Ask the Expert

Ask the Expert

What Stops the Reinforcing Steel in Damp, Porous Concrete from Corroding (Usually)?

John Broomfield, Corrosion Engineering Solutions Ltd.

Meet the Author

John Broomfield

John Broomfield is a Fellow of ICorr, AMPP, and the Concrete Society. He is a Chartered Materials Engineer and Chartered Scientist. He is also a Level IV Senior Cathodic Protection Engineer and an AMPP/NACE International Corrosion Specialist. He has over 40 years of experience in dealing with deterioration and durability problems in the built infrastructure, specialising in reinforced concrete, corrosion of steel-framed structures, and conservation of historic buildings and monuments. He has worked on projects all over the 
world and undertaken condition surveys, repair feasibility studies, life cycle 
cost analysis, corrosion risk analysis, repair specification, and repair design. 
He specialises in the application of electrochemical techniques for the investigation, rehabilitation, and design of durable new construction.

Concrete

Concrete has been used for millennia in various forms, principally as unreinforced mass concrete. The Romans used a form based on volcanic ash extensively, one of the finest remaining examples being the Pantheon in Rome.

The development of Portland cement by Joseph Aspdin in the early 1800s using simple, widely available materials and then the development of reinforced concrete by François Hennebique in the late 1800s led to the development and use of reinforced concrete for buildings, bridges, and other major structures. There had been attempts to use other metals to reinforce concrete, but iron and steel turned out to be the most compatible due to the similarity of their thermal expansion coefficients [1].

Concrete is a composite of cement powder and water mixed with coarse and fine aggregates. It is the cement that binds the aggregates together as it hydrates. The most common binder is Portland cement, made from limestone and clay roasted and ground in a kiln. It is a complex mixture of calcium compounds such as silicates, aluminates, and iron oxides that, when combined with water, form a calcium silicate hydrate gel that binds the concrete mix together. The hydration process, when completed, leaves a level of porosity in the hardened concrete of the order of 10%. These pores contain calcium hydroxide both in solution and as a precipitate, along with some sodium and potassium oxides/hydroxides.

While strong in compression, concrete is weak in tension, requiring reinforcement in many applications. Steel exposed to water and oxygen will oxidise unless effectively starved of oxygen or completely dried out. Absence of water in concrete can occur in indoor environments or behind external cladding. Absence of oxygen can occur in submerged concrete. For normal outdoor exposure, the steel would be subject to corrosion at a rate that would be harmful over the lifetime of a structure due to the ingress of water and oxygen through the pore system unless otherwise protected.

Corrosion Resistance of Reinforcement

Fortunately, the excess calcium hydroxide in the concrete pores, combined with some sodium and potassium hydroxides, elevates the alkalinity at the steel surface to around pH 12.5 to pH13. At this point in the Pourbaix diagram [2], iron is passivated, forming a thin, protective, self-sustaining oxide layer with a very low corrosion rate. As long as the concrete cover to the steel remains intact, sufficiently alkaline, and uncontaminated, the steel will remain in good condition despite the presence of oxygen and water at the concrete and steel surfaces, or perhaps we should say that the protection of the steel is because of 
the presence of oxygen and water to maintain the protective passive oxide film. We therefore have reinforced concrete structures that 
can last 100 years or more without showing any signs of 
reinforcement corrosion.

A true passive layer is a very dense, thin layer of oxide that leads to a very slow rate of oxidation (corrosion). There is some discussion as to whether or not the layer on the steel is a true passive layer. It seems to be thick compared with other passive layers and it consists of more than just metal oxides but, as it behaves like a passive layer, it is generally referred to as such.

Corrosion scientists and engineers spend much of their time trying to find ways of stopping the corrosion of steel by applying protective coatings to steel. Metals such as zinc and polymers such as acrylics or epoxies are used to stop corrosive conditions from forming on steel surfaces. The passive layer is the corrosion engineer’s dream coating, as it forms itself and will maintain and repair itself as long as the passivating (alkaline) environment is maintained.

