Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

Integrity of Infrastructure Materials 

and Structures

Publication No. FHWA-HRT-09-044 october 2009
FOREWORD 

Corrosion-induced deterioration of both reinforced concrete and steel bridges exposed to 

chlorides is a pervasive problem that challenges the design of new structures and the 

maintenance of existing ones. Because of concerns regarding long-term serviceability of 

epoxy-coated reinforcing steel in bridge decks and substructures, enhanced attention has 

focused on these materials in recent years. An important consideration in the case of existing 

steel bridges is the development of monitoring methods and technologies for characterizing 

the deterioration rate. For exposed steel surfaces, determination of the as-constructed 

deterioration rates is critically important for maintenance schedules, especially for weathering 

steels. Furthermore, for new construction, specification of unpainted weathering versus 

painted steel bridges has important cost-performance implications. In addition, steel performance 

monitoring can be facilitated by sensor technologies where accessibility is difficult 

(e.g., suspension cables, box beams, and cable stays). This investigation was initiated for two 

purposes: (1) to evaluate stainless steel (SS) type 2304 (UNS S32304) as a corrosion-resistant 

reinforcement in concrete and (2) to develop sensor technology for characterizing corrosion rate 

on existing steel bridges in situ. 

Jorge E. Pagán-Ortiz

Director, Office of Infrastructure 

Research and Development 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

in the interest of information exchange. The U.S. Government and the State of Florida assume no 

liability for its content or use thereof. This report does not constitute a standard, specification, or 

regulation. 

The U.S. Government and the State of Florida do not endorse products or manufacturers. Trade 

and manufacturers’ names appear in this report only because they are considered essential to the 

objective of this document. 

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts it programs and processes to 

ensure continuous quality improvement. 
TECHNICAL DOCUMENTATION PAGE 

1. Report No. 

FHWA-HRT-09-044 

2. Government Accession No. 3. Recipient’s Catalog No. 

5. Report Date 

October 2009 

4. Title and Subtitle 

Integrity of Infrastructure Materials and Structures 

6. Performing Organization Code 

FAU-OE-CMM-0802 

7. Author(s) 

Richard D. Granata and William H. Hartt 

8. Performing Organization Report No. 

9. Performing Organization Name and Address 10. Work Unit No. 

Florida Atlantic University 

Sea Tech Campus 

101 North Beach Road 

Dania Beach, FL 33004 

11. Contract or Grant No. 

DTFH61-05-C-00003 

13. Type of Report and Period Covered 

Final Report 

12. Sponsoring Agency Name and Address 

Office of Infrastructure Research and Development 

Federal Highway Administration 

6300 Georgetown Pike 

McLean, VA 22101-2296 14. Sponsoring Agency Code 

15. Supplementary Notes 

The Contracting Officer’s Technical Representative (COTR) was Y.P. Virmani, HRDI-10. 

16. Abstract 

Corrosion of bridges, both of steel and reinforced concrete construction, constitutes a major maintenance problem for the 

United States. In the case of reinforced concrete bridges, recent attention has focused on corrosion-resistant reinforcements 

because of concerns that epoxy-coatings, which are presently employed for corrosion protection, may not provide the 

75- to 100-year service life that is now required for major structures. A component of this research addressed two aspects of 

serviceability of 2304 stainless steel (SS) (UNS S32304) as reinforcement in concrete bridges. The first aspect addressed 

concerns regarding possible susceptibility to stress corrosion cracking in chloride-contaminated pore water, and the second 

aspect focused on determination of the critical chloride concentration, CT, to initiate active corrosion. The latter effort involved 

both accelerated aqueous tests and longer-term exposure of reinforced concrete slabs. No stress corrosion cracking was detected, 

and a value was defined which CT exceeds. 

In the case of steel bridges, an accelerated corrosion test was developed for weathering steel with a range of exposure conditions 

that demonstrated sensitivity to chloride environments. The protective oxide layer (patina) of weathering steel was degraded 

above 0.5 wt percent chloride. Above 1 wt percent chloride, the protective oxide could have been severely degraded. Sensors 

were able to indicate the corrosion rate of coupon material exposed to the same environment. Sensors allowed direct and 

immediate observation of the impact environmental changes had on corrosion rate. X-ray diffraction showed that the corrosion 

products produced in cyclic test chambers were similar to those observed under field conditions. Sensors were capable of 

monitoring corrosive conditions within suspension bridge cables and other steel bridge geometries that were difficult to access. 

17. Key Words 

Reinforced concrete, Reinforcing steel, Stainless steel, Bridges, 

Corrosion resistance, Atmospheric corrosion, Steel, Corrosion 

sensors 

18. Distribution Statement 

No restrictions. This document is available to the public 

through the National Technical Information Service, 

Springfield, VA 22161. 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 

85 

22. Price 

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

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 ft2 

m2 square meters 1.195 square yards yd2 

ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2 

VOLUME 

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3 

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 th International System of Units. Approp e riate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
iii 

TABLE OF CONTENTS 

CHAPTER 1. INTRODUCTION................................................................................................ 1

STEEL FOR CONCRETE REINFORCEMENT ............................................................... 1

STEEL FOR STRUCTURES AND CABLES...................................................................... 2

CHAPTER 2. RESEARCH COMPONENT #1: 2304 SS REINFORCING BARS IN 

CHLORIDE-CONTAMINATED ENVIRONMENTS.............................................................. 5

OBJECTIVE ........................................................................................................................... 5

MATERIAL............................................................................................................................. 5

CHAPTER 3. RESEARCH APPROACH #1 ............................................................................. 7

TASK 1.1. STRESS CORROSION CRACKING................................................................ 7

Procedure ............................................................................................................................ 7 

TASK 1.2. CORROSION PROPERTIES OF TYPE 2304 SS REINFORCEMENT....... 9

Accelerated Corrosion Test Procedure ............................................................................... 9 

Reinforced Concrete Exposures........................................................................................ 11 

CHAPTER 4. RESULTS AND DISCUSSION #1.................................................................... 15

TASK 1.1. STRESS CORROSION CRACKING............................................................. 15

TASK 1.2. CORROSION PROPERTIES OF TYPE 2304 SS REINFORCEMENT.... 15

Accelerated Test Method .................................................................................................. 15 

Concrete Specimen Exposures.......................................................................................... 17 

CHAPTER 5. RESEARCH STUDY #1 FINDINGS................................................................ 21

CHAPTER 6. RESEARCH STUDY #2: HIGHWAY BRIDGE STEEL 

COMPONENTS SUBJECT TO SIMULATED ATMOSPHERIC EXPOSURE................. 23

OBJECTIVE ......................................................................................................................... 23

Material............................................................................................................................. 23 

CHAPTER 7. RESEARCH APPROACH #2 ........................................................................... 25

TASK 2.1. LABORATORY TEST METHOD FOR PRODUCTION OF 

PROTECTIVE AND NONPROTECTIVE OXIDE LAYERS IN CHLORIDE 

ENVIRONMENTS ............................................................................................................... 25

Wet/Dry Cycle .................................................................................................................. 25 

Exposure Tests.................................................................................................................. 25 

Coupon Preparation .......................................................................................................... 28 

Weight Loss ...................................................................................................................... 28 

X-ray Diffraction Analyses............................................................................................... 29 

TASK 2.2. CORROSION RATES OF ACCELERATED TEST SPECIMENS 

USING GALVANIC SENSORS.......................................................................................... 30

Approach........................................................................................................................... 30 

Sensor Design ................................................................................................................... 31 

Zero Resistance Ammeter Data Logger............................................................................ 32 

Sensor Active Area ........................................................................................................... 33 

Sensor Anode Fabrication................................................................................................. 35 

Sensor Cathode Fabrication .............................................................................................. 35 
iv 

Electrode Separator........................................................................................................... 35 

Sealer................................................................................................................................. 35 

Sensor Electrical Connection............................................................................................ 36 

Exposure Testing .............................................................................................................. 36 

TASK 2.3. DEVELOPMENT OF PROTOTYPE CABLE CORROSION 

SENSORS .............................................................................................................................. 37

Cable Sensors.................................................................................................................... 37 

Cable Sensor Tests............................................................................................................ 39 

XRD for Cable Sensor Tests............................................................................................. 40 

CHAPTER 8. RESULTS AND DISCUSSION #2.................................................................... 41

TASK 2.1. LABORATORY TEST METHOD FOR PRODUCTION OF 

PROTECTIVE AND NONPROTECTIVE OXIDE LAYERS IN CHLORIDE 

ENVIRONMENTS ............................................................................................................... 41

Weight Loss ...................................................................................................................... 41 

First Set Test ..................................................................................................................... 42 

Influence of Sodium Chloride........................................................................................... 42 

Influence of pH ................................................................................................................. 45 

Influence of Wetting Time................................................................................................ 47 

Second Set Test................................................................................................................. 50 

XRD and Corrosion Rate.................................................................................................. 51 

Weathering Steel—15-Cycle Exposure with Protective Patina........................................ 52 

Weathering Steel—30-Cycle Exposure with Protective Patina........................................ 52 

Weathering Steel—30-Cycle Exposure with Nonprotective Patina Exposed to High 

Chloride Concentration..................................................................................................... 53 

Weathering Steel—30-Cycle Exposure with Nonprotective Patina Exposed to 

High Time of Wetness ...................................................................................................... 53 

Carbon Steel—30-Cycle Exposure with Nonprotective Patina Exposed to High 

Chloride Concentration..................................................................................................... 53 

Analyses of Carbon and Weathering Steel Corrosion Products ....................................... 53 

Summary of XRD Analysis .............................................................................................. 53 

TASK 2.2. CORROSION RATES OF ACCELERATED TEST SPECIMENS 

USING GALVANIC SENSORS.......................................................................................... 54

Reaction to Humidity and Salt Application...................................................................... 54 

Corrosion Rate Determination .......................................................................................... 56 

RESULTS OF TASK 2.3. PROTOTYPE CABLE CORROSION SENSORS ............... 59

Cable Sensor Response to Test Conditions ...................................................................... 59 

XRD Results for Cable Test Specimens ........................................................................... 61 

CHAPTER 9. RESEARCH STUDY #2 FINDINGS................................................................ 65

CHAPTER 10. CONCLUSIONS............................................................................................... 67

APPENDIX.................................................................................................................................. 69

CALCULATIONS ................................................................................................................ 69

Example 1. Convert Weight/Area (Corrosion in g/inches2

) to mils (or mm) 

Corrosion Penetration ....................................................................................................... 69 
v 

Example 2. Conversion of ZRA Current to Coulombs..................................................... 70 

Example 3. Conversion of Sensor Output (μA) to Corrosion Rate (mpy or mmpy)........ 71 

Example 4. Comparison of Mass Loss and Sensor Results in Terms of Penetration ...... 71 

REFERENCES............................................................................................................................ 73
vi 

LIST OF FIGURES 

Figure 1. Photo. 2304 SS bar after bending.................................................................................... 7

Figure 2. Illustration. A bent specimen in the restrained position.................................................. 7 

Figure 3. Photo. Test tank with cover............................................................................................. 8 

Figure 4. Photo. Top view of two specimens with C-clamps in the test tank................................. 8 

Figure 5. Photo. High temperature experiment arrangement.......................................................... 9 

Figure 6. Photo. Straight as-received 2304 SS bar with epoxy-mounted ends and an 

electrical lead ................................................................................................................................ 10 

Figure 7. Illustration. Accelerated experimental arrangement...................................................... 10 

Figure 8. Photo. Test system......................................................................................................... 11 

Figure 9. Illustration. Simulated deck slab specimen design........................................................ 12 

Figure 10. Photo. SDS specimens reinforced with 2304 SS under test ........................................ 13 

Figure 11. Graph. Accelerated corrosion test data........................................................................ 15 

Figure 12. Graph. Cumulative distribution plot of CT for 2304 SS from accelerated testing....... 16 

Figure 13. Graph. Potential data for the 2304 SS-reinforced concrete specimens ....................... 17 

Figure 14. Graph. Macrocell current data for the 2304 SS-reinforced concrete specimens......... 17 

Figure 15. Graph. Concrete chloride concentration profiles determined from 10 cores .............. 18 

Figure 16. Chart. Standard SAE J2334 cyclic test with five cycles/week.................................... 25 

Figure 17. Photo. CARON® environmental chamber for cyclic SAE J2334 tests ....................... 27 

Figure 18. Photo. Specimens on holder rack and in soak tank ..................................................... 27 

Figure 19. Graph. Example of X-ray powder diffraction spectrum.............................................. 29 

Figure 20. Illustration. Atmospheric corrosion sensor (Model FAU2) ........................................ 31 

Figure 21. Illustration. Anode detail for atmospheric corrosion sensor ....................................... 32 

Figure 22. Photo. Data logger incorporating a ZRA..................................................................... 33 

Figure 23. Graph. Sensor output for 0.7-inch active anode steel washer diameter for one 

SAE J2334 cycle in the standard solution..................................................................................... 34

Figure 24. Graph. Sensor output for 0.8-inch active anode steel washer diameter for one 

SAE J2334 cycle in the standard solution..................................................................................... 34

