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
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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
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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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0
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2
3
4
5
6
7
8
9
10
11
12
13
14
15
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18
19
20
21
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0 7 14 21 28 35 42 49 56
Dis
bo
nd
em
en
t (m
m)
Treatment Period (days)
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
38
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
40
0
1
2
3
4
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7
8
9
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0 7 14 21 28 35 42 49 56
Dis
bo
nd
em
en
t (m
m)
Treatment Period (days)
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