impressed current cathodic protection for reinforced structures: investigation into the use of tin...

7/27/2019 IMPRESSED CURRENT CATHODIC PROTECTION FOR REINFORCED STRUCTURES: INVESTIGATION INTO THE USE OF

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IMPRESSED CURRENT CATHODIC PROTECTION

FOR REINFORCED STRUCTURES: INVESTIGATION

INTO THE USE OF TIN ANODES

Mervyn George

Registration Number: 091572529

Submitted for the qualification ofB.Eng (Hons) Civil Engineering

School of the Built Environment, Heriot-Watt University2012-03-28


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DECLARATION

I Mervyn George, confirm that this work submitted for assessment is my own and is expressed in

my own words. Any uses made within it of the works of other authors in any form (e.g. ideas,

equations, figures, text, tables, programmes) are properly acknowledged at the point of their use.

A full list of the references employed has been included.

Signed: .

Date: 28/04/2013


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AcknowledgmentDuring the course of this dissertation I had the privilege to work with different engineering

students and professors who broadened my knowledge. I would like to thank my dissertation

professor Dr. Olisanwendu Ogwuda for guiding me throughout the entire year with the

procurement of all experimental equipments. I would also like to thank Mr. Mohammad Musleh,

who helped me setup my electrical schematic and guide me through the entire experiment.

Special credits goes to the suppliers for delivering the materials on time and making it this research

a reality.

Finally none of this would have been possible if I dont acknowledge my sincere gratitude to Rami

Mansour for tirelessly helping me throughout my four years in this university. Sincere thanks to

Baraa Mohammad and Haider Abbas for doing the same. You know I love you.


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GlossaryAcid

Containing an excess of hydrogen ions over hydroxyl ions.

Alkaline

Containing an excess of hydroxyl ions over hydrogen ions.

Anode

The electrode through which direct current enters an electrolyte.

Anodic Area

The part of the metal surface that acts as an anode.

Bond

A piece of metal conductor, either solid or flexible, usually of copper, connecting two

points on the same or on different structures, to prevent any appreciable change in the

potential of the one point with respect to the other.

Carbonation

The chemical reaction between carbon dioxide and the calcium hydroxide present in

Portland cement.

Cathode

The electrode through which direct current leaves an electrolyte.

Cathodic Area

The part of the metal surface that acts as a cathode.

Cathodic Protection (CP)

A means of rendering a metal immune from corrosive attack by causing direct current

to flow from its electrolytic environment into the entire metal surface.


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Cell

A complete electrolytic system comprising of a cathode and an anode in electrical

contact with an intervening electrolyte.

Chloride Extraction (CE)

It is a technique used to extract chloride to mitigate chloride-induced corrosion.

Conductor

A substance (mainly a metal or carbon) in which electric current flows by the

movement of electrons.

Continuity BondA bond designed and installed specifically to ensure the electrical continuity of a

structure.

Control Sample

A material of known composition that is analysed along with test samples in order to

evaluate the accuracy of an analytical procedure. Also known as check sample.

Corrosion

The chemical or electrochemical reaction of a metal with its environment, resulting in

its progressive degradation or destruction.

Corrosion Interaction

The increase or decrease in the rate of corrosion, or tendency towards corrosion, of a

buried or immersed structure caused by the interception of part of the cathodic

protection current applied to another structure or current from other source.

Current Density

The current per unit geometrical area of the protected structure in contact with the

electrolyte.


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Electrode

A conductor of the metallic class (including carbon) by means of which current passes

to or from an electrolyte.

Electrolyte

A liquid, or the liquid component in a composite material such as soil, in which the

electric current flows by movement of ions.

Electronegative

The state of a metallic electrode when its potential is negative with respect to another

metallic electrode in the system.

Electropositive

The state of a metallic electrode when its potential is positive with respect to another

metallic electrode in the system.

Electrolyte

A liquid, or the liquid component in a composite material such as soil, in which the

electric current flows by movement of ions.

Galvanic action

A spontaneous chemical reaction which occurs in a system comprising a cathode and

an anode in electrical contact and with an intervening electrolyte, resulting in

corrosion of the anode.

Hydration (of cement)

The chemical and physical reactions between cement and water from which the

material derives its strength.


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Immunity

Potential shifts on the monitoring reference cells being more negative than -720 mV

on interrupting the current. This is the standard used for steel in seawater and is the

value at which corrosion is thermodynamically impossible since the anode reaction

cannot be supported.

Impressed Current Cathodic Protection (ICCP)

The current supplied by a rectifier or other direct-current source (specifically

excluding a sacrificial anode) to a protected structure in order to attain the necessary

protection potential.

Interaction test

A test to determine the severity of corrosion interaction between two buried or

immersed structures.

Ion

An atom, or group of atoms, carrying a positive or negative electrical charge.

Neutral

Containing equal concentrations of hydrogen ions and hydroxyl ions.

Passivity

The state of the surface of a metal or alloy susceptible to corrosion where its

electrochemical behavior becomes that of a less reactive metal and its corrosion rate is

reduced.

pH value

A logarithmic index for the concentration of hydrogen ions in an electrolyte.

Pitting

A non-uniform corrosion of a metal whereby a number of cavities, not in the form of

cracks, are formed in the surface.


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Polarization

Change in the potential of an electrode as the result of current flow.

Polarization Cell

A device inserted in the earth connection of a structure that drains only a small current

from the source used to provide cathodic protection for the structure, but provides a

low resistance path to currents from high d.c. voltages and all a.c. voltages carried by

the structure.

Primary Structure

A buried or immersed structure cathodically protected by a system that may constitute

a source of corrosion interaction with another (secondary) structure.

Protected Structure

A structure to which cathodic protection is applied.

Protection Current

The current made to flow into a metallic structure, with respect to a specified

reference electrode in an electrolytic environment, has to be depressed in order to

effect cathodic protection of the structure.

Protection Potential

The more negative level to which the potential of a metallic structure, with respect to

a specified reference electrode in an electrolytic environment, has to be depressed in

order to effect cathodic protection of the structure.

Protective Coating

A dielectric material adhering to or bonded to a structure to separate it from its

environment in order to prevent corrosion.

Reaction (anodic, cathodic)

A process of chemical or electrochemical change, particularly taking place at or near

an electrode in a cell.


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Sacrificial Anode Cathodic Protection (SACP)

An anode attached to a metal object, such as a boat or underground tank, to inhibit the

object's corrosion. The anode is electrolytically decomposed while the object remains

free of damage.

Stray Current

Current flowing in the soil or water environment of a structure and arising mainly

from cathodic protection, electric power or traction installations, and which can pass

from the environment into the structure and vice versa.

Secondary Structure

A buried or immersed structure that may be subject to corrosion interaction arising

from the cathodic protection of another (the primary) structure.

