Grout Acidification of Ribbon Anode in Impressed Current. Cathodic Protection Systems in Concrete. Martin Cheytani

Transcription

1 Grout Acidification of Ribbon Anode in Impressed Current Cathodic Protection Systems in Concrete Martin Cheytani Masters of Philosophy School of Material Science and Engineering Faculty of Science University of New South Wales Australia September 2017

2 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Cheytani First name: Martin Other name/s: Abbreviation for degree as given in the University calendar: MPhil School: Materials Science and Engineering Faculty: Science Title: Grout acidification of ribbon anode in impressed current cathodic protection systems in concrete Abstract 350 words maximum: Impressed current cathodic protection (ICCP) technology has been used for the corrosion protection of chloride contaminated reinforced concrete structures in Australia and globally for the past years. Mixed Metal Oxide (MMO) Coated Titanium ribbon anode mesh has been the most widely used anode for ICCP systems on bridges and wharves. In recent years, there have been many reports in Australia identifying acidification problems associated with ribbon anode installations, with the problem being most evident in tidal/splash zones of the structures. Based on these reports, issues such as the type of grout encapsulating the anodes and grout cover to the anode were commonly reported as the potential contributing causes of acidification problems. It has been reported that the likely primary cause of acidification is ingress of water to the anode surface. Various methods of preventing water ingress have been specified, however no systematic research work has been performed to verify the long-term performance of such methods for minimising, eliminating or preventing acidification problems in ICCP installations. The primary aim of the present research is to verify a methodology for preventing water ingress to the ribbon anode in water exposure conditions and using accelerated testing to confirm that this method can minimise the acidification problem related to water ingress. The experiments simulate the typical problems of low grout cover and cracking which allows water ingress to the ribbon anode. Following the sealing of the cracks in some samples, accelerated cathodic protection was performed for unrepaired and repaired samples. The objective of the test is to assess the mechanism of grout acidification under these conditions and to verify the effectiveness of the method of anode encapsulation. The results of the present research work confirm that the anode embedment methods currently in use by the industry, often combined with sub-par workmanship, allow water ingress to the ribbon anode, and these are the primary causes of acidification. The results also confirm that the application of a cementitious waterproofing coating, which minimises water ingress to the ribbon anode, can limit or stop the occurrence of grout acidification problems in existing ICCP installations. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). Signature.. Witness Signature 15/09/ Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award:

3 ORIGINALITY STATEMENT I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. Signed... Date...

4 COPYRIGHT STATEMENT I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed... Date... AUTHENTICITY STATEMENT I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Signed... Date...

5 Preface & Acknowledgements This thesis is submitted as a requirement of my Master of Philosophy Thesis, in the School of Material Science and Engineering, University of New South Wales. I would like to extend my gratitude to my thesis supervisor, Associate Professor Sammy Lap Ip Chan for his ongoing help and support with my research. I would also like to thank Faisal Alanazi, for providing the cast concrete samples. I would like to acknowledge the ongoing support Remedial Technology Pty Ltd throughout the entire process. i

6 Abstract Impressed current cathodic protection (ICCP) technology has been used for the corrosion protection of chloride contaminated reinforced concrete structures in Australia and globally for the past years. Mixed Metal Oxide (MMO) Coated Titanium ribbon anode mesh has been the most widely used anode for ICCP systems on bridges and wharves. In recent years, there have been many reports in Australia identifying acidification problems associated with ribbon anode installations, with the problem being most evident in tidal/splash zones of the structures. Based on these reports, issues such as the type of grout encapsulating the anodes and grout cover to the anode were commonly reported as the potential contributing causes of acidification problems. It has been reported that the likely primary cause of acidification is ingress of water to the anode surface. Various methods of preventing water ingress have been specified, however no systematic research work has been performed to verify the long-term performance of such methods for minimising, eliminating or preventing acidification problems in ICCP installations. The primary aim of the present research is to verify a methodology for preventing water ingress to the ribbon anode in water exposure conditions and using accelerated testing to confirm that this method can minimise the acidification problem related to water ingress. ii

7 The experiments simulate the typical problems of low grout cover and cracking which allows water ingress to the ribbon anode. Following the sealing of the cracks in some samples, accelerated cathodic protection was performed for unrepaired and repaired samples. The objective of the test is to assess the mechanism of grout acidification under these conditions and to verify the effectiveness of the method of anode encapsulation. The results of the present research work confirm that the anode embedment methods currently in use by the industry, often combined with sub-par workmanship, allow water ingress to the ribbon anode, and these are the primary causes of acidification. The results also confirm that the application of a cementitious waterproofing coating, which minimises water ingress to the ribbon anode, can limit or stop the occurrence of grout acidification problems in existing ICCP installations. Keywords: Corrosion, Concrete, Grout Acidification, Impressed Current Cathodic Protection, Anode iii

8 Abbreviations ICCP CP T/R MMO ph ma V DC mm AS W/W Impressed Current Cathodic Protection Cathodic Protection Transformer Rectifier Mixed Metal Oxide Potential of Hydrogen Milliampere Volts Direct Current Millimetre Australian Standard Weight by Weight iv

9 List of Figures Figure Electrochemical corrosion process of steel 5 Figure Concrete deterioration caused by corrosion 6 Figure ICCP system diagram 14 Figure Typical discrete anode installation 17 Figure Typical perpendicular anode installation 18 Figure Typical flat anode installation 19 Figure Typical cementitious waterproofing grout application 24 Figure Concrete sample elevation and top view 26 Figure Concrete sample anode installation 26 Figure Experiment 1 sample setup 30 Figure Experiment 1 acidification formation on top of sample 31 Figure Experiment 1 grout acidification visible at anode/grout interface 32 Figure Experiment 1 uniform grout acidification along anode 32 Figure Experiment 2 sample setup 33 Figure Experiment 2 samples prior to cutting 34 Figure Experiment 2 Sample 1 - uncoated sample 35 Figure Experiment 2 sample 2 - coated sample 35 Figure Experiment 3 sample preparation 39 Figure Experiment 3 samples during phase 1 40 Figure Experiment 3 samples during phase 2 41 Figure Experiment 4 sample preparation 45 Figure Experiment 4 sample after testing (prior to cutting) 46 Figure Experiment 4 cross section of sample at water ingress point 46 Figure Experiment 4 cross section of sample at location with no water ingress 46 v

10 List of Tables Table Standard EMF series 12 Table Experiment 2 current, voltage and resistance readings 37 Table Experiment 3 current, voltage and resistance readings 43 Table Experiment 4 current, voltage and resistance readings 48 vi

11 Contents Preface & Acknowledgements i Abstract ii Abbreviations iv List of Figures v List of Tables vi Chapter 1: Literature Review 1.1 Introduction Corrosion in Concrete Carbonation Chloride Corrosion Process Corrosion Consequences Corrosion Prevention & Protection Measures Mix Design and Concrete Cover Alteration of Construction Details Coating Application Corrosion Resistant Reinforcement Corrosion Inhibitors Cathodic Prevention Galvanic Protection Hybrid Anode Chloride Extraction Impressed Current Systems 14 vii

12 1.4 ICCP and Grout Acidification ICCP Installation Anode Design Grout Material Grout Acidification International Standards Industry Practices 23 Chapter 2: Methodology and Approach 2.1 Research Aim Sample Design Salt Water Concentration Accelerated Testing Testing Methods 28 Chapter 3: Experiments 3.1 Overview Experiment 1 Establishing the Standard Procedures Aim Sample Preparation Results Experiment 2 - A Comparison Between Coated and Uncoated Aim Sample Preparation 33 viii

