Civil Engineering Project Management (4th Edition)

Table 19.1
Site concreting and reinforcement 237
British Standard CP114:1948 Standard mixes by weight
Equivalent volume Works Dry weight of aggregates per 50 kg cement (kg)
mix proportions cube at
cement:sand: 28 days Sand Coarse aggregates
aggregate (N/mm 2 ) 38 mm Max. size 19 mm Max. size
Workability Workability
Low Medium Low Medium
1:1:2 30 65 165 135 145 110
1:11 ⁄2:3 25.5 80 200 165 165 135
1:2:4 21 90 225 190 190 155
Compaction factor 0.82–0.88 0.88–0.94 0.82–0.88 0.88–0.94
Slump (mm) 25–50 50–100 12–25 25–50
Notes: (1) Weights are based on use of Zone 2 sand (see Table 19.4) aggregates of relative
density 2.6. If Zone 3 sand (finer) is used, reduce sand weights by about 10 kg and
increase coarse aggregate by same amount. If the sand is crushed rock, reduce weight of
coarse aggregate by 10 kg. (2) Columns for aggregate size have been reversed from that
shown in BS 114 to agree with order used in Tables 19.2–19.4.
BS 5328 has been withdrawn in December 2003 and superseded by BS
8500:2002 Parts 1 and 2 which adopt the European Standard EN 206-1:2000
which is a complex, many-paged document covering many types of concrete
and requirements for differing circumstances which do not need to be considered
here. However, it maintains the same four categories of concrete
specification as BS 5328:1997, namely – ‘designed concrete’; ‘prescribed concrete
mixes’, ‘standard concrete mixes’, and ‘designated concrete’. These are
described in Section 19.2.
Where a characteristic strength at 28 days is specified (as in ‘designed concrete’),
it is defined as a grade, for example, ‘C.30’ where 30 represents the
nominal cube strength in N/mm 2 . The strength is that which can be expected
to be achieved with proper control of the quality of materials and the mixing.
There is also an important grade of concrete specified in BS 8007:1987, Design
of concrete structures for retaining aqueous liquids. This is particularly for concrete
works associated with the water and wastewater industries, and is classed
as grade C35A.
Since the production of CP 114:1948, a need for higher strength concretes,
coupled with more detailed studies of the chemistry of concrete and the advantages
of using different types of aggregates, cements and admixtures to meet
varying conditions, has led to requiring concrete mixes to be designed to meet
some specific strength together with such other requirements as are considered
necessary. BS 8500 now sets out the main current requirements; while a number
of other British Standards cover the use of special aggregates, special cements
and additives. When any of these special ingredients are to be used, the procedures
to be followed should be detailed in the specification or else provided