Figure 25. Photo. Bottom side of a sensor mounted on its holder experiencing under-paint 

corrosion ....................................................................................................................................... 35 

Figure 26. Photo. Four sensors set up on the cross-shaped holding rack ..................................... 37 

Figure 27. Photo. Components and fabrication of the cable sensor.............................................. 38 

Figure 28. Photo. Completion of the cable sensor........................................................................ 38 

Figure 29. Graph. First test of corrosion sensor wetted, dried out, rewetted, and redried............ 39 

Figure 30. Illustration. Cable specimen showing arrangement of strands and sensors ................ 40 

Figure 31. Graph. A606 corrosion as a function of the concentration of NaCl............................ 43 

Figure 32. Graph. SAE1010 corrosion as a function of the concentration of NaCl ..................... 43 

Figure 33. Graph. Relative corrosion between A606 and SAE1010 ............................................ 44 

Figure 34. Graph. A606 corrosion as a function of chloride concentration during a 

one soak/cycle exposure ............................................................................................................... 45 

Figure 35. Graph. A606 corrosion as a function of chloride concentration during a 

two soak/cycle exposure ............................................................................................................... 46 

Figure 36. Graph. SAE1010 corrosion as a function of chloride concentration during a 

one soak/cycle experiment............................................................................................................ 46 
vii 

Figure 37. Graph. SAE 1010 corrosion as a function of chloride concentration during a 

two soak/cycle experiment............................................................................................................ 47 

Figure 38. Graph. Relative corrosion versus NaCl concentration during exposure to a 

one soak/cycle environment.......................................................................................................... 47 

Figure 39. Graph. A606 corrosion as a function of chloride concentration at pH 6..................... 48 

Figure 40. Graph. A606 corrosion as a function of chloride concentration at pH 8..................... 48 

Figure 41. Graph. SAE1010 corrosion as a function of chloride concentration at pH 6.............. 49 

Figure 42. Graph. SAE1010 corrosion as a function of chloride concentration at pH 8.............. 49 

Figure 43. Graph. Corrosion of A606 and SAE1010 versus chloride concentration for the 

second test set ............................................................................................................................... 50 

Figure 44. Graph. Relative corrosion versus chloride concentration............................................ 50 

Figure 45. Graph. Output for a Cu-A606 atmospheric corrosion sensor using soaking 

solution 3-1 ................................................................................................................................... 55 

Figure 46. Graph. Output for Cu-A606 sensor during a 15-cycle test.......................................... 55 

Figure 47. Graph. Corrosion of A606 versus NaCl concentration ............................................... 56 

Figure 48. Graph. Corrosion (weight loss) of A606 coupons and calculated mass-loss for 

A606 sensors versus NaCl concentration for 15-cycle exposure.................................................. 58 

Figure 49. Graph. Corrosion (weight loss) of SAE1010 coupons and calculated mass-loss 

for SAE1010 sensors versus NaCl concentration for 15-cycle exposure ..................................... 58 

Figure 50. Graph. Response of cable sensor before and after dilute Harrison solution ............... 59 

Figure 51. Graph. Response of cable sensor during constant 50-percent RH exposure after 

dilute Harrison solution................................................................................................................. 60 

Figure 52. Graph. Response of cable sensor during constant 100-percent RH exposure after 

dilute Harrison solution................................................................................................................. 60 

Figure 53. Graph. XRD pattern of steel rods in cable sensor bundle after single soak in 

dilute Harrison solution and exposure in cyclic chamber for 40 days.......................................... 63 
viii 

LIST OF TABLES 

Table 1. Listing of information for 2304 SS................................................................................... 5

Table 2. Composition for 2304 SS.................................................................................................. 5 

Table 3. Concrete mix design ....................................................................................................... 11 

Table 4. Chloride concentrations at activation in accelerated tests .............................................. 16 

Table 5. Alloying elements and Legault-Leckie corrosion index of the steels............................. 23 

Table 6. Compositions of soak solutions for the first test set ....................................................... 26 

Table 7. Compositions of soaking solutions for the second test set ............................................. 28 

Table 8. Reference peak angles and intensities for the main iron oxidation products................. 30 

Table 9. Solution compositions used for sensor exposure tests.................................................... 36 

Table 10. Cathode-anode combinations for the atmospheric corrosion sensors........................... 36 

Table 11. Tests for cable interstitial sensor .................................................................................. 40 

Table 12. Exposure chart for the first exposure test on coupons 01–96....................................... 42 

Table 13. Exposure chart for the second set tests on coupons 01–48 (one soak only)................. 42 

Table 14. Observed major peak intensities using XRD and corrosion rates ................................ 52 

Table 15. Cumulative microampere hourly value readings (Ah) recorded by sensor type 

during 15 cycles ............................................................................................................................ 57 

Table 16. Percentage corrosion components in specimens determined by XRD ......................... 62 
ix 

ABBREVIATIONS AND SYMBOLS 

Abbreviations 

ASTM ASTM International, also known as American Society for Testing and 

Materials 

CNC Computerized numerical control 

DOT Department of transportation 

ECR Epoxy-coated reinforcing 

EDAX Energy dispersive analysis by X-ray 

ERF Gaussian error function 

FAU Florida Atlantic University 

FDOT Florida Department of Transportation 

FDOT-SMO Florida Department of Transportation State Materials Office 

FHWA Federal Highway Administration 

LCCA Life-cycle cost analysis 

mmpy Millimeters per year 

mpy Mils per year (thousands of inch corrosion penetration) 

mV Millivolt 

N Normal (chemical concentration unit, 1 equivalent per 1 liter of solution) 

pcy Pounds per cubic yard 

PREN; PRE Pitting resistance equivalent number 

PVC polyvinyl chloride 

RH Relative humidity 

SAE Society for Automotive Engineers 

SEM Scanning electron microscopy 

SCE Saturated calomel electrode 

SDS Simulated deck slabs 

SS Stainless steel 

w/c water-to-cement ratio 

wt percent Weight percent 

XRD X-ray diffraction 

ZRA Zero resistance ammeter 
x 

Symbols 

α Greek letter alpha 

 Greek letter beta 

 Greek letter gamma 

 Greek letter theta 

 Greek letter delta 

 Greek letter pi 

Ω Ohm

μA Microamperes 

a Atomic weight 

A Exposed area of the coupon 

As Exposed area of the sensor 

Cn Cumulative coulomb reading 

CRA606 Corrosion rate for A606 

CRrelative Relative corrosion rate 

CRSAE1010 Corrosion rate for SAE1010 

Cs Cl-

 concentration at the concrete surface 

CT Initiation of corrosion 

De Effective diffusion coefficient 

F Faraday constant 

ILL Index (Legault-Leckie) 

Ii the average microampere reading 

Ix Intensity in X-ray spectrum 

m Mass 

mn Mass loss of the coupons after n cycles 

n Number of equivalents 

t Sampling rate 

T Time 

x Depth
1 

CHAPTER 1. INTRODUCTION 

The United States has a major investment in its highway infrastructure because its operational 

performance, in conjunction with that of other transportation modes, is critical to the Nation’s 

economic health and societal functionality. While deterioration of structures with time is a 

normal and expected occurrence, the rate at which this has occurred for reinforced concrete 

highway bridges is affected by winter application of deicing salts in northern locations. Since the 

advent of a clear roads policy in the 1960s, deterioration has been abnormally advanced and has 

posed significant challenges, both economically and technically. Also important is similar 

advanced deterioration of reinforced concrete bridges in northern and southern coastal locations 

as a consequence of sea water or spray exposure (or both). In either case, the deterioration is a 

consequence of the aggressive nature of the chloride ion in combination with moisture and 

oxygen.(1) Over half of the total bridge inventory in the United States is of the reinforced 

concrete type, and these structures have been particularly susceptible to corrosion. A recent study 

indicated that the annual direct cost of corrosion to bridges is $5.9–$9.7 billion.(2) If indirect 

factors are also included, this cost can be as much as 10 times higher.(3) 

STEEL FOR CONCRETE REINFORCEMENT 

As this problem has manifested itself during approximately the past 40 years, technical efforts 

have been directed toward understanding the deterioration mechanism, monitoring the rate of 

deterioration and condition assessment, and developing prevention and intervention strategies. 

With regard to understanding the deterioration mechanism, steel and concrete are in most aspects 

mutually compatible. This is exemplified by the fact that in the absence of chlorides, the 

relatively high pH of concrete pore solution (pH  13.0–13.8) promotes formation of a protective 

oxide (passive) film such that the corrosion rate is negligible, resulting in decades of relatively 

low maintenance result. In the presence of chlorides even at concentrations at the steel depth as 

low as 1.0 pcy (0.6 kg/m3

) (concrete weight basis), the passive film may become locally 

disrupted, and active corrosion commences.(4) Once this occurs, solid corrosion products form 

near the steel-concrete interface and cause tensile hoop stresses around the reinforcement. This 

ultimately leads to concrete cracking and spalling. Because corrosion-induced deterioration is 

progressive, inspections for damage assessment must be routinely performed, and present 

Federal guidelines require a visual inspection every 2 years.(5) If indicators of deterioration are 

not addressed, public safety is at risk. For example, corrosion-induced concrete spalls form as 

potholes in a bridge deck, and they contribute to unsafe driving conditions. In the extreme, 

structural failure and collapse may result. 

Methods of life-cycle cost analysis (LCCA) are commonly employed to evaluate and compare 

different materials selection and design alternatives for bridge construction. This approach 

considers both initial cost and the projected life history of maintenance, repair, and rehabilitation 

expenses that are required to achieve the design life. These methods are evaluated in terms of the 

time value of money from which present worth is determined. Comparisons between different 

material selection and design options can then be made on a normalized cost basis. 

In the early 1970s, research studies were performed that qualified epoxy-coated reinforcing 

(ECR) steel as an alternative to black bar for reinforced concrete bridge construction.”(6,7) For the 
2 

past 30 years, ECR has been specified by most State transportation departments for bridges, 

decks, and substructures exposed to chlorides. At the same time, ECR was augmented by the use 

of low water-to-cement ratio (w/c) concrete possibly with pozzolans or corrosion inhibitors (or 

both) and concrete covers of 65 mm or more.(8) However, premature corrosion-induced cracking 

of marine bridge substructures in Florida indicated that ECR is of little benefit for this type of 

exposure.(See references 9–12.) While performance of ECR in northern bridge decks has 

generally been good to-date (30+ years), the degree of corrosion resistance afforded in the long 

term for major structures with design lives of 75–100 years is still uncertain. 

In response to the above concerns regarding ECR, interest has focused on more corrosionresistant alternatives to ECR—stainless steel (SS) in particular—during the past 15 years. Such 

alloys may become competitive on a life-cycle cost basis since the higher initial expense of the 

steel may be recovered over the life of the structure via reduced maintenance costs arising from 

corrosion-induced damage. 

STEEL FOR STRUCTURES AND CABLES 

Chloride and moisture can have major impacts on infrastructure components other than 

reinforced concrete. Structural steel with damaged paint, weathering steel, and high-strength 

steel in suspension bridge cables deteriorate because of wet-dry cyclic exposures in the presence 

of aggressive ions that accelerate corrosion processes. An essential aspect of these processes is 

the formation of corrosion products. The corrosion products can accelerate corrosion by 

undercutting paint on painted steel or by retaining aggressive chloride and ionic species in 

nonprotective oxide layers on any steel. Conversely, corrosion products can form protective 

oxide layers on weathering-type steels in favorable but not adequately defined environments. A 

better understanding of the mechanisms resulting in the formation of corrosion products in cyclic 

wet-dry environments in the presence of certain aggressive ions would enable more effective 

corrosion control measures. The automotive industry has successfully identified and found 

suitable solutions to specific issues pertaining to the paint undercutting mechanisms (known as 

cosmetic corrosion). This industry has developed the methodology of correlating accelerated 

testing and corrosion product identification with field studies for better understanding corrosion 

mechanisms and has applied the methodology to automotive perforation corrosion. Following 

similar methodologies, the steel industry has worked with the Federal Highway Administration 

(FHWA) and State transportation departments to identify issues related to steel and uncoated 

weathering steel materials, yielding useful information in design and maintenance guidelines. 

While peripheral issues have been identified, no jointly funded research has been initiated on 

these issues, and an adequate understanding of the processes is needed. 

Weathering steel and, to a lesser extent, structural steel develops a protective oxide layer 

when exposed to wet/dry conditions in the absence of aggressive environmental influences. 

Steel suppliers and the FHWA provide guidelines for determining the suitability of weathering 

steel for specific bridge applications.(13) Included in these guidelines is the recommendation 

for assessing the environmental suitability of weathering steel at a specific site. The wet/dry 

conditions required for the development of protective oxides on weathering steel and the 

presence of aggressive corrosive agents should be determined. The determination could 

lead to an assessment of the performance of weathering steel under the existing conditions 

at the specific site. 
3 

Many details addressing the procedures for macro and microenvironment assessment for 

assuring the performance of weathering steel are described elsewhere.(14) In that work, bimetallic 

couples including the steel material of interest were used to generate a galvanic current that was 

proportional to the structure’s corrosion rate. For this proposed work, corrosion rate assessment 

by modified corrosion sensors that correlate better with the field performance will be developed. 

