Corrosion of Reinforcement in Concrete

Corrosion of reinforcement can be triggered by several factors. Do any of you know what might cause this?

I think chemicals that come in contact with the concrete, like salt from the sea?

Exactly! Ingress of chlorides from seawater and de-icing salts is a significant contributor. Can anyone think of another cause?

What about carbon dioxide? Doesn't it interact with concrete too?

Great point! Carbonation affects the pH of the concrete, which compromises the protection around the steel reinforcement. Together with moisture and oxygen, these factors create a conducive environment for corrosion.

So, if we limit moisture, we can limit corrosion?

Exactly! Remember this acronym: C-MO, standing for Chlorides, Moisture, and Oxygen, as the key culprits of corrosion. Let's move on to how these elements interact in the corrosion process.

Can you explain how that process works?

Of course! The interaction forms electrochemical cells, leading to rust formation, which expands and causes cracks in the concrete.

Let’s delve deeper into how the corrosion process occurs. By forming electrochemical cells, ions migrate between anodic and cathodic areas. Can anyone explain what happens at these sites?

I believe at the anodic site, the steel loses electrons? This is where the rust forms?

Yes! Well done! Anodic reactions occur where the steel corrode, while cathodic areas involve reduction reactions. The formation of rust expands significantly, leading to cracking and spalling.

But why is it a problem if the rust is bigger than the steel?

When the rust occupies more volume, it creates internal pressure, thus leading to cracking in concrete, which can cause failure of the structure.

What type of corrosion is most dangerous then?

Pitting corrosion can be more insidious because it targets localized areas, leading to serious damage while appearing minor externally. We’ll see how to protect against all these types next!

What strategies do you think could be implemented to protect reinforcement from corrosion?

Using special coatings, like epoxy?

Exactly! Epoxy or galvanized coatings create a barrier against elements. Any other ideas?

Corrosion inhibitors would help too, right?

Correct! Adding these to the concrete mix can help protect the reinforcing steel. How about the structural aspects?

I know low permeability is important!

Yes! Low permeability minimizes harmful substance ingress, protecting the steel. Remember to ensure adequate concrete cover as well!

What about cathodic protection? How does that work?

Good question! Cathodic protection involves applying a voltage to counteract the electrochemical reactions causing corrosion. This helps to delay or minimize it. To recap, remember the prevention strategies: coatings, inhibitors, low permeability, and proper cover!