in concrete. This phenomenon was 

particularly pronounced for the poorly performing bars due to development of coating cracks, 

which was the most frequent form of coating deterioration. Accumulation of multiple rust 

layers beneath disbonded coating is also a common corrosion morphology observed on 

severely corroded ECRs. 

9. Reduced adhesion was usually initiated at the initial coating defects. It was much more 

pronounced on the top mat ECRs, irrespective of whether they were removed from ECR topblack bottom slabs or the ECR top-ECR bottom slabs, compared to those extracted from the 

bottom mat. The ECRs removed from the bottom mat also exhibited the lowest number of 

final defects and the strongest knife adhesion. No consistent trend was found between the 

level of macrocell current density and the extent of adhesion loss. Earlier FHWA studies 

investigated the coatings’ adhesion using solution immersion tests and cathodic disbonding 

tests.[2,4] Based on the review of the test results, the adhesion, as tested by solution 

immersion and cathodic disbonding tests, appeared to be a poor indicator of long-term

performance of the coated bars in concrete. These findings suggest that there is no direct 

relationship between loss of adhesion and the effectiveness of ECR to mitigate corrosion. 

10. According to impedance modulus, AC resistance, macrocell current density data, and autopsy 

results, the excellent performance of test slabs containing ECRs in both mats comparable to 

stainless steel bars may be attributed to the facts that electrical resistance was very high 

between the two ECR mats, and the ECRs in the bottom mat suppress the corrosion activity 

at the top mat ECR by minimizing the size of the available cathode. 

11. This 7-year laboratory and outdoor exposure study confirmed that using ECRs in the top mat 

of simulated bridge decks can reduce the corrosion susceptibility to at least 50 percent of the 

black bar case, even when ECR with poor coating condition is used. If ECRs are used in 

both mats in uncracked concrete, this corrosion resistance can increase dramatically, and can 

approach the corrosion-resistant level of stainless steel reinforcement. This conclusion is 

valid even when they contain coating defects. 

48 
REFERENCES 

1. McDonald, D.B., Sherman, M.R., and Pfeifer, D.W., The Performance of Bendable and 

Nonbendable Organic Coatings for Reinforcing Bars in Solution and Cathodic 

Debonding Tests, Report No. FHWA-RD-94-103, Federal Highway Administration, 

McLean, VA, January 1995, 148 pp. 

2. McDonald, D.B., Sherman, M.R., and Pfeifer, D.W., The Performance of Bendable and 

Nonbendable Organic Coatings for Reinforcing Bars in Solution and Cathodic 

Debonding Tests: Phase II Screening Tests, Report No. FHWA-RD-96-021, Federal 

Highway Administration, McLean, VA, May 1996, 121 pp. 

3. McDonald, D.B., Pfeifer, D.W., and Blake, G.T., The Corrosion Performance of 

Inorganic-, Ceramic-, and Metallic-Clad Reinforcing Bars and Solid Metallic 

Reinforcing Bars in Accelerated Screening Tests, Report No. FHWA-RD-96-085, Federal 

Highway Administration, McLean, VA, October 1996, 112 pp. 

4. McDonald, D.B., Pfeifer, D.W., and Sherman, M.R., Corrosion Evaluation of EpoxyCoated, Metallic-Clad, and Solid Metallic Reinforcing Bars in Concrete, Report No. 

FHWA-RD-98-153, Federal Highway Administration, McLean, VA, December 1998,

137 pp. 

49 

Figure 45. Slab #1 front, rear, and top views with specifi

c

ations

OUTDOOR EXPOSURE AND AUTOPSIED BARS a) Front vie

w b) Rear vie

w

51

Bent

Top mat

Bottom mat Bla

c

k

Specimen ID 1A 1B

Coating D

Coating defect (%) N/A N/A

Coating D

Bar shape

(straight/bent) Bent

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications c) Top vie

w
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 46. Slab #1 extracted rebars condition

52
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 47. Slab #1 after autopsy

53
a) Front view b) Rear view

54

Figure 48. Slab #2 front, rear, and top views with specifications

c) Top view

Top mat

Bottom mat Coating F

Specimen ID 2A 2B

Coating F

Coating defect (%) 0.004 0.5

Coating F

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.004 0.5

d) Slab specifications
Figure 49. Slab #2 extracted rebars condition

Figure 50. Slab #2 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

55
a) Front view b) Rear view

56

Figure 51. Slab #3 front, rear, and top views with specifications

c) Top view

Top mat

Bottom mat Black

Specimen ID 3A 3B

Coating C

Coating defect (%) N/A N/A

Coating C

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications
Figure 52. Slab #3 extracted rebars condition

Figure 53. Slab #3 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

57
b) Rear view a) Front view

58

c) Top view

Top mat

Bottom mat Black

Specimen ID 4A 4B

Coating C

Coating defect (%) N/A N/A

Coating C

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications

Figure 54. Slab #4 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 55. Slab #4 extracted rebars condition

59
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 56. Slab #4 after autopsy

