Project on Concrete Mix Design for various grades of Concrete

PROJECT ON CONCRETE MIX DESIGN FOR VARIOUS GRADES OF CONCRETE

Introduction to concrete mix design

Mix design:It is process of mixing the concrete ingredients like cement,fine aggregates,coarse aggregates and water.

It is the process of selecting suitable ingredients for production of concrete of required strength,durabilityand workability as economical as possible is known as concrete mix design.

There are three types of mixes,

-Nominal mix

-Standard mix

-Designed mix

For calculating above M25 garde of concrete we need to use the concept of Designed mix.

Here we are calculating the M35 grade of concrete with and without Flyash so the M35 garade of concrete is mostly used in the important constructions hence the mix design is very much essential.

By the the referance of some standard codes the proportion are going to be calculate.

Aim:To achieve the right praportions of concrete ingredients according to the requirements for,

1. M35 grade of concrete with flyash
2. M35 grade of concrete without flyash

Lets start the mix design for,

1.M35 grade of concrete with flyash:

• Stipulations for proportioning

a)Grade of concrete-M35

b)Type of cement-Ordinary Portland Cement,43 grade of cement conforming to IS 8112

c)Type of mineral admixture:Fly ash conforming to IS 3812(part 1)

d)Maximum nominal size of aggregates-20mm

e)Minimum cement content-340 kg/m^3 (From table 5 of IS 456:2000-Exposure condition)

f)Maximum water cement ratio-0.45 (From table 5 of IS 456:2000-Exposure condition)

g)Workability-100mm (slump value for pumpable concrete)

h)Exposure condition-Severe (for reinforced concrete)

i)Method of concrete placing-Pumping

j)Degree of supervision-Good

k)Type of aggregates-Crushed angular aggregate

l)Maximum cement content-450 kg/m^3

m)Chemical admixture type-Superplasticizer

• Test data for materials:

a)Cement used-OPC 43 grade conforming to IS 8112

b)Specific gravity of cement-3.15

c)Fly ash-Conforming to IS 3812 (part 1)

d)Specific gravity of fly ash-2.2

e)Chemical admixture-Superplasticizer conforming to IS 9103

f)Specific gravity of-Coarse aggregate and Fine aggregate =2.74

g)Water absorption-Coarse aggregate and Fine aggregate are 0.5% and 1.0% respectively

h)Free surface moisture-Coarse aggregate and Fine aggregate are nil.

i)Sieve analysis-Coarse aggregate-Conforming to table 2 of IS 383

-Fine aggregate-Conforming to grading zone 1 of table 4 of IS 383

• Target mean strengthfor mix proportioning:

f'ck=fck+1.65 S

Where , f'ck=Target average compressive strength at 28 days

fck=Charecteristics compressive strength at 28 days

S=Standard deviation

From table 2 of IS 10262:2019,standard deviation,S=5 N/mm^2

Therefore,Target strength=35+1.65*S

=43.25 N/mm^2

• Selection of water cement ratio:

From the table 5 of IS 456:2000 for severe exposure,maximum water cement ratio =0.45

Based on experience,adopt water cement ratio as 0.40

0.40<0.45 , Hence OK

• Selection of water content:

From table 4 of IS 10262:2019,maximum water content for 20mm aggregate=186 litre(for 25 to 50mm slump)

Estimated water content for 100mm slump=186+6/100*186

=197 litre

As superplasticizer is used ,the water content can be reduced upto 30%

Based on trials water content reduction of 29% is achieved with plasticizer

Hence the arrived water content=197*0.71=140 litre

• Calculation of cement content:

Water cement ratio=0.40

Cement content =140/0.4=350 kg/m^3

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

350 kg/m^3>320 kg/m^3, Hence OK.

• Proportion of volume of coarse aggregate and fine aggregate content:

From table 5 of IS 10262:2019,volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (Zone 1) for water cement ratio of 0.5=0.6

In present case the water cement ratio is 0.40

-Therefore,the volume of coarse aggregate needs to be increased to decrease the fine aggregate content

-As water cement ratio is lower by 0.10,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).

