Adhesion of Epoxy Coating to Steel Reinforcement under Alkaline Conditions

by

Rana Masoudi

A thesis submitted in conformity with the requirements for the degree of Master of Applied Science

Department of Civil Engineering University of Toronto

© Copyright by Rana Masoudi 2013

ii

Adhesion of Epoxy Coating to Steel Reinforcement under Alkaline

Conditions

Rana Masoudi

Master of Applied Science

Department of Civil Engineering University of Toronto

2013

Abstract

Epoxy-coated reinforcement was developed in the 1970s and became the primary corrosion

protection technique in North America. Throughout the years, ECR has exhibited mixed results,

with some regions and jurisdictions reporting good corrosion protection while others reported

poor field performance of ECR. It has been established that epoxy coating can lose its adhesion

in a wet environment thus providing poor corrosion protection of reinforcing steel. However,

limited research has been done on the influence of concrete pore solution on adhesion of epoxy

coating to reinforcing steel. This research investigates the effect of high alkali conditions on

performance of ECR bars. Based on the test results, it was found that the rate of disbondment

increases as the hydroxyl ion concentration increases and presence of high temperature

accelerates the disbondment process.

iii

Acknowledgments

I would like to thank my supervisor, Professor R. Doug Hooton, for his continual guidance and

encouragement throughout the project.

This research would not have been possible without the support of everyone in the concrete

group. Thank you for your mentorship, friendship and support. Special thanks is given to

Professor Peterson, Olga, Reza, Soley and Mohammad.

I would especially like to thank my parents, Bijan and Zohreh and my sister Mana, for their

continuous motivation and unconditional support throughout this entire process.

.

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Table of Contents

Chapter 1 Introduction .................................................................................................................... 1

1.1 Background Information ..................................................................................................... 1

1.2 Scope and Objective ........................................................................................................... 1

Chapter 2 Literature Review ........................................................................................................... 3

2.1 Chloride-Induced Corrosion ............................................................................................... 3

2.2 Development of Epoxy Coating .......................................................................................... 4

2.2.1 Production of Epoxy-Coated Reinforcement .......................................................... 5

2.3 Factors Affecting Adhesion of Epoxy Coating to Steel ...................................................... 6

2.3.1 Moisture .................................................................................................................. 7

2.3.2 Temperature ............................................................................................................ 8

2.3.3 pH ............................................................................................................................ 8

2.3.4 Coating Damage .................................................................................................... 10

2.4 Cathodic Delamination of Organic Coatings ........................................................ 10

2.5 Field Performance ................................................................................................. 11

2.5.1 Florida ................................................................................................................... 11

2.5.2 Indiana ................................................................................................................... 12

2.5.3 Iowa ....................................................................................................................... 13

2.5.4 Kansas ................................................................................................................... 13

2.5.5 Minnesota .............................................................................................................. 14

2.5.6 New York & Pennsylvania ................................................................................... 14

2.5.7 Ontario .................................................................................................................. 15

2.5.8 Oregon ................................................................................................................... 16

2.5.9 Virginia ................................................................................................................. 16

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Chapter 3 Experimental Procedure ............................................................................................... 17

3.1 Materials ........................................................................................................................... 17

3.1.1 Cementitious Material ........................................................................................... 17

3.1.2 Aggregates ............................................................................................................ 18

3.1.3 Epoxy-Coated Reinforcement ............................................................................... 19

3.2 Mix Design ........................................................................................................................ 19

3.2.1 Casting .................................................................................................................. 19

3.2.2 Curing ................................................................................................................... 20

3.3 Test Procedure .................................................................................................................. 21

3.3.1 Quality Control of ECR Bars ................................................................................ 21

3.3.2 Sample Preparation ............................................................................................... 23

3.3.3 Immersion of ECR bars in high alkaline solution ................................................. 24

3.3.4 ECR bars Cast in Concrete ................................................................................... 25

3.3.5 Cathodic Disbondment Test .................................................................................. 28

3.3.6 Compressive Strength Test ................................................................................... 31

3.3.7 Rapid Chloride Permeability Test (RCPT) ........................................................... 31

3.3.8 Chemical Analysis of Epoxy Sample ................................................................... 31

3.3.9 Image Analysis of Epoxy Sample ......................................................................... 32

Chapter 4 Results and Discussion ................................................................................................. 34

4.1 Overview ........................................................................................................................... 34

4.2 Compression Strength Test Results .................................................................................. 34

4.3 Rapid Chloride Permeability Test Results ........................................................................ 35

4.3.1 Total Charge Passed .............................................................................................. 35

4.4 Quality Control ................................................................................................................. 35

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4.4.1 Holiday Detection ................................................................................................. 35

4.4.2 Coating Thickness Measurement .......................................................................... 36

4.5 Cathodic Disbondment Test Results ................................................................................. 37

4.5.1 Series A Cathodic Disbondment Test Results ...................................................... 37

4.5.2 Series B Cathodic Disbondment Test Results ...................................................... 39

4.5.3 Series C Cathodic Disbondment Test Results ...................................................... 39

4.5.4 Series E Cathodic Disbondment Test Results ....................................................... 42

4.5.5 Cathodic Disbondment Test Results for series A Cast in High-Alkali Cement Concrete ................................................................................................................ 42

4.5.6 Cathodic disbondment Test Results for Series D Cast in Low-Alkali Cement Concrete ................................................................................................................ 44

4.5.7 Variability Analysis .............................................................................................. 46

4.6 Chemical Analysis ............................................................................................................ 50

4.7 Image Analysis .................................................................................................................. 52

4.8 Comparison of Test Results .............................................................................................. 53

4.8.1 Comparison of Results for ECR Bars Immersed in NaOH Solution .................... 53

4.8.2 Series A Cast in High-alkali Cement vs. Series D Cast in Low-alkali Cement Concrete ................................................................................................................ 55

Chapter 5 Conclusions and Recommendations ............................................................................. 56

5.0 Conclusions and Recommendations ................................................................................. 56

5.1 Conclusions ....................................................................................................................... 56

5.1.1 Adhesion of Epoxy Coating to Steel under Alkaline Conditions ......................... 56

5.1.2 Cause of Disbondment of Epoxy Coating from Steel under Alkaline Conditions ............................................................................................................. 57

5.2 Recommendations ............................................................................................................. 57

Chapter 6 References .................................................................................................................... 59

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Appendices .................................................................................................................................... 65

Appendix A-Pore Solution pH Calculation .............................................................................. 65

Appendix B-Mix Design .......................................................................................................... 68

Appendix C-Compressive Strength Test Results ..................................................................... 70

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List of Tables

Table 2.1 ECR Field Performance Summary Chart ...................................................................... 13

Table 3.1 Estimated Pore Solution pH .......................................................................................... 17

Table 3.2 Cement Chemical Analysis ........................................................................................... 18

Table 3.3 Aggregate Properties ..................................................................................................... 18

Table 3.4 Epoxy Coated Reinforcement Information ................................................................... 19

Table 4.1 Variability analysis results for series A at 21 °C exposure........................................... 47

Table 4.2 Variability analysis results for series A at 38 °C exposure........................................... 47

Table 4.3 Variability analysis results for series C at 21 °C exposure ........................................... 48

Table 4.4 Variability analysis results for series C at 38 °C exposure ........................................... 48

Table 4.5 Variability analysis results for series A cast in high-alkali cement concrete ............... 49

Table 4.6 Variability analysis results for series D cast in low-alkali cement concrete ................ 49

Table 4.7 Series A vs. Series C test results ................................................................................... 53

Table 4.8 Series A cast in high-alkali cement vs. Series D cast in low-alkali cement ................. 55

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List of Figures

Figure 3.1 Concrete Consolidation ............................................................................................... 20

Figure 3.2 Concrete samples prior to curing ................................................................................. 20

Figure 3.4 Thickness gauge .......................................................................................................... 23

Figure 3.3 ECR bar holiday detector ............................................................................................ 23

Figure 3.5 ECR bars immersed in NaOH solution ....................................................................... 24

Figure 3.6 ECR bar end patched prior to Cathodic Disbondment test .......................................... 25

Figure 3.7 ECR concrete cylinders placed in solution after demolding ....................................... 26

Figure 3.8 Sealed containers placed in the 38⁰C room to accelerate testing ................................ 26

Figure 3.9 Extracting ECR bar for adhesion testing ..................................................................... 27

Figure 3.10 CD test setup .............................................................................................................. 29

Figure 3.11 X-cut through the coating for knife adhesion test ..................................................... 29

