Thesis

The author holds the copyright on this thesis but permission has been granted for QUT Staff to
photocopy this thesis without reference to the author.
AN INVESTIGATION INTO NANO-TECHNIQUES AND
THEIR ROLE IN THE PREDICTION OF THE
DEGRADATION AND REDEVELOPMENT OF IRON
OXIDE LAYERS WITH RESPECT TO TEMPERATURE
IN CORRODED STEEL BARS IN MARINE EXPOSED
CONCRETE
Taylah M. Gesch
Student No. 09156119
A thesis submitted in partial
fulfilment of the requirements of
the subject BEB801 Project 1 in the
Bachelor of Engineering Degree.
School of Civil Engineering & Built Environment,
Queensland University of Technology,
June 2017

BEB801 Queensland University of Technology Project 1
i
ABSTRACT
This paper discusses the use of Nano-techniques in the investigation of the passive oxide layer around
the steel reinforcement bars inside marine concrete, especially in harsh environments such as
temperature, humidity and different concrete pore solutions. It was found that the key durability
concern in marine concrete is the chloride attack on the steel reinforcement, and humidity and
temperature was found to be a contributing factor towards this degradation mechanism. After
discovering this, it was found that an investigation can be completed into the behaviour of corrosion
on reinforcement through the use of Nano-techniques. Furthermore, an unusual phenomenon was
discovered through the research, where corrosion of the reinforcement seemed to decrease after a
specific temperature. This sparked questions andled to the project proposal. Through further research
into past laboratory investigations, it was determined that temperature, humidity and the concrete
pore solution have substantial effects on the corrosion on reinforcement when subjected to chloride
ions. To discover whether the project proposal can be justified, an experiment was proposed where
three different types of high temperatures and a humidity of 85% with two different types of concrete
pore solutions are tested on N24 reinforcement bar specimens. These specimens are subjected to
different cycles of weathering to simulate real world conditions, and are then tested through the use
of Raman Spectroscopy and XRD. Conclusions could not be made regarding the results as this was a
proposed testing method; however, possible conclusions were made with knowledge linking to the
past investigation results.
Keywords
Durability
Marine Concrete
Chloride Attack
Chloride Ingress
Chloride Ions
Temperature
Humidity
Concrete Pore Solution
Nano-technology
ACKNOWLEDGEMENTS
I would like to thank my lecturer and mentor, Dr. Xuemei Liu, for supporting me through my
endeavours and tangents. She kept me on the right path and allowed me to investigate topics I was
very much interested in investigating. Without her direction and mentoring I would have produced a
paper half the quality, so I thank her very much. I also thank my university peers who discussed their
research papers with me and supported me through my research. Lastly, I would like to thank
Queensland University of Technology for providing me with the resources required to complete my
paper.

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TABLE OF CONTENTS
Abstract ............................................................................................................................................. i
Keywords........................................................................................................................................ i
Acknowledgements............................................................................................................................ i
List of Tables .................................................................................................................................... iv
List of Figures .................................................................................................................................... v
List of Symbols .................................................................................................................................vii
Chapter 1: Introduction ..................................................................................................................... 1
1.1 Purpose and Objectives...................................................................................................... 1
1.2 Need for Research.............................................................................................................. 1
1.3 Scope................................................................................................................................. 2
1.4 Organisation of Thesis........................................................................................................ 3
Chapter 2: Background Information................................................................................................... 4
2.1 Durability of Concrete ........................................................................................................ 4
2.2 Destructive Mechanisms on Concrete in Marine Environments.......................................... 5
2.3 Chloride Attack on Reinforced Concrete............................................................................. 5
2.3.1 Chloride Sources......................................................................................................... 5
2.3.2 Corrosion Process....................................................................................................... 6
2.3.3 Chloride Ingress.......................................................................................................... 7
2.4 Humidity and Temperature ................................................................................................ 7
2.4.1 Cracking and Spalling due to Temperature.................................................................. 7
2.4.2 Relative Humidity..................................................................................................... 11
2.5 Service Life....................................................................................................................... 14
2.6 Summary.......................................................................................................................... 15
Chapter 3: Literature Review........................................................................................................... 17
3.1.1 Fe-SEM..................................................................................................................... 17
3.1.2 Raman Spectroscopy ................................................................................................ 22
3.1.3 XRD .......................................................................................................................... 24
3.2 Passive Layer.................................................................................................................... 28
3.2.1 Temperature Effects on the Passive Layer................................................................. 30
3.3 Past Investigation............................................................................................................. 31
3.3.1 Investigation A – (R. R. Hussain, Alhozaimy, Negheimish, & Zain, N.A.) ..................... 31
3.3.2 Investigation B – (Singh & Singh, 2012)..................................................................... 38
3.3.3 Investigation C – (S. E. Hussain & Rasheeduzzafar, 1993) .......................................... 48
3.3.4 Investigation D – (Alhozaimy et al., 2014) ................................................................. 52
Chapter 4: Testing Proposal............................................................................................................. 57

iii
4.1 Testing Introduction......................................................................................................... 57
4.2 Variables.......................................................................................................................... 57
4.3 Approximate Method....................................................................................................... 57
4.4 Results ............................................................................................................................. 58
4.5 Conclusion ....................................................................................................................... 59
Reference List.................................................................................................................................. 60

iv
LIST OF TABLES
Table 1: Average Composition of seawater (Holland, 2012) ............................................................... 5
Table 2: Comparison of Vacuum Emission Sources (Nessler, 2017) .................................................. 18
Table 3: Description of Raman Scattering Photon Frequencies (Instruments, 2017) ......................... 22
Table 4: Usual Features in the Raman Spectra (extracted from Michigan (2006))............................. 24
Table 5: Strengths and Limitations of XRD (Dutrow & Clark, 2017)................................................... 27
Table 6: Chemical Reactions to Form Passive Layer (Alhozaimy et al., 2014) .................................... 29
Table 7:Materials and Material Properties used in Investigation...................................................... 32
Table 8: Chemical Compositions and their Names from the Raman Spectroscopy Results................ 41
Table 9: Chemical Composition of Concrete used for Investigation.................................................. 52

v
LIST OF FIGURES
Figure 1: Scope of Investigation......................................................................................................... 3
Figure 2: Concrete Column Subjected to the Three Categories Within a Marine Environment (Mehta,
1991)................................................................................................................................................. 4
Figure 3: Effect of Climatic Environment on Reinforced Concrete in the Marine Environment (Mehta,
1991)................................................................................................................................................. 8
Figure 4: Influence of different tidal and climatic zones on the performance of marine structures
(Mehta, 1991) ................................................................................................................................... 9
Figure 5: Repair Strategy I (Val & Stewart, 2003).............................................................................. 10
Figure 6: Repair Strategy II (Val & Stewart, 2003)............................................................................. 10
Figure 7: Statistical parameters of random variables (Val & Stewart, 2003) ..................................... 11
Figure 8: Corrosion Potential of Reinforcement at 30o
C and 85% R.H. (Alhozaimy, Hussain, Al-Zaid, &
Al-Negheimish, 2011) ...................................................................................................................... 12
Figure 9: Corrosion Potential Under Coupled Severe Chloride and Temperature at 85% R.H. (Alhozaimy
et al., 2011) ..................................................................................................................................... 13
Figure 10: Corrosion Potential of Reinforcement at 50o
C and 85% R.H. (Alhozaimy et al., 2011) ...... 13
Figure 11: Corrosion Potential of Reinforcement at 40 o
C and 85% R.H (Alhozaimy et al., 2011) ...... 13
Figure 12: The Field Emissions Scanning Electron Microscope (Nessler, 2017) ................................. 17
Figure 13: Magnified Positioning of First and Second Anodes (Nessler, 2017) .................................. 18
Figure 14: Overview of Vacuum Emission Setup (Nessler, 2017) ...................................................... 18
Figure 15: Electromagnetic Lenses Overview (Nessler, 2017) ........................................................... 19
Figure 16: Course of Electron Trajectory and Magnetic Lenses Field (Nessler, 2017) ........................ 19
Figure 17: Final Lens of Fe-SEM (Nessler, 2017) ............................................................................... 20
Figure 18: Representation of Electron Beam on Specimen (Nessler, 2017)....................................... 20
Figure 19: Simplified Electron Trajectory after Meeting Specimen (Nessler, 2017) ........................... 21
Figure 20: In-Depth Analysis of Electron Trajectory (Nessler, 2017).................................................. 21
Figure 21: Overall View of Electron Path after Contact with Specimen (Nessler, 2017)..................... 21
Figure 22: Energy Level Comparison for Raman Scattering for (a) Stokes Scattering and (b) Anti-Stokes
Scattering (Michigan, 2006)............................................................................................................. 23
Figure 23: Representation of Photon Striking Specimen (Science, 2017) .......................................... 23
Figure 24: Behaviour of X-Ray Diffraction (University, 2017)............................................................ 25
Figure 25: Graphic Representation of Incident Ray Electrons (Dutrow & Clark, 2017)....................... 25
Figure 26: Basic Features and Set-Up of XRD Machine (University, 2017)......................................... 26
Figure 27: Applications of XRD (Dutrow & Clark, 2017) .................................................................... 26
Figure 28: Typical development of passive layer aroundreinforcement bars exposed to a concrete pore
solution (Singh & Singh, 2012) ......................................................................................................... 29
Figure 29: 1mm, 10mm and 2mm reinforcement sample................................................................. 33
Figure 30: Three Reinforcement Bar Conditions............................................................................... 33
Figure 31: Steel Specimens in Resin Mould ready for Analysis.......................................................... 34
Figure 32: Elemental Composition of the Different Types of Steel Tested Based on the Photo Electron
Spectroscopy................................................................................................................................... 34
Figure 33: Embedded steel in Concrete with Exposed Martensite used for Analysis......................... 35
Figure 34: SEM Image of Steel and Concrete Interface..................................................................... 35
Figure 35: EXDA Analysis of Passive Layer........................................................................................ 36
Figure 36: EXDA Analysis of Passive Layer from Closer..................................................................... 36
Figure 37: XRD Results from the Passive Layers of the Steel Reinforcement..................................... 37
Figure 38: XRD Peaks with Steel Identifications................................................................................ 37
Figure 39: Compositions of SPSs with varying pH levels ................................................................... 38
Figure 40: Chemical Compositions of Reinforcement Bars ............................................................... 39

