innovative cathodic protection systems for the corrosion

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Innovative Cathodic Protection Systems for The Corrosion Safeguard ofReinforced Concrete Structures

Nick Critchley1, Blane McGuiness1 & Oliver Gasior1

1 Marine and Civil Maintenance Pty Ltd

Abstract: A large variety of cathodic protection systems for the corrosion protection of reinforced concrete is available to asset owners and operators. This can make appropriate selection challenging for those responsible for concrete infrastructure. Our paper will review some of the most deployed systems with respect to performance, suitability and sustainability based on experiences with designing and installing both impressed-current and the newer part impressed-current, part sacrificial, anode systems.

Impressed-current cathodic protection systems were the system of choice in Australia in the late 90’s and early 2000’s for the protection of reinforced concrete structures, particularly for wharf and bridge infrastructure assets. Protection is often required for these assets in the marine environmentas chlorides in seawater penetrate the concrete cover and, once beyond initiation levels at the depthof the steel reinforcement, cause corrosion. If left unchecked, the pitting nature of chloride-generated corrosion can be catastrophic, particularly for structures with pre-, or post-tensioned reinforcement.

Part impressed, part sacrificial anode-based systems entered the market in the early 2000’s with the stated advantages of less cabling, control and monitoring requirements which were widely viewed as a major disadvantage of impressed-current cathodic protection systems. This type of system has also evolved since inception with both external and internal power options for the impressed- current phase now available.

There is now a substantial body of information available regarding both systems and some of which is presented below for consideration.

Keywords: Cathodic Protection, Durability, Anode, Design Life

1.0 Introduction

Cathodic protection has provided owners of reinforced concrete infrastructure a highly effective option for controlling reinforcement corrosion. This is particularly so for coastal assets, such as wharves and bridges which are exposed to seawater and in turn the corrosive effects that follow as chlorides migrate through the concrete cover to the reinforcement. Cathodic protection technology has evolved considerably over the past 30 years since its commercialisation in the Australian market.Today there are a range of options with respect to deploying cathodic protection for reinforced concrete to ensure that optimum value is provided. Within the paper below, four commercially available systems are discussed and case studies presented, these include:

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Impressed-Current Cathodic Protection (ICCP) Hybrid Anode Cathodic Protection (HACP) Internally Powered Dual Phase Hybrid Anodes Embedded Discrete Galvanic Anodes (SACP)

2.0 Impressed-Current Cathodic Protection (ICCP)

2.1 Technology Profile

Impressed-current cathodic protection systems have been widely used in Australia since the early 90’s. The anode material most used is manufactured from titanium and coated in a mixed metal oxide (MMO) coating. There are generally two types of anode arrangement deployed for ICCP systems, one being ribbon, which is either installed into substrate concrete or fixed to steel reinforcement using non-conductive spacers, and the second type being discrete anode installations. Discrete anodes are installed into drilled or cored holes in the substrate. Anode ribbon and discrete anodes are connected via titanium conductor bars or wires which are in turn connected to junction boxes and transformer rectifier units (TRU) which constantly power the system. This array makes upthe positive side of the circuit.

Figure 1 – ICCP Ribbon Anode

A negative side of the circuit is established via a direct connection to the steel reinforcement which, like the positive side of the circuit, is cabled back to junction boxes and TRU. Monitoring is achieved by embedding reference electrodes in the concrete and these electrodes are cabled beck to junction boxes and TRU for monitoring purposes. Following installation of all system components, ICCP systems are energised and the shift of the steel potential monitored to allow for initial current/voltage setting. After an initial period, the system is then tested for compliance with AS2832.5, Section 2.3. an extract of which is provided below:

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Initial and continuous adjustment of the cathodic protection system shall be based on meeting at least one of the following criteria which are listed in no priority order:

a) Potential decay criterion. A potential decay over a maximum of 24 h of at least 100 mV from the instantaneous off potential.

b) Extended potential decay criterion. A potential decay over a maximum of 72 h of at least 100 mV from the instantaneous off potential subject to a continuing decay and the use of reference electrodes (not potential decay sensors or pseudo reference electrodes) for the measurement extended beyond 24 h.

c) Absolute potential criterion. An instantaneous off potential (measured between 0.1 s and 1 s after switching the d.c. circuit open) more negative than −720 mV with respect to Ag/AgCl/0.5M KCl.

d) Absolute passive criterion. A fully depolarized potential, or a potential which is continuing to depolarize over a maximum of 72 h after the cathodic protection system has been switched off, which is consistently less negative than −150 mV with respect to Ag/AgCl/0.5M KCl.