Structure/Electrolyte Potential

The difference in potential between a structure and a specified reference electrode in

contact with the electrolyte at a point sufficiently close to (but without actually

touching) the structure to avoid error due to the voltage drop associated with any

current flowing in the electrolyte.

NOTE: similar terms such as metal/electrolyte potential, pipe/electrolyte potential,

pipe/soil (water) potentials etc., as applicable in the particular context are used.

Unprotected Structure

A structure to which cathodic protection is not applied.

Source: Structural Technologies

http://structuraltechnologies.com/CathodicProtection/CathodicProtectionGlossary


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Table of ContentsList of Figures and Tables............................................................................................ 12

Abstract ........................................................................................................................ 14

1. Chapter 1 - Introduction ............................................................................................... 151.1 History ............................................................................................................................... 16

1.2 Types of Corrosion ............................................................................................................ 16

1.3 Mechanism of a chloride-induced corrosion ...................................................................... 17

1.4Summary ........................................................................................................................... 182. Chapter 2Literature Review .................................................................................... 19

2.1 Deterioration process of reinforced concrete structures ..................................................... 19

2.2 Corrosion mitigation and concrete repair strategy ............................................................. 20

2.2.1 Traditional Concrete replacement ..................................................................... 20

2.2.1 Corrosion Inhibition ........................................................................................... 21

2.2.1 Electrochemical methods of repair .................................................................... 21

2.3 Cathodic Protection - Overview ......................................................................................... 22

2.4 Recent Studies on Cathodic Protection .............................................................................. 222.5 Steel-Concrete Bond .......................................................................................................... 23

2.6 Comparisons of Cathodic Protection with other techniques .............................................. 24

2.7 Advantages of Cathodic Protection ................................................................................... 26

2.8 Summary ............................................................................................................................ 26

3. Chapter 3Properties of Tin ...................................................................................... 273.1 Physical Properties ............................................................................................................. 27

3.2 Chemical Properties .......................................................................................................... 28

3.3 Application of Tin (Sn) ..................................................................................................... 28

3.4 Use of Tin in the Built Environment ................................................................................. 28

3.5 Use of Tin as anode............................................................................................................ 29

3.6 Dissertation Work .............................................................................................................. 29

3.7Summary .......................................................................................................................... 304. Methodology and Experimental Work ..................................................................................... 31

4.1 Experimental WorkProposal ........................................................................................ 31

4.2 Preliminary Experiment .................................................................................................... 31

4.3 Main Experiment ............................................................................................................... 33


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4.3.1 Acceleration of Corrosion ................................................................................. 34

4.3.1.1 Methodology .................................................................................................. 36

4.3.1.2 Schematic ....................................................................................................... 37

4.4 Impressed Current Method ............................................................................................... 37

4.5 Parameter of Analysis ....................................................................................................... 38

4.6 Summary ........................................................................................................................... 40

5. Analysis and Results .................................................................................................... 415.1 Corrosion behaviour and cracking behaviourBackground Study .................................. 41

5.2 Mass loss measurement ..................................................................................................... 42

5.3 Analysis ............................................................................................................................ 42

6. Discussion and Conclusion .......................................................................................... 446.1 Interpretations ................................................................................................................... 446.2 Conclusion ........................................................................................................................ 45

6.3 Future Work ...................................................................................................................... 45

7. References .................................................................................................................... 468. Appendix I ................................................................................................................... 499. Appendix II .................................................................................................................. 5010.Appendix III ................................................................................................................. 5211.Appendix IV................................................................................................................. 5312.Appendix V .................................................................................................................. 54


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List of Figures and TablesFigure

Number Page Number

1 Illustration of Chloride-Induced Corrosion .................................................... 16

2 Magnesium wound steel reinforcement (SACP) ........................................... 31

3 Control Samples and Ammeter Readings (ICCP) ......................................... 32

4 Set-up for Acceleration of Corrosion.......................................... 33

5 Overhead view of the acceleration setup............................................. 34

6 Schematic of the acceleration corrosion test setup.................. 36

7 ICCP setup with simultaneous acceleration. Tin mesh is used as the anode 37

8 Measured weight of steel and tin mesh 38

9 Current vs. Time for OPC beams 40

10 Corrosion Current vs. Time .. 42

11 Measured weight of steel, tin mesh .... 42

12 Pitting corrosion formed during acceleration of corrosion .... 43

A1 Cube placed inside compression machine.... 52

A2 Corrosion products formed in saline solution....53

A3 Corroded beams after electrochemical acceleration .... 53

Table

Number Page Number

1 Various treatment options for chloride-induced corrosion.......................... 24

2 Properties of Tin ......................................................................................... 26

3 Concrete mix design specification............................................................... 34


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4 Measured weights of reinforcement in all beams....................................... 35

5 Percentage Mass losses of steel reinforcements......................................... 41

T1 Gantt chart highlighting the sequence of events for the Project................... 49

T2 Gantt chart highlighting the tasks proposed for December 2012................. 49


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AbstractThesis Title: Impressed Current Cathodic Protection:

An Investigation into the use of tin anodes

Degree: Bachelors of Civil Engineering

Year of Convocation 2013

Name Mervyn George

University Heriot-Watt University

This report presents the result of a laboratory investigation into the use of tin anodes in an

impressed cathodic protection setup to mitigate chloride induced corrosion in reinforced

concrete beams (RC). Two control samples (500 x 100 x 100 mm) were constructed which had

undergone acceleration of corrosion through electrochemical methods. Simultaneously, two

reinforced concrete beams of the same dimension were embedded with a mesh made up of

60% tin and 40% lead. The beams were analysed based on the corrosion current produced

during the experiment and the percentage of mass loss before and after the experiment. It was

observed that the tin mesh along with the supplementary voltage of 0.5 V provided enough

electrons to dissipate chloride ions as chloride gas instead of forming corrosion products on

the reinforcement. It was also noted that the tin mesh didnt deplete in the process which

reinforces the concept of this dissertation.


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1.1 History

Most metals exist in nature as oxides or sulphur ores and energy is expended in

extracting or winning the metals from their native state. The reserve of metal winning is

corrosion, in which metals revert to stable compounds similar to those found in nature. For

corrosion to occur, as with any chemical reactions, two primary questions arise i.e. will a

metal corrode in a given environment? (2) How fast will it corrode in the specified

environment? Thermodynamics and Kinetics are two broad subjects that can answer the

former and later respectively. As these are two varied topics and out of the scope of this

research, it wont be studied into in detail (Handbook of Corrosion (2005) Corrosion. 978-0-

306-48624-1 US: Springer US)

1.2 Types of Corrosion

a) Uniform Corrosion: As the name suggests, corrosion happens throughout the steelsurface and it is often predictable. Uniform corrosion accounts for 70% of all metal

failures.

b) Localised Corrosion: Unlike uniform corrosion, these types of corrosion in whichthere is intense attack at localized sites on the surface of a component whilst the rest ofthe surface is corroding at a much lower rate - either because of a natural property of

the component material (such as the formation of a protective oxide film) or because

of some environmental effect. Indeed the main surface may be essentially

unsatisfactory corrosion control. In such circumstances, if corrosion protection breaks

down locally then corrosion may be initiated at these local sites. Chloride-induced

corrosion causes localised corrosion. (ASTM Standard G78, 2012)

As mentioned before, chloride induced corrosion is one of the primary causes of

localized corrosion and this research will largely focus on this and methods to curb the

corrosion. One of them being the use of Cathodic Protection Systems and specifically

looking into new materials for anode material. The use of tin as an anode has not been

studied upon as a suitable anode in such a system and the effectiveness of this element is

largely the focus of the dissertation.


