Self Healing Concrete - What will they think of next?

[Chaotic_Warlord]

http://www.physorg.com/news159641694.html

Basically it's concrete that has had the chemical compounds changed so that is only cracks in hairline widths so that on a rainy day it can fix itself... Neat stuff.




There's a flash video in the link site that shows how it's better than standard concrete.

[PapaSmurf2k3]

sweet!!!

[PoorManQ45]

Dirka Dirka!

[alms24sebring]

lol thats messed up. Very interesante tho. I dont think it could heal back to a new straight line of concrete after a bend like that. It looks like just the cracks would mend like in clay. I wonder after time if would deteriorate or sag towards the bottom after so many years of rain and/or temperature fluctuations.

[Poyzinous]

Interesting concept. I wonder how far they can take this???

[Mr1der]

god I wish I was self healing....

[Dattebayo]

SO this means they have to make this new concrete thicker to compensate for it's properties.

[PoorManQ45]

SO this means they have to make this new concrete thicker to compensate for it's properties.

[Dattebayo]

If they would give a time for how long it takes to revert to the original shape, then this would be useful for roads that don't get alot of use.

But using a substance that needs water is dangerous for a road.

[PapaSmurf2k3]

If they would give a time for how long it takes to revert to the original shape, then this would be useful for roads that don't get alot of use.

But using a substance that needs water is dangerous for a road.

Well they are basically talking about a beam deflection when they say the 3% strain test (simply supported on both ends, loaded in the middle). Roads aren't built like this, they are completely supported from the bottom. Also, he says it takes from 1 to 5 wet-dry cycles to fully heal.

The substance doesn't "need" water, it just needs it to repair itself. Seeing as how it rains anyway, why not use it? I'd be interested in seeing how it stands up to freezing while wet. If it absorbs water, then freezes, the water will expand and propagate the crack.

It also doesn't say anything about the material's hardness, or friction characteristics (traction).

[ADDirishboy]

Somehow I can't see this being implemented in AZ...

[PapaSmurf2k3]

SO this means they have to make this new concrete thicker to compensate for it's properties.

I didn't see where it said that either...
I suppose if you were using it to do a repair, then yeah you would have to use more to compensate for steel rebar that would no longer be needed, or you could just back-fill it (depending on the situation).

[Dattebayo]

Yes, I am aware it was about deflection, but I was thinking more about that rut that appears on heavily traveled roads from the asphalt spreading out in heat... It seems to me that any material capable of bending in that manner would be susceptible to that kind of problem as well. If it is capable of slef healing that kind of issue too, then it would be useful as well, but only in less- traveled roads because how long it takes for it to heal.

[Dattebayo]

I didn't see where it said that either...
I suppose if you were using it to do a repair, then yeah you would have to use more to compensate for steel rebar that would no longer be needed, or you could just back-fill it (depending on the situation).

Well, that's just it- they didn't address any of the questions I have about this stuff.

I can only assume that because it bends like it does, that re-bar cannot be used and due to that, the structure would have to be nearly three times thicker to be useful.

[PapaSmurf2k3]

Ah I see what you're saying.
I was always under the impression that the ruts in the road were more from the material underneath it deforming somehow, or the surface actually wearing a bit (getting back to that hardness characteristic I was talking about).

I'm also assuming that under normal operation, the concrete doesn't crack/break, so its ability to heal in higher traffic areas shouldn't be effected. I guess I really don't know enough about road construction and wear to really make any scientific claims though.

[alms24sebring]

I think it might be a better invention for buildings to resist earthquakes as I think I saw it said. I feel it would be too soft for roads, even roads less traveled on. Im sure it would cost alot more too so whats the point in spending the money on hundreds of miles of road that hardly get traveled, all for alittle self healing that it doesnt need. I no the roads around here that are hardly traveled, their perfectly flat.

If its too soft or too flexable for city traffic, there would be bad wheel grooves all the way up the road in who knows how short of a time period. If a building with this technology survived a earthquake, how would they fix the now curved concrete? If something is warped, its impossible to get it back to true flat again. I think we just need to see this self healing crap in a demonstration and what exactly they mean

[PapaSmurf2k3]

Don't think that just because it can bend doesn't mean it isn't strong. Steel can bend like a mofo and its VERY strong.