Compliance with at least one of the above criteria shall be achieved within 6 months oralternatively, within a longer period as agreed with the structure’s owner.

Common advantages and limitations of an ICCP system are as follows:

Advantages: Performance measured against well-established and understood criteria. Highly effective in heavily chloride-contaminated structures Ability to control voltage and current Very cost effective, particularly when deployed as a preventative measure in new structures Long design life is achievable

Limitations: External, reliably continuous power source is required near the structure Large amounts of cabling and electrical systems which can be subject to vandalism, impact

damage and general wear and tear Ongoing monitoring and adjustment are required

2.2 CASE STUDY – Munna Point Bridge Rehabilitation

The Munna Point Bridge in Noosa Heads, Queensland was built in the late 1970s. Over 1.8 million trips in each direction are made across the 106-metre bridge and it is one of only two routes to reach the primary tourism attractions of Hastings Street, Main Beach, and Noosa National Park. As such, it is a critical piece of infrastructure to facilitate Noosa’s economy as a lifestyle and tourism destination.

In the 1990’s, large cracks appeared in the precast concrete piles and cast-insitu pile caps. The causewas identified as a combination of chloride attack and alkali silica reaction (ASR).

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In 2014, engineers analysed options for addressing the deterioration; these ranged from repair to replacement and the conclusion of this analysis was that remediation of the structure would providethe most viable solution. A performance specification for a design and construct contract was then prepared with the aim of extending the service life of the bridge by fifty years.

2.2.1 Project Highlights Custom designed ICCP system with design life of 50 years. Rehabilitation of the structure was carried out for approximately half of the price of

replacement (either in part or fully) Project executed under a collaborative Design & Construction model ICCP, consisting of ribbon anodes cast into the new concrete encasement, was proposed

for the tops and sides of all pile caps

2.2.2 Key Challenges

Many aggregates in Australia and throughout the world contain silica. When used in concrete, thesereact with alkalis in the cement to produce an expansive gel which in turn can cause concrete to expand and crack. Notably, the ASR reaction requires the presence of water. The piles of Munna Point bridge are in saltwater, with the pile caps in the tidal and splash zone. The ensuing ASR cracks allowed chlorides to reach and corrode prestressed steel strands in the piles and reinforced steel in the pile caps.

There is no “silver bullet” to solve ASR problems in existing concrete. The Federal Highway Administration (FHWA) in the United States says, ‘the term “mitigation” is used in lieu of “repair” because the methods described [in their ASR Handbook] are generally not able to, nor are they intended to, repair or restore the original properties or integrity to the ASR-affected structure. Rather, the intention is to reduce future expansion of the structure or to lessen the detrimental impact of future expansion’.

2.2.3 Implementation

AccessAs every part of the bridge required some treatment and there were restrictions from a large array of public activities, an innovative access approach which minimised impact on users was of paramount importance.

As most of the work was concentrated on the substructure, access was mostly water-based. Underwater work was carried out by divers working from a dive support vessel. Repairs and cathodic protection on the pile caps were undertaken from submersible steel platforms suspended by chains from the deck soffit.

Access to the span soffits for repairs and coating was provided by a floating platform which could be raised and lowered via webbing slings attached to the bridge crash barriers. To repair the corroded crash barrier posts and rails, a one-man, aluminium cage was designed and built. This was clipped over the top rail and was sufficiently light to be moved by hand as required.

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Figure 2 – Floating Access to Deck Soffits

InstallationFor this project, the ICCP system was installed inside the pile cap encasement reinforcement layer. Where the original concrete surface was undamaged, the mesh ribbons were attached directly to the concrete. To ensure efficient performance of the system, three zones were implemented across the pilecap, these being the tidal, splash and atmospheric. During the concrete repair of the parent pilecap, steel reinforcement was exposed and was tested for electrical continuity.Where discontinuity was discovered, additional steel bars were welded in place to address the issue.