Factors that Accelerate Corrosion in Reinforcement

However, the passivating environment is not always maintained. For reinforced concrete in normal atmospheric exposure, two conditions can break down the passivating environment without attacking and destroying the concrete itself. One process is carbonation, and the other is chloride attack.

Carbonation occurs when the naturally occurring carbon dioxide (CO2) in the air reacts with the alkaline oxides/hydroxides in the concrete pore water. The dissolution of CO2 in water forms carbonic acid, a weak acid that does not attack the cement paste or the aggregates in the concrete but reduces the pore water pH below 10. At that point, the passive layer on the steel breaks down, and the steel is vulnerable to corrosion. Carbonation moves as a front through the concrete cover. The rate of progress of the carbonation front is approximated by a simple diffusion equation where the depth of carbonation x at time t after construction is given by:

x = kt1⁄2

Where k is a constant. The carbonation front is a transition in pH from about 12.5 to 8.5 and is a few millimetres wide. The depth of carbonation can be measured using an indicator solution, sprayed on to a freshly exposed profile through the cover concrete. An example is shown in Figure 1.


Right: Figure1: Phenolphthalein
Indicator Applied to Freshly Broken
Concrete to Measure the Carbonation
Depth on a Reinforced Concrete
Window Mullion.

The other condition leading to the de-passivation of steel is exposure to chloride ions (Cl-), generally from sea salt or de-icing salts. In this case, the chlorides diffuse into the concrete and build up in the concrete cover until there is sufficient concentration at the steel surface to break down the passive layer. There is no moving front, but there is a threshold for corrosion at the steel surface when the chloride ions successfully compete with the hydroxyl ions and break down the passive layer. The threshold is generally taken as being in the range of 0.2 to 0.4% chloride by mass of cement for low-alloy carbon steels in Portland cement- based concretes. It should be noted that for the newer “low carbon concretes,” the threshold has yet to be confirmed and may reduce with age [3].

Once the steel is de-passivated by carbonation or by chlorides, reinforcement in atmospherically exposed concrete will start to corrode. The most common corrosion process forms porous iron oxides with a volume several times that of the steel consumed. This leads to tensile forces which will crack and delaminate the concrete cover [4]. There are field techniques for measuring the carbonation depth in concrete and for sampling for chlorides.  There are also non-destructive techniques for estimating the corrosion condition. Reference electrode potential measurements can identify areas of actively corroding steel and a polarisation resistance kit can estimate the corrosion rate [4,5].

Remedial Measures for Corrosion in Concrete

There are a range of techniques for preserving and restoring the passive layer on steel. These include the application of coatings, physical repair of the concrete, and a range of electrochemical techniques. Coatings are preferred for preventing the ingress of chlorides and CO2. BSEN 1504-2 [6] gives details on the selection and performance of anti-carbonation coatings and of penetrating sealers that resist chloride ingress. It has been found that anti- carbonation coatings are effective in controlling the corrosion rate in carbonated concrete by controlling moisture ingress as well as CO2 [7]. However, penetrating sealers applied to chloride contaminated concrete are less effective in slowing corrosion once the corrosion threshold chloride concentration has been exceeded at the steel surface.Electrochemical techniques such as re-alkalisation, chloride extraction, impressed current and galvanic cathodic protection are all effective in preventing corrosion of the steel, regardless of the extent of de-passivation if used appropriately [4].

