Many articles have been published on corrosion protection systems for increasing the life expectancy of steel reinforcement bars. The performance of these protective systems is documented but not necessarily in a manner for easy understanding.

As in all documents with a scientific bent, the authors range from experts who are well informed and have carried out the pertinent research to those who have a clear commercial interest in finding fault, and creating an environment of uncertainty. In addition, many authors do not declare the reasons, or own particular interest, in publishing their works.

This article has been written on the basis of trying to help overcome the effect of overtly commercially biased publications and help generate an interest in focusing on the true purpose of corrosion protection systems. Jotun is a supplier of fusion-bonded epoxy for coating reinforcement bars, so it could be argued that there is a commercial bias to this article, but there is also a firm belief that fusion-bonded epoxy coating adds value, and has a definite place in the construction world for corrosion protection of reinforcement bars.

Here are three quotations that readers of scientific reports should note when reading published information.

Rutherford Rogers, librarian at Yale: "We're drowning in information and starving for knowledge".

AndrŽ Gide, novelist: "Believe those who are seeking the truth; doubt those who find it."

Japanese proverb: "If you believe everything you read, better not read."

The problem

There are many examples of concrete structures that have failed due to corrosion of the reinforcement bars. The magnitude of the problem can be seen if one takes the US as an example. Reinforcing steel corrosion has been identified as the primary form of degradation in reinforced concrete structures. In the US alone, there are close to 600,000 bridges, with concrete and steel bridges making up the vast majority.

The average annual cost to maintain highways and bridges in the US over the next 20 years has been projected at $56.6 billion. Reinforcing steel corrosion is a major problem in many parts of the world.

In the US, the overall costs of reinforcing steel corrosion have been estimated at more than $150 billion per year (www.corrosion-club).

Corrosion process

Corrosion is a natural process and is a result of the inherent tendency of metals to revert to their more stable compounds, usually oxides.

Normally, the alkalinity of the concrete provides a passive environment around the bars in which corrosion will not occur. Amongst other factors, the presence of chlorides (in the original mix or entering the concrete) will break down the alkali passive state.

A corrosion cell can now be generated with the additional presence of water and oxygen, corrosion begins and the bar will start to lose its reinforcement properties.

Corrosion creates rust (a mixture of the various iron oxides and hydroxides) which is characterised by a higher volume than the original metallic iron.

This expansion creates internal stresses on the surrounding concrete producing staining, spalling and cracking of the concrete.

Regional factors

There are regional factors that influence the corrosion rate in rebars. In the Middle East, the climate and environment play important roles in corrosion and longevity of structures. The weather is hot and humid with a high chloride level. These, combined with the high water tables (hot subkha), irrigation and saline waters surrounding the Gulf, create the perfect environment for severe corrosion.

A few points to note:

The world's seas have a salinity between 33 and 41 parts per thousand. This level is 40-41 over most of the Red Sea and Arabian Gulf waters, and can exceed 50 in limited areas of the latter. The high salinity is the result of extremely high evaporation, insignificant rainfall and river inflow, and restricted exchange with the open ocean.

Due to temperature and solar radiation, it is expected that the annual rates of corrosion reactions in the Gulf would be 10 to 20 times faster than in parts of the US and Europe.

It has been calculated that actively corroding steel will typically corrode at a rate of up to 1 mm/year in normal environments and therefore in harsh climates, conducive to corrosion, this rate is increased.

Thus, it is would be logical that structures in the Greater Gulf region should be designed from the start to combat corrosion and prolong their life.

Corrosion protection

So how do we protect against corrosion? There are several techniques that can be employed to reduce corrosion and/or the rate of corrosion. Some are more expensive than others and some require greater technical skill during planning, design, application and construction.

Corrosion control can be seen in two basic ways:

1) Active protection, such as cathodic protection which actively controls the environment to reduce corrosion.

2) Passive protection which involves creating a barrier to one or more of the chemical requirements for corrosion.

This article will not review the benefits or drawbacks of systems, other than fusion bonded epoxy, as they are easily found in reviews and the author might be accused of prejudice. However, it is true to say that for optimum performance a corrosion protection system will depend on several components in combination with each other.

A brief summary of some corrosion protection methods is given in Table 1.

Looking back in time, we are made aware of the problems surrounding fusion-bonded expoy-coated rebar (FBECR). There are examples when the performance has been very poor and there is no denying that this has happened. On the other hand, there are thousands of structures that are still in very good condition with little or no corrosion on the reinforcement bars.

At the same time, we look at structures with no FBECR but other corrosion protection systems and can observe many instances of spalled, damaged and cracked concrete couple with corroded reinforcement bars.

This is because of one key factor in that nature always sides with the hidden flaw. This means that unless we have a perfect defect-free system - which is impossible, then sooner or later nature will find a way that allows corrosion to occur.

The balance of cost and avoiding the flaw is the essence of selecting the appropriate anti-corrosion system.

For better, clearer and more informed understanding of the suitability of the various corrosion protection systems two areas need careful evaluation: the real performance of corrosion protection systems and the cost of building in corrosion protection systems.

