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RE: W/C ratio, was:purposely permeable concrete

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Why is the soils engineer specifying w/c ratio?

The old theory is that if you lower the w/c ratio you will have less shrinkage.  A lower w/c ratio will reduce bleed water and reduce permeability, but has not much effect on shrinkage.  

Harold Sprague

-----Original Message-----
From:	Jeff Smith [SMTP:smthengr(--nospam--at)]
Sent:	Monday, June 08, 1998 11:14 AM
To:	seaoc(--nospam--at)
Subject:	W/C ratio, was:purposely permeable concrete

On a similar subject, I am working on a job where the soils engineer
required a concrete water cement ratio of .45 for slabs on. Basically this
means you end up with a 5000 psi or more mix unless you substitute additives
in lieu of more cement. Locally, the additives costs at least as much as the
cement. The slabs only need to be 3000 psi for structural reasons. I believe
the w/c requirement is for permeability reasons. Has anyone had a similar
experience with an economical work around?

Jeff Smith