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Science Technology

Conductive Concrete Offers Building Security 162

Posted by timothy from the lacks-transparency dept.
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."
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Conductive Concrete Offers Building Security

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  • Wow... (Score:3, Funny)

    by Ooblek ( 544753 ) on Thursday March 21, 2002 @02:31PM (#3202304)
    Anyone remember the name of that psychologist that put dogs in a room with an electrified floor? I wonder if they'll start putting this stuff into jail cells and mental hospitals. You know, the prisoner/patient/subject mouths off they can give them a jolt. All in the name of science, of course.

    • Pavlov (Score:3, Informative)

      by GMontag ( 42283 )
      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.
      • Are you sure? I thought he did bells at feeding time and it was someone else that jolted the dogs into submission. Whatever.
        • The bells at feeding time was one of the other experiments. He also did the showing of shapes to mean different upcoming events. One was an oval, the other a circle. Then he gradually rounded the oval until the dog could not distinguish between them.

          At that point the dog would go nuts!
    • And you thought a cat on a HOT sidewalk was funny!
    • I wonder if I could use this to power my surface mount speakers behind my drywall?
    • Boss - "Smith, I want that report on my desk in 20 minutes. Or I press the button."

      ...19 minutes later...

      Smith - "Hey pimply-faced-youth intern! Can you just sit at my desk for a moment while I run downstairs? I have an important call coming in, thanks."

      Tsk tsk. Smith should know better than to fuck with the PFY.
  • So, does this mean that in the future, demolition companies could just HERF a building down instead of going inside and setting explosives?

  • Blocks Cell Phones? (Score:3, Insightful)

    by hoggoth ( 414195 ) on Thursday March 21, 2002 @02:32PM (#3202313) Journal
    I wonder what kind of cell phone signal I would get in a conductive-concrete building? Probably next to none...
    • It looks like we may have found the perfect material for building theaters!
    • This is an excellent point. What cell phone, radio, 802.11b signals, will this interfere with?

      I'm already having issue with my 802.11b network at home that won't go through 2 freakin' walls. I imagine this stuff will wreak havoc with all sorts of electronic communications.

      -jason
    • None (or, very very limited). I think that is the point - when the article talks of the counter-intelligence uses for this material, cell phone signals would fall under the same category as other EM signals.

    • Re:Blocks Cell Phones? (Score:2, Informative)

      by IsaacW ( 543020 )
      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.
      • 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 )

  • "...but it's still cool stuff."

    Wouldn't "hot stuff" be more appropriate? :)

  • Cost and Uses (Score:2, Insightful)

    by Digitalia ( 127982 )
    Is the cost per cubic foot much greater than standard concrete? If not, then I'd be interested in the implications for using it as a residential flooring substrate. Rather than going for a standard radiant heating system, would it be more efficient to employ this?
    • I believe the article said it was 2-3 times the cost of regular concrete.
      • I think the website also said that this type of concrete would be just a "thin" coating on the top of regular concrete. I am not sure how "thin" but I think it says on the website. (I don't want to go back to that horribly designed website because it is so ugly). So for the icy-bridge example, the cost increase wouldn't be huge compared to the cost of the entire bridge-deck slab. I'm sure the same thing applies for walls in buildings.
    • I found an article [slashdot.org] on New-Technologies [new-technologies.org] which was a good read on the subject. It had people to contact, other related links on the subect. It also said that it wouldn't cost much more to produce than regular concrete. It used some stuff like left over by-products from steel production.

    • I'd love to know the cost of this relative to standard concrete as well... imagine being able to flip a switch when it starts snowing, to heat your driveway, steps and sidewalk so nothing accumulated on them. Now THAT would be something.

      ~Philly
    • Well it's probably still less expensive than radiant flooring, in which pipes or hoses are run before the flooring is poured, through which hot water runs. You won't have to hire people with extensive skill at setting up the piping, and it might be more efficient.
    • Electric heat costs 2-3 times as much as gas. Ok if you make 2-3 times as much money and like walking barefoot to the kitchen at night to munch Oreos without waking your wife wit "Ooh, ooh, ahh, cold floor! cold floor!"