vi
Figure 41: Rust Retentions of LA and PC Steel Bars wetted with pH 6.5............................................ 39
Figure 42: Rust Retention of LA and PC Wetted with pH 12.5........................................................... 40
Figure 43: Rust Retention for LA and PC Steel at pH 9.5 ................................................................... 40
Figure 44: Corrosion Rate of LA and PC Steel at pH Levels after 22 Weeks Exposure ........................ 41
Figure 45: Raman spectra for LA Steel after 22 Weeks of Exposure in pH6.5 .................................... 42
Figure 46: Raman spectra for PC Steel after 22 Weeks of Exposure in pH 6.5 ................................... 42
Figure 47: Raman spectra of Rust for LA steel at pH of 9.5 after 22 Weeks....................................... 43
Figure 48: Raman spectra of Rust for PC steel at pH of 9.5 after 22 Weeks ...................................... 43
Figure 49: Raman spectra of Rust for LA steel at pH of 12.5 after 22 Weeks..................................... 44
Figure 50: Raman spectra of Rust for PC steel at pH of 12.5 after 22 Weeks..................................... 44
Figure 51: XRD Results for LA Steel in pH 6.5.................................................................................... 45
Figure 52: XRD Results for PC Steel in pH 6.5 ................................................................................... 45
Figure 53: XRD Results for LA Steel in pH 9.5.................................................................................... 46
Figure 54: XRD Results for PC Steel in pH 9.5 ................................................................................... 46
Figure 55: XRD Results for LA Steel in pH 12.5.................................................................................. 47
Figure 56: XRD Results for PC Steel in pH 12.5 ................................................................................. 47
Figure 57: Chemical Composition of Three Types of Plain Concrete ................................................. 48
Figure 58: Pore Solution Compositions and Three Cement Pastes with Different Chloride Contents 49
Figure 59: The Effect of Temperature on Free Chlorides in a Pore Solution with 2.43% C3A with
Different Chloride Level................................................................................................................... 50
Figure 60: The Effect of Temperature on Free Chlorides in a Pore Solution with 7.59% C3A with
Different Chloride Level................................................................................................................... 50
Figure 61: The Effect of Temperature on Free Chlorides in a Pore Solution with 14% C3A with Different
Chloride Level.................................................................................................................................. 51
Figure 62: Effect of the Temperature on Free Chlorides in a Pore Solution of Differing C3A values ... 51
Figure 63: Composition of simulated pore solutions ........................................................................ 52
Figure 64: XPS Spectra of the Passive Film on Steel at 25o
C for 3, 9 and 19 minutes in SPS............... 53
Figure 65: XPS Spectra of the Passive Film on Steel at 25o
C for 3, 9 and 19 minutes in SPSL ............. 53
Figure 66: Thickness of Passive Layers Based on Pore Solutions....................................................... 54
Figure 67: Raman Spectra for Passive Film for SPS at 25o
C ............................................................... 54
Figure 68: Raman Spectra for Passive Film for SPSL at 25o
C.............................................................. 55
Figure 69: Raman Spectra for Passive Film for SPSL at 55o
C.............................................................. 55

vii
LIST OF SYMBOLS
ASTM American Society for Testing and Materials
C0 Surface chloride content
C(x, t) Chloride content at depth x and time t
D Diffusion coefficient
Deff Effective chloride diffusion coefficient, m2
/s
D(t) Diffusion at time t
erf Error function
EDS/EDX Energy Dispersive X-Ray Spectroscopy
Fe-SEM Field Emission Scanning Electron Microscopy
FT-IR Fourier Transform Infrared Spectroscopy
ITZ Interfacial Transition Zone
kV Kilovolts
mm Millimetre
MPa Megapascals
Pft Probability of cracking and spalling at time t
SPS Simulated Pore Solution
SPSL Simulated Pore Solution with Lime
t Time
Ti Time to corrosion initiation
Tcr1 Time to first cracking
V Volts
w/c Water to cement ratio by weight
x distance from concrete surface
XRD X-ray Diffraction

1
CHAPTER 1: INTRODUCTION
1.1 Purpose and Objectives
The purpose of this paper was to research and evaluate the impact of corrosion on steel reinforcement
in concrete columns exposed to marine environments. More specifically, the passive film developed
around the steel reinforcement was investigated and a strong focus was directed at the effect of
temperature and humidity on the development and degradation of the passive film. Since concrete is
homogenous it is difficult to predict the effect of corrosion on specific areas of the steel reinforcement.
Similarly, it is difficult to assume how the passive film around the reinforcement steel develops and
corrodes. Therefore, the research focused on seven primary objectives:
1. Research and determine the temperature and humidity levels that heavily impact the
concrete (through cracking and spalling) and steel reinforcement which may limit the service
life of the structure
2. Establish the key chemical properties in reinforcement steel and concrete that may be used
for comparisons in laboratory workings
3. Investigate the rate in which the concrete is expected tocrack and spall based on past research
and temperature and humidity to develop a timeline of service life and chloride ingress
4. Research and investigate the time it takes for a passive layer to form around a reinforcement
steel bar submerged in concrete
5. Investigate the timeline of passive layer degradation due to corrosion
6. Record the temperatures in which the steel reinforcement bars redevelop a passive layer or
corrode to point of destruction using Nano-techniques
7. Provide a summary of results collated by multiple research papers and practicals completed
by researchers
These objectives will be met by the end of this research paper.
1.2 Need for Research
Concrete is a commonly used material in marine structures, ranging from jetties to bridges to even oil
rigs. However, the marine environment is harsh and is abundant in chemicals that can heavily degrade
the concrete structures, reducing the service life of the structures and causing premature failure.
There are some areas in the world where corrosion in the reinforcement of concrete is a major
issue and causes severe damage. One of the areas where this is a primary issue is the Middle East. This
is namely due to the high humidity and varying temperatures (S. E. Hussain & Rasheeduzzafar, 1993).
Furthermore, Holland (2012) mentions that out of the 595000 bridges (that existed at the time of the
report) 13% of these bridges were structurally deficient, with 15% of these deficiencies caused by
corrosion. It has now been reported by Association of Consulting Structural Engineers (ASCE) that out
of the 614387 bridges, only 9.1% are structurally deficient (ASCE, 2017). Although the percent of
deficiencies has decreased over the last four years, the amount of bridges that are structurally
inadequate is still extreme,especially whensuch a high percentof the bridges are structurally deficient
due to corrosion. The Middle East, although providing little available statistics on the deficiencies of
the existing structures, is investigating ways to decrease corrosion rate at high humidity and
temperatures as this is the main form of corrosion within this region.

2
This a strong durability concern for concrete structures and, as it is the primary form of
deterioration, more understanding must go into this process in order to increase the service life and
safety of concrete structures around the world.
1.3 Scope
The scope for the following paper is provided below in Figure 1.1, which was created to develop a
timeline of this project and to meet the objectives outlined in Section 1.1. After initial research was
completed into the key durability concerns of concrete in marine environments, further research was
completed to discover what experimental works have been completed regarding the key durability
concerns. These objectives have been completed and can be seen in the background information
(Chapter 2) and the literature review (Chapter 3).
Based on the findings from the literature review (which was developed based off information
collated in Chapter 2) past laboratory experiments were investigated. This was done to ensure an
understanding of the content and to avoid duplicate experimental productions. These laboratory
experiments focus on the region of Saudi Arabia and the Middle East as there are high durability
concerns for concrete structures due to temperature and humidity. From this, an experiment was
developed using N36 Australian Standard reinforcement steel, two different types of pore concrete
solution and three different temperatures. Nano-technology including Fe-SEM, Raman Spectrometry
and XRD were utilised to investigate certain stages of the passive films of the reinforcement bars.
Property testing of the reinforcement steel and the concrete mixes was performed to
understand the chemistry of the materials. Through doing this a relationship could be set to
understand the actions taking place during the experiment. Furthermore, two different types of
concrete pore solutions were developed: basic simulated pore solution (SPS) and a simulated pore
solution with lime (SPSL). The different temperatures tested were 20o
C, 40o
C and 60o
C. This enabled
a steady relationship between temperatures and avoided any extreme results.
The results of the durability and corrosion assessment were used to investigate the behaviour
of the passive film around the reinforcement steel and, if possible, use for future reference when
developing a new model for service life.

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Figure 1: Scope of Investigation
1.4 Organisation of Thesis
• Chapter 2: Background Information
o Durability
o Destructive Mechanism
o Chloride Attack
o Humidity and Temperature
• Chapter 3: Literature Review
o Nano-techniques
o Passive Layer
o Past Investigation
• Chapter 4: Testing Proposal
Durability concerns in marine concrete
Service life estimation
inaccurate
Reduction in passive layer in
steel reinforcement
Corrosion rate of reinforcement
steel due to temperature and
humidity
Conduct literature review of
durability concerns
Nano-techniques used in
experimentation
Effect of temperature of
development of passive layer
Past experiments completed
in key durability concerns
Develop testing method
Mechanical Property
Research
Durability testing
Conclusions