Figure 3.12 Delaminating the disbonded epoxy ........................................................................... 29

Figure 3.13 Epoxy samples saved in vials .................................................................................... 32

Figure 3.14 Epoxy pieces used for chemical analysis .................................................................. 32

Figure 3.15 FT-IR analysis ........................................................................................................... 33

Figure 4.1 Coating Thickness Measurement ................................................................................ 36

Figure 4.2 Series A disbondment vs. exposure period Cathodic Disbondment test results at 21

and 38 °C....................................................................................................................................... 37

x

Figure 4.3 Cathodic Disbondment results for series A exposed to pH 13, 13.5, and 14 for 7 d at

38 °C ............................................................................................................................................. 39

Figure 4.4 Series C disbondment vs. exposure period Cathodic Disbondment test results for 21 d

and 38 °C....................................................................................................................................... 40

Figure 4.5 Cathodic Disbondment results for series C exposed to pH 13, 13.5, and 14 for 14 d at

38 °C ............................................................................................................................................. 41

Figure 4.6 Cathodic Disbondment test results for series A cast in high-alkali cement concrete .. 43

Figure 4.7 Cathoidc Disbondment test results for series A cast in high-alkali cement concrete

exposed to concrete exposed to H2O, pH 13, and pH 14 for 90 d ................................................ 44

Figure 4.8 Cathodic Disbondment test results for series D cast in high-alkali cement concrete

exposed to H2O, pH 13, and pH 14 for 30 d ................................................................................ 45

Figure 4.9 Cathodic Disbondment test results for series D cast in low-alkali cement concrete ... 45

Figure 4.10 Rebar D & A cast in low- and high-alkali cement concrete for period of 90 d and

exposed to water ........................................................................................................................... 46

Figure 4.11 Chemical Analysis results for 90 days old epoxy samples ........................................ 51

Figure 4.12 (a) Untreated epoxy sample, (b) epoxy sample cast in high-alkali cement concrete

and exposed to water for 90 d, (c) epoxy sample cast in high-alkali cement concrete and exposed

to pH 13 for 90 d, and (d) epoxy sample cast in high-alkali cement concrete .............................. 52

Figure 4.13 ECR bars exposed to pH 14 for 14 d at 38 ⁰C ........................................................... 54

1

Chapter 1 Introduction

1.1 Background Information

Reinforced concrete is an integral component of our infrastructure. Concrete structures provide

good long-term performance and durability if designed and maintained properly. However, the

deterioration of concrete structures as a result of the corrosion of reinforcing steel is a major

concern, particularly in coastal structures and regions where deicing salts are used during winter

maintenance months.

To delay the rate of concrete deterioration and increase the service life of reinforced concrete

structures, researchers have recommended a series of corrosion prevention strategies. Of these,

the use of epoxy-coated reinforcement (ECR) was identified as an effective method and became

the primary corrosion protection technique in North America in the 1970s (Manning, 1996).

However, in the mid-1980s, the premature deterioration of concrete structures as a result of the

corrosion of epoxy-coated reinforcing steel was observed in Florida (Manning, 1996).

Nevertheless, ECR provided good corrosion protection in many other regions. As a result, there

is much controversy surrounding the field performance of ECR. Although it has been established

that ECR does not perform well in a moist environment (Weyers et al, 2006), little research has

been done on the influence of concrete pore solution alkalinity on the performance of ECR. It is

therefore necessary to examine the performance of ECR under different alkali conditions to

determine whether the alkalinity of the concrete pore solution can affect the epoxy coating

performance. This could help to explain the reason behind the mixed field performance exhibited

by ECR because different regions or jurisdictions use different types of cement, with varying

cement alkali content.

1.2 Scope and Objective

The objective of this research was to examine the adhesion of an epoxy coating to steel under

wet, alkaline conditions. Epoxy-coated reinforcing bars were obtained from both ECR suppliers

2

and contractors. The adhesion of the epoxy coating to the steel was measured using the Cathodic

Disbondment (CD) test devised by the Ministry of Transportation, Ontario (MTO) LS-420.

Prior to the adhesion testing, the samples were immersed in NaOH solutions with pH values of

13, 13.5, and 14 simulating range of pH values found in concrete pore solutions, to compare the

effect of the cement alkali content on the adhesion of the epoxy coating to the steel. The

exposure times for the samples ranged from 7 to 56 days.

To further investigate the relationship between the cement alkali content and the adhesion of the

coating to the steel substrate, the ECR bars were cast in concrete. Two different types of cement

were used, a high-alkali cement and a low-alkali cement, to provide a basis for comparison.

Chemical and image analyses of the epoxy samples were also performed to determine whether

there were any chemical or physical changes in the epoxy coating after exposure to the high

alkaline solutions.

3

Chapter 2 Literature Review

As previously stated, the purpose of this study was to examine the adhesion of epoxy coating to

steel reinforcing bars under high-alkali conditions. Although the corrosion of reinforcing steel

was not part of the study, an overview of the chloride-induced corrosion of the reinforcement is

provided to emphasize the motivation behind the development of epoxy coated steel. Following

the summary of chloride-induced corrosion, a brief history of the epoxy coating development is

provided. In addition, a review of factors that affect the adhesion of the epoxy coating to steel is

presented. This is followed by a summary of the field performance of epoxy coated steel from

different regions in the US and Ontario.

2.1 Chloride-Induced Corrosion

The durability of steel-reinforced concrete is a major concern for the majority of transportation

agencies. One major issue affecting its durability is the corrosion of reinforcing steel.

The corrosion of the reinforcing bars embedded in concrete is caused by either carbonation or

chloride ion ingress. However, the main cause of the reinforcing steel corrosion affecting

structures such as bridge, parking, and marine structures is chloride-induced corrosion

(Balakumaran et al., 2013). In North America, the use of deicing salts such as sodium chloride

during winter maintenance months is one of the principal causes of the chloride-induced

corrosion of bridge decks and parking structures (Balakumaran et al., 2013).

The chloride ions that initiate the corrosion may come from internal or external sources. The

internal sources usually consist of the chlorides cast in concrete by the addition of chloride set

accelerators such as calcium chloride, or as a result of the contamination of the mix materials

(Glass & Buenfeld, 2000). The external chloride sources usually diffuse into the concrete as a

result of the use of deicing salts or from the sea salt found in a marine environment (Glass &

Buenfeld, 2000).

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When the chlorides come from an external source, the quality of the concrete and its

microstructure play important roles in the time to corrosion of reinforcing steel (Glass &

Buenfeld, 2000). However, the reinforcing steel in concrete is protected from corrosion by a

passive film produced by the alkaline environment of the concrete (Böhni, 2005). The corrosion

of reinforcing steel begins when this passive layer becomes unstable when chloride ions at the

steel surface reach or exceed a threshold value (Böhni, 2005). This threshold value is generally

in the range of 0.4–1% by cement mass (Böhni, 2005), this value can also be expressed as a

chloride/hydroxyl ratio, where corrosion can take place when chloride concentration exceeds 0.6

of the hydroxyl concentration in the pore solution (Broomfield, 2007). That is when the passive

layer protecting the reinforcing steel breaks down. In addition, substantial amounts of moisture

and oxygen must also be present for the corrosion reaction to proceed (Böhni, 2005).

Corrosion of steel in concrete can occur as either macrocell or microcell. The corrosion caused

by the presence of chloride ions is localized, with corroded areas separated by areas of clean

passive reinforcing steel (Broomfield, 2007). This phenomenon is known as microcell formation

or pitting corrosion (Bertolini et al., 2004). While, macrocell corrosion is identified as uniform

corrosion caused by carbonation of concrete or by presence of very high chloride concentration

at the steel surface. The corrosion of the reinforcement is accompanied by a localized cross-

sectional loss and the build-up of corrosion products such as ferrous oxide (Broomfield, 2007).

These corrosion products occupy more space than the original steel. This results in the

development of tensile stresses on the surrounding concrete, which eventually leads to the

cracking and spalling of the concrete cover (Broomfield, 2007). The corrosion of reinforcing

steel in concrete can cause a reduction in the load-carrying capacity of a reinforced concrete

structure, which, in a severe case, can result in its collapse (Pradhan & Bhattacharjee, 2011).