Therefore,the corrected volume of coarse aggregate for the water cement cement ratio of 0.4=0.62

(Note:If coarse aggregate is not of angular type ,then also the volume of coarse aggregate may be required to be increased suitably,based on experience)

For pumpable concrete these values are reduced by 10%

Therefore,Volume of coarse aggregate=0.62*0.9=0.56

Volume of fine aggregate content=1-0.56=0.44

• Mix calculations:

The mix calculation per unit volume of concrete shall be as follows:

a)Volume of concrete=1 m^3

b)Volume of cement= Mass of cement*1/Specific gravity of cement*1000

=350*1/3.15*1000

=0.111 m^3

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

=140/1000

=0.140 m^3

d)Volume of chemical admixture=Mass of chemical admixture*1/specific gravity of admixture*1000

=7.6*1/1.145*1000

=0.006 m^3

e)Volume of aggregate (CA and FA)=(a-(b+c+d))

=0.743 m^3

g)Mass of coarse aggregate=f*Volume of coarse aggregate*specific gravity of CA*1000

=0.743*0.56*2.74*1000

=1140 kg/m^3

h)Mass of Fine aggregate=f*volume of FA*specific gravity of FA*1000

=0.743*0.44*2.74*1000

=896 kg/m^3

• Mix proportions for trial 1:

Cement =350 kg/m^3

water =140 kg/m^3

Fine aggregate =896 kg/m^3

Coarse aggregate=1140 kg/m^3

Chemical admixture=7 kg/m^3

Water cement ratio=0.4

Trial Mix Ratio =1:2.44:2.85

• The slump shall be measured and water cement and dosage of admixture shall be adjusted for achieving the required slump on trial.The mix proportion shall be reworked for the actual water content and checked for durability requirement.
• Two more trials having variation of 10% of water cement ratio in Clause X shall be carried out and a graph between three water cement ratios and corresponding strengths shall be plotted to work out the mix proportions for given target strength for field trials.However ,durability shall be met.

2.M35 grade of concrete :

• Stipulations for proportioning

a)Grade of concrete-M35

b)Type of cement-Ordinary Portland Cement,43 grade of cement conforming to IS 8112

c)Type of mineral admixture:Fly ash conforming to IS 3812(part 1)

d)Maximum nominal size of aggregates-20mm

e)Minimum cement content-340 kg/m^3 (From table 5 of IS 456:2000-Exposure condition)

f)Maximum water cement ratio-0.45 (From table 5 of IS 456:2000-Exposure condition)

g)Workability-100mm (slump value for pumpable concrete)

h)Exposure condition-Severe (for reinforced concrete)

i)Method of concrete placing-Pumping

j)Degree of supervision-Good

k)Type of aggregates-Crushed angular aggregate

l)Maximum cement content-450 kg/m^3

m)Chemical admixture type-Superplasticizer

• Test data for materials:

a)Cement used-OPC 43 grade conforming to IS 8112

b)Specific gravity of cement-3.15

c)Chemical admixture-Superplasticizer conforming to IS 9103

d)Specific gravity of-Coarse aggregate and Fine aggregate =2.74

e)Water absorption-Coarse aggregate and Fine aggregate are 0.5% and 1.0% respectively

f)Free surface moisture-Coarse aggregate and Fine aggregate are nil.

g)Sieve analysis-Coarse aggregate-Conforming to table 2 of IS 383

-Fine aggregate-Conforming to grading zone 1 of table 4 of IS 383

• Target mean strengthfor mix proportioning:

f'ck=fck+1.65 S

Where , f'ck=Target average compressive strength at 28 days

fck=Charecteristics compressive strength at 28 days

S=Standard deviation

From table 2 of IS 10262:2019,standard deviation,S=5 N/mm^2

Therefore,Target strength=35+1.65*S

=43.25 N/mm^2

• Selection of water cement ratio:

From the table 5 of IS 456:2000 for severe exposure,maximum water cement ratio =0.45