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1.3 - Mechanism of Chloride Induced Corrosion

The steel embedded in concrete is naturally protected against corrosion through

passivation of steel surface due to high alkalinity of concrete (pH>12.5). As a result of

passivation of steel, an oxide layer is formed during the hydration of cement (Kassir and

Ghosn, 2002). This passive layer does not stop corrosion; it reduces the corrosion rate to an

insignificant level. Typically the passive corrosion rate for steel in concrete is 0.1 ,

without this passive layer, steel could corrode at rates three times higher than this magnitude.

In marine structures, chloride ions are derived from de-icing salts in cold environments or from

exposure to sea water. The chloride ions get incorporated into this oxide layers creating ionic

defects and permitting easy ionic movements. The chloride ions also compete with hydroxyl

ions for localization of high activity of the metals, thus preventing these reaction sites from

becoming passivated (ACI-Committee 222, 2001). As a consequence it leads to active

corrosion and the corrosion deposits increases the volume of the steel reinforcement leading to

surface cracks, delamination and spalling. Figure 1, illustrates the process of corrosion with

respective half-cell reaction.

Figure 1: Illustration of chloride-induced corrosion (Cement, Concrete and

Aggregates, Australia (2006)


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1.4- Summary

This chapter details the major problem facing the construction sector in the United Arab

Emirates i.e. Corrosion and Corrosion related consequences. It also gives the reader a brief

into the history of corrosion and the mechanism of chloride-induced corrosion which mostly

affects countries near the coastal line.

The ongoing research for this dissertation is on, one of the most effective ways to curb

chloride-induced corrosion i.e. Cathodic Protection of Reinforced Structures specifically

looking into the effectiveness of tin to be used in an impressed cathodic protection system. The

next chapter goes through an in-depth literature survey on Cathodic Protection, deterioration

processes of reinforced concrete structures and the feasibility of tin as a suitable anode in an

Impressed Cathodic Protection System (ICCP).


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Chapter 2 Literature Review2.1

Deterioration processes of reinforced concrete structures

A brief understanding of chloride induced corrosion has been discussed in the previous

chapter. It has become of utmost priority to predict the residual life of structures and structural

elements in order to make a better judgement on the structural integrity and serviceability

during the course of its design life. These predictions are very useful in enhancing the

rehabilitation strategies and analysing various cost-effective options.

There are a number of models for estimating the residual life of reinforced concrete structure

and their respective elements with regard to corrosion. Tuutti (1982) proposed a prediction

based on the damaged model in which the life cycle of a corrosion damaged building is

described as a two-stage process

1. Initiation Stage: Corrosion initiates as sufficient amount of impurities reach thereinforcement.

2. Propagation Stage: After it penetrates into the concrete surface the damage builds upand reaches the limit state. It is during this time that the failure becomes unacceptable.

The service life as proposed by Tuutti (1982) is as follows

Sufficient understanding of corrosion and its deteriorated on process have led to the

development of various reinforced corrosion mitigating techniques and concrete rehabilitation.

These are briefly discussed in the next section


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2.2 Corrosion mitigation and concrete repair strategy

Highway and building structures are deteriorating at alarming rates worldwide. The choice of

an appropriate rehabilitation and repair technique and material will be determined from full

understanding of the underlying cause(s) of the problem. Corrosion of the steel reinforcement

could lead to structural weakness due to loss of cross-section of the steel reinforcement or pre-

stressing wire (Neville, 2002). These can be broadly classified into the following groups

1. Traditional Concrete Replacement2. Electrochemical Repair Methods3. Corrosion Inhibitors

2.2.1 Traditional Concrete Replacement

Traditional concrete replacement consists of removal of defective concrete in an

attempt to eliminate the cause of the problem. Furthermore, one of the potential problems with

the patch repair using cementitious materials is to prevent subsequent ingress of pollutant,

including chloride ions. To overcome this problem the patch-repaired structure can be coated

using various surface coatings in order to prevent further ingress of aggressive ions from the

environment (Zhang, 2006)

In summary, traditional patch repair is a short term remedy that can be carried out to

delaminated and spalled areas. Conventional patch repair of corroded concrete structures

inevitably introduces an incipient anode effect. This is caused due to different

electrochemical behaviour of steel reinforcement in the new concrete repair material and the

surrounding old, but sound, concrete which may still be contaminated with chloride. The newly

chloride-free patched area becomes less negatively potential and start to corrode.

Conventional patch repairs treats only symptoms and not the cause and incipient anodeeffect makes this a never ending process. Hence, corrosion engineers have to look into various

other long term corrosion mitigating solutions.


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2.2.2 - Corrosion Inhibition

Corrosion inhibition work by chemically raising the threshold of chloride required to

initiate de-passivating the reinforcement and initiate corrosion. Corrosion inhibition have been

used for many years in the automotive industry and have been demonstrated to be effective in

new-build concrete, in particular the use of calcium nitrate as an admixture to fresh concrete.

However, the application of corrosion inhibitors to existing chloride-contaminated concrete

has been shown to be less effective (Alexander, 2006)

2.2.3 - Electrochemical methods of repair

Cathodic Protection (CP) and Chloride Extraction (CE) are both classified as methods

of repair using electrochemical technique and are used to arrest chloride deposition whichleads to corrosion. Both CP and CE require an active electrical circuit to be established which

forces the steel reinforcement cage to become cathodic (non-corroding) by providing an

external anode (corroding). CP can be applied in two ways: (a) by an Impressed Current

Cathodic protection (ICCP) system in which CP uses a permanent external anode connected to

an electrical power supply such as a transformerrectifier; or (b) the second approach, which

is known as the sacrificial anode system (SACP) and uses a metal anode (such as zinc) with a

higher natural galvanic potential than that of steel to establish the necessary drive potentialdirectly connected to the steel structure to be protected (Highways Agency, 2002).

Chloride extraction is similar to ICCP in that a external DC voltage is used to drive

the whole process; however, an anode is connected in series using a suitable electrolyte to

complete the circuit. The drive voltage for CE is very much higher than CP as the aim is to

draw the negative chloride ions away from the reinforcement towards the anode and out of the

concrete.

