Page 262 - Civil Engineering Project Management, Fourth Edition

Civil Engineering Project Management
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Table 19.3
Weight of aggregate to be used per 100kg of cement (kg)
Grade of concrete BS 5328:1981 Ordinary Prescribed Mixes*
Max. size 40mm Max. size 20mm
Workability Workability
Medium High Medium High
C20P 660 600 600 530
C25P 560 510 510 460
C30P 510 460 460 400
Workability – slump (mm) 50–100 80–170 25–75 65–135
*Grades C20P and C25P were later designated Standard Mixes ST4 and ST5 in
BS 5328:1997 as shown in Table 19.2.

Table 19.4
BS 5328:1981 Percentage by mass of fine aggregate to total aggregate

Grade of concrete Sand Percentage of sand (fine aggregate in total aggregate)
grade Max. size 40mm Max. size 20mm

Workability Workability
Medium High Medium High
Zone 1 35% 40% 40% 45%
C20P Zone 2 30% 35% 35% 40%
C25P Zone 3 30% 30% 30% 35%
C30P Zone 4 25% 25% 25% 30%
Workability – slump (mm) 50–100 80–170 25–75 65–135
Grades C7.5P, C10P and C15P have been omitted.

19.4 Grading of aggregates and their suitable mixing

The 1981 edition of BS 5328 (referred to in Section 19.1) provided a useful table
showing the amount of aggregate per 100 kg cement in what were then
termed (see Section 19.2), Ordinary prescribed mixes as shown in Table 19.3, and
the percentage of fine aggregate to total aggregate in these mixes as shown in
Table 19.4. The grading of the fine aggregate was then as BS 882:1973 which
defined the grading for four zones of fine aggregate as shown in Table 19.5.
Although BS 882:1973 has now been revised, Tables 19.3–19.5 are still of
practical use as a guide to determining the ratio of fine to coarse aggregate
required to make a dense mix. Of the four Zone gradings shown in BS
882:1973, Zones 2 and 3 were the most used for forming a suitable concrete
mix. Zone 1 grading (the coarsest) tended to give a harsh concrete and also