The correlation to field performance requires several years and considerably impedes both 

development time and understanding of specific parameters affecting corrosion rates. It has been 

determined that field performance can be simulated in laboratory cyclic tests by comparing 

corrosion products observed in the field to those generated in the laboratory.(15) The laboratory 

conditions must be adjusted to yield similar corrosion products. Modifying chloride and/or 

sulfate exposure and drying conditions in the simulated tests can result in the development of 

corrosion products similar to those observed in the field. This correlation can speed validation 

and development of monitoring and control methods by a factor of about 30. Specifically, 

corrosion products on field samples, samples in simulated tests, and corrosion sensors must be 

closely matched so that appropriate conclusions can be drawn from testing and monitoring. 

The present report includes two research components of concern for highway bridges exposed to 

chloride contaminated service environments: (1) corrosion properties of 2304 SS reinforced in 

concrete and (2) monitoring of steel corrosion in atmospheric exposures. Accomplishments 

regarding each of these components are also presented and discussed in this report. 

5 

CHAPTER 2. RESEARCH COMPONENT #1: 2304 SS REINFORCING BARS IN 

CHLORIDE-CONTAMINATED ENVIRONMENTS 

OBJECTIVE 

The objective of this component of the study was to expand the scope of the companion 

FHWA/Florida Department of Transportation (FDOT)-sponsored research project by 

investigating the possible susceptibility of stainless alloy 2304 SS (UNS-S32304) to stress 

corrosion cracking under conditions relevant to reinforcing steel in concrete (task 1.1) and 

conducting both accelerated and long-term corrosion experiments on stainless alloy 2304 

reinforcement (task 1.2). 

MATERIAL 

The microstructure of duplex SS such as 2304 is comprised of approximately equal amounts 

of ferrite and austenite phases. Table 1 lists information for this alloy including the supplier, the 

as-received surface condition, and the pitting resistance equivalent number (PREN, also referred 

to as PRE), as defined by the following equation: 

PREN = wt%Cr + 3.3·wt%Mo + 16·wt%N (1)

Table 1. Listing of information for 2304 SS. 

Designation 

Common 

Designation 

As-Received 

Condition PREN Supplier 

UNS-S32304 2304 SS Pickled 25 UGITECH 

Likewise, table 2 lists the composition of this alloy. In general, duplex SS exhibits relatively high 

strength and ductility as well as beneficial corrosion properties including resistance to 

sensitization-induced intergranular corrosion, and high resistance to stress corrosion cracking. 

All experiments were performed using #5 (16-mm-diameter) bars. 

Table 2. Composition for 2304 SS. 

Alloy C Mn P S Si Cr Ni 

Type 2304 SS 0.03 1.16 0.026 0.002 0.45 22.33 4.16

Note: C = carbon, Mn = manganese, P = phosphorus, S = sulfur, Si = silicon, Cr = chromium, 

and Ni = nickel. 

7 

CHAPTER 3. RESEARCH APPROACH #1 

TASK 1.1. STRESS CORROSION CRACKING 

Procedure 

For these experiments, 2304 SS bars approximately 0.50 m long were bent to a radius bend four 

times the diameter of the bar (a 4D-radius) as seen in figure 1. Next, a strain gauge was mounted 

on the outside diameter of the bent bar approximately 15 cm from the midpoint of the bend. 

Specimens were then mounted individually in a vise, bent further to the point where the two side 

lengths were parallel, and restrained in this position using a custom configured C-clamp. Care 

was exercised to ensure that specimens did not relax when removed from the vise to avoid a 

situation where the critically stressed region (outside diameter at the center of the bend) went 

into residual compression. Figure 2 shows a schematic representation of a specimen in the bent 

and restrained state. The location of the maximum tensile stress, strain gauge, and C-clamp are 

shown as blue, red, and green, respectively. 

Figure 1. Photo. 2304 SS bar after bending. 

Figure 2. Illustration. A bent specimen in the restrained position. 
8 

All exposures were performed in two polyethylene tanks using a simulated pore solution that 

consisted of 0.30N KOH + 0.05N NaOH (initial pH = 13.44), where N is a chemical 

concentration unit indicating normal. One tank was maintained at room temperature, and 

chlorides were added to this in 1–2 weight (wt) percent increments on alternate days. The 

solution was titrated for OH-

 before, and after, Cl- was added to determine any pH change with 

time. Figure 3 shows one of the test tanks, and the two ends of a specimen can be seen 

protruding through the cover. Lead wires from the strain gages appear in the foreground of the 

figure. Likewise, figure 4 shows a top view of two specimens positioned in a tank with the cover 

removed. The second tank was maintained at 65 C and a constant chloride content of 

15 wt percent. Each specimen was placed in a separate plastic cylinder that was wrapped with 

insulation. Temperature was maintained by a heating element and a temperature probe in the 

plastic cylinder, the latter being connected to a thermostat. 

Figure 3. Photo. Test tank with cover. 

Figure 4. Photo. Top view of two specimens with C-clamps in the test tank. 
9 

Figure 5 shows two specimens positioned in temperature-controlled cylinders. In all cases, the 

bend was submerged in the simulated pore solution to a depth of 5 cm. The gauges were 

monitored for any strain decrease that would be indicative of cracking. Specimens were also 

examined daily. The higher temperature exposures were terminated after about 1 month, but the 

ambient temperature exposures continued for 1 year. 

Figure 5. Photo. High temperature experiment arrangement. 

TASK 1.2. CORROSION PROPERTIES OF TYPE 2304 SS REINFORCEMENT 

Accelerated Corrosion Test Procedure 

The accelerated test method for these experiments consisted of potentiostatic polarization of 

10 identical 152-mm-long 2304 SS reinforcing bar specimens at +100 mVSCE using a single 

locally designed and constructed potentiostat, where SCE is the potential versus saturated 

calomel electrode. A 10-Ω resistor was in series with each specimen, and voltage drop was 

monitored. Exposure was in synthetic pore solution of the same composition noted above 

(0.30N KOH + 0.05N NaOH) to which chlorides were incrementally added. This potential 

(+100 mVSCE) is considered conservative in that it exceeds the free corrosion potential that 

should occur in actual structures. In the absence of or with low chlorides, even black steel should 

be passive at this potential such that polarization should occur readily with low current demand. 

After a steady state was achieved after several days in the synthetic pore solution, chlorides were 

incrementally added. Corrosion was considered to have initiated once current density increased 

to 10 μA/cm2

, as calculated from the voltage drop across the 10-Ω resistor. The Cl- concentration 

that resulted from this achieved density was taken as the critical value for pitting and corrosion 

initiation, and it served as an important materials selection and design parameter in LCCA. 

Exposure of individual specimens was terminated once corrosion was initiated. Figure 6 shows a 

specimen ready for exposure with epoxy end mounts and an electrical lead, figure 7 shows a 

schematic representation of the experimental setup, and figure 8 shows the test system. 
10 

Figure 6. Photo. Straight as-received 2304 SS bar with epoxy-mounted ends 

and an electrical lead. 

Figure 7. Illustration. Accelerated experimental arrangement. 
11 

Figure 8. Photo. Test system. 

Reinforced Concrete Exposures 

Long-term exposure of three concrete slab specimens that were reinforced with 2304 SS was also 

performed. The concrete mix, designated STD1, had five bags of cement and a 0.50 w/c which 

yielded high permeability. The coarse aggregate was Florida limestone, and the fine aggregate 

was a local silica sand. The target mix design is shown in table 3. 

Table 3. Concrete mix design. 

Material Quantity 

Cement (bags) 5

Cement, kg 213

Water, kg 107

w/c 0.50

Fine aggregate, kg 652

Coarse aggregate, kg 753

The specimens were fabricated at the Florida Department of Transportation State Materials 

Office (FDOT-SMO) in Gainesville, FL, and they were designated as simulated deck slabs 

(SDS). These were intended to simulate a northern bridge deck or slab exposed to chlorides from 

either deicing salts or sea water. Figure 9 provides a schematic illustration of the specimen 

design where three straight bars comprised a top layer, and three bars comprised a bottom layer. 

Concrete cover for all bars was 25 mm, and triplicate specimens were prepared. Prior to casting, 

the reinforcement was degreased by cleaning with hexane, and heat shrink tubing was applied at 

the bar ends. This application provided an electrical barrier at the concrete-reinforcement 

interface, leaving only the center portion of the reinforcement within approximately 25 mm of 
12 

the exposed concrete surface. The casting procedure involved placing freshly mixed concrete in 

the specimen molds in two lifts followed by consolidating each lift for 20–30 s on a vibration 

table. The first lift filled the specimen mold approximately half full, and the second lift 

completely filled the mold. The surface of the specimens was troweled smooth using a wooden 

or metal float. After 24 hours, the molds were dissembled. The specimens were removed, placed 

in sealed plastic bags, and stored for 6 months. 

Figure 9. Illustration. Simulated deck slab specimen design. 

Upon delivery to Florida Atlantic University (FAU), an electrical connection was established 

between bars in each of the two layers of each slab using a SS wire in conjunction with a drilled 

hole and connection screw at one end of each bar. Periodically, a 10-Ω resistor was temporarily 

inserted in the circuit between the two bar layers, and voltage drop across this was measured. 

From this procedure, the macrocell current was calculated. The specimen sides were coated with 

an ultraviolet-resistant paint and inverted relative to their orientation at casting. A plastic bath 

with a vented lid was then mounted on what was the bottom formed face. Prior to ponding, the 

specimens were stored outdoors in a covered location for 2 months at the FAU Sea Tech 

Campus, which is approximately 300 m inland from the Atlantic Ocean southeast of 

Ft. Lauderdale, FL. The initial week of ponding was with potable water to promote saturation 

or a high humidity pore structure so that upon ponding, diffusion and not sorption would be 

the primary Cl-

 ingress mechanism. This was followed by cyclic 1 week wet/1 week dry 

ponding with 15 wt percent sodium chloride (NaCl). The salt water ponding commenced on 

August 10, 2005. Figure 10 shows the three specimens under test. 
13 

Figure 10. Photo. SDS specimens reinforced with 2304 SS under test. 

15 

CHAPTER 4. RESULTS AND DISCUSSION #1 

TASK 1.1. STRESS CORROSION CRACKING 

Initial pH of the ambient temperature test solution was 13.45; however, the pH decreased to 

13.30 with incremental Cl-

 additions due to the common ion effect. No strain changes that 

could be related to crack development were noted, and visual low power microscopic inspection 

failed to reveal any cracking. This was the case for both the ambient and elevated temperature 

exposures. It is concluded that the specimens were not susceptible to stress corrosion cracking in 

the simulated pore solution. 

TASK 1.2. CORROSION PROPERTIES OF TYPE 2304 SS REINFORCEMENT 

Accelerated Test Method 

Figure 11 plots current density versus exposure time for the 10 identical 2304 SS specimens. 

The pH data is also shown, which appears as a near horizontal line slightly above a value of 

12 and [Cl-

] versus time according to the incremental additions. Current density was between 

10 and 12 μA/cm2

 initially but decreased to zero to 2 μA/cm2 during the first few days of 

exposure, presumably reflecting repair of defects in the passive film. For most specimens, a 

definitive transition from this low current density to much higher values occurred at a particular 

time, which reflected the onset of active pitting. The time at which this occurred covered a 

relatively broad range from 295 hours for specimen 9 to 1,608 hours for specimen 7. The data 

interruption near 1,000 hours resulted from a power outage that lasted several days due to 

Hurricane Katrina in August 2005. 

Figure 11. Graph. Accelerated corrosion test data. 
16 

Table 4 shows the [Cl-

] at which individual specimens activated. As such, these values are 

indicative of the critical chloride concentration for initiation of corrosion, CT. The fact that these 

values extend over a range suggests that the threshold concentration is a distributed parameter 

rather than a discrete number as reported previously by others.(16–18) Figure 12 shows a 

cumulative distribution function plot of these data which allows projection of the probability of 

corrosion initiation at a particular [Cl-

]. This analysis assumes the data are normally distributed. 

By way of comparison, a companion study using this experimental method reported CT for black 

bar as 0.24–0.30 wt percent Cl-

.

(19) Thus, CT for 2304 SS was about 17 times greater than for 

black bar according to this experimental method. However, the companion study referenced 

above questioned accuracy of this approach for correctly ranking reinforcements according to CT

compared to performance in concrete.(19)

Table 4. Chloride concentrations at activation in accelerated tests. 

Specimen Number [Cl-] wt Percent 

1 6.83 

2 9.25 

3 5.61 

4 8.34 

5 6.52 

6 9.25 

7 9.86 

8 6.83 

9 5.00 

10 7.58 

Figure 12. Graph. Cumulative distribution plot of CT for 2304 SS from accelerated testing. 
17 

Concrete Specimen Exposures 

The SDS specimens were exposed for 929 days. Figure 13 shows the resultant potential data. For 

the most part, potentials were in the range -150 to -200 mVSCE; however, specimen 2304-1 in 

particular had negative excursions which reached -356 mVSCE on one occasion. Figure 14 shows 

the corresponding macrocell current data. With the exception of one reading for specimen 

2304-1, the currents were below the detection limit and considered zero. The one finite current 

reading of 0.1 μA for specimen 2304-1 occurred at the same time as the most negative potential 

excursion for this same specimen (404 days exposure) that was mentioned previously. 

