Stress Corrosion Cracking (SCC) of a Reinforcement Bar

Mechanisms of SCC are complex and research is ongoing.

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Though oxygen typically plays a critical role in many SCC environments, there are studies documenting SCC in environments with essentially no O₂.

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How certain are you restriction of O2 to the embedded bars is effective enough to assume that oxygen will not be present in sufficient amounts necessary for SCC?

Carbonization of the concrete is a more likely cause of corrosion of the rebar.

History would say no!, there must be many millions of bent bars use over a very long time. They are usually in places where they do see a load.

Thank you so much for delineation, Sir.

How could carbonation be a concern (does it incite SCC, consequentially) ?

The conversion of calcium hydroxide (by reaction with carbon dioxide) to calcium carbonate reduces pH.

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Typically pH values experienced by rebar encased in concrete are above 12. In that alkaline condition steel is passivated, i.e. it forms stable protective layer that minimizes corrosion. When pH falls below 9, that protection is no longer in place.

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A whole myriad of problems can begin at that point. Swelling and cracking of the cement due to corrosion products is one big concern, because the cracks make the re-bar more open to atmosphere and accelerate degradation.

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In typical scenarios, not involving something like stainless re-bar, high temperature, and high tension; general and pitting corrosions will be the concern instead of SCC.

Thank you so much indeed for the delineation, Sir.

The concrete structure (near the beach) is partially submerged under water.

It's likely susceptible to salinity ingress.

Is ICCP (Impressed Current Cathodic Protection) a viable retro-fit (to safeguard the
re-bars) for this concrete structure ?

What should have been a feasible design at the first instant ?

Regards.

There is no way for me to give you a reasonable helpful answer to either of your last two questions.

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There is simply not enough information to suggest good options from this point or what the best design would have been. Unfortunately it isn't just a matter of answering a few questions either.

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I can say that your options going forward will be highly dependent on how advanced the corrosion is and the specifics of the structure.

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Also, when judging old structures, keep in mind that many of the advantages we have today may not have have been available to those designing/building the structure.

In my humble opinion, impressed current cathodic protection can't hurt (unless you over load it and have hydrogen embrittlement). No coating is perfect and all concrete will have some cracks that could allow water in. If your steel is in a location that you can use cathodic protection you should use it if you want it to last a long time.

Studies have shown that protected steel structures underground (not positive about water) have an undetermined lifespan because all the pipes that have been tested and dug up after being protected have had little or no degradation.

Drew K

The potential for harm from a decision to deal with the problem by retrofitting impressed current cathodic protection, stems from the possibility that sufficient investigation may not be conducted to determine the extent of damage.

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Worst case scenario, the powers that be opt to buy a solution involving impressed current cathodic protection and decide not to spend what is necessary to evaluate the extent severity of the corrosion....but in reality, there is nothing much to protect, just pies of rust...