2.2 Development of Epoxy Coating

In the late 1960s, many concrete bridge decks were found to deteriorate only a few years after

their construction (Manning, 1996). Transportation agencies had to invest significantly in the

repair of concrete bridge decks that were deteriorating as a result of the chloride-induced

corrosion of reinforcing steel (Glass & Buenfeld, 2000). To improve the service life of a

structure, it was recommended by Ministry of Transportation Ontario to:

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1) Increase the clear concrete cover depth (Manning, 1996),

2) Improve the overall concrete quality by decreasing the concrete permeability and

maximum allowable water-to-cement ratio (Manning, 1996), and

3) Use water proofing membranes (Manning, 1996).

However, the above improvements did not significantly reduce the rate of concrete deterioration,

and additional research was required to further improve the performance of concrete bridge

decks (Manning, 1996). The only corrosion protection measure available in the late 1960s was

the use of concrete sealers and waterproofing membranes (Manning, 1996).

In the early 1970s, the US Federal Highway Administration funded research on the use of

organic coatings as a method of corrosion protection (Weyers et al., 2006). The research

identified use of epoxy coating as an excellent and effective corrosion protection strategy. As a

result, epoxy-coated reinforcement (ECR) became the predominant corrosion protection

technique in North America (Hansson et al., 2000). ECR was considered an effective corrosion

prevention technique because the coating provided a physical barrier to chlorides at the concrete

rebar interface, which delayed corrosion (Weyers et al., 2006).

2.2.1 Production of Epoxy-Coated Reinforcement

The manufacturing of epoxy-coated reinforcement involves four major steps:

1) Surface Preparation:

The exterior of the steel is in contact with oxygen from the atmosphere, which results in

the formation of a layer consisting of dust and iron oxide (Lorenzo, 1997). The presence

of this layer does not provide a good surface for coating application. Thus, the surface of

the steel must be cleaned of any contaminants prior to coating application. This process is

performed by either sand blasting, grit blasting, or shot blasting, and leaves the

reinforcing steel with a rough profile and a nearly white finish (Lorenzo, 1997).

2) Heating

Once the reinforcement is clean, it must be heated in an induction oven, where the bar is

rotated as it passes through the oven (Lorenzo, 1997). The rebar must be heated

6

uniformly to a temperature that depends on the type of epoxy powder to be used

(Lorenzo, 1997). However, a temperature of 80°C is common for epoxy-coated steel

(Lorenzo, 1997).

3) Powder Application

The epoxy powder is sprayed onto the heated steel. The powder particles melt upon

contact with the reinforcing steel and enter their gel stage upon contact (Lorenzo, 1997).

4) Cooling

The final step is the cooling and curing of the epoxy-coated bar. Once the coating has

been applied, the hardening process starts, which is followed by a quenching process

using water misting (Lorenzo, 1997). Once the bar has cooled down, it is checked for

flaws or breaks in the coating, and to see whether it meets the coating-thickness

requirement (Lorenzo, 1997).

American Society for Testing and Materials (ASTM) and the Ontario Provincial Standard

(OPSS) Specification provide regulations for epoxy-coated reinforcement in ASTM A775 and

ASTM A934 for bendable and non-bendable coatings and in OPSS 1442.

2.3 Factors Affecting Adhesion of Epoxy Coating to Steel

The quality of the epoxy coating plays a major role in its corrosion protection in chloride-

contaminated concrete. To protect reinforcing steel from deleterious substances, the epoxy

coating relies on its adhesion to the steel substrate, and this adhesion influences the field

performance of ECR (Lorenzo, 1997). A good quality epoxy adheres well to the steel and

provides a physical barrier that prevents the arrival of chloride ions or other aggressive ions at

the coating/steel interface (Sprinkel et al., 2000). The adhesion of the epoxy coating to the steel

is provided by:

1) Chemical or adsorption adhesion

Chemical or adsorption adhesion has been described as follows: “High polarity exists in

the epoxy resin chain and the cured epoxy polymer due to the presence of aliphatic

7

hydroxyl and ether groups. The presence of metal oxides in the treated steel surface

causes a very strong electromagnetic attraction between both materials. The strength of

coating adhesion to steel is directly proportional to the hydroxyl group content of the

epoxy compound. The formation of chemical bonds between active hydrogen in the steel

surface and epoxide groups in the coating contributes to coating adhesion” (Vaca-Cortés

et al., 1998, p. 2).

2) Mechanical interlocking

Mechanical interlocking has been described as follows: “A roughened surface,

pretreatment of the steel surface, or the presence of porous oxides on the surface allow

prepolymeric epoxy resin and curing agents to penetrate into the crevices and pores

provided by the pretreatment. Upon polymerization, the coating becomes mechanically

embedded in the metal surface or the surface oxide structure. The cavities and pores

formed during surface preparation provide a larger surface area for electrochemical

reactions, further increasing the adhesive strength of the coating” (Vaca-Cortés et al.,

1998, p. 3).

However, the presence of certain conditions can affect the bond between the epoxy and the steel.

These conditions include:

1) Moisture,

2) Temperature,

3) pH, and

4) Coating damage

Each of these conditions and their influence on the adhesion of the epoxy coating are reviewed.

2.3.1 Moisture

Prolonged exposure of the steel to moisture can significantly affect the adhesion of the epoxy

coating to the steel (Sprinkel et al.,1997). Water can permeate through the coating and reach the

metal/coating interface, and the presence of water at this interfacial region can be responsible for

the epoxy coating losing its adhesion to the steel. Water can reach the metal/coating interface by

8

either diffusing through the coating or being transported to the metal/coating interface as a result

of the presence of discontinuities in the coating (Sprinkel et al.,1997). Thus, the presence of a

moist layer at the epoxy/steel interface results in the disbondment of the epoxy coating to the

steel. Consequently, the presence of a continuously wet environment can cause the disbondment

of the epoxy coating (Sprinkel et al.,1997).

Sprinkel et al. (2000) reported that epoxy-coating disbondment increases significantly at a

internal relative humidity greater than 60% and “For marine structures, the relative humidity of

the concrete is continuously greater than 80%.” (Sprinkel et al., 2000, p. 32). Therefore, a

concrete environment that contains adequate moisture for the corrosion of reinforcing steel to

take place also has sufficient moisture to cause the disbondment of the coating (Sprinkel et al.,

2000).

2.3.2 Temperature

The presence of a high temperature alone does not affect the adhesion of the epoxy coating to the

steel. High temperatures only affect the coating adhesion when moisture is present (Lorenzo,

1997). As stated earlier, the presence of moisture alone results in adhesion loss, but the presence

of a high temperature in a case where sufficient moisture is present will only accelerate the

disbondment process (Lorenzo, 1997). For example, Lorenzo (1997) stated that if an ECR

sample was placed in water at a high temperature and another sample was placed in an oven at

the same temperature, the sample that was immersed in water had a higher adhesion loss than the

one placed in the oven at the same temperature.

2.3.3 pH

As stated in the previous section, there has been much controversy surrounding the field

performance of epoxy-coated steel. It has been established that epoxy does not perform well in a

moist environment. It loses its adhesion, and the presence of high temperatures accelerate the

disbondment process. However, there has been limited research on the effects of highly alkaline

conditions on the adhesion of epoxy to steel. The type of cement used in the concrete may

contribute to the adhesion of the epoxy to the steel.

9

The type of cement used influences the chemical composition of the concrete pore solution.

According to Nixon and Page (1987, p. 1838), “the ultimate concentration of sodium and

potassium and hydroxyl ions in the pore solution of a cement paste depends on the content of

sodium and potassium in cement.” Thus, it is very important to determine the alkalinity of a pore

solution, which is described by a pH value. Based on studies by Diamond and Penko (1992), it is

concluded that there is a direct relationship between the alkali content of the cement and the

hydroxyl ion concentration of the pore fluid, where the hydroxyl ion concentration increases with

an increase in the alkali level of the cement. In addition, presence of supplementary cementing

materials reduces the alkalinity and the pH of concrete pore solution (Nixon & Page, 1987).

However, it is expected that there is a direct relationship between the hydroxyl ion concentration

in the concrete pore solution and the adhesion loss of epoxy coating from steel.

The factors affecting the adhesion of an epoxy coating to steel were examined by McHattie et al.

