Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Fw: Swimming Pool and Rebar/Anchor Bolt Corrosion in Adjacent Foundation

[Subject Prev][Subject Next][Thread Prev][Thread Next]

Nels,

Another option is to use a passive cathodic protection system utilizing sacrificial anodes.  I use to live in a townhouse complex where one of the units was having foundation problems (sliding down the hill).  They put in some steel underpinning and then wired the underpinning to some buried rods.

Thomas Hunt, S.E.
ABS Consulting


----- Forwarded by Tom Hunt/Americas/ABS on 06/26/2003 02:31 PM -----
THunt(--nospam--at)absconsulting.com

06/26/2003 02:12 PM

To
<seaint(--nospam--at)seaint.org>
cc
Subject
Re: Swimming Pool and Rebar/Anchor Bolt Corrosion in Adjacent Foundation






Nels,


You can do a lot to slow further corrosion if you can eliminate the moisture and oxygen from reaching the rebar.  With wet pool water this must have created a great battery effect.  You could fill all the cracks and then coat the entire footing but as you said this would only be a partial fix.  Another more exotic fix would be to install an inverter and run reverse flow DC through the rebar.  This is not uncommon in large refinery work where you have a lot of steel H piles that can be eaten up by the electricity in the soil from all the equipment grounding.  The trick would be knowing how much electricity to put in the system and where to attach the nodes.  One unknown with this system is that you are not sure if all the associated rebar is touching each other.  To do it right you might have to take some meter readings.  You may find some information on this from the NACE website:


http://nace.org/nace/index.asp



Thomas Hunt, S.E.

ABS Consulting




"Nels Roselund, SE" <njineer(--nospam--at)att.net>

06/26/2003 09:52 AM

Please respond to
<seaint(--nospam--at)seaint.org>

To
<seaint(--nospam--at)seaint.org>
cc
Subject
Swimming Pool and Rebar/Anchor Bolt Corrosion in Adjacent Foundation







I've looked at a residence with horizontal cracks in the foundation stem walls, varying from hairline to 1/4"+, visible from the crawl space.  Also visible from the crawl space and from the outside perimeter of the house: vertical hairline cracks at anchor bolts at the tops of stem walls.  The house is about 40 years old.  Corroded rebar is visible in areas where the rebar is close to the vertical face of a stem wall and the surface has popped off; rust-color can be seen deep in the largest of the horizontal cracks.  There is a swimming pool near one side of the house.
 
This is the second house of about the same era, each with a nearby swimming pool, that I've looked at with this condition.  The owner of the first one was trying to get insurance money for earthquake damage for the cracks and was not interested in my stated opinion on their cause.  The more recent case owner wants to know what to do about the cracks.
 
It seems that chlorinated swimming pool water [splash or overflow] is the culprit.  It won't do any good to fill the cracks, as the owner had hoped.  It seems to me that the concrete is permanently damaged, now having a low pH, and subject to continued corrosion, even if kept dry.  The corrosion process will continue, probably whether or not the water source is brought under control.  Permanently intercepting swimming pool splash and overflow, and draining it away from the house and the site is important, and may slow the process, but a real fix seems to be a much more intrusive replacement project.
 
Have you found and dealt with this kind of problem?  My guess is that there are a lot of these conditions out there waiting to be found.
 
Nels Roselund
Structural Engineer
South San Gabriel, CA

njineer(--nospam--at)att.net