Corrosion in Alternative Types of Concrete

It is important to recognise that the concrete cover to the steel must sustain the passive layer throughout the life of the structure if there is a corrosion risk. The performance of Portland cement concrete, and concretes with blended cements is well understood. However, there is now a new range of low-carbon cements being made available to the construction industry. In a recent article in CM [3], I expressed concern about the long-term corrosion protection afforded to low-alloy steel reinforcement by novel cement materials. Are there sufficient alkali reserves available over 50 to 100 year design lives to ensure the steel cannot corrode? Is anyone testing them? The recent problems with reinforced autoclaved aerated concrete (RAAC) are also interesting. RAAC is a very low-density concrete with minimal resistance to the ingress of water and CO2. It was designed for ease of handling and low cost. Much of the press-coverage around this issue is confused. RAAC has many problems and failure mechanisms and many are not corrosion related. These problems include poor placement of reinforcement, poor placement of units [bearing shelves], deterioration through wetting & drying cycles and negligible to zero cover to the reinforcement. However, RAAC was supposed to be used in a dry, indoor environment where the corrosion risk to the reinforcement is minimal. RAAC beams were often installed under flat roofing. Any leaks would expose the concrete to wetting and drying, which would allow rapid carbonation and rapid breakdown of the passive layer with subsequent reinforcement corrosion. Flat roofs have a limited life, and identifying leakage can be difficult, especially above false ceilings. The problems were foreseeable and were foreseen by many, but not necessarily always by those with the responsibility and budgets for keeping the buildings safe. Moreover, this is not just a corrosion issue or a failing of the material – if your roof is leaking, you have bigger problems than just how it might affect any RAAC that might be present.

Summary

We can therefore see that the alkaline reserves in the concrete pore water leads to the formation and maintenance of the protective passive layer on the reinforcing steel. This is crucial to the durability of steel-reinforced concrete exposed to normal atmospheric conditions. Those responsible for the maintenance of reinforced concrete structures need to understand how and why reinforcing steel is protected from corrosion. If corrosion occurs, the correct techniques must be used to assess the cause and extent of the problem and the correct treatment applied to control corrosion and maintain the asset for the required life.

References

  1. 
Paul Lambert Reinforced Concrete: The History, Properties and Durability of Reinforced Concrete , Technical Note 1 Corrosion Prevention Association, Bordon Hants, 2018.
  2. 
Pourbaix, M. (1974). “Applications of Electrochemistry in Corrosion Science and in Practice.” Corrosion Science Vol. 14: p. 25-82.
  3. 
Broomfield, J.P The Corrosion Resistant Properties of Novel Cements, Concretes, and Reinforcement, Corrosion |Management July/Aug 2023 pp 22-23.
  4. 
John Broomfield, Corrosion of steel in concrete, 3rd edition Publ. CRC Press, London, 2023.
  5. 
Concrete Society Technical Report 60, Electrochemical Tests for Reinforced Concrete. Concrete Society, Camberley, 2004.
  6. 
BS EN 1504-2 (2004) Products and Systems for the Protection and Repair of Concrete Structures – Definitions, Requirements, Quality Control and Evaluation of Conformity: Part 2: Surface Protection Systems for Concrete.
  7. 
Seneviratne, A. M. G., Sergi, G. Page, C.L. (2000). “Performance characteristics of surface coatings applied to concrete for 
control of reinforcement corrosion.” Construction and Building Materials 14: 55-59.

Volunteer Assessors

The Institute of Corrosion is currently in the process of becoming a Full
Licensee of Engineering Council, in order to be able to provide CEng,
IEng and EngTech, directly through ICorr in future. This will be a major
improvement to our membership offering and member retention.

We are now looking for Professional Registration assessors (for both
Applications and Interview assessment purposes).

  • Are you Engineering Council registered at CEng level?
  • Do you want to give back to the profession by helping the next
    generation of engineers achieve professional registration?
  • We are looking for volunteers to become Professional Registration
    Interview (PRI) assessors who will be reviewing, assessing, and
    interviewing applicants.

By giving us your time, you will be doing vital work ensuring the future of
the profession. All we need from you is 6 hours of your time per month.

If this is of interest to you, please reply: F.A.O Anthony Setiadi admin@icorr.org  and we will be in touch with you about the next steps.

Young Engineer Programme 2024: Launched and Off to a Successful Start

Young Engineer Programme 2024: Launched and Off to a Successful Start

YEP 2024 Sprints Out of the Blocks

Standing at the forefront of the corrosion industry, the Institute of Corrosion understands the critical nature of preparing the next generation of corrosion engineers to tackle the significant challenges and threats that corrosion poses to the world’s infrastructure and economy. Which is why we are delighted to announce the launch of the Young Engineer Programme (YEP) 2024.