4
CHAPTER 2: BACKGROUND INFORMATION
2.1 Durability of Concrete
Concrete subjected to marine environments are exposed to multiple deterioration devices. These
devices can be classified under two main headings: Physical and Chemical. Under these headings, the
main durability categories include Humidity and Temperature, Freezing and Thawing, Life-Cycle,
Volume Changes due to Moisture Change, Resistance to Sulphate Attack, Chloride Resistance and Steel
Corrosion, and Chemical Attack. The durability of concrete is dependent on many of these factors, and
many of them interact, causing more harm to the concrete under investigation. These harmful
mechanisms are discussed further in this section with clear understanding of the research path
developed.
In a marine environment, concrete is subject to pressures from the ocean. AS3600 states that
when designing for concrete specifications must be determined regarding location, exposure and
minimum strength. This is outlined in Section 4.0 of AS3600, where the exposure environment outlines
sections of the concrete to which the marine environment is acting. Specifically, Table 4.3 of AS3600
briefly mentions concrete structures in sea water that are permanently submerged, within the spray
zone and in a tidal/splash zone (Limited, 2009). Figure 2 (Mehta, 1991) shows this exact scenario. From
Figure 2, the maximum degradation on the concrete column occurs within the tidal zone. When
considering this and applying the knowledge of wave power, this situation is understandable. The
abrasive action of the waves against the concrete column, coupled with a harsh, fluctuating
atmospheric environment could cause degradation to a concrete structure. AS3600 recognises this by
classifying the tidal/splash zone as C2. Table 4.4 in AS3600 claims that a minimum compressive
strength for a concrete structure under C2 classification must be 50MPa (Limited, 2009). Therefore, it
can be concluded that to design for such a harsh environment, a stronger concrete must be used.
Figure 2: Concrete Column Subjected to the Three Categories Within a Marine Environment (Mehta, 1991)

5
As concrete is exposed to three zones (submerged, spray and tidal/splash) there are a variety
of ways that concrete in a marine environment can become vulnerable. These are discussed in more
detail within this section.
2.2 Destructive Mechanisms on Concrete in Marine Environments
Within a marine environment there are multiple mechanisms that can result in destruction to the
concrete structural element. The most detrimental destructive mechanism is corrosion of the
reinforced steel bars within the concrete structure. This is caused by a number of factors, including
the water/cement ratio, aggregate mixes and their chemical interactions and environmental
exposures (Holland, 2012). Previously mentioned, AS3600 accounts for concrete cover in relation to
the environmental factors to which the concrete is exposed. This is done for extending the service life
of the concrete so corrosion of the reinforcing bars does not occur prematurely.
As corrosion is the most detrimental destructive mechanism to concrete in marine
environments, it is further investigated in this paper. Furthermore, the discussion of other durability
concerns will link to corrosion of concrete structures, such as humidity and temperature of the
surrounding environment as well as the effects this has to the service life of concrete.
2.3 Chloride Attack on Reinforced Concrete
The primary durability concern for concrete in marine environments is chloride attack on reinforced
concrete, also known as corrosion. As most, if not all, concrete in marine environments is reinforced,
this can become a real problem.
2.3.1 Chloride Sources
Seawater varies throughout the world in terms of chemical compositions and the amounts of
chemicals found; however, all seawater contains the same dissolved salts:
→ Sodium Chloride (NaCl)
→ Magnesium Sulphate (MgSO4)
The table below, extracted from Holland (2012), shows the average concentration of these salts (with
other ions found) and their individual ions within seawater.
Table 1: Average Composition of seawater (Holland, 2012)
Ions Concentration (g/litre)
Na+
11.00
K+
0.40
Mg2+
1.33
Ca2+
0.43
Cl-
19.80
SO4
2-
2.76
Simple analysis of Table 1 shows chloride is the dominant ion within water with the largest
concentration g/litre of 19.80.
In addition to dissolved salts found within the seawater, there are many other chemical
interactions occurring in the surrounding environment, especially in the atmosphere where gases can
react with the concrete depending on the environmental situation (discussed further in this paper).

6
Oxygen (O2) is a dominant chemical found in both the atmosphere, seawater and the concrete itself.
Oxygen found in the concrete is usually entrapped air due to construction issues such as incorrect
tampering or poor attention to specifications. Oxygen has a substantial role to play in the corrosion
process.
Additionally, there are two sources of chloride contamination: internal and external. An
external source has been discussed (chloride ingress in seawater); however, another chloride source
includes the use of de-icer salts (more commonly used in colder temperatures and discussed further
in this paper)(Bertolini, Elsener, Pedeferri, Redaelli, & Polder, 2004). Internal sources of chloride
include those developed in the aggregate used in the concrete mix. Some aggregates used may have
been washed with seawater before being used in the mix and some may have even been dredged
from a saltwater environment (Bertolini et al., 2004)
From this brief analysis of chloride sources, chloride avoidance is quite difficult to achieve
within a marine environment. Therefore, methods must be applied to prolong the service life of
concrete.
2.3.2 Corrosion Process
The corrosion process is a simple chemical interaction between water and oxygen. The process of
corrosion within a reinforced concrete environment is slightly more involved as there are many
sources of chloride that can cause extensive corrosion when introduced to water and oxygen. Neville
A, (1995) explains this process in detail.
Steel in concrete has the potential to create different electrochemical regions, these being
regions of anodic and cathodic classification. With these opposite electrochemical actions, an
electrolyte that can exist purely from the pore water developed in the hardened cement paste, can
connect these two regions. The reinforced steel, when initial hydration of the cement begins, can self-
generate a protective, passive layer that consists of Fe2O3. As long as the steel keeps the concrete
strong, this layer of iron and oxygen will stay intact (Neville, 1995). However, this layer deteriorates
when it comes into contact with chloride ions.
The ions of Iron (Fe2+
) exists at the anode where it is passed into a solution. The electrons
(negatively charged) that are also at the anode then pass through the electrolyte to the cathode,
interact with the water and oxygen and form hydroxyl (OH-
). The hydroxyl then carries through the
electrolyte back to the anodic region where it interacts with the Fe ions to create ferric hydroxide,
which is converted to rust due to further oxidation. The chemical equations for the anodic reactions
and cathodic reaction, respectively, are outlined below.
Anodic Reactions:
𝐹𝑒 → 𝐹𝑒2+
+ 2𝑒−
𝐹𝑒2+
+ 2𝑂𝐻−
→ 𝐹𝑒(𝑂𝐻)2
4𝐹𝑒(𝑂𝐻)2 + 2𝐻2 𝑂 + 𝑂2 → 4𝐹𝑒(𝑂𝐻)3
Cathodic Reactions:
4𝑒−
+ 𝑂2 + 2𝐻2 𝑂 → 4𝑂𝐻−
As mentioned previously, for corrosion to occur on the reinforcement the passivity layer
created must be penetrated by chloride ions. When this is achieved, the anodic region forms while
the passivity surface acts as the cathodic region. The chemical equations for this reaction is as follows:

7
𝐹𝑒2+
+ 2𝐶𝑙−
→ 𝐹𝑒𝐶𝑙2
𝐹𝑒𝐶𝑙2 + 2𝐻2 𝑂 → 𝐹𝑒(𝑂𝐻)2 + 2𝐻𝐶𝑙
2.3.3 Chloride Ingress
Chloride ingress is also a main form of chloride attack, where there are three modes of recorded attack
causing this durability concern. These are diffusion, permeation and absorption (Holland, 2012). The
primary form of chloride ingress is chloride diffusion, which is discussed below.
2.3.3.1 Chloride Diffusion
Chloride ions act in a specific way when attacking the reinforcing steel bars in concrete.
Holland (2012) mentions that diffusion occurs due to the concentration gradient of the chlorides. This
means that chloride ions move from high concentrated areas to low concentrated areas of the steel
bars in order to maintain a chemical equilibrium. Fick’s second law provides a modelled understanding
on diffusion coefficient and can model the ingress of chlorides (Kim et al., 2016). There are multiple
methods to determining the diffusion coefficient; however, these will not be discussed in this paper.
𝜕𝑐
𝜕𝑡
= 𝐷𝑒𝑓𝑓
𝜕2
𝑐
𝜕𝑥2
The diffusion coefficient is also heavily dependent on the chemistry of the cement, the water
to cement ratio and the age of the structure under consideration. The diffusion coefficient is discussed
in further detail within Section 2.4.1.2.
2.4 Humidity and Temperature
The effects of humidity and temperature on concrete is also a durability concern within marine
environments. Many sources discuss the detrimental effect of humidity and temperature on
reinforced concrete. Alhozaimy et al. (2011) outlines in his papers that since corrosion is treated as an
electrochemical and thermodynamic phenomenon, it is heavily influenced by temperature and
humidity, each of which vary from place due to seasonal differences. Humidity and temperature cause
one major durability concern: cracking and spalling. This is discussed in detail below.
2.4.1 Cracking and Spalling due to Temperature
These two actions are detrimental to the durability of concrete and are very common in reinforced
concrete structures exposed to marine environments. Cracking first occurs due to environmental
exposure of the concrete. According to Neville (1995), corrosion of steel reinforcement is rare within
the concrete that is completely submerged in seawater. Considering this, AS3600 discusses concrete
that is completely submerged in seawater does not require such a large reinforcement cover as
opposed to the concrete found at the tidal/splash zone (Limited, 2009). These raised questions
regarding the ideal areas where steel corrosion occurs. It was found that atmospheric temperature of
the surrounding environment has a substantial effect on corrosion, especially cracking and spalling.
2.4.1.1 Climate
Heat was the first environmental factor considered in concrete durability. Theoretically, heat can be
considered a “…driving energy source…”(Mehta, 1991) that can increase the rate at which
deterioration mechanisms can act. In saying this, heat can be also be considered as an aggravating
factor for concrete where there are multiple deterioration mechanisms acting. As the deterioration of
marine concretes is primarily a chemical reaction, the age old relationship between heat and chemical

8
reaction can be applied here, saying that the rate of chemical reactions is doubled with every ten
degree increase in temperature (Mehta, 1991).
It has been established that marine concrete within the tidal/splash zone needs the largest
concrete cover, meaning that chloride ingress is more likely to occur within this region of the concrete
structure. When observing this region of the concrete structure it can be seen that it is exposed to
atmospheric fluctuations and can sometimes be completely submerged in sea water depending on
tidal actions. Therefore, these concrete structures can be exposed to continuous cycles of freezing
and thawing, heating and cooling and wetting and drying (Mehta, 1991). With such fluctuated actions
affecting the concrete structure, deterioration of the materials can occur, leading to cracking and
spalling along the column. Referring to Figure 2, the thinning section of the concrete column contains
cracking due to such harsh environmental conditions. Concrete strength can also help control these
harsh actions, and AS3600 also accounts for this. The Australian Standards have specified that
concrete within this zone must be 50MPa. This is to ensure the wave actions do not degrade the
material, allowing the temperature fluctuations to, in turn, deteriorate that concrete.
Mehta (1991) references Fookes et al. when categorizing the world climates. According to Fookes
et al. the world can be divided into four main temperature regions:
1. Cool: freezing temperatures
2. Temperate: annual average temperature from 10-20o
C with freezing temperatures scarce and
moderate rainfall
3. Hot and dry: desert and summer temperatures beyond 45o
C and little to no rainfall
4. Hot and wet: tropical climates with high annual temperatures not exceeding 300
C
According to past research and observation, deterioration was at its highest (over a 10-year period) in
the hot-dry and hot-wet climates. Figure 3 outlines the effect of time for deterioration within these
zones.
Figure 3: Effect of Climatic Environment on Reinforced Concrete in the Marine Environment (Mehta, 1991)
Furthermore, Figure 4 shows the rate of concrete conditioning over time. It is clear that concrete
within the hot-wet and hot-dry regions deteriorated at a faster rate than the concrete within the
temperate and cool zones (Figure 4a).