Apparently, the specimen exhibited momentary corrosion activity followed by repassivation. 

Figure 13. Graph. Potential data for the 2304 SS-reinforced concrete specimens. 

Figure 14. Graph. Macrocell current data for the 2304 SS-reinforced concrete specimens. 
18 

While no cores were taken from the 2304 SS-reinforced SDS specimens, 75-mm-diameter cores 

were taken from identical companion specimens subjected concurrently to the same exposure. 

However, the cores were taken at different times. Once acquired, the cores were dry sliced 

parallel to the top surface at 6.4-mm intervals, and the individual slices were ground to powder. 

The powder samples were then analyzed for [Cl-

] using the FDOT wet chemistry method.(20) 

Figure 15 shows a plot of [Cl-] data for these as a function of depth into the concrete. 

Figure 15. Graph. Concrete chloride concentration profiles determined from 10 cores. 

From each of the above [Cl-] profiles, a value for the effective diffusion coefficient, De, was 

calculated using a least squares fit to the one-dimensional solution to Fick’s second law as seen 

in the following equation: 

C(x,T) = Cs · ERF 















 5.0 TD )(2

x

e (2)

Where: 

C(x,T) = [Cl

] at depth, x, into the concrete after time, T. 

Cs = [Cl

] at the concrete surface. 

ERF = Gaussian error function. 

D = Effective diffusion coefficient.

This solution assumes that Cs and De are spatially and chronologically constant, whereas they 

are, in fact, distributed parameters and may vary with exposure time and concrete age.(21) The 

solution also assumes that initial [Cl-

] in the concrete was zero. Using the average De for the 10 

determinations (2.59·10-11

 m

2

/s), [Cl-] was calculated at the top bar depth at 929 days using 

equation 1 and assuming Cs = 18 kg/m3 (7.22 wt percent cement basis). This yielded a value of 

12.5 kg/m3

 (4.51 wt percent cement). It is concluded, assuming the momentary potential and 

macrocell current activity cited above in conjunction with figure 13 and figure 14 did not 

constitute corrosion initiation, that CT for 2304 SS exceeds this value. In the recently completed 

companion study references above, CT for black bar at a probability of 2-percent activation was 
19 

1.0 kg/m3

 (0.35 wt percent cement) and for 20-percent activation 1.9 kg/m3 (0.69 wt percent 

cement).(19) If the above cited minimum CT for 2304 SS (12.5 kg/m3

) were to correspond to 

2-percent probability of corrosion initiation for this reinforcement, then CT for 2304 SS exceeds 

that of black bar by a factor of 12.5. If, on the other hand, this CT for 2304 SS pertains to 

20-percent probability of activation, then the improvement relative to black bar is by a factor 

greater than 6.6. 

21 

CHAPTER 5. RESEARCH STUDY #1 FINDINGS 

There are several conclusions that can be drawn from the first research study. First, the exposure 

of U-bend specimens fabricated from 16-mm-diameter 2304 SS to simulated pore solution with 

chlorides at an ambient temperature of 165 o

C failed to reveal any susceptibility to stress 

corrosion cracking. Second, the critical chloride concentration to initiate corrosion of 2304 SS 

specimens polarized to +100 mVSCE while exposed to simulated pore water to which chlorides 

were incrementally added ranged from 5.00–9.86 wt percent Cl-

. In addition, no definitive 

corrosion initiation occurred after 929 days for three concrete slab specimens with 2304 SS 

reinforcement that were ponded with a Cl- solution. Some momentary activity followed, but 

repassivation did occur for one specimen. Last, the Cl-

 threshold to initiate active corrosion of 

2304 SS in concrete was greater than 12.5 kg/m3

 (4.51 wt percent cement). 

23 

CHAPTER 6. RESEARCH STUDY #2: HIGHWAY BRIDGE STEEL COMPONENTS 

SUBJECT TO SIMULATED ATMOSPHERIC EXPOSURE 

OBJECTIVE 

The objective of this component of the study was to expand the knowledge base of atmospheric 

corrosion monitoring on highway bridge steel components. The objective was accomplished in 

three parts. First, an accelerated cyclic method for the production of protective/nonprotective 

oxide layers on bare steel specimens in chloride environments (task 2.1) was validated. Next, 

short-term corrosion rates were monitored during accelerated laboratory cyclic exposures 

performed using galvanic sensors to provide a better understanding of the corrosion mechanisms 

on bare steel coupled to a cathodic material (task 2.2). Last, prototype galvanic sensors of 

uncoated high strength steel strands were developed and evaluated for suspension cable inservice performance monitoring (task 2.3). 

Material 

Two types of steel, A606-04 (a thin-gauge weathering steel) and SAE1010 (a common carbon 

steel with no weathering resistance), were used for the following experiments. Table 5 shows the 

respective alloying elements present in the different steels (the remainder was iron, Fe) as well as 

their respective Legault-Leckie (American Society for Testing and Materials (ASTM) G 101) 

atmospheric corrosion resistance indices.(22) A higher index (ILL)—which is based on elemental 

composition—indicated a higher weathering ability (corrosion resistance) of the steel. Steel with 

a minimum ILL of 6 is considered a weathering steel. There is a large difference between the 

A606-04 and SAE1010 steels used in this study. 

ILL = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (%P) (3) 

Table 5. Alloying elements and Legault-Leckie corrosion index of the steels. 

Material Percent Cu Percent Ni Percent Cr Percent Si Percent P ILL

SAE1010 0.02 0.01 0.03 0.008 0.008 0.73

A606-04 0.33 0.17 0.46 0.33 0.01 6.40

Note: Cu = copper, Ni = nickel, Cr = chromium, Si = silicon, and P = phosphorus. 

For cable sensors, high-strength steel wire was obtained from Small Parts, Inc.©, made in 

accordance with ASTM A228 and supplied in straight 1,828.8-mm lengths. The ASTM A228 

chemistry specifications were C = 0.700 to 1.00 percent, Fe  98.4 percent, and Mn = 0.200 to 

0.600 percent.(23) Tensile strength was at least 220,000 psi. An elemental analysis by scanning 

electron microscopy/energy dispersive analysis by X-ray determined that Mn was in the stated 

range. Casual work fabricating with this wire indicated high stiffness, although no quantitative 

mechanical testing was performed. 

25 

CHAPTER 7. RESEARCH APPROACH #2 

TASK 2.1. LABORATORY TEST METHOD FOR PRODUCTION OF PROTECTIVE 

AND NONPROTECTIVE OXIDE LAYERS IN CHLORIDE ENVIRONMENTS 

Wet/Dry Cycle 

The Society for Automotive Engineers (SAE) established an accelerated test under dry/wet 

conditions to test metal coatings under highly corrosive environment known as Standard SAE 

J-2334.(24) The test has been characterized as, “J2334 Best Correlation to 5-Year Data (Field) at 

80-Cycles.”(25) The cycle is shown in figure 16. The five-cycle per week option maintained the 

dry condition during weekends. The soak solution specified in the standard is 0.5 percent NaCl + 

0.1 percent CaCl2 + 0.075 percent NaHCO3. 

Figure 16. Chart. Standard SAE J2334 cyclic test with five cycles/week. 

Exposure Tests 

Standard SAE J-2334 was the starting point for the first set test, and alternative soak solutions 

were used. The behaviors of the steels varied at different chloride compositions. Four chloride 

concentrations were selected for the salt application. The chloride concentrations ranged from no 

chloride to a 5-wt percent composition solution, corresponding to an environment with very high 

salt deposition similar to a bridge that undergoes regular salt deicing processes. To account for 

environments that were subject to acid rain, each chloride concentration was subdivided—one 

group had a pH 6 and the other had a pH 8. Time of wetness and chloride exposures played 

an important role in the corrosion of steel. To study the influences, half of the exposure 

environments included a second 15-minute salt soak 3 hours after the first one. Table 6 

summarizes the compositions of the soak solutions. 
26 

Table 6. Compositions of soak solutions for the first test set. 

Solution NaCl (wt Percent) NaHCO3 (wt Percent) 

1-1 0.0 0.000 

1-2 0.0 0.075 

1-3 0.5 0.000 

1-4 0.5 0.075 

1-5 2.0 0.000 

1-6 2.0 0.075 

1-7 5.0 0.000 

1-8 5.0 0.075 

An environmental chamber manufactured by CARON® Model 6030 was used for the 

experiment (see figure 17). The humidity and temperature inside the chamber were controlled 

and programmed. The wet stage started every day at 8 a.m. At 2 p.m., the dry stage started, and 

the first soak was performed. For the tests with two soaks, the second soak was performed at 

5 p.m., 3 hours after the first one. There were 6 coupons of each steel type exposed to each 

solution, which created a total of 192 coupons for the entire experiment. Specifically, the 

192 coupons were calculated by multiplying 2 steel types by 8 solutions by 2 soaking methods 

by 6 coupons (3 for 15 cycles plus 3 for 30 cycles). Weight losses were reported as the average 

of three specimens. 

The 16 racks, fabricated from polyvinyl chloride (PVC) to accommodate 12 coupons each, were 

custom made for holding the coupons in the chamber (1 rack for each environment). Six coupons 

of each material were placed on each rack. One rack held six coupons of A606 steel and six 

coupons of SAE1010 steel. Two racks (24 coupons) were soaked in the same container. This 

arrangement allowed all coupons to be soaked within the same 15-minute time period. Images of 

a rack and soaking container are shown in figure 17 and figure 18. 
27 

Figure 17. Photo. CARON® environmental chamber for cyclic SAE J2334 tests. 

Figure 18. Photo. Specimens on holder rack and in soak tank. 

After obtaining the data from this first set test (15 and 30 cycles), a second set test was 

carried out. These steels showed the most interesting behavior at chloride levels between 

zero and 2 wt percent. Based on the results of the first set test, a narrower and lower range of 

seven chloride concentrations was chosen in addition to 0.5-wt percent concentration as a 

reference point (reproduction). The second set test (15 and 30 cycles) was performed to obtain 
28 

details in this concentration range. This time, only pH 8 was considered, and one soak was 

performed. Table 7 lists the different solutions used for the second set test. 

Table 7. Compositions of soaking solutions for the second test set. 

Solution NaCl (wt Percent) NaHCO3 (wt Percent) 

2-1 0.1 0.075 

2-2 0.2 0.075 

2-3 0.3 0.075 

2-4 0.5 0.075 

2-5 0.7 0.075 

2-6 1.0 0.075 

2-7 1.3 0.075 

2-8 1.6 0.075 

For these experiments, 8 PVC racks held 12 coupons each (1 rack for each environment) with 

6 coupons of each material. A set of 96 coupons was prepared for this second set test. The total 

number of coupons was calculated by multiplying 2 steel types by 8 solutions by 1 soaking 

method by 6 coupons (3 for 15 cycles and 3 for 30 cycles). Weight losses were reported as the 

average of three specimens. 

Coupon Preparation 

Very clean contaminant-free surfaces were needed for this experiment. The procedures to 

prepare the coupons follow. 

A606 Steel 

The1.5-mm thick material was cut to approximately 102-mm by 102-mm coupons. A 2.5-mm 

hole was drilled for the label attachment. The surface was bead blasted for 3 minutes on each 

side using type AC (60–120 mesh, 0.12–0.25-mm-diameter) type glass beads. The four sides 

were measured to assure squareness of the coupons and recorded. A label was attached 

consisting of a nylon zip tie engraved with the specimen identification. The specimens were 

dipped in methanol and drained on clean laboratory wipes. They were then dried with hot air for 

2 minutes to prevent water condensation. The coupons were equilibrated in a desiccator for 

1 hour, weighed, and stored in the desiccator until the beginning of exposure testing. 

SAE1010 Steel 

The 0.76-mm-thick material was cut to 76- by 102-mm coupons and prepared in the 

same manner described for the A606 material except bead blasting was required for only 

1 minute per side. 

Weight Loss 

Data after 15 and 30 cycles of exposure were required for each of the 16 environments for the 

first set test. According to ASTM Standard G1 for evaluating corrosion rate, three coupons were 

needed for each weight loss measurement.(26) There were 6 coupons for each steel for the 
29 

16 environments (6·2·16 = 192 coupons). After exposure, coupons were cleaned in a solution of 

hydrochloric acid, hexamethylenetetramine (inhibitor), and reagent water as specified in ASTM 

Standard G1.(26) The coupons were then dried and weighed. 

X-ray Diffraction Analyses 

After exposure, some corrosion products were collected before cleaning. For each environment 

and material, corrosion products were collected for X-ray diffraction (XRD) analysis. The 

corrosion products were then ground with mineral oil for powder analysis. 

Powder XRD was performed on some of the corrosion products to characterize the 

correspondence between chamber condition and field exposure. A Philips® Model PW1710 

system with DiffTech® Visual XRD control software was used for the measurements. The X-ray 

source used for the analysis was a copper Kα1 with a wavelength of 0.154056 nm. 

The spectrum had a number of counts plotted versus angle of diffraction (see figure 19). 