60
b) Rear view a) Front view

61

Top mat

Bottom mat Black

Specimen ID 5A 5B

Black

Coating defect (%) N/A

Bla

N/A

ck

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) N/A N/A

d) Slab specifications

c) Top view

Figure 57. Slab #5 front, rear, and top views with specifications
Figure 58. Slab #5 extracted rebars condition

Figure 59. Slab #5 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

62
b) Rear view a) Front view

63

Top mat

Bottom mat Black

Specimen ID 6A 6B

Coating B

Coating defect (%) N/A N/A

Coating B

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications

c) Top view

Figure 60. Slab #6 front, rear, and top views with specifications
Figure 61. Slab #6 extracted rebars condition

Figure 62. Slab #6 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

64
b) Rear view a) Front view

65

Top mat

Bottom mat Black

Specimen ID 7A 7B

Coating A

Coating defect (%) N/A N/A

Coating A

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.5 0.004

d) Slab specifications c) Top view

Figure 63. Slab #7 front, rear, and top views with specifications
Figure 64. Slab #7 extracted rebars condition

Figure 65. Slab #7 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

66
a) Front view b) Rear view

67

Top mat

Bottom mat Black

Specimen ID 8A 8B

Coating F

Coating defect (%) N/A N/A

Coating F

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) 0.004 0.5

d) Slab specifications c) Top view

Figure 66. Slab #8 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 67. Slab #8 extracted rebars condition

68
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 68. Slab #8 after autopsy

69
b) Rear view a) Front view

70

c) Top view

Top mat

Bottom mat Coating B

Specimen ID 9A 9B

Coating B

Coating defect (%) 0.5 0.004

Coating B

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications

Figure 69. Slab #9 front, rear, and top views with specifications
Figure 70. Slab #9 extracted rebars condition

Figure 71. Slab #9 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

71
a) Front view b) Rear view

72

Top mat

Bottom mat Coating A

Specimen ID 10A 10B

Coating A

Coating defect (%) 0.5 0.004

Coating A

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications c) Top view

Figure 72. Slab #10 front, rear, and top views with specifications
Figure 73. Slab #10 extracted rebars condition

Figure 74. Slab #10 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

73
b) Rear view a) Front view

74

Top mat

Bottom mat Black

Specimen ID 11A 11B

Coating B

Coating defect (%) N/A N/A

Coating B

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications c) Top view

Figure 75. Slab #11 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 76. Slab #11 extracted rebars condition

75
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 77. Slab #11 after autopsy

76
b) Rear view a) Front view

77

Top mat

Bottom mat Coating C

Specimen ID 12A 12B

Coating C

Coating defect (%) 0.5 0.004

Coating C

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

d) Slab specifications c) Top view

Figure 78. Slab #12 front, rear, and top views with specifications
Figure 79. Slab #12 extracted rebars condition

Figure 80. Slab #12 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

78
a) Front view

c) Top view

b) Rear view

Top mat

Bottom mat Black

Specimen ID 13A 13B

Coating C

Coating defect (%) N/A N/A

Coating C

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.5 0.004

79

d) Slab specifications

Figure 81. Slab #13 front, rear, and top views with specifications
Figure 82. Slab #13 extracted rebars condition

Figure 83. Slab #13 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

80
Top mat

Bottom mat Black

Specimen ID 14A 14B

Coating E

Coating defect (%) N/A N/A

Coating E

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

81

d) Slab specifications

Figure 84. Slab #14 front, rear, and top views with specifications
Figure 85. Slab #14 extracted rebars condition

Figure 86. Slab #14 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

82
Top mat

Bottom mat Black

Specimen ID 15A 15B

Coating D

Coating defect (%) N/A N/A

Coating D

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

83

d) Slab specifications

Figure 87. Slab #15 front, rear, and top views with specifications
Figure 88. Slab #15 extracted rebars condition

Figure 89. Slab #15 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

84
Top mat

Bottom mat Black

Specimen ID 16A 16B

Stainless Steel

Coating defect (%) N/A N/A

Stainless Steel

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) N/A N/A

a) Front view

c) Top view

b) Rear view

85

d) Slab specifications

Figure 90. Slab #16 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 91. Slab #16 extracted rebars condition

86
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 92. Slab #16 after autopsy

87
Top mat

Bottom mat Coating D

Specimen ID 17A 17B

Coating D

Coating defect (%) 0.004 0.5

Coating D

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

88

d) Slab specifications

Figure 93. Slab #17 front, rear, and top views with specifications
Figure 94. Slab #17 extracted rebars condition

Figure 95. Slab #17 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

89
Top mat

Bottom mat Black

Specimen ID 18A 18B

Coating F

Coating defect (%) N/A N/A

Coating F

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

a) Front view

c) Top view

b) Rear view

90

d) Slab specifications

Figure 96. Slab #18 front, rear, and top views with specifications
Figure 97. Slab #18 extracted rebars condition

Figure 98. Slab #18 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

91
a) Front view

c) Top view

b) Rear view

92

Top mat

Bottom mat Black

Specimen ID 19A 19B

Coating F

Coating defect (%) N/A N/A

Coating F

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.004 0.5

d) Slab specifications

Figure 99. Slab #19 front, rear, and top views with specifications
Figure 110. Slab #19 extracted rebars condition