(1996), where the effects of the surface treatment, temperature, and pH value on the disbondment

of epoxy-coated steel were examined. To determine what role the pH value of the concrete plays

in the disbondment of the epoxy coating, samples were tested using the cathodic disbondment

test at three different pH values. The ECR was placed at pH 7, 11, and 13.5 while the test was in

progress. Tests were conducted on bendable and non-bendable coatings for 7 and 14 days. In

these experiments, a high level of disbondment was observed at pH 13.5, while pH 7 and 11

exhibited similar lower levels of disbondment. Darwin and Scantlebur (1999) also studied the

adhesion of an epoxy coating to steel under alkali conditions. Their samples were immersed in

KOH, NaOH and simulated pore solution at pH values of 12, 13, 13.5, and 14. Also some

samples were immersed in KOH, NaOH and LiOH solutions with addition of KCl, NaCl and

LiCl respectively to determine if the presence of chlorides contributes to adhesion loss. Their test

results showed that the rate of epoxy-coating delamination increased as the hydroxyl ion

concentration of the solution increased. However, samples immersed at pH 12 did not show any

disbondment after being exposed to that solution for a period of 6 months. It was suggested that

at pH values below 13, there is no delamination of the epoxy coating from the steel. As stated

earlier, the study by McHattie et al. (1996) examined low pH values to determine the effects of

alkali conditions on the adhesion of an epoxy. Concrete with a high-alkali cement usually has a

pH value approaching 14 and low-alkali cement is close to 13. Thus, testing ECR at pH 7, which

10

is only present after carbonation of the concrete has taken place, is not a good method for

determining the effect of the alkali content on the adhesion of the epoxy coating. To get a better

understanding of the cement alkali content and its relationship with adhesion loss in an epoxy

coating, additional research is necessary.

2.3.4 Coating Damage

The presence of flaws or any discontinuities in the coating contributes to a loss in the adhesion of

an epoxy coating to steel (Vaca-Cortés, 1998). It has been determined that an epoxy coating can

be damaged during the shipping and handling of the bars (Hansson et al., 2000). However, most

of the damage occurs during their installation, and during the placing and compacting of the

concrete (Hansson et al., 2000). This type of damage is usually not detected because it is hidden

within the concrete (Hansson et al., 2000).

The presence of deleterious substances such as chlorides and water can result in the disbondment

of the epoxy coating, because these can enter the coating/steel interface through the damage

present on the coating (Vaca-Cortés, 1998). This can result in the corrosion of reinforcing steel

because that region is no longer protected by the coating. The formation of corrosion products at

the defect sites will loosen the bond between the epoxy coating and the steel thus resulting in its

disbondment (Vaca-Cortés, 1998).

2.4 Cathodic Delamination of Organic Coatings

In addition to conditions discussed in Section 2.3, cathodic delamination is “an important

process, which promotes degradation of organic coatings” (Deflorian & Rossi, 2006, p. 1736).

Cathodic delmination is defined as “Areas of a metal surface covered with an organic coating

may become sufficiently cathodic to catalyze a cathodic reaction beneath the coating This

cathodic reaction may be purposely induced or it may be corrosion induced because of separation

of anodic and cathodic areas. The cathodic reaction or the products of the cathodic reaction,

adversely affect the bond between the coating and the substrate and coating separates from

metal” (Leidheiser et al., 1983, p. 20).

Cathodic disbondment of the coating from the substrate is a major concern. The disbondment is

caused by the local alkaline environment where oxygen reduction takes place, thus producing

11

hydroxyl ions (Deflorian & Rossi, 2006). Disbondment of organic coating from the substrate

caused by high alkaline conditions is caused by the following mechanisms:

1) Oxide reduction (Deflorian & Rossi, 2006):

The highly alkaline environment attacks the oxide interface at the steel surface. Thus

removing the oxide layer to which the coating is binding causing the detachment of the

coating from steel (Deflorian & Rossi, 2006).

2) Alkaline hydrolysis or Saponification (Deflorian & Rossi, 2006):

Disbondment caused by high pH values results in degradation of the epoxy polymer due

to alkaline hydrolysis also referred to as saponification (Watts, 1989). The hydroxyl ions

attack the polymer which results in chemical degradation of the coating.

3) Attack of the coating/ metal interface (Deflorian & Rossi, 2006):

The oxide reduction breaks the bond between the coating and steel and the high pH

attacks the polymer (Deflorian & Rossi, 2006). This results in degradation of the

coating/substrate interface results in interfacial weakening leading to delamintaiton of the

coating (Watts, 1989).

2.5 Field Performance

There have been many mixed reviews of the field performance of epoxy-coated steel. In some

regions, ECR provides good corrosion protection, while in others, it performs poorly. This

section provides a summary of the field performance of ECR from different states in the US and

in Ontario. A summary of field performance along with cement types specified by Department of

Transportation from each jurisdiction is provided in Table 2.1.

2.5.1 Florida

In 1977, the Florida Department of Transportation (FDOT) began using epoxy-coated

reinforcement for corrosion protection in its concrete bridge decks.

12

Epoxy-coated reinforcement was used in the construction of the bridges connecting the Florida

Keys (Sagüés & Lau, 2009). In 1993, in an investigation conducted on 20 bridges by the FDOT,

it was found that the structures exhibited early signs of corrosion only 5–12 years after their

construction (Sagüés & Lau, 2009). It was determined that the corrosion of the epoxy bars was

initiated by defects in the coating. Extensive disbondment of the ECR was observed in areas

exposed to salt water and in chloride-free concrete. Disbondment occurred as a result of

“concrete pore water penetrating under the coating defects” (Manning, 1996, p. 352). Once the

chloride threshold was reached, corrosion occurred “on the exposed metal at the imperfections in

the coating” (Manning, 1996, p. 352). The structures showing early corrosion were found to have

concrete with high permeability (Sagüés & Lau, 2009).

In 2009, Sagüés & Lau assessed 18 ECR marine bridges. Concrete structures with intermediate

concrete permeabilities exhibited ECR corrosion damage, while the severity of the ECR

corrosion was lower in locations with low permeability and thick concrete cover (Sagüés & Lau,

2009). However, extensive disbondment of the epoxy coating was observed throughout the

structures, even in locations where the concrete did not exhibit any sign of corrosion. In the late

1980s, the Florida Department of Transportation stopped specifying the use of epoxy-coated bars

in bridge structures and discontinued their use for marine bridge structures because they did not

provide adequate corrosion protection (Manning, 1996).

2.5.2 Indiana

In 1995, a field evaluation of six bridges with epoxy-coated reinforcement was conducted at the

request of the Indiana Department of Transportation to determine the in-service condition of

ECR in concrete bridge decks (Hasan & Ramirez, 1995). The selected bridges had been in

service for six to eight years. No evidence of corrosion or disbondment of the epoxy-coated steel

was observed upon an evaluation of the field data. Thus, it was concluded that epoxy-coated

steel provides good corrosion protection for bridge decks in the state of Indiana. No recent

studies on the performance of ECR in Indiana were found; therefore, it is believed that there are

no problems with it.

13

2.5.3 Iowa

A study done for the Iowa Department of Transportation examined the condition of the epoxy

coating in cracked and uncracked concrete locations with approximately 30 years of age (Ward-

Waller, 2005). From a laboratory analysis and field evaluation, it was determined that the

corrosion protection of ECR was lower in cracked concrete and decreased with age, but no

evidence of corrosion was observed in the rebars at the uncracked locations. Although the rebars

in the cracked locations showed signs of corrosion, no delamination or spalling of the concrete

was observed in those locations. In addition, the epoxy coating was found to be more brittle in

older structures, and the disbondment of the coating was more likely in the cracked concrete and

older structures (Ward-Waller, 2005). Overall, epoxy coating was found to provide good

corrosion protection in Iowa bridge decks.

Table 2.1 ECR Field Performance Summary Chart

Location Average Age of

Structures

Year of Study Cement Type Disbondment

Florida 24 years 2009 Low-alkali cement Yes

Indiana 18 years 1995 No spec on cement alkali but local cements are 0.40-0.68% Na2Oe (J. Olek, Personal

Communication, November 20, 2012) No

Iowa 30 years 2005 Max 0.6% Na2Oe (P. Taylor, Personal Communication, November 20, 2012)

Not reported

Kansas 10 years N/A Low alkali (0.35-0.45% Na2Oe) Not reported

Minnesota 32 years 2008 Max. 0.6% Na2Oe due to ASR Yes after 30

years of being in service

New York and Pennsylvania

12 years 1999

If ASR aggregates then

14

2.5.4 Kansas

Field and laboratory evaluations were performed on two bridge decks that had been in service for

10 years (Smith & Virmani, 1996). Based on the laboratory and field data, it was found that ECR

provides good corrosion protection in concrete bridge decks, and no disbondment of the coating

was observed at the time of the study. Considering the short time frame of this evaluation, a

more recent study would provide better information regarding the performance of ECR in

Kansas. However, even though a long term study on the field performance of epoxy coating in

Kansas could not be found, it is believed that obvious problems with epoxy-coated bars have not

been experienced.

