Calculation of mix design of M20 grade concrete as per IS 456-2000 code? Estimation of mix design as per IS code standard

The mix design is generally calculated to determine the accurate proportions of concrete materials like cement, sand, coarse aggregates and water content for the specified grade of concrete. The complete concepts of how to calculate the mix design of concrete as per IS 10262 procedure is explained in my previous post follow that with below specified link. In this article you can able to learn how to calculate the mix design of M20 grade with the available material properties of cement, fine aggregates, coarse aggregates and water.

What is the mix design of concrete and different steps followed in mix design as per IS 10262 code standard.

Data required in mix design calculation for M20 grade

The following data is assumed as per the mix design calculation of M20 grade

Characteristic compressive strength : 20Mpa

Cement type : OPC 53 grade

Maximum size of coarse aggregates : 20mm

Workability required at the construction site  : 100mm

Exposure condition : Moderate

Concrete placing method : pump able concrete

Specific gravity of cement : 3.15

Specific gravity of coarse aggregates : 2.80

Specific gravity of fine aggregates : 2.70

Fine aggregates sieve analysis : conforming to zone II of table IS 383

Mix design of M20 grade concrete

The following steps are considered in the mix calculation of concrete as per IS 10262 and IS 456 code standard

Step 1: Calculation of target strength

Target strength is calculated by using

σ’ck =  σck+1.65S

Where S = standard deviation value it was considered from table 1 of IS 10262

From the above table the standard deviation value for M20 grade concrete mix is 4

So, Target strength = 20+1.65(4)

= 26.6 N/mm²

Step 2: selection of water cement ratio

The water cement ratio is taken from table number 5 of IS 456: 2000 code related to the exposure condition see in below table

For the moderate condition related to the plain concrete the value of water cement ratio is 0.6

Based on the number of trials using concrete mix adopt the water cement ratio of 0.55

Here 0.55 < 0.6 hence it is safe.

 Step 3: Selection of water content

The value of the water content is selected from table 2 of IS 10262 code book

The below specified water content is related to the various size of coarse aggregates

For the maximum size of 20mm aggregates the value of water content is taken as 186 liters.

This water content is applicable for 25 to 50mm slump value and for every increase in 25mm slump value the water content is need to increase by 3%.

Here in this case the slump value is 100mm. The value of water content increased by 6% and final water content = 186+(6/100)186 =    197.16 liters

Step 4: Calculation of cement content

For the available values of water content and water cement ratio we can easily determine the cement content.

From step 3 and 4 we have W/C = 0.55, Water content = 197.16

Cement = 197.16/W = 197.16/0.55 = 358.47 kg/m³ < 450 kg/m³ ( maximum cement content ), Hence ok.

Step 5: Proportion of volume of coarse aggregates and fine aggregates

The volume of coarse aggregates per unit volume of total aggregates values are initially considered from table 3 of IS 10262 code provisions related to the different fine aggregates zone condition

As per the zone II of 20 mm size aggregates

Volume of coarse aggregates per total aggregates = 0.62

This value of volume of aggregates is valid for 0.5 w/c ratio, for every increase in 0.05 W/C ratio the value of volume of coarse aggregates per total aggregates decreased by 0.01, in the same process for every decrease in 0.05 W/C ratio the value of volume of coarse aggregates per total aggregates increased by 0.01.

Hence final volume of coarse aggregates becomes = 0.62-0.01 = 0.61

Now the volume of fine aggregates = 1-0.61 = 0.39

Step 6: Estimation of concrete mix calculation

a. Assume volume of total concrete = 1m³

b. Volume of cement = (Mass of cement / Specific gravity of cement) x (1/1000)

= (358.47/3.15)X(1/1000)

= 0.1138m³

c. Volume of water = (Mass of water / Specific gravity of water) x (1/1000)

= (197.16/1) X (1/1000)

= 0.19716

d. Total volume of aggregates = 1-b-c = 1- 0.1138-0.19716 = 0.68904

Mass of coarse aggregates = d X volume of coarse aggregates X specific gravity of coarse aggregates X 1000

= 0.68904X0.61X2.8X1000

= 1176.88 kg/m³

Mass of fine aggregates = d X volume of fine aggregates X specific gravity of fine aggregates X 1000

= 0.68904X0.3961X2.7X1000

= 736.90 kg/m³

Calculation of mix proportion for trial

Cement = 358.47 kg/m³

Fine aggregates = 736.90 kg/m³

Coarse aggregates = 1176.88 kg/m³

Water = 197.16 kg/m³

Final mix of M20 grade concrete as per IS 10262 code

Cement : Fine aggregates : Coarse aggregates at W/C

358.47 : 736.90 : 1176.88 at 197.16

Divide entire values with cement

We get final mix proportion as 1: 2.055 : 3.283 at 0.55

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Conclusions of mix design of M20 grade concrete 

The above explained concepts are related to the complete step by step calculation of mix design of M20 grade concrete as per IS 10262 code standards. As per the above calculation the final mix ration of M20 grade concrete is obtained as 1: 2.055 : 3.283 at 0.55 w/c ratio.

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