Challenge

Project on Concrete Mix Design for various grades of Concrete

AAparna Kn2 Sept 2022

1)Calculation of concrete Mix design for M35 with using Fly ash

Aim: To calculate the concrete mix design for M35 with Fly ash

Introduction:

Concrete mix proportioning or Mix Design is a process that consists of two interrelated steps: (1) selection of the suitable ingredients and (2) determination of their relative quantities to produce, as economically as possible, concrete of the appropriate workability, strength and durability. These proportions will depend on the characteristics of ingredients used.With concrete-making materials of given characteristics, the choice of variables are cement paste-aggregate ratio in the mixture, water-cement ratio in the cement paste, sand-coarse aggregate ratio in the aggregate and the use of construction
chemicals. The overall objective of mix design is the selection of the suitable ingredients among the available materials and determining the most economical combination that will produce concrete with certain minimum performance characteristics.

Objective:

To achive desired/ designed strength,durability,workability in the given environment condition.
To produce concrete as economically as possible.

Step 1:Stipulations for proportioning : The data required for calculating the concrete mix design are

Grade : M35
Type of cement : OPC 43 grade
Type of mineral admixture : Fly ash
Maximum nominal size of aggregate : 20 mm
Minimum cement content : 320 kg/m^3 (From Table 5 of IS 456:2000)
Maximum water-cement ratio : 0.45 (From Table 5 of IS 456:2000)
Workability : 100mm (slump value for pumpable concrete)
Exposure condition : Severe (for reinforced concrete)
Method of concrete placing : Pumping
Degree of supervision : Good
Type of aggregate : Crushed Angular aggregates
Maximum cement content : 450 kg/m^3
Chemical admixture type : Super plasticizer

Step 2:Test data for material:

Cement used : OPC 43 Grade conforming to IS 8112
Specific gravity of cement : 3.15
Chemical admixture : Super plasticizer conforming to IS9103
Specific gravity of fly ash : 2.2
Specific gravity of coarse aggregate : 2.74
Specific gravity of fine aggregate : 2.74
Water absorption of coarse aggregate : 0.5%
Water absorption of fine aggregate : 1.0%
Free surface moisture of coarse aggregate and fine aggregate : Nil
Sieve Analysis : For coarse aggregate: test conforming to table 2 IS383

For fine aggregate :Zone 2 cponforming to table 4 IS383.

Step 3:Target strength for concrete

The target means strength for specified characteristic cube strength at 28 days

f’ck = fck + 1.65 s
f’ck is target average compressive strength at 28
fck is characteristics compressive strength at 28 days
s is Standard Deviation values ( from Table 1 of IS 10262 – 2009)

The value of s for M35 from Table 1 is 5.0 N/mm2
f'ck= 35+ 1.65(5)

f'ck =43.25 N/mm^2 (Target mean strength).

Step 4: Selection of Water cement ratio:

From Table 5 of IS 456 2000 for sever exposure condition maximum water-cement ratio is 0.45( for reinforced concrete)

Based on experience,water cement ratio will be taken as = 0.4

hence water cement ratio=0.4

Step 5: Selection of water content

From table 2 IS 10262:2009, maxium water content for 20mm aggregate = 186liters ( for the slump value 25-50mm).Acoording to specification which we have taken the slump value is 100mm ,therefore the water contant must be increased . As per clause 4.2, there will be 3% increase in water content for every 25mm slump .Therefore to obtain the slump value of 100m there will be 6% increase in water concent.

Water content for 100mm slump = 186+(6\100)*186

=197l

As superplastizer are used, the water content can be reduced upto 30%

Water content = 197* 70\100=140 where (100-30=70).

Hence the arrived water content = 140liters(approximately taken)

Step 6: Calculation of cement content

Water cement ratio = 0.4

Cementitious material (cement+ fly ash)=water content/water cement ratio

=140/0.4

=350kg/m^3

From table 5 of IS 456 minimum cement content for 'sever' exposure condition =320kg/m^3

Since 350kg/m^3 > 320kg/m^3, hence ok.

The percentage of fly ash to be increased will be based on project requirement .Here we have increased the cementitious content by 10%.

