[TowerTalk] Conductivity of concrete

[Jim Lux]

On 7/18/13 10:33 AM, Drax Felton wrote:
> I've read that concrete is conductive even after completely setting.   Does anyone know what it's actual mho's or conductivity is?     I'm sure it ranges based on composition but was just wondering about an average bag of properly mixed Quickete as an example.
>

"enhanced conductivity concrete" has a resistivity of 1-40 Ohm-Meter. 
But that's special because it's been enhanced. Normal concrete that is 
that conductive is likely to lead to corrosion, often because of excess 
chloride ions.

Normal concrete is 30-90 Ohm-Meter  (that's what IEEE Std 80 for 
grounding substations says to assume)

That turns into about 10-50 mS/meter.  Definitely more conductive than 
the 5 mS/m used for "Average" soil in modeling codes.  (that's why it 
works as part of a grounding electrode system)


The conductivity goes up (it gets less resistive) as the frequency gets 
higher.  At microwave frequencies a number like 150 mS/m is typical.