CONCRETE MIX DESIGN



Data for Mix Proportioning :

The following data are required for mix proportioning of a particular grade of concrete:

  1. Grade designation
  2. Type of cement
  3. Maximum nominal size of aggregate
  4. Minimum cement content
  5.  Maximum water-cement ratio
  6. Workability
  7.  Exposure conditions
  8.  Maximum temperature of concrete at the time of placing
  9.  Method of transporting and placing
  10.  Early age strength requirements, if required
  11.  Type of aggregate
  12.  Maximum cement content
  13.  Whether an ad mixture shall or shall not be used and the type of admixture and the condition of use           
  14. Step 1: Determination of  Target mean Strength of concrete

ft= fck+1.65.s

Where,  

ft = target mean compressive strength at 28 days in N/mm2

 fck = Characteristic compressive  strength of concrete at 28 days  in N/mm2

S = standard deviation in  N/mm2 ( refer table 1 given below)

Table 1 : Assumed Standard Deviation 

Sl No

Grade of Concrete

Assumed Standard Deviation (N/mm2)

1

M 10

3.5

2

M 15

3

M 20


4.0

4

M 25

5

M 30



5.0


 
6 M 35  
7 M 40  
8 M 45  
9 M 50
10 M 55  

Step II : Selection of  Water Cement

(w/c)  Ratio

  • Choose  w/c ratio against max w/c ratio for the requirement of durability. (Refer Table 2  and Table 3 given below).
    Table 2 : Durability Criteria As per IS 456: 2000 ( For Aggregates of 20 mm nominal maximum size)

Exposure

Plain Concrete

Reinforced Concrete

 

Min Cement in Kg/m3

Max w/c

Min Grade

Min Cement

in Kg/m3

Max w/c

Min Grade

Mild

220

0.60

--

300

0.55

M 20

Moderate

240

0.60

M 15

300

0.50

M 25

Severe

250

0.50

M 20

320

0.45

M 30

Very Severe

260

0.45

M 20

340

0.45

M 35

Extreme

280

0.40

M 25

360

0.40

M 40

Table 3 : Adjustment to minimum cement content for aggregates other than 20 mm nominal max size aggregates As per IS 456: 2000

Sl No

Nominal Max Aggregate

Adjustment to minimum cement content in Table 2 in Kg/m3

1

10

+40

2

20

0

3

40

-30

Step III: Selection of water content :

The quantity of maximum mixing water per unit volume of concrete can be determined from table 4 and table 5 given below.

Table 4 Maximum Water content per cubic metre  of concrete for nominal maximum size of aggregate. ( For angular coarse aggregate and slump range 25-50 mm )

Sl No

Nominal Maximum size of Aggregate (in mm)

Maximum Water Content  (in Kg)

1

10

208

2

20

186

3

40

165

Table 5:  Correction to values in table 4 for other site conditions

Sl No

Condition

Correction

1

Sub – Angular Aggregates

-10 kg

2

Gravel+ Crushed Aggregates

-20 kg

3

Rounded Gravel

-25 kg

4

For every slump increase of 25 mm

+ 3 %

5

Use of Water reducing Admixture

-5 to - 10 %

6

Use of superplasticzing Admixtures

-20 %

Step IV : Calculation of Cementitious Material Content

Calculate the cement content from w/c ratio and final water content arrived after adjustment. Check the cement content calculated against the minimum cement content specified in table 2. The greater of the two values shall be adopted.

Step V :  Proportion of volume of coarse aggregate

For w/c ratio of 0.5 , table 6 is to be used .

Table 6 Volume of Coarse  Aggregate per unit volume of total aggregate for different zones of Fine Aggregate .

Sl No

Nominal Maximum size of Aggregate (mm)

Volume of coarse aggregate per unit volume of Total Aggregate for Different Zones of Fine Aggregate

Zone IV

Zone III

Zone II

Zone I

i)

10

0.50

0.48

0.46

0.44

ii)

20

0.66

0.64

0.62

0.60

iii)

40

0.75

0.73

0.71

0.69

orrection in Coarse aggregates values

  • For every  +0.05 change in w/c ratio : -0.01
  • For Every -0.05 change in w/c ratio : +0.01
  • For pumpable concrete mix : - 10 %

Step VI:  Final Mix Calculations :

  1. Volume of concrete = 1 m3
  2. Volume of cement = Mass of waterSpecific gravity of cement x 11000
  1. Volume of water =  Mass of waterSpecific gravity of water x 11000
  1. Volume of chemical admixture  = Mass of chemical admixture Specific gravity of admixture  X 11000
  1. Volume of all in aggregates = [a- (b+c+d)]
  1. Mass of coarse aggregates = e x Volume of Coarse aggregate x  Specific gravity of coarse aggregate x 1000.
  1. Mass of fine aggregate = e x Volume of fine aggregate x Specific gravity of fine aggregate x 1000.

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