Electrical surface resistivity of cement/concrete 2

[yshij]

Does any one know what's the surface resistivity (electrical property) of cement or concrete? Could it be 10^15 ohm?

Thanks

 

[cuky2000]

Are interested in resistance or resistivity? Resistivity is a generic normalized value given in Ohm-m. The resistivity for concrete could varies from 30 to 90 Ohm-m depend on the moisture level.

Keep in mind that concrete is an hygroscopy material that retain moisture for relative long time.

 

[yshij]

cuky2000,

Thanks for your answer. According to the info you gave, the concrete is electrically conductive - with the range 0 - 10^5 Ohm-cm. Is it right?


Thanks
Jack

 

[cuky2000]

Dear Yshij,

The upper resistivity range of 10⁵ Ohm-cm that you mentioned could be possible in very long dry season typically of desert areas.

In regular climate, the hygroscope property of concrete retains the soil moisture for around 30 days without significant reduction on resistivity.

A safe approach for grounding requirement in power stations and several other electrical facilities is to consider the concrete with sufficient moisture. If your application is different you should evaluate the site environment condition and choose the resistivity more suitable for the application.

In accordance with IEEE Std 80 the concrete resistivity ranges are as follow:

1- Wet............. 1x10⁸ to 1x10¹¹ Ohm-cm.
2- Dry............. 21 to 100. Ohm-m (2,100 to 10,000 Ohm-cm)

_{Note: Ohm-m =100 Ohm-cm.}

 

[cuky2000]

CORRECTION:

The data showed in the above post should be switched as follow:

1- Dry............. 1x10⁸ to 1x1011 Ohm-cm.
2- Wet............. 21 to 100. Ohm-m (2,100 to 10,000 Ohm-cm)

 

[BarryMartin]

Be careful with the stated values of concrete resistivity. Although 10,000 ohm-cm is a good value for typical concretes used for highways there are many formulations that have much higher resistivties. Polymer concretes or addition of fly ash cause significantly raise the resistance. In addition, the surface of concrete can dry out. While the environment 1 to 2 inches deep is rather stable, the surface can and does go through wet-dry cycles that significantly effect the resistivity.