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)

60 Properties of structural concrete
Stepl
From Table 2.7-2, at the standard water/cement ratio of 0.5, the 28-
day strength is 40 N/mm 2 • Figure 2.7-2 then shows that if a w/c ratio
of 0.5 gives 40 N/mm 2 then the w/c ratio that gives the target mean
strength (43 N/mm 2 ) is 0.47 approximately. This is inside the permitted
maximum of 0.60. Therefore adopt a w/c ratio of 0.47.
Step2
From Table 2.7-3, for 10 mm nominal maximum size uncrushed
aggregate, the water content to give a 10-30 mm slump is 180 kg/m 3 .
Step3
From eqn (2.7-2),
cement content = J.~~ = 385 kg/m 3
> 300 kg/m 3 and < 550 kg/m 3
Step4
From eqns (2.7-3) and (2.7-4), total aggregate content
[ 385 180] 3
= 2600 1 - 3150 - 1000 = 1815 kg/m
StepS
From Fig. 2. 7-3, for a slump of 10-30 mm, a w/c ratio of 0.47 and a fine
aggregate in grading zone 4, the proportion of fine aggregate is 27.5 to
32% by weight, say 30%. Therefore
Ans.
fine aggregate content = 0.30 x 1815 = 545 kg/m 3
coarse aggregate content = (1 - 0.30) x 1815 = 1270 kg/m 3
The required mix proportions are:
cement content: 385 kg/m 3
water content: 180 kg/m 3
fine aggregate content: 545 kg/m 3
coarse aggregate content: 1270 kg/m 3
Example 2. 7-3
Repeat Example 2.7-2 if the target mean strength is 32 N/mm 2 at 7 days,
and all other given data remain unchanged.
SOLUTION
Stepl
From Table 2.7-2, at the standard w/c ratio of 0.5, the 7-day strength is
27 N/mm 2 • In Fig. 2.7-2, the starting line is intersected by a curve at 25
N/mm 2 and one at 30 N/mm 2 • By visual interpolation, plot the curve
that intersects the starting line at 27 N/mm 2 • From this interpolated
curve, we see that if a w/c ratio of 0.5 gives 27 N/mm 2 at 7 days, then the
w/c ratio that gives the 7-day target mean strength (32 N/mm 2 ) is 0.46
approximately.