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)

DoE mix design method 57
always happen, so that in practice it is usually necessary to
interpolate between two curves in the figure.
(1d) If the wlc ratio as obtained in Step (1c) exceeds the maximum wlc
ratio specified for durability (see Table 2.5-7), then adopt the
lower value-resulting in a concrete having a higher strength than
required.
Step 2 Determining the water content
Given the slump or VB time, determine the water content from Table
2.7-3.
In using Table 2.7-3, when coarse and fine aggregates of different
types are used, the water content W is estimated as follows:
W = ~Wr + jwc (2.7-1)
where Wr = water content appropriate to the type of fine aggregate;
We = water content appropriate to the type of coarse aggregate.
The aggregate type in Table 2.7-3 refers to all the aggregates used
and not just the coarse aggregate. Indeed, the fine aggregate has a
considerably greater specific surface area and hence a greater influence
on the workability: this explains the greater weight, ~, assigned to Wr in
eqn (2.7-1).
Step 3 Determining the cement content
C (k I 3) _ water content (from Step 2)
ement content g m - 1 . (f S )
w c ratio rom tep 1
(2.7-2)
The value given by eqn (2.7-2) should be checked against any maximum
or minimum cement contents that may have been specified, for
durability for example; see Durability in Section 2.5(e). If the cement
content calculated from eqn (2.7-2) is below a specified minimum, this
Table2.7-3 Approximate free-water contents (kg/m 3 ) required to give various
levels of workability (after DoE [35])
Slump (mm): 0-10 10-30 30-60 60-180
VB time (seconds): > 12 12-6 6-3 3-0
Maximum
size of Type of
aggregate (mm) aggregate
10 Uncrushed 150 180 205 225
Crushed 180 205 230 250
20 Uncrushed 135 160 180 195
Crushed 170 190 210 225
40 Uncrushed 115 140 160 175
Crushed 155 175 190 205