  • A great big Faraday cage (Score:5, Interesting)

    by InterruptDescriptorT ( 531083 ) on Thursday March 21, 2002 @02:33PM (#3202334) Homepage
    I'm not a huge expert in the realm of physics (dammit, Jim, I'm a computer scientist!), but is this anything like a massive Faraday cage, which would prevent electromagnetic waves for entering and exiting?

    I shudder to think of the day when we will work in protective buildings like these, keeping company secdrets safe from Van Eck phreakers and war drivers, but also keeping out the mellow, smooth sounds of Office Light Jazz 94.7. :-)
    • 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).

    • I shudder to think of the day when we will work in protective buildings like these, keeping company secdrets safe from Van Eck phreakers and war drivers, but also keeping out the mellow, smooth sounds of Office Light Jazz 94.7. :-)

      Some people already work in such buildings. When I interviewed at the NSA back in the late 80s, they were putting up a Tempest-protected office building.
    • Ok.. taking this idea for a stretch
      will this make our buildings vulnerable to a
      EM Pulse (like the one from a nuke).

      EM Pulse comes through.. generates large amounts of voltage in building.. building melts.

      Hrm...
    • Don't worry. You'll just connect to officelightjazz.com and listen to the streaming radio. Heck, some people do this already. :-)
    • This could be instrumental in clearing up some of the rampant wireless network security problems that have hit the net lately. Build the exterior of the building out of this stuff, and conventional materials inside. No more drive-bys.

      I mean, hey, at least you'd have to walk in the door before phreaking the signal...
      GMFTatsujin
  • Cool! Built in lightning rods, too?

  • Floating concrete structures?!? (Score:4, Funny)

    by MonkeyBot ( 545313 ) on Thursday March 21, 2002 @02:35PM (#3202349)
    So this stuff can conduct electricity, meaning it could generate a magnetic field, right? So you could theoretically generate a magnetic field to hold a concrete structure made from this stuff in the air. Does this mean that my goal of making a floating castle like all the bad guys in RPG video games have is finally within reach?
    • So this stuff can conduct electricity, meaning it could generate a magnetic field, right? So you could theoretically generate a magnetic field to hold a concrete structure made from this stuff in the air. Does this mean that my goal of making a floating castle like all the bad guys in RPG video games have is finally within reach?

      Certainly, until the rebels cut power to or carve up the plate on the ground you're pushing against, or until your castle melts to slag from resistive heating due to the vast currents required ;).

      Thought about the same thing a while back, and concluded that the Koopa Ship method is more practical ;).

      • Not melt, explode! (Score:2, Interesting)

        by MonkeyBot ( 545313 )
        Certainly, until the rebels cut power to or carve up the plate on the ground you're pushing against, or until your castle melts to slag from resistive heating due to the vast currents required ;).

        Actually, the concrete, if it is like normal concrete, would probably explode instead of melting...the little air pockets inside it expand until they break the structure. It's neat. Hold a blowtorch to some concrete sometime---it crackles!

  • Wow! (Score:3, Funny)

    by ShaniaTwain ( 197446 ) on Thursday March 21, 2002 @02:36PM (#3202367) Homepage
    That unomaha site has one of the worst web designs I'ver ever seen. I guess it's not that important that scientist be designers, but readability would be a good thing to strive for. I don't need every paragraph to be a different color. Is this a side effect of too much exposure to conductive concrete?
    • I just sent an email alerting Vincent Flanders. I'm sure he'll love this one.
    • Agreed. Somebody went to a lot of trouble to make it suck that much. Take a look at the HTML; some pages were authored with Microsoft Word 9, others with Microsoft PowerPoint.

      The bridge-deicing idea isn't unreasonable. From their numbers, for $500 per storm, you could de-ice a bridge 200' long and 4 lanes wide. That compares favorably with sending out snowplows, salt trucks, and such.

  • Comment removed based on user account deletion

  • music studio (Score:3, Interesting)

    by crow ( 16139 ) on Thursday March 21, 2002 @02:38PM (#3202382) Homepage Journal
    I remember when a friend was recording a radio theatre show, the studio had chicken wire on all the walls (behind accoustic foam in most places) to minimize inteferrence from outside signals. You don't want your microphone cable picking up radio signals when recording a performance. This material could be ideal for construction in applications like that where you want to block out outside signals.
    • Sure. Use it in movie theatres and performance halls to neuter those dumbass, suit-wearing, cellphone talking, consult-the-business-model, Viper driving, 30-something, "Hey, Bob, look at us: we're executives!" weenies who cannot be bothered to turn off their cell phones long enough for the others around them to enjoy a whole movie without an interruption from a phone beeping the tone sequence from Close Encounters.