The durability of repairs using CP has been well established, provided the systems are

actively monitored (Chess, 1998). Advances in remote monitoring technology have reduced

monitoring costs significantly in recent years. The durability of repairs using CE is less well

established. The efficiency of the CE to remove chlorides from around the reinforcement to

establish passivity of the reinforcement can vary significantly from structure to structure. CE

may be required at intervals during the life of the structure as the remaining chlorides migrate

towards the steel reinforcement. The advantage of CE over CP is the short-term duration of the

repair works (Chess, 1998).


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ICCP systems also generate hydroxyl ions around the reinforcement, which raise the

alkalinity of the concrete surrounding the reinforcement, helping to re-establish the passivity

of steel. This can give rise to an increased risk of alkali-silica reaction if reactive aggregates

are present in the concrete. The higher the impressed current, the greater the risk of alkali-

silica reactions.

Hence ICCP systems are not suitable for short-term purposes. For long-term solution

of controlling corrosion, application of CP is considered the only technique proven to

stop/mitigate ongoing corrosion of steel reinforcement. This is particularly the case for

chloride-contaminated concrete.

2.3 Cathodic Protection Overview

For long term solutions, Cathodic Protection is the only technique to mitigate corrosion.

Cathodic protection of reinforced concrete is an electrochemical method to stop or mitigate

corrosion especially chloride induced corrosion by supplying current from an external source

to suppress an internal current flow due to the process of corrosion The external current can be

achieved in two ways (Atkins, n.d)

1. Coupling the steel with active metal like zinc, magnesium etc which is termed asSacrificial Cathodic Protection System (SACP)

2. The external current may be derived from the mains operated low voltage DC powersupply (transformer or rectifier) which is termed as Impressed Current Cathodic

Protection System (ICCP)

2.4 Recent Studies on Cathodic Protection

Both SACP and ICCP are proven to be feasible protection systems but the impressed

current offers greater flexibility with regard to its ability to provide necessary current to the

system. The sacrificial cathodic protection system is most effective if the concrete resistivity

is low or the anode is placed in a very low resistivity environment like soil as the driving

voltage is relatively low (Atkins, n.d.)

The first use of tin as an anode was experimentally performed by Sir Humphrey Davy

in 1823 when it was first commissioned to investigate the corrosion of copper sheathing of the

hulls of wooden naval ships. During this time, Davy worked on various another metals like

iron and zinc to protect copper. Davy concluded that cast iron worked best because it lasted


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longer and remained electrically more active than zinc and tin (On Corrosions of Copper

Sheeting, 1824)

Separate studies were conducted by researchers from Obafemi Awolowo University on

the effects of tin composition on Al-Zn-Mg alloy as sacrificial anode in seawater. The results

obtained in the experiments conducted with various percentages of tin compositions showed

that anode efficiency increased with the increase in tin content (Umoru, Ige, 2007). This study

reinforces the theory that tin has increased efficiencies of alloys as sacrificial anodes but the

effect of tin as a standalone anode for impressed current systems are yet to be studied.

In addition, for the last 15-20 years, researchers have made considerable advances in

the developments for new anode materials. Conductive coating anodes based on variety of

carbon pigmented solvents have been researched and well documented. However the electric

and electrochemical properties depended on the graphite content. It exhibited poor mechanical

properties and became porous after exposing it for 12 days (Darowicki, et.al n.d.). From 1997,

researchers have been working on thermal sprayed titanium coatings for cathodic protection of

RC structures (R. Brousseau, et.al 1997). The main objective of this paper was to reduce the

driving voltage of reinforced concrete samples which is the similar objective of thisdissertation but using tin mesh anodes rather than pre-coated metals. Other studies have been

conducted with mixed metal oxide coated titanium mesh, anode designs based on utilising zinc

rich paints and also magnesium embedded anodes (Department of Transport, UK, 2002).

2.5 Steel-Concrete Bond Strength

Impressed Current Cathodic Protection (ICCP) as widely known as a technique to

mitigate corrosion and various corrosion by-products. Another study that adds value to this

dissertation is the increase in the steel-concrete bond by the use of ICCP. Hydrogen, Potassium

and sodium ions migrate towards the steel-concrete interface which pays an important role

against the bond loss at the interface. (Garcia, et.al, 2012)

It was noted that when Ordinary Portland Cement (OPC) was mixed with fly-ash the

bond strength increased. This was due to the decrease in the hydrogen-ion content. Since this

is an academic research with time constraints, the control samples have to be developed with

bare minimum specification in-order to analyse the effectiveness of the tin mesh anode.


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2.6 Comparisons of Cathodic Protection with other techniques

Before selecting a suitable solution for corrosion damaged structures, the advantages and

limitations for different methods have to be evaluated. Irrespective of the selected treatment

for control or rehabilitation of damaged structures, it is most important to minimise future

chloride contamination by dealing with the source of the problem. The main treatments are

summarized in, Table.1,


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Table 1 : Various Treatment Options for chloride-induced corrosion (Department of Transport, UK, 2002)

Treatment Solution Comments

Do Nothing It is generally acceptable if the whole

structure is awaiting partial or complete

repair of the damaged structure

Coatings Silane, a toxic chemical compound is

typically used for structures exposed to

chlorides. However, if sufficient chloride

has already penetrated into the structure,

then this application may mitigate corrosion

but may not completely stop it.

Concrete Replacements Sometimes, due to long exposure to chloride

contaminated environments, it may be

viable to completely replace the damagedstructure.

Cathodic Protection Unlike other solutions, Cathodic protection

offers protection to the whole area against

corrosion. It reduces the frequent concrete

repairs and other maintenance requirements.

It requires permanent current source to run

the system and also requires periodic

monitoring. Cathodic protection has an

effective life of more than 100 years and is

proven to be a reliable and long term

solution

Stainless Steel Bars Stainless steel looks like the most viable

option as it has high resistance to corrosion.

But stainless steel is a very expensive option

and it has possible issues with galvanic

coupling. Also stainless steel is not suitable

for hot marine environment.


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2.7 Advantages of Cathodic Protection

The principal advantage of CP over traditional repair is that only the damaged concrete

areas (i.e. spalled, delaminated or severely cracked) need to be replaced. Concrete that is

contaminated with chloride, but otherwise sound, can remain since the possibility of

subsequent corrosion will be prevented by the appropriate electrochemical process. The costs

involved in the installation and operation of the CP system are more than offset by the savings

that result from the reduction in concrete repair quantities and shorter duration of site work. In

many cases the reduction in repair may obviate the need for temporary propping with a

consequent reduction in costs. (Das, et.al, 2010)

Cathodic protection does not restore lost steel, but provided that the steel has sufficient

reserves of strength then CP can provide a cost-effective solution. Even when the strength is

inadequate it is possible, in many cases, to combine CP with strengthening. With a well-

designed and installed CP system, the costs of operation and maintenance would be extremely

low. It is now well recognised that in most cases CP can provide a cost-effective solution to

stop corrosion and the importance is acknowledged with codifying by a number of national

and international standards (BSI, 2000; NACE, 2000).