Figure 101. Slab #19 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

93
a) Front view

c) Top view

b) Rear view

Figure 102. Slab #20 front, rear, and top views with specifications

Top mat

Bottom mat Black

Specimen ID 20A 20B

Black

Coating defect (%) N/A

Bla

N/A

ck

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) N/A N/A

d) Slab specifications

94
Figure 103. Slab #20 extracted rebars condition

Figure 104. Slab #20 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

95
Top mat

Bottom mat Black

Specimen ID 21A 21B

Coating D

Coating defect (%) N/A N/A

Coating D

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.5 0.004

a) Front view

c) Top view

b) Rear view

96

d) Slab specifications

Figure 105. Slab #21 front, rear, and top views with specifications
Figure 106. Slab #21 extracted rebars condition

Figure 107. Slab #21 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

97
Top mat

Bottom mat Black

Specimen ID 22A 22B

Coating A

Coating defect (%) N/A N/A

Coating A

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

98

d) Slab specifications

Figure 108. Slab #22 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 109. Slab #22 extracted rebars condition

99
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 110. Slab #22 after autopsy

100
Top mat

Bottom mat Black

Specimen ID 23A 23B

Black

Coating defect (%) N/A

Bla

N/A

ck

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) N/A N/A

a) Front view

c) Top view

b) Rear view

101

d) Slab specifications

Figure 111. Slab #23 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 112. Slab #23 extracted rebars condition

102
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 113. Slab #23 after autopsy

103
Top mat

Bottom mat Black

Specimen ID 24A 24B

Coating A

Coating defect (%) N/A N/A

Coating A

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.5 0.004

a) Front view

c) Top view

b) Rear view

Figure 114. Slab #24 front, rear, and top views with specifications

d) Slab specifications

104
Figure 115. Slab #24 extracted rebars condition

Figure 116. Slab #24 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

105
Top mat

Bottom mat Black

Specimen ID 25A 25B

Coating B

Coating defect (%) N/A N/A

Coating B

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

106

d) Slab specifications

Figure 117. Slab #25 front, rear, and top views with specifications
Figure 118. Slab #25 extracted rebars condition

Figure 119. Slab #25 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

107
Top mat

Bottom mat Black

Specimen ID 26A 26B

Stainless Steel

Coating defect (%) N/A N/A

Stainless Steel

Bar shape

(straight/bent) Straight Straight

Precracked No Yes

Coating defect (%) N/A N/A

a) Front view

c) Top view

b) Rear view

108

d) Slab specifications

Figure 120. Slab #26 front, rear, and top views with specifications
Figure 121. Slab #26 extracted rebars condition

Figure 122. Slab #26 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

109
Top mat

Bottom mat Stainless Steel

Specimen ID 27A 27B

Stainless Steel

Coating defect (%) N/A N/A

Stainless Steel

Bar shape

(straight/bent) Straight Straight

Precracked Yes No

Coating defect (%) N/A N/A

a) Front view

c) Top view

b) Rear view

Figure 123. Slab #27 front, rear, and top views with specifications

d) Slab specifications

110
Figure 124. Slab #27 extracted rebars condition

Figure 125. Slab #27 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

111
a) Front view

c) Top view

b) Rear view

Figure 126. Slab #28 front, rear, and top views with specifications

Top mat

Bottom mat Black

Specimen ID 28A 28B

Coating E

Coating defect (%) N/A N/A

Coating E

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.004 0.5

d) Slab specifications

112
Figure 127. Slab #28 extracted rebars condition

Figure 128. Slab #28 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

113
Top mat

Bottom mat Coating E

Specimen ID 29A 29B

Coating E

Coating defect (%) 0.004 0.5

Coating E

Bar shape

(straight/bent) Straight Straight

Precracked No No

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

Figure 129. Slab #29 front, rear, and top views with specifications

d) Slab specifications

114
Figure 130. Slab #29 extracted rebars condition

Figure 131. Slab #29 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

115
Top mat

Bottom mat Black

Specimen ID 30A 30B

Coating C

Coating defect (%) N/A N/A

Coating C

Bar shape

(straight/bent) Straight Straight

Precracked Yes Yes

Coating defect (%) 0.004 0.5

a) Front view

c) Top view

b) Rear view

116

d) Slab specifications

Figure 132. Slab #30 front, rear, and top views with specifications
Figure 133. Slab #30 extracted rebars condition

Figure 134. Slab #30 after autopsy

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

117
Top mat

Bottom mat Black

Specimen ID 31A 31B

Coating E

Coating defect (%) N/A N/A

Coating E

Bar shape

(straight/bent) Bent Bent

Precracked No No

Coating defect (%) 0.5 0.004

a) Front view b) Rear view

118

d) Slab specifications c) Top view

Figure 135. Slab #31 front, rear, and top views with specifications
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 136. Slab #31 extracted rebars condition

119
a) Top bars

b) Bottom bars

*A-T: Top left bar, B-T: Top right bar, A-B1&B2: Bottom left bars, B-B1&B2: Bottom right bars

Figure 137. Slab #31 after autopsy

120
HRDI-10/06-04(1M250)E

Recycled

Recyclable