In this year’s programme, we’re building on the success of previous years. Coordinated and managed by Young ICorr for the first time, YEP 2024 promises to be an even more enriching and transformative journey for aspiring corrosion professionals.

Young Engineer Programme 2024: Key Takeaways

  • YEP is meticulously designed to cover the spectrum of corrosion management, from the fundamentals of corrosion to the intricacies of materials selection, integrity management, and beyond.
  • The curriculum is structured to ensure participants gain not just theoretical knowledge, but also hands-on experience through real-life case studies and team projects.
  • As in previous years, perhaps the most exciting aspect of this year’s YEP is the real-life case study challenge, where participants will apply their learning to solve actual corrosion problems, culminating in a presentation to a panel of judges.
  • The winning team will be awarded an all-expenses-paid trip to the AMPP 2025 Conference in Nashville, USA, confirming ICorr’s commitment to rewarding excellence and innovation.

YEP 2024 – Kicking Off in London

YEP 2024 kick-started with an inaugural event in London, marking a momentous beginning to a year-long journey dedicated to nurturing tomorrow’s corrosion management experts.

This event wasn’t simply a formal introduction to the programme. It was a vibrant gathering of passionate individuals, including the selected participants, esteemed ICorr members, and distinguished speakers from the corrosion community.

Meet the Participants

This year, we’re thrilled to welcome twenty-six early-career professionals from diverse backgrounds, including engineering, science, and research, all sharing a common goal: to excel in the field of corrosion.

Representing a broad spectrum of companies and academic institutions, they bring a wealth of perspectives and a shared eagerness to dive deep into the world of corrosion. Their diversity is not just in their professional backgrounds but also in their aspirations, with each looking forward to contributing to and benefitting from this unique learning experience.

Drum roll, please, as we bring this year’s YEP participants on stage!

  • Alvaro Gonzalez Fuentes, Wood Thilsted
  • Alyshia Keogh, University of Manchester
  • Amy Johnstone, Kent PLC
  • Ben Hudson, Premtech
  • Berenika Syrek-Gerstenkorn, Scottish Power
  • Christina Igube, C-Probe Systems
  • Clayton Bevas, Jacobs
  • Dilshad Shaikhah, University of Leeds
  • Ellie Lowe, DNV
  • Fatima Mehnoune, Intertek CAPCIS
  • Georgie Bond, Johnson Matthey
  • Joe Linkson, Wood Thilsted
  • Katie Atkins, Johnson Matthey
  • Kevin Lam, bp
  • Kishan Ramesh, Plant Integrity Management
  • Lukasz Ramowski, Saipem
  • Mohammed Muqueeth, Plant Integrity Management
  • Muhammad Haris, Brunel University
  • Noor Ghadarah, Saipem
  • Roberto Alcivar, vHPM UK
  • Rochelle Holness, Genesis Energies
  • Roisin Harris, Ramboll
  • Samuel Brown, Wood PLC
  • Tom Robinson, Saith Ltd
  • William Adu-Poku, Altrad Babcock
  • Yulia Sergeykina, BP

YEP 2024: The Year Ahead

As the participants embark on their journey, YEP 2024 will unfold over the rest of the year with a series of evening lectures and workshops. Oh, and, of course, the eagerly anticipated case study project.

Each session is an opportunity for participants to learn from and interact with experts in the field, developing not just their technical skills but also their professional network, as YEP 2024 covers topics that include:

Date Topic of Event / Workshop
Jan 2024 Fundamentals of Corrosion
Feb 2024 Materials / Welding
Mar 2024 NDT & Corrosion Monitoring
Apr 2024 Coatings & Linings
May 2024 Previous Case Study / Delivery of Case Study to the Teams
Jun 2024 Corrosion under Insulation / Fire Proofing
Jul 2024 Cathodic Protection
Aug 2024 Production Chemistry / Chemical Treatments
Aug 2024 Annual Corrosion Forum – Energy Transition (Free space for YEP)
Sep 2024 Integrity Management / Fitness For Service
Oct 2024 Presentation Skills
Nov 2024 Presentations of Case Study

 

Let the Battle Begin!

