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RE: BOCA, exposed concrete 4,500psi

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Having worked in south Florida, it is common practice to specify the
minimum amount of cement in a mix that corresponds with a 5 bag,  6 bag,
6 1/2 bag mixes.  These typically range from 4500-7000 psi.  The idea is
that the more cement in the mix reduces the amount of voids and
therefore the permeability (not entrained air which actually will tend
to reduce the permeability of the concrete) of the concrete which tends
to "seal up" the reinforcement from the salts in the air (or from the
road in the North).  

Specifying minimum strength is a round-a-bout way of accomplishing this.

-----Original Message-----
From: Bill Polhemus [mailto:polhemus(--nospam--at)]
Sent: Thursday, August 26, 1999 12:53 PM
To: seaint(--nospam--at)
Subject: RE: BOCA, exposed concrete 4,500psi

I think it would be interesting for you to note what the actual concrete
strengths are that you're getting on your job.

My experience here in Texas is that you'd have to "go some" to get less
4800-5000 psi concrete, even if 4000 is specified. I have specified up
9500 psi before with scarcely a murmur from concrete suppliers. If you
specify 4500 psi, the suppliers say "comin' right up!" (with Texas
drawl, of

Besides, I would think concrete chemistry would have much more to do
imperviousness to chemical attack viz. from deicing salts than simply
specified strength.

> -----Original Message-----
> From: Peieng5590(--nospam--at) [mailto:Peieng5590(--nospam--at)]
> Sent: Thursday, August 26, 1999 10:46 AM
> To: seaint(--nospam--at)
> Subject: Re: BOCA, exposed concrete 4,500psi
> Here in Maryland our local codes fokes want us to use 4,500
> psi concrete for all non-residential exterior concrete...