9
Therefore, a final idea can be developed that temperature has a substantial effect on the
durability of concrete, causing cracking and spalling due to different temperature actions. However,
these issues need to be understood and controlled in order for any marine structures to exists and
remain static in nature. Therefore, probabilistic methods were developed in order to predict the
likelihood of cracking and spalling.
2.4.1.2 Probabilistic Models
A main concern regarding cracking and spalling of concrete, among other main concerns, is the cost
of repair and maintenance. When concrete begins to crack and before spalling begins, it would be
ideal if a safety assessment on the deteriorating structure was completed. This can decrease
maintenance costs and can possibly avoid catastrophic actions occurring in the future.
When developing a model regarding costs, it is important to have repair strategies in place.
Val & Stewart (2003) outline two repair strategies to provide some boundaries in regard to controlling
cracking and spalling. It should be mentioned that these repair strategies are not put to practice, but
simply provide a comparison between a poor (repair strategy I) and good (repair strategy II) scenario.
These steps have been put into Figures 5 and 6 below.
Figure 4: Influence of different tidal and climatic zones on the performance of marine structures (Mehta, 1991)

10
Figure 6: Repair Strategy II (Val & Stewart, 2003)
As mentioned these repair strategies are a guide. In the real world maintenance and repair
strategies would most likely be dependent on the local practices, structure type, resource availability
and regulatory requirements.
With repair strategies put into place, the probability of spalling based on cracking and the
penetration of chloride ions can be developed.
Chloride content (C(x,t)) within the concrete at a distance of x at any time can be modelled by
the following equation:
𝐶( 𝑥, 𝑡) − 𝐶0 [1 − erf (
𝑥
2√𝐷𝑡
)]
In order to develop a time line for the above probability model, it is assumed in industry that
corrosion of the reinforcement bars begins when the concentration of chloride at the depth of
reinforcement reach the concentration threshold, known as Cr. In regards to the chloride content
probability model, the variables involved each act differently to one another; therefore, they are all
dependent on certain aspects.
Surface chloride content depends primarily on the proximity of the concrete structure to the
seawater (Val & Stewart, 2003). As mentioned previously, concrete completely submerged in water is
not likely to corrode as oxygen is not readily available while concrete within the tidal/splash zones and
atmospheric zones are vulnerable to corrosion due to ready oxygen, fluctuating cycles of atmospheric
actions such as wetting and drying, freezing and thawing. After analysis was completed by researchers
investigating the durability of concrete in marine environments, it was discovered that surface
chloride developed a lognormal distribution (Val & Stewart, 2003). Over time, it would be expected
that surface chlorides would increase; however, with a typical lognormal distribution it can be said
that surface chloride increased within the first few years of the concrete structures life. Eventually a
reduction in surface chlorides was observed and thus, a conclusion was made that surface chloride
can be a constant value after a certain life-span of the concrete structure.
In regards to the diffusion coefficient, the complexity of the action makes it difficult to develop
a probabilistic model that would account for all factors this coefficient is dependent on, these being
typical properties of concrete. There are a few complicated models that can replace a suitable model
for the diffusion coefficient; however, these other models do not completely satisfy each concrete
property. Val & Stewart (2003) outline one of the complex models below:
Figure 5: Repair Strategy I (Val & Stewart, 2003)

11
𝐷 = 0.15
1 + 𝜌𝑐
𝑤
𝑐
1 + 𝜌𝑐
𝑤
𝑐
+
𝜌𝑐 𝑎
𝜌 𝑎 𝑐
(
𝜌𝑐
𝑤
𝑐 − 0.85
1 + 𝜌𝑐
𝑤
𝑐
) 𝐷 𝐻20 (𝑚2
/𝑠)
It can be seen from the above formula that finding an accurate diffusion coefficient can be complex.
However, past data that has been collected over the years does suggest that the diffusion coefficient
decreases over time, meaning it can also be considered constant for older structures (Val & Stewart,
2003).
2.4.1.3 Probability of Cracking and Spalling
The issue of cracking and spalling of the concrete cover has been classified as a serviceability failure,
and if not repaired immediately can often lead to more detrimental damage occurring to the structure,
often causing plastic damage and can, over all, weaken the concrete structure and reduce the limit
state design.
Cracking of a concrete structure is heavily influenced by the following factors of concrete:
concrete cover, bar spacing, material properties, quality of concrete and the overall corrosion rate.
Val & Stewart (2003) mention that a concretes structure is under threat only when crack width
exceeds 0.3-0.5mm and are not immediately repaired. However, the probability of cracking and
spalling can be found before any of this occurs in the concrete structure based on the following
equation:
𝑃𝑓( 𝑡) = Pr( 𝑇𝑖 + 𝑇𝑐𝑟 ≤ 𝑡) = Pr( 𝑇𝑖 + 10𝑇𝑐𝑟1 ≤ 𝑡)
Figure 7 shows the statistical parameters of random variables based on the probability of
cracking and spalling, also showing the distribution action, mean density of the concrete in question
and the coefficient of variation.
2.4.2 Relative Humidity
The corrosion of reinforcement bars in concrete in marine environments can be influenced by the
relative humidity of the location in which the concrete structure is located. Alhozaimy (2011)
investigates a set of data developed from a laboratory investigation designed to mimic a typical coastal
gulf region in a humid environment with varying temperatures. The results found from these
laboratory investigations comply with other researchers in the field, such as Neville (1995). With such
a large publication gap between these two sources, a conclusion can be made that this area is still
misunderstood and unclarified within this area of engineering.
Figure 7: Statistical parameters of random variables (Val & Stewart, 2003)

12
2.4.2.1 The Investigation
Thirty specimens of reinforced concrete were tested in three different temperatures: 30o
C, 40o
C and
50o
C with a total chloride concentration varying from 0-5% in water. The environmental control
chambers each contained a relative humidity of 85%. After the initiation of the experiment and after
some time, results were collated.
It should be mentioned that concrete, being heterogeneous in nature, makes the corrosion
process vary throughout the steel bars; therefore, final results of this investigation show corrosion to
be a non-uniform phenomenon (Alhozaimy et al., 2011). Figure 8, 9, and 10 show the non-linear
relationships between chloride potential and the corresponding temperatures in which the concrete
was tested. It was found that the chloride degradation of the reinforcement bars increased over time
for temperatures of 30 and 40o
C within an environment of 85% relative humidity; however, looking
closely, the relationship between these variables decreases over time for concrete in the 50o
C
chambers at 85% relative humidity. Although some areas of Figure 10 shows fluctuations in this area,
the overall relationship is declining. Neville (1995) mentions that the optimum relative humidity for
corrosion to occur in reinforcement bars in marine concrete is between 70-80%; however, the source
also mentions that the corrosion rate decreases with relative humidity values greater than this. Neville
(1995) suggests that the diffusion of oxygen through the concrete and reinforcement bars decreases
due to relative humidity increase.
Figure 11 shows the combined relationship, that is, the corrosion potential under coupled
severe chloride at an 85% relative humidity. It can be seen the chloride potential decreases
significantly with a 5% chloride content between 40 and 50o
C; however, the overall trend line shows
a small yet steady decline for all chloride percentages between 40 and 50o
C.
Figure 8: Corrosion Potential of Reinforcement at 30oC and 85% R.H. (Alhozaimy, Hussain, Al-Zaid, & Al-Negheimish, 2011)

13
Figure 9: Corrosion Potential of Reinforcement at 40 oC and 85% R.H (Alhozaimy et al., 2011)
Figure 10: Corrosion Potential of Reinforcement at 50oC and 85% R.H. (Alhozaimy et al., 2011)
Figure 11: Corrosion Potential Under Coupled Severe Chloride and Temperature at 85% R.H. (Alhozaimy et al., 2011)