13 3.3.3 Results Experiment 3 - Simulation of Poor Workmanship Aim Sample Preparation Results Experiment 4 - Capacity of Waterproofing Coating to Stop the Ingress of Water Aim Sample Preparation Results 45 Chapter 4: Discussion 4.1 General Limitations and Improvements 51 Chapter 5: Conclusion and Future Research 5.1 Conclusion Future Research 54 References 55 Appendices 57 Appendix A: Photos Appendix B: Accelerated Testing Calculations ix

14 Chapter 1: Literature Review 1.1 Introduction Reinforced concrete is still the primary fundamental composite material for building much of today s highly efficient structures. The high compressive strength of concrete and the high tensile strength of steel reinforcement, allow for the construction of thinner, lighter, stronger and more cost-effective structures. Reinforced concrete failure is mainly caused by corrosion of the steel reinforcement as a result of the destabilisation of the oxide layer formed on the steel surface during the hydration process of concrete. When the passivity of the steel partly or completely breaks down, either as a result of carbonation or chloride contamination of the concrete, the corrosion process will start. This means that the electrochemical potential of the steel becomes more negative and forms anodic areas in some locations, while the other portions of the steel the passive layer will remain intact and will form cathodic areas. Impressed current cathodic protection (ICCP) is one of the common methods for protecting reinforced concrete structures where chloride induced corrosion is the primary cause of reinforcement corrosion and concrete spalling. ICCP was first introduced to Australia in the 1980s, and since then ICCP systems have become one of the most widely used methods for the corrosion protection of marine structures in Australia. However, in recent years, the maintenance of cathodic protection systems has become problematic, not due to the failure of ICCP systems providing corrosion protection to the structures, but due to various issues associated with high maintenance costs of some of the components of the systems. Grout 1

15 acidification has also been identified as one of the problems with ICCP systems installed in marine environments, and particularly in the tidal and splash zones of wharves and bridges. In addition to the aesthetic issues associated with grout acidification, if left unrepaired, it may impact on the performance of the ICCP system and the long term corrosion protection of the structure. The topic of my research is related to grout acidification in existing ICCP installations, and the provision of measures to eliminate this problem in new systems. 1.2 Corrosion in Concrete Steel reinforcement embedded in concrete has a physical and chemical layer of oxide of protection against corrosion. Reinforcing steel in new good quality concrete does not corrode even if sufficient moisture and oxygen are available. New concrete generally has a highly alkaline ph of above 13, which is attributed to high levels of calcium hydroxide. The interaction between high levels of hydroxyl ions (OH - ) and the steel reinforcement form an insoluble ferric oxide film around the reinforcement, causing the steel to passivate and create a protective oxide layer. This oxide layer provides protection to the steel reinforcement by preventing metal atoms from dissolving, however this passive layer cannot always be maintained. Chloride and carbonation ingress to the level of steel reinforcement as a result of, poor quality concrete, concrete cracking and insufficient concrete cover to reinforcement, can lead to a decrease in concrete alkalinity and a breakdown of the protective oxide layer. This contamination process can be caused by two types of attacks; 2

16 1.2.1 Carbonation Carbonation is the introduction of carbon dioxide (CO2) to the concrete. Depending on the permeability of the concrete and level of hydration, carbon dioxide penetrates and dissolves into the concrete pores. The mixture of carbon dioxide into the calcium hydroxide (Ca(OH)2) rich concrete reacts to form calcium carbonate: Ca(OH) 2 + CO 2 -> CaCO 3 + H 2O Consumption of Ca(OH) 2 decreases the ph of the concrete to as low as 8.5, which is well below the necessary alkalinity required to keep the steel passivated. The decrease in ph causes the deterioration of the oxide layer, enabling the corrosion process Chloride The diffusion of chloride ions into the concrete through the concrete cover or through cracks that form in the concrete, is the primary mechanism of chloride contamination of concrete structures. In Australia, many structures are built in coastal locations which are exposed to airborne chlorides, or are in direct proximity to seawater. The quality of concrete, porosity, concrete cover to reinforcement, and shrinkage cracking of the concrete, are the primary enablers of chloride ingress. When the chloride reaches the steel reinforcement, the breakdown of the protective oxide layer occurs and corrosion initiation starts. 3

17 1.2.3 Corrosion Process Chloride ingress and carbonation contamination are the two main methods which contribute to the degradation of the steel reinforcement s protective oxide layer. Regardless of the cause, once the alkalinity of the concrete at the level of steel reinforcement decreases to a level beyond the steel passivation threshold, the electrochemical process of steel corrosion will begin. The process of steel corrosion in concrete begins with the variance in steel potential in different locations of one continuous steel element. The variance in steel potential is caused by the localised contamination of the concrete and breakdown of the passive layer, which leads to creation of the anodic and cathodic areas. Where the oxide layer is damaged, steel generates positively charged iron ions and release electrons. This area, known as the anodic area, becomes the host of the oxidation process, where electrons are released from the anode and flow to the cathode. At the cathode, electrons react with an external source of water and oxygen and produce hydroxyl ions. The hydroxyl ions at the cathode then react and produce ferrous hydroxide at the anode, which when exposed to oxygen and oxidised, produce hydrated ferric oxide (rust). The electrochemical corrosion process of steel is shown in Fig

18 Figure Electrochemical corrosion process of steel [1] Corrosion Consequences The process of this electrochemical reactions, culminates in the production of iron oxide (rust) at the anode. The formation of iron oxide is many times the volume of the original steel, causing an expansive internal pressure within the concrete structure. As shown in Fig. 1.2, the build-up of this internal pressure leads to the eventual degradation of the structure, causing spalling, cracking, loss of section, a decrease in structural strength and eventual collapse if no protection or prevention measures are taken. For this reason, corrosion of reinforcement in concrete is a major influence on the life and health of structures in highly corrosive environments. This has led to the development of corrosion protection and prevention systems, to minimise the impacts of corrosion in reinforced concrete structures and prolong the life of infrastructure. 5

19 Figure 1.2 Concrete deterioration caused by corrosion [2] 1.3 Corrosion Prevention & Protection Measures For new structures corrosion prevention measures may include; modifying the concrete mix to decrease concrete permeability; adjusting steel depth, to provide adequate concrete cover; changes in construction designs to minimise the exposure of some key structural elements to chloride ingress; applying coating application to limit chloride ingress into the concrete; use of corrosion resistant reinforcement; use of inhibitors to fresh concrete, and the application of impressed current cathodic prevention systems. For existing structures, coating applications, galvanic cathodic protection, hybrid anode systems, chloride extraction and impressed current cathodic protection systems are the most common methods used for corrosion protection of concrete structures Mix Design and Concrete Cover The quality of concrete is a major component for determining the durability of reinforced concrete structures. Concrete contains a network of interconnected pores, which can provide a path of ingress for water and oxygen. The porosity of concrete can be controlled by altering the water/cement ratio. A lower level of water to cement ratio can decrease the number of 6

20 pores or their size, thus reducing the permeability and resistivity of the concrete. Further, the addition of mineral admixtures, such as silica flume, fly ash and slag can have a significant effect in reducing the corrosion rate of reinforced concrete structures. The concrete cover depth to the first layer of steel reinforcement also has an influence on the ingress of chloride ions. Sufficient concrete cover depth is stated in various standards, and the adequate amount of cover is subject to the exposure conditions of the structure. For dense high-quality concrete with adequate concrete cover, carbonation induced corrosion does not generally pose a major problem, however, for structures exposed to marine environments, the ingress of chloride ions is highly problematic. The diffusion and capillary absorption of chloride ions can be very high in marine environments, especially in tidal and splash zones Alteration of Construction Details With the construction of bridges and wharves in marine environments, in addition to the specific code requirements related to exposure conditions (concrete cover etc), there have been improvements in the design and construction of new structures. Some of these improvements include designing the main structural elements away from direct exposure to chloride contamination. This measure can greatly minimise chloride exposure, and improve the structure s long-term resilience to corrosion. Other examples include small adjustments in the height of the main deck for wharves which can substantially reduce the exposure conditions of certain key structural elements to chloride ingress. 7

