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Re: W/C ratio, was:purposely permeable c

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Have you considered a vapor barrier?  If the purpose is to prevent moisture 
migration thru the slab, I think that a more positive method than a low w/c 
should be used.

I have seen effloresence on vinyl tile here in *dry* Tucson.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Jeff Smith wrote:

. > The soils report says...
. > 
. > " to further reduce the potential for moisture to migrate through the
. > slabs-on-grade as a vapor, as well as to reduce concrete shrinkage, we
. > recommend that the concrete mix specified for the slab on grade floors 
. > have a water/cement ratio of .45 or less."
. > 
. > This is a non-profit low income housing project, in many places there is
. > sheet vinyl flooring. The site soils are expansive and the top foot or so 
. > is disturbed, so the site work includes removing several feet of soil, 
. > bringing in new soil and raising the elevation of the entire site due to 
. > some civil/road/grading issues. I have been told that certain admixtures 
. > and plasticizers yield unpredictable finish results because the top 
. > hydrates at a different rate than the center. Given the same cost, I 
. > would prefer adding cement rather then admixtures.
. > 
. > Jeff Smith
. >