A concrete mix which is designed on the basis of test of the strength conducted in the laboratory on the trial mixture of cement and aggregate to be actually used in the construction is termed as controlled concrete. Strength tests in kg/sq. cm are done by filling the moulds of 15 cm cubes with the concrete used at the works and testing those cubes after curing 28 days.

Indian standard IS : 456 – 1978 specifies the following grades of concrete M-5, M-7.5, M-10, M-15, M-20, M-25, M-30, M-35, and M-40. In the designation of a concrete mix, letter M refers to the mix and the number to the specified characteristic compressive strength of 15 cm cube at 28 days, express in N/mm2.

M-5 and M-7.5 grades of concrete may be used for lean concrete bases and simple foundations for masonry walls. Grades of concrete lower than M-15 shall not be used in reinforced concrete.

Previously IS : 456 – 1964 specified the following grades of concrete M-100, M-150, M-200, M-250, M-300, M-350 and M-400.

Now in order to draw a relation between the IS : 456 – 1964 and IS : 456 – 1978 it is noted that 1 N/mm2 = 10 kg/cm2. Therefore M-10, M-15 grades of concrete of IS : 456 – 1978 corresponds to M-100 and M-150 grades of concrete respectively of IS : 456 – 1964.

Nominal mix concrete may be used for concrete of grades as below :

PROPORTION FOR NOMINAL MIX DESIGN

Grade of concrete IS 456-1978
Grade of concrete IS 456-1964
Nominal Mix
Total quantity of dry aggregates by mass per bag (50 kg) of cement, to be taken as the sum of the individual masses of fine and coarse aggregates in kg (Generally 1:2 proportions).
Quantity of water in litre per bag of cement (50 kg)
M 5
M 50
1:5:10
800
60
M 7.5
M 75
1:4:8
625
45
M 10
M 100
1:3:6
480
34
M 15
M 150
1:2:4
350
32
M 20
M 200
1:1 ½:3
250
30

The determination of the proportions of cement, aggregates and water to attain the required strength shall be made as follows :

1.  By designing the concrete mix; such concrete shall be called design mix concrete or

2.  By adopting nominal concrete mix; such concrete shall be called Nominal mix as 1:4:8, 1:3:6 etc. For Nominal-mix proportions is arbitrarily fixed.


For high grade concrete mix design procedure is adopted. The definition of “concrete mix design” for a given purpose is the art of obtaining a concrete of the required properties, at the lowest cost, by a suitable choice of materials and of the proportions in which they are employed. In designing a mix for a particular grade of concrete is followed invariably by making of trial mixes, the mix proportions have to adjusted and the refinements carried to the stage where optimum proportions have been attained.