14
The results discovered in this investigation was not expected. It was expected that with the increase
in chloride under any temperature there should be an increase in corrosion potential. Neville (2011)
proposes two reasons for this unexpected trend:
1. At such high temperatures the oxygen solubility in the pore solution decreased, resulting in
oxygen controlled corrosion at high temperatures as opposed to chloride controlled
corrosion.
2. Shortage of oxygen at high relative humidity and high temperature conditions due to blockage
of concrete pores at high relative humidity and high temperatures resulting in break of
interconnected concrete pores
Data for any concrete in environments with extreme boundary conditions such as relative humidity
and high temperatures is very scarce, hence the understanding of corrosion in these environments is
lacking in the industry. There is also a lack of numerical modelling and, hence, the service life of the
concrete under investigation is difficult to predict. This is discussed further in Section 2.5 regarding
the service life of concrete in marine environments.
Since oxygen is needed for the corrosion process and based off these results and reasoning’s
regarding the decline in corrosion at a boundary condition it can be said that the corrosion decrease
is due to the decrease of soluble oxygen in the concrete at the interfacial transition zone (ITZ) and the
high relative humidity creating a disconnection between concrete pores (Alhozaimy et al., 2011).
Therefore, the oxygen path to the steel bars is blocked.
Based on this information and knowing that the corrosion increases for temperatures of 30
and 40o
C and decreases for 50o
C, it can be understood that the corrosion mass loss increases for 30
and 40o
C and decreases for 50o
C. Corrosion mass loss is detrimental to the structure and can result in
weakened steel bars, hence resulting in a smaller limit state design over time. However, for the 50o
C
temperature case, the corrosion mass loss has a slight exception. The corrosion mass loss increases
with a total chloride concentration of 1%; however, after that for 3% and 5% total chloride
concentration, the corrosion mass loss then reduces. Therefore, a conclusion can be made that with
a high chloride content and a high temperature, corrosion seems to reduce.
It is when this occurs that the concrete and steel bars develops something unexpected.
Alhozaimy (2011) discusses that under limiting oxygen controlled corrosion, that is, when the chloride
concentration is high and the temperature exceeds 50o
C, the stable iron oxide layer may be
reproduced around the steel reinforcing bars, preventing further chloride attack and maintaining the
current quality of the steel bars.
If this is the case, and there is a threshold that the concrete and steel bars reach before
repairing itself, research needs to be completed in order to develop this idea further. As well as this,
with further research, numerical models could be developed and incorporated into future analysis of
concrete structures in marine environments and can be implemented to service life software.
2.5 Service Life
There are three main software programs that exist in order to predict the service life of concrete: Life-
365, DuraCrete and CHLODIF. Each of these probability models were designed in different areas of the
word and each serves a similar purpose: estimating the service life of concrete in a marine
environment. Life-365 was developed in North America, while CHLODIF was developed in Croatia
(Oslakovic, Bjegovic, & Mikulic, 2010). DuraCrete was developed in Europe and stands for
“Probabilistic Performance Based Durability Design of Concrete Structures” (Oslakovic et al., 2010). All

15
three models are based on chloride diffusion through concrete and into steel reinforcement bars.
Fick’s Law is the primary equation these software programs run off; however, these programs will
produce only one evaluation of time to corrosion as they are solely dependent on one input parameter
at a time (Bentz, 2003). Since concrete structures are variable in nature, these programs are not
completely satisfactory to the evaluation of service life.
Service life prediction models are becoming popular as they are cost-beneficial programs,
creating service life predications before the structure’s integrity is lost. There are two main
probabilistic methods in determining the service life of a structure: implicit and explicit (Bentz, 2003).
Implicit methods integrate density functions in order to model chloride transport. There are
advantages to this method; however, a disadvantage is the mathematics behind such equations can
be extremely complex. Life-365 includes direct equations for temperature and time-dependent
changes on the concrete structure; however, the surface chloride levels, as mentioned earlier, can
become a complex bundle of equations (Bentz, 2003). Therefore, the implicit methods of determining
the service life is not a simple calculation. The explicit methods do not involve such modifications of
the main equations. Two of these methods are based on reliability methods well known in the industry
named first-order reliability method (or FORM) and second-order reliability method (or SORM) (Bentz,
2003). These methods are useful for developing a small probabilistic model on failures and are not
specifically useful for corrosion analysis.
Although these programs are developed to estimate the service life of these structures, a
corrosion analysis through these programs is not a completely satisfactory solution. These programs
only develop a corrosion analysis based on one input at a time and, since the basis if chloride transport
can be variant depending on the concrete matrix, a confident result is almost impossible to achieve.
In addition to this, with the theory that steel bars within the concrete may begin to heal itself after
reaching a certain temperature and relative humidity, these programs do not account for actions
dependent on more than one variable.
2.6 Summary
The initial background research on durability in concrete subjected to marine environments revealed
that there are certain gaps in the current research, especially in the areas regarding service life
software and the impact of temperature and humidity on the corrosion rate of steel reinforcement.
Firstly, it was found that, theoretically, at a specific temperature and relative humidity,
corrosion of the steel reinforcement within a concrete structure in a marine environment begins to
decrease. At 50o
C and a relative humidity of 85%, the corrosion rate of steel bars within a laboratory
environment began to decrease according to Alhozaimy (2011). Reasons for this were provided in
Section 2.4.2.1; however, the reason to which this project depends will involve the reduced oxygen
access to the steel bars at a relative humidity of 85% and 50o
C, reducing the potential of corrosion and
allowing the steel bars to redevelop an iron oxide layer that was once destroyed by chloride ions. If
this theory is correct, this suggests the steel bars cure themselves within a certain environment and
maintain their stable condition.
To investigate this theory further, Nano-techniques could be employed. Techniques such as
Field Emission Scanning Electron Microscopy (Fe-SEM), X-ray Powder Diffraction (XRD), Raman
Spectrometry and X-ray Photoelectron Spectroscopy (XPS) can be applied to view the redevelopment
of an iron oxide layer at a specific environmental temperature within a laboratory environment.
Therefore, this project will revolve around the following:

16
The investigation of Nano-techniques (Fe-SEM, Raman Spectroscopy and XRD) and their ability to
confirm the degradation and redevelopment of the iron oxide passive layer of steel reinforcement
at certain temperatures and humidity where concrete is exposed to harsh marine environments.

17
CHAPTER 3: LITERATURE REVIEW
3.1 Nano-techniques
Nano-technology, as mentioned in Section 2.6, is one of the key techniques applied to understand the
degradation and redevelopment of the passive layer around the reinforcement steel within concrete
exposed to marine environments. The three Nano-techniques that will be involved in the project are:
→ Fe-SEM
→ Raman Spectroscopy
→ XRD
These Nano-techniques are described in detail in the following sections in order to understand exactly
how they work and how they are of great use when investigating the passive film of reinforcement
steel.
3.1.1 Fe-SEM
Field Emission Scanning Electron Microscope (Fe-SEM) is, simply put, a microscope that uses electrons
instead of light (Janssen, 2017). The object being assessed is scanned by electrons that have been
released through a field emission source (Janssen, 2017). This is explained below when the microscope
itself is investigated. Figure 12 below shows the basic workings of a Fe-SEM
3.1.1.1 The Vacuum
All microscopes that use electrons to assess objects have high-vacuum instruments in order
to prevent unwanted electrical discharge and to allow the electrons to travel to the object unimpeded
(Nessler, 2017). Fe-SEMs with a perfect vacuum theoretically have an infinite life-cycle, therefore it is
Figure 12: The Field Emissions Scanning Electron Microscope (Nessler, 2017)

18
important to care for the Fe-SEM. Furthermore, a perfect vacuum also produces accurate results as
the electron particles are uninterrupted on their journey to the object under investigation (Nessler,
2017).
A Fe-SEM has two different types of vacuum levels that allow different emission sources.
These are thermionic emitters and field emitters (Nessler, 2017). These different types of vacuums
are compared in Table 2.
Table 2: Comparison of Vacuum Emission Sources (Nessler, 2017)
Thermionic Emitters Field Emitters
→ Use electric current to heat up filament
→ Lowers the work function of filament
→ Electrons more readily drawn off
filament with electric field
→ Two most common instruments used
for filament are lanthanum hexaboride
and tungsten
→ Require extremely high, clean vacuums
→ Utilize two anode plates below gun
assembly (Figure 13 and 14)
→ First anode plate is the extraction
voltage (usually in range of 3-5kV) and
draws the electrons from source
→ Second anode has accelerating voltage
associated (determines velocity of the
electrons as they travel down vacuum)
The field emitter is the most common type of vacuum used, and for this project this vacuum
type will utilised. It was mentioned in Table 2 that there are two anode plates below the gun assembly.
This can be seen in Figure 14. The gun of the Fe-SEM determines two factors regarding the resolution:
accelerating voltage and initial crossover diameter (Nessler, 2017). According to Nessler (2017)
“resolution is the ability to separate (resolve) two closely spaced points (particles) as two separate
entities”. When comparing the two factors, there are major differences between the two. The
accelerating voltage (developed from the second anode) usually ranges between 500and 30000 V and
involves electric current. The other component, the initial crossover, is the diameter of the beam that
connects with the object being investigated (Nessler, 2017). In order to provide accurate results, this
beam must be smaller in diameter then the particles being assessed while also containing enough
electrons to develop acceptable results. In this case, this beam would need to be smaller than the iron
oxide particles on the reinforced steel and have a beam current density suitable for this project.
Figure 14: Overview of Vacuum Emission Setup (Nessler, 2017)
Figure 13: Magnified Positioning of First and
Second Anodes (Nessler, 2017)

19
3.1.1.2 The Lenses
The electromagnetic lenses are the next influential process in the Fe-SEM. At this stage of the process,
the electron beam can be altered based on the exposure to this electromagnetic field. The basic design
of these lenses are given in Figure 15 while a more specific design is given in Figure 16.
As seen in Figure 16, the magnetic lens field is circular in nature, meaning that electrons
passing through this beam demagnify as it passes through this area of the field. Furthermore, the
strength of this magnetic field is largest at the very edge of the lens, as represented in Figure 16
(Nessler, 2017). Therefore, the electrons passing through the beam that are closest to this
electromagnetic lens will have their path slightly altered whereas those travelling closer to the centre
of the beam with not alter their path (Nessler, 2017). This results in a loss of electrons through the
beam. This must be taken into consideration when developing the initial crossover.
The final lens in the Fe-SEM process gives the instrument its name and is the final
manipulation of the electron beam before it impacts the object under investigation. The final lens is
made up of raster coils, which scan the electron beam over the surface of the object. Figure 17 shows
the layout of this final lens and Figure 18 shows how this electron beam is scanned onto the object.
Figure 15: Electromagnetic Lenses Overview (Nessler, 2017)
Figure 16: Course of Electron Trajectory and Magnetic Lenses Field
(Nessler, 2017)

20
3.1.1.3 Results
The results from Fe-SEM are recorded after the electron beam strikes the specimen. When this beam
hits the specimen, the electrons are then ricocheted at a certain angle from the degraded specimen,
shown simply in Figure 19. Figure 20 and 21 show this process in more detail. The initial electrons (or
the backscattered electrons) are of little importance. The secondary electrons, on the other hand, are
directed into the electron collector and sent through to the photomultiplier where results are collated
and delivered to a computer program. The secondary electrons are of import as these are the
electrons that ricochet off the specimen at the areas of concern.
Figure 17: Final Lens of Fe-SEM (Nessler, 2017)
Figure 18: Representation of Electron Beam on Specimen
(Nessler, 2017)

