Concrete ~ a composite with many variables, represented by
numerous gradings which indicate components, quality and
manufacturing control.
Grade mixes: C7.5, C10, C15, C20, C25, C30, C35, C40, C45, C50,
C55, and C60; F3, F4 and F5; IT2, IT2.5, and IT3.C = Characteristic compressive
F = Flexural
IT = Indirect tensile
NB. If the grade is followed by a `P', e.g. C30P, this indicates a
prescribed mix (see below).
Grades C7.5 and C10 † Unreinforced plain concrete.
Grades C15 and C20 † Plain concrete or if reinforced containing
lightweight aggregate.
Grades C25 † Reinforced concrete containing dense
aggregate.
Grades C30 and C35 † Post-tensioned reinforced concrete.
Grades C40 to C60 † Pre-tensioned reinforced concrete.
Categories of mix: 1. Standard; 2. Prescribed; 3. Designed; 4. Designated.1. Standard Mix † BS guidelines provide this for minor works or
in situations limited by available material and manufacturing
data. Volume or weight batching is appropriate, but no grade
over C30 is recognised.- Prescribed Mix † components are predetermined (to a recipe)
to ensure strength requirements. Variations exist to allow the
purchaser to specify particular aggregates, admixtures and
colours. All grades permitted. - Designed Mix † concrete is specified to an expected
performance. Criteria can include characteristic strength,
durability and workability, to which a concrete manufacturer will
design and supply an appropriate mix. All grades permitted. - Designated Mix † selected for specific applications. General
(GEN) graded 0†4, 7„5†25 N/mm^2 for foundations, floors and
external works. Foundations (FND) graded 2, 3, 4A and 4B,
35 N/mm^2 mainly for sulphate resisting foundations.
Paving (PAV) graded 1 or 2, 35 or 45 N/mm^2 for roads and drives.
Reinforced (RC) graded 30, 35, 40, 45 and 50 N/mm^2 mainly for
prestressing.
See also BS EN 206-1: Concrete. Specification, performance,
production and conformity, and BS's 8500-1 and -2: Concrete.
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strengths at 28 days (N/mm^2 )Concrete Production---Specification