Project on Concrete Mix Design for various grades of Concrete

An example of given concrete mix design steps for concrete of M35 grade is followed as per IS:10262-2009.

1. Stipulations for Mix Design Concrete.  

•  Grade designation : M35 
•  Type of cement : OPC 53 grade confirming to IS 8112
• Maximum nominal size of aggregate: 20 mm
• Minimum cement content : 340 kg/m^3
• Maximum water - cement ratio : 0.45
• Workability : 50-100 mm (slump)
• Exposure condition : Very Severe (for reinforced concrete)
• Method of concrete placing : Pumping 
• Degree of supervision : Good
• Type of aggregate : Crushed angular aggregate 
• Maximum cement content : 450 kg/m^3 
• Chemical admixture type : Super Plasticizer 

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

• Specific gravity of cement : 3.12
• Specific gravity of Coarse aggregate : 2.74 
• Specific gravity of Fine aggregate : 2.56

3. Target Strength for Mix Proportioning 

 ftarget=fck +1.65x S

Explanation

'ftarget' is the target average compressive stregth at 28 days ,

'fck' is the characteristic compressive strength at 28 days, and 

's' is the standard deviation

As per the table I of IS: 10262-2009, standard deviation, s = 5.0 N/mm^2

Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm^2

4. Selection of water/cement ratio 

From Table 5 of IS 456:2000, 

Maximum water-cement ratio = 0.45

5. Selection of Water Content 

From Table 2 of IS 456 , maximum water content = 186 litres (for 25 to 50 mm slump range ) for 20 mm aggregate .

Estimated water content for 100mm slump = 186+(6/100)x186=197 liter .

(Note : If Super plasticizer is used , the water content can be reduced upto 20% and above .)

Based on trials with Super plasticizer water content reduction of 25% has been achieved , Hence the arrived water content = 197-[197 x (25/100)]=147 litres.

6. Calculation of cement content

Water-cement ratio = 0.45

Cement content =147/0.45 = 350 kg/m^3

From Table 5 of IS 456, minimum cement content for Very Severe exposure condition = 340 kg/m^3 

350kg/m^3 >340kg/m^3, hence , O.K.

7. The Proportion of the volume of coarse aggregate and fine aggregate content 

From Table 3 of IS 10262, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50=0.62.

In the present case , the water - cement ratio is 0.45. Therefore , the volume of coarse aggregate is required to be increased to reduce 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- cemnt ratio). Therefore . the corrected proportion of the volume of coarse aggregate for the water - cement ratio of 0.45=0.63.

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= 0.63 x 0.9 = 0.567.

Volume of fine aggregate content = 1- 0.5657 = 0.433

8. Mix Calculations

a) Volume of concrete = 1m^3

b) Volume of cement = ( Mass of cement/Specific Gravity of cement ) X (1/1000) =(350/3.12)X(1/1000)

=0.112m^3

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

=9147/1) X (1/1000)

=0.147m^3

d) Volume of superplasticizer = (mass of superplasticizer / specific gravity of admixture) X (1/1000)

=(7/1.145)X(1/1000)

=0.006m^3

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

=1-(0.112+0.147+0.006)

=0.735m^3

f) Mass of coarse aggregate = volume of all aggregate X volume of fine aggegate X specific gravity of fine aggregate X 1000

= 0.735x0.433x2.56x1000

=814.73 kg 

9. Concrete mix proportions 

• Cement = 350kg/m^3
• water = 147 kg/m^3
• Super plasticizer = 7 kg/m^3
• fine aggregates= 814.73 kg/m^3 
• Coarse aggregate = 1141.88 kg/m^3
• w/c = 0.45

Concrete Mix Ratio obtained 

The mix ratio of M35 as obtained is 1:2.32:3.26 (Cement:Fine aggregate: Coarse aggregate )

This is the procedure for mx design calculation of M35 grade concrete.