21
The use of Fe-SEM to view topographical details on a specimen’s surface is very useful in
determining the behaviour of the iron oxide passive layer surrounding steel reinforcement after being
subjected to different temperatures and humidity. This process is seen in past methodologies and will
be utilised in the suggested methodology in this paper.
Figure 19: Simplified Electron Trajectory after Meeting Specimen
(Nessler, 2017)
Figure 20: In-Depth Analysis of Electron Trajectory (Nessler, 2017)
Figure 21: Overall View of Electron Path after Contact with Specimen
(Nessler, 2017)

22
3.1.2 Raman Spectroscopy
Raman Spectroscopy is an important tool for identifying different molecules and minerals on specific
items (Michigan, 2006). Raman Spectroscopy is a technique based on the scattering of light in which
the behaviour of this light is classified as inelastic (Instruments, 2017). Michigan (2006) explains that
light scattered from a crystal or molecule usually has an elastic behaviour and these scattered photons
have the same frequencies and wavelengths as the original photon before being scattered. The Raman
Effect (the basis in which Raman Spectroscopy exists) occurs when a small fraction of scattered
photons reaches an optical frequency different from the original photons and becomes inelastic
(Michigan, 2006). This can occur when a change in vibrational, electronic or rotational energy
transpires in the photons (Michigan, 2006).
There are three different types of light frequencies in Raman Scattering, these being Rayleigh
scattering, Stokes frequency and Anti-Stokes frequency (Instruments, 2017). Table 3 below provides
the definitions of each behaviour of scattering.
Table 3: Description of Raman Scattering Photon Frequencies (Instruments, 2017)
Rayleigh Scattering Molecule within specimen with no “Raman-
active” modes absorbs the photon with a
frequency known as 𝑣0. This molecule (excited
by laser action) returns to the basic vibrational
state and emits the same light with the same
basic frequency of 𝑣0.
Stokes Frequency The “Raman-active molecule on specimen
absorbs a photon (in its basic form of vibrational
state) with frequency of 𝑣0 and part of this
photon’s energy is transferred to the “Raman-
active” mode with a new frequency of 𝑣 𝑚. This
results in a reduction of the frequency of the
scattered light to 𝑣0 − 𝑣 𝑚.
Anti-Stokes Frequency The “Raman-active” molecule on specimen
absorbs a photon (in its excitation state) with
frequency 𝑣0. The extra energy of this excited
mode is released and the photon returns to its
basic vibrational state, resulting in the scattered
light being 𝑣0 + 𝑣 𝑚.
According to Instruments (2017), approximately 99.999% of all photons in spontaneous
Raman activity experience Rayleigh scattering, meaning about 0.001% of all photons fall under the
Stokes frequency or Anti-Stokes frequency.
Raman Spectroscopy is made up of an excitation laser, an illumination system and light
collection optics, a wavelength selector (Spectrophotometer or filter) and a detector (Instruments,
2017). The specimen is usually illuminated with the laser beam and the scattered light is collected and
sent to the detectors through the filters.
Figure 22 shows how Stokes scattering and Anti-Stokes scattering works in a virtual state. The
initial state shown in Figure 22 is known as the ground state due to the fact that “the thermal
population of vibrational excited states is low” (Michigan, 2006) at room temperature (Michigan,
2006). Therefore, the scattered photon will have lower energy than that in the excitation state. Figure
23 shows the actions of the photon when it strikes the specimen.

23
Raman scattering is different for different molecules, which is why Raman scattering is a
terrific device for determining the interaction between molecules. The vibrations of the photons
against the different molecules vary with different molecule types. For example, the vibrations for an
O-H bond are usually very low (Michigan, 2006). Table 4, extracted from Michigan (2006), provides
examples of different frequency ranges in different organic molecules.
Figure 22: Energy Level Comparison for Raman Scattering for (a) Stokes Scattering and (b) Anti-Stokes Scattering
(Michigan, 2006)
Figure 23: Representation of Photon Striking Specimen (Science, 2017)

24
Table 4: Usual Features in the Raman Spectra (extracted from Michigan (2006))
Frequency Range (in cm-1
) Band Assignment Remarks
2700-3100 C-H alkyl free vibration Medium intensity in Reman
2230 C ≡ N stretch Very strong band in Raman,
found in most cyanide based
compounds
2190-2300 C ≡ N (triple bond stretch) Very strong in Raman
2100-2140 C ≡ C (triple bond stretch) Very strong in Raman
1650-1750 C = O stretch Ketones appear on the lower
wavelength side, aldehydes
appear on the higher side
1600-1675 C = C stretch Very strong in Raman
1580-1620 C = C stretch Very strong in Raman
990-1010 Aromatic ring breathing Appears at 992 cm-1
for
benzene, around 1004 cm-1
for
toluene
650-850 C-Cl stretch Strong in Raman
It can be seen from Table 4 that Carbon (C) has a strong influence in Raman Spectroscopy, as
are Chloride ions. Therefore, it is clear that Raman Spectroscopy works in identifying any changes to
specimen’s due to chloride infiltration.
3.1.3 XRD
X-ray Diffraction (XRD) is used to identify phases of crystalline materials and can provide information
on crystalline cell dimensions (Dutrow & Clark, 2017). It is described as a rapid analytical process based
on X-ray interference on a finely ground crystalline sample (Dutrow & Clark, 2017).
XRD is based on Bragg’s Law: 𝑛𝜆 = 2𝑑𝑠𝑖𝑛𝜃. Portland State University (2017) explains Bragg’s
Law in great detail, mentioning that the Bragg’s developed an idea regarding why faces of crystals
reflect X-ray beams at different angles, hence theta (𝜃) in Bragg’s Law. The variable d represents the
distance between atomic layers in the crystal under investigation, lambda represents the wavelength
of the incident beam (similar to that in Raman Spectroscopy) and n is a simple integer (University,
2017). Since this discovery Bragg’s Law has been adapted and can be used in many applications,
including the investigation of ions, neutrons, electrons and protons (University, 2017).
XRD works in a way that Bragg’s Law can be applied. Similar to Raman Spectroscopy, a beam
is generated andit strikes the specimen under investigation. The incidentbeam is then recorded, along
with the angle in which this beam rebounds. However, unlike Raman Spectroscopy, this beam is made
of monochromatic X-rays. These X-rays are generated using cathode ray tubes which are then filtered
to produce a radiation that is collimated to concentrate and directed at the specimen (Dutrow & Clark,
2017). The diffracted X-rays are collected, processed and counted then scanned through different 2𝜃
angles in order to develop a range of different diffraction directions. Figure 24 shows X-ray diffraction
in its simplest form.

25
3.1.3.1 How it Works
XRD machines have three elements: X-ray tube, sample holder and an X-ray detector. As mentioned
by Dutrow & Clark above, X-rays are produced in the cathode ray tube. This done by heating the
filament and, in turn, producing electrons that then accelerate towards the specimen. Different
materials create different wavelengths and XRD is dependent on this. When the electrons strike the
specimen, wavelengths are created and this can determine the characteristics of the specimen
(Dutrow & Clark, 2017). A common graphical representation of this procedure is shown in Figure 25.
Figure 26 below also shows the set-up of a typical XRD machine along with the behaviour of the
incident and diffracted rays.
Figure 24: Behaviour of X-Ray Diffraction (University, 2017)
Figure 25: Graphic Representation of Incident Ray Electrons (Dutrow & Clark, 2017)

26
3.1.3.2 Applications
There are many applications for an XRD machine, including use in geology, material science,
engineering and biology. For this paper, the use of an XRD machine is for both engineering and
chemical composition. Figure 27 (extracted from Dutrow & Clark (2017)) lists other applications of the
XRD machine.
Figure 26: Basic Features and Set-Up of XRD Machine (University, 2017)
Figure 27: Applications of XRD (Dutrow & Clark, 2017)

27
Table 5: Strengths and Limitations of XRD (Dutrow & Clark, 2017)
Strengths Limitation
→ Data interpretation is easy to
understand and interpret
→ Data is unambiguous and mineral
determination is straight forward
→ Fast technique (less than 20 minutes)
to determine results
→ Sample preparation is simple and fast
→ Non-destructive technique
→ Measure thickness of thin films
→ Homogenous specimens are best for
XRD
→ Requires specimen to be ground into
powder
→ When the specimen is made of mixed
material there is <2% detection of
sample
It is clear from Table 5 that the strengths of using XRD outweigh the limitations of the device
and the strengths of this process are extremely beneficial for data collection and result interpretation.
Therefore, this process will be used in this paper.

