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RE: Flowable Backfill

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"Flowable backfill" is what is called CLSM (Controlled Low Strength
Material) by ACI and "controlled density fill" by others. It's basically a
high water-cement ratio concrete with little or no course aggregate,
designed to have a low enough strength so you can excavate it later if you
have to, but it's still a lot stronger than dirt. If you have access to
ACI's Manual of Practice, it's described in ACI 229R.  Typical compressive
strength is a few hundred psi. Most ready mix plants have mix designs for
this material in our area, and your highway department probably has some
standard mixes as well.

-----Original Message-----
From: Ed Fasula [mailto:tibbits2(--nospam--at)metro.lakes.com]
Sent: Monday, August 28, 2000 3:34 PM
To: seaint(--nospam--at)seaint.org
Subject: Flowable Backfill


We're designing the reinforced concrete cap for a cylindrical fiberglass
wetwell.  The mfgr. calls for the cap slab to bear on perimeter compacted
soil.  Since the cap will be at grade with heavy truck traffic, I asked the
geotechnical engineer to spec the backfill & compaction.

He recommended "flowable backfill."  Which I understand as basically a weak
mix of concrete.  We called a couple of ready-mix plants and they were not
familiar with it.  Can someone give us the pros & cons of this stuff and a
design mix or a lead to one?  Is it safe to just give the mix design to the
plant and have them treat it as a typical concrete order?

Regards,

Ed Fasula E.I.T.



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