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RE: Lean concrete as structural fill?

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ACI 116R, Cement and Concrete Terminology, defines "lean concrete" as
"concrete of low cement content" and defines "controlled low strength
materials" as "materials that result in a compressive strength of 1200
psi or less".  As others have noted, "controlled low strength material"
seems to be the preferred term for what is also called "flowable fill".

I tend to think of lean concrete as concrete with a 28-day compressive
strength of less than 3000 psi but probably greater than 1200 psi, i.e.
just a relatively weak concrete due to the low cement content.  I would
expect "lean concrete" to have a "normal" slump range vs flowable fill.
I have used flowable fill/ controlled low strength material as fill
material, with admixtures to improve flowability and resulting in the
300 psi compressive strength range.  

Either can be used, depending upon your strength and flow expectations. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

> -----Original Message-----
> From: Jim Wilson [mailto:wilsonengineers(--nospam--at)] 
> Sent: Wednesday, July 06, 2005 1:29 PM
> To: seaint(--nospam--at)
> 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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