      (Can't remember where I get the first part of that rant - somewhere/sometime off a previous slashdot post. My apologies to the original author...)

      • Re:music studio (Score:3, Funny)

        by swb ( 14022 )
        Are they related to those dumbass, cargo-pants weaing, PDA using, Slashdot-reading, Honda-driving, 30-something, "Hey, Raj, look at us! We're geeks!" weenies who can't be bothered to turn off their cell phones, pagers, PDAs and notebooks in the movies?

  • Concrete circuitry? (Score:4, Funny)

    by indole ( 177514 ) <fluxistNO@SPAMgmail.com> on Thursday March 21, 2002 @02:39PM (#3202388) Homepage


    How about drywall transistors and logic-gate carpets?

    I wont be happy till my split-level serves pr0n.

  • Now there is what every trucker needs for those cold winter days.
    Brought to you by science.
    • Good For The Truckers- Bad For the Homeless.

      I worked in a grocery store and there was a vent down at the bottom of our dock. Hot air came out of it so a homeless guy started sleeping down there.

      One night a truck backed down in to make a delivery while he slept....

      .
  • the heating properties alone look great to me.. I live on a hill, and my sidewalk is always a nightmare in the winter.. how much do these concrete pavers the article mentions run and where can I buy them? I'm sick of using a sled to get to the bottom of my sidewalk!
  • The best problem this solves (besides saving people's lives by reducing ice-related car accidents) is that it would eliminate the need for salt on bridges. I don't know exactly what salt does to the environment, but I'm sure that dumping a lot of salt on the roads/bridges and letting it seep in to the ground can't be good for the ecosystem.

    It kills slugs too. Who knows what good slugs do for our environment? Haha

    • Ever notice around bridges, along the edge of the roadway that there is no grass, only dirt? Even from a bridge that's been there 20 years. That's what salt does to the environment.

      Most places only put as much salt as is necessary (Edmonton for example puts 6-12% salt in sand for the roads) as it's expensive and doesn't work below a certain temp.

      As for slugs - I don't know what they do for the environment, but they sure are tasty!

  • Sounds like these guys have never studied thermodynamics. It takes 333kJ to melt a single kilogram of ice. To melt it in, say, 10 minutes (= 600 seconds) would require 555 watts. Not so bad? Consider the following: Conservatively estimate a bridge to be 10 meters wide by 250 meters long and having 2 centimeters of ice. That's 50 m^3 = 50,000 kg of ice. A mere 28 MegaWatts. Per ice storm. Per bridge. Assuming 100% efficiency. Oh yeah, no problem.

    Please study a little science before you post stories from similarly unclued "visionaries".

    • But if you can keep the ice from forming the water could run off the bridge and not freeze.

      -- Tim
      • Lemme 'splain something to ya. When you have a process removing heat you've got to add heat at the same rate to keep the temperature the same. It doesn't matter if the water is already frozen or not if the temperature is below 0C the energy requirements are the same (modulo a little runoff, but in that case it must be raining so it isn't 0C anyway, not to mention 2 cm is an understatement).

    • I think the idea is: resistively-heated concrete could maintain the bridge deck temperature above freezing, so that no ice needs to be melted in the first place.

    • Re:Non-freezing bridges? (Score:1, Interesting)

      by Anonymous Coward
      Well for one thing where on earth is there going to be a road & highway department (in a country that can afford heatable concrete) that's going to let an inch of ICE fully form before they decide to do something about it?

      For another thing two CM of ice is 12-40 CM of snow (depending on humidity). That's an awfully big dump for the majority of the world the majority of the time; most of the time in most of the world you'll be dealing with small fractions of this.

      For another thing, why would you possibly need to melt all the ice that quickly (even assuming you were stupid enough to let that much form in the first place)? Why not just let the thing run at lower wattage 24x7 (when it is snowing, or at night)? It only needs to keep the snow that is there from refreezing, and to melt any new accumulation.

