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)

Aggregates 23
of concrete mainly indirectly, through its important effect on the water/
cement ratio required for a specified workability. A badly graded
aggregate requires a higher water/cement ratio and hence results in a
weaker concrete.
In practice, the grading of an aggregate is determined by sieve analysis,
in which the percentage of the aggregate passing through each of a series of
standard sieves is determined. For the grading to comply with BS 882, the
percentages for the coarse aggregate should fall within the limits in Table
2.3-1; for the fine aggregate, the limits should fall within the overall limits
in Table 2.3-2 and, additionally, not more than one in ten consecutive
samples shall have a grading outside the limits for any of the gradings C, M
or Fin Table 2.3-2. In Table 2.3-2, the gradings of the fine aggregates are
divided into three zones, ranging from the coarser zone C through the
medium zone M to the finer zone F. The division into zones is largely based
on the percentage passing the 600 ,urn (No. 25) sieve. It has been found
that in a fresh concrete mix, the content of the fine aggregate passing the
600 ,urn sieve has an important effect on the workability. Furthermore,
many naturally occurring sands divide themselves at this particular size.
Table 2.3-1 Grading limits for coarse aggregate
Percentage by weight passing the standard sieves
Nominal size of aggregate
Standard
sieve (rnrn) 40 rnrn to 5 rnrn 20 rnrn to 5 rnrn 14 rnrn to 5 rnrn
50.0 100
37.5 90-100 100
20 35-70 90-100 100
14 90-100
10 10-40 30-60 50-85
5 0-5 0-10 0-10
Table 2.3-2 Grading limits for fine aggregate
Percentage by mass passing BS sieve
Additional limits for grading
Sieve Overall
size limits c M F
10.00 rnrn 100
5.00 rnrn 89-100
2.36 rnrn 60-100 60-100 65-100 80-100
1.18 rnrn 30-100 30-90 45-100 70-100
600 .urn 15-100 15-54 25-80 55-100
300 .urn 5-70 5-40 5-48 5-70
150 .urn 0-15