Toward the end of the programme, a pivotal moment awaits our participants: the case study presentation. Each event, workshop, and talk is leading to this test of knowledge and chance to showcase innovation, teamwork, and the ability to apply theoretical learning to real-world corrosion challenges.

Having delved deep into the case study, each team will stand before a panel of judges to present their findings and proposed solutions. This culmination of months of hard work, learning and collaboration is a high-stakes affair – the winning team will not only earn the accolade of their peers, but also be rewarded with an all-expenses-paid trip to the AMPP 2025 Conference in Nashville, USA.

YEP 2024 Is an Event for All Corrosion Professionals

While we must strictly limit the number of participants in YEP, this doesn’t mean you can’t follow along! Indeed, we welcome the wider corrosion community to support this invaluable initiative.

Whether you’re a seasoned professional or someone with a budding interest in corrosion management, there’s much to learn and share.

Please, feel free to engage with the Institute of Corrosion and YEP 2024 through our events, as well as our updates on the ICorr blog and social media, and consider how you might contribute to or benefit from ICorr’s initiatives.

Don’t forget, if you’re interested in diving deeper into the topics covered by the YEP or learning more about corrosion management, visit the ICorr website for a wealth of resources, including publications, upcoming events, and membership information.

YEP 2024: A Final Word from Young ICorr

We couldn’t close this article without hearing from the Young ICorr committee. Izabela Gajewska, MICorr, Corrosion & Integrity Engineer at Intertek CAPCIS told us:

It was great to finally meet the successful YEP 2024 candidates from various engineering companies across the UK in person! They all seemed to be as enthusiastic about the programme as we are!

We’re delighted to have such a group of participants in this year’s YEP. I can’t wait to get going in earnest, and witness how the programme decreases the gap in knowledge between junior and senior engineers!

As ever, we would like to extend special thanks to our generous YEP sponsors, AMPP: Association for Materials Protection and PerformanceBP and Wood Thilsted (Anthony Setiadi), and also to the speakers at the launch event: ICorr President Stephen Tate, Dr Jane Lomas, and ICorr Corrosion Engineering Division Chair / YEP Committee Dr Danny Burkle.

Requirements for Referees – Requests for Endorsements and Applications for Professional Membership

Guidelines for Assessors

As a general rule, the Institute of Corrosion does not recommend specific companies, products, or individuals, except for our training operations, in which case all trainers and training providers must meet specific levels of competency (as per individual course requirements) and be certified accordingly. These are also people well known to our governing boards and council members. In terms of ICorr membership applications, it is the role of the Professional Assessment Committee (PAC) assessor to match the details supplied by the applicant—application form, CV, copies of qualifications, training, and referee reports—to the Institute Membership Regulations for the grade in question—identifying and listing the key attributes of the individual and any non-conformances relevant to the person’s application. It is essential that referees know the applicant in a professional capacity prior to endorsing their application and submitting it to HQ. If any Assessor is concerned at all about recommending an applicant for membership, then you are reminded to please list your particular concerns in Section 2 of the PAC Form – Part. 2. I refer this to the PAC Chairman for decision for the following reasons:

Ongoing Safeguards

Please note that in order to achieve a range of assessor feedback and to avoid delays in the processing of applications, the institute’s membership application form and supporting documents will normally be sent by ICorr HQ to several PAC assessors at the same time, i.e., there is always a further review after your own one, and it is very likely that somebody on the PAC assessment group will know the applicant. If that is not the case, our PAC chair (Paul Lambert) will usually call the individual concerned for some clarifications, especially if they are not residents of the UK.

