Doug,
Concrete may be made to work as an insulator, but conditions will have to be
carefully controlled. Most concrete tends to be somewhat hygroscopic,
although this varies with mix variables including type of aggregate used. I
have heard that large concrete pads are successfully being used as
alternatives to ground rods in some RF applications. I believe that the
military has done a lot of work in this area, using massive grids of welded
rebar to distribute conductivity within the slab.
Anyway, you will need to ensure that the cement used is a low moisture
absorbing type. Your local masonry supplier should be able to help with
this. Use only insulators, such as quartz sand, for aggregate. Some pre-mix
may contain foundry slag and other metallic aggregate.
If you are unable to purchase low moisture absorbing mix, and must use the
stuff from the home center, I would suggest that you use bonding compound to
replace much or all of the water in the mix. I have used 100 percent bonding
compound with great success, the resulting concrete being much stronger and
more water resistant. The only drawback is the higher cost.
I would strongly recommend performing conductivity testing on samples before
using a particular mix. A prolonged 95 percent humidity test would probably
be wise.
I am delighted to hear that there are others out there willing to try
"crazy" methods and materials.
Good Luck,
Scott Lacey
-----Original Message-----
From: POWELL, DOUG [SMTP:[email protected]]
Sent: Friday, August 20, 1999 5:40 PM
To: EMC-PSTC (E-mail)
Subject: Concrete as an insulator???
Hello all,
I have a very innovative engineer who has come up with a design idea
that
uses concrete as an insulating compound in a very large inductor for
a 200
kW switching power supply. Yup, this is the stuff you buy down at
the local
building supply company. He was very proud of the idea, but until
he came
up with it I think he was pretty desperate. I'm thinking I should
make him
desperate again but would like to be able to give him a clearly
reasoned-out
explanation.
Has anyone ever had experience with using concrete or mortar in a
high
voltage application? What are the concerns here? It is my
understanding
that it does not actually "dry" but it cures with all the water
contained
inside.
thanks,
-doug
=======================================
Douglas E. Powell, Compliance Engineer
Advanced Energy Industries, Inc.
1625 Sharp Point Dr.
Fort Collins, Colorado 80525 USA
---------------------------------------
970-407-6410 (phone)
970-407-5410 (e-fax)
mailto:[email protected] <mailto:[email protected]>
http://www.advanced-energy.com <http://www.advanced-energy.com/>
=======================================
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