21 1.3.3 Coating Application Protective coatings are generally applied to the external surface of newly constructed structures as a prevention measure, prior to the exposure and ingress of chloride ions which leads to reinforcement corrosion. Coatings can be complex blends of epoxy, acrylic and silane treatments, all of which are suited to different structures and environments. Coatings vary from chemical resistance protective coatings, impregnating treatments to anti-carbonation and chloride ion protective coatings. Protective coatings can provide a level of protection for marine structures in areas which are not directly exposed to harsh conditions, and need to be applied prior to the ingress of chloride ions. This involves a reasonable initial financial cost prior to the occurrence of issues with a structure, and is often overlooked due to the initial application cost during construction Corrosion Resistant Reinforcement The last defence in stopping corrosion is at the reinforcement steel. There are various types of corrosion resistant reinforcement which are can be used: Epoxy Coated Reinforcement Epoxy coated reinforcement comprises the application of organic coatings (epoxies) to carbon steel reinforcement, serving as a barrier for isolating the steel reinforcement from moisture, oxygen and chloride ions, and thus preventing corrosion. Epoxy coated steel 8

22 reinforcement was first introduced in the 1970s in the United States as a method of minimising the deterioration of reinforced concrete bridge components. Documentation on the performance of epoxy coated reinforcement shows favourable performance in structures with low corrosion risk. However, where such systems have been used in highly corrosive environments, poor performance has been observed. Significant evidence of corrosion of epoxy coated reinforcement has been documented after 5-10 years from the date of construction [12]. The main reasons for failure include: Under-coating corrosion, caused by the migration of water, oxygen and chlorides through the concrete and through the epoxy to the steel surface; Wet adhesion loss resulting in separation between the coating and substrate; Disbondment of the epoxy coatings from the reinforcing steel initiating at coating defects. Galvanised Steel Reinforcement Galvanised steel reinforcement is the application of a zinc coating applied by dipping prepared steel reinforcement into a molten bath of zinc. Galvanised steel reinforcement has been used over the past 50 years in many countries as a method of prolonging the service life of steel reinforcement [12]. It has been documented that this prevention method can provide a substantial increase in protection of concrete structures affected by carbonation, though in marine structures with chloride induced corrosion, the service life can be too short to be justified. 9

23 Stainless Steel Reinforcement Stainless steel refers to a group of corrosion resistant metals with alloys containing a minimum of 12% chromium. Stainless steel has been used around the world in structures in aggressive marine environments, as it resists corrosion in chloride contaminated structures. Due to the high cost of manufacturing, stainless steel reinforcement is not viable for large marine structures. It has been suggested that stainless steel may be suitable in reinforced concrete elements in high risk areas such as in tidal/splash zones, and at the outer layer of reinforcement, however the risk of galvanic corrosion between stainless steel and mild steel reinforcement must be considered [12] Corrosion Inhibitors Corrosion inhibitors are chemicals added to concrete during construction to decrease the corrosion rate. Corrosion inhibitors can be grouped into three categories, anodic, cathodic or mixed. Inhibitors are used as a preventive measure in structures which are expected to be susceptible to future chloride-induced corrosion. There are still questions about the dosage required as well as other issues such as evaporation and leaching out from concrete. There is a belief that corrosion inhibitors may delay the initiation of corrosion, however there is no established evidence of its ability to reduce the corrosion rate after the initiation of corrosion [12] Cathodic Prevention Cathodic prevention is an electrochemical technique involving the application of a small electrical current distributed via a system of anodes embedded in the concrete during 10

24 construction. It is based on the philosophy that a small impressed current will prevent pitting corrosion, compared to a high current which is required to supress ongoing corrosion. As cathodic prevention systems are installed during construction, their cost is substantially lower than impressed current cathodic protection systems. Cathodic prevention systems are typically designed for a current density of 10 ma/m² with an operating current ranging from 1-2 ma/m² [12]. Such a system is similar to cathodic protection, however with a lower current density requirement and increased ease of installation during construction Galvanic Protection The use of sacrificial anode systems in concrete structures has increased in recent years, as the search for simpler (requiring less monitoring and maintenance) cathodic prevention and protection system increases. A sacrificial anode system is based on an electrochemical reaction between dissimilar metals, where one metal preferentially corrodes over another. Which metal corrodes preferentially is based on the electrochemical series of metal potentials as shown in Table 1.1. When two metals are connected, the lower potential metal will corrode. 11

25 Table 1.1 Standard EMF series [3] Based on this as well as the feasibility of metal selection, sacrificial anodes are made from pure aluminum, magnesium or zinc. The selection of sacrificial anodes is based on the environment in which it will be used in, varying from soil to salt water to brackish water. Sacrificial anode systems are widely used for the protection of steel and reinforced concrete elements located in water and soil. For concrete structures, zinc anodes are generally used. Zinc anodes come in a variety of shapes and sizes to meet the requirements of the system design, and allowing for flexible installation methods. Sacrificial anodes are generally used on structures which exhibit early signs of corrosion, as their level of protection is limited to the potential differences between dissimilar metals. This limits the usability of sacrificial anode systems, especially for structures exposed to harsh marine environments. In addition to this, sacrificial anodes must generally be used in low resistivity concrete and may require a large number of sacrificial anode to meet the design requirements. Sacrificial anode systems generally have a limited design life of years, and full replacement is required after expiration. 12

26 1.3.8 Hybrid Anode The hybrid anode system is a relatively recent development and differs from a purely galvanic system. The hybrid anode process can be grouped into two phases; Phase 1 involves the installation of a sacrificial anode system and the implantation of a temporary current with the aim of realkalising active pits, stopping active corrosion and returning the steel to a passive state. Phase 2 involves the removal of external current and the galvanic protection of the steel maintained by the sacrificial anode system. Similar to typical galvanic systems, hybrid anode systems are not suited to areas with high resistivity and high corrosion activity. Performance data from site applications reveals that it is unlikely that hybrid anode systems can achieve the level of protection set by the current cathodic protection criteria in accordance to AS [12] Chloride Extraction Chloride extraction, otherwise known as desalination, is a temporary electrochemical process for extracting chloride ions from existing highly chloride contaminated structures. The process is carried out using high current density distributed via an externally installed system of steel mesh. Once the level of chloride is typically less than 0.4% W/W of cement, the system is removed and an external coating is applied to the structure. 13

27 Impressed Current Systems Impressed current cathodic protection systems are the most widely used corrosion protection systems for structures located in and around harsh marine environments. Impressed current systems were first introduced to Australia in the 1980s, and since then the technology has reached maturity and has become a proven method of corrosion protection for marine structures in Australia. Figure 1.3 ICCP system diagram [4] ICCP systems work similarly to chloride extraction systems however involve the permanent embedment of anodes in the structure. By impressing an external DC current between the anode through the electrolytic (concrete) and to the steel reinforcement, the total steel area becomes cathodic. The impressed current system eliminates the local corrosion current with only the protection current flowing into the structure. During this process, an ICCP system will extract the chloride away from the reinforcement towards the anode, increasing the alkalinity level around the steel reinforcement. This increase of alkalinity allows for the 14

