A "self-healing" asphalt

Paved roads are nice to look at, but they’re easily damaged and costly to repair. Erik Schlangen demos a new type of porous asphalt made of simple materials with an astonishing feature: When cracked, it can be “healed” by induction heating. (Filmed at TEDxDelft.)

(Hammer)

(Laughter)

(Microwave beeps) (Laughter)

You probably all agree with me

that this is a very nice road.

It's made of asphalt,

and asphalt is a very nice material to drive on,

but not always, especially not on these days as today,

when it's raining a lot.

Then you can have a lot of splash water in the asphalt.

And especially if you then ride with your bicycle,

and pass these cars, then that's not very nice.

Also, asphalt can create a lot of noise.

It's a noisy material,

and if we produce roads like in the Netherlands,

very close to cities, then we would like a silent road.

The solution for that is to make roads

out of porous asphalt.

Porous asphalt, a material that we use now

in most of the highways in the Netherlands,

it has pores and water can just rain through it,

so all the rainwater will flow away to the sides,

and you have a road that's easy to drive on,

so no splash water anymore.

Also the noise will disappear in these pores.

Because it's very hollow, all the noise will disappear,

so it's a very silent road.

It also has disadvantages, of course,

and the disadvantage of this road is that raveling can occur.

What is raveling? You see that in this road

that the stones at the surface come off.

First you get one stone, then several more,

and more and more and more and more,

and then they -- well, I will not do that. (Laughter)

But they can damage your windshield,

so you're not happy with that.

And finally, this raveling can also lead to more and more damage.

Sometimes you can create potholes with that.

Ha. He's ready.

Potholes, of course, that can become a problem,

but we have a solution.

Here you see actually how the damage appears in this material.

It's a porous asphalt, like I said, so you have only

a small amount of binder between the stones.

Due to weathering, due to U.V. light, due to oxidation,

this binder, this bitumen,

the glue between the aggregates is going to shrink,

and if it shrinks, it gets micro-cracks,

and it delaminates from the aggregates.

Then if you drive over the road, you take out the aggregates --

what we just saw here.

To solve this problem, we thought of self-healing materials.

If we can make this material self-healing,

then probably we have a solution.

So what we can do is use steel wool just to clean pans,

and the steel wool we can cut in very small pieces,

and these very small pieces we can mix to the bitumen.

So then you have asphalt

with very small pieces of steel wool in it.

Then you need a machine, like you see here,

that you can use for cooking -- an induction machine.

Induction can heat, especially steel; it's very good at that.

Then what you do is you heat up the steel,

you melt the bitumen,

and the bitumen will flow into these micro-cracks,

and the stones are again fixed to the surface.

Today I use a microwave because I cannot take

the big induction machine here onstage.

So a microwave is a similar system.

So I put the specimen in, which I'm now going to take out

to see what happened.

So this is the specimen coming out now.

So I said we have such an industrial machine in the lab

to heat up the specimens.

We tested a lot of specimens there,

and then the government, they actually saw our results,

and they thought, "Well, that's very interesting. We have to try that."

So they donated to us a piece of highway,

400 meters of the A58, where we had to make

a test track to test this material.

So that's what we did here. You see where we were making the test road,

and then of course this road will last several years

without any damage. That's what we know from practice.

So we took a lot of samples from this road

and we tested them in the lab.

So we did aging on the samples,

did a lot of loading on it, healed them with our induction machine,

and healed them and tested them again.

Several times we can repeat that.

So actually, the conclusion from this research is that

if we go on the road every four years

with our healing machine -- this is the big version

we have made to go on the real road --

if we go on the road every four years

we can double the surface life of this road,

which of course saves a lot of money.

Well, to conclude, I can say

that we made a material

using steel fibers, the addition of steel fibers,

using induction energy to really

increase the surface life of the road,

double the surface life you can even do,

so it will really save a lot of money with very simple tricks.

And now you're of course curious if it also worked.

So we still have the specimen here. It's quite warm.

Actually, it still has to cool down first

before I can show you that the healing works.

But I will do a trial.

Let's see. Yeah, it worked.

Thank you.

(Applause)