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3.2 Passive Layer
When reinforcement steel bars come into contact with a concrete mix, a passive layer is developed
around the outside of the steel. This passive film is made of iron oxide (Fe3O3) and works to protect
the steel reinforcement from any corrosion. Since the concrete solution helps create this passive layer
around the steel, the chemical interactions of the concrete must be understood.
During the hydration of the cement, calcium silicate hydrate (C-S-H) is the primary hydration
product and is the first binding phase in a cement paste (Allen, Thomas, & Jennings, 2007). This C-S-H
gel has a composition of (CaO)SiO2(H2O) (Allen et al., 2007). It is widely believed that a small portion
of any chloride present in the concrete is drawn out and removed from the concrete pore solution
during this hydration process, and that the remaining free chloride ions not removed during the initial
hydration phase pose a serious threat to the degradation of the reinforcement bars (Glass, Reddy, &
Buenfeld, 2000). Other products found within cement, gravels, water and sand make the concrete mix
highly alkaline, including sodium and potassium ions (R. R. Hussain, Alhozaimy, Negheimish, Al-Zaid,
& Singh, 2015). Hussain (2015) mentions that these ions within these aggregate mixes move through
the concrete pore solution, and this migration of ions causes this alkaline mix of concrete. When the
reinforcement bars come into contact with this alkaline mix a series of chemical reactions occur to
create a thin passive film around the steel. The reactions also create considerable changes in the
properties of the concrete, including the microstructure and strength of the pore solution (R. R.
Hussain et al., 2015). Passive layers vary in development due to different pore solutions as they vary
in many elements, including hydroxyl ions, temperature and the solubility of metal cations (Alhozaimy,
Hussain, Al-Negheimish, Al-Zaid, & Singh, 2014). These elements also slightly impact the alkalinity of
the concrete pore solution; however, this small change can increase the corrosion rate of the steel bar
(Alhozaimy et al., 2014).
“The protection characteristics of the passive film develop in the initial nucleation and growth
stage of film formation” (Alhozaimy et al., 2014). Nucleation is known as the first step in the
development of a new thermodynamic phase or structure; therefore, the development of the passive
layer involves nucleation. The first step of the development of the passive layer is nucleation growth
and then the formation of the thin layer of iron oxide occurs (R. R. Hussain et al., 2015). As mentioned,
the passive layer development is dependent on the solubility of metal cations, among others. This
reaction between the metal cations and oxygen within the concrete and the growth of the passive
layer occurs in the already existing passive layer (Alhozaimy et al., 2014). It should be mentioned that
reinforcement bars, before being placed into concrete, already have a thin oxide layer that develops
as soon as the newly formed steel reacts with the air in the atmosphere. The oxygen disperses through
the oxide lattice surrounding the steel bar (responsible for creating oxides) and the growth of the
passive film begins (R. R. Hussain et al., 2015). The chemical equations for the development of the
passive oxide layer are laid out in Table 6.
Despite the variances in chemical compositions of the passive oxide layer (due to different
pore solutions and inhomogeneous concrete), Abreu et al. (2006) states that as long as a passive layer
exists around the steel reinforcement, the steel will not corrode when embedded in concrete.
However, partial or complete degradation of the passive film is known as depassivation, and this
primarily occurs when chloride ions penetrate the concrete (through external and/or internal means)
and come into contact with the passive film (Ghods, Isgor, McRae, & Gu, 2010). When chloride is
naturally found within concrete (often due to aggregate contents and typical cracking and spalling) it
would be expected that the passive layer around the steel would degrade easily; however, Ghods et
al. (2010) discusses a chloride concentration threshold that must be reached before clear degradation
begins. This is known as ‘chloride-depassivation threshold’. Studies in this area are vast yet results

29
vary, so it is difficult to say for certain why the chloride-depassivation threshold is different for so
many different concrete types; however, it has been found that the alkalinity of the concrete pore
solution, the presence auxiliary ions, the steel conditions, the chloride binding potential of the
concrete, oxygen availability and the surface conditions of the reinforcement bar are all variables in
deciding the chloride-depassivation threshold (Abreu et al., 2006).
Table 6: Chemical Reactions to Form Passive Layer (Alhozaimy et al., 2014)
𝐹𝑒 → 𝐹𝑒++
+ 2𝑒−−
This chemical equation represents the reaction
of the iron cations on the steel lattice.
𝑶 𝟐 + 𝟐𝑯 𝟐 𝑶 + 𝟒𝒆−
→ 𝟒𝑶𝑯−
The life-span of this equation is dependent on
the electrons that are developed at the
interfacial cathodic zone. This oxygen reduction
is the most common thermodynamic cathodic
reaction in a typical alkaline solution
𝑭𝒆++
+ 𝟐𝑶𝑯−
→ 𝑭𝒆(𝑶𝑯) 𝟐 This result of this equation is known as ferrous
hydroxide.
𝟒𝑭𝒆(𝑶𝑯) 𝟐 + 𝑶 𝟐 + 𝟐𝑯 𝟐 𝑶 → 𝟒𝑭𝒆(𝑶𝑯) 𝟑 After ferrous hydroxide is developed, another
reaction occurs where ferric hydroxide is
developed.
𝟐𝑭𝒆(𝑶𝑯) 𝟑 → 𝑭𝒆 𝟐 𝑶 𝟑 ∙ 𝑯 𝟐 𝑶 + 𝟐𝑯 𝟐 𝑶 This is known as hydrated ferric oxide. This is
created after the ferric hydroxide decomposes
and this forms a stable passive layer.
𝑭𝒆(𝑶𝑯) 𝟑 → 𝑭𝒆𝑶𝑶𝑯 + 𝑯 𝟐 𝑶 This final equation is known as the chemical
composition of the passive layer surrounding
steel bars
The reactions are activated by a number of aspects, one of them being the internal
temperature of the concrete (Alhozaimy et al., 2014). In saying this, the external environment of the
steel bars (both outside and within the concrete) has a very strong influence on the development of
the passive oxide layer. Figure 28 shows the typical development process of the passive film layer
while being exposed to a concrete pore solution.
Figure 28: Typical development of passive layer around reinforcement bars exposed to a concrete pore solution
(Singh & Singh, 2012)

30
The passive layer is measured on a nano-scale; therefore, the use of nano-techniques such as
Raman Spectroscopy, XRD and Fe-SEM are extremely beneficial for calculating and identifying the
behaviour of the passive film. Hussain (2014) briefly mentions that a nano-scale investigation can
complete a characterisation analysis as well as the typical breakdown action of the film due to
corrosion and several other environmental factors. This is very helpful when the behaviour of the
passive layer is still relatively unknown. An investigation into the passive layer and its behaviour when
exposed to certain environmental factors would be beneficial into understanding the degradation of
concrete structures in marine environments.
3.2.1 Temperature Effects on the Passive Layer
Temperature is a factor that is commonly disregarded as most focus on the more detrimental effect
of corrosion in reinforcement, such as chloride penetration to the passive film layer. However, it is
often mentioned that temperature is one of the key factors in the chemical reactions of concrete,
including that of corrosion. Concrete cover of the steel reinforcement has been previously mentioned
in Chapter 2 of this paper, stating that within the tidal/splash zone concrete strength and concrete
cover are both rather large to account for such harsh environments. This concrete cover is an active
system where the chemical compositions of the concrete changes with the time of exposure to the
harsh environments (Hu, Cheng, Li, Deng, & Wang, 2015). Chloride, carbon dioxide (CO2) and sulphate
(SO4
2-
) are frequently discussed as the main contributors to the decay of the reinforcement (cracking
due to corrosion); however, coupled effects including temperature and carbonation also have the
potential to degrade the reinforcement (Hu et al., 2015). The proposed testing methodology will
consider this in the investigation to develop results for future studies.

31
3.3 Past Investigation
Since it would be beneficial to investigate the passive layer of the reinforcement steel under corrosion
using nano-techniques, research into past investigations regarding this topic was conducted. The
following papers explore the impacts of different effects on the passive film of steel bars embedded
in concrete.
3.3.1 Investigation A – (R. R. Hussain, Alhozaimy, Negheimish, & Zain, N.A.)
The following investigation discusses the factors affecting the passive layer of steel bars in concrete
under sever environmental conditions through the use of nano-technology. The investigation was
completed by Hussain, Alhozaimy, Al-Negheimish and Al-Zaid in Saudi Arabia. This paper was
conducted due to the minimal research completed on the coupling effect of chloride and temperature
and the effect this has on reinforcement in concrete.
3.3.1.1 Technology
Nano-technology used during this experiment are outlined below:
• Tungsten SEM and Fe-SEM
o Used for the steel passive layer and corrosion results as well as viewing the
ITZ between the embedded steel and the concrete
• EDS/EDX
o Used for the passive film and ITZ classifications
• XRD
o Use for peak location and identification of compounds in the passive film
layer
• FT-IR
o Used for material orientation to view the geometry of particles
• Photo Electron Spectroscopy
o Used for material characterisation of various types of steels
3.3.1.2 Materials
Table 7 shows the materials used for this investigation and outlines the material properties
on order to understand the make of these materials.

32
Table 7:Materials and Material Properties used in Investigation
Material Properties
Reinforcing Steel
Retrieved from 5 different local sources (Gulf
region):
→ Sabic Hadeed Steel (A)
→ Ittefaq Steel (B)
→ Muhaidib Steel (C)
→ China Steel (D)
→ Korean Steel (E)
Coarse Aggregates
20mm:
→ Retrieved from Saudi Ready Mix
Company
→ Bulk Specific Gravity = 2.58
→ Absorption = 1.56%
10mm
Company
Crushed Sands
Company
→ Absorption = 2%
→ Fine Modulus= 4.41
Silica Sands
Company
→ Fine Modulus = 1.04
Cement
→ Retrieved from Al-Yammamah Cement
Company
→ Type I cement
Sodium Chloride
→ 99.9% pure
→ Retrieved from VWR Chemicals
Water → Basic tap water
3.3.1.3 Preparations
Reinforcement:
• Mild Steel (MS) was prepared from 5 different production sources (deformed and plain black
steel)
• Diameters differed from 6mm to 12mm
• Cut into 1000mm, 10mm and 2mm segments (in order to work with various SEM and XRD
machines) (Figure 29)
Reinforcement testing:
• Bars are being tested in three surface condition types
• Surface condition types are polished, black oxide mill scale and brown rust (Figure 30)

33
Concrete:
• Mixed according to ASTM C-192
• Aggregates with absorption water were added into mixer
• Cement and remaining water were added after a few rotations of the mixer
• Slump test was performed
• Setting time was tested
Pore Solution:
• Synthetic pore solution was prepared with 7.4g of sodium hydroxide and 36.6g of potassium
hydroxide per litre of calcium hydroxide (saturated)
• This solution was kept under continuous magnetic stirring and then filtered (to remove
calcium oxide from solution)
• Portland cement was sieved and 100g of extract was mixed with 100ml of distilled water
• Concrete prism was developed with a circular hole through specimen to insert steel bar –
distilled water filled hole
o This was done to filter the pore solution from concrete
• Pore solution of NaCl was added to simulate aggressive environment
• Oxygen concentration was high during experiments
Figure 29: 1mm, 10mm and 2mm reinforcement sample
Figure 30: Three Reinforcement Bar Conditions