      Finally, "assuming 100% efficiency" ?? So what? What if it's not 100% efficient? What else is the waste product going to be besides heat?
      • I gave a concrete example but "quickly" doesn't really factor in. P = E x t. Therefore E = P/t. In other words, if you take longer it will use the same amount of energy at a lower power. Still mighty expensive.

        Keeping something from freezing requires exactly the same amount of energy as melting it. Exactly. This is obvious to anyone who has studied science or used an ice cube.p. The waste produce is always heat. But it isn't always released near any ice. What about the sides and bottom of this road? What about patches of ice? What about transmission issues?

      • Well for one thing where on earth is there going to be a road & highway department (in a country that can afford heatable concrete) that's going to let an inch of ICE fully form before they decide to do something about it?
        Fortunatly, where I live in Alaska the DOT is not obsessed with keeping the roads bare. It is quite common to have an inch or two snow/ice pack on the roads in the winter. The snow plows use grooved blades, which in turn grooves the ice in the direction of travel. Your tires grip the ice grooves quite well.

        Salt isn't used because it doesn't work when it gets really cold. I think the magic temperature is 0F, since Mr. Fahrenheit used a salt & ice mixture to define 0F. (I'm not entirely sure about this.)

        • That's what Mr F tried to do, with a scale from freezing salt water to body temperature. Unfortunatly he messed up, so 100F ended up slightly above body temperature, and the temperateure of salt water depends on the concentration of salt, and also the type of salt - sodium chloride having a different point to say potassium chloride.
        • I was told that the temperature of the salt ice mixture was the coldest temperature that Fahrenheit could find. As such, 0 degrees Fahrenheit is an overwhelmingly crude approximation of absolute 0.
    • Yep, and this doesn't take into account that it could be -30 when the snow starts, and you haven't kept the bridge heated since it hasn't snowed for the last 3 weeks, so you have to heat up the bridge a whole lot in -30 weather while the wind (from the snowstorm) is sucking almost all that thermal energy away (and the cold wind will be hitting the big bridge surface you want to heat from both above and below). How much you think its gonna cost now?
      • For people who talk all geeky, this site sure is scientifically illiterate. The heat of fusion (esp of water) vastly overpowers the specific heat of even something as large as a bridge. Wind could be a problem, though.
    • they already have heated parts of road in midtown here.(finland). it's supposedly just about the same price as it would be to use conventional salt and/or machines to keep the ice/snow out. AFAIK they turn it off at -15C or so.
    • Sounds like these guys have never studied thermodynamics.

      If by "these guys" you mean "The University of Omaha", I think you'll lose that bet. Their "Conductive Concrete for Bridge Deicing" [unomaha.edu] experiement indicates that the average power generated by the conductive concrete was about 591 W/m^2, consistant with successful past efforts at electrical bridge deicing. Their estimated energy cost for this amount of power is $0.70 to $1.00 /m^2 per storm, which sounds perfectly reasonable.

      Please read the links before trying to make yourself sound smarter than everyone else.

  • heating (Score:3, Interesting)

    by DragonWyatt ( 62035 ) on Thursday March 21, 2002 @02:46PM (#3202456) Homepage
    The most obvious use is heating.

    But wouldn't it be cheaper and simpler to embed, say, a PVC 2-inch pipe in the concrete, and run warm water through that? Note that you can use this method with just about anything (dirt, asphalt, etc) and keep it from freezing.

    If you want a method to directly heat it using electricity, run stainless steel pipe instead, and use it as a load.

    I've frequently wondered why civil engineers haven't implemented either of the above techniques before. Chalked it up to "roads don't freeze enough".

    Thoughts?
    • but that pipe could impare the structual integrety of the span. The hover dam had pipes rin thru it to cool the concrete while it was being poored, when they were done they filled the pipes with concrete.

      -- Tim
    • The pipes could compromise the structual integrety.

      The hoover dam had pipes layed in for cooling purposes, the pipes were then filled with concrete.

      -- tim
    • The article did mention the buried pipe method, but notes that it's expensive to put the pipes in to start with, and then when they split, corrode through, or plug up, you've got to jackhammer through the concrete to fix them. The point about repairs is good, but I do wonder how a grid of buried pipes could be more costly than paying two or three times as much for conductive concrete.

