Conductive Concrete Offers Building Security

zdburke writes: "In a slightly different spin on the electromagnet-protected server room in Stephenson's Cryptonomicon, the folks at the National Research Council have developed concrete that conducts electricity, or 'percolates,' allowing it to serve as an electromagnetic shield. Current uses lean toward heated loading docks, non-freezing bridges, and grounding large-scale electrical equipment, but the counter-espionage idea is cool. The NYTimes has a brief story, and the folks at UN Omaha have some great pictures. It's not exactly new (it won a Popular Science prize in 1997) but it's still cool stuff."

Comments

Pavlov

[GMontag]

Anyone remember the name of that psychologist that put dogs in a room with an electrified floor?

Pavlov. That was one of several experiments involving behaviour modification.

Re:A great big Faraday cage

[CanadaDave]

This is exactly the same concept. The conducting electrons in the conductor material in the concrete "shield" are all mobile, and arrange themselves with respect to the stationary atomic cores so as to set up electric fields which will cancel out the electromagnetic fields which impinge upon it. So no electric field escapes, or at least some of it will, some of it won't. The amount of attenuation is all a function of frequency. Cell phones in the GHz range are especially supceptable, whereas very long radio waves aren't attenuated as much.

BTW, you could always just get whatever radio station you want through the internet (land-line).

Static Control

[markmoss]

It sounds like the concrete still has a pretty high resistance, so I wouldn't count on a reasonable thickness forming a good Faraday cage. With the conductive stuff costing At 2 or 3 times as much, you could likely get a better cage for less by just hanging metal mesh inside the forms and pouring regular concrete. (The mesh is part of your reinforcement, too.)

And the suggested use of electrically heated payment leaves me wondering where they plan to get free electricity.

But there is one good application for this. Electronics manufacturers need to control static throughout their facilities. Fixed objects are grounded by hooking up wires, but people walk around, circuit boards and parts are carried around on carts, etc., and the only way to ground these while in motion is through the floor. So we paid plenty for conductive tile, and some sort of conductive underlay. If we could have put a conductive layer in the concrete slab itself, it would have saved a bunch (even at 3x the price of regular concrete), and it would be more reliable and lower maintenance.

Re:Blocks Cell Phones?

[IsaacW]

Assuming that the conductive concrete formed a single, closed shell around the cell phone, none.

Basic physics will tell you that a closed conductive surface subject to an external electromagnetic field will exhibit no such field inside it's perimeter. I believe that the derivation is related to Guass's and Maxwell's laws of electromagnetics.

Don't throw your wood stoves out yet

[Bollux]

This conductive concrete has some interesting properties. The number one use that leaps to mind is EMI protection.

But for heating? Forget it! Two replies to this article mentioned something about how much energy it would require to melt ice. Now add the energy required to heat up the concrete. And know, that while electricity works quickly, it is just about the most expensive way to heat your home/whatever.

You might consider also, that while an abode of conductive material might be a great way to absorb stray radio signals coming your way, what are is your dwelling going to be emitting if you are hooking up AC voltage to it? If a micro-watt cell phone freaks you out, consider thousands of watts pumping through your house :) (I don't think anyone has proven that non-ionizing radiation causes cancer yet, so no worries...)

Radiant heating systems are the way to imbed a heat source in concrete. The technology is gaining in popularity all the time, as it deserves.

Read more about it for yourself at: http://www.radiantcompany.com/ They are for profit, but the prices seem reasonable. They advocate do-it-yourself and lots of good info on the website.

It would be great to hear from an HVAC engineer on this, but I don't think they will tell you much different.

Bollux (a BSME)

Re:Blocks Cell Phones?

[DrMegaVolt]

Its called a Farady cage. The field leakage would be related to the frequency of oscillation of that field - wavelengths on the order of and smaller than the largest hole in the cage would leak out ( or in )

Re:Question for a Civ Eng:

[big tex]

Harder.

I am a field engineer on a bridge construction project. I do concrete and overlays.

In most areas of bridges near water epoxy coated or galvanized rebar is used instead of black (bare) steel. The problem is that when steel rusts, it expands, popping the concrete around it.
When you build reinforced concrete the term 'cover' refers to the minimum distance the rebar must be from the outside faces of the concrete - basically the distance between the steel and the corrosion. This 'cover' is typically between 2 - 5 inches.
Overlay concrete (of which this conductive concrete is a type) is the riding course, or the top layer you actually ride on. It is poured seperately due in part to the large effort required to get the nice arched surface that rides so well. Overlays are typically 1 1/2 to 3 inches thick.
So, a "thin" layer, thiner than the typical cover, with metal particles spread uniformely enough to conduct electricity is bound to corrode like a bastard.

There are ways that you could combat this, though. Galvanize the parts, imbed a wire mesh that is plastic coated and electrficy that, apply one hell of a sealant, or put an ungodly amount of DCI (corrosion inhibiter) in the mix. DCI has a number of side effects that make it hard to place, displaces a fair amount of water, and it is really hard to finish smoothly.