2.5.5 Minnesota

In 2006, in an investigation sponsored by the Minnesota Department of Transportation, an in-

depth study of four epoxy-coated bridge decks was conducted (Fratta et al., 2008). These bridges

were constructed in 1973 and 1978. The same bridges were assessed in 1996, and this field

evaluation was just a follow up to determine the field performance of the epoxy within this

period. The purpose of the investigation was to determine the condition of the epoxy coating and

assess its field performance after almost 30 years of service through a series of field

measurements and laboratory tests. Based on the data obtained from the field, it was determined

that for three of the bridges that the epoxy coating was generally in very good condition and

exhibited only minor signs of corrosion activity. However, one of the bridges exhibited moderate

to severe signs of corrosion. Although only a minimal amount of delamination was observed in

all of the bridge decks, coating disbondment was observed in both corroded and non-corroded

rebars. In the condition assessment of the bridge decks conducted in 1996, the epoxy coating on

all four bridges had presented good adherence. Thus, it was suggested that the adhesion of the

coating had deteriorated over the subsequent ten years, and it could be concluded that the coating

loses its adherence as it ages (Fratta et al., 2008).

2.5.6 New York & Pennsylvania

In another study, 13 bridges in New York and 16 in Pennsylvania were investigated

(Sohanghpurwala & Scannall, 1999). These bridges were built with epoxy-coated reinforcing

steel in 1977–1993. The ages of the concrete bridge decks ranged between 12 and 28 years at the

15

time of the study. The purpose of the investigation was to determine the field performance of the

epoxy-coated reinforcement and assess its corrosion protection. Through data gathered from

laboratory and field evaluations, it was found that most of the bars collected from the bridge

decks showed no sign of corrosion, while some of the bars showed small amounts of corrosion.

Scannall and Sohanghpurwala (1999, p. 51) conducted a probability distribution analysis and

found that “more than 50% of epoxy coated rebars in bridge decks in Pennsylvania and New

York exhibit some degree of adhesion reduction within 6 to 10 years of placement in concrete.”

2.5.7 Ontario

The Ontario Ministry of Transportation conducted field performance tests of various bridge

decks built with epoxy-coated reinforcement in response to the poor performance of ECR in the

Florida Keys (Manning, 1996). The first assessment conducted by the MTO was in 1988. This

study concluded that epoxy coating steel significantly reduces corrosion activity in comparison

with black steel in the initial 9 years of the structure’s service life (Pianca et al., 2005). However,

its long-term performance was unknown. Another study was carried out by the MTO in 1992, to

further assess the performance of ECR in structures. This study examined 12 concrete bridge

structures with ages ranging from 1 to 14 years of service. Although the bridges were found to be

in good condition, coating disbondment was observed along the reinforcing steel in both

chloride-contaminated concrete and non-chloride-contaminated concrete (Schell et al., 2005).

The MTO conducted another field evaluation of the previously mentioned bridge structures.

These structures had been in service for 17–20 years at the time of the study (Schell et al., 2005).

The study concluded that some bars were corroding, and the concrete in some barrier walls in the

structures were delaminated. The coating was found to be intact in some locations but debonded

from the steel, while in one of the structures, it was found that the coating was deteriorated and

completely debonded from the steel (Schell et al., 2005). Based on these results, the MTO did

not recommend the use of ECR because it was not successful in preventing corrosion over the

long term (Schell et al., 2005). As of 2013 the MTO has discontinued use of epoxy-coated

reinforcing steel for future construction (T. Merlo & S. Schell, Personal Communication, March

7, 2013).

16

2.5.8 Oregon

In 1998 and 1989, the Oregon Department of Transportation conducted field evaluations of the

Yaquina Bay bridge located in Newport, Oregon (Griffith & Laylor, 1999). This structure had

been in service for 9 and 18 years, at the times of these studies. The 1998 and 1989 results for the

structure indicated that the coating adhesion was reduced in most locations. A significant amount

of debonding was observed in samples taken from the tidal zone, while samples from the dry

zone exhibited better adhesion. There was also evidence of corrosion in the reinforcement

located within the tidal zone. It should be noted that the severity of the reinforcement corrosion

observed in 1998 was similar to that found in the 1989 testing. The Oregon Department of

Transportation concluded that the use of epoxy-coated steel is not recommended for coastal

bridge structures and recommended frequent inspection of the existing structures built with

epoxy coated steel (Griffith & Laylor, 1999).

2.5.9 Virginia

The Virginia Department of Transportation performed a series of field evaluations to determine

the performance of epoxy-coated reinforcement (Weyers et al., 2006). In 1996, a field

evaluation was conducted on marine structures that were 7 and 6 years old at the time of the

investigation. This study concluded that the ECR was corroding and that the coating was

debonded from the steel (Weyers et al., 2006). This adhesion loss was believed to be occurring

even without the presence of chlorides and was classified as wet adhesion loss. Corrosion

products were observed under the coating in the majority of the reinforcement (Weyers et al.,

2006).

Another study was conducted on bridge decks exposed to deicing salts. The bridge decks studied

were 17 years old. Based on field evaluations and laboratory tests, it was found that 35 out of 36

bars had lost their adhesion, and 11 of the 36 ECR specimens exhibited corrosion under the

epoxy coating (Weyers et al., 2006). Overall, it was found that ECR was corroding in Virginia

bridge decks. Thus, the use of stainless steel was recommended for future construction (Weyers

et al., 2006).

17

Chapter 3 Experimental Procedure

3.1 Materials

Two concrete mixtures having the same water to cementitious ratio but different cement type were

tested to determine the influence of the cement alkali content on the adhesion of the epoxy coating to

steel. Further, five different types of epoxy-coated reinforcing steel were used in this investigation.

3.1.1 Cementitious Material

One of the two aforementioned mixtures contained CSA Type GU, general-use Portland cement, and

the other contained ASTM Type I PC-1 Alpena cement. The GU cement was from the Mississauga

cement plant of Holcim Ltd., and the PC-1 Alpena cement was from the Alpena, Michigan, plant of

Lafarge. In this paper, the GU cement is referred to as the high-alkali cement and the PC-1 Alpena

cement is referred to as the low-alkali cement. The chemical analysis of the cements are presented in

Table 3.2. In addition, the Na2O% equivalent and the estimated pH value of the pore solution is

calculated and presented in Table 3.1. The GU cement has a Na2O% equivalent of 1.01% while

Alpena cement has 0.56%, low alkali cement is considered to be below 0.6% sodium oxide

equivalent. For calculation of the estimated pH of pore solution refer to Appendix A.

Table 3.1 Estimated Pore Solution pH

Cement Type Na2Oe%

(a) Estimated pH of Pore solution

Mix 1 GU 1.01 13.9

Mix 2 PC1-Alpena 0.56 13.5

18

Table 3.2 Cement Chemical Analysis

3.1.2 Aggregates

The crushed dolomitic limestone coarse aggregates used were supplied by Holcim from the

Dufferin Aggregates Milton quarry. The physical properties of the aggregates are provided in

Table 3.3.

Table 3.3 Aggregate Properties

Property Dufferin Aggregate

Fineness Modulus 5.2

Absorption 1.79%

Relative Density (SSD) 2.73

Loose Bulk Density (SSD) [kg/m3] 1551

Rodded Bulk Density (SSD) [kg/m3) 1447

Parameter Holcim GU cement PC-1 Lafarge Alpena Cement

LOI (1000⁰C) % 2.24 2.2

SiO2 % 19.47 19.99 Al 2O3 % 5.12 4.75 Fe2O3 % 2.31 2.81 CaO % 62.03 63.20 MgO % 2.47 2.79 SO3 % 3.98 2.65 K2O % 1.16 0.54 Na2O % 0.25 0.21

TiO2 % 0.26 0.24

SrO % 0.09 0.06 P2O5 % 0.13 0.10 Cl % 0.04 -

ZnO % 0.01 0.06 Cr2O3 % 0.01 0.02 Mn2O3 % 0.08 0.17 Total % 99.64 99.79 Na2O % 1.01 0.56

19

3.1.3 Epoxy-Coated Reinforcement

Five different series of epoxy-coated reinforcements were used in this investigation. The 15M

reinforcing bars were acquired either directly from two different coating plants or from

contractors. Information regarding these ECR bars is available in Table 3.4.

Table 3.4 Epoxy Coated Reinforcement Information

Rebar Age Source Coating Plant Bar No.