Software detected peaks from the spectrum, which were observed as significant increases in 

counting rate (intensity) in the figure. Each peak at a specific angle had a relative intensity 

associated. Two parameters ( and Ix) were used to compare with a database. For this study, 

only peak angles and their associated relative intensities were required for crystallographic 

compound searches. 

Figure 19. Graph. Example of X-ray powder diffraction spectrum. 

The focus of this analysis was on four iron oxides identified during the on-site (field) exposure: 

goethite, akaganeite, lepidocrocite, and maghemite. A fifth compound, butlerite, was observed in 

the cable sensor study.(27) The database used for the comparison is the online edition of the 

American Mineralogist Crystal Structure Database.

(28) Each crystalline configuration had 

numerous peaks, and a listing of all of them would be unnecessary because in the case of a 

mixture of several crystalline configurations, identifying the main two or three peaks via relative 

intensity was usually sufficient. The main reference angle peaks for an X-ray wavelength of 

0.1541838 nm and associated intensities are presented in table 8. 
30 

Table 8. Reference peak angles and intensities for the main iron oxidation products. 

Iron Oxide Angle (2)

Relative Intensity 

(Percent Max) 

21.29 100.00 

33.31 46.86 Goethite, 

-FeOOH 36.75 77.50 

11.83 100.00 

11.88 96.87 Akaganeite, 

-FeOOH 26.76 89.46 

14.29 100.00 

27.16 64.11 Lepidocrocite, 

 -FeOOH 36.54 52.08 

35.71 100.00 

35.77 45.59 Maghemite, 

 -Fe2O3 63.13 40.81 

17.83 100.00 

28.21 55.29 Butlerite, 

Fe[SO4](OH)·2H2O 29.10 24.79 

33.15 100.00 

54.05 45.13 Hematite,

-Fe2O3 49.46 37.43 

35.46 100.00 

30.10 28.24 Magnetite,

Fe3O4 62.58 41.32 

The table lists the location (by angle) of the three largest peaks observed for each iron oxide 

and the relative intensity (peak) of each peak. The largest peak is taken as the reference 

(100 percent), and the remaining two peaks are listed as percentages of the largest peak. For 

example, if the largest peak has an intensity of 500 and the second peak has an intensity of 250, 

the relative intensities would be 100 and 50 percent, respectively. If a third peak for this 

compound has an intensity of 400, its relative intensity would be 80 percent. Determining which 

oxides are present in a sample requires examining the patterns for peaks at the angles where 

having 100-percent relative intensities and verifying the presence of secondary and tertiary peak 

angles are expected. Computer algorithms usually perform these functions. 

TASK 2.2. CORROSION RATES OF ACCELERATED TEST SPECIMENS USING 

GALVANIC SENSORS 

Approach 

Galvanic corrosion sensors were developed to (1) react to humidity and chloride concentration, 

(2) be easily deployable on a steel structure, (3) give an indication of the corrosion rate of the 

structure, and (4) obtain data comparable with the data from the chamber exposure. 
31 

Sensor Design 

Several primary designs were tested before selecting the final design described in figure 20 

and figure 21. 

When the sensor was exposed to high humidity, a meniscus formed on the edge of the insulating 

nylon washer, making an electrolytic connection between the steel and the cathode (copper or 

gold). Nylon polymer performed better than several other polymer materials evaluated for this 

sensor application. During galvanic corrosion, electrons moved to the cathode, producing a 

current, which was recorded by the data logger connecting the two external copper leads. When 

dry, no electrochemical reactions occurred, and no current (electrons) flowed. Intermediate 

conditions yielded moderate current values. 

Preliminary studies showed that the electric connections and the seal between the insulating 

nylon washer anode and cathode required extra care. If water infiltrated under the washer, a 

crevice corrosion phenomenon was possible that provided alternate current paths that were not 

measurable by the data logger (errors). 

Figure 20. Illustration. Atmospheric corrosion sensor (Model FAU2). 
32 

Figure 21. Illustration. Anode detail for atmospheric corrosion sensor. 

The sensors were built with several elements. The center screw had a diameter of 6.6 mm with 

20 threads per 25.4 mm by 25.4 mm long made of brass with copper or gold plating. The 

insulating nylon washers were machined from a 0.508-mm thickness Nylon 6/6 flat washer with 

a 6.6-mm inside diameter to 17.4-mm outside diameter, and a thickness of 0.508 mm. Both steel 

washers had a 33.02-mm outside diameter and a 10.16-mm inside diameter. The A606 steel 

washer (anode) was 1.52 mm thick, and the SAE1010 washer (alternate anode) was 0.762 mm 

thick. For SAE1010 sensors, an extra nylon shimming washer with a 9.906-mm inside diameter, 

a 15.748-mm outside diameter, and 6.890-mm thickness was used in between the shoulder 

washer and the steel washer. The shoulder washer was made of Nylon 6/6 with an inside 

diameter of 6.604 mm, an outside diameter of 9.525 mm, a shoulder diameter of 14.275 mm, and 

a thickness of 1.524 mm. Finally, nuts were Nylon 6/6 with matching-screw thread with a width 

of 11.11 mm across the flats and a height of 6.10 mm. 

Zero Resistance Ammeter Data Logger 

To obtain the data from the sensors, zero resistance ammeter (ZRA) loggers were developed.(14)

A zero resistance ammeter is an electronic device that converts current at its input into voltage at 

its output. This device imposes no (zero) voltage drop to the input circuit. It is designed to 

measure small currents (on the order of 1–100 μA) without interfering with (polarizing) the 

circuit being measured. The ZRA was embedded in a data logger circuitry that acquired data 

every 10 minutes. The data were summed and stored every hour. It collected up to 2 months of 

data while powered by a single lithium 9V battery. The data loggers had a full range of 100 μA. 

This maximum current was a design parameter for the sensors. The sensor output was intended 

to be limited to 100 μA. A picture of a data logger is presented in figure 22. 
33 

Figure 22. Photo. Data logger incorporating a ZRA. 

The data was transferred from the data logger via a serial port to a computer in a hexadecimal 

format. A Microsoft Excel macro was used to transfer hexadecimal data to corrosion current 

values, and data could then be plotted normally in decimal format. 

Sensor Active Area 

As discussed previously, the sensors reacted to humidity and temperature. A flat steel surface 

seemed to be the best choice, representing the as-fabricated surface of a structure. It proved to be 

a simple and relatively cost-effective way to manufacture the sensor. 

The current flowing between the two electrodes was limited to 100 μA during the wet cycle 

when the maximum currents occurred for optimal data acquisition by the logger. Because the 

anode surface was the controlling parameter, the surface area of the steel was limited in size to 

keep the output from exceeding the 100-μA value. The maximum corrosion rate was expected to 

decrease or stay constant with time, which permitted short duration exposure tests to be 

performed on simplified sensors to determine the optimal surface area. 

Figure 23 shows no off-scale output, whereas figure 24 shows a slight off-scale output 

(flattened peak) from the 16th to 17th hours during the wet portion of the J2334 cycle. To 

optimize the output range of the sensors, a 19.05-mm diameter active area was specified for the 

steel washer (anode) to allow use of a significant portion of the logging scale without exceeding 

the maximum value of 100 μA. 
34 

1 inch = 25.4 mm 

Figure 23. Graph. Sensor output for 0.7-inch active anode steel washer diameter for 

one SAE J2334 cycle in the standard solution. 

1 inch = 25.4 mm 

Figure 24. Graph. Sensor output for 0.8-inch active anode steel washer diameter for 

one SAE J2334 cycle in the standard solution. 

For a flat surface desired for the sensors, a disk (washer) was fabricated and then painted 

(masked) to leave a circular area of bare steel at the center. The paint proved to be an issue 

during a previous test, as shown in figure 25. Under-paint corrosion occurred, and additional 

steel surface was subject to corrosion, giving undesirable results. Later, urethane-based powder 

coating was selected because of its excellent corrosion resistance and salt tolerance. 
35 

Figure 25. Photo. Bottom side of a sensor mounted on its holder experiencing 

under-paint corrosion. 

Sensor Anode Fabrication 

The same steels (lots) as the ones used for the chamber exposure were used to make the 

steel washers. They were machined using computerized numerical control (CNC) and then 

blasted using AC grade glass beads (60–120 U.S. screen, 0.124–0.25mm) to obtain a 

contaminant-free surface. 

Sensor Cathode Fabrication 

Previous studies showed that copper was a good compromise between cost and performance for 

the cathode even if gold was the best choice.(29,30) To be more cost effective, brass screws were 

copper- or gold-plated to make the cathodes. 

Electrode Separator 

Preliminary tests showed that nylon was a good choice for the separating material. It was neither 

too hydrophilic nor hydrophobic and provided a good surface tension to keep the water on its 

surface while still allowing the sensor to dry. 

Sealer 

Several sealing materials have been used in preliminary designs. A rubber adhesive was used to 

seal the different parts together and to impede the water from infiltrating between the parts. 
36 

Sensor Electrical Connection 

Electrical connection was a special consideration. Classical soldering could not be used because 

of issues concerning the high temperature and the flux flow that would contaminate the steel 

surface. In addition, typical low temperature solders melt during powder coat curing which 

would damage the connection. After consideration of the constraints on this connection, the 

copper leads (14-gauge wires) were threaded, and the steel washer was tapped. Next, silver 

epoxy (conductive) was used as a thread locker to make sure the connection was established. The 

same connection was used for the copper lead on the central screw followed by an insulation 

overcoat (caulk). The electrical connections to the sensor lead wires were soldered and caulked 

with marine sealant to avoid the formation of a galvanic couple that might introduce errors. 

Exposure Testing 

To be consistent with task 2.1, the same exposure cycle (SAE J-2334) and exposure chamber 

were used for the sensor exposures so that corrosion values of the coupons could be compared 

with the coulomb values of the sensors. After the first set test, the most interesting environments 

were determined, and it was decided that the sensor would be exposed to six environments. 

Table 9 presents the compositions of the solutions used during this test. The sensors were given 

a 15-cycle exposure. 

Table 9. Solution compositions used for sensor exposure tests. 

Solution 

NaCl 

(wt Percent) 

NaHCO3 

(wt Percent) 

3-1 0.2 0.075 

3-2 0.3 0.075 

3-3 0.5 0.075 

3-4 0.7 0.075 

3-5 1.0 0.075 

3-6 1.3 0.075 

To hold the sensors horizontally, polyacrylate racks were custom made to fit in the exposure 

chamber. Figure 26 shows the setup for the sensors on the racks. A set of four different sensors 

(one of each type) was exposed per rack. Sensors were built following the construction matrix 

presented in table 10. Consequently, a total number of 24 sensors were built for the purpose of 

the exposure test. 

Table 10. Cathode-anode combinations for the atmospheric corrosion sensors. 

 Anode (Washer) 

SAE1010 (Q) A606 (W) 

Cathode (Screw) Copper (C) C-Q C-W 

 Gold (G) G-Q G-W 
37 

The number preceding the sensor’s name is the number of the solution used for the soaking 

(e.g., sensor 1-G-Q is an SAE1010 (Q) sensor with a gold (G) screw, and solution 3-1 (1) was 

used for the soaking). 

Figure 26. Photo. Four sensors set up on the cross-shaped holding rack. 

TASK 2.3. DEVELOPMENT OF PROTOTYPE CABLE CORROSION SENSORS 

Cable Sensors 

Galvanic corrosion sensors were developed based on the steel and copper galvanic couple. The 

intent was to create a small sensor capable of insertion within the bridge suspension cable 

strands’ parallel interstitial spaces. The sensor would respond to corrosive conditions producing 

a current proportional to the steel’s corrosion rate in a wet or salt-laden environment within the 

cable. If the interior cable environment was dry, corrosion-inhibited, or protected by waterdisplacing compounds, no significant current would be expected from the sensor. 

High-strength iron wire that had a diameter of 0.08 cm and a length of 3.5 cm acted as the anode. 

A copper wire with a diameter of 0.02 cm and a length of 20 cm was the cathode. The surface 

area ratio of Cu to Fe was approximately 1.4. An 11-M resistor was soldered between the 

anode and cathode. The two lead wires were connected to the electrode ends opposite the 

resistor. Figure 27 and figure 28 show the parts used for the cable sensor and fabrication. The 

resistor and black lead wire were soldered to the iron anode, and the copper cathode was 

soldered to the red lead wire. The soldered areas were coated with epoxy and covered with 

shrinking olefin tube. The iron anode was cleaned using abrasive paper and methanol alcohol 

and then dried. After drying, porous fiberglass sleeving material was used to cover, or 

electrically insulate, the iron anode. The copper cathode was then wound around the sleeving 

material. A larger diameter fiberglass sleeve was placed over the anode-cathode assembly, and 

heat shrink tubes were installed at the sensor ends. The cable sensor was complete after the ends 

were sealed with marine-grade caulking. The response was tested by wetting it with 2 percent 
38 

salt solution and allowing it to dry. Figure 29 shows the maximum current due to the corrosion of 

steel less than 100 μA (design maximum). The fiberglass sleeving electrically insulated the 

anode and cathode from each other. It also insulated the sensor for the cable strands, but it 

allowed water, if present, to soak into the sensor. 

