Just to add a bit of trivia to this discussion, concrete increases substantially in conductivity in the presence of ionizing radiation (x-rays, gamma rays). This is well known and documented in the nuclear hardening community. This is an indication of an inherent population of free charge carriers in concrete (be they water-based, or other).
Jim ________________________________________________________ Dr. Jim Knighten e-mail: jim.knigh...@sandiegoca.ncr.com <mailto:jim.knigh...@sandiego.ncr.com> Senior Consulting Engineer NCR 17095 Via del Campo San Diego, CA 92127 http://www.ncr.com <http://www.ncr.com> Tel: 858-485-2537 Fax: 858-485-3788 ***** Notice the Area Code change from 619 ***** -----Original Message----- From: jrbar...@lexmark.com [mailto:jrbar...@lexmark.com] Sent: Monday, August 23, 1999 6:43 AM To: emc-p...@ieee.org Subject: Re: Concrete as an insulator??? Doug, Concrete is a fairly good conductor-- much more conductive than most soils. Electric utilities, radio stations, and amateur-radio operators often use "Ufer grounds", which consist of steel rebar encased in poured concrete as the lightning-protection grounds for large power transformers and antenna towers. For example, if I sink an 8-foot-long 1/2" diameter copper-clad-steel ground rod into my backyard I would get about 25-ohms ground resistance. If I drill a 6" diameter hole 8-feet-deep and put a piece if 1/2" rebar into it, then fill the hole with concrete, I will get about 2-ohms ground resistance (essentially proportional to 1/surface area). Some sources of information on Ufer grounds are: * The Grounds for Lightning and EMP Protection, by Block (PolyPhaser). * http://www.scott-inc.com/html/ufer.htm * http://www.psihq.com/iread/ufergrnd.htm * http://www.contesting.com/_towertalk/9709/0636.html Quite a few articles and books on Electrostatic Discharge (ESD) control mention that plain concrete is ESD-safe. When we were laying out the IBM Lexington card line about 1984 we briefly considered leaving the floors as unsurfaced concrete. We couldn't stand the contamination from concrete dust, though, so we wound up spending $1,000,000 on conductive vinyl tile over the concrete. John Barnes KS4GL Advisory Engineer Lexmark International --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