All you need for a road is a flat, smooth surface that resists wear and has good traction characteristics. This stuff might not be that much more expensive than regular concrete either.

[PapaSmurf2k3]

I can only assume that because it bends like it does, that re-bar cannot be used and due to that, the structure would have to be nearly three times thicker to be useful.

I'm not so sure that rebar can't be used, so much as it isn't needed at that point. Rebar is simply there to help with tensile forces. Concrete is very strong in compression, but pretty weak in tension (such as the outside of an arc), so if the surface under it were to change, it would almost certainly crack without rebar. This is why rebar is only used in the tensile force section of concrete (the bottom).

This stuff seems to have that tensile strength either built right in, or it doesn't require rebar because it can bend a little bit before cracking (or both). And when you eliminate the rebar, you eliminate the chance of rebar corroding and weakening the structure/flaking the concrete off.

[alms24sebring]

Don't think that just because it can bend doesn't mean it isn't strong. Steel can bend like a mofo and its VERY strong.

All you need for a road is a flat, smooth surface that resists wear and has good traction characteristics. This stuff might not be that much more expensive than regular concrete either.

Thats what I call a perfect road, its very difficult to make anything perfect. A smooth surface w great traction but low wear has all the pros with no cons.

I dont know I still think this prototype is too soft for road work, but, Im sure its a good start for modification. Besides we dont even know if 1 ton or 20 tons was applied. Constant traffic and heavy 18 wheelers daily, along with weather (besides rain), sounds lokke too much too me. Its not memory concrete. Again, id like a demo.

[Dattebayo]

It needs a secondary form of support for making bridges, tho. This is what I mean when I say it will have to be three times as thick.

[alms24sebring]

but thats 3 times the weight

[Dattebayo]

Bingo.

[PapaSmurf2k3]

It needs a secondary form of support for making bridges, tho. This is what I mean when I say it will have to be three times as thick.

Well you're still going to have a steel substructure for bridges and such. I'm sure its yield strength and modulus of elasticity is still nowhere near as good as steel's would be.

[Dattebayo]

Using steel would put you back at the same issues, I think. Until they start using nickel or some other rust-proof metal it's just going to soak up water and we're back at square one again.

[PapaSmurf2k3]

Just on bridges is what I'm saying. You wouldn't need rebar per say, but you'll still need big gigantic freaking I-beams.
Actually, depending on the bridge, you COULD make it entirely out of this stuff. Hell, you could make it entirely out of the old stuff too. Not like it hasn't been done before:

[PoorManQ45]

So then... This helps with compression cracks on the vertical plane, but what about tension and/or compression stresses on the horizontal plane?? Also know as expansion and contraction.

[PapaSmurf2k3]

No, it doesn't help with compression at all. Concrete is already strong as hell in compression (which you can use to your advantage and design around that), but weak in tension. Did you read this thread at all?

[PoorManQ45]

No, it doesn't help with compression at all. Concrete is already strong as hell in compression (which you can use to your advantage and design around that), but weak in tension. Did you read this thread at all?

Yes. I've read the whole thing.

I'm am not sure of the issues that this flexible concrete will resolve.

Can you provide an example of when concrete cracks from the force in the direction that is shown in the test?

Most cracks develop from normal expansion and contraction of the slab from going through heating cycles. Or if your underlying support collapses.

I don't see how this stuff will help in either situation.

Note: I'm only thinking about it in road applications right now.

[PapaSmurf2k3]

Or if your underlying support collapses.

I'm under the impression that the underlying support of a road shifts every now and then, or gets compressed as you drive over it, etc. Anyway, regardless of the reason, the bottom edge of a surface goes under tension forces, and the top goes through compression



That is why the concrete has rebar. Its because it is weak in tension, and needs more "oomph" to hold it together and to not strain the concrete. Concrete can not get strained very much at all before it cracks, where as this new concrete can, hence the reason for not needing rebar.

[PapaSmurf2k3]

I'm saying everything in that picture will still be the same, except for "re-enforced concrete deck". With this new stuff, you'll just have "concrete deck".