Figure 27. Photo. Components and fabrication of the cable sensor. 

Figure 28. Photo. Completion of the cable sensor. 
39 

Cable Sensor Response

0

20

40

60

80

100

0 100 200 300 400 500 600

Time (h)

Current (

A)

Wetted;

Dried;

Rewetted; and,

Redried

Figure 29. Graph. First test of corrosion sensor wetted, dried out, rewetted, and redried. 

Cable Sensor Tests 

A test specimen for the sensors consisted of 12 rods bundled with 3 sensors which had either 

loosely or well-sealed wrappings. Corrosion products were characterized and compared using 

XRD as in task 2.1. The anode and cathode surface areas were selected and tested to provide 

sensor output in the data logger’s measurement range. 

Figure 30 shows deployment locations within the multistrand cable specimen. Three tests were 

performed within a single multistrand specimen. A set of 18 tests were performed with the 

sensors (after single immersion in 1

/10 Harrison solution) including drying, wet, and cycled 

exposures. Dilute Harrison solution consisted of 0.35 percent ammonium sulfate, (NH4)2SO4, 

and 0.05 percent NaCl. Table 11 provides the test matrix, which was modified to acquire 

additional data in some cases. The dry tests were soaked for 15 minutes in dilute Harrison 

solution then equilibrated (dried) on the laboratory bench top (50 percent relative humidity (RH)) 

while collecting data. The wet tests were soaked for 15 minutes in dilute Harrison solution and 

then equilibrated in a closed plastic container (100 percent RH) while collecting data. The cycled 

tests were not initially soaked before starting the cyclic test to observe the response to 

condensing humidity. They were then soaked for 15 minutes in dilute Harrison solution and 

returned to the cyclic chamber, and data were collected throughout the process. 
40 

1 inch = 25.4 mm 

Figure 30. Illustration. Cable specimen showing arrangement of strands and sensors. 

Table 11. Tests for cable interstitial sensor. 

Wrapping Type 

Number of 

Dry Sensors 

Number of 

Wet Sensors 

Number of 

Cycled Sensors 

Loose 

(specimen bundle) 

3

(L1)

6

(L2, L3)

9

(L1, L2, L3)

Water-tight 

(specimen bundle) 

3

(T2)

6

(T3, T4) 

9

(T1, T2, T3)

L = loose wrap. 

T = tight wrap. 

C = cyclic exposure. 

XRD for Cable Sensor Tests 

XRD was performed on corrosion products obtained from test specimen rods. The corrosion 

products on the sensor anodes were not expected to produce sufficient corrosion product to 

obtain useful results in each test. 
41 

CHAPTER 8. RESULTS AND DISCUSSION #2 

TASK 2.1. LABORATORY TEST METHOD FOR PRODUCTION OF PROTECTIVE 

AND NONPROTECTIVE OXIDE LAYERS IN CHLORIDE ENVIRONMENTS 

Weight Loss 

To obtain values that could be compared, a corrosion value was computed, which consisted of a 

ratio between the weight loss and the exposed area. Time was not taken into account in that 

calculation. To compare data of a 15-cycle exposure to a 30-cycle exposure, an average 

corrosion rate over a single cycle was computed by dividing the corrosion value by the number 

of cycles to which the coupon was exposed. 

Calculations of the exposed surface area were made from the measurement of the four sides of 

the coupons. An average was performed on each set of two parallel sides and then multiplied 

with the edge areas summed to obtain the final exposed area. Some SAE1010 coupons had a hole 

made by the manufacturer for eventual hanging. The area of the hole and the edges were taken 

into account for the exposed area calculation. 

Labeling the coupons was executed by beginning A606 coupon labels with “W” and SAE1010 

coupon labels with “0.” They were numbered consecutively from 01 to 96 for each kind of steel. 

The following two exposure charts, table 12 and table 13, provide information on the 

environments that were applied to the coupon identification numbers. 

To assess the advantage of using weathering steel (A606) against carbon steel (SAE1010) in a 

particular environment, the corrosion value of A606 relative to SAE1010 can be calculated by 

computing the following: 

1010

1010 606

SAE

SAE A

relative CR

CR CR CR   (4) 

Where: 

CRrelative = Relative corrosion value. 

CRSAE1010 = Corrosion value for SAE1010. 

CRA606 = Corrosion rate for A606. 
42 

Table 12. Exposure chart for the first exposure test on coupons 01–96. 

Solutions Used for Soaking (NaCl Percent, pH) 

Soaks Cycles 

1-1 

(0, 6) 

1-2 

(0, 8) 

1-3 

(0.5, 6) 

1-4 

(0.5, 8)

1-5 

(2, 6) 

1-6 

(2, 8) 

1-7 

(5, 6) 

1-8 

(5, 8) 

01 13 25 37 49 61 73 85 

15 02 14 26 38 50 62 74 86 

03 15 27 39 51 63 75 87 

04 16 28 40 52 64 76 88 

05 17 29 41 53 65 77 89 

1 

30 

06 18 30 42 54 66 78 90 

07 19 31 43 55 67 79 91 

15 08 20 32 44 56 68 80 92 

09 21 33 45 57 69 81 93 

10 22 34 46 58 70 82 94 

11 23 35 47 59 71 83 95 

2 

30 

12 24 36 48 60 72 84 96 

Table 13. Exposure chart for the second set tests on coupons 01–48 (one soak only). 

Solution Used for Soaking (NaCl Percent, pH)

Cycles 

2-1 

(0.1, 8) 

2-2 

(0.2, 8) 

2-3 

(0.3, 8) 

2-4 

(0.5, 8) 

2-5 

(0.7, 8) 

2-6 

(1.0, 8) 

2-7 

(1.3, 8) 

2-8 

(1.6, 8) 

01 07 13 19 25 31 37 43 

15 02 08 14 20 26 32 38 44 

03 09 15 21 27 33 39 45 

04 10 16 22 28 34 40 46 

30 05 11 17 23 29 35 41 47 

06 12 18 24 30 36 42 48 

If the relative corrosion value was positive, weathering steel corroded less than the carbon steel 

during the exposure, meaning the patina impeded corrosion. Conversely, if the relative corrosion 

rate was negative, carbon steel performed better than weathering steel. 

First Set Test 

The complete set of data, which included individual specimen dimensions and weights, is 

available.(31) An example calculation is given in the appendix for converting the data to units 

used in this report. Compilations of the data are in the following sections. The data are plotted 

and discussed as the average results of triplicate specimens unless stated otherwise. 

Influence of Sodium Chloride 

For both steel types, wetting times, or the pHs, a higher concentration of chloride led to a higher 

corrosion rate as shown in figure 31 and figure 32. 
43 

Figure 31. Graph. A606 corrosion as a function of the concentration of NaCl. 

Figure 32. Graph. SAE1010 corrosion as a function of the concentration of NaCl. 

During the corrosion process, Fe0 (metallic iron) was oxidized to Fe2+ in the solution. NaCl was 

present as the solvated ions, Na+

 and Cl-. When no salt was present on the surface of the steel, 

Fe2+ recombined with OH–

 to form oxide and hydroxyoxide corrosion products (rust), as follows: 

  2   2)( HOHFeOHFe 2 2

2 (5)

When salt was present, an intermediate product was involved and the following reaction 

occurred: 

 

2 2)( FeClClOHFe 2  2OH (6) 

At this point, the oxide layer was damaged, the insoluble ferrous oxide was replaced by a soluble 

iron (II) chloride, and it was washed away by the condensing humidity during the wet cycle. This 

description is a simplification of a more complex process. 
44 

The most interesting feature was the weathering ability of A606 as a function of the chloride 

concentration. The results obtained from the first set test are summarized in figure 33, which 

shows the relative corrosion of A606 versus SAE1010. Figure 33 shows that while A606 

developed its protective layer when using 0.5 percent NaCl at pH 6 and pH 8 (solutions 1-3 and 

1-4), the two-soak exposure made it less protective. When using two soaks, the coupons were 

more exposed to NaCl (especially Cl- and water). 

Relative corrosion between A606 and SAE1010

-30

-20

-10

0

10

20

30

40

50

% Difference

0.5% NaCl, pH 6

0.5% NaCl, pH 8

2% NaCl, pH 6

2% NaCl, pH 8

5% NaCl, pH 6

5% NaCl, pH 8

1 Dip 2 Dips

15 cycles 30 cycles 15 cycles 30 cycles

Figure 33. Graph. Relative corrosion between A606 and SAE1010. 

Solutions 1-1 (zero percent NaCl and pH 6) and 1-2 (zero percent NaCl and pH 8) results are not 

shown in figure 33 because very little corrosion occurred due to the absence of chloride. 

Consequently, calculating the ratio (percentage) is problematic because the error factors are of 

the same magnitude as the results themselves. In addition, the ratios are not of interest for such 

low corrosion rates. 

In figure 33, it is apparent that A606 performed very well in 0.5 percent NaCl and pH 6 

(solution 1-3) and 0.5 percent NaCl and pH 8 (solution 1-4) for both one and two soaks, whereas 

poorer performances were found with the higher concentration NaCl solutions. Weathering steel 

was not as useful when high concentrations of NaCl were present. This result is consistent with 

suggestions of 0.1–1.0 percent maximum chloride concentrations for well-performing 

weathering steels.(31) From these data, the interesting range of NaCl concentration, regarding 

weathering ability of A606, appears to be zero to 2 wt percent, justifying the choice of solutions 

for the second set test. 
45 

Influence of pH 

Two different pH values were selected to study pH’s influence on the corrosion of steel. 

Figure 34 through figure 37 present the corrosion values observed during the first set test. To 

clearly study pH’s influence, the only parameter varied in each graph was the pH of the solution 

used during the soaking process. Data after 15 and 30 cycles are presented. 

Figure 34 through figure 37 suggest that regardless of the type of steel, wetting time (one or two 

soaks/cycle), or exposure time, a lower pH yields a slightly higher corrosion rate. The variation 

of the pH does not appear to have a critical role in the early corrosion stage when the corrosion 

value is slightly affected. 

Regarding the weathering ability of A606, figure 38 suggests that pH had a stronger effect 

with low NaCl. Conversely, at a high concentration of NaCl (5 percent) and a high number of 

cycles (30), pH had no effect. 

Figure 34. Graph. A606 corrosion as a function of chloride concentration during a 

one soak/cycle exposure. 
46 

Figure 35. Graph. A606 corrosion as a function of chloride concentration during a 

two soak/cycle exposure. 

Figure 36. Graph. SAE1010 corrosion as a function of chloride concentration during a 

one soak/cycle experiment. 
47 

Figure 37. Graph. SAE 1010 corrosion as a function of chloride concentration during a 

two soak/cycle experiment. 

Figure 38. Graph. Relative corrosion versus NaCl concentration during exposure to a 

one soak/cycle environment. 

Influence of Wetting Time 

Environments including one soak/cycle and two soaks/cycle were used to study the influence of 

the wetting time on the corrosion of the steels and the weathering ability of A606. Results are 

presented in figure 39 through figure 42. 
48 

Figure 39. Graph. A606 corrosion as a function of chloride concentration at pH 6. 

Figure 40. Graph. A606 corrosion as a function of chloride concentration at pH 8. 
49 

Figure 41. Graph. SAE1010 corrosion as a function of chloride concentration at pH 6. 

Figure 42. Graph. SAE1010 corrosion as a function of chloride concentration at pH 8. 

Figure 41 and figure 42 show that the wetting time with high NaCl concentrations had a strong 

effect on SAE1010 as well as A606. Values with two soaks were much greater than those with 

one soak, especially for pH 8. Considering pH 6, corrosion values were becoming similar for the 

highest NaCl percentage. Increased wetting time and higher NaCl concentration had less 

influence on corrosion. A possible explanation is that at a high NaCl concentration, the oxide 

layer was saturated with NaCl, and the additional NaCl did not cause further change. However, 

at a lower pH of 6, corrosion increased, which suggests that a lower pH had a synergistic effect 

with NaCl to further saturate the oxide layer with chloride. 
50 

Second Set Test 

The complete set of data, which includes individual specimen dimensions and weights, is 

available.(33) An example calculation is given in the appendix for converting the data to units 

used in this report. Compilations of the data are presented in figure 43 and figure 44. 

The data are plotted and discussed as the average results of triplicate specimens unless 

stated otherwise. 

Figure 43. Graph. Corrosion of A606 and SAE1010 versus chloride concentration for 

the second test set. 

Figure 44. Graph. Relative corrosion versus chloride concentration. 

Based on the first set of test results, an interesting range of chloride concentration was 

determined for the soaking solution, which was greater than zero and less than 2 percent NaCl. In 

these tests, only pH 8 was used with chloride concentration (0.1–1.6 percent NaCl), which was 

the only factor that was varied. 
51 

Note that for 0.1–1.6 percent NaCl, the corrosion value of SAE1010 was always greater than the 

value of A606, meaning that in that range of concentration, weathering steel was performing as 

expected by forming a protective oxide. 

A606 performed well for 15 cycles. For a NaCl concentration greater than 0.5 wt percent, 

the weathering ability after 30 cycles seemed to decrease. This decrease is observed in figure 44 

where the 30-cycle data falls below that of the 15-cycle data. Issues might be encountered for 

longer exposure times because the corrosion rates for A606 increase for 30 cycles compared 

to 15 cycles. 

