Mix design - Concrete Mix Design, Quality Control and Specification - page 191

Mix design
Ken Day's specific surface/mix suitability factor (MSF) technique has been
used in many countries over more than 30 years and has been the basis for
“instant” mix designs given over the telephone for immediate use, with no
more information than a sand grading, a verbal description of the appear-
ance of the coarse aggregate, and the use to which the concrete was to be
put (details later). The system still works and provides a necessary require-
ment for the degree of cohesion (= sandiness) needed for a mix to avoid
segregation at any required workability. However, the consequences of
exceeding this necessary minimum are now less severe, since additional
admixture rather than additional cement is now the remedy.
It had been intended to eliminate this technique from the new edition,
but several people, Roberto Torrent prominent among them, invited to an
informal review of the chapter protested that they still used the technique
to at least provide a lower limit to mix fineness and, in some cases, as a
basis for correcting mixes when change occurred in the grading of one or
more of the constituent materials of a mix in current use. The method is
therefore still provided toward the end of this chapter.
Several other factors complicate the mix design problem to the extent
that the latest edition of Francois de Larrard's excellent work Concrete
Mixture Proportioning runs to 400 pages. It is our intention here to reduce
the necessary theory to a relatively few pages by combining theory with a
degree of experimentation. It is contended that the process of mix design
needs to be integrated with that of quality control of both incoming mate-
rials and the resulting concrete, and that even small producers need to
remain alert to both positive and negative changes in the situation (i.e.,
to future technical developments). Two consequences arise from this con-
tention. One is that every producer needs to either establish his own trial
mix facility or reach an agreement with an independent lab, so as to stay
amenable to offers of alternative materials and, subject to the provision
of encouraging data by the offering supplier, prepared to carry out trial
mixes, preferably actually used in a noncritical location. The other con-
sequence is that the day when it might have been useful for purchasers of