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Re: Spec needed for 3000 psi concrete

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Stan Scholl wrote,
"I agree. Specify 2500 psi. If good quality conc.is desired for water
tightness and other desireable qualities, also specify a min. cement
content, so that you don't end up with about a 4 sack mix. If a min.
cement content is specified the end result will be much more than 3000psi
but you don't have to pay for a deputy inspector. Note that I said "end
up with 4000 psi".  My point is that it is not usually necessary to
specify more than 2500psi. "
 
    Thank you Stan! I've always wondered why so many specs list a relatively low strength but require w/c = 0.40 or even lower, guaranteeing that the concrete would be much stronger than the specified strength. Now I know. But why is it done outside the UBC area?
 
Jim Getaz
Winchester, Va.