“Maximum water-cementitious material ratios (w/cm) of 0.40 to 0.50 that may be required for concretes
exposed to freezing and thawing, sulfate soils or waters, or for corrosion protection of reinforcement will
typically be equivalent to requiring f’c of 5000 to 4000 psi, respectively. Generally, the required average
compressive strengths, f’cr, will be 500 to 700 psi higher than the specified compressive strength, f’c.
Because it is difficult to accurately determine the w/cm of concrete, the f’c specified should be reasonably
consistent with the w/cm required for durability. Selection of an f’c that is consistent with the maximum
permitted w/cm for durability will help ensure that the maximum w/cm is not exceeded in the field. For
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example, a maximum w/cm of 0.45 and f’c of 3000 psi should not be specified for the same concrete
mixture. Because the usual emphasis during inspection is on concrete compressive strength, test results
substantially higher than the specified compressive strength may lead to a lack of concern for quality and
could result in production and delivery of concrete that exceeds the maximum w/cm.”