Cementitious material content =350*1.10=385kg/m^3

Water content =140kg/m^3

So, water cement ratio will be =140/385=0.36

Fly ash of 30% to the total cementitious material content =385*0.3=115kg/m^3

Cement =385-115=270kg/m^3

Cement quantity saved using fly ash addition =350-270=80kg/m^3.

Step 7: Calculation of coarse aggregate and fine aggregate

From Table-3 of I.S 10262:2009 volume of coarse aggregate for 20mm size aggregate and fine aggregate (Zone 1) for water-cement ratio of 0.50 is 0.60 .

In present case the water/cement ratio is 0.4,therefore the volume of coarse aggregate needs to be increase to decrase the fine aggregate content.The volume of coarse aggregate to the total aggregate is increased at the rate of 0.01 for every decrease in water cement ratio by 0.05 and decrease the rate of 0.01 for every increase in water cement ratio by 0.05.So, the water cement ratio which we have taken is 0.4 so there will be increased by 0.02 .

Therefore the final volume of coase aggregate will be = 0.62(0.6+0.02)

For pumpable concrete it can be reduced by 10%, so the value of coarse aggregate will be 0.62*0.9=0.558

Volume of fine aggregate will be 1-0.558=0.442.

Therefore the volume of coarse aggregate is 0.558 and the voulme of fine aggregate is 0.442

Step 8: Mix calculation

Volume of concrete: 1m^3
Voulme of cement: (mass of cement/specific gravity of cement )*(1/1000) = 350/3.15*1/1000=0.11m^3
Voulme of water:(mass of water /specific gravity of water )*(1/1000) = 140/1*1/1000=0.140m^3
Voulme of chemical admixture:(mass of chemical admixture /specific gravity of chemical admixture )*(1/1000)= 7/1.145 * 1/1000 = 0.006m^3 ( where mass of chemical admixture = 2% of cementitious material =350*2/100=7)
Volume of aggregate : (F.A & C.A) = (a-(b+c+d) =(1-(0.11+0.140+0.006))=0.744m^3
Mass of coarse aggregate : e * Volume of coarse aggregate * specific gravity of coarse aggregate*1000= 0.744 * 0.558 * 2.74 * 1000 = 1137.5kg/m^3
Mass of fine aggregate : e * volume of fine aggregate * specific gravity of fine aggregate*1000 = 0.744 * 0.442 * 2.64 * 1000 = 868.15 kg/m^3

Step 9: Mix proportion:

Cement = 350 kg/m^3

Water = 140 litres

Fine aggregate = 868.15 kg/m^3

Coarse aggregate = 1137.5 kg/m^3

Chemical admixture = 7 KG/m^3

water-cement ratio = 0.40

Mix Ratio : 1: 2.48 : 3.25

2)Calculation of concrete Mix design for M50 without using Fly ash

Aim: To calculate the concrete mix design for M50 without Fly ash

Step 1:Stipulations for proportioning : The data required for calculating the concrete mix design are

Grade : M50
Type of cement : OPC 43 grade
Maximum nominal size of aggregate : 20 mm
Minimum cement content : 320 kg/m^3 (From Table 5 of IS 456:2000)
Maximum water-cement ratio : 0.45 (From Table 5 of IS 456:2000)
Workability : 100mm (slump value for pumpable concrete)
Exposure condition : Severe (for reinforced concrete)
Method of concrete placing : Pumping
Degree of supervision : Good
Type of aggregate : Crushed Angular aggregates
Maximum cement content : 450 kg/m^3
Chemical admixture type : Super plasticizer

Step 2:Test data for material

Cement used : OPC 43 Grade conforming to IS 8112
Specific gravity of cement : 3.15
Chemical admixture : Super plasticizer conforming to IS9103
Specific gravity of coarse aggregate : 2.74
Specific gravity of fine aggregate : 2.74
Water absorption of coarse aggregate : 0.5%
Water absorption of fine aggregate : 1.0%
Free surface moisture of coarse aggregate and fine aggregate : Nil
Sieve Analysis : For coarse aggregate: test conforming to table 2 IS383

For fine aggregate :Zone 2 cponforming to table 4 IS383.