Figure 3 – Pile Cap Cross Section

The junction boxes were positioned high on each pier on the upstream end of the headstock and all cabling from the positive, negative and reference connections to the junction boxes were embeddedwithin the concrete columns. This approach ensures durability of the system, minimises mechanical damage risks and maintains the appearance of the structure.

The cables from the junction boxes to the transformer rectifier unit were carried in conduits to the TRU mounted on a bracket on the north abutment wing wall. This location allowed it to be readily

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connected to the mains power while putting it out of reach from below. A lockable gate was cut in the fence to add security to the cabinet, which was also lockable.

The cost of the ICCP system was a small portion of the overall contract amount and provided high value by safeguarding the durability of the most at-risk element of the structure being the pile cap.

3.0 Hybrid Anode Cathodic Protection (HACP)


Hybrid anode-based systems entered the market in the late 2000’s with the stated advantages of less cabling, control and monitoring requirements, which were widely viewed as a significant disadvantage of impressed-current cathodic protection systems. The Hybrid anode system concept ischaracterised by the combination of both Impressed-current and galvanic techniques. Hybrid anode systems typically consist of an array of Zinc (Zn) anodes embedded into the concrete substrate at 300mm centres and are encased within a highly alkaline paste to ensure the anode remains active throughout its design life. The anode array is connected via a string of XLPE insulated Titanium (Ti) wire and energised (Impressed-current Phase) using a temporary power source set to deliver a constant voltage of 8-9 Volts DC. In some instances, the voltage can be set lower to minimise hydrogen embrittlement risk in pre-stressed or post-tensioned structures. During the initial impressed-current phase, active corrosion sites are re-alkalised, which stops active corrosion and returns the steel to a passive state. The impressed-current is continuously maintained for a minimum duration of about nine days and continues until the required 50kC of electrical charge has been passed to the reinforcing steel for each square metre of its surface area.

Figure 4 – Typical Hybrid Anode

Once the 50kC/m2 criterion is achieved, the system can be disconnected from the external power source. The anodes are then “ commoned ” with the structure, which commences the “Galvanic Phase” of the design. The galvanic phase aims to maintain th e passivity gained from the IC phase by providing a small current flow between the anodes and the steel due to the galvanic potential difference between the two metals.

In general terms, advantages and limitations can be summarized as follows:

Advantages: Ability to provided targeted “hot spot” protection to identified elements only

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Less cabling when compared to ICCP systems Reduced monitoring and maintenance requirement

Limitations: Inability to control current outputs after the initial IC phase of the anodes Anodes designed to be consumed, therefore having a finite design life Design life depends on current output, which may vary over time Challenging to replace or upgrade following consumption of the anode cores

3.2 CASE STUDY: Brotherson Dock Life Extension Project

The BDLE project aims to extend the useful life of the Brotherson Dock container wharf structures at Port Botany. The wharf structures were built 40 years ago and subjected to harsh environmental conditions and operational wear and tear. Chlorides from seawater have slowly ingressed into the concrete and caused corrosion of the embedded reinforcement steel. Corroded steel expands, which cracks, spalls and then delaminates the concrete cover layer, resulting in loss of structural capacity and reduced structure life. The project scope included repairing the existing damage and controlling the risk of future corrosion of the wharf structure.

3.2.1 Project Highlights

Custom-designed electro-chemical protection system with anode life capability of 50 years. Approximately 2,000m of quay face that required repair and hybrid installation consisting of:

o 250m2 of defective concrete removed and reinstatedo 16,000 D500 Hybrid Anodes o 7,500 D1000 Hybrid Anodes o 7,590m2 of Silane applied to the concrete capping beam and deck surfaceo 156 embedded reference electrodeso 114 corrosion coupons

Installation ofICCP underwater anodes along the quay line includingo Installation of 23km of cablingo Installation of 77 immersed MMO ICCP anodes o Installation of 20 Ag/AgCl Reference electrodes

Installation of 20 monitoring boxes to provide real time performance monitoring of the system.

