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RE: Lean concrete as structural fill?

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Interesting question.  I was recently on a project where the geotech spec'd
out something very similar.

Their recommendation was:
"Controlled fill below foundations should consist of either crushed Grading
W base course or City Class S flowable fill"

According to the City Specs:
Class S Design Comp. Strength = 200 psi*
        28 Day Comp. Strength = 200 psi
* Class S sand/cement slurry shall obtain a 7-day compressive strength of
200 psi.

So, you might want to check with your local City Standard Specifications and
see if they have some sort of a sand/cement slurry specification and go with
that.

Dave Maynard, PE
Gillette, Wyoming

> -----Original Message-----
> From: Jim Wilson [mailto:wilsonengineers(--nospam--at)yahoo.com]
> Sent: Wednesday, July 06, 2005 1:29 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Lean concrete as structural fill?
>
>
> We are working with a contractor who has asked to use
> lean concrete as structural fill under footings and
> slabs for a single story building.  Through google
> searches, I've come up with matches to lean concrete,
> cement bound material (CBM) and flowable backfill.
> Are these all essentially the same product?  They
> don't appear to be well defined in terms of material
> properties, though I found one reference to 500psi
> minimum strength.  The flowable fill I have worked
> with in the past was 700psi. Also, these products are
> only mentioned in the context as being used for
> roadway sub-bases.  I'm guessing they are not commonly
> used in building construction because they are
> relatively costly compared to gravel backfills.
>
> By comparison to regular gravels, this seems very
> acceptable as structural fill, but I'm looking for a
> second opinion.  And is there an appropriate spec or
> even a product name to call this material for building
> use?
>
> Regards,
> Jim Wilson, PE
> Stroudbsurg, PA
>
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