Soil Resistivity and Reinforcing Corrosion Protection 1

[vgillespie]

Is there a guidline for how to specify the type of corrosion protection on foundation reinforcing steel based on the soil resistivity (ohm-meters)? At what level (ohm-meters)is the soil non-corrosive and when would you provide epoxy coated rebar or cathodic protection?

 

[Sean2]

The reinforcing steel should NEVER project outside the concrete, and should always be given the appropriate level of concrete cover. In my (limited) experience, soil resistivity is not usually a factor in the design of reinforced concrete foundations.

The UK's Building Research Establishment (BRE) has published a very useful digest (BRE Digest 363) covering the design of concrete in the ground. (Make sure you get the LATEST edition.) It refers specifically to pH and Sulfate exposure.

Your main concern with the reinforcing steel will arise if you consider that the concrete is vulnerable, and the steel may be exposed during the design life of the structure. If this happens, the structure has failed (even if it has not actually collapsed yet).

However, I suspect you will be more up to date on concrete technology than I.

 

[dennisz]

Sean2 says "reinforcing steel should NEVER project outside the concrete".

While that's probably true for structural purposes, it is the best available grounding electrode for electrical earthing purposes. Do dot underestimate this point. Concrete-encased electrodes (Ufer-type) are vastly superior to the other common methods & materials typically used.

The technique I am referring to is simply this: At the electrical main service location, bend & project an inter-connected ½” min. rebar section out of the foundation towards the surface (within 6” is best), about 24” away from the foundation walls. The usual steel-ties (at least 8) are adequate for electrical-bonding to remaining concrete-encased rebar-reinforcing system. You may want to temporally cap the rebar end in the exposed trench to prevent injury & to further aid in its identification.

This does not make foundation contractors electricians, as they will use the same materials & techniques common to them. Under most varying soil conditions, direct buried copper conductors would effectively last only about 20-years before they become too corroded. The adage Better, Faster, Cheaper certainly applies to this technique. The foundation engineering industry has an excellent opportunity to further enhance the safety & operation of all electrical power consuming devises! Please pass this information along; it deserves to become “The Standard” thanks. dennisz.