The performance of the installed CP systems would be monitored using embeddablereference electrodes and other monitoring probes. All reference electrodes could be integrated

into a monitoring unit and could be interrogated either manually or through automatic data

logging devices which could be operated locally or remotely. In addition, the monitoring

reference electrodes for ICCP systems would function to control the system output to provide

adequate levels of protection. (Das, et.al, 2010)

2.8 Summary

This chapter summarizes on the recent studies on Cathodic Protection and details the

critical analysis of various options of corrosion mitigation techniques as shown in Table 1.

The chapter concludes on the advantage of Cathodic Protection System and consolidates on

the fact that the only guaranteed method of mitigating corrosion due to chloride penetration is

ICCP.

The next chapter looks into the properties of anode materials focusing on the Tin (Sn) whichis part of the group 14 of the periodic table.


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Chapter 3 Properties of TinTin (chemical symbol, Sn) is a chemical element which is the main group element in

group 14 of the periodic table. This metal forms part of the post transition metals which

means that it cannot be oxidized easily. Tin is also an element with highest number of stable

isotopes. Properties are given in table 2

3.1 Physical Properties

Table 2: Properties of Tin (CRC Handbook of Chemistry and Physics)

Name Properties

Element Classification Metal

Density (g/cc) 7.31

Metal Point (K) 505.1

Appearance silvery-white, soft, malleable, ductile metal

Atomic Radius (pm) 162

Atomic Number 50

State at room temperature Solid

Block P

Boiling Point (C) 2586

CAS Number 7440-31-5


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3.2 Chemical Properties

Tin is relatively unaffected by both water and oxygen at room temperatures. It does not

significantly corrode, rust or react in any abnormal way. At high temperatures, the metal reacts

with water and oxygen to form tin oxide.

Also, tin is attacked slowly by dilute acids such as hydrochloric acid and sulphuric acid. Dilute

acids are mixtures that contain small amounts of acid dissolved in large amounts of water. This

makes tin as a good protective covering. (Emsley, 2011)

3.3 Application of Tin (Sn)

Tin has a wide application in the Electrical and Electronics industries, majorly used as

solder wires which are widely used to join electrical components due to its weak melting point.

Tin is also used as a coating to mitigate corrosion. Tin cans for example are made of tin

coated steel which are used to preserve food products. Tin chlorides is used as a mordant in

dyeing textiles and for increasing the weight of silk. Stannous fluoride is used in some

toothpastes. (Emsley, 2011)

3.4 Use of Tin in the Built Environment

Tin has been principally used as an architectural element in alloying of metals such as

copper to form bronze and the coating of tin on harder metals such as iron or steel. Tin roofs,

a type of tin plate was originally used for armour but eventually as a roofing material. It is also

widely used for decorative purposes such as ornamental windows and door lintels.

Although tinplate is widely available today as a roofing material, but it is fairly

expensive since the initial cost is more than any other common roofing materials like asphalt

or built-in roofs. Since a well maintained tinplate roof typically last several times longer than

either of these types of roofing, it is more economical when cost is prorated over the longer

lifespan. (Emsley, 2011)


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3.5 Use of Tin as an anode

Researchers at the Toyota Research Institute developed an insertion type of tin anode

material for use of a magnesium-ion battery that shows superior voltages and capacity. They

confirmed the materials performance in rechargeable Mg-ion (Magnesium ion) batteries by

coupling it with a Mo6S8 cathode in a conventional battery electrolytethat necessary

compatibility and cyclability being an important result, they noted. The use of tin as an

insertion-type anode would allow for the evaluation of future, high voltage/capacity Mg-ion

battery cathodes using conventional battery electrolytes, they concluded. (Green Car Congress,

2012)

Apart from the above mentioned applications, tin has not been used in the construction

industry as an anode for cathodic protection of reinforced concrete structures. Although the

purpose of this research is to prove that tin can be efficiently used to mitigate corrosion in

reinforced concrete samples, it could provide a huge breakthrough considering the cost benefits

and its long term benefits as an anode in an impressed Cathodic Protection setup. (Emsley,

2011)

3.6 Dissertation Work

In this research, solder wires (60% tin, 40% lead) have been soldered into a mesh to

act as an anode, which are embedded in concrete beam samples. The tin mesh is placed 40 mm

from the casting face and separated by a distance of 30 mm from the reinforcement.

The tin mesh and the reinforcement were electrically connected to each other and to a

stable source of direct current which were provided by a DC Voltage Supply.

Before the start of the main experiment, a preliminary experiment was conducted to

finalise on the qualification of tin as an anode. The details of this experiment are mentioned in

the following chapters.


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3.7 Summary

To summarize, tin has various applications in the field of electronics, food industry and

as advanced anode in lithium batteries. This chapter aimed at providing basic physical and

chemical properties of tin. The next chapter will look in detail of the experimental procedures

and methodology of this research.


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Chapter 4 Methodology and Experimental Work4.1 Experimental WorkProposal

In a study conducted by researchers from Bradford University on corrosion of steel

reinforcement concrete cubes at compressive strengths of 20, 30 and 45 MPa, they concluded

that concrete cubes with the least compressive strength showed early signs of corrosion after

undergoing corrosion accelerations tests. This is primarily because of loose pore structure that

allows penetration of chloride and moisture to the steel/concrete interface. After exposure of

the steel bar for 1 day showed small pits and small forms of rust were infested. After the end

of the experiment (15th day), the steel reinforcement showed increased amount of rust and pits.

It was also noticed that the cross-section of the reinforcement decreased because of the increase

in pits (Abosrra et.al, 2011).

The proposed experimental work for the upcoming semester is to compare corrosion of

normal reinforced concrete specimens (control) with reinforced concrete specimens protected

with ICCP. The experiment is designed to analyse the effectiveness of Tin to act as an anode.

To understand the effectiveness of tin as a primary anode, the control samples had to be

designed for lower compressive strength as described in the above research studies for quickerresults. Hence the compressive strength of the control samples was designed for 28 MPa. See

Appendix III and figure 5 and figure 6 shown further details on mix design and standard

compression tests performed.

4.2 Preliminary Experiments

Experiment #1

To understand the principle of Cathodic Protection in general, two sets of experiments

were conducted. In one experiment, the steel rod was dipped in 200ml of sea water. The steel

rod was spirally wound with magnesium strips, thus making it a SACP. Since magnesium

(Mg) lies above steel (iron) in the galvanic series, it acts as a sacrificial anode to protect steel

from reverting back to its natural state i.e. iron ore or ferric oxide (Fe2O3) better known as rust.