28 regeneration of the protective passive oxide layer which passivates the steel. Such a system can provide long term protection to steel reinforcement in harsh marine environments. The design, materials selection, installation, commissioning and monitoring of cathodic protection systems are detailed in AS , Australian Standard for Cathodic Protection of Metals, Part 5: Steel in Concrete Structures [11]. 1.4 ICCP and Grout Acidification In Australia in recent years, cementitious grout acidification around the anode in ICCP systems has become a notable and problematic industry issue. Acid generation at the anode has been known since Faraday in 1834, whereby the positive pole that attracts oxygen, acids [6]. Chess and Bloomfield [7] write; During normal ICCP system operation, the predominant chemical reaction taking place around the anode is either the release of oxygen or the evolution of chlorine. In most welldesigned and operated systems, oxygen evolution is most common. The resulting development of H+ ions during the anodic reaction reduces the high ph (alkaline) nature of the concrete and acids are generated. It is understood that acidification at the anode interface will occur, however there has been no notable research into methods for minimising the occurrence of this phenomena. 15

29 The chemical reactions during the use of ICCP at the anode surface can be broken down into the following stages [13]; 1. The oxidation of water at the anode surface results in the production of hydrogen ions: 2H 2O O 2 + 4H + + 4e - 2. A reduction in ph due to the consumption of alkalinity at the anode surface can also occur due to the oxidation of hydroxyl ions: 4OH - 2H 2O + O 2 + 4e - 3. The oxidation of chloride ions to chlorine gas can occur: 2Cl - Cl 2 + 2e - 4. The chlorine gas consequently dissolves in water to form hypochlorous acid and hydrochloride acid: Cl 2 + H 2O HOCl + HCl In the implementation of ICCP today, is has been found that there is a variance in grout acidification from structure to structure. The following are aspects which are believed to have an influence on the level of acidification. 16

30 1.4.1 ICCP Installation ICCP systems are specified in conjunction with concrete repair mostly for structures with chloride initiated corrosion problems Anode Design There are two common types of anodes which are mostly used in ICCP systems. Both anodes use the same Mixed Metal Oxide (MMO) activated Titanium mesh, however with a variance in shape and method of installation. Discrete Anodes Discrete anodes have been developed in the past decade and are being increasingly used in ICCP systems. Discrete anodes consist of a mesh Mixed Metal Oxide Coated Titanium ribbon formed into a cylindrical shape. The benefit of discrete anodes over mesh ribbon anodes is the possibility of fully inserting the anode into the concrete and reducing the potential exposure of the anode to water in the tidal and splash zones. Discrete anodes are also favourable in deep concrete elements (such as beams and columns) where protection can be provided from a central location to all layers of reinforcement. Figure 1.4 Typical discrete anode installation [5] 17

31 Ribbon Anodes Ribbon anode is found in the majority of structures operating ICCP systems. Ribbon anode is installed in slot cuts along the concrete elements. There are two main slot cut designs: Perpendicular installation into the slot cut where the ribbon anode is installed perpendicular to the concrete surface. This design has financial benefits as less concrete cutting is required. While in theory this installation design can provide a similar level of protection, it appears that this installation method often results in an increased level of grout acidification due to the low grout cover at the anodes edge. Figure 1.5 Typical perpendicular anode installation [5] For flat installation of ribbon anode, the anode is installed parallel to the concrete surface. Flat installation requires a larger slot cut when compared to perpendicular anode installation, however provides greater ability to control the quality of workmanship due to the increased slot cut dimensions. 18

32 Figure 1.6 Typical flat anode installation [5] Grout Material The are no requirements in the standards regarding the type of grout material to be used for encapsulating anodes. In most installations, polymer modified material with relatively low resistivity has been used due to the ease of application and the quality attributes of the grout (low shrinkage etc). In recent years, and as a response to acidification problems, grout material with high ph has been specified in various applications. There is no research related to the impact of the resistivity of grout or the level of ph in the grout material on the performance of cathodic protection systems. While in theory, using high ph, low resistivity grout is beneficial in reducing acidification, it is unlikely that the type of grout will have any impact on the typical acidification problems that are due to water ingress to the anode and are the subject of this research. 19

33 The type of grout may have an impact on reducing the acidification which is not caused by water ingress to the anodes. This is a potentially new area of research Grout Acidification The primary causes of grout acidification are: 1) Acidification at the anode possibly due to high current density. Chess and Bloomfield [7], write: High current density output anode systems such as embedded wires, meshes or ribbons are likely to generate more local acidity than high coverage anode systems. (and therefore, the anode may be situated in) a pocket of stagnant acidic electrolyte, particularly if the ICCP system is not designed or operated correctly. The acidification problem is limited to the grout surrounding the anode. This type of acidification is associated with both ribbon and discrete anodes and is unrelated to exposure conditions (atmospheric or tidal). The parameters controlling this type of acidification are the anode current density, which is limited by the standard to 110 ma/m 2 of anode surface and the type of grout (resistivity, ph level etc) which is not specified in the standards (refer to section 1.5). This type of acidification is outside the scope of this research work. 2) Acidification caused by ingress of water to the anode. In this case, the entire grout surrounding the anode exhibits acidification problems. This type of acidification is 20

34 commonly reported in Australia as most of the ICCP applications are for marine structures in tidal and splash zones. A paper released in 2014 titled Review of Cathodic Protection Systems for Concrete Structures in Australia [8], comments that grout acidification is mainly associated with ribbon anode located in tidal and splash zones. Observations of such structures suggest that: Direct exposure of the ribbon anode to water is the primary cause of acidification process initiation. For anodes installed in tidal and splash zones, in nearly all cases of typical anode installation, the problem of grout acidification was evident. An article presented in Material Performance 2014, by NACE in paper (4082) [9], writes: Acidification at the anode-concrete interface occurs when the anode current density is excessive (typically >110 ma/m² for MMO titanium anodes) in chloride-contaminated concrete. This can happen when: Cementitious grout is not sealed and permits salt water penetration. Local portions of the anode system are wet. Improper system design requires a high current density to achieve adequate CP. Acid generation at the anode-concrete interface when the anode current density is too high. Incompatibility to certain cementitious materials when utilized with CP 21

35 Incomplete grouting inside saw-cut slots Papers on the subject of acidification provide information on what is believed to be the contributing factor to the acidification issue, however do not provide any recommendations or conclusions. The issue of grout acidification has been identified, though no research into minimising the phenomena has been conducted. 1.5 International Standards There are three widely used relevant standards for cathodic protection applications. These include: The European International Standard ISO NACE (US) Standard SP Australian Standard AS None of the above standards address the issue of grout acidification. Each standard recommends a current density of 110 ma/m² for the anode surface, however this is in relation to anode life, rather than any issues related to grout acidification around the anode. Global standard bodies and anode manufactures have adopted the limit put in place by the Federal Highway Administration [10]. The only reference to potential grout acidification problem in AS [11] is; 22

36 In tidal/splash zones, factors such as the proximity of anode materials relative to the concrete surface, the anode detailing, the type of grout selected, and the use of an oxygen diffusive barrier, can all impact on the likelihood that anode backfill failure will occur. A review of the applicable standards associated with anode installations in concrete reveal that there are no specific details or requirements associated with the method of installation of the anodes in tidal/splash zones. 1.6 Industry Practices Developments in overall system design, as well as close reviews of system performance through the years means that impressed current systems are continually being improved, with the aim of minimising weaknesses in ICCP system design. Some developments include changes to anode installation details, the development of new high ph encapsulating grouts and the trial of waterproofing systems for the anode slot cuts. One method currently being trialed by the industry is the application of a cementitious waterproofing grout on top of anode installations. Following grout installation or repairs at anode locations, a 2.5 mm waterproofing layer, as shown in Fig. 1.7, is applied on the top and sides of the anode slot cut, with the aim of sealing potential de-bonding or movement cracking between the concrete and the repair material. This method has been implemented in recent years, however no scientific research has been undertaken to understand its effectiveness. 23

