Concrete and rebar were made for each other, like cheese and onion, prawns and Marie Rose sauce, or Sturton and port*.

However, rebar is not especially flexible, meaning that complex shapes have to be reinforced with either lots of smaller pieces of rebar, or rebar that has been expensively and time-consumingly bent to shape. Wire rope, however, is jolly flexible - flexible enough to bend into complex shapes - but obviously lacks the rigidity of rebar.

So. Reinforce your complex concrete shape with wire rope and then, once the concrete has set, run a few thousand amps through the wire rope. The wire will melt, and then solidify into rigid, perfectly bent rebar.

[*You may be sceptical. However, Sturton enters a sort of transcendental state when plied with port of sufficient quality and quantity. Those who have witnessed this have described the transformation as awe-inspiring. He is widely believed to be the only human capable of connecting directly, at a synaptic level, with port. Major port producers have been known to pay him simply to drink their product; many reputations have been made - and lost - in this way.]
-- MaxwellBuchanan, Aug 09 2019

glass fiber https://basalt-rebar.com/
[Voice, Aug 11 2019]

The construction of the last paragraph alone is bunworthy. Wire we not all allowed up to two buns?
-- Voice, Aug 10 2019


We saw what you did there, [Voice].

The object is obviously to have a reinforcement material which is flexible on installation, but subsequently becomes rigid and strong in tension (as concrete is strong in compression).

Thin-walled flexible tubes that can be filled later would work; the problem is choosing a material. Molten steel could be pumped through under pressure, but that would cause the concrete to spall - whatever it is has to have a melting point below 100C.
-- 8th of 7, Aug 10 2019


I think the opposite would be more useful..... ie rotten new buildings that are easier to demolish by melting their internal reinforcing rods.
-- xenzag, Aug 10 2019


//melting point below 100C// Seriously? If a rebar in [set] concrete were at 150°C it would cause problems?
-- MaxwellBuchanan, Aug 10 2019


At 150C the residual moisture in the concrete will flash to steam and disrupt the crystallization.

What about tubes filled with glass fibre, with resin pumped through under pressure after assembly ? That would confer considerable tensile strength, and the concrete would give fire resistance.
-- 8th of 7, Aug 10 2019


Why didn't ancient Roman concrete need rebar?
-- 2 fries shy of a happy meal, Aug 10 2019


Largely because it was never stressed in tension.
-- MaxwellBuchanan, Aug 10 2019


Nature has to use small units to make the strength. I wonder if there is a , short 'fibre', relative to rebar length, that can be mixed in with the pour. A bit like fiberglass. Strands of cross-linking recycled plastic?
-- wjt, Aug 11 2019


I'm wondering if, by fluidizing a dry mixture containing denser ferrous particulates, sound could be used to create cymatic shapes within the forms themselves before water is applied.
Running a large current through the ferrous particle web while dry would fuse them together to make a contiguous metal grid-work before introducing moisture.
-- 2 fries shy of a happy meal, Aug 11 2019


But introducing moisture will bring about a change in volume, disrupting the structure you've created ... and how do you guarantee complete homogeneity in such a matrix ?
-- 8th of 7, Aug 11 2019


By turning off the sound and air-flow once the pattern is set before adding moisture.
-- 2 fries shy of a happy meal, Aug 11 2019


Timing is out. [2fries], I imagine your implementation to be wet, that is after pour but before finishing. The sound and current building structures through the setting concrete.
-- wjt, Aug 11 2019


// I imagine your implementation to be wet, that is after pour but before finishing. The sound and current building structures through the setting concrete.//

I'm not explaining it properly.

Only when the mixture is 'dry' can air-flow from beneath be used to fluidize it.
Sound waves of certain frequencies will produce a standing wave node mesh of the densest materials in the mix while it is fluidized based on the shape of the forms, placement of acoustic emitters, and frequency/ amplitude/ amplification of sound waves.
If those densest particulates are ferrous in nature then, when both the air-flow and the sound waves cease, that cymatic shape will be trapped within a now 'un-fluidized' powder again.
Running a strong electric current through this ferrous cymatic shape will cause the ferrous material to fuse together and assume a contiguous metal framework within the forms.
Water could then be injected from the center of the forms outwards, or forced in by pressure to crystallize the concrete.

As [8th] said above;
//At 150C the residual moisture in the concrete will flash to steam and disrupt the crystallization.//
so any attempt to fuse the ferrous material within the concrete while wet would weaken the structure around your inner framework.
Manipulating the mixture while dry is the only way to go.
-- 2 fries shy of a happy meal, Aug 11 2019


Could you fluidise powder without air? Just by using the right (amplitude & frequency) vibrations...
Either way, it will need to be UNDER the concrete, so mostly for pre-cast structures.
-- neutrinos_shadow, Aug 11 2019


Couldn't you just form your complex shape out of metal and then shotcrete over it?
-- pertinax, Aug 11 2019


//Could you fluidise powder without air? Just by using the right (amplitude & frequency) vibrations//

I wondered if that's what the ancient Romans did. Nowadays we use vibrating rods to allow trapped air to escape the concrete. Continuous vibration would have the same effect of non-solidifying as would spinning in a concrete-truck yet would allow layers to be added to existing hand-poured patches while still wet and releasing trapped air.