Based on experience,adopt water cement ratio as 0.40

0.40<0.45 , Hence OK

• Selection of water content:

From table 4 of IS 10262:2019,maximum water content for 20mm aggregate=186 litre(for 25 to 50mm slump)

Estimated water content for 100mm slump=186+6/100*186

=197 litre

As superplasticizer is used ,the water content can be reduced upto 30%

Based on trials water content reduction of 29% is achieved with plasticizer

Hence the arrived water content=197*0.71=140 litre

• Calculation of cement content:

Water cement ratio=0.40

Cementitious material(cement+fly ash) content=140/0.4=350 kg/m^3

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

350 kg/m^3>320 kg/m^3, Hence OK

Now ,to proportion a mix containing fly ash the following steps are suggested;

-The percentage of fly ash needs to be decided based on the project requirements and quality of materials

-In some cases increase in cementitious material can be warrented.Increase in cementitious material content and its percentage may be based on experience and trial(here lrts increasing the cementitious material content by 10%)

Cementitious material content =350*1.1=385 kg/m^3

water content =140 kg/m^3

so, water cement ratio =140/385=0.365

Fly as @30% total cementitious material content =385*30%=115 kg/m^3

Cement (OPC) =385-115=270 kg/m^3

Saving of cement while using fly ash =350-270=80 kg/m^3

Fly as being used =115 kg/m^3

• Proportion of volume of coarse aggregate and fine aggregate content:

From table 5 of IS 10262:2019,volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (Zone 1) for water cement ratio of 0.5=0.6

In present case the water cement ratio is 0.40

-Therefore,the volume of coarse aggregate needs to be increased to decrease the fine aggregate content

-As water cement ratio is lower by 0.10,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).

Therefore,the corrected volume of coarse aggregate for the water cement cement ratio of 0.4=0.62

(Note:If coarse aggregate is not of angular type ,then also the volume of coarse aggregate may be required to be increased suitably,based on experience)

For pumpable concrete these values are reduced by 10%

Therefore,Volume of coarse aggregate=0.62*0.9=0.56

Volume of fine aggregate content=1-0.56=0.44

• Mix calculations:

The mix calculation per unit volume of concrete shall be as follows:

a)Volume of concrete=1 m^3

b)Volume of cement= Mass of cement*1/Specific gravity of cement*1000

=270*1/3.15*1000

=0.086 m^3

c)Volume of flyash=Mass of fly ash*1/specific gravity of flyash*1000

=115*1/2.2*1000

=0.052 m^3

d)Volume of water=Mass of water*1/specific gravity of water*1000

=140/1000

=0.140 m^3

e)Volume of chemical admixture=Mass of chemical admixture*1/specific gravity of admixture*1000

=7.6*1/1.145*1000

=0.006 m^3

f)Volume of aggregate (CA and FA)=(a-(b+c+d+e))

=0.716 m^3

g)Mass of coarse aggregate=f*Volume of coarse aggregate*specific gravity of CA*1000

=0.716*0.56*2.74*1000

=1098 kg/m^3

h)Mass of Fine aggregate=f*volume of FA*specific gravity of FA*1000

=0.716*0.44*2.74*1000

=863 kg/m^3

• Mix proportions for trial 1:

Cement =270 kg/m^3

Fly ash =115 kg/m^3

water =140 kg/m^3

Fine aggregate =863 kg/m^3

Coarse aggregate=1098 kg/m^3

Chemical admixture=7 kg/m^3

Water cement ratio=0.4

Result: Trial Mix Ratio =1:2.56:3.26

Where 1 bag consists of 50 kg cement

2.56 times 50 kgs of fine aggregates

3.26 times 50 kgs of coarse aggregates

• The slump shall be measured and water cement and dosage of admixture shall be adjusted for achieving the required slump on trial.The mix proportion shall be reworked for the actual water content and checked for durability requirement.
• Two more trials having variation of 10% of water cement ratio in Clause X shall be carried out and a graph between three water cement ratios and corresponding strengths shall be plotted to work out the mix proportions for given target strength for field trials.However ,durability shall be met.