Not Bentonite the concrete stuff?

[Mr Hehound]

Hi guys - I'm having a mental block. What's the resistance earth resistance lowering product called that goes into concrete.

Not the Bentonite clay, the concrete stuff.

Thanks

 

[Marvo]

As far as I know an Ufer earth is achieved with just a concrete mass. Maybe there is an additive but I haven't heard of it.

 

[Knobhead]

As Marvo said the system is an Ufer earth.

No treatment needed for the concrete but an earth pit is needed for access to the rebar terminations. Some systems (American) the mesh is brazed at overlap points.

The last switchroom I installed had three access points along the length of the side wall for bonding points.

Ufer earthing was discovered by an American for use by the military at desert refuelling depots. Guess what his name was?

 

[Guest55]

er , Geoff ?

;-)

 

[Mr Hehound]

Ufer earthing was discovered by an American for use by the military at desert refuelling depots. Guess what his name was?

Herbert Ufer? (Wikipeadia)

Thanks Tony / Marvo - will add a proper thanks on the computer when I get home.

Someone once told me they sometimes use an additive. Must've been pulling my plonker.

 

[Knobhead]

They may use an additive, we used standard Portland concrete but if I remember right some lime was added (it’s a long time ago.) It was also bonded to the main structural steelwork so we had all bases covered.
The MET was damn near 4 metres long, that many things were tied back to it. Four 95mm² from each of the three transformers took a fair bit of room.

The Wiki article is quite good, there is a better one by American standards. It’s worth looking for. It goes in to brazing the mesh to form a contiguous mat.

 

[Engineer54]

Hi guys - I'm having a mental block. What's the resistance earth resistance lowering product called that goes into concrete.

Not the Bentonite clay, the concrete stuff.

Thanks

The product you're talking about is ''Marconite'' it's a conductive additive to portland cement that takes the place of the sand in the mortar mixture. Generally known as a rod or electrode enhancer.

It is far better than Bentonite in most ground type conditions and as i say will generally provide for better results. What's more, unlike Bentonite in some soils /ground is always considered as a permanent installation.

Where rods are concerned, for both Bentonite and Marconite, bore holes of at least 50mm are required to be drilled, the wet mixture is then poured into the b/hole and the rod dropped in. You will still need an absolute minimum of 2.4m of depth for electrode to be plausible

 

[Marvo]

I don't think you can mix Marconite into concrete, I think it's only for use as a cementicious type mix in a hole as you describe not for use in slabs and foundation structures that have an MPa rating.

 

[Knobhead]

It’s an Ufer slab not a rod borehole.

 

[Engineer54]

I don't think you can mix Marconite into concrete, I think it's only for use as a cementicious type mix in a hole as you describe not for use in slabs and foundation structures that have an MPa rating.

Perhaps this will help explain better Marvo.

http://www-public.tnb.com/eel/docs/furse/Total_Solution_TSC-0912_Earth_Electrode_Backfills.pdf

The brand name is Fursecem now, but it was first named after it's creator Marconi Industries (Marconite) for use on RF anttenas and the like, back i think in the 70's.

 

[Marvo]

When the OP mentioned concrete I thought he was contemplating using the foundations or slab of a building as an Ufer earth and not backfill for a rod. I think we're talking about two entirely different types of earth.

 

[Mr Hehound]

Sorry guys - my bad terminology. Meant the backfill cement / slurry stuff. Marconite as Eng 54 says.

Sorry for causing confusion.

 

[Engineer54]

When the OP mentioned concrete I thought he was contemplating using the foundations or slab of a building as an Ufer earth and not backfill for a rod. I think we're talking about two entirely different types of earth.

They actually call it Conductive concrete on the Furse web page, but it's really a mortar, as concrete is only concrete when it has ballast/stone in the mix!! But it is really good stuff, if you can bore the holes for it. You'd need a hell of a lot of it on your rod installations mind, the depth that you say you have to go down too!! lol!!

 

[Marvo]

We have something similar to bentonite around these parts but never used Marconite and never seen or heard of it being used here, we'd probably have to import it. I'd be interested in giving it a go if you fancy sending me a few bags on apro Only problem I can see is in the sand areas we'd probably need to get a odex rig on site to sleeve a hole then backfill with a rod and remove the sleeve.

Fingers crossed, most of the TT systems we've installed this year we haven't needed to go below about 10 meters and only needed a single rod. Pot luck really one last year we knocked an array of 8x 12meter rods and even with parallel paths from the foundation steel of the pumpstation we were still sat with >50ohms and had to resort to additional earth mats. The earthing ended up costing more than the control panel.