I don't think vibration alone will fluidize a dry mixture. It would just cause it to settle more compactly.

//Couldn't you just form your complex shape out of metal and then shotcrete over it?//

This is done now. the concrete ends up light and fluffy. You have to jiggle concrete to let the air out."
-- 2 fries shy of a happy meal, Aug 11 2019


// Running a strong electric current through this ferrous cymatic shape will cause the ferrous material to fuse together and assume a contiguous metal framework within the forms. //

I wonder if microwave irradiation would work to heat it.

With resistive heating, as the metal particles fuse together, their resistance will decrease. Therefore, if you try to do it in sections (because your power source can't supply enough current to melt the whole thing at once), you'll melt one section successfully, but then, when you try to do an adjacent section, the current will mostly flow through the already-fused section and not fuse the new section.

But microwaves could potentially be aimed at the unfused section, while the fused section was grounded (not necessarily even deliberately, but just by being part of a building constructed on the ground) and therefore would reflect the energy that hits it back into the unfused section. (Though it might be the case that the unfused section is too well-grounded too, due to granular contact, but I doubt it. That granular contact would actually seem to be where the heat is produced, due to the microwave-induced current.) A stirrer, or moving the microwave source around a bit, would ensure that the whole volume got heated, rather than just the antinodes of a particular standing wave pattern.

The only issue that occurs to me now is that the ferrous material closer to the microwave emitter will be heated the most and will therefore fuse first, blocking heating of the ferrous material beyond.

A solution to that could be to have multiple microwave emitters, each not strong enough to fuse the ferrous material, and use beamforming to heat the far ferrous material, with the constructive interference, before heating the near ferrous material. However, beamforming relies on coherent radiation, and, AFAIK, all magnetrons radiate incoherently, while the available coherent microwave sources are too powerless for significant heating. Time to invent a coherent magnetron, maybe.
-- notexactly, Aug 12 2019


[notexactly], the maser predates the laser, so that part is ready.
-- neutrinos_shadow, Aug 12 2019


//With resistive heating, as the metal particles fuse together, their resistance will decrease. Therefore, if you try to do it in sections (because your power source can't supply enough current to melt the whole thing at once), you'll melt one section successfully, but then, when you try to do an adjacent section, the current will mostly flow through the already-fused section and not fuse the new section.//

Could totally be wrong about this... it's just the way I see it in my head but,

if the particulates are all separate to begin with then the current will need to be large enough to fuse its own pathway through or there would be no circuit to allow for an electrical discharge in the first place.

If the initial current is strong enough then a circuit will be achieved and a contiguous pattern will emerge and fuse within the dry powder.

The amount of material fused will depend on the amount of ferrous material accumulated in any given position within the mesh and the points from which the current was released.
-- 2 fries shy of a happy meal, Aug 12 2019


Sorry I don't see it. Adding water and then making a good 'mix' disrupts all the good work done in making the acoustic/electric lattice in the dry mix. Allowing water to soak through a dry mixture works but I wouldn't want to put real forces on it.
-- wjt, Aug 12 2019


Why not? A bag of concrete left out in the rain turns just as hard as if it were mixed in a bucket.
-- 2 fries shy of a happy meal, Aug 12 2019


It may seem so, but it isn't. It's not homogenous, and that causes structural weakness. The core has a different structure and density to the outside.

The outer portions set first, and harden first, while the core is still dry and powdery. Then over time, when then outer portion is fully reacted, water diffuses through into the inner part which sets much more slowly as it is initially water-deficient. Water doesn't just catalyse the setting process; it is a critical component of the final structure and becomes permanently bonded into the matrix.

Because it sets very slowly, the core is typically much harder than the outside - and because it not only swells but gets hot as it sets, that can cause the outside to crack. The cracks may not be obvious to the naked eye, but they're there - and are one of the routes though which water reaches the core to complete the setting process.

Good quality concrete is dependant on exact proportions of ingredients (including water), very thorough mixing, and subsequent expulsion of as much air as possible.