Series A Brand New ECR manufacturer X 15 M

Series B Brand New ECR manufacturer Y 15 M

Series C 2 Years Contractor X 15 M

Series D Brand New Contractor X 15 M

Series E Brand New ECR manufacturer Y 15 M

3.2 Mix Design

3.2.1 Casting

Prior to casting, the moisture content of the sand and coarse aggregate were measured according

to ASTM C 70 and C 566, respectively. The concrete mix design was adjusted after the moisture

content of the sand and aggregates were measured.

The aggregate was washed prior to mixing to rinse off the layer of dust surrounding it. A glacial

sand from CBM’s Sunderland pit was used. The materials were mixed in a concrete mixer with a

capacity of 17 L. Sand, cement, and aggregates were added to the mixer and were mixed for 1

min after which water was added to the mix. The materials were mixed according to ASTM

C192/C 192 M–12a.

Post mixing, concrete made with both high- and low-alkali cements were placed in six 100 ×

200-mm molds and thirty six 50 × 100-mm plastic cylinder molds. However, prior to concrete

placement, the ECR bars were placed in the center of the 50 × 100-mm cylinder molds, and then

the molds were filled with two layers of concrete. A rod was used for consolidating the concrete

surrounding the ECR and the 100 × 200-mm concrete cylinders (Figure 3.1). The consolidation

was performed as specified in ASTM C 192/C 192 M–12a.

20

3.2.2 Curing

The concrete cylinders were capped as shown in Figure 3.2 and placed in a moist cure room at a

relative humidity of 100% and a temperature of 23⁰C. All the concrete cylinders were demolded

the next day. The 100 × 200-mm concrete cylinders were labeled and placed back in the moist

room until the required tests were conducted. The thirty six 50 × 100-mm concrete cylinders

containing the ECR bars were demolded and placed in three different pails and immersed at pH

13 (0.1 mol/L NaOH), pH 14 (1 mol/L NaOH), and distilled water (pH 7) and placed in a 38⁰C

room to accelerate the testing.

Figure 3.1 Concrete Consolidation

Figure 3.2 Concrete samples prior to curing

21

3.3 Test Procedure

As mentioned in Section 3.2.2, thirty six 50 × 100-mm concrete cylinders containing ECR bars

were cast to determine the influence of the cement alkali content on the adhesion of the epoxy

coating. The six 100 × 200-mm concrete cylinders were cast, and the rapid chloride permeability

test and the compressive strength test were performed at 56 days and 7 and 28 days, respectively.

In addition to the ECR bars cast in concrete, ECR bar series A,B,C and E were tested by placing

them in varying pH solutions at different temperatures to determine the influence of pH and

temperature on the rate of disbondment of the epoxy coating from steel. This section provides

information regarding the sample preparation and test procedures used for testing the adhesion of

the epoxy coating to steel and regarding the image and chemical analyses performed on the

epoxy samples.

3.3.1 Quality Control of ECR Bars

A total of 288 No. 15 ECR bars were tested in this experiment. The ECR bars were obtained

from two different ECR suppliers. Further information is available in Table 3.4. Upon receiving

the ECR bars from contractors and coating suppliers, the bars were labeled. The labels had a

letter designating the source the bars were received from. As stated earlier, The ECR bars used in

this project were obtained directly from the ECR manufacturer as well as from contractors using

ECR bars in their projects. The purpose was to determine whether there were any differences

between the types of ECR bars supplied to the contractors and the ones supplied to University of

Toronto for adhesion testing.

After labeling, it was ensured that the ECR bars complied with the ASTM A775/A775M-07b

and OPSS 1442 standards.

3.3.1.1 Holiday Detection

Prior to adhesion testing, Electrometer 269 holiday detector was used to ensure that there were

no holidays present on the surface of the ECR bars (Figure 3.3). A holiday detector consists of a

power source, inspection electrode and a ground wire. The ground wire is used to connect the

coated bar to a 67.5 V power source. The inspection electrode is a sponge which is connected to

the positive side of the circuit. The sponge must be dampened with water prior to use. The wet

22

sponge is moved along the surface of the coating in order to penetrate defects and make a

conductive path to the substrate (Lorenzo, 1997). Presence of discontinuities on the coating

results in current flow which activates the detector. The detector then produces an audible signal

to notify presence of a holiday on the surface of the coating. However, prior to holiday detection

test all ECR bars were examined to determine if there were any visible imperfections on the

surface of the coating. Once it was determined that the bars were in a good shape, the holiday

detector was used. Any signal from the holiday detector was checked carefully to identify the

location of the defects.

According to ASTM A775/A775M-07b all ECR bars must be checked for coating continuity by

using a holiday detector prior to shipment. On average there should not be more than 3 holidays

per meter on a coated steel reinforcing bar.

3.3.1.2 Coating Thickness

Once it was determined that a uniform coating was present on the reinforcing steel, the thickness

of the epoxy coating was measured using Mikrotest IV automatic thickness gauge to ensure that

it met the ASTM A775/A775M-07b requirements (Figure 3.4). Prior to testing the gauge was

inspected carefully to ensure that the tip of the magnet was clean and free of dust or any other

contaminants which may have transferred on to the magnet from prior measurements. To verify

that the thickness gauge was operating properly, a reference sample with a known coating

thickness was first used.

The Mikrotest thickness gauge operates on magnetic principal. The thickness of the coating is

proportional to the magnetic attraction between the magnet and the steel substrate (Lorenzo,

1997). Once the magnet is pulled away from the surface, the coating thickness at that particular

point can be read from the movable dial. The thickness of the ECR bars were measured at six

different points between deformations on each side. The average thickness of each ECR bar was

calculated and compared with the ASTM A775/A775M-07b requirement. ASTM mandates a

thickness of 175–300 µm (7–12 mils) for reinforcing steel Nos. 10–16.

23

Figure 3.4 Thickness gauge

3.3.2 Sample Preparation

Once the quality control of the received ECR bars was completed, samples were prepared for the

cathodic disbondment test. The ECR bars were prepared according to the Ministry of

Transportation, Ontario LS-420 test method. A hole with a diameter of 3 mm was drilled

between the deformations exposing an area of steel thus creating an intentional defect for the

Figure 3.3 ECR bar holiday detector

24

cathodic disbondment process to take place. Another hole with a diameter of 3 mm was drilled at

one end of the reinforcing steel to attach a screw and provide a ground connection. While the

other end of the bar was sealed with a rubber coating.

3.3.3 Immersion of ECR bars in high alkaline solution

Post sample preparation, the samples were placed in various pH solutions. A total of 72 bars

from each series A, B, C, and D were tested. From these 72 samples, 12 bars were placed in an

NaOH solution with pH 13, 12 in an NaOH solution with pH 13.5, and 12 in an NaOH solution

with pH 14 at 21⁰C, whereas the remaining were placed in the same solutions, but at 38⁰C

(Figure 3.5). The ECR bars were placed in the same solutions but at two different temperatures

in order to determine the influence of temperature on the disbondment of the epoxy coating from

steel.

Figure 3.5 ECR bars immersed in NaOH solution

25

In order to maintain the desired pH level of the solutions, a pH probe was used for measuring the

pH of each solution once a week and the pH was adjusted accordingly. However, this was not

done on all samples initially. This is further explained in Chapter 4.

3.3.3.1 Preparation of samples after exposure period

Once the exposure period was completed, the samples were removed from the solutions and

dried. The exposed end of the ECR bar closest to the defect was sealed with rubber coating in

order to ensure that there was no steel area exposed other than the intentional defect created

during sample preparation (Figure 3.6). The ECR bar was dried at room temperature for a

minimum of 4 h prior to conducting the cathodic disbondment test.

3.3.4 ECR bars Cast in Concrete

The reinforcing bars cast in concrete with high- and low-alkali cements were from series A and

series D, respectively. After demolding, the samples were placed in pails and sealed at NaOH

with pH 13, pH 14, and distilled water at 38⁰C in order to accelerate the testing (Figure 3.7 and

3.8). In this part of the experiment, distilled water was used as one of the solutions for

determining whether there was a greater rate of disbondment in a neutral pH moist environment

or under highly alkaline conditions. Having ECR bars cast in concrete with both high- and low-

alkali cements that exhibited similar properties and were exposed to the same conditions would

provide a good basis of comparison for the determination of the influence of the cement alkali

content on the adhesion of the epoxy coating to steel.