Further, once the application has passed all these stages, it will be included in a final summary list to go to the Quarterly Council Meetings. This is circulated to all council members for comment, and they are free to notify any objections to membership at the grade requested. Overall, the institute processes are very rigorous, are designed to maintain high standards, and usually take 4-6 months altogether, according to the exact timing of the Council meetings.

Welcome to the Wales and South-West Regional Branch of ICorr

Welcome to the Wales and South-West Regional Branch of ICorr

A New Regional Branch to See in the New Year

The turn of the year saw the first of what we hope will be several exciting regional branch announcements this year: we’re thrilled to introduce a significant addition to the Institute of Corrosion (ICorr) family – the Wales and South-West Regional Branch.

This new regional branch is set to host its inaugural event and Annual General Meeting (AGM) on 21st March 2024, marking a significant milestone in our continuous effort to expand our reach and impact across the UK. You’re all welcome to attend – read on for more information.

Reaching Out to a Region of Diverse Industries

The Wales and South-West region is home to a diverse range of business sectors, from aerospace, chemical plants, and construction products to energy production, inspection and analytical services, oil and gas, petrochemicals, renewables, and steel and metal manufacturing/recycling.

This diversity not only underlines the economic vibrancy of the region, but also highlights the need for greater knowledge, experience, and collaboration to overcome the complex corrosion challenges that these industries face.

In recognition of this, the Wales and South-West Regional Branch has been established with a clear mandate to develop and share knowledge regarding corrosion and its prevention, fostering a collaborative environment that brings together industry and academia.

Uniting Industry and Academia

The branch is also ideally positioned to bridge the gap between the region’s diverse industries and leading universities. This synergy is aimed at not only sharing existing knowledge, but also sparking new ideas and innovation for corrosion prevention. By doing so, the branch is set to become a pivotal force in both the practical and creative aspects of corrosion management.

A Focus on Future Engineers

A crucial aspect of the regional branch’s mission is the development of future generations of corrosion and materials engineers.

Through targeted presentations from industry professionals and academics, the branch aims to address local industry needs and challenges within the broad subject of corrosion. Moreover, the branch is committed to promoting learning and sharing experiences among experts within the region, thereby enriching the professional community.

Yearly Programme of Events

The branch has ambitious plans to define a yearly programme of events that includes:

  • Meetings
  • Guest visits
  • Speakers
  • Workshops
  • Roadshows

Not only will these present ideal opportunities for industry professionals to broaden and deepen their professional networks, but we also aim to engage undergraduates, schools, apprenticeship programs and colleges, in our goal to encourage interest in corrosion and its prevention from a wide audience.

Your Invitation to the Inaugural Event and AGM

The first official event and inaugural AGM promises to be a landmark occasion. Scheduled for 21st March from 12 pm to 2 pm with lunch provided, the event will feature presentations on Microbiologically Induced Corrosion – a critical topic given its impact across several sectors represented in the region.

Speakers include Director of Consultancy Services at R-TECH Sarah Bagnall and Dr Gareth Williams, Consultancy Services Manager of ECHA Microbiology, whose insights will be invaluable.

The event will also include a laboratory tour, providing attendees with a unique opportunity to see corrosion science in action.

Register Now to Join Us

Located at R-TECH Materials, Testing House, Kenfig Industrial Estate, Margam, Port Talbot, SA13 2PE, this event is not to be missed.

Registration will close on Monday, 18th March.

If you are interested in attending or becoming part of this forward-looking and vibrant new regional branch, please reach out to us at swchair@icorr.org for further information.

A Note from the ICorr President

ICorr President Stephen Tate is enthusiastic for the future of this new branch, saying, “The establishment of the Wales and South-West Regional Branch of ICorr is a testament to our commitment to advancing the field of corrosion science and engineering.

Through this new branch, we look forward to fostering a community of professionals and academics who are dedicated to tackling corrosion challenges and contributing to the sustainable development of the region’s industries. I’m convinced that its membership will be instrumental in making a lasting impact in the field of corrosion prevention.”