Supply and installation of 4 x Transformer Rectifier Units


The major challenge of the project was to ensure shipping operations were maintained without disruption throughout the project. The project team worked closely with the operators to ensure that the installers were provided adequate space to perform the works efficiently and safely. Given that Port Botany is a highly dynamic port, the shipping schedules can change at a moment’s notice. Multiple work fronts and a highly mobile work crew ensured that operational delays were managed to reduce the overall exposure of delays and disruption.

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Figure 5 – Schematic of working zones within the BDLE Project

Port Botany is subject to harsh wind and swell conditions, which also posed a significant challenge that needed to be carefully managed. A considerable amount of work was within the tidal zones, and having the right balance between the high and low tide works was critical in ensuring the project deadlines were met.

In 2020 the global pandemic was a unique challenge that most organisations had to face, and the BDLE Project was not exempt from that challenge. During the pandemic height, there was significant disruption to the global supply chain of items supplied from overseas vendors. This risk was managed with careful planning and cooperation with vendors..

3.2.3 Implementation

A c c e s s The Brotherson Dock Life Extension Project’s access platforms were designed to facilitate the installation of the Hybrid & Impressed-current Cathodic Protection Systems and complete the concrete repair works as prescribed. The platforms were designed to be multipurpose and able to complete several different tasks.

The temporary access decks were engineered to be as lightweight and as low-profile as possible. Furthermore, it was imperative to avoid having any structural elements protruding above the kerb so that the risk of fouling with mooring lines was minimised. The access platforms were designed to Australian Standard AS 4997-2005 – Guidelines for the design of maritime structures and, where additional guidance was required beyond the scope of the Australian Standard, reference was also made to BS6349 – Maritime Structures.

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Figure 6 – Bespoke Access Decks for BDLE

D e s i g n & I n s t a l l a t i o n The hybrid anode system was designed with a 50-year design life. The system is broken up into two distinct zones, the areas above the water line being protected using an array of Zinc Hybrid anodes, with each capping beam having an individual design based on its measured corrosion risk. An ICCP water anode system protects the submerged sections of the counterfort units.

Figure 7 – Typical anode layout

The anodes specified on the project were 1100 mm long, 18 mm diameter and 220 mm long, 18 mm diameter. The 220mm anodes were installed in the bulk of the capping beam face, whereas the 1100mm anodes were installed exclusively in the bottom row of anodes where the protection zone is larger.

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Figure 8 – Anode Installation Details

Figure 5 shows a section view of the capping beam highlighting the anode installation details. The anodes were installed as per the prescribed anode patterns (See Figure 4) in the capping beam at approximately 300mm centres. The anodes were installed in predrilled holes at a 15-degree angle. During the impressed-current phase, a total of 50kC/m2 of steel surface areas was to be passed before connecting the anodes directly to the steel reinforcement for the galvanic phase.

The Hybrid anodes system was powered using a portable TRU unit with 20 configurable zones of up to 9V and 2.5A, each with 15 reference inputs. The portable TRU’s can be powered by either 24Vdc batteries mounted external to the unit or via mains power via a weatherproof IP68 connector, allowing the portable TRU to be exposed to the elements. The TR’s were developed to ensure that the units could deliver the project requirements as per the specifications.

Figure 9 – Data 2 Desktop – Realtime Monitoring portal of Charging Hybrid Anodes

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4.0 Internally Powered Dual Phase Hybrid Anodes


Internally powered hybrid anodes utilise a dual phase current supply arrangement to provide both an impressed and galvanic current to the reinforced concrete elements being protected.During Phase One of the system’s operation, inbuilt batteries within the anode unit are able to output between 2.5 – 16Ah with a battery rating 1.5 to 3V.

The Phase One Impressed-current component is designed to passivate actively corroding reinforcement and typically operates in this phase for two to three months (depending on the environment and material characteristics of the concrete element).

Once the internal battery is sufficiently depleted, the anode will automatically switch to Phase Two, a galvanic maintenance phase whereby a secondary internal zinc anode with a zinc weight ranging from 100 to200g will provide a long-term galvanic current. Under this phase, passivity of the reinforcement is maintained with an estimated design life of 30+ years.