      But the real reason heated pavement isn't used much is because electricity costs too much. You don't want to pay the power bill for trying to heat up the freaking outdoors! Conductive concrete won't change that. With buried pipes, you can also heat with a gas or oil furnace, which costs quite a lot less (90% efficient, compared to about 30% overall in the electric system), but it still costs too much in northern climates. And in southern climates where you'd only have to turn on the heat a few days a year, few people think snow is a big enough problem to add thousands to their initial construction cost.
      • Actually one of the Universities here in Ohio has quite a few of their main walkways kept clean from snow and ice using the burried pipe method. They use excess heat from the electric plant so it is basically free. They are pretty far south so they are in the transitional area where they get enough snow to bother with it but not enough that it overworks the plant.

        p.s.
        the school is Miami of Ohio, the best public school in Ohio .
        • College of Wooster does it too, except that the sidewalks are the roofs of the steam conduits from the power plant to the building. I was always under the impression that this kind of thing was common in North-Central Ohio.
        • Do they alwo use the waste heat from the electric plant to heat the buildings? Just how much electricity does this power plant produce? I know of Michigan colleges that heat their buildings from an electric plant, but there sure isn't enough extra heat to clear the sidewalks when it stays around 10 F for weeks...

          Anyhow, note that the conductive concrete won't allow you to use the co-generated "free" heat, but requires the expensive electricity.
    • In Northern CA we have neighborhoods full of '60s houses dubbed "Eichlers". They use this method of heating.


      When the pipes leak, you have a jackhammering road crew in your living room to fix them.


      They also have huge glass windows all around most of the outer walls. Lets in a lot of light, lets out a lot of IR and heated air. Obviously designed when gas and oil were 3 cents/ton.

  • Now even the underprivileged will be able to afford to stop the MLB from reading their minds. No more tinfoil hats!
  • The Soviets pioneered innovative uses of concrete way back in the '80s [go.com]... though I don't think they were that interested in *counter*-espionage...

  • Would having conducting concrete make it easier or harder to prevent electrochemical corrosion in reinforced concrete?

    Intuition is telling me "yes to both", but I'm not a Civ...
  • If your intrested in kind of stuff New-Technologies [new-technologies.org] has a good article [new-technologies.org] about it. They also have a bunch of links to related sites reguarding concrete advancements.
  • "The initial development evolved from a discussion I had with a graduate student,"
    Isn't that how everything starts off in academia?
  • Awhile ago there was talk about a government agency that ionized their concrete walls to attract airborn particles, which could then be swept away with a sponge-mop. The result was very clean air in the building (assuming the walls were cleaned frequently).

    It sempt like a good idea but I haven't heard anything else about it for quite awhile. Perhaps someday this tech will be common in homes, as people are becoming more conscious of home and workplace health in our increasingly estrogenic society.
  • Radient heating. If they can use this to heat loading docks et. al. then how about my bathroom floor? Those stone tiles are so dang cold on the tootsies...
    • Or even the toilet seat. Low level current should be enough to keep it nice and toasty. Really would only need a few degrees above room temp to be MUCH more comfortable
      • Or even the toilet seat. Low level current should be enough to keep it nice and toasty. Really would only need a few degrees above room temp to be MUCH more comfortable

        There are heated toilet seats purchasable.

        The problem, as with all great inventions, is the idiot factor. Joe Schmoe cracks the toilet seat or busts the wires with wear. One dark night he stumbles into the bathroom, whizzes on the seat, salty urine hits electric current, and it's "Don't Whizz on the Electric Fence" time. And then we get another lawyer-flinging spurious lawsuit or Darwin Awards candidate.

        Don't underestimate the Idiot Factor. $cientogi$t$ would be a long extinct class of vicious nutball without it.
  • You can now go beyond wearing the tinfoil cap and build bunkers out of this (you want to be physically secure, too, don't you?) where you can run about naked telepathically communing with the trusted few you allow to enter, as well as your 26 cats of course.

    Of course, remember, just because you're paranoid doesn't mean they aren't out to get you...
  • How much juice will a cubic meter of the stuff use per degree celsius? Would widespread use of this concrete create a major spike in energy consumption or would it be more efficient than current heating methods. I, for one, am sick of seeing power being wasted and never ending power generator construction.
  • .....Could give new meaning to the words Information Superhighway

    :-)
  • Wow. Could you image transparant conducting concrete. I think it could lead to some very interesting lighting effects.

