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Re: Concrete Slabs-on-Grade

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Specifying concrete for slabs by psi is a mistake in my opinion. It is
easy to get high psi with crappy mixes. Specifying as large of aggregate
as possible, making the contractor use decent pumps (not grout pumps),
using adequate thickness, placing joints at adequate spacing, specifying
at least a 5 sack mix (of PC- not part PC and part fly ash), controlling
water, wetting the subgrade and curing will usually result in a quality
job as it always has.

Stan Scholl, P.E.
Laguna Beach, CA

On Tue, 30 Jul 2002 12:01:25 -0500 "Jim Kestner"
<jkestner(--nospam--at)somervilleinc.com> writes:
> It seems today that there are more problems (curling, shrinkage 
> cracks,
> etc.) with concrete slabs-on-grade then in years past. Years ago 
> when we
> used 3000 psi and few if any additives, there were fewer problems. 
> What has
> changed?
> 
> Today, we use 4000 psi concrete, more admixtures, faster schedules, 
> less
> skilled workers, etc. I seemed to recall that we use 4000 psi in 
> slabs for
> more durability but we really don't need much durability in schools,
> offices, clinics, etc. I could see using 4000 psi for industy or 
> warehouses
> and sidewalks...perhaps 3500 psi for retail. Should we reconsider 
> where we
> are using 4000 psi?
> 
> Jim K.
> 
> 
> 
> 
> 
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