Figure 3.6 ECR bar end patched prior to Cathodic Disbondment test

26

Figure 3.7 ECR concrete cylinders placed in solution after

demolding

Figure 3.8 Sealed containers placed in the 38⁰C room to

accelerate testing

27

3.3.4.1 Preparation of samples after exposure period

When the concrete samples reached the required testing time, the concrete was split open using

CARVER hydraulic unit. The concrete cylinder was placed on a steel block between the moving

bolster and top bolster. The hydraulic unit was then pumped to build enough force to split open

the concrete as shown in Figure 3.9 in order to extract the ECR bar. Once the ECR bar was

extracted, it was cleaned and checked visually for coating uniformity. The exposed end of the

ECR bar was sealed as described in Section 3.3.3.1.

Figure 3.9 Extracting ECR bar for adhesion testing

28

3.3.5 Cathodic Disbondment Test

The adhesion of the epoxy coating to steel was tested according to the Ministry of Transportation

LS-420 and ASTM A775 Cathodic Disbondment (CD) test for epoxy-coated reinforcing bars.

ASTM G8 also provides the cathodic disbondment test procedure for pipeline coatings. Both

tests follow similar procedures.

A 16 unit Cathodic Disbondment equipment with a supply voltage of 120 V from Paintronic

systems was used. A totoal of 9 ECR bars at a time were tested for CD test. The prepared ECR

bar was placed in an 800 ml beaker with its sealed end facing the bottom of the beaker. A 3%

NaCl solution was added until 100mm of the bar length was submerged. A platinum cover anode

was then placed in the electrolyte solution and it was connected to a positive terminal while the

ECR bar was connected to a negative terminal as shown in Figure 3.10. Since the anode was

platinum covered its end was sealed with rubber coating to prevent damage to the copper core.

The calomel reference electrode was then inserted in the 3% NaCl solution and the power supply

was turned on. The power supply was adjusted until the polarized potential of steel stabilized at

1.5 ± 0.2 V with respect to calomel electrode. A thermometer was placed in the electrolyte to

monitor the temperature. The bar remained in the 3%NaCl solution for a period of 7 days at 23 ±

2 ⁰C. The voltage was adjusted every 2 hours during the first 8 hours and twice every 24 hours

thereafter.

At the end of the test, a knife adhesion test was performed after removing the sample from the

solution. The ECR bar was dried for 1 hour and an “X” was cut through the defect as shown in

Figure 3.11. A utility knife was used for delaminating the disbonded coating as shown in Figure

3.12. The average diameter of the exposed steel surrounding the defect was measured in order to

determine the amount of disbondment that has occurred (Figure 3.13). A total of 3 ECR bars

were tested per exposure period and the average result of the 3 ECR bars tested was used to

report the level of disbondment of the bars.

29

Figure 3.10 CD test setup

Figure 3.11 X-cut through the coating for knife adhesion test

Figure 3.12 Delaminating the disbonded epoxy

30

The principle of this test is that “water, oxygen, and other ions are present at the steel surface

either by permeating through the coating or moving along the coating/steel interface via a defect,

and an electrochemical cell with anode and cathode is established. When cathodic polarization is

applied to a corroding metallic surface, the surplus or excess of electrons provided reduces the

rate of the anodic reaction and increases the rate of the cathodic reaction” (Vaca-Cortés et al.,

1998, p. 9).thus “generating hydrogen gas and hydroxide group as a result of water reduction at

the defect site. The hydrogen gas escapes as bubbles while the hydroxide ions remain in the

solution.” (Raghunathan, 1996, p. 20) The hydrogen gas escaping in the form of bubbles from

the defect site creates “a lifting force as it tries to escape from underneath the coating, which

exposes new regions of steel to cathodic disbondment effect” (Raghunathan, 1996, p. 19).

Figure 3.13 Disbondment diameter measurement

31

This test is reported to provide a good prediction with respect to the performance of ECR bars in

concrete (McHattie et al., 1996). This test measures the ability of the epoxy coating to resist

disbondment.

3.3.6 Compressive Strength Test

Compressive strength tests were performed at 7 and 28 days. Two concrete cylinders per mix

were tested. The test was done in accordance to ASTM C39-05.

3.3.7 Rapid Chloride Permeability Test (RCPT)

The RCPT test was done according to the ASTM C1202 standard. Two concrete cylinders per

mix were tested for RCPT at 56 days. The 100x200 mm concrete cylinders were saw cut into

100x50 mm discs. Therefore a total of 4 concrete discs were tested per mix.

3.3.8 Chemical Analysis of Epoxy Sample A Perkin Elmer Spectrum BX Fourier Transform Infrared (FTIR) spectrometer was used for

determining whether any chemical changes in the coating occurred upon exposure to moisture

and highly alkaline conditions. The samples did not require any preparation as an Attenuated

Total Reflectance (ATR) accessory was available for the analysis which allows samples to be

examined in their original state without any preparation. The delaminated epoxy removed from

the ECR bars cast in high alkali cement concrete and exposed to pH 13, 14 and distilled water for

a period of 90 days, was labeled and placed in vials (Figures 3.13 & 3.14). Each epoxy sample

was placed on the ATR top plate using tweezers. Once the sample was in its desired location, the

pressure arm was positioned over the sample. Thus, locking the sample in a precise position

(Figure 3.15). The instrument was connected to the computer which utilized the Spectrum FTIR

software which “records the interaction of infrared radiation (light) with experimental samples,

measuring the frequencies at which the sample absorbs the radiation and the intensities of the

absorptions. Determining these frequencies allows identification of the sample’s chemical

makeup, since chemical functional groups are known to absorb infrared radiation at specific

frequencies.” (Bayer & Zamanzadeh, 2004, p. 3).

32

3.3.9 Image Analysis of Epoxy Sample

The same epoxy samples used for the chemical analysis were used for the image analysis. The

epoxy pieces were removed from the vials using tweezers. The samples were placed on a slide

and covered with a cover slip. Both sides of the untreated and treated samples were observed

using an optical microscope under 40× magnification for comparison purposes.

Figure 3.13 Epoxy samples saved in vials

Figure 3.14 Epoxy pieces used for chemical analysis

33

Figure 3.15 FT-IR analysis

34

Chapter 4 Results and Discussion

4.1 Overview

As described in Chapter 3, a cathodic disbondment (CD) test was performed on a total of 288

ECR bars. The goal was to determine the influence of moisture, temperature, and the presence of

alkaline conditions on the performance of an epoxy coating on steel. As stated in Chapter 2, it

has been established that the presence of moisture, along with high temperature, accelerates

coating disbondment. However, very few studies have examined the influence of high-alkaline

conditions on the performance of an epoxy coating. This chapter provides the results of the

experiments described in Chapter 3.

4.2 Compression Strength Test Results

As described in Chapter 2, a total of six Ø100 × 200 mm concrete cylinders were cast per mix.

Four of these were used for a compression strength test. Two concrete cylinders were tested at 7

and 28 d to compare the compressive strengths obtained from each mixture. The compression

test results are shown in Table 4.1, which show the values of the average compressive strengths

of the two concrete cylinders tested per age test and provide an indication of the quality of the

concrete.

Table 4.1 Compressive Strength Test Results

Compressive Strength

(MPa) Mix No. Mix Properties 7 Days 28 Days

Mix 1 W/C = 0.5, High-Alkali Cement 29.28 34.2

Mix 2 W/C = 0.5, Low-Alkali Cement 27.92 33.8

Based on the compressive test results, it can be seen that Mix 1 and Mix 2 had similar

compressive strengths. Because the ECR bars were cast into two different mixtures, and the

35

purpose of the study was to determine the influence of the cement alkali content on the adhesion

of epoxy coatings on steel, it was important for the concrete mixtures to have similar properties

in order to provide a good basis for comparison.

4.3 Rapid Chloride Permeability Test Results

4.3.1 Total Charge Passed

The procedure for the rapid chloride permeability test (RCPT) was described in Chapter 3. The

total charges passing through the specimens are presented in Table 4.2, which shows the

averages for the concrete discs cut from the Ø100 mm × 200 mm concrete cylinders, as

described in Chapter 3.

Table 4.2 Rapid Chloride Permeability Test Results

Charge Passed (Coulombs)

Mix No. 56 Days Mix 1 (high-alkali cement) 2423 Mix 2 (low-alkali cement) 2230

Based on the ASTM C1202 guide for the interpretation of the results, the charges passed for Mix

1 and Mix 2 represent moderate chloride ion penetrability values. The RCPT test was performed

for each mix to ensure that they had similar permeability values. This was important because all

of the ECR samples from the aforementioned mixes were placed in pH 13 and pH 14 NaOH

solutions and in water, and the ingress of these ions may affect the adhesion of the epoxy coating

on steel.