After 3 days of initiating the experiment, the magnesium due to high reactivity, tends to

naturally lose its electrons to protect steel. Hence the magnesium dissipated under the saline

conditions and protected the steel. This shows that sacrificial anode materials have to be


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During the course of both the experiments, it was compared to a control sample. It was noticed

that the impressed current method (0.5V) provided less ferrous deposits on the cathode (red

colour) as opposed to the control sample which was not protected (See figure 3)

4.3 Main Experiment

Following the drawbacks and results from all 4the preliminary experiments described

in section 4.1, the main experiment was performed with an ICCP setup in concrete.

Corrosion as is known today is fairly a slow process and it could take effectively years to be

noticed in marine structures. If not carefully maintained, it could go un-noticed and would

Figure 3: (top left); Control Sample (top right); Ammeter showing corresponding current reading (bottom);Comparison between the protected sample and control sample (Photos taken after 30 days)


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subsequently lead to failure of a structure. To recreate corrosion under real-life conditions in a

lab setup would be impractical considering the time-frame of this research. Hence, the one

solution would be to accelerate corrosion under special circumstances. The following sections

are the list of stages that need to be accomplished in order for any meaningful

analysis2to2be2undertaken.

4.3.1 Acceleration of Corrosion

The first stage that was accomplished was to accelerate corrosion in control samples as a base

to compare with the impressed current system. The steel reinforcements were measured prior

to start of this experiment as loss/gain of cross-sectional area could give an indication of the

extent of corrosion in the control samples. Figure 4 and figure 5 shows the setup for the

experiment

Figure 4 Set-up for Acceleration of Corrosion


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Two control samples have been casted with the following mix design for a beam of volume

0.05 m3 as shown in table 3 which gives a concrete strength of approx. 25 MPa as shown in

table 3

Table 3: Concrete Mix Design Specification

Material Weight ( kg)

Cement 2.92

Water 1.05 L

Coarse Aggregates - 20mm 4.82

Fine Aggregates -10mm 3.2

Fine Aggregates (Less than 10mm) 2.4

Figure 5: Overhead view of the acceleration setup


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All control samples were reinforced with steel rebars at the centre, 30 mm from the base of

the beam. The weight of the steel before casting are as shown in Table 4

Table 4: Measured weights of reinforcements in all beams

Name Weight (g)

Control Sample A 102.5

Control Sample B 103.0

Control Sample C 102.5

Sample with Tin Mesh A 103.0

Sample with Tin Mesh B 103.0

Sample with Tin Mesh C 103.0

4.3.1.1 Methodology

The beam specimens were partially (7.5cm) immersed into a seawater solution at

room temperature after 3 days of curing for 21 days. The pre-wetting allows keeping the initial

D.C. to a manageable low value. Then, the exposed steel bars were connected to the positive

terminal of a constant 30 volt D.C. power supply, to make the steel bars act as anodes. This

high voltage was used to accelerate the corrosion and shorten the test period. The negative

terminal of the DC power source was connected to a stainless steel mesh placed near the beams

in the solution, and sat on a stainless steel plate placed beneath the beams. The stainless steel

plate and the mesh were used as the cathode, and isolated from the beams. Moreover, the steel

mesh was cleaned periodically to prevent the deposition of calcium; on the surface .Each time

the current intensity showed a sudden increase indicated the cracking of the beam by corrosion.

In order to determine the time at which the specimen cracked (referred to as corrosion time),

the intensity of the electric current was recorded at different time intervals. The beams were

visually inspected daily for cracks while the current flow was continuously monitored using

an ammeter. Following the weight of the steel bar was measured, and recorded for weight loss

measurement before the accelerated corrosion test was started. (Reddy et.al, 2011)


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4.3.1.2 Schematic

Figure 6 shows the schematic for the electrical arrangement. The negative terminal of the DC

Voltage is connected to the stainless steel mesh and base plate using an alligator clip. The

positive terminal of the DC voltage was connected to the respective steel reinforcement of the

control samples.

4.4 Impressed Current Method

The method for Cathodic Protection was be pre-dominantly based on the preliminary

experiments conducted as described in section 4.2, experiment #3.

A voltage of 0.5 V was be equally distributed over the tin mesh simultaneously when the

samples are being accelerated simultaneously. Since the preliminary experiment with solder

wires should positive results in terms of reduced corrosion products on tin and non-depletion

of solder wire. Figure 7 shows the detailed experimental setup

Figure 6: Schematic of the acceleration corrosion test setup

Figure 7- ICCP setup with simultaneous acceleration. Tin Mesh is used as

the anode


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4.5 Parameter of Analysis

The sole parameter of analysis in this research was loss in weight of the steel reinforcement.

As well documented, once a steel reinforcement undergoes corrosion or accelerated corrosion,

rust products form on top of the reinforcement thus increasing the overall weight of the steel.

(Reddy et.al, 2011)

Therefore, the weight of the steel as mentioned before have been measured and the

comparative weight of the reinforcements between the control samples and the samples with

tin mesh were analysed.

Refer to figure 8 for readings of the weight of steel and tin mesh.


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Figure 8 (top left) Measured weight of steel reinforcement (top right) Measured weight of tin mesh (bottom)

completely cast beams with steel reinforcement and tin mesh.


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4.6 Summary

This chapter has looked into detail the methodology to be carried out for the proposed

experiments and the parameter of analysis that could then be summarized into an academic

conclusion in the field of engineering and in particular reinforced concrete structures along the

perimeter of the coastal lines of Dubai. Chapter 5 looks into the analysis of the extracted data.


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Chapter 5 Analysis and Results

5.1 Corrosion Current and Cracking Behaviour Background Study

During the process of corrosion, the negatively charged ions (chloride) is being attracted by

the steel reinforcement bars when current is applied from the electrolyte (salt solution) into the

concrete and toward the positively charged steel bars. As the chloride-ion reaches the steel-

concrete interface above the acceptable concentration, the steel surface begins to corrode. The

cracking development, due to corrosion at the rebar, leads to increased salt water access to the

steel surface, creating a direct current path between the reinforcement and the electrodes in

solution. Any sudden increase in the current flow indicated a reduction in electrical resistance.

During a study in acceleration of corrosion as described in section 4.3.1.1, the Ordinary

Portland Cement (OPC) beams recorded a decrease from 772 to 689 mA, for 12 hours, and

then the current started to increase from 689 to 758 mA for the next 12 hours. This is due to

the chloride solution reached the steel-concrete interface, a current path is created along with

a decrease in electrical resistivity of the beam. Therefore, the significant differences in current

recordings. (Reddy et.al, 2011). Figure 9 shows the current readings for various compositionsof ordinary Portland cement

Figure 9: Current vs. Time readings for various OPC beams


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5.2 Mass Loss Measurements

It is very well known that the most precise method to determine the degree of corrosion

in embedded steel is the mass loss measurement (Reddy et.al, 2011). Therefore, in-order to

determine the mass loss of the corroded reinforcing steel, the beams were completely brokento retrieve the entire bar. Table 3 will be used as the reference for comparison of any mass

loss/gain and the percentage can be obtained for both.

