Okay, so you saw in the video where we talked about how smart materials can be used to improve concrete structures. So one of the things that they talked about was the idea of reinforcing concrete with Nitinol. And I wanted to mention something a little bit more about Nitinol.

Nitinol is a shape memory alloy. This is an example of a Nitinol sample. It's a nickel titanium alloy. And it has a very unusual property. Normally, when you take a material and you plastically deform it, so I bend the material, and I bend it and straighten it out.

Then what happens is I've actually passed dislocations through that material, or little ripples that mean that that material is now plastically or permanently deformed, in this case. Now in Nitinol, what's weird about it is it doesn't deform that way. It deforms because you're actually passing what we call twins.

In other words, it's like you're taking the whole lattice and just Zig zagging it, and in doing so, it actually remembers its original structure. So, if I take this material, and it's a nice little spring, and I take it and I stretch it out and I make it into something that doesn't look like it's a spring anymore.

Well, what I can do now is I actually take this and just gently warm it up, what happens is it's gonna form right back into the spring because it remembers the shape it was in to begin with. And that's the beautiful thing about a shape memory on an alloy.

Now how would you use that in a concrete? Normally you wouldn't think of that as a material you'd use in a concrete. However, if you actually embed Nitinol into concrete, then when it breaks, if the concrete is under some stress and it actually fractures, you can actually then apply heat to that thing by resistively heating up the Nitinol.

And it'll actually contract and pull the beam back into shape. And so it can actually ask as a reinforcement to give you enough time to actually let you get out. And so people call this a self-healing or repairing concrete. Now, there are other things that you can add to concrete.

For example, we talked in the lecture about sensors. And sensors can be added into the concrete, and the idea of a sensor is a material that you would embed, like a fiber optic sensor in the material. Such that it would detect, whether or not, for example, the rebar is corroding.

And so in this case they actually used the thermal conductivity of the rebar as a way to measure whether or not the rebar is actually undergoing some sort of internal failure through corrosion. And so inventing these sensors is tremendously advantageous. The other thing that they will put into these materials is piezoelectrics.

So for example, if I take a piezoelectric material, that's a material that when you apply, for example, a mechanical force it will generate electricity. Or you flip it around in this case, and if you apply electricity to it, it will apply a mechanical force or change shape. And so, for example, one of the things they will do is they will put in screws with bolts on them that have Piezoelectric materials built into them.

And then if that nut starts to come off or loosen, they can actually trigger the piezoelectric materials to actually expand and take up the slack so the nut is now tightened again without you physically going in there and tightening the nut. So that's one advantage of a material that you might embed in it.

Another thing you can do with materials is use them as sensors. So you might pass a vibration through the concrete and then detect it on the other end to determine whether or not there's a failure inside the concrete. So other things that they're doing with concrete are primarily changing the additives.

So for example, you may add something that will make the concrete either Eco/Green concrete. So that's a material that would have, for example, the ability to uptake CO2 over an extended period of time and actually try to reduce the CO2 footprint of the concrete. So it's formulated such that it involves for perhaps, less CO2 production in its manufacture and it actually takes up more CO2 while it's in existence, and so they call it Eco or Green concrete.

They also use I mentioned earlier which is another additive, all right. In this case again you're trying to use the fact that you've got a whole bunch of aluminum silicates leftover after you've burned your coal and you're adding it to the concrete. So there's lots of things going on in concrete and I think the challenge going forward is gonna be to figure out how you can make concrete not only greener, but also stronger so that you can increase the number of possible applications you'd be using it in the future.