Figure 10 - Fusion T2 Anode Cut-Away (image courtesy of Vector Corrosion Technologies)

The design intent of these anodes is to provide long term electrochemical treatment to the reinforced concrete elements with minimal maintenance and human intervention. Through the elimination of external power supplies and temporary power cables, the ease of installation is increased, allowing for a more cost-efficient solution based on reduced labour and access requirements when compared to traditional Impressed-current and Hybrid Anode systems.

Further advantages can also be realized in a reduction of the number of anodes required when compared to a standard galvanic system. Due to the initial high charge density provided under phase one, internally-powered, dual phase hybrid anodes can operate more efficiently due to their higher driving voltage that aids in passivating actively corroding steel, reducing ongoing current requirements to maintain the achieved level of passivation.

In general terms, the advantages and limitations can be summarized as follows:

Advantages:1. Combines high level ICCP performance with long term, maintenance free galvanic protection2. Increased installation efficiencies and reduction in overall system costs3. Ability to provided targeted “hot spot” protection to identified elements only

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4. Reduced monitoring and maintenance requirements5. Increased performance when compared to traditional SACP systems

Limitations:1. Inability to control current outputs2. Anodes designed to be consumed therefore having a finite design life3. Difficult to replace or upgrade following consumption of the anode cores4. Difficult to install in areas of highly congested steel reinforcement

Figure 11 - Fusion T2 Anode Standard Installation Detail (image courtesy of Vector Corrosion Technologies)

4.2 CASE STUDY: Geraldton Port Berth 3 Extension

The works undertaken to the Berth 3 Extension were undertaken as part of a larger maintenance programme that was completed over 2 years at Geraldton Port. Measuring approximately 40m in length, the Berth 3 Extension is situated at the Western end of Berth 3.

Figure 12 - Berth 3 Extension with Port of Geraldton

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Over the years, the southern berths have been exposed to the harsh northerly winds and have exhibited signs of deterioration. Whilst remediation works have been undertaken to other berths along this section of the facility, a Fusion Anode Hybrid System was designed and installed to provideprotection to the steel reinforcement to allow for preventative maintenance and long-term durability.

4.2.1 Project Highlights

Largest installation of Fusion Anodes globally at the time of installation Supply and installation of 6,800 Fusion Anodes, distributed across the deck soffit Complete installation of the system in approximately 2 months Installation of three monitoring boxes to allow for ongoing performance assessments and

monitoring

4.2.2 Design & Installation

The Fusion Anode system was designed utilising T2-135 anodes with an overall system design life of more than 25 years. All anodes were installed to the deck soffit of the Berth 3 Extension with a specified maximum spacing of 320mm.

In line with the manufacturer’s recommendation, anode strings were restricted to a maximum stringof 10 anodes.

To allow monitoring and assessment of the system, whilst minimising the requirement for extensive system maintenance, three test zones were installed at representative locations as seen below. Each test zone incorporated permanent reference electrodes and an isolation switch to allow for instant-off measurements and depolarisation assessments.

Figure 13 - Deck Soffit Anode Plan

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Due to the dual phase approach of these anodes, performance assessment criteria were not readily available, nor were previous case histories for comparison. As such, consideration was given to available standards and industry best practice to devise assessment criteria consistent with the individual stages of the system’s operation.

The following criteria were adopted:

Stage 1To establish whether the Anode System is providing corrosion protection tothe reinforcement during Stage 1, the system shall meet at least one of the criteria below:

a. Corrosion rate, less than 2 mA/m2 in all Anode regions.b. A potential that is consistently less than -150 mV with respect to Ag/AgCl/0.5M KCL

after a maximum of 72 hours following the circuit being disconnected, either directlyfollowing current phase or during sacrificial anode stage.

c. An ‘Instant Off’ potential that is more negative than -720 mV with respect to Ag/AgCl/0.5M KCl (“Absolute Potential Criterion”).

d. A minimum 100 mV potential decay ("Potential Decay Criterion"). The potential decay is determined as the difference between the "Instant Off" potential and the potential measured after the Anode System circuit being disconnected for a minimum period of 4 hours and a maximum period of 24 hours. A potential decay over a maximum of 72 hours of at least 100 mV from the instantaneous off potentialis considered acceptable subject to a continuing decay.