5.3 Analysis

The beams were corroded as per the schematic in section 4.3.1.2, and a multimeter is used to

record the readings in every 1 hour interval in a 60 hour test duration. Readings are taken

simultaneously for the three control samples and the tin mesh embedded beams. Table 5 shows

the percentage of mass loss of reinforced bars after acceleration of corrosion.

Table 5: Percentage Mass losses of Reinforced Bars after Accelerated Corrosion Exposure

Specimen Initial Mass (g) Final Mass (g) Mass Loss (%)

Control Sample A 103.0 86.8 16

Control Sample B 103.0 89.8 12.81

Tin Mesh A 103.0 91.4 11.2

Tin Mesh B 103.0 95.4 7.3


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Figure 13 shows a graph between corrosion current and time. The readings were taken for a

span of 67 hours for control samples and ICCP samples. All data values are attached in

Appendix V

0.00040.00060.0008

0.0010.00120.00140.00160.0018

0.0020.00220.00240.00260.0028

0.0030.00320.00340.00360.0038

0.0040.00420.00440.00460.0048

0.005

0 5 10 15 20 25 30 35 40 45 50 55 60 65

CorrosionCurrent(mA)

Time (Hours)

Control Sample - 30 V

Figure 10 Corrosion Current vs. Time

0.0003

0.00032

0.00034

0.00036

0.00038

0.0004

0.00042

0.000440.00046

0.00048

0.0005

0.00052

0.00054

0.00056

0.00058

0.0006

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

CorrosionCu

rrent(mA)

Time (Hours)

Impressed Cathodic Protection - Tin Mesh Anode ( 0.5 V)

Figure 11 Corrosion Current vs. Time for ICCP with Tin Mesh Anodes


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Chapter 6 Discussion and Conclusion6.1 Interpretation

From figure 10, the control samples have been corroded according to the theory

outlined in section 5.1. The rise of the corrosion current at the 10 th, 19th and 40th hour indicates

the peak at which cracks and delamination started to occur on the control samples.

Comparing this with figure 11 which was embedded with tin mesh anodes with a

voltage of 0.5 V, the physical cracks and delamination were very insignificant although few

could be seen as a result of excess salinity in the electrolyte. The significant change from both

these graphs are the decrease in corrosion current which consolidates on the theory that Sn

electrons and the excess driving voltage dissipated the chloride ions as gas rather than

collecting on the reinforcement in the form of corrosion rust products. Also concluding from

the mass loss percentages from table 5 proves that comparatively tin mesh has mitigated

corrosion to some extent. Hence, the first objective for feasibility i.e. the theory of tin mesh to

work as an appropriate anode in reinforced concrete has been achieved in this research.

Figure 12: Pitting corrosion formed during acceleration

of corrosion


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6.2 Conclusion

The objectives outlined during the initial stages of this dissertation have been achieved

i.e.

1. The driving voltage of tin mesh has been established as 0.5 V which provided enoughelectrons to dissipate chloride ions as chloride gas

2. The control samples have been accelerated successfully for comparison between thetwo sets of beams

3. The mass loss of steel reinforcement for the tin mesh embedded beams arecomparatively less than the control sample reinforcements

4. The corrosion current for the tin mesh embedded beams are significantly less than thecorrosion current of the control sample

6.3 Future Work

During the course of this dissertation few alterations have been made to suit the time

frame of this research and they are as follows -

1. Corrosion has been accelerated to see faster results and it would be more realisticto not accelerate corrosion and to perform a salt ponding test where the beams aresubjected to immersion of beams in saline solution for 90 days

2. The duration of this experiment was limited to 67 hours. The results would havebeen more diverse if the experiment was performed for a time frame of 100 hours

and intervals of every minute could be recorded through a current data logger.

3. The driving voltage could be increased to a value between 0.5-1 V which wouldprovide better results

4. While breaking the beams to retrieve the reinforcement it was noticed that thereinforcement decreased in length for the control samples. More research in this

area could clarify the results.

5. Also, using 100% manufactured tin mesh instead of using the composition used inthis research for steady results


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References

ASTM Standard G78, 2012, "Standard Guide for Crevice Corrosion Testing of Iron-Base

and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous

Environments," ASTM International, West Conshohocken, PA, 2003, DOI:

10.1520/C0033-03, www.astm.org.

ACI Committee 222 (2001) '222R-01: Protection of Metals in Concrete Against

Corrosion (Reapproved 2010).' Technical Documents 1, 41

Atkins - North America (n. d.) Atkins - Technical Journal [online] available from

[24 October 2012]

Cement Concrete & Aggregates Australia (2009) Chloride Resistance of Concrete[online] available from

[19 Nov 2012]

CONRETE.' Technical University of Gdansk, Department of Anticorrosion Technology

N/A, 129-149

D.V. Reddy*, J-B Edouard, K. Sobhan and S.S. Rajpathak (2011) 'DURABILITY OF

REINFORCED FLY ASH-BASED GEOPOLYMER CONCRETE IN THE MARINE

ENVIRONMENT.' 36th Conference on Our World in Concrete & Structures -, (-) -

G.K Glass (2003) Advanced Concrete Technology. Oxford: Elsevier Ltd.

Green Car Congress (2012) Toyota researchers show superior performance for tin anode

for Mg-ion batteries with conventional electrolytes [online] available from

[17 March 2013]


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H. Marchebois a, S. Touzain a, S. Joiret b, J. Bernard a, C. Savalla,. (2002) 'Zinc-rich

powder coatings corrosion in sea water: influence of conductive pigments.' Progress in

Organic Coatings 45, 415-421

Handbook of Corrosion (2005) Corrosion. US: Springer US

International Concrete Sustainability Conference (n. d.) Evaluation of Service Life of

Reinforced Concrete Structures in the Middle East [online] available from

[19 Nov 2012]

J Garcia, F Almeraya, C.Barrios, C. Gaona, R. Nunez, I.Lopez, M.Rodriguez, A.

