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Re[2]: W/C ratio, was:purposely permeable concrete

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Is there some corrosion problems at this site?  We're having to use 4500
psi, Type V concrete with a .45 w/c ratio for all of our jobs in Las Vegas.
 Some of the California sites require this also if the ground is hot.

Neil Moore, S.E.

>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

The "soils" (Geotechnical) Engineer is likely recommending a low water to cement
ratio to mitigate high sulfate content in the soils.  What does their report say
about sulfate content in the soil?  See 1997 UBC Table 19-A-4.  It is unlikely 
the they are addressing strength of concrete issues.  As a GE, I would leave 
that for the SE.

Tom Benson at Lowney Associates