An example of given concrete mix design steps for concrete of  M 25 grade is followed as per IS: 10262-2009.

I. Stipulations for Mix Design Concrete

Grade designation              :        M 25

Type of cement                     :        OPC 53 grade confirming to IS 8112

Maximum nominal size of aggregate    :         20 mm

Minimum cement content                       :           300 kg/m3

Maximum water-cement ratio                :           0.50    

Workability                                                 :           50-75 mm (slump)

Exposure condition                                   :           Mild (for RCC)

Method of concrete placing                     :           Pumping

Degree of supervision                               :           Good

Type of aggregate                               :           Crushed angular aggregate

Maximum cement content                       :           450 kg/m3

II. Test Data for Materials (to be determined in the laboratory)

Specific gravity of cement : 3.15

Specific gravity of Coarse aggregate : 2.84

Specific gravity of Fine aggregate : 2.64

III. Procedure for Mix Design of M 25 Concrete

Target Strength for Mix Proportioning

ftarget = fck + 1.65 x s

where,

f’ck = target average compressive strength at 28 days,

fck = characteristic compressive strength at 28 days, and

s = standard deviation

as per the table I of IS: 10262-2009 , s = 4.0 N/mm2

Therefore, target strength = 25 + 1.65 x 4.0 = 31.6  N/mm2

IV. Selection of Water/Cement Ratio

From Table 5 of IS 456,

maximum water-cement ratio = 0.50.

V. Selection of Water Content

From Table 2, maximum water content = 186 liter (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump = 186+(3/100) x 186 =191.6 litres.

VI. Calculation of Cement Content

Water-cement ratio = 0.50

Cement content = 140/0.50 = 383.3 kg/m3

From Table 5 of IS 456,

Minimum Cement Content for ‘MILD’ exposure condition = 300 kg/m3

383.3 kg/m3 > 300 kg/m3, hence, O.K

VII. Proportioning of the Volume of Coarse Aggregate and Fine Aggregate Content

From Table 3. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for a water-cement ratio of 0.50 is 0.62.

 In the present case, the water-cement ratio is 0.50. Therefore, the volume of coarse aggregate is required to be increased to decrease the fine aggregate content.

As the water-cement ratio is lower by 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio). Therefore, the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.50 = 0.62.

 Note – In case the coarse aggregate is not angular one, then also the volume of coarse aggregate may be required 10 be increased suitably, based on experience.

For pumpable concrete, these values should be reduced by 10 percent.

 Therefore, volume of coarse aggregate = 0.62 x 0.9 = 0.56.

 Volume of fine aggregate content =1 – 0.56 =0.44

VII. Mix Calculations

a) Volume of concrete = 1m3

b) Volume of cement  = (Cement mass/specific gravity of Cement) X (1/1000)

                                     = (383.3/3.15) X (1/1000)

                                        = 0.122 m3

c) Volume of water =(Mass of water/specific gravity of water) X (1/1000)

= (191.6/1) X (1/1000)

= 0.1916 m3

d) Volume of all aggregate =  (a- (b+c))

=  1 – (0.122 + 0.1916)

=  0.6864 m3

e) Mass of coarse aggregate = Volume of all Aggregate X Volume of C.A X Specific Gravity of C.A X 1000

= 0.6864 x 0.56 x 2.84 x 1000

= 1087.75 kg

f) Mass of fine aggregate  = Volume of all Aggregate X Volume of F.A X Specific gravity of F.A X 1000

= 0.6864 x 0.44 x 2.64 x 1000

= 800.94 kg

IX. Concrete Mix Proportions

Cement                     = 383.2 kg/m3

Water                        = 191.6 kg/m3

Fine aggregates       = 800.94 kg/m3

Coarse aggregate    = 1087.75 kg/m3

W/c                            = 0.5

Check out our post on M40 grade concrete mix design here.

Know more about the basic concepts of concrete mix design here.