Properties of concrete - Concrete Mix Design, Quality Control and Specification - page 92

5.1.8 Freeze-thaw attack
Under conditions of freezing and thawing, concrete can suffer significant
damage, particularly if the water contains salt. The typical solution to
potential freeze-thaw damage is air entrainment, which has been effective
over the years. One bone of contention is whether high strength concrete
still requires air entrainment for frost resistance due to the small pore sizes
rendering the water not freezable. There is no question that test cylinders
cured in a water tank and frozen while saturated will show a benefit from
air entrainment in even very high strength concrete. However the self-
desiccation and the difficulty of resaturation would seem to suggest that
air entrainment may not be necessary.
5.2 MECHANICAL PROPERTIES
5.2.1 Compressive strength
Compressive strength is well established as the primary criterion of concrete
quality. Mix design has generally meant designing a mix to provide a given
strength. Although strength is often not the most important requirement,
the reason for its use as a performance criterion is clearly shown by the step
following its selection in most mix design procedures. This is to convert the
strength requirement into a water to cement ratio. The relationship between
strength and w/c is generally attributed to Abrams (1929). Actually Féret
(1896) preceded him and proposed a more accurate proportionality, that
between strength and the ratio of cement to water plus voids (Neville, 2011).
It may be that accuracy was not the important thing, partly because the w/c
itself was arguably more important than the strength it was assumed to
represent. Partly because the simplicity of the concept was as important as
its accuracy.
Although the concept of w/c is simple, and its approximate implementation
is also simple, it would be a difficult criterion to enforce by testing. An
accurate way of establishing the w/c ratio of a given sample of production
concrete (of which the w/c ratio versus strength relationship has already
been established) is to test its strength. It is perhaps unfortunate that w/c
ratio rather than c/w ratio came to be the popular parameter since, over a
substantial range, strength has an almost linear relationship with c/w ratio.
So much of the importance of strength is as a test method and a means of
specification for w/c ratio.
A primitive way of designing a mix, assuming that only one fine and one
coarse aggregate were involved, would be to make a mix of any reasonable
proportions (say 1:2:4) and fairly high slump (say, 100 mm). If a sample
of this concrete were heavily vibrated for several (say, 15) minutes in a
sturdy container (such as a bucket, not as small as a cylinder mold) then