Self Healing Concrete - What will they think of next?

[Chaotic_Warlord]

I think you guys are over thinking this. The demonstration in the video is showing that it can withstand 4x the amount of pressure per square inch than standard concrete and still won't break. Yeah it bends, but I think that is the point, this is how it keeps from developing large cracks or breaking. If you think about it a road surface isn't one layer and while they sustain massive amounts of force on them through there use they aren't having tons of pressure on any one section for extended periods of time. Think about a loft section in a roof, it may say not to exceed 250 lbs per square inch but a full sized man can walk on it because while he may weigh more than 250lbs, he's not putting all of that weight on any one square inch/foot of the floor. The same premise works here, while you may have a truck that weigh x amount of lbs or tons, they aren't putting all that weigh on any square ft of road surface, not to mention the DOT has set guidelines as to how much a a vehicle can weigh (GVWR) so I'm sure this has been taken into account. I don't think it would bend as easily as you guys think it would.

I see this getting a lot of use with runway construction (which is 5x thicker than standard road surfaces) or with bridge construction where the bridge has a bit of give anyway to prevent from destroying itself.

[Loki]

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.

You never want concrete under tension though.

[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.

You never want concrete under tension though.

That is correct. Unfortunately constant heating, cooling, and freezing create a constant changing pressure in the slab.

[Dattebayo]

What about for structural purposes? Imagine a parking garage made out of this stuff...

[PapaSmurf2k3]

That is correct. Unfortunately constant heating, cooling, and freezing create a constant changing pressure in the slab.

That's why concrete has expansion joints in it.

What about for structural purposes? Imagine a parking garage made out of this stuff...

What about it?

[PoorManQ45]

That is correct. Unfortunately constant heating, cooling, and freezing create a constant changing pressure in the slab.

That's why concrete has expansion joints in it.

Yep, still not enough though.

[scotttak]

What about for structural purposes? Imagine a parking garage made out of this stuff...

imagine replacing the slabs that martial artists use for breaking with this stuff. instant lulz.

[sx moneypit]

What about for structural purposes? Imagine a parking garage made out of this stuff...

imagine replacing the slabs that martial artists use for breaking with this stuff. instant lulz.

[Dano]

Pretty neat!

[AppleBonker]

Dave, I think you're looking at this all wrong. Yes, this material will bend more than what you currently know as concrete. However, it still requires roughly the same amount that would crack and catastrophically damage standard concrete. So unless the stresses on the structure are triple what they currently see, you wont notice any flexing. That image is near the failure point, and current concrete would be split in half on the ground already.

As far as the water freezing and aiding in crack propagation, I don't see that happening either. Currently, water doesn't expand with that much force in concrete, and it takes many thermal cycles for it to become a problem. In this case, the water may freeze and develop a crack, but once the ice thaws the cement will heal itself. Then again, it's been a little while since I actually studied this stuff. I probably have my old notes and textbooks at home somewhere though, and I'm sure this concept was discussed in at least one of my classes.

[Chaotic_Warlord]

Dave, I think you're looking at this all wrong. Yes, this material will bend more than what you currently know as concrete. However, it still requires roughly the same amount that would crack and catastrophically damage standard concrete. So unless the stresses on the structure are triple what they currently see, you wont notice any flexing. That image is near the failure point, and current concrete would be split in half on the ground already.

As far as the water freezing and aiding in crack propagation, I don't see that happening either. Currently, water doesn't expand with that much force in concrete, and it takes many thermal cycles for it to become a problem. In this case, the water may freeze and develop a crack, but once the ice thaws the cement will heal itself. Then again, it's been a little while since I actually studied this stuff. I probably have my old notes and textbooks at home somewhere though, and I'm sure this concept was discussed in at least one of my classes.

That's pretty much what I said in my second post.

[PapaSmurf2k3]

As far as the water freezing and aiding in crack propagation, I don't see that happening either. Currently, water doesn't expand with that much force in concrete, and it takes many thermal cycles for it to become a problem. In this case, the water may freeze and develop a crack, but once the ice thaws the cement will heal itself. Then again, it's been a little while since I actually studied this stuff. I probably have my old notes and textbooks at home somewhere though, and I'm sure this concept was discussed in at least one of my classes.

Water expands with monumental forces when it freezes. It shapes our ridges/mountain faces. Hell, it busted the old man on the mountain clean off his rocker.

This is what I'm saying- (Example): The concrete gets damaged in the winter and develops an 80 micron crack. It then rains out during the day, at 36 degrees (typical new england s***). Nighttime comes and the temp drops to 22. The water freezes, expands, cars drive over it and create pressure spikes, and all that pushes that crack open to 170 microns... which is past the "zero barrier" threshold for which the concrete can heal itself. Will it be better than normal concrete? Hell yeah, but I don't see it being the perfect surface.

[AppleBonker]

Does the water freezing generate enough stress to create cracks of that size (I have no idea any of the strength characteristics of this material)? I don't know. I'm sure it is being tested for, however. And it certainly sounds like an interesting project.

And, at what temperature does the healing occur? Will it heal just above freezing? If so, the concrete may adequately heal between thermal cycles so that 80 micron crack seals itself before it can be enlarged to 170 microns. Definitely possible, but again without being actually involved in the research, none of us would know. Still interesting to think about in either case.

[PapaSmurf2k3]

but again without being actually involved in the research, none of us would know.

Yup. We should be able to give a good guess though. As to whether it can freeze past the "zero barrier mark", from 80 microns, I'm not really sure, but if it were borderline to begin with (160 microns), then it definitely could. And yes, water freezes with enough force to propagate cracks for sure. Ever see frost heaves on roads? That's nothing but water.

From what I gathered from the article, the concrete needs liquid water to "pull" calcium deposits out of it, which is soluble in water... and then when the water dries, the calcium deposit remains... so really it should be anywhere above the freezing point of water (or maybe a little below, because calcium/water mixtures freeze at lower temperatures), and below the boiling point.

[AppleBonker]

And yes, water freezes with enough force to propagate cracks for sure. Ever see frost heaves on roads? That's nothing but water.

Absolutely. But this is after numerous thermal cycles slowly growing the crack and allowing a larger volume of water to enter the void. If the concrete were to heal the small cracks fast enough, they wouldn't be able to grow to the critical point of failure. That is where my question lies. Sorry if I didn't really make that clear.

[PapaSmurf2k3]

Ah I see what you're saying... I guess I just assume water is going to get under it one way or another