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Re: Water/cement ratio 1997 UBC

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> 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.

How does this test account for water that is already chemically bound to the
cement?  It seems like it would be a rather rough approximation.  Please pass
along any references you can find on the topic.

> 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.

This may depend on the kind of work that is being done, but letting the
contractor alter the mix on site seems hazardous, as you may not get the desire
concrete strength, either.  The test data for the mix would no longer be
valid.  It would be better to deal with the problem ahead of time by using
admixtures instead to get a level of workability that the contractor is
comfortable with.