4.4 Quality Control

4.4.1 Holiday Detection

The LS420 mandates ECR bars used for CD test are free of any coating discontinuity. Therefore,

all ECR bars were carefully checked for holidays as described previously. All ECR bars were in

a good condition as they were received directly from the manufacturer and were recently coated,

except series C and D bars, which were received directly from contractors. Coating discontinuity

of some of these bars was noticed around steel bar deformations. Areas with visible defects were

sealed with epoxy; the bars were dried for a minimum of 3 hours and were checked for defects.

36

Once, it was determined that no coating discontinuity was present the bars were prepared for CD

test.

4.4.2 Coating Thickness Measurement

The average coating thickness values for each bar is shown in Figure 4.1, which are the average

values for six locations along the bar on each side, as explained in Chapter 3. The ASTM

thickness limits are also shown.

As shown in Figure 4.1, the coating thicknesses of all of the ECR bars are within the ASTM

A775/A775M-07 range from 175– to 300 µm. The lower coating thickness limit is “set due to

durability and corrosion performance concerns” (Lorenzo, 1997, p. 48), while the upper limit is

“set to maintain a certain mechanical anchorage capacity in the steel bar” (Lorenzo, 1997, p. 48).

Figure 4.1 Coating Thickness Measurement

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Series A- CD Test Results

Series A-pH 13 T=38°C Series A-pH 13.5 T=38°C Series A-pH 14 T=38°C

Series A-pH 13 T=21°C Series A- pH 13.5 T=21°C Series A- pH 14 T=21°C

4.5 Cathodic Disbondment Test Results

4.5.1 Series A Cathodic Disbondment Test Results

Figure 4.2 provides the CD test results for Series A bars at 21 and 38 °C.

Figure 4.2 Series A disbondment vs. exposure period Cathodic Disbondment test results at

21 and 38 °C

As stated in Chapter 3, a total of three ECR bars were tested per exposure period after treatment

in solutions at pH 13, 13.5, and 14. The disbondment values presented in Figure 4.2 are the

average disbondment values for these three ECR bars. The pH of the NaOH solutions were

monitored once a week using a pH probe from the beginning in order to maintain the desired pH

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values. The pH of the solutions did not change in the first 14 days. However, NaOH pH 14 and

pH 13.5 started to drop to pH 13 after 28 days, therefore the solutions were monitored closley in

order to maintain the desired pH value.

The disbondment value at the 0 days of exposure period is that of the base case ECR sample. The

base case is the disbondment value for the untreated (no exposure) ECR bar. The disbondment

diameter of the untreated sample was recorded as 3.5 mm, which is below the 4-mm acceptance

requirement stated in OPSS 1442. The disbondment for the untreated sample provided a basis of

comparison to determine the influence of high-alkaline conditions and temperature on the

disbondment of the epoxy coating from the steel. As shown in Figure 4.2, there was higher

disbondment at pH 14.

The presence of a high temperature also resulted in a higher rate of disbondment. For example,

as shown in Figure 4.2, when exposed to pH 13, 13.5, and 14 at 21 °C, series A bars had a lower

disbondment than the same bars exposed to the same solutions but at 38 °C. For example, the

average disbondment recorded for series A bars at 38 °C after 7 d of exposure to pH 14 was 16

mm, while the value recorded for series A at 21 °C exposed to the same solution and for the

same duration was 12.5 mm. Therefore, the presence of high temperature accelerated the

disbondment process.

In general, the most significant change in the adhesion of the epoxy coating occurred during the

first 7 d of exposure. The average disbondment increased from 3.5 mm for the untreated sample

to 16 mm after exposure to pH 14 at 38 °C after 7 days, 14.5 mm for pH 13.5 at 38 °C, and 14

mm for pH 13 at 38 °C after 7 days of exposure. The average disbondment increased at a steady

rate from 7 d to 28 d for rebar A at 38 °C; there was little or no change when the duration of

exposure was increased from 28 d to 56 d. Rebar A exposed to pH 14 at 21 °C followed the same

trend as ECR bars at 38 °C, with the greatest change in disbondment occurring in the first 7 d of

exposure and then continuing to increase at a steady rate from 7 to 28 d. However, on increasing

the exposure period from 28 d to 56 d at pH 14, the average disbondment increased from 16 mm

to 19 mm. Unlike the ECR bars previously mentioned, the average disbondment for rebar A

exposed to pH 13 and 13.5 at 21 °C increased significantly during the first 28 d of exposure; the

change then slowed down when the exposure period was increased to 56 d.

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Figure 4.3 Cathodic Disbondment results for series A exposed to pH 13, 13.5, and 14 for 7 d

at 38 °C

4.5.2 Series B Cathodic Disbondment Test Results

Series B bars were obtained directly from ECR bar supplier Y. No disbondment was observed in

series B. Although these ECR bars were exposed to the same solutions and temperatures as series

A, no adhesion loss was observed after conducting the CD test, even after exposing the ECR bar

to pH 14 at 38 °C for 56 d. It was initially assumed that a longer exposure period might be

required for the coating to lose its adhesion. Thus, the sample was exposed to a pH 14 solution

for 112 d, and the CD test was conducted on three ECR bars. Again, no disbondment was

observed.

4.5.3 Series C Cathodic Disbondment Test Results

Series C bars were obtained from a contractor. At the time of investigation, these ECR bars were

approximately 2 years old. The bars were originally obtained from supplier X, and the contractor

intended to use them in a bridge deck construction project. The ECR bars used in this experiment

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Series C- CD Test Results

Series C-pH 13 T=38°C Series C- pH 13.5 T=38°C Series C- pH 14 T=38°C

Series C- pH 13 T=21°C Series C- pH 13.5 T=21°C Series C-pH 14 T=21°C

were the remainder of the ECR bars used for the bridge deck construction. Figure 4.4 provides

the CD test results for series C at 21 and 38 °C.

Figure 4.4 Series C disbondment vs. exposure period Cathodic Disbondment test results for

21 d and 38 °C

As shown in Figure 4.4, the lowest level of disbondment was observed in series C exposed to pH

13 at 21 °C. In addition, the average disbondment diameter was highest for series C exposed to

pH 14 at 38 °C. The average disbondment for the untreated ECR bar was 9.5 mm, which was 5.5

mm above the allowable disbondment value stated by OPSS 1442. As previously mentioned,

series C bars were obtained through a contractor, though they originally came from the same

41

supplier as series A. However, these bars were 2 years old, and as discussed in Chapter 2 it is

known that the adhesion of an epoxy coating degrades as it ages, which could explain the higher

average disbondment of the untreated sample.

As seen in Figure 4.4, series C exposed to pH 13 at 38°C had a lower average rate of

disbondment in its first 7 d of exposure. However, the average disbondment for these ECR bars

was lower than series C bars exposed to pH 13.5 at 38°C in the first 7 d of exposure. The most

significant difference was observed at 28 d of exposure. The average disbondment for pH 13 at

38°C was 17.5 mm, while at pH 13.5 and 38°C, it was 15.8 mm, corresponding to a difference of

1.75 mm. However, at 56 d, their disbondment values became similar. Please note that the pH of

this particular solution was not initially monitored. Thus, after obtaining the aforementioned

results, a pH probe was used to measure the pH value of all solutions, and it was found that the

pH level had dropped from 13.5 to 13.0 for this particular solution. As a result, the pH levels of

all solutions were monitored more closely and adjusted accordingly, as stated in Section 3.3.3.

Overall, there was a higher level of disbondment at higher pH values (Figure 4.5) and upon

exposure to higher temperatures.

Figure 4.5 Cathodic Disbondment results for series C exposed to pH 13, 13.5, and

14 for 14 d at 38 °C

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4.5.4 Series E Cathodic Disbondment Test Results

Series E bars were obtained directly from supplier Y to further investigate the disbondment of

ECR bars from this particular manufacturer. As stated earlier, no disbondment was observed in

series B. However, a significant level of disbondment was observed in ECR bars obtained from

supplier X. Both ECR suppliers employ the same coating procedure and must conform to the

ASTM A775 standard. Therefore, it was of particular interest to investigate the reason why no

disbondment was observed in series B. Thus, series E was acquired from the same supplier to

determine if any disbondment would be observed. Series E was exposed to the same conditions

as series A, B, and C. However, after conducting the CD test, similar to series B, no disbondment

was observed after 28 d of exposure to NaOH solutions at pH 13, 13.5, and 14. The test was

discontinued for series E bars, because it was ant