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Magnetic Concrete

Magnetite, iron filings, concrete mix, water.
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Recently an article about clear concrete appeared on slashdot. This technology embeds optical fibers into concrete. See-through walls. Cool.

So now replace the optical fibers with magnetite or similar. Stir, shake, add lemon and serve for a weakly magnetic concrete structure in your desired shape.

Not quite sure what you'd use it for, besides screwing up cellphone reception and sticking tools to the wall, but there's gotta be a use somewhere.

RayfordSteele, Apr 01 2004

Baked http://www.alvsten-.../New%20Magnetic.htm
Sorry, but one Dr Bengt Alvsten beat you to it. [DrCurry, Oct 04 2004, last modified Oct 21 2004]

[link]






       Magnetic picture frames of course. No more holes.   

       Railway structures for Maglev trains, perhaps.
Laughs Last, Apr 01 2004
  

       Erasing floppy disks
Making your CRT TV picture disappear
Rotating your room to face North, when the Earth's poles reverse.
Attracting Boy Scouts during their navigation training.
No demolition dust (sticks together).
Don't do this near a steel mill: the steel dust would make your house look like a fur ball.

By the way: how would you polarise it?
Ling, Apr 01 2004
  

       it would do it itself - magnets always point in the same direction.
miasere, Apr 02 2004
  

       Probably not when they are in concrete though (s'pose depending on the strength).
Might be easier to put regular iron filings in the concrete and then magnetise them afterwards...
Aren't problems like this the reason engineers go to university...
MikeOliver, Apr 02 2004
  

       Mike that is civil engineering and materials science 2 separate disciplines
engineer1, Apr 02 2004
  

       //it would do it itself - magnets always point in the same direction//   

       Um, not always.
Detly, Apr 02 2004
  

       Ah, so we need to consult a civil engineer and a materials science engineer.
Which are you engineer1?
MikeOliver, Apr 02 2004
  

       I would think it would polarize itself as it hardened; maybe I'm wrong.   

       Not likely to be strong enough for maglev, although the shielded room idea is intriguing.
RayfordSteele, Apr 03 2004
  

       I think that if you vibrated the concrete while it's still wet the magnets would align themselves. You could also make the forms magnetic to help.   

       Passing a stong magnetic field over the still wet concrete should line them up. I wonder if flipping a stong magnetic field over the concrete would help vibrate the concrete?
Laughs Last, Apr 04 2004
  

       Non of the above i'm either a mechanical engineer or an automotive engineer depending on how you want to read my qualifications.   

       however i did have to do a bit of materials so know i don't know enough and making the assumption that all UK courses acredited by the IMECHE must be similar assumed that other similarly qualified engineers may not know either.
engineer1, Apr 04 2004
  

       Do this right with your ferro cement boat ... and you will always be headed in the right direction ... one pole or the other.
fasteddy, Apr 04 2004
  

       <wonders about the potential for corrosion problems with all the ferrous bits>
bristolz, Apr 04 2004
  

       How about if, instead of iron & magnetite, rare earth powdered magnetic material was used? For example, Neodymium?
If you want to see how strong these magnets are, open up an old, failed hard-disk drive (special keys required). There are two magnets inside, which when placed together, can barely be separated by sliding, never mind pulling.
Be careful with these magnets - don't get then anywhere near your TV, floppies or anything electrical - just in case.
This material wouldn't corrode at all, but I think you would have trouble walking around with steel toe-cap boots.
Edit: on second thoughts, it would clump around the reinforcement.
Ling, Apr 04 2004
  

       Engineering university? Been there, done that.   

       The clumping problem would be a tricky one to solve, even with weaker magnetite. Hmm...
RayfordSteele, Apr 06 2004
  

       You wouldn't have to use magnetic concrete in the whole building, just discreetly in areas where you need in. In private rooms to block mobile phone signals, places to hang things on, behind the door as a doorstop, for holding up tools... parking your car on the ceiling...
mailtosalonga, Apr 06 2004
  

       Would a room lined with magnets actually block cell reception any better than a room lined with lead?
ye_river_xiv, Sep 05 2011
  

       In the manufacture of steel, it's usual (is it not?) to trap thermal stresses in the hardening metal, as a way of controlling its characteristics, often in a very site-specific way. Presumably the trick doesn't work with concrete, because the latter hardens so slowly that any stress anneals out of it, and also because thermal, or other initial stress isn't that great to begin with. The best you can do is prestressing with embedded rebar.   

       But suppose you allowed ferroconcrete to cure in a magnetic field, imposing calculated stresses, which became locked in once the material hardened, and the piece was removed from the external field.
mouseposture, Sep 05 2011
  

       //if you vibrated the concrete while it's still wet the magnets would align themselves//   

       Wouldn't they also clump together into one big blob?
Wrongfellow, Sep 05 2011
  

       You need to vibrate the concrete long enough, but not too long. Luckily that is aready standard practice. After pooring, concrete is normally "rodded". This is done by inserting and removing a vibrating rod several times. This helps remove air pockets and also helps larger rocks sink below the surface for a smooth finish. If you do it too much, the rocks sink to the bottom and you get non-uniform concrete.   

       Assuming that your magnetic particles are weak enough that they will be pulled apart by friction during mixing, I suspect that the standard amount of rodding might be enough to allow them to spin but not enough to let them move very far. Normaly the rod is made of steel, so you might want to change that to something that won't pick up a lot of magnetic particles.
scad mientist, Sep 08 2011
  

       // something that won't pick up a lot of magnetic particles //   

       Errrr, concrete ?
8th of 7, Sep 08 2011
  
      
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