Performance data can be obtained from supplier's literature, market-sponsored reviews and articles found on the Internet. The greatest difficulty is the analysis of results, as many publications derive their findings from structures that have suffered stress. These highlight the problems of corrosion protection systems rather than address the greater number of buildings that do not show stress or corrosion problems.

Today, we are all fighting costs and have mandates to reduce costs to remain competitive. A quotation including substantial corrosion protection components will be higher than one that does not carry that corrosion protection safety net. There is a tendency to look at the initial cost of a project and gloss over the costs of maintenance, repair and other costs that appear after the structures have been commissioned. The end result is a structure that has minimal corrosion protection will start to manifest problems a few years after commissioning. The various people initially involved in choosing the construction package are quite likely to have moved on, and therefore liability becomes an issue.

Designing adequate corrosion protection at the beginning of project is the logical step to take to avoid these problems.

Performance

What about FBECR? Taking note of the warnings about the variety of information and articles available, one can find many commentaries written in favour of one or another corrosion protection system.

To cite just one example, there is a web page on the Internet of the National Institute of Standards and Technology (NIST) of the US, in which the role and use of epoxy-coated rebar of the US is highlighted.

The page features testimony that Richard Wright, the then-director director of the Building and Fire Research Laboratory at the NIST gave to the House of Representatives in 1994. His testimony, to a House committee on science, space and technology and a sub-committee on technology, environment and aviation, was part of a hearing titled "Creating Tomorrow's Surface Transportation Systems." Here is an excerpt from his report:

"Corrosion-resistant Epoxy Rebar Development

The premature deterioration of concrete bridge decks in northern states where deicing salts were used became a major problem during the 1960s and early 1970s. Although these bridge decks were designed for lives of 50 years or more, they needed to be replaced some 5 to 10 years after construction. The premature deterioration was caused by deicing salts inducing the rapid corrosion of steel reinforcing bars.

Industry developed epoxy coated reinforcing bars in response to performance criteria and test methods produced by NIST under FHWA's (Federal Highways Authority) sponsorship.

Epoxy-coated reinforcing bars were introduced into the field in 1973 and now are used extensively to prevent corrosion in reinforced concrete - services lives now exceed 20 years.

In addition to concrete bridge decks, the use of epoxy-coated rebars has been extended to parking garages, water treatment plants, and many other types of structures. This project is an outstanding example of sponsored research by FHWA which significantly benefited the nation."

I believe that the only system that will prevent corrosion of the reinforcing bar is the use of a non-corrosive material for the manufacture of the bar. Other than that, all the systems - however well they perform under laboratory-controlled environments - will have a flaw in some part of the construction chain between manufacture of the material to setting of the concrete.

The actual performance of corrosion protection systems lies somewhere between the perfect solution reported in data sheets and the disasters reviewed in articles. Even the disasters reviewed do not compare the effect of coating to having no coating at all that would be much worse. The reasons for this lie in the differences between controlled laboratory conditions and 'real life' utilisation, and the mass of information that has been published with its interpretation by unqualified or biased peoples.

A certain quantity of myths surround these anti-corrosion products, often fuelled by claims during hard sales. There is an obligation to counter these myths and return the real performance properties to a level understood by all.

To this end, an association has been set up in the Gulf to review the current perspective of epoxy-coated reinforcement bars and to confirm the performance of FBECR. Performance is being measured using simple, well-documented corrosion test methods, common in the coatings industry. Once performance data are obtained the aim is to integrate the tests into local industry standards to improve the final quality of the product.

Since FBECR was introduced in the 1970s there have been many improvements to the manufacture and application of the product - from the quality of the steel, the epoxy coating to the application, testing and inspection of the final product.

One driver of this improvement is the development of the ASTM (American Society For Testing and Materials) A775M specification for epoxy-coated reinforcing steel bars. This specification covers all the expected areas for the production of quality coated bar, but also makes reference to job site practices.

If powder manufacturers and coaters follow the guidelines found in the ASTM A775M specification, then there is no excuse for poor quality coated bar appearing at the job site. Once there, the handling needs to be done with care as damage will reduce the effectiveness of the protection system. This however, is no different to any system used in daily life - misuse of any item will lead to poorer performance be it a car, a plane, a toy or paint.

The final solution

Ultimately, there will be a breakdown in the system due to a variety of reasons, but a good protection system will extend the longevity of the structure over one with a poor or no protection system.

There is a cost penalty when employing any corrosion protection system. However, due to the added life expectancy of the structure, the payback times are very short.

A report based on life cycle cost analysis from the Concrete Reinforcing Steel Institute (CRSI) quotes:

"The payback period required to offset the modest premium for specifying epoxy coating is often as little as a one to two year life extension."

Additional performance data were obtained from a 10-year marine exposure test by Florida Department comparing FBECR with uncoated bar in a concrete piles. The piles were 'autopsied' and the epoxy-coated bars were found to be in excellent condition. The black bars showed corrosion distress in less than four years.

Most systems will perform well if handled correctly and the increase in cost to the overall project should not be an argument against employing these technologies, as in a quality-conscious society the benefits outweigh the cost.