Specification - Concrete Mix Design, Quality Control and Specification - page 109

Specification
In the third edition of this topic, Ken Day expressed the hope that the
practice of mindlessly specifying minimum cement contents and requiring
mixes to be submitted and not subsequently varied will have finally died
out. However, at the publication of this edition, the practice is still alive.
It is certainly not confined to the United States; British and European
codes require minimum cementitious contents and maximum water to
cementitious materials ratios (w/cm), and transportation departments in
Australia also specify particular penetrability performance. Globally most
consultants still require mixes to be submitted for approval.
The margin between specified strength and the mean strength required to
provide it represents an enormous worldwide expenditure in cost (and green-
house gas) and billions of dollars are still spent in rectifying deteriorated
old concrete and in investigating understrength new concrete. These costs
are only reducible by improved technology in concrete production and
smarter in specification. Specifiers must have a better understanding of the
true requirements of their structure and must ensure the development of
better technology in concrete production by allowing producers to profit
by it. However it is important not to go overboard in increasing costs by
excessive specification detail where not essential.
Chapter 10 of the current edition makes it very clear that the concrete
producer must be responsible for designing and controlling concrete mixes,
if only because control action must be based on early age results, and taken
without waiting for incontrovertible justification. However, there are other
reasons. The producer must obtain cooperation from his suppliers and he
should be allowed to profit from the development of his expertise. Producers
should be encouraged to establish standard mixes and should be allowed to
use them wherever possible. Some purveyors of materials, including cement
replacement materials and admixtures, and of proprietary mix design and
control systems, will be able to offer substantial assistance.
It might be certainly simpler, if you have the necessary knowledge, to
specify that particular aggregates, cement and other materials that shall be
used in conservative proportions than to specify limits on the properties of