XRD and Corrosion Rate 

Several corrosion specimens were analyzed by XRD and correlated with their corrosion rates. 

The results are given in table 14 and discussed below. Table 14 presents the peaks and their 

intensities relative to the individual compound’s major peak. These are semiquantitative 

percentages and do not intend to represent a quantitative rust composition. The results give 

indications concerning the composition of the rust and can be related to the results found in 

field studies. Additional XRD analyses are discussed in chapter 8. 
52 

Table 14. Observed major peak intensities using XRD and corrosion rates. 

Specimen 

Exposure 

Description 

Corr. Rate 

(mm/y) 

Goethite 

 -FeOOH 

Lepidocrocite

 -FeOOH 

Maghemite 

 -Fe2O3

Akaganeite 

 -FeOOH 

W67 

(A606) 

2 percent NaCl 

pH 8 

1 soak 

15 cycles 0.039 76.5 21.4 0 0

W23 

(A606) 

0.5 percent NaCl 

pH 8 

1 soak 

30 cycles 0.043 100 11 0 0

W88 

(A606) 

5 percent NaCl 

pH 8 

1 soak 

30 cycles 0.122 100 8.3 17.7 0

W70 

(A606) 

2 percent NaCl 

pH 8 

2 soaks 

30 cycles 0.140 100 14.1 42.9 0

070 

(SAE1010) 

2 percent NaCl 

pH 8 

2 soaks 

30 cycles 0.132 100 0 22.3 0

Weathering Steel—15-Cycle Exposure with Protective Patina 

Coupon W67 was exposed to a solution of pH 8 containing 2 percent NaCl using one soak/cycle. 

Weight loss results showed that it developed a protective layer (see table 14). 

The intensity peak was achieved by metallic iron (the substrate) at 44.7 degrees. The second 

peak of this pattern was at 21.7 degrees, which was the goethite strong peak. Its second strongest 

peak was present at 36.5 degrees. A small 27.8-degree peak indicated that lepidocrocite was 

present in the oxide layer. 

Weathering Steel—30-Cycle Exposure with Protective Patina 

Coupon W23 was exposed to a solution of pH 8 containing 0.5 percent NaCl using 

one soak/cycle. Weight loss results showed that it developed a protective layer (see table 14). 

The peak with the highest intensity at 21.7 degrees corresponded to the goethite peak, which was 

81 percent of the protective patina. The second peak was also identified at 36.3 degrees. Peaks at 

14.8 and 27.6 degrees corresponded to lepidocrocite. These smaller peaks indicated that there 

was little of this crystal phase in the oxide layer. 
53 

Weathering Steel—30-Cycle Exposure with Nonprotective Patina Exposed to High 

Chloride Concentration 

Coupon W88 was exposed to 5 percent NaCl using one soak/cycle. Weight loss results showed 

that it did not develop a protective layer (see table 14). 

Goethite was the main constituent of the oxide layer with peaks at 21.6 and 36.3 degrees. An iron 

peak was also present at 44.9 degrees and was likely due to metallic iron particles being 

undermined from the surface by corrosion or from scraping the coupon surface to remove the 

oxide for analysis. A small amount of maghemite was identified at 63.5 degrees. The first two 

maghemite peaks may have coalesced with the 36.3-degree peak of goethite. 

Weathering Steel—30-Cycle Exposure with Nonprotective Patina Exposed to High Time of 

Wetness 

Coupon W70 was exposed to 2 percent NaCl at pH 8 using two soaks/cycle (see table 14). 

Weight loss results showed that it did not develop a protective layer. 

Goethite was identified by its main peak at 21.5 degrees. Its second peak was also present at 

36.19 degrees. The relatively high intensity peak at 63.3 degrees indicated that a large fraction of 

maghemite was present in the oxide layer. The first two peaks of maghemite coalesced with the 

36.3-degree peak of goethite. 

Carbon Steel—30-Cycle Exposure with Nonprotective Patina Exposed to High Chloride 

Concentration 

Coupon 070 was exposed to 2 percent NaCl at pH 8 using two soaks/cycle (see table 14). Weight 

loss results showed that it did not develop a protective layer. Goethite was the main constituent 

of the oxide layer. Maghemite was also observed at 63.6 degrees. 

Analyses of Carbon and Weathering Steel Corrosion Products 

XRD analyses were made on corrosion products obtained from additional specimens after 

completion of the cyclic tests. These are discussed in the next section. 

Summary of XRD Analysis 

The XRD results obtained from the coupons tested in the accelerated exposure chamber were in 

general agreement with the field study results given in table 14.(24) High wetting time developed 

maghemite and lepidocrocite, while high chloride developed maghemite and sometimes 

akaganeite. Goethite was present in every corrosion product whether it was protective or not. 

Thus, increasing the concentration of chloride, providing additional chloride exposure (a second 

soak), and increasing the wetting time all had the same effect in the laboratory as in field 

exposure. For example, specimens W67 and W23 exhibited low corrosion relative to W88, W70, 

and 070. The conditions of 2 percent NaCl (or lower) with a single soak represented low chloride 

and relatively drier conditions for W67 and W23. Conversely, conditions of 2 percent NaCl (or 

higher) with two soaks represented higher chloride and wetness exposures. 
54 

The exposure chamber experiments produced results similar to those observed for steel in field 

exposure. Maghemite was found in almost all nonprotective corrosion products. One anomaly 

was the absence of akaganeite in the high chloride-soaked specimens, which may have been due 

to fresh water condensing humidity rinsing away chloride during the wet cycle portion. 

Generally, the laboratory tests were able to reproduce the conditions found during field exposure, 

especially with regard to high corrosion rate and maghemite correlation. Comparison of the 

laboratory and field exposures was not straightforward because the laboratory conditions could 

be controlled while the field conditions were dependent on natural (variable) environmental 

changes during the exposure. 

TASK 2.2. CORROSION RATES OF ACCELERATED TEST SPECIMENS USING 

GALVANIC SENSORS 

Reaction to Humidity and Salt Application 

One of the successes of the sensor design described in the previous chapter was due to its very 

good response to humidity and NaCl. In figure 45, when the wet cycle began, the output 

immediately increased due to the completion of the current path, and the current was recorded by 

the data logger. The current remained stable during the time the metal was corroding; salt 

deposits and amorphous corrosion products were washed out by the ambient condensing 

humidity. Once the salt was applied, the current increased, responding to the corrosion rate of 

the material being exposed to a more aggressive environment. The wet stage occurred between 

the 6th and 12th hours, and soaking occurred at the 11th hour. After soaking the specimen, the 

dry cycle began, resulting in an increased current as the electrolyte layer dried. This increased 

the conductivity and infusion of oxygen through the thinner layer. When the drying was 

complete, the current dropped to zero. In the dry cycle, localized corrosion could occur as well as 

corrosion product crystallization and resizing of the crystallites. 

Sensor output for the 15-cycle exposures is presented in figure 46. During the eighth cycle, the 

wet stage did not start because of an experimental chamber failure. The salt soaking was still 

performed, and each sensor responded the same way but with differing magnitudes. The outputs 

had the shape of a spike corresponding to the time needed for the salt solution to dry in the 

chamber. This unplanned event shows the reproducibility of the output for a given event over the 

whole sensor population, showing another success for the sensors. In the figure, D-W indicates 

approximate dry-wet periods. 
55 

24h cycle sensor 1-C-W

0

10

20

30

40

50

60

70

80

90

123 45678 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (Hours)

Current (

A)

Wet stage

Soaking in salt

Figure 45. Graph. Output for a Cu-A606 atmospheric corrosion sensor using 

soaking solution 3-1. 

Output for Sensor C-W using Solution 3-1

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180 200 220240 260 280 300 320 340 360 380 400

Time (Hours)

Current (μA)

Figure 46. Graph. Output for Cu-A606 sensor during a 15-cycle test. 

The output for the last three cycles after the weekend break was also interesting. Current 

readings dropped for each kind of steel, even more for A606. In the standard SAE J2334, the 

weekend break was optional. The reason why the corrosion rate decreased may be related to the 

crystallization time needed for the oxides to form. Oxides that constitute the protective layer 

needed to crystallize during the dry stage. If the dry stage was too short, the final 

crystallographic reformation was not complete, and consequently the protective layer was not 

completely formed. It is known that weathering steel requires dry and wet cycles to perform 

well, but the time required has not been characterized. If a corrosion performance test is to be 

developed further, drying time during weekends should be required or perhaps extended. Other 

data support this last statement. For the first set test (weight loss coupons), six weekend dry 

stages were performed, whereas for the second set test, only two weekend breaks were 

performed. By combining data obtained with the two exposure tests (see figure 40 and figure 

43), figure 47 was created. 

D-W-D-W-D-W-D-W-D-W-D-W-D-W-D-W-D-W-D-W-D-W-----D-----W-D-W-D-W-D 
56 

Corrosion of A606 as a function of NaCl concentration

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0123456

NaCl wt%

Corrosion Penetration (mm)

15 cycles

30 cycles

Figure 47. Graph. Corrosion of A606 versus NaCl concentration. 

In figure 47, the corrosion value dropped between 1.6 and 2.0 wt percent NaCl. The data for 

1.6 wt percent concentration was from the second set test, whereas the data for 2.0 wt percent 

concentration was from the first set test. The drop was due to the option of the experimental 

protocol that was not supposed to have a significant effect on the results according to standard 

SAE J-2334. The results show that drying time was an important factor when dealing with the 

corrosion of weathering steel. Weekend drying time should be included in the standard and 

should be a topic for additional study. The role of drying time was easily studied by cyclic 

coupon and sensor tests. 

Corrosion Rate Determination 

The sensors were intended to provide information about the corrosion rate of the material from 

which they were fabricated. To verify that the output of the sensors represents the actual 

corrosion rate in the same environment, the output of the sensors can be compared (see table 15) 

with the results obtained during the exposure of the coupons. 

By integrating microamperes over the time, coulombs (i  t = C) are found, which are related to 

weight loss using Faraday’s law. All microampere readings were averaged by the data logger 

over the sampling time of 1 hour (3,600 s). An example calculation is given in the appendix. 
57 

A coulomb is equal to amperes multiplied by seconds, as seen in equation 7. 

C tI

n

i

n  i



 

1

6 3600 (7) 10

Where: 

Ii = The average microampere reading on the ith hour; 

t = The sampling rate (1 per hour). 

Cn = The cumulative coulomb reading at the nth hour. 

Table 15. Cumulative microampere hourly value readings (Ah) recorded by sensor 

type during 15 cycles. 

Solution 

(Percent NaCl, pH 8) G-W C-W G-Q C-Q 

3-1 (0.2 percent) 7,261 5,618 7,116 4,861 

3-2 (0.3 percent) 7,116 6,807 9,382 7,291 

3-3 (0.5 percent) 9,141 8,836 9,755 10,189 

3-4 (0.7 percent) 10,281 9,557 9,194 9,977 

3-5 (1.0 percent) 8,954 9,244 9,001 10,462 

3-6 (1.3 percent) 7,377 9,302 8,626 9,099 

Note: G = gold; C = copper; W = A606; Q = SAE1010 

To obtain a value that can be compared with the coupon data, equation 8 is used. 

  2

1

2 965002 2

84.55

rr

C

nFA

aC

A

m n

s

n

c

n



   (8) 

Where: 

Ac = Exposed area of the coupon. 

As = Exposed area of the sensor. 

r2 = Outer radius of exposed area of the sensor. 

r1 = Inner radius of exposed area of the sensor. 

mn = Mass loss of the coupons after n cycles. 

Cn = Cumulative coulombs after n cycles, calculated using equation 7. 

F = Faraday constant. 

n = Number of equivalents (two for the case of iron). 

a = Atomic weight. 
58 

Plotting the sensor data and the coupons data gives figure 48 and figure 49. For both figures, the 

dashed boxes identify over-range sensor data. 

Figure 48. Graph. Corrosion (weight loss) of A606 coupons and calculated mass-loss for 

A606 sensors versus NaCl concentration for 15-cycle exposure. 

Figure 49. Graph. Corrosion (weight loss) of SAE1010 coupons and calculated mass-loss 

for SAE1010 sensors versus NaCl concentration for 15-cycle exposure. 

For A606 steel (see figure 45), corrosion values calculated from the sensors were lower than 

those from the weight loss experiment (even after applying a 2X factor). However, the first 

three data points of sensors and coupons followed the same trend. The trend indicated that the 

more chlorides present in the solution, the higher the corrosion value. The last three (higher) 

concentrations reached a maximum corrosion value for the sensors. An explanation is that the 

output was off-scale, as can be seen on the sensors’ output data. The amperes or coulombs 

obtained reached the maximum value (scale) that the data logger could record, indicated by 

a plateau with increasing chloride concentration. Consequently, those six data points (three 

for the G-W sensors and three for the C-W sensors) were invalid and should not be compared 

to weight loss data. 