37 Figure 1.7 Typical cementitious waterproofing grout application [5] 24

38 Chapter 2: Methodology and Approach 2.1 Research Aim The aim of the following experiments is to provide information regarding the effectiveness of applying a cementitious waterproofing grout coating to a structure with ICCP to stop water ingress to the anode. The industry is currently applying such systems on marine structures with ICCP systems affected by grout acidification, however with no research into the system s effectiveness. As the process of acidification is quite slow, conducting accelerated testing in a laboratory environment can provide information which otherwise may take several years to collect. For this research, a system for accelerated testing needed to be developed. The experiments were conducted with cylindrical concrete samples installed with ribbon anodes, mirroring a concrete pile as found in a typical marine wharf or bridge. The cylinders were partially immersed in salt water, transformer rectifier units were connected and accelerated testing in the form of high cathodic protection current was applied to the cylinders. The experiments assessed the ability for cementitious waterproof material to minimise or stop water ingress at the grout/water interface. It was expected that a layer of waterproofing grout would provide protection against localised grout acidification. 2.2 Sample Design Samples were created using general concrete mixing methods. 32 MPa concrete mixture was used with 5 mm aggregate. 25

39 Each cylindrical sample was designed with a diameter of 150 mm and height of 300 mm. There were four identical anode slot cuts, each 30 mm in width and 20 mm in depth, providing 20 mm cover to each anode. Concrete Sample Elevation View Exposed Steel Rebar Embedded Steel Rebar 4 Bars Per Full Sample 25 mm Diameter Cut Slot for Anode Embedment 290 (H) x 30 (W) x 20 (D) 300 mm Concrete Cylinder 300 x 150 mm 30 mm 150 mm Concrete Sample Top View Steel Rebar 25 mm Diameter 30 mm 20 mm Cut Slot for Anode Embedment 150 mm Figure 2.1 Concrete sample elevation and top view 26

40 There were four 330 mm long and 25 mm diameter mild steel bars placed in the center of each cylinder replicating the steel reinforcement and acting as the cathode. All four bars were welded together in two concrete encapsulated locations. All samples replicated installations of ribbon anode with a typical flat anode design and grouted with the same low resistivity repair mortar suitable for ICCP applications. Figure 2.2 Concrete sample anode installation 2.3 Salt Water Concentration To simulate a marine environment, the samples were placed in salt water (sodium chloride) solution. The salt water solution was formulated based on the average salinity of ocean water. Seawater has a salt concentration of 35 parts per thousand, or 35 g of salt per liter of water. 3.5 g/l was used to create the solutions and ensured that the salinity of the solutions was constant in all of the test samples. The samples were stored in a dry environment prior to their use in the experiments. 2.4 Accelerated Testing Accelerated testing was carried out during the experimental process for all samples. The process was carried out by increasing the current of the anode multiple times over what is 27

41 required in general ICCP system application. Since the process of corrosion and acidification in concrete generally takes many years, accelerated testing is the only method of simulating the formation of acidification in a laboratory setting within reasonable time constraints. The accelerated testing calculations are detailed in Appendix B. The material specification for the anode used specifies an expected design life of 100 years. For the following experiments, the effect of accelerated testing on the Mixed Metal Oxide (MMO) coating of the anode was not considered. 2.5 Testing Methods The following testing methods were used: Periodic recording of operating current and voltage Periodic visual inspection, and in particular of the incidence of grout acidification. 28

42 Chapter 3: Experiments 3.1 Overview Four experiments were conducted as part of this research. Below is a brief description of each experiment: Experiment 1: Trial experiment to establish the standard procedures, conducted to verify the overall operating parameters, current and voltage, and assess the maximum current that can be impressed for the sample. Experiment 2: A comparison between coated and uncoated samples. The aim of this experiment was to assess whether waterproofing coating can provide better protection to the anodes by sealing newly applied mortar material and sealing any cracks which may form between the grout in the slot cut and the original concrete. Experiment 3: Based on the results of experiment 2, it was decided to conduct experiment 3 using scenarios where water can ingress to the anode. A simulation of poor workmanship outcomes was created with low or nil ribbon cover. Experiment 4: The aim of this experiment was to test the capacity of the waterproofing coating to provide protection and stop the ingress of water to the anode. An identical grout encapsulation defect was created for each anode, and comparisons between samples with and without waterproofing coating were carried out. 29

43 3.2 Experiment 1 Establishing the Standard Procedures Aim Experiment 1 was conducted primarily to verify the overall operating parameters of the ICCP system for the concrete sample setup. Experiment 1 was performed to gain information about the level of cathodic protection current which could be impressed to the steel in the concrete cylinders at the maximum voltage of the power supply units Sample Preparation Experiment 1 was conducted using a reinforced concrete cylinder with two anodes installed in slot cuts at a depth of 40 mm. Since test samples were in limited supply, this varied (40 mm slot cut 2 anodes) sample was used for the trial. As can be seen in Fig. 3.1, the sample was partially immersed in salt water and the cylinder connected to a single power unit. Experiment 1 was carried out over 70 days. The duration of the experiments was set by laboratory and time constraints. Detail recording of data is not available for this sample because the experiment was intended as an initial trial only. Figure Experiment 1 sample setup 30

44 3.2.3 Results The results from experiment 1 showed that a maximum current of Volts (which is the maximum voltage of the power supply unit used in the experiment), could be impressed between the two anodes. It is important to note that in actual ICCP installations, the maximum voltage at the anode is 8 V to prevent damage to the anodes. This parameter was not applied in this experiment or any subsequent experiments, as to allow for accelerated testing. It was noted that there were changes in resistance during the test, therefore current and voltage trends needed to be closely monitored in subsequent experiments. To achieve increased control over anode current distribution, multiple power supply units were required for future experiments. Current was applied for 70 days at an average of 170 ma between two anodes. This level of current caused high levels of acidification as seen in Fig. 3.2 below. Figure 3.2 Experiment 1 acidification formation on top of sample 31

45 As shown in Fig. 3.3, the concrete sample was cut in half after completion of the experiment. A visual observation identified acidification of the grout surrounding the anode. Considerable de-bonding between the anode and the concrete was apparent. There was no visible damage to the original concrete due to acidification. Uniform acidification was found along the anode strip, as shown in Fig. 3.4, and it is believed to be caused by uniform current distribution. Figure 3.3 Experiment 1 grout acidification visible at anode/grout interface Figure 3.4 Experiment 1 uniform grout acidification along anode 32

46 3.3 Experiment 2 - A Comparison Between Coated and Uncoated Aim This experiment compared two samples, one uncoated and one coated. The aim of the experiment was to assess whether waterproofing coating can provide better protection to the anodes by sealing newly applied mortar material and sealing cracks which may form between the grout in the slot cut and the original concrete. An analysis of circuit resistance was carried out with the aim of providing information on the internal effects of the coating on the ICCP system Sample Preparation Experiment 2 comprised of two samples, each with four anodes, as shown in Fig The construction and embedment of the anodes was identical in both samples, however in sample 2, additional cementitious waterproofing coating was applied to the slot anode area. The aim of the coating was to provide better protection to the anode by sealing cracks which may form between the grout in the slot cut and the original concrete allowing potential water ingress to the anode. Figure Experiment 2 sample setup 33