Martinez-Villafane, J.M. Bastidas (2012) 'Cement and Concrete Composities.' Effect of

Cathodic Protection on Steel-Concrete bond strength using ion-migration measurements

34, 242-247

Jure Franciskovic, Boris Miksic, Ivan Rogan and Mijo Tomicic (2006) 'Protection and

Repair of Reinforced Concrete Structures by means of MCI- Inhibitors and Corrosion

Protective Materials.' Structural Engineering Conference on Bridges, Longus Co. Ltd. 1, -

K. Darowicki, J. Orlikowski, S. Cebulski*), S. Krakowiak (N/A) 'CONDUCTING

COATINGS FOR CATHODIC PROTECTION OF REINFORCED

L. Abosrra, A.F. Ashour ., M. Youseffi (2011) 'Corrosion of steel reinforcement inconcrete of different compressive strengths.' Construction and Building Materials 25,

3915-3925

L.E. Umoru and O.O. Ige (2007) 'Effects of Tin on AluminumZincMagnesium Alloy

as Sacrificial Anode in Seawater.' Journal of Minerals & Materials Characterization &

Engineering 7, 105-113


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Mamdouh Hamouda (N/A) 'Durable Concrete in UAE Environment.' International

Conference of Improving Concrete Performance - Dubai N/A, N/A

Mumtaz K. Kassir*, Michel Ghosn (2002) 'Chloride-induced corrosion of reinforcedconcrete bridge decks.' Cement and Concrete Research 32, 139-143

On the corrosion of copper sheeting by seawater, and on methods of preventing this

effect, and on their application to ships of war and other ships". Proceedings of the Royal

Society, 114 (1824), pp 151-246 and 115 (1825), pp 328-346.

R. Brousseau, B. Arsenault, S. Dallaire, D. Rogers, T. Mumby, and D. Dong (1997)

'Sprayed Titanium Coatings for the Cathodic Protection of Reinforced Concrete.' JTTEES

ASM International 7, 193-196

Sunil C. Das; Homayoon Pouya; Eshmaiel Ganjian (2010) Corrosion Mitigation of

Chloride-contaminated reinforced concrete structures: a state-of-the-art review . UK: ICE

Publishing


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Appendix I Project Planning Document

T1: Gantt chart highlighting the sequence of events for the Project

T2: Gantt chart highlighting the tasks proposed for December 2012.


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Appendix II Acceleration Tests


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Page 51 of55


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Page 52 of55

Appendix III Standard Laboratory TestsBS 1881-119:2011 - Testing concrete. Method for determination of compressive strength usingportions of beams broken in flexure (equivalent cube method)

The casting of sample concrete cubes (150 x 150 x 150 mm) for compression test analysis was

carried out on the 20th of November 2012.

After 28 days, the concrete cubes were placed inside a compression test machine (UTest Material

Testing Machine).

Figure A1 (a) Cube placed inside a compression machine (b) Cracked cube after 28days (Photos taken on 10th

December 2012)


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Page 53 of55

Appendix IV Experimental Imageries

Figure A2 (a) Corrosion products formed on the saline solution (ICCP) (b) Control Samples duringAcceleration of Corrosion (Time : 24th Hour)

Figure A3 Corroded beams after electrochemical acceleration of corrosion (Hour 68)


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Page 54 of55

Appendix V Data ReadingsTin Mesh Control Sample- 30 V ICCP - 0.5 V

Time

Current

(mA) Time Current (mA) Time

Current

(A)

14:00 36.3 14:00 38.4 14:00 0.36

15:00 5.82 15:00 30.78 15:00 0.35

16:00 1.14 16:00 1.35 16:00 0.51

17:00 1.1 17:00 1.33 17:00 0.4

18:00 1.09 18:00 1.288 18:00 0.36

19:00 0.93 19:00 1.293 19:00 0.34

20:00 1.15 20:00 1.563 20:00 0.34

21:00 1.22 21:00 1.353 21:00 0.6122:00 0.98 22:00 1.456 22:00 0.39

23:00 0.98 23:00 2.112 23:00 0.37

0:00 0.88 0:00 1.398 0:00 0.39

1:00 0.81 1:00 1.322 1:00 0.35

2:00 0.81 2:00 1.344 2:00 0.35

3:00 0.78 3:00 1.35 3:00 0.34

4:00 0.79 4:00 1.385 4:00 0.34

5:00 0.78 5:00 1.387 5:00 0.34

6:00 0.78 6:00 1.373 6:00 0.35

7:00 0.8 7:00 1.348 7:00 0.368:00 0.99 8:00 1.895 8:00 0.33

9:00 1.15 9:00 1.319 9:00 0.34

10:00 0.98 10:00 1.309 10:00 0.33

11:00 0.99 11:00 1.311 11:00 0.32

12:00 0.98 12:00 1.346 12:00 0.32

13:00 0.96 13:00 1.345 13:00 0.33

14:00 1.15 14:00 1.349 14:00 0.33

15:00 1.17 15:00 1.348 15:00 0.33

16:00 1.24 16:00 1.317 16:00 0.33

17:00 1.14 17:00 1.42 17:00 0.33

18:00 1.01 18:00 1.425 18:00 0.35

19:00 1.02 19:00 1.489 19:00 0.37

20:00 1.02 20:00 1.52 20:00 0.36

21:00 1.05 21:00 1.56 21:00 0.36

22:00 1.01 22:00 1.472 22:00 0.41

23:00 1.01 23:00 1.47 23:00 0.41


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0:00 0.88 0:00 1.009 0:00 0.4312

1:00 0.69 1:00 0.84 1:00 0.42

2:00 0.67 2:00 0.85 2:00 0.43

3:00 0.63 3:00 0.624 3:00 0.43

4:00 1.02 4:00 0.966 4:00 0.4413

5:00 1.1 5:00 1.02 5:00 0.4512

6:00 1.2 6:00 1.25 6:00 0.456

7:00 1.29 7:00 1.72 7:00 0.47

8:00 1.04 8:00 0.67 8:00 0.45

9:00 1.04 9:00 0.67 9:00 0.45

10:00 0.71 10:00 0.495 10:00 0.45

11:00 0.71 11:00 0.494 11:00 0.45

12:00 0.7 12:00 0.461 12:00 0.47

13:00 0.7 13:00 0.461 13:00 0.47

14:00 0.83 14:00 0.495 14:00 0.48

15:00 0.85 15:00 0.494 15:00 0.48

16:00 0.91 16:00 0.461 16:00 0.48

17:00 0.82 17:00 0.471 17:00 0.48

18:00 0.9 18:00 0.441 18:00 0.48

19:00 0.91 19:00 0.44 19:00 0.48

20:00 0.82 20:00 0.47 20:00 0.57

21:00 0.82 21:00 0.471 21:00 0.58

22:00 0.851 22:00 0.465 22:00 0.58

23:00 0.861 23:00 0.472 23:00 0.56

0:00 0.893 0:00 0.475 0:00 0.591:00 0.93 1:00 0.478 1:00 0.59

2:00 0.9 2:00 0.488 2:00 0.59

3:00 0.89 3:00 0.5 3:00 0.59

4:00 0.83 4:00 0.501 4:00 0.59

5:00 0.82 5:00 0.498 5:00 0.59

6:00 0.81 6:00 0.506 6:00 0.58

7:00 0.81 7:00 0.51 7:00 0.58

8:00 0.68 8:00 0.48 8:00 0.56