// the concrete ends up light and fluffy. //

How interesting; a contrast to the results achieved by some cooks, whos meringues have the consistency of a paving slab.
-- 8th of 7, Aug 12 2019


So we need the water in the "dry" mix, but not reacting/combining...
How about doing the dry mixing below freezing? Have small crystals of ice through-out the mix too, while keeping everything cold & dry. When the distribution is right, apply heat (with the aforementioned microwave/maser).
-- neutrinos_shadow, Aug 12 2019


//The outer portions set first, and harden first, while the core is still dry and powdery. Then over time, when then outer portion is fully reacted, water diffuses through into the inner part which sets much more slowly as it is initially water-deficient. Water doesn't just catalyse the setting process; it is a critical component of the final structure and becomes permanently bonded into the matrix.//

That's why I suggested injecting water from the inside outwards.
The constant movement while transporting truckloads of concrete to keep it from setting whip large amounts of air into the wet mixture. This air then needs to be partially removed with the use of vibrating wands.
I doubt that water injection into the center of a dry cement powder has ever been tested for strength against a mixed batch and I bet five bucks that it will be much denser than a conventional pour since absolutely no air enters during the mixing process.
-- 2 fries shy of a happy meal, Aug 13 2019


Injection causes a concentration bubble.

This is quite interesting , how to form an almost instantaneous, very homogeneous, mixture. The ingredients have to go from separate piles through a riffled shuffle where the same components move different distances, ending with homogeneity. Maybe the spiders know.
-- wjt, Aug 13 2019


//So. Reinforce your complex concrete shape with wire rope and then, once the concrete has set, run a few thousand amps through the wire rope. The wire will melt, and then solidify into rigid, perfectly bent rebar.//

This is an excellent idea that I can see no flaw with - except that steel expands on heating, and this will shatter the concrete.
-- hippo, Aug 13 2019


// [notexactly], the maser predates the laser, so that part is ready. //

Indeed it does, but I've never heard of masers having significant output power, or being used for heating. I've only ever heard of them being used as frequency standards, and that only when I was trying to find out what they were good for (actually hoping to use one for heating, I think), because I'd never heard of a use for one before that.

// Adding water and then making a good 'mix' disrupts all the good work done in making the acoustic/electric lattice in the dry mix. //

When you're mixing the water in, you've already solidified the lattice, haven't you? After solidifying it, you can suck out the remaining powder around it with a vacuum cleaner and mix the concrete in a proper mixer, and then pour it back in (or just use some other powder in the first place, which you suck out).
-- notexactly, Aug 13 2019


//Injection causes a concentration bubble.//

Yes and no. If only centrally injected then sure.

If the injectors retract from the center outwards injecting an ever increasing, (but carefully measured) volume of water, perhaps as a mist, then not only would the correct ratio of water to powder be assured, but the tubule as it retracts would create the only voids within the mix and can also be carefully calibrated to only displace the exact amount needed to optimize crystallization of the concrete without needing to release any trapped air.

...and I bet it's stronger than conventional.
I've been working with concrete and mortar products since masons used to have to make our own mixes because there was no friggin Ultra-flex 3 so you had to know what worked and always over-did it because call-backs mean working for free.
You learn a lot more than you want to know about concrete hand mixing it for a quarter century and dealing with the results.
The concrete powder is never denser after mixing with water than it was as a powder jiggled in the bag. Figure out how to homogenously give concrete the water it needs to set without whipping it up and it will be 'way' stronger than conventional. Jiggle the forms themselves acoustically to allow particulates to find their own positions and strengthen it 'way' more than that.
-- 2 fries shy of a happy meal, Aug 13 2019


What's wrong with [neutrinos] ice idea? You don't need to actively heat the concrete as long as ambient temperature is above freezing. Just poke a thin probe in and heat up the probe enough to melt some ice on the inside. The heat from the bonding will melt more ice and Bob's your housecleaner.
-- Voice, Aug 14 2019


Thinking along the ice logic, what would supercritical frozen water act like on the concrete powder mixture?
-- wjt, Aug 17 2019


^ My guesses:

If mixed into powder... not much. The water would would try to crystallize for a few seconds before it turned back into regular old water.

If injected into powder the water would form inner icicles displacing powder until compression was reached causing multiple branchings... and then turn back into regular old water.

If added to powder of the same temperature as the super-critical water then...

... water crystallization will interfere with concrete setting and you'll end up with crete-slushie until again the ice melts and the concrete does what it always does.
If the dry mix is kept at that same temperature super-critical as the water then you'll get... nada I think. The water will continue to nucleate while any trapped volume remains liquid until freezing on its own and expanding any surrounding crystals.>br>Fluff-crete.
-- 2 fries shy of a happy meal, Aug 17 2019


Since trapped air is such an issue, why not replace it with a highly mobile gas such as hydrogen or helium ?
-- 8th of 7, Aug 17 2019


Ooh, displace the air with hydrogen AND oxygen, then to get rid of any bubbles, light a match! Gets rid of bubbles and provides water!
-- neutrinos_shadow, Aug 18 2019


I see nothing wrong with this.
-- sninctown, Aug 18 2019



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