I have seen similar corrosion here in the midwest. Specific case was a
10' long expanding bell style anchor. The 3/4" rod penetrated from a
loam into a sand layer at 5' of vertical depth. In the area 6" above the
soil interface, the rod had suffered corrosion which necked the rod down
to 7/16" diameter. Above and below this 1' long area, the rod had only
minor surface corrosion. The different soil pH in this localized area
had done all the damage. This anchor had been in the ground for 25
years.
This prompted me to adopt a personal standard: Encase all rods in at
least 3" radial concrete, and be carefull enough in the guy rod angle
that you do not over stress and crack the concrete. The easiest way to
do this is to make the guy anchors a drilled pier with the guy head
slightly above the surface. It takes some soils work, but it can be
done. Unfortunately it doubles or triples the cost of the anchor point.
This has made me rather unpopular in some circles.
Barring this sort of design and installation, the option is to dig down
the anchor shaft every 5 years and check the whole length for corrosion
including washing off the top of the concrete with water and a scrub
brush. If you find a problem, the only solution that I know of is to go
out away from the tower, behind the existing anchor block and start over
with a new anchor block and rod.
de n0yvy steve
ROBERT WANDERER wrote:
>
> This is true Revision F
> The moving force behind this revision is Anchor Guard who manufacture
> cathodic protection. I
> don't know for sure, but I think they sell the grounding products they're
> calling for in 222-F.
> Could it be they aren't altruistic?
>
> The problem is that you can severe corrosion on the anchor rod between the
> part that's in
> concrete and the part that's in soil. Likewise the part in soil if soil
> layers vary in their pH.
> Anchor Guard has an interesting monograph (7 pg) on the subject. Send me fax
> # or
> snail mail address and I'll pass it along. Send this to my work e-mail, please
> <bobwanderer@polyphaser.com>
>
> Aluminum, Galvanize, Tin are attacked by alkaline soil. This soil
> predominates in the western
> part of the US. Copper is attacked by acidic soil, common in the eastern
> states.
>
> If the two dissimilar metals are far enough apart, there ought not be any
> problem. Distance
> would probably depend on the conductivity of the soil. I personally think
> there are other
> causes, although this particular scenario does probably occur often enough to
> be of concern.
>
> 73,
> Bob Wanderer AA0CY
> Sr Appl Engr
> PolyPhaser Corp.
>
> ----------
> From: Frank Donovan[SMTP:donovanf@sgate.com]
> Sent: Wednesday, April 23, 1997 1:20 PM
> To: Bill Tippett; towertalk@contesting.com
> Subject: Re: [TowerTalk] Verticals of Rohn 25
>
> As a matter of interest to Towertalkians, the new version of EIA/TIA-222
> specifies that copper wire SHALL NOT be used for ground wires, ground rods
> or ground clamps. All new towers installed under EIA/TIA-222
> specifications must use galvanized ground rods, galvanized steel wire (ie
> guy wire!) for grounding conductors, and galvanized connectors or
> exothermically welded connections. Tinned copper wire may be substituted
> for galvanized steel wire when the conductor must be buried. Bare copper
> is no longer allowed in any grounding application, either at the tower
> base or at the guy anchors.
>
> This change came about as a result of research that demonstrated that
> copper ground rods in proximity to tower foundations and steel guy anchors
> tended to accelerate the corrosion of the steel members, leading to sudden
> catastrophic failure!
>
> 73
> Frank
> W3LPL
> donovanf@sgate.com
>
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>
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