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RE: Corrosion in Water Reservoirs

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Too bad you didn't look at ACI 350R-89 "Envinronmental Engineering
Concrete Structures" before doing your design.  For one thing, 1-1/4"
cover doesn't seem nearly enough to me, 2" would be better for a surface
which will be constantly damp from condensation.  Also, what crack
widths do you expect?  If you used 24.000 psi allowable steel stress or
USD, you can expect to get sufficiently wide cracks to allow moisture to
migrate up to the bottom bars and eventually corrode them, with spalling
of the cover due to the greater volume occupied by the rust.  As far as
carbonation, I've only heard it referred to when heaters used to keep
fresh concrete from freezing are not properly vented.  At this point,
your only hope is a waterproof coating, which will probably have to be
applied to a dry surface depending on the coating manufacturer's
recommendations.  ACI 350 may have recommendations for you

> ----------
> From: 	Sleiman Serhal[SMTP:mony(--nospam--at)]
> Sent: 	Sunday, November 02, 1997 11:21 PM
> To: 	seaoc(--nospam--at)
> Subject: 	Corrosion in Water Reservoirs
> I have a water reservoir in the basement of an RC house. The cover of
> the reservoir is part of the concrete floor.
> The question is: do I need to waterproof the bottom of the slab (cover
> reservoir) to protect my reinforcement ?
> I have used a concrete cover of 3cm (1.25") in the slab because I
> didn't
> want to increase the slab thickness.
> I'm asking this question because I have read that carbonation of
> concrete - thus weakening of the concrete cover ability to protect the
> reinforcement from corrosion - is highest when relative humidity is
> around 70% and temperature is around 25°C (80°F). Since the relative
> humidity in the reservoir will always be 100%, I'm not sure if this
> leads to high carbonation rate or not.
> Thanks in advance,
> Moni Serhal, MSCE