47 Both samples were partially immersed in salt water. All anodes were properly encapsulated with grout. Two power units were used for this experiment. Experiment 2 was carried out over 92 days, with an equivalent of 14.9 years of current applied based on steel density of 20 ma/m 2 of steel surface [11]. Calculation details can be found in Appendix B. The duration of the experiments was set by laboratory and time constraints Results Visual Inspection During the experiment and prior to cutting open the cylinders for a detailed inspection, acidification was visible at the top of each sample. As seen in Fig. 3.6, the level of acidification at the top of the uncoated sample was more prominent. No acidification was visible on the grout/water surface. Coated Uncoated Figure 3.6 Experiment 2 samples prior to cutting 34

48 The two samples were cut open for a detailed inspection. The results revealed similar levels of acidification around the anodes in both samples. There was no evidence that water had penetrated to the ribbon anode in both the coated and uncoated cylinders. Due to the lack of localised water ingress, the acidification around the anode was found to be uniform along the length of the ribbon anode. As shown in Fig. 3.7 and Fig. 3.8, the visual inspection revealed that grout acidification occurred at the anode/grout interface, and the concrete had not visually degraded from the acidification. Uncoated Figure 3.7 Experiment 2 Sample 1 - uncoated sample Coated Figure 3.8 Experiment 2 sample 2 - coated sample The visual conclusion from experiment 2 was that the most likely cause of acidification (as known and reported in the industry) is poor anode installation detail and workmanship. The grout cover to the anode in our samples was 20 mm. It appears that properly applied grout prevented water ingress to the level of the anode. In this case, the additional measure of cementitious waterproofing application was not required. It is important to note that site 35

49 conditions and structures under loading may generate cracks between the grout and the original concrete, and in such cases, waterproofing may assist in the long-term prevention of water ingress to the anode. Current, Voltage and Circuit Resistance As detailed in Table 3.1, a low accelerated trial current of 30 ma was applied to each cylinder for the first 21 days. After finding no side effects from the accelerated testing, the current was increased to 150 ma in order to accelerate the process. The power units available for this experiment were limited to 22 V, and therefore the current was decreased on the in order to provide equal current to each concrete test sample. An analysis of the voltage and current trends between the two samples, as depicted in Table 3.1, revealed that the sample coated with a waterproofing coating had a significantly higher circuit resistance than the uncoated sample. The voltage which was required to impress the set current was always found to be higher in the sample with a waterproofing coating (Sample 2). 36

50 Experiment 2 - Current, Voltage and Resistance Readings Time Reading Date Current (ma) 1 Uncoated Voltage (V) 2 Coated 1 Uncoated 2 Coated Resistance (Ohms) Days Days Days Days Total Average Table 3.1 Experiment 2 current, voltage and resistance readings Trends show a constant voltage increase over time at set current levels. There are many potential causes of this phenomenon. Further research in this area can provide more information, however it is believed that the increase in voltage may be caused by: Drying out of the grout encapsulating the anode as a result of the hydration of the mortar, as the water is not replenished due to the presence of a coating acting as a barrier. A side effect of a high CP current which was applied. More likely, de-bonding between anode and concrete/grout due to acidification around the anode surface. 37

51 It is important to note that another area of research which could be valuable for ICCP applications is the determination of the impact of grout resistivity on the surrounding anodes on the overall operating voltage of the system. 3.4 Experiment 3 - Simulation of Poor Workmanship Aim Based on the results of experiment 2, it was decided to conduct experiment 3 using scenarios where water can ingress to the anode. A simulation of poor workmanship outcomes was carried out including low or nil ribbon cover Sample Preparation Experiment 3 was comprised of two half concrete samples (two anodes in each sample, based on sample availability), in which each anode is controlled by an individual power supply unit (four power units) and prepared in a different way. The same current was delivered to each anode and the voltage levels were monitored. 38

52 Experiment 3 Sample Preparation Anode 1 Anode 2 Anode 3 Anode 4 Coated No coating Large crack Direct water ingress Figure 3.9 Experiment 3 sample preparation As shown in Fig. 3.9, each anode was prepared as follows: Anode 1: A single layer 1 mm waterproofing coating was applied to the surface of the sample. Anode 2: No coating was applied to the surface of the sample. Anode 3: There was a large crack next to the anode. The anode stayed encapsulated in grout, however with direct water contact. Anode 4: Direct water ingress. The anode was directly exposed to the water. Experiment 3 was carried out over 25 days, with an equivalent of 7.8 years current applied based on design current density of 20 ma/m 2 of steel surface [11]. Calculation details can be found in Appendix B. The duration of the experiments was set by laboratory and time constraints. 39

53 3.4.3 Results Visual Inspection This experiment can be grouped into two phases: Phase 1: As shown in Fig. 3.10, for the first four days, anodes 1 and 2 showed no signs of direct water ingress to the anode. Some level of acidification had begun to form at the top of anodes 1 and 2. Anodes 3 and 4 exhibited signs of grout acidification around the anode locations which were directly exposed to the water. No acidification was found on the tops of anodes 3 and 4. Experiment 3 Phase 1 of Testing Anode 1 Anode 2 Anode 3 Anode 4 Coated No coating Large crack Direct water ingress Figure 3.10 Experiment 3 samples during phase 1 40

54 Phase 2: As shown in Fig. 3.11, for the remainder of the experiment, direct water ingress to the anode in anode 1 had taken place. A pinhole below the water level had developed in anode 1 possibly due to localised poor grout/coating application providing a direct path of water to the anode causing localised current dumping. Anode 2 did not show any signs of acidification caused by localised water ingress. As shown in Fig. 3.11, acidification was visible at the top of anode 2. As the acidification was away from the water/grout interface it was outside the scope of this research. Note that a higher level of acidification was expected in Anode 2 compared to Anode 1 due to no coating being applied to the Anode 2 specimen. The anomaly in the observation here may be attributed to the adequate anode encapsulation during the construction of the Anode 2 sample compared to the Anode 1 sample. Anodes 3 and 4 continued to exhibit heavy signs of grout acidification. Experiment 3 Phase 2 of Testing Anode 1 Anode 2 Anode 3 Anode 4 Coated No coating Large crack Direct water ingress Figure 3.11 Experiment 3 samples during phase 2 41

55 A visual inspection of experiment 3 concluded that: As seen in anode 1, the additional measure of cementitious waterproofing application was not sufficiently applied around the anodes slot. A properly applied layer of 2.5 mm may be required. The location of water ingress caused a high level of localised acidification. In support of the results from experiment 2, a visual inspection of anode 2 showed that properly applied grout can prevented water ingress to the anode. It is important to note that site conditions and structures under loading may generate cracks between the grout and the original concrete, and in such cases, sufficient waterproofing may assist in the long-term elimination of water ingress to the anode. In the case of anodes 3 and 4, direct water ingress to the anode caused visible acidification at the location of water ingress within 24 hours. Current, Voltage and Circuit Resistance Similar results were found in experiments 2 and 3. As detailed in Table 3.2, the resistance of anode 2 (no localised water ingress) was consistently higher than that of the anodes exposed directly to the water. From experiment 2 it was concluded that an initial low accelerated current was not required. The experiment was initiated with 100 ma impressed per anode, and a subsequent decrease of current was required at two stages of the experiment as shown in Table 3.2, since the available power units used for this experiment were limited to 22 V. 42

56 Experiment 3 - Current, Voltage and Resistance Readings Time 3 Days (Phase 1) 8 Days (Phase 2) 14 Days (Phase 2) 25 Days Total Reading Date Current (ma) Anodes (Fig. 3.9) Anodes (Fig 3.9) Voltage (V) Resistance (Ohms) Average Table 3.2 Experiment 3 current, voltage and resistance readings The readings show that the voltage for anode 1 was relatively high until the water penetrated through to the anode. It is believed that any ingress of water to the anode directly influenced the level of resistance around the anode and in turn the level of current distribution. A decrease in resistance can be linked to the development of the water ingress to the anode, and on visual inspection, it can be concluded that a decrease of localised resistance (where direct water ingress is prevalent) will greatly increase the formation of localised grout acidification and deterioration. Low voltage is noted for anodes 3 and 4 where a section of the anode is exposed to water. 43