Stage 2To establish whether the Anode System is providing corrosion protection tothe reinforcement during Stage 2, the system shall meet at least one of the criteria below:

a. Steel current density, between 0.2 – 2.0 mA/m2.b. Corrosion rate, less than 2 mA/m2 in all Anode regions.

Through this approach, not only was the installation able to be verified, but it was also possible to monitor and assess the ongoing performance comparatively with other ICCP and Galvanic systems.

Another key challenge that was identified and led to this system being adopted was the requirementto keep the facility fully operational during all shipping movements. Under standard site conditions, all under-wharf works needed to cease during berthing operations. During this time, it was also essential that any electrical cabling and connections were either fully installed/encapsulated or isolated, to prevent any spark risks. Due to the full encapsulation of the anodes and their internal configurations, anodes could be installed and commissioned in a much shorter period compared to alternative systems. Furthermore, the system was able to eliminate all external power sources and electrical cabling, allowing for an accelerated and unimpeded installation program under restricted conditions.

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4.2.4 Initial Assessment

Once commissioned, all monitoring zones showed an initial shift between the natural potential and instant-on potential, with an average more than 100mV (negative shift). After a period of 24 hours, all references measured a potential shift in excess of 290mV (negative shift) between the natural potential and the 24 hour on potential.

Illustrated below are the initial monitoring data points depicting the initial potential shifts observed and the transition between phase one and phase two. As detailed above, all results are presented asON POTENTIALS and do not form part of any performance assessments undertaken in accordance with the specified Stage 1 and Stage 2 assessment criterion.

Natural

Immediate On

24-hour On

-514-528-524-526-524-600

-400

-200

0

200

East (Zone 1)Central (Zone 2)West (Zone 3)

ON Potential vs Time

Time (Weeks)

mV

Figure 14 - Initial Fusion Anode Assessment Results

5.0 Embedded Discrete Galvanic Anodes (SACP)


Embedded Discrete Galvanic Anodes consist of a sacrificial zinc core encapsulated in a proprietary activating medium. There are a variety of proprietary systems available, all of which incorporate interconnected strings of anodes embedded into contaminated areas of reinforced concrete. Grouted into drilled holes (measuring approximately 25-38mm in diameter), the anodes are connected in strings varying from 10 – 40 anodes in total.

Protection is provided to the steel reinforcement via preferential and sacrificial corrosion of the zinc core within the area where the anode array is installed. As with hybrid anodes, these systems do not require external power supplies or extensive cabling arrangements.

Depending on the product, the zinc component of the anode is either pre-encapsulated in an activating mortar, or the mortar is applied around the anode following drilling and positioning withinthe anode hole.

Phase Transition

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Figure 15 - Duoguard PatchGuard Connect Anode (image courtesy of Duoguard Australia)

Figure 16 - Galvashield CC Anode (image courtesy of Duoguard Australia)

Like galvanic anodes installed around the internal perimeter of patch repairs to prevent incipient anode effects, discrete galvanic anodes are dependent on the calculated steel density of the areas tobe protected. The system output is established via either an increase or decrease in the anode spacing to provide an appropriate current density suitable to the application.

In general terms, this anode system can be summarized as follows:Advantages:

1. Increased installation efficiencies and reduction in overall system costs 2. Ability to provided targeted “hot spot” protection to identified elements3. Reduced monitoring and maintenance requirements

Limitations:1. Inability to control current outputs2. Anodes designed to be consumed, therefore having a finite design life3. Difficult to replace or upgrade following consumption of the anode cores4. Less effective than powered Hybrid Anodes due to the absence of a highly charged initial

phase5. Difficult to install in areas of highly congested steel reinforcement6. Not suitable for all chloride contamination levels and environments

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5.2 CASE STUDY: Wakehurst Parkway Bridge Remediation

Middle Creek Bridge No.3 (RTA Bridge No. 148) is the third bridge that spans across Middle Creek at Narabeen Lakes. The bridge is made up of a total of six (6) spans of various lengths and was constructed circa 1943. Initial durability inspection and testing was undertaken for the bridge, focusing on tidal and atmospheric elements only. These elements included pier columns, headstocks, girders, and the deck soffit.

