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Re: Water/cement ratio 1997 UBC

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It was suggested that there is no test to measure w/c ratio.  This is not
the case since there is a relatively new  test to meanure w/c ratio in the
field.  What  they do is take a sample of wet concrete and put it in a
micro-wave oven until the weight stops changing.  They then use the weights
to calculate a w/c ratio.  My belief that this is being used in the NYC
area if not other locations.  This test makes it possible to check the w/c
ratio in the field and to get some results while it is still possible to
use the data to do something about it.  It was my impression that this was
an ASTM standard but I cannot find it on their site.  I heard about this
test from William Phelan with Euclid Chemical Company.

While I believe that people often go overboard in specifying w/c ratios
there are some cases where it is appropriate and should be one of the
options.  It needs to be appreciated that  there is not always an objective
way of measuring certain types of future performance at the time of
construction.

On the other hand, if you are trying to control shrinkage setting a low w/c
ratio will often result in greater shrinkage.   In order to maintain the
low w/c ratio and to keep the concrete workable the contractor finds that
he has to add more water and cement to meet the criteria.  The increase in
water and cement directly leads to more shrinkage.


Mark Gilligan