  • Static Control (Score:3, Informative)

    by markmoss ( 301064 ) on Thursday March 21, 2002 @03:16PM (#3202675)
    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.
    • Regular concrete is already so conductive that electrical codes require it to be tied into the grounding system of the building of which it is a part, and one of the acceptable ways to construct a building's main grounding point is to embed a length of metal pipe in the concrete of the building's foundation (assuming direct contact between the concrete and the actual planet Earth.

      If you're standing barefoot on a damp concrete floor and come into contact with a "hot" or "live" wire, you'll learn very quickly (within one/one hundred twentieth of a second, or one/one hundredth for 50Hz locations) how conductive concrete can be, assuming, of course, that you survive the lesson.

  • now maybe those alien abductions will stop and I can get on with my life. :)
  • Again, the URL is: http://www.majcher.com/nytview.html [majcher.com]

    It's a simple HTML/javascripty thing to automatically generate a random NYTimes login every time you want to view a story. Just cut and paste the nytimes.com url you want to view, and hit the button.

    If you could, please try to save the page locally and use it from your server or desktop, to keep the traffic to my server reasonable. Distribute at will.
  • Would be great for movie theaters and the like...
  • SpinalTap could have really used this technology when Niles was wielding his wireless guitar...

    "These go to eleven."

  • I thought a big use for these were going to be for heated runways - so you don't have to worry about de-icing them anymore. (I just hope they don't heat them too much and then you have a bunch of lizards just hanging out on the runway warming themselves.)

  • 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)
    • You use one or the other depending on what you want. A key point with conductive concrete is it's best used as an outdoor slab (not heating an enclosed space) and it only has to keep the thermal mass at about 33 degrees F when it's snowing (and never warmer). When your temp differential is high (ie it's -10F or colder) it rarely snows (atmosphere can't hold much moisture, so the weather system dumps it's snow somewhere warmer before it got to you. Remember the Arctic is technically a desert), so it's OK if the slab is only +20F or colder, with a simple non-feedback system. So you're only trying to heat at about 30 degrees above ambient you can incorporate feedback (temperature measuring and control) to reduce input energy even more.

      Radiant heating works best when you're trying to heat an enclosed space. Consider the envornment and pick the appropriate technology. Where I live, radiant (hot water in concrete) is pretty common, but you wouldn't try to heat the driveway that way, because you would have to maintain probably about +40F even when it's -40F outdoors (an 80 degree differential). You need some amount of overheating as a way of preventing failure, if you heating system freezes it is totally useless and needs almost complete rebuilding. Certain antifreeze systems can be employed but they have other problems; in general you should build it with enough BTUs and backups to keep it above freezing at all envisioned temperatures and power outages. Electic hot water boilers are common but natural gas is readily available here so most people use a gas over electric (for backup) system.

      Since radiant can be electically heated and it's slightly less efficent than thermal (electricity to water to concrete to objects vs electricity to concrete) it's not a given that it would be more efficent.
  • geesh, slogging my way through this enormous book - i haven't read about any 'electromagnet protected server room' yet - thanks for giving it away.
  • If large structures are made with conductive concrete, it could create a broad spectrum RF nightmare in cities.

    Today, large buildings reflect radio signals, creating interference for many signals in the shorter wavelength (6m to 30cm) bands. Imagine how much worse this would be if the buildings them selves had strong electromagnetic fields, or worse yet, emitted AC fields?

    Also, these structures will convert radio signals and other EMF into electric current. Theoretically, it is possible that such current could be in the tens of milliamps or even higher, making for passive RF radiators.

    I know we already use a lot of steel in buildings, but this is usually grounded and steel is a really poor conductor compared to something like copper or silver. I'm assuming this conductive concrete has much better electric conductivity than steel.

    Vortran out

  • voltage (Score:3)

    by ocie ( 6659 ) on Thursday March 21, 2002 @05:26PM (#3203776) Homepage
    Something I discovered with a neon transformer is that most things are conductive to some degree if you apply enough voltage :) concrete included.
  • *throws snowshovel out window*

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