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)

58 Properties of structural concrete
minimum must be used- resulting in a reduced w/c ratio and hence a
higher strength than the target mean strength. If the calculated cement
content is higher than a specified maximum, then the specified strength
and workability cannot simultaneously be met with the selected
materials; try changing the type of cement, the type and maximum size
of the aggregate.
Step 4 Determining the aggregate content
Having calculated the water content and the cement content, the total
aggregate content is in practice obtained quickly from a chart in the DoE
document [35]. However, it can be easily calculated from first principles.
~or each cubic metre of fully compacted fresh concrete,
[ volume occupied] = 1 _ cement content _ water content
by the aggregate Yc Yw
(2.7-3)
where Yc ( =l= 3150 kg/m 3 ) is the density of the cement particles and
Yw ( = 1000 kg/m 3 ) is that of water. Therefore
total aggregate content (kg/m 3 )
= Ya X [volume occupied by aggregates (eqn 2.7-3)] (2.7-4)
where Ya is the density of the aggregate particles. The DoE [35]
;~~~m~~~~,s }~:t ~~~~~~!~r::~~eng~~e avaa~~b~~o6" ~~~~~d f~~ t~;~s~:~
aggregate.
Step 5 Determination of the fine and coarse aggregate contents
How much of the total aggregate content should consist of fine aggregate
depends on the grading of the latter. Table 2. 7-4 classifies fine aggregate
into grading zones 1, 2, 3 and 4. The general principle in mix design is
this: the finer the grading of the fine aggregate (i.e. the larger its surface
area per unit weight) the lower will be the proportion, expressed as a
percentage of the total aggregate, required to produce a concrete of
otherwise similar properties.
Table2.7-4 Grading limits for DoE mix design procedure
Percentage by weight passing standard sieves
Standard Grading Grading Grading Grading
sieve zone 1 zone 2 zone 3 zone 4
10mm 100 100 100 100
5mm 90-100 90-100 90-100 95-100
No.7 (2.36 mm) 60-95 75-100 85-100 95-100
No.14 (1.18 mm) 30-70 55-90 75-100 90-100
No. 25 (600,um) 15-34 35-59 60-79 80-100
No. 52 (300 ,urn) 5-20 8-30 12-40 15-50
No. 100 (150,um) 0-10 0-10 0-10 0-15