57 3.5 Experiment 4 - Capacity of Waterproofing Coating to Stop the Ingress of Water Aim Building on experiments 2 and 3, the aim of experiment 4 was to test the capacity of the waterproofing coating to provide protection and stop the ingress of water to the anode with the use of a standardised and uniform defect between the test anodes. An identical grout encapsulation defect was created for each anode, and comparison between samples with and without waterproofing coating was carried out Sample Preparation Experiment 4 comprised of one sample (four anodes). For each anode slot, a 10 mm hole was drilled through the grout into the anode surface, to simulate water ingress to an anode which may form due to structure movement and grout shrinkage. Continuity between the drilled anode location and the anode s external portion was conducted and confirmed (resistance of less than 2 ohms). Based on the technical data sheet of the waterproofing material, a 2.5 mm cementitious waterproofing coating was then applied to anodes 3 and 4, filling in the holes and encasing the two anode slots in the waterproofing material. Due on the voltage limitations in the previous experiments, 4 new power supply units with the ability to reach 32 V were used for this experiment, in which each anode was separately powered. 44

58 Experiment 4 Sample Preparation, Prior to Testing Anode 1 Anode 2 Anode 3 Anode 4 No coating No coating Coated Coated Figure 3.12 Experiment 4 sample preparation Experiment 4 was carried out over 38 days, with an equivalent of 16.5 years current applied based on design current density of 20 ma/m 2 of steel surface. Calculation details can be found in Appendix B. The duration of the experiments was set by laboratory and time constraints Results Visual Inspection Visual inspection of the samples was carried out throughout the experimental procedure. It was found that anodes 3 and 4 were not exposed to direct water ingress, due to the application of a waterproofing coating. Acidification, and liquid discharge was found at the top of the samples for anode 3 and 4. As expected based on previous experiments, anodes 1 and 2, showed high levels of acidification at the point of water ingress to the anode. 45

59 Experiment 4 Sample After Testing Anode 1 Anode 2 Anode 3 Anode 4 No coating No coating Coated Coated Figure 3.13 Experiment 4 sample after testing (prior to cutting) A dissection of the sample was carried out after the 38-day experiment. The following images were taken after dissection of the concrete sample, Fig at the drilled location (under the water level, at the point of water ingress to the anode) and Fig above the water level. It is evident that the increased level of acidification at the point of water ingress greatly increases the level of grout deterioration as seen in Fig anodes 1 and 2. Anode 1 Anode 2 Anode 1 Anode 2 Anode 4 Anode 4 Anode 3 Anode 3 Figure 3.14 Experiment 4 cross section of sample at water ingress point Figure 3.15 Experiment 4 cross section of sample at location with no water ingress 46

60 A visual inspection of experiment 4 concluded that; Localised water ingress to the anode can greatly influence the level of acidification and grout deterioration around the anode. A 2.5 mm of cementitious waterproofing coating provided protection to the anode from direct water ingress, as shown in Fig 3.14 anodes 3 and 4. Where water ingress does reach the anode, as shown in Fig anodes 1 and 2, a considerable level of grout acidification was evident. In locations where the anode was not exposed to direct water ingress as in Fig. 3.15, the level of grout acidification was minimal. Current, Voltage and Circuit Resistance Table 3.3 shows a resistivity trend in the anode slot cuts coated and uncoated with a waterproofing coating. It is noted that anode 4, in the beginning stages of the experiment did show lower than expected levels of resistance, however this did stabalise during the experiment. It is believed this could be caused by micro environmental factors around the anode. Table 3.3 shows that similarly to experiments 2 and 3, the resistance reading for the coated samples was much higher. 47

61 Experiment 4 Current, Voltage and Resistance Readings Time Reading Date Current (ma) Anodes (Fig. 3.12) Anodes (Fig. 3.12) Coated Coated Coated 4 Coated Voltage (V) Resistance (Ohms) 3 Days Day Days Days Days Days Average Table 3.3 Experiment 4 current, voltage and resistance readings 48

62 Chapter 4: Discussion 4.1 General The direct result of the research suggests that proper encapsulation of the anode in water exposure zones and the application of a waterproofing coating can eliminate grout acidification problems caused by water ingress. From the experiments, it was found: Direct water ingress to the anode has a direct effect on the level of localised grout acidification formation. The experiments revealed that in locations where direct water contact to the anode occurs, the level of localised grout acidification is greatly increased (Fig. 3.14). If there is no direct water ingress to an anode, generally uniform acidification along the anode surface will develop (Fig. 3.4). There was no evidence to suggest that anodes which have been installed with sufficient grout cover, which do not exhibit any signs of cracks, will suffer from localised grout acidification as shown in experiment 2, Fig. 3.6, Fig. 3.7 and experiment 3, Fig anode 2. For newly installed ICCP systems in concrete structures, well designed anode placement and quality control measures during the anode installation work can create a barrier against the occurrence of localised grout acidification. However, it is important to note, that many structures will have imposed loads and stresses placed on them, and these external influences have not been simulated in these experiments. 49

63 There was no visual evidence of acidification causing the deterioration of the existing concrete surface. All acidification witnessed during the experiments was of the grout material. A sufficiently applied layer (2.5mm) of cementitious waterproofing grout can provide protection to the anode from cracks or imperfections in grout in areas where ingress of water can occur. An anode which is exposed to direct water ingress will have a lower resistance level when compared to an anode which does not have direct water ingress. The information gathered from this research confirms the theory that localised acidification can be caused by water ingress to the anode, and confirms that the current industry practice of applying a cementitious waterproofing grout in the aim of suppressing localised acidification, can provide a level of protection in certain circumstances, against water ingress. This research project has provided evidence that the application of a waterproofing coating of sufficient thickness (2.5 mm) can eliminate the ingress of water to the anode level in a laboratory environment and can minimise and greatly limit localised acidification caused by water ingress. Many aspects of the experimental procedures had to be developed throughout the course of the 4 experiments. Since there has been no prior systematic research in this field, many aspects of the research had to be trialed. 50

64 This research developed a methodology of conducting accelerated testing, as well as sample design, T/R unit current and voltage limitations and the use of separate zoning for anodes for greater control of current delivery to each anode. This research procedure and methodology can lay a foundation for future research in this area. 4.2 Limitations and Improvements It must be noted that there are many variables which must be considered when conducting experiments which attempt to simulate a harsh marine environment. In the marine environment, constant water exposure including waves, storms etc may have an impact on the grout material encapsulating the anode, and in particular, on the interface area between the grout material and original concrete. It is important to note that the difficulties in achieving proper curing of the anode grout due to tidal variations under site conditions, may have an impact on the long-term performance of the grout. Movement of the structure especially if the installation of anodes is carried out while the structure is under loading from normal operation (wharf or bridge) may impact on the formation of cracks at the interface between original concrete and grout. The variation of material properties between the grout and original concrete may contribute to the formation of cracks at the interface between the original concrete and grout. In addition, the bond between the new grout and original concrete due to poor surface preparation of the slotted area may contribute to the formation of cracking at the interface between the original concrete and grout. 51