The same phenomena occurred for the SAE1010 sensors output. These sensors indicated that 

sensors made of SAE1010 were providing higher output values than (higher corrosion rate) that 

those made of A606. The higher rate was inferred by the coulomb values achieving maximum 

(plateau) values at lower chloride concentrations in figure 48 and figure 49 or higher values in 

table 15, especially for the copper cathode sensors. This result was reasonable due to the 

weathering ability of A606. Above a chloride concentration of 0.7 wt percent, the sensors 
59 

produced an off-scale output that was invalid for quantitative comparisons. The first three sensor 

data points for both A606 and SAE1010 followed the trend of the coupon data where higher 

NaCl concentration indicated a higher corrosion value. 

In general, sensors were able to indicate the corrosion rate of material exposed to the same 

environment, although a scale (proportionality) problem should have been considered. The 

sensors were sensitive to chloride concentration. A smaller active anode area or a wider range 

data logger is suggested for future studies. Table 15, figure 48, and figure 49 suggest that copper 

cathodes provide more consistent results than the gold cathodes. 

RESULTS OF TASK 2.3. PROTOTYPE CABLE CORROSION SENSORS 

The main sources of moisture for cables are rainwater and condensation. These moistures are 

often mimicked by dilute Harrison solution for corrosion testing.(33) The solution contains 

ammonium sulfate and NaCl usually found in atmospherically deposited moisture. 

Cable Sensor Response to Test Conditions 

Cyclic 

Figure 50 presents the sensor responses of dry specimens exposed to SAE J2334 cyclic 

conditions (except no soaking) followed by a experiencing a single soak in dilute 

(

1

/10 concentration) Harrison solution after 32 days and continuing the cycling without additional 

soaks. In each case, the sensors yielded little or no response until wetted by the dilute Harrison 

solution after 32 days. Each sensor showed a large increase in response after wetting. The 

responses observed were expected for wetted sensors. The specific nature of the response varied 

somewhat depending upon wetness saturation of the sensor within the specimen. In figure 50, the 

large response after wetting was followed by a large decrease corresponding to drying of the 

sensor. Subsequently, small responses that corresponded to the high humidity phase in the 

exposure chamber were observed every 24 hours. 

Figure 50. Graph. Response of cable sensor before and after dilute Harrison solution. 
60 

Soaked 

Figure 51 presents typical cable sensor responses of specimens soaked for 15 minutes in dilute 

(

1

/10 concentration) Harrison solution followed by equilibration under static conditions of 

50 percent RH. Figure 52 presents the typical responses for similar tests for 100 percent RH. The 

responses showed that the more tightly wrapped specimens and those under the higher relative 

humidity maintained higher levels of current for longer times than loosely wrapped specimens or 

those under lower RH. These responses were consistent with corrosion that occurred in the 

presence of sufficient moisture. 

Figure 51. Graph. Response of cable sensor during constant 50-percent RH exposure after 

dilute Harrison solution. 

Figure 52. Graph. Response of cable sensor during constant 100-percent RH exposure after 

dilute Harrison solution. 
61 

XRD Results for Cable Test Specimens 

Table 16 and figure 53 show the XRD results for the corrosion products that were obtained from 

the cable specimen rods. The most notable difference compared to the coupon materials was the 

presence of butlerite. Butlerite is a ferrihydroxysulfate compound, and its formation is due to the 

presence of sulfate from the dilute Harrison solution used to wet the sensors. 
62 

Table 16. Percentage corrosion components in specimens determined by XRD. 

Condition 

Specimen 

0 = SAE1010, 

W = A606 

Percent 

Goethite

Percent 

Maghemite 

Percent 

Lepidocrocite 

Percent 

Other 

024 40 60 — — 

041 43 57 — — 

042 46 54 — — 

060 61 39 — — 

063 48 52 — — 

069 — 74 — 26 Hematite 

072 20 65 15 — 

W63 40 29 31 — 

1-soak

W69 37 32 31 — 

021 43 57 — — 

024 28 40 32 — 

032 56 44 — — 

035 42 58 — — 

038 41 31 28 — 

041 24 76 — — 

042 45 55 — — 

W01 20 80 — — 

W09 56 — 44 — 

W21 37 37 26 — 

W24 24 45 31 — 

W33 59 — 41 — 

W35 35 65 — — 

W38 25 41 34 — 

2-soak

W48 44 56 — — 

L1C 15 16 25 44 Butlerite 

L2C 15 22 23 40 Butlerite 

L3C 15 13 26 46 Butlerite 

T1C 8 27 15 50 Butlerite 

T2C 12 24 12 52 Butlerite 

Cable specimen 

rods near sensors 

(see table 11) 

T3C 19 45 17 19 Butlerite 

The bolded text, “0,” represents SAE1010 material. 

— Indicates that data was not found. 

L = loose wrap. 

T = tight wrap. 

C = cyclic exposure. 
63 

Figure 53. Graph. XRD pattern of steel rods in cable sensor bundle after single soak in 

dilute Harrison solution and exposure in cyclic chamber for 40 days. 

65 

CHAPTER 9. RESEARCH STUDY #2 FINDINGS 

There are several findings from the second research study, which include the following: 

 An accelerated corrosion test was developed for weathering steel corresponding to a 

range of exposure conditions that demonstrated sensitivity to chloride environments. 

 The protective oxide layer (patina) of weathering steel was degraded above 

0.5 wt percent chloride. Above 1 wt percent chloride, the protective oxide was 

severely degraded. 

 Sensors were able to indicate the corrosion rate of coupon material exposed to the same 

environment. 

 Sensors allowed direct and immediate observation of the impact that environmental 

changes had on corrosion rate. 

 XRD showed that the corrosion products produced in cycle test chambers were similar to 

those observed under field conditions. 

 Bridge cable sensors were developed which were capable of monitoring corrosive 

conditions within suspension bridge cables and other occluded geometries. 

67 

CHAPTER 10. CONCLUSIONS 

The findings of both research studies comprise the following general conclusions of this report: 

 Exposure of U-bend specimens fabricated from 16-mm-diameter 2304 SS to simulate 

pore solution with chlorides at ambient temperature and 65 o

C failed to reveal any 

susceptibility to stress corrosion cracking. 

 The critical chloride concentration required to initiate the corrosion of 2304 SS 

specimens polarized to +100 mVSCE while exposed to simulated pore water to which 

chlorides were incrementally added ranged from 5.00–9.86 wt percent Cl-

. 

 No definitive corrosion initiation occurred after 929 days for three concrete slab 

specimens with 2304 SS reinforcement that were ponded with a Cl-

 solution. For one 

specimen, some momentary activity followed by repassivation occurred. 

 The Cl-

 threshold to initiate active corrosion of 2304 SS in concrete was greater than 

12.5 kg/m3

 (4.51 wt percent cement). 

 An accelerated corrosion test was developed for weathering steel corresponding to a 

range of exposure conditions that demonstrated sensitivity to chloride environments. 

 The protective oxide layer (patina) of weathering steel was degraded above 

0.5 wt percent chloride. Above 1 wt percent chloride, the protective oxide was 

severely degraded. 

 Sensors indicated the corrosion rate of coupon material exposed to the same environment. 

 Sensors allowed direct and immediate observation of the impact of environmental 

changes on corrosion rate. 

 XRD showed that the corrosion products produced in cycle test chambers were similar to 

those observed under field conditions. 

 Bridge cable sensors were capable of monitoring corrosive conditions within suspension 

bridge cables and other occluded geometries.

69 

APPENDIX 

CALCULATIONS 

In this appendix, calculations that were used to convert laboratory measurements to units in text, 

tables, and graphs are provided as examples. 

Example 1. Convert Weight/Area (Corrosion in g/inches2) to mils (or mm) Corrosion 

Penetration 

Data for specimen W48: test condition was 30 cycles, 2 soaks, 0.5 percent NaCl, and pH 8. 

Typical Data 

Weight 

(Initial) 

Weight 

(Final) 

Area 

(L by W2) 

Corrosion 

( wt/inches2

 ) 

Coupon W48 124.90766 g 119.02947 g 34.16 inches2 0.1721 g/inches2

1 inch = 25.4 mm 

1 oz = 28.35 g 

 

Convert to centimeters: 

22 2

2

2 /02667.054.2/1

54.2

/1721.0 cmg cmg

cm

in ing   

















(9)

Convert weight per surface area to penetration (divide by density): 

cmgcmg 00339.0/87.7/02667.0 cm

2 3   (10)

Also: 

0.00339 cm  10 mm/cm = 0.0339 mm (11)

Convert to mils (1 inch = 1,000 mils): 

mils

in

mils

cm

in

cm 33.1 1000

54.2

00339.0   (12) 

These are the penetration rates in mm, m, cm, or mils for corrosion occurring on one surface. In 

the case of corrosion occurring on both sides, the overall thickness loss would be doubled. 
70 

Example 2. Conversion of ZRA Current to Coulombs 

    CsACti )( (13) 

Where: 

I = Current. 

t = Time. 

A = Amperes. 

s = Seconds. 

C = Coulombs. 

 ZRA data logger recorded averaged current (i) each hour. 

 The eight-bit analog-to-digital converter stored the sum of six readings in hexadecimal 

format, that is, the summed eight-bit readings (0 to 255 hex) were summed to give a 

value between zero and 05 FA (hex) and stored. 

 Stored data were downloaded from the logger to the computer. Scaling was 

255 (hex) = 100 μA (full-scale). 

 Microsoft Excel® macro converted hexadecimal to decimal, divided by 6, and scaled by 

100/255. 

 The result was μA average current reading per hour. 

 The Microsoft Excel® macro also summed the hourly average current readings (in 

microamperes) and multiplied them by 3,600 s to yield microcoulombs (i  t = C). 

Example: For constant, half-scale readings (50 μA) for 15 days converted to coulombs: 

C

h

s

day

h days sA

C C A 8.64 360024 1050# 15 6     (14) 

Note that the data logger recorded a value equal to an average current value each hour. In this 

example, 0.18 C was measured each hour. Summing (integrating) these hourly values for 15 days 

yielded 64.8 C. 
71 

Example 3. Conversion of Sensor Output (μA) to Corrosion Rate (mpy or mmpy) 

Faraday’s Law of Electrolysis: 

nF

Ita

m  (15) 

Where: 

m = Mass (g). 

I = Current (A). 

t = Time (s). 

a = Atomic weight; (g). 

n = Number of equivalents, eq, (number of electrons exchanged, for Fe = Fe2+ + 2e- ). 

F = Faraday’s constant, 96,500 C per equivalent. 

For 1 μA output per year (recall that C=A  s): 

g moleeq eqC

A molegs

nF

Ita

m 0091.0

)/500,96)(/2(

)/8.55)(1015.3)(10( 6 7

  



 (16) 

For 1 μA output in an area of 1 cm2

 and given an iron density of 7.87 g/cm3: 

mpy mmpy in

mils

cm

in

g

cm

cm

g cmA 012.046.0 1000

54.287.7

0091.0/1

3

2

2      * (17) 

1 mpy = 0.0254 mmpy 

* Indicates same result as in D. Jones.(34)

Equation 17 demonstrates the conversion of constant or average current density to mils per year 

or mm per year. The data logger provided the average of six current measurements at 10-minute 

intervals each hour. These hourly averages are summed and presented in table 15. 

Example 4. Comparison of Mass Loss and Sensor Results in Terms of Penetration 

For reference for this example, refer to figure 48 and figure 49. For the ATM sensor, the sensor 

anode area, the location where mass loss occurred, and the mass corresponding to coulombs 

obtained with the data logger must be calculated. 

Sensor anode area is the two-dimensional ring between the inner washer, r1 , and the outer coated 

perimeter, r2: 

    2 2

2

2 2 2

1

2

2 58.1504.0 54.2 250.0375.0 cm cm

in

cm sensor rrA in in    

 





      (18) 

To calculate the mass loss from the downloaded converted sensor output (microamperes), 

substitute C = A  s, (i.e., replace It in equation 15 with the coulomb value). For example, use 
72 

the first value (7,261 μA) in table 15 that is an hourly value requiring conversion to seconds 

(1 h = 3,600 s) as follows: 

g moleeq eqC

moleghsAh

nF

Ita

m 0076.0

)/500,96)(/2(

)/8.55)(/3600)(107261( 6

  



 (19) 

The calculated mass loss per unit area of the sensor anode is converted to penetration using the 

density of iron as follows: 

mm

cm

mm

g

cm

cm

g 0061.0 10

87.758.1

0076.0 3

2  (20) 

For the cable sensor, no direct comparison with weight loss was possible with the available data. 

An estimate of corrosion rate (penetration) was made based on sensor area and current output. 

Area calculation where: 

Anode wire diameter = 0.08 cm. 

Active length = 2.5 cm. 

Anode area is dl = 3.14  0.08 cm  2.5 cm = 0.63 cm2

. 

Sensor output: 

From equation 17, 1 μA/cm2

 = 0.46 mpy. For a 0.63-cm2 sensor giving a current reading of 

1 μA, the current density is (1 μA / 0.63 cm2

) = 1.6 μA / cm2, and a sensor reading of 1 μA 

corresponds to 0.74 mpy as follows: 

x

mpy

A

A 46.0

6.1

1  

 , x = 0.74 mpy (21)
73 

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