Ground Grid - Indoor installation

[TSun]

I was recently reviewing a ground grid study for an indoor installation and saw something that struck me as odd. The ground grid is installed beneath the basement, air cured, concrete floor of a building. There is steel re-bar inside the concrete slab. Yet the study still lists the resistance of the slab as 10,000 ohm-meters. This seems high to me.

Has anyone had previous experience with this type of installation that could verify whether this is or isn't a plausible resistance value for air cured concrete with re-bar?

References to technical documents would be much appreciated. I have already looked through the office copies of IEEE 80, IEEE 81, IEEE 665 and the IEEE Green Book. I so far haven't been able to locate anything indicating the resistance of air cured concrete for indoor installations.

 

[7anoter4]

Concrete mixes using Type III Portland cement with ternary combinations of Class F fly ash, silica fume and slag could present up to 1000 ohm-m resistivity. See:

http://www.claisse.info/2010 papers/m19.pdf

Usually under the concrete floor, it is an isolation layer –polyethylene or rubber
of 2-5 mm thick and this layer of high resistivity could influence the resistance measurement.

 

[Kiribanda]

TSun,
Just for my own curiosity, why there is a copper ground grid under the steel re-bar concrete basement at the first place?
What type of electrical installation do you have?

 

[TSun]

It is a commercial building with indoor 15kV equipment. With the way they modeled the room, the ground grid is necessary to keep step and touch potentials to an acceptable level but I am not sure that the room was modeled correctly.