Mix design - Concrete Mix Design, Quality Control and Specification - page 202

To be at their most competitive, concrete producers need to either estab-
lish their own trial mix facility or reach an agreement with an indepen-
dent lab to assess offers of alternative materials. Subject to the provision of
encouraging data by the offering supplier, the concrete producer can carry
out trial mixes, preferably actually used in a noncritical location. There may
be some materials or combinations of materials that a technically advanced
specifier knows to be unsatisfactory in some respect but, this excepted, it
is undesirable that the prospective purchaser should inhibit the process of
optimisation or the selection of material suppliers by the concrete producer,
although he may reasonably require a wider range of test and performance
records of a proposed mix before approval.
A major advantage of this proposal is that a producer would develop a
standard range of mixes for all purchasers with the same requirements.
This would be of substantial assistance in achieving close quality control
and enable the producer to economically provide a more complete range of
tests. Specifiers and purchasers should also be aware that the field of such
materials is undergoing a period of rapid change and that national stan-
dards and the like may well not be up to date on all possibilities.
But now it is time to get Hudson's more detailed advice. For this edition
Hudson has contributed his methods of mix origination. Hudson is cur-
rently responsible for operational performance of 16 million cubic metres
of concrete per annum produced in 485 plants in 12 countries, so he is
worth taking notice of.
Obviously, there are many different methods of concrete mix design in
practice today. These designs range from the very basic 1 shovel of cement,
2 shovels of sand, and 4 shovels of coarse aggregates, through to some
sophisticated software programs that require proprietary test methods and
results to determine constituent proportions.
In this chapter, we will discuss a successful method of concrete mix
design that does not rely on individual constituent characteristics, but
rather how a group of materials perform when proportioned together for
a given production facility or batch plant. There are many methodologies
for designing concrete mixes. In reality, the scope or range of material
proportions that can make a workable concrete are relatively narrow, with
some broad rules of thumb and common sense setting some boundar-
ies. In this chapter, we will not discuss high-performance or value-added
concretes, but concentrate on the main volume of concrete that most com-
mercial ready mix concrete plants will produce and deliver, the “vanilla”
concrete (normal grade strength and workability concretes) (20-40 MPa,
50-150 mm slump). These concretes will typically consist of one or two
sands, anywhere from one to six coarse aggregates, a cement (maybe ordi-
nary Portland cement or a cement that has some supplementary cementi-
tious materials (SCMs) such as fly ash or slag added). Some admixtures
(normally water reducing and/or air entraining) and of course water.