34
3.3.1.4 Results
After the test was complete, the final chemical composition of the reinforcement bars was determined
via the nano-techniques outlined. Photo Electron Spectroscopy was used for all reinforcement bars to
find the chemical composition.
The samples were cut, polished and covered in resin moulds as seen in Figure 31. These
specimens were then analysed using Photo Electron Spectroscopy and the results are outlined in
Figure 32.
The results outlined in Figure 32 can help understand the future reactions to corrosion the
reinforcement will experience. For example, Bar A has a low carbon content, making it more resistive
to corrosion; however, Bars B and D have high content of carbon, meaning corrosion is highly likely in
these bars. Furthermore, Bar D also has high contents of Sulphur and Magnesium, which means Bar D
will be even more prone to corrosion.
Figure 31: Steel Specimens in Resin Mould ready
for Analysis
Figure 32: Elemental Composition of the Different Types of Steel Tested Based on
the Photo Electron Spectroscopy

35
For analysis of the steel bars themselves, a small section of concrete was cut around the steel
bar in order to fit into the SEM machine. Figure 33 shows the cut concrete and the location of the steel
bar.
Bar C was analysed under SEM and the passive layer around the steel was observed. Figure 34
shows the results from the SEM test and it is clear that there is a non-uniform passive layer. EXDA was
then conducted to truly analyse the passive layer and the surrounding influences on it behaviour.
Figure 35 and 36 show block and spot spectrums at random areas of the reinforcement bar and it can
be seen that after viewing the passive layer from further away (Figure 35) the number of elements
reduce when viewing the layer from a closer distance (Figure 36). In Figure 35, the iron levels have
increased, meaning the passive layer is being more closely observed.
Figure 33: Embedded steel in Concrete with Exposed
Martensite used for Analysis
Figure 34: SEM Image of Steel and Concrete Interface

36
XRD was also performed on the steel bars in order to understand the analysis of the
compounds within the passive layer. The results for this XRD analysis are seen in Figure 37. From this,
it was concluded that there are multiple forms of iron oxides in the passive layer, including Hematite,
Figure 35: EXDA Analysis of Passive Layer
Figure 36: EXDA Analysis of Passive Layer from Closer

37
Magnetite and Magnesioferrite, as well as others outlined in Figure 37. More specifically, Figure 38
show these peaks as quantitative and show each element at each peak.
Figure 37: XRD Results from the Passive Layers of the Steel Reinforcement
Figure 38: XRD Peaks with Steel Identifications

38
3.3.1.5 Conclusions
Despite the extensive use of different nano-techniques, no definitive results have been provided to
truly classify the passive layer and the corrosion behaviour. Although it has been confirmed through
graphical representation that the passive layer is made up of a number of iron oxides, there are still a
number of challenges when trying to confirm a non-uniform layer such as this. Conclusions regarding
the aim of the project have been met, describing the factors that affect the passive film. These factors
included chloride penetration and different pore solutions, as well as the effect different
reinforcement bars have on the passive film.
These factors will be taken on board and considered for the proposed testing method.
3.3.2 Investigation B – (Singh & Singh, 2012)
The following investigation examines three different types of concrete pore solutions with two
different types of steels and the effect of corrosion on these variables. It was produced by Singh and
Singh in 2012 and discusses relevant variables in regard to the proposal topic.
3.3.2.1 Conditions
Rusts formed on two different steels (low allow (LA) and plain carbon (PC)) were analysed using nano-
techniques of XRD and spectroscopy under the following conditions:
• Pore solution of high alkalinity (pH > 12.5) contaminated with a salinity solution
• Pore solution of reduced pH (pH < 10) contaminated with a salinity solution
• Acidic pore solution contaminated with chloride ions
• Wetting and drying cycles
3.3.2.2 Materials and Methods
The steel specimens were embedded in a simulated pore solution made from the following
composition:
4 𝑔/𝑙 𝑁𝑎𝑂𝐻 + 9.8
𝑔
𝑙
𝐾𝑂𝐻
This SPS was prepared by dissolving these chemicals into distilled water. The tests were completed
after the inclusion of the chloride ions. Figure 39 shows the compositions of the three different SPSs
created. It can be seen that the three solutions have different pH levels of 6.5, 9.5 and 12.5 while all
other values are the same. Therefore, the only variable that is independent of the others is the pH. It
should also be mentioned that the amount of NaCl is over the chloride threshold for kickstarting
corrosion. This is to ensure corrosion occurs in the bars through the SPS.
Figure 39: Compositions of SPSs with varying pH levels

39
Figure 40 outlines the chemical compositions of the reinforcement bars used in this
investigation. The reinforcement bars have a diameter of 32mm and were cut at 2cm lengths. These
specimens were also mounted in alkali resistant thermostatic resin to expose the cross-section only
as this area is required for the nano-technologies used in this investigation.
As mentioned, the reinforcement bars are to be wetted and dried to simulate the harsh
environments in which they may be found. The polished cross-sections were targeted during this
phase with three different electrolytes as described in Figure 39. These cross-sections were then dried
by being placed in 50o
C for 2 hours. These specimens were then transferred to a humidity chamber
and stored in an environment of 45o
C ± 0.5o
C at 95% humidity. To generate the dry conditions, the
specimens were removed from the humidity chambers after 7 days and exposed to dry conditions for
a further 7 days, varying between temperatures of 30 and 40o
C. The specimens were subjected to the
wetting and drying conditions for a further 22 weeks, forming rust around these bars. These bars and
the rust conditions were then analysed via Raman Spectroscopy and XRD.
3.3.2.3 Results
The following graphs reveal a number of exposure results, each different from the last. Figure 41
shows that the LA steel retains rust much more than the PC steel. However, the steel retentions seem
to decline after 8 test cycles for both the PC and LA steels.
For the pH solution 9.5, the rust retention for LA is still considerably higher than PC only after
3 wetted cycles. After this there is an incline in rust retention for both LA and PC until the cycles reach
8 weeks, at which they begin to steadily decline. Figure 42 shows this.
Figure 40: Chemical Compositions of Reinforcement Bars
Figure 41: Rust Retentions of LA and PC Steel Bars wetted with pH 6.5

40
Figure 43 shows the rust retention for LA and PC steel at pH of 12.5. These results are
considerably different from the previous. LA is still higher in rust retention than PC; however, this time
LA is much higher in rust retention. There is still a relatively steady decrease at 8 cycles for both LA
and PC steels. These results suggest that at pH 12.5, rust retention is rarely stable and impervious.
The rate of corrosion for the two steels are outlined in Figure 44. This corrosion was recorded
based on the weight loss of the specimens. It was expected that the most acidic pH (6.5) have the
highest corrosion rate in both LA and PC. However, PC is more susceptible to corrosion than that of
Figure 43: Rust Retention for LA and PC Steel at pH 9.5
Figure 42: Rust Retention of LA and PC Wetted with pH 12.5

41
LA steel. Although LA steel was higher in rust retention, the corrosion rate of PC was much higher. LA
steel has a faster corrosion rate, however, as the curve declines faster than PC steel after a pH of 9.5.
After these initial results were recorded, the steel bars were analysed using Raman
Spectroscopy. Figures 45 to 50 show the results from the Raman Spectroscopy analysis. In orde to
understand the result more clearly, the peaks were extracted and placed into a table to easily view
the different chemical combinations. Table 8 clarifies the chemical combinations.
Table 8: Chemical Compositions and their Names from the Raman Spectroscopy Results
Chemical Composition Name Stability
𝜸 − 𝑭𝒆𝑶𝑶𝑯 Lepidocrocite
Un-stable and non-
protective oxides
𝜷 − 𝑭𝒆𝑶𝑶𝑯 Akageneite
𝑭𝒆𝑶𝑶𝑯 Iron hydroxide
𝜹 − 𝑭𝒆𝑶𝑶𝑯 Ferroxyhite
Stable and protective
oxides
𝜸 − 𝑭𝒆 𝟐 𝑶 𝟑 Maghemite
𝜶 − 𝑭𝒆𝑶𝑶𝑯 Geothite
Based on Table 8, and considering Figures 45 and 46, the peaks from the Raman spectra are
(at greatest) lepidocrocite and maghemite for LA. Therefore, it can be said that areas of this passive
layer was defensive towards corrosion (maghemite) and vulnerable towards corrosion (lepidocrocite).
For the PC, both peaks were recorded as lepidocrocite, meaning that the PC was unstable during this
corrosion.
Figure 44: Corrosion Rate of LA and PC Steel at pH Levels after 22 Weeks
Exposure

42
(at greatest) maghemite for LA. Therefore, it can be said that areas of this passive layer was defensive
towards corrosion (maghemite). For the PC, both peaks were recorded as lepidocrocite, meaning that
the PC was unstable during this corrosion.
Figure 45: Raman spectra for LA Steel after 22 Weeks of Exposure in pH6.5
Figure 46: Raman spectra for PC Steel after 22 Weeks of Exposure in pH 6.5

43
(at greatest) maghemite for LA. Therefore, it can be said that areas of this passive layer were defensive
towards corrosion (maghemite). For the PC, both peaks were recorded as lepidocrocite, meaning that
the PC was unstable during this corrosion.
Figure 47: Raman spectra of Rust for LA steel at pH of 9.5 after 22 Weeks
Figure 48: Raman spectra of Rust for PC steel at pH of 9.5 after 22 Weeks

44
For all graphs, LA was high in defensive mechanisms of corrosion and PC was weak in defence
of corrosion as all of the highest peaks in all pH values was considered lepidocrocite. These results
corroborate with those found in Figures 41-44.
Figures 51-56 shows the results from the XRD analysis. An XRD analysis was needed as the use
of Raman Spectroscopy only produces one set of the same results, making the conclusions erroneous.
The use of XRD can provide the research conclusions with more evidence, confirming the results two-
fold.
Figure 49: Raman spectra of Rust for LA steel at pH of 12.5 after 22 Weeks
Figure 50: Raman spectra of Rust for PC steel at pH of 12.5 after 22 Weeks

45
Based on all Figures from 51-56, a conclusion can be made that the LA steel exhibits strong
peaks in goethite and maghemite, meaning it is very defensive in corrosion. However, PC steel shows
high peaks in lepidocrocites, meaning PC is low in corrosion defence. Therefore, these results
corroborate with the Raman Spectroscopy results.
Figure 51: XRD Results for LA Steel in pH 6.5
Figure 52: XRD Results for PC Steel in pH 6.5

46

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