Rebar and DC current

[ghostbuster7]

New site to be designed.

Measured 10 to 20 amps dc ground current at site.(Source of DC current will never go away and is generated by some other group).

What is the best way to protect the rebar in the concrete from electrolysis?

Epoxy coatings?

Galvanizing?

Sacrificial anodes?

Thanks

 

[ScottyUK]

Might be better asked at forum338

Where does the interfering source come from - your own facility or external? If external then you would have reasonable grounds to request them to modify their installation.

I think you'll have a rapid turnover using sacrificial anodes. I don't know much about coatings for steel in this application. Have you considered an impressed current CP system of your own, or including your structure within the protected zone if an ICCP system is the origin of your problem?

 

[7anoter4]

I agree with Scotty, of course. However the rebar coating-the embedded part-is not necessary. The grounding grid in the vicinity made of bare copper-or copperweld- could be a problem. A good cathodic protection-as Scotty already mentioned-could be useful. To use a tin of zinc coated copper is too late now, I guess. The contact between rebar and the copper conductor could be protected by putty or shrinking tubes-or both. An xlpe insulated jumper could be also useful.

 

[ghostbuster7]

I have reposted this in as suggested the corrosion group.

Answers etc.

The DC current is stray current from a city transportation system.They freely admit they are generating stray current and it is up to any new building designs to "accomodate" this stray current situation.

Rebar inside this concrete slab will corrode faster with this DC current flow ,will build up additional internal concrete stress and eventually weaken this concrete slab.

That is the real concern and is a very odd design requirement with very little technical information available.

Thanks for your help.

 

[dpc]

Coated rebar is fairly common. But I think you need to engage a local corrosion engineer with experience in dealing with this issue. It's outside a typical EE's area of expertise. No shame in seeking assistance - and you'll sleep better.

 

[rasevskii]

In the early days of electric streetcars (trams) which run on 600V DC supply, it was found that corrosion of iron gas and water pipes, telephone cable sheaths, and other metal structures occured close to the DC substations (or DC generating stations) where the DC current returned to the generators from the rail tracks. The solution, still used today, was to install drainage cables from the structures to the negative DC busbar in the substation (or DC generating station) The overhead supply, or third rail is the positive pole, the tracks the negative.

In the case of your project, it might be useful to consider a drainage cable from the rebar system to the rail track. It seems that the corrosion occurs at the point where the current leaves the underground structure and flows into the Earth near the substation, a drainage cable bypasses this route.

The above partly from the Electric Railway Handbook, published before 1917.

Just a historical note...

rasevskii

 

[SceneryDriver]

Is fiberglass rebar or glass-reinforced concrete an option?

SceneryDriver

 

[davidbeach]

Ring the site with a bare Cu ring and then tie the sides of the ring together through the foundation. Give the current an easy path outside the rebar.