Dean has summed it up. There is also an article "Current technologies curb
rebar corrosion" by Martin McGovern in Concrete Repair Digest,
August-September 1996, which describes various electro-chemical approaches.
The pun is intended.

-----Original Message-----
From: Dean Koga [mailto:[log in to unmask]]
Sent: Tuesday, December 15, 1998 11:49 PM
To: [log in to unmask]
Subject: Re: Electrochemical concrete repair


On Mon, 14 Dec 1998, Marilyn Harper wrote:

>      Is this related to a process I heard about that can be used to
prevent
>      deterioration of concrete in ocean-front buildings?  The lecture
> was about
>      spectacular and rapidly deteriorating 50s buildings in Havana,
> but the same
>      would probably apply to Miami Beach and other such places.  The
> process had
>      something to do with using an electrical current to change the
> positive
>      charge on the concrete to negative (or maybe the other way round,
> I'm not
>      very good at physics!), which apparently inhibits the
> deterioration due to
>      the salt in the air, or something like that.  The architect I
> heard seemed
>      to be saying that that (very expensive) process is virtually the
> only way
>      to save concrete structures near the ocean.

. . .>
>      Anyone know anything about this??
>
There was a talk about this at the most recent APT Conference by Scott
Kreilick.  He discussed the various deterioration mechanisms for concrete
and its reinforcing, and methods to change or reverse the electrochemical
processes that cause the rot.

Salts can rot both the concrete and the rebar.  Dissolved salts in the
concrete can crystallize when the water evaporates.  Thhe forces of
crystallization can break the concrete matrix.  Salts can also corrode the
steel, and corrosion jacking can ensue, or the steel will just dissolve.
Electrochemical repairs involve passing a current through the concrete,
using the reinforcing steel as one pole, and an external current carrying
material (usually metal), called an anode.  The anode is placed in
an electrolyte solution, chosen to give the desired results.

If the electrolyte and anode are chosen properly, and the current is run
through the concrete for a long enough time (up to two months), the
chloride ions will migrate to the surface of the concrete and the salt
deterioration processes will stop.

There was an extensive article in the APT Bulletin last year about
electrochemical realkalination repairs to concrete.  Hope this helps.

Dean Koga
New York