Step 3:Target strength for concrete

The target means strength for specified characteristic cube strength at 28 days

f’ck = fck + 1.65 s
f’ck is target average compressive strength at 28
fck is characteristics compressive strength at 28 days
s is Standard Deviation values ( from Table 1 of IS 10262 – 2009)

The value of s for M35 from Table 1 is 5.0 N/mm2
f'ck= 50+ 1.65(5)

f'ck =58.25 N/mm^2 (Target mean strength).

Step 4: Selection of Water cement ratio:

From Table 5 of IS 456 2000 for sever exposure condition maximum water-cement ratio is 0.45( for reinforced concrete)

Based on experience,water cement ratio will be taken as = 0.4

hence water cement ratio is =0.4

Step 5: Selection of water content

Water content for 100mm slump = 186+(6\100)*186

=197l

As superplastizer are used, the water content can be reduced upto 20%

Water content = 197* 80\100=157.6 where (100-20=80).

Hence the arrived water content = 158liters

Step 6: Calculation of cement content

Water-cement ratio = 0.4

Water content = 158 kg

Cement content = 158/0.4 = 395 kg/m^3

From table 5 of IS 456 minimum cement content for 'sever' exposure condition=320kg/m^3

Since 395kg/m^3 > 320kg/m^3, hence ok.

Step 7: Calculation of coarse aggregate and fine aggregate

From Table-3 of I.S 10262:2009 volume of coarse aggregate for 20mm size aggregate and fine aggregate (Zone 1) for water-cement ratio of 0.50 is 0.60 .

Therefore the final volume of coase aggregate will be = 0.62(0.6+0.02)

For pumpable concrete it can be reduced by 10%, so the value of coarse aggregate will be 0.62*0.9=0.558

Volume of fine aggregate will be 1-0.558=0.442.

Therefore the volume of coarse aggregate is 0.558 and the voulme of fine aggregate is 0.442

Step 8: Mix calculation

Volume of concrete: 1m^3
Voulme of cement: (mass of cement/specific gravity of cement )*(1/1000) = 395/3.15*1/1000=0.125m^3
Voulme of water:(mass of water /specific gravity of water )*(1/1000) = 158/1*1/1000=0.158m^3
Voulme of chemical admixture:(mass of chemical admixture /specific gravity of chemical admixture )*(1/1000)= 7.9/1.145 * 1/1000 = 0.0068m^3 ( where mass of chemical admixture = 2% of cementitious material =395*2/100=7.9)
Volume of aggregate : (F.A & C.A) = (a-(b+c+d)=(1-(0.125+0.158+0.0068))=0.710m^3
Mass of coarse aggregate : e * Volume of coarse aggregate * specific gravity of coarse aggregate*1000= 0.710 * 0.558 * 2.74 * 1000 = 1144kg/m^3
Mass of fine aggregate : e * volume of fine aggregate * specific gravity of fine aggregate*1000 = 0.710 * 0.442 * 2.64 * 1000 = 828.5kg/m^3

Step 9: Mix proportion:

Cement = 395 kg/m^3

Water = 158 litres

Fine aggregate = 828.5 kg/m^3

Coarse aggregate = 1144kg/m^3

Chemical admixture = 7.9 KG/m^3

water-cement ratio = 0.40

Trial Mix Ratio : 1: 2.09 : 2.9

Conclusion:

The calculated mix proportion should be checked by making trial mixes. Only a sufficient
amount of produce the required workability should be used, regardless of the
amount calculated. The trial mixes should be tested for workability, cohesiveness,
finishing properties and air content as well as for yield and density. If any one of the
properties, except the last two, is unsatisfactory, adjustments to the mix proportion are
necessary. Although there are sound technical principles that govern mix proportioning,
for several valid reasons the process is not entirely in the realm of science. Since mix
proportion have great influence on the cost and properties of concrete, it is important that
engineers who are often called on to develop or approve mix proportion be familiar with
the underlying principles and the commonly used procedure.

Project on Concrete Mix Design for various grades of Concrete

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