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Re: CMU in water/wastewater

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Bill,

Personally, I probably would not be concern in general with the use of CMU
vs. concrete.  While you can likely get a concrete mix that is in general
denser than most or all CMU, you could likely still get a CMU block that
would be dense enough for some of the concerns that you raise.  To me, the
biggest concern would be whether it is hollow CMU or grouted solid.  If
you choose to use "heavy weight" CMU that is fully grouted (at least where
there will water at some times and no water at others...especially if it
is subjected to freezing), then I would think that it likely would not be
much different than using concrete in terms of exposure type
situations/issues.

The use of "heavy weight" CMU and fully grouting it might drastically
reduce the cost benefits of CMU, especially if you use 12" block and if it
must be reinforced (lifting those 12" CMU blocks usually results in more
labor, especially if they have to be lifted over rebar).  You might also
look into precast concrete...it might have cost savings relative to CIP
concrete and even masonry...and any concerns about exposure to moisture
should be moot as you can specify a nice dense concrete just as you would
if you use CIP concrete.

Regards,

Scott
Adrian, MI

On Wed, 14 Dec 2005, Sherman, William wrote:

> I have been asked to consider the use of CMU for flow divider walls in a
> wastewater basin, for cost reduction vs concrete.  My understanding is
> that CMU has been used in submerged conditions in water treatment, but
> I'm not sure about wastewater applications.  Do any others have
> experience with submerged CMU?
>
> I would assume that submergence in water actually helps keep a "moist
> cure" and prevents drying, although the top of wall would be above the
> water surface.  Anyone had any problems with the exposed portion of CMU
> due to differential moisture or due to potential freezing in a moist
> condition?  Or problems during maintenance with basins dewatered, i.e. a
> change in moisture conditions?
>
> The location in the wastewater treatment process is at a point where
> hydrogen sulfide attack is not a significant problem.  But it seems
> undesirable to allow waste materials to seep into relatively porous CMU
> vs a denser concrete, even if the CMU maintains its strength.  Any other
> thoughts on such usage?
>
>
> William C. Sherman, PE
> (Bill Sherman)
> CDM, Denver, CO
> Phone: 303-298-1311
> Fax: 303-293-8236
> email: shermanwc(--nospam--at)cdm.com
>
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