Challenge

Project on Concrete Mix Design for various grades of Concrete

NNeha Solanki26 Nov 2022

Aim : To calculate the Concrete Mix Design for M35 grade concrete with Flyash & M50 grade concrete without Flyash.

Introduction : The concrete mix design involves a process of preparation in which a mix of ingradients creates the required strength and durability for the concrete structure. Because every ingradient in the mix consists of different properties. It is the method of finding the proportion of cement, sand and aggregate for a perticular grade of concrete to achieve the target strength in the structures. The Mix Design is done according to the requirenment of the concrete strength. By doing design mix the desired properties of concrete either in fresh state or in harden state can be achieved. To obtain the desired strength of concrete the use of additives like admixtures, retarders etc is introduced other than the basic ingradients. The admixture can be accelerators or retarder as per the requirenment of external ingradient introduced. For example in this project the flyash is the external ingradient which need as admixture to gain the desired strength of concrete.

Objective : The objective of this project is to design a mix of M35 grade concrete containing flyash and a M50 grade concrete without flyash. The mix will be prepared as per IS Method. ( concrete proportioning guideline from IS 10262:2009 and recommented guidelines from IS 10262:1982)

Procedure :

PART 1 : M35 GRADE MIX DESIGN CONCRETE WITH FLYASH

Step 1 ( Data Required )

Grade of concrete : M35

Type of cement : OPC 43 Grade

Type of mineral admixture : Flyash

Maximum nominal size of aggregate : 20mm

Minimum cement content : 320 kg/m^3 ( Table 5 of IS 456:2000 )

Maximum water/cement ratio : 0.45

Workability : 100 mm ( Slump for pumpable concrete )

Exposure condition : severe

Method of concrete Placing : pumping

Maximum cement content : 450 kg/m^3

Chemical admixture : super plasticizer

Specific Gravity of cement : 3.15

Specific Gravity of coarse aggregate : 2.74

Specific Gravity of fine aggregate : 2.74

ZONE II

( Table 4 , IS 383

Step 2 ( Target Mean Strength )

f'ck = fck + 1.65s

here

f'ck = target mean strength at 28 day

fck = characterstic compressive strength at 28 day = 35 N/mm^2 ( M35 Grade )

s = standard deviation = 5 N/mm^2 ( Table I of Is 10262:2009)

Therefore ;

f'ck = 35 + 1.65x5 = 43.25 N/mm^2

Step 3 ( Water-cement ratio)

The maximum water cement ratio to design M35 grade concrete can be found from Table 5 of IS 456:2000

Therefore ; w/c ratio = .045

Step 4 ( Water content )

From table 2 Is 10262:2009, maximum 186 liters ( for 25 to 50 mm water content for 20mm slump range)

Now from clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So a 6% is to be added in this case

water content = 186 + (6/100)*186 = 197 litre

But with super plasticizer water content reduced to 20%

now water content = 197 x 0.8 = 158 litre

Step 5 ( calculation of cementitious content )

Assumed w/c ratio = 0.45

Total cementious content = 158/0.45 =351 kg/m^3

The cementious content has to be increased in order to attain good workability and strength. So we should increase the cementious content by 10%

Final cementious content = 351x1.10 = 386 kg/m^3 ( it is ok as minimum cement content is 320 kg/mm^3)

now water content for 386 cement content = 158/386 = 0.40

Flyash content is taken as 30% of the total cementious content = 386x .3= 115.8 kg/m^3

Cement content = 386 - 115 = 271 kg/m^3

Step 6 ( Volume of coarse aggregate and fime aggregate )

The volume of coarse aggregate is required to be decresed the fine aggregate content. As the water-cement ratio is lower by 0.06. The proportion of volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every +/- 0.05 change in water-cement ratio )

Therefoe the corrected proportion of volume of coarse aggregate 0.63 for w/c ratio of 0.45

But for pumpable concrete these value should be reduced up to 10% .

Therefore the volume of coarse aggregate = 0.63x0.9 = 0.567

Volume of fine aggregate = 1-0.567 = 0.433

Step 7 ( Mix Calculation )

Volume of concrete : 1m^3
Volume of cement = [Mass of cement ]/[specific gravity of cement]x (1/1000)=(271/3.25)x(1/1000)= 0.0833m^3
Volume of flyash = [Mass of flyash]/[specific gravity of flyash] x (1/1000) = (115.8/2.2)x(1/1000) = 0.056
Volume ofm water = [Mass of water]/[Specific gravity of water]x (1/1000) = (158/1)x(1/1000) = 0.158 m^3
Volume of chemical admixture = [Mass of admixture]/[Specific Gravity of admixture] = ( 7.6/1.145)x(1/1000) = 0.006m^3
Volume of all in aggregate = [1-(.0833+.056+.0158+.006)] = 0.8389m^3
Mass of coarse aggregate = ( volume of all aggregate) x ( volume of coarse aggregate x specific gravity of coarse aggregate x1000 = 0.8389 x 0.567x2.74x1000 = 1303.3 kg/m^3
Mass of fine aggregate = ( volume of all aggregate) x ( volume of fine aggregate x specific gravity of fine aggregate x1000 = 0.8389x .433x 2.74x1000 =995.3 kg/m^3

Step 8 ( Mix Proportion )

Cement = 271 kg/m^3

Flyash =115 kg/m^3

Water = 158 l/m^3

Fine aggregate = 995.3 kg/m^3

Coarse aggregate = 1303.3 kg/m^3

Chemical admixture = 7 kg/m^3

water-cement ratio = 0.40

Part 2 : M50 GRADE MIX DESIGN CONCRETE WITHOUT FLYASH

Step 1 ( Data required )

Grade of concrete : M50

Type of cement : OPC 53 Grade