65 These issues cannot be eliminated under site conditions. This leads to the conclusion that improvement of the detail of anode encapsulation is required to eliminate the possibility of any defects at the interface between the new grout and original concrete. Consideration of applying additional measures to eliminate the potential formation of cracks under site conditions should be considered if ribbon anode is considered for use in tidal zones. Consideration should also be given to the potential use of alternative anodes such as discrete anodes with embedment details that can eliminate potential water ingress. 52

66 Chapter 5: Conclusion and Future Research 5.1 Conclusion The results of the research work confirm that the anode embedment methods currently in use in the industry, combined with incidences of poor workmanship, which allow water ingress to the anodes in tidal and splash zones, are considered to be the primary causes of acidification. In the laboratory environment, adequate grout cover to the anode may be sufficient in eliminating water ingress to the anode and potential acidification problems. None of the standards currently used for new ICCP systems discuss the potential formation of cracks at the interface between the grout material and original concrete, and water ingress in tidal and splash zones where there is continuous direct water exposure. The results confirm that the application of a cementitious waterproofing coating (which limits or even eliminates the ingress of water to anodes in tidal zones) can minimise grout acidification problems in existing ICCP systems. It is noted that there may be an increase of operating voltage in ICCP systems for structures where waterproofing coating has been applied. The chemical composition of the coating used in the research, its impact on ICCP system voltage increases and the impact of such increases on the long-term operation of ICCP systems were not part of the current research work. In summary, this research has provided information and confirms that the current method of applying a cementitious waterproofing coating can provide a level of protection against localised water ingress and acidification. It has also laid a foundation for future research in 53

67 accelerated laboratory concrete testing for acidification of impressed current cathodic protection systems. 5.2 Future Research The field of cathodic protection can benefit from further research in the area of acidification and the methods for minimising its impact. Some other areas in which further research can be carried out into include: Assessment of the level of acidification at the anode interface, providing that external water ingress is eliminated. The impact of current density on acidification. Current limitation in standards for anode current density (110 ma/m 2 of anode surface area) are mainly related to anode life only. The impact of grout characteristics on acidification. Aspects include ph level and resistivity. The impact of the amount of grout encapsulating the anode on the acidification process (size of hole for discrete anode and embedment details for ribbon anode). The impact of waterproofing coating resistivity on the operating voltage of CP systems. 54

68 References Figures: [1] Dowling, J 2012, Corrosion Mechanisms, SteelConstruction.info, Accessed 15 February 2017, [2] Reinforced Concrete, Galvanizers Association, Accessed 15 February 2017, [3] Lewarchik, R 2014, Understanding Corrosion Inhibitive Pigments, Prospector, Accessed 25 January 2017, [4] Broomfield, J, Impressed Current Cathodic Protection, Accessed 9 March 2017, [5] Figures 1.4, 1.5, 1.6, 1.7 provided by Remedial Technology Pty Ltd Literature: [6] Faraday, M (1834), Experimental Researches In Electricity, Seventh Series, Philosophical Transactions, 124, [7] Chess, PM, Broomfield, JP (2003), Cathodic Protection of Steel In Concrete, CRC Press, Page 63 [8] Cheaitani, A (2014), Review of Cathodic Protection Systems for Concrete Structures in Australia Lessons Learnt and Future Directions, Corrosion & Prevention 2014 Paper, Adelaide, Remedial Technology Pty Ltd, Accessed January 2017, 55

69 e-paper pdf [9] Cheaitani, A, Holloway, L, Karajayli P (2014), Cathodic Protection of Steel in Concrete in Australia: History And Current Status, Savcor Group, Remedial Technology Pty Ltd, Accessed February 2017, tion%2012%20.pdf [10] Steven F. Daily and Steven D. Somerville, P.E. Using Cathodic Protection to Control Corrosion of Masonry Clad Steel Framed Buildings, Corrpro Companies, Inc. Accessed December 2016, Papers/Cathodic-Protection-of-Reinforced-and-Prestressed-Concrete- Structures.ashx?la=en&hash=0C9843DAB7E0D D497C204DA03B4DC1CB [11] Standards Australia, 2008, AS Cathodic Protection of Metals, Part 5: Steel in Concrete Structures. [12] Cheaitani, A (2010), Durability Issues Associated with the Design of Reinforced Concrete Structures in Marine Environments, Accessed March 2017, 209%20.pdf [13] W Green and J Katen, 2017, Acidification Induced Deterioration of Concrete Cathodic Protection Systems and its Management, Australasian Corrosion Association Inc, Corrosion & Materials, Vol 42 No 2, May 2017, pp

70 Appendices Appendix A: Photos Sample Preparation Experiment 1 Experiment 2 Experiment 3 Experiment 4 Appendix B: Accelerated Testing Calculations Experiment 2 Experiment 3 Experiment 4 57

71 Appendix A - Photos

72 Sample Preparation 01 Samples 02 Samples 03 - Surface Preparation 04 - Surface Preparation

73 Sample Preparation 05 Grout Mixing 06 - Grout Application 07 - Grout Application 08 - Grout Application

74 Experiment 1 01 Day 1 02 Day Day Day 70

75 Experiment 1 05 Experiment Setup 06 Cut Sample Grout Acidification at Anode Interface 07 Cut Sample Uniform Grout Acidification Along Anode 08 Cut Sample

76 Experiment 2 01 Sample Preparation (Waterproofing Grout) (Blue Reference Not Used) 02 Sample Preparation (Blue Reference Not Used) 03 Experiment Setup 04 Experiment Process

77 Experiment 2 05 Acidification on Uncoated Sample 06 Acidification on Uncoated Sample 07 Uncoated Sample After Experiment 08 Coated Sample After Experiment

78 Experiment 2 09 After Experiment - No Visible Grout Acidification (uncoated Sample) 10 After Experiment - No Visible Grout Acidification (Coated Sample) 11 Minor Level of Grout Acidification (Uncoated Sample) 12 Minor Level of Grout Acidification (Coated Sample)

79 Experiment 3 01 Anode 1 Sample Preparation 02 Anode 2 Sample Preparation 03 Anode 3 Sample Preparation 04 Anode 4 Sample Preparation

80 Experiment 3 05 Experiment Setup 06 Condition if Samples After 25 Days 07 Water Ingress at Anode 1 Causing Acidification 08 Water Ingress at Anode 1 Causing Acidification

81 Experiment 3 09 Anode 1 After Experiment 10 Anode 2 After Experiment 12 Anode 3 After Experiment 11 Anode 4 After Experiment

82 Experiment 3 13 Grout Acidification Caused by Water Ingress to Anode 1 14 Grout Acidification Caused by Water Ingress to Anode 1 15 Acidification Comparison between Anodes 1 and 2 (1 on Left) 16 Level of Grout Acidification Ununiform Along Anode 3

83 Experiment 4 01 Sample Preparation (Anode 1) 02 Sample Preparation (Anode 2) 03 Sample Preparation (Anode 3) 04 Sample Preparation (Anode 4)

84 Experiment 4 05 Experiment Setup 06 Sample in Salt Water Solution 07 Transformer Rectifier Unit 08 Acidification at Top of Anodes 3 and 4

85 Experiment 4 09 Surface Grout Acidification at Anode 1 10 Surface Grout Acidification at Anode 2 12 No Surface Grout Acidification Anode 3 11 No Surface Grout Acidification Anode 4

86 Experiment 4 13 Surface Grout Acidification Anode 1 14 Surface Grout Acidification Anode 2 15 No Surface Grout Acidification Anode 3 16 No Surface Grout Acidification Anode 4

87 Experiment 4 17 Minor Grout Acidification in Locations with No Direct Water Ingress 18 Water Ingress Location (Anodes 1 and 2 at Top, 3 and 4 Bottom) 19 Grout Acidification Water Ingress to Anode 20 Grout Acidification Water Ingress to Anode