23 May 2009

We could all use some protection

Occasionally in the office we have external suppliers come in and give lunch and learn presentations so that we'd hopefully specify their products in our designs. I love these lunch and learns; the content and quality of the presentations vary wildly but I'm a sucker for free food, so I always go.

On Monday, we're having a presentation on Cathodic Protection of Concrete Structures:

For those who don't know, the big problem with concrete, especially near road surfaces in places where snow and ice is a problem, is the corrosion of the steel reinforcing bars (rebars) inside. Concrete is permiable, so dissolved chlorides come in and cause the steel to corrode. Concrete is also really strong in compression but really weak in tension. There are two main problems with this: 1) that rebar is there to give the concrete strength in tension, and if you remove some steel, then your concrete structure isn't as strong anymore, and 2) rust takes up more space than the original steel, so this results in tensile stresses within the concrete as the rust tries to expand, which will cause the outer cover of concrete to spall off. Very bad stuff.

Now there are a few ways to combat this. The main thing we do now that we didn't do in decades past is use much more concrete cover (thickness of concrete between the exposed surface and the rebar). This will greatly delay the ingress of chlorides. Other options are coating the rebar with epoxy so that the chlorides can't get to it or using stainless steel.
Cathodic protection is another method. In an electrochemical cell, the anode corrodes and the cathode doesn't. So if you connect a block of metal to your steel that has a higher electrochemical potential than steel, this will act as a sacrificial anode, itself rusting while pushing more electrons into the steel and preventing it from rusting. You can also used impressed current cathodic protection, which uses a power source.

However, the email notice for the lunch and learn said Catholic Protection.

With recent news out of Ireland, I guess it would be a good idea to have protection from Catholics.

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At May 25, 2009 8:37 p.m., Blogger Theo Bromine said...

Spellcheck FAIL would be my guess.


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