The durability assessment concluded: The total damage area was estimated to be approximately 36m2 with the majority of the

deterioration identified along exposed pier column faces and areas where the exposure to splash water was highest.

Overall, the pier columns appeared to be in moderately good condition (36% pier columns exhibiting no visual deterioration). The remaining 64% had varying degrees of damage which appeared to have resulted from general deterioration over time and chloride ingress.

Based on the overall condition of the structure, remediation works were specified and completed, including concrete repairs, installation of a Sacrificial CP System, and application of protective coatings.

5.2.1 Design & Installation

The SACP system design incorporates protection to the piles across three individual zones:

Zone 1 – SACP for buried/submerged section of the pile Zone 2 – Above water SACP to tidal zone Zone 3 – Above water SACP to atmospheric zone

Figure 17 - Wakehurst Parkway SACP System Zoning

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For zones 2 and 3, discrete sacrificial anodes were installed in strings consisting of 7 anodes per zone, per pile for zone 3, and 9 anodes per zone, per pile for zone 2.


Due to limited external power to the bridge structure and the adjoining abutments, an ICCP system was not considered feasible. A Sacrificial Anode system was adopted to eliminate any requirement for ongoing external AC power.

It was further assessed that, based on the chloride levels in the piles, an SACP system would be sufficient in providing long term protection to the steel reinforcing. Ongoing monitoring and assessment of the system would be able to be carried out with a Bridge Monitoring Unit (BMU).

5.2.3 Initial Assessment

Initial assessment of the SACP system for each pile junction box showed potential shifts with an average of more than 150mV.

Figure 18 - Initial Savcor Smart Zinc Connect Assessment Results

Under the right conditions, SACP systems can provide protection levels similar to those of ICCP systems ().

SACP systems, as typified in this case study, are suited to locations where external power is problematic, and/or the overall driving voltage and design current density can be lower than what would typically be applied with ICCP. In these scenarios, design lives of 20-25 years are readily achievable and can provide a more cost-effective solution, both in terms of initial installation costs and ongoing monitoring and maintenance.

6.0 Discussion & Conclusion

As evidenced by the variety of cathodic protection systems and applications discussed, there are many options available for providing ongoing corrosion protection to concrete reinforcement. To ensure that the most appropriate system is deployed, it is critical that the structure is thoroughly investigated by appropriately qualified personnel and root causes of any deterioration are identified. If chloride-induced corrosion is identified as the cause of concrete cracking, delamination and spalling, a cathodic protection system in conjunction with other repair techniques may offer a suitable solution.

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Design of a remediation strategy including cathodic protection also needs to be performed by suitably qualified personnel who – ideally - have been involved in the investigation of the structure. The designer of the CP system needs to consider not just the result of the investigation but also the environment, power availability, the interests of stakeholders, the project scale and budget, and the appetite of the client for ongoing management of the structure. Thorough consideration of these aspects and, in many circumstances, balancing competing needs will ensure that optimum performance, suitability and sustainability is achieved.

In general terms, the systems now available are diverse enough to allow balancing of upfront procurement and installation costs, ongoing maintenance costs and the overall serviceability/design life of the system. Considering these system factors (in addition to complementary remediation techniques), a Whole of Life maintenance plan can address these aspects and incorporate financial modelling to assess the life cycle costs of each option.

The large variety of cathodic protection options available ensures that, in most circumstances, a suitable option can be selected to ensure continuing use of the structure for whatever period the owner requires.

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7.0 Acknowledgement

The Authors would like to thank Remedial Technologies, Savcor Products, Vector and Douguard for provision of information and images. We would additionally like to thank Alan Bird for peer review ofthe paper.

8.0 References

1. AS 2832.5-2008 – Cathodic Protection of Metals. Part 5: Steel in concrete structures2. Hybrid Anode Treatment for the Management of Corrosion to Reinforced Concrete Bridge

Piles in an Estuarine River Dr. Liam Holloway, Principal Engineer, MEnD Consulting Pty Ltd3. http://remedialtechnology.com.au/30/Galvanic-Systems/4. https://www.duoguard.com.au/hybrid-3/

http://remedialtechnology.com.au/30/Galvanic-Systems/

https://www.duoguard.com.au/hybrid-3/

innovative cathodic protection systems for the corrosion

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