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.

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: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.