F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

56
(lb)
(lc)
Properties of structural concrete
Suppose the target mean strength so obtained is 43 N/mm 2 at
28 days.
Given the type of cement and aggregate, use Table 2.7-2 to
obtain the compressive strength, at the specified age, that
corresponds to a free w/c ratio of 0.5.
Suppose ordinary Portland cement and uncrushed aggregate
are used. Then Table 2.7-2 shows that the compressive strength is
40 N/mm 2 at 28 days (and 27 N/mm 2 at 7 days and so on). This
pair of data (40 N/mm 2 , w/c ratio = 0.5) will now be used to
locate the appropriate strength-w/c ratio curve in Fig. 2.7-2, as
explained below.
In Fig. 2.7-2, follow the 'starting line' to locate the curve which
passes through the point (40 N/mm 2 , w/c ratio = 0.5); in this
particular case, it is the fourth curve from the top of the figure.
This curve shows that, to obtain our target mean strength of
43 N/mm 2 , we need a w/c ratio of 0.47.
Note that in Fig. 2.7-2 a curve happens to pass almost exactly
through our point (40 N/mm 2 , w/c ratio = 0.5); this does not
Ne
e
-z
0•4 0·6 Q-7 0·8 0•9
water I cement ratio
Fig. 2.7-2 Relationship between cube compressive strength and free-water/
cement ratio (after DoE [35])