Project on Concrete Mix Design for various grades of Concrete

1. AIM: Calculate the Concrete Mix Design for M35 grade concrete with fly ash.

Introduction:

Stipulation for Proportioning.

1. Grade designation: M35
2. Type of cement: OPC 43 grade conforming to IS 8112
3. Type of mineral admixture: Fly ash conforming to IS 3812 ( Part 1)
4. Maximum nominal size of aggregate: 20mm
5. Minimum cement content: 340 kg/m^3 ( From table 5 of IS 456:2000 - Exposure condition)
6. Maximum water-cement ratio: 0.45 ( From table 5 of IS 456:2000 - Exposure condition)
7. Workability: 100mm (Slump value for pumpable concrete)
8. Exposure condition: Very Severe (For reinforced Concrete)
9. Method of Concrete placing: Pumping.
10. Degree of Supervision: Good.
11. Aggregate: Crushed angular aggregate.
12. Maximum cement content: 450 kg/m^3.
13. Chemical admixture type: Superplasticizer.

Test data for materials:

1. Cement used: OPC 3 grade Conforming to IS 8112.
2. The specific gravity of cement: 3.15
3. Fly ash: Conforming to IS 3812 (Part 1)
4. The specific gravity of fly ash:2.2
5. Chemical admixture: Superplasticizer conforming to IS 9103.
6. The specific gravity of Coarse aggregate=2.74 and Fine aggregate=2.74
7. Water absorption: Coarse aggregate = 0.5% and Fine aggregate = 1.0%
8. Free Surface moisture: Coarse aggregate = Nil and Fine aggregate = Nil.
9. Sieve Analysis: Coarse aggregate

Fine aggregate: Conforming to grading Zone 1 of Table 4 IS 383.

Target strength for Mix proportioning:

f'ck = fck + 1.65 * S.

where f'ck = Target average compressive strength at 28 days.

fck = Characteristics Compressive strength at 28 days.

S = Standard Deviation.

From table 1 of IS 10262: 2009,

Standard deviation, S=5 N/mm^2

Therefore Target strength = 35 + 1.65*5

= 43.25 N/mm^2.

Selection of water-cement ratio:

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

Based on experience, the adopted water-cement ratio is 0.40.

0.40<0.45, Hence OK.

Selection of water content:

From table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 liters ( For 25mm to 50mm Slump range).

Therefore estimated water content for 100mm Slump = 186+(6/100)*186

= 186+11.16

= 197.16 Approximately = 197 liters.

As Superplasticizer is used the water content can be reduced up to 20% and above based on trials water content reduction of 20% is achieved with a plasticizer.

Hence the arrived water content => 197*(100%-20%)

=> 197*(80%)

=> 197*(0.80)

=> 157.6 Approximately= 157 liters.

Calculation of Cement content:

Water-cement ratio=0.4

Cement Content = 157/0.4

= 392.5 Approximately= 392 kg/m^3.

From table 5 of IS 456 minimum cement content for very severe exposure conditions = 340 kg/m^3.

392kg/m^3 > 320kg/m^3. Hence ok.

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

1. The percentage of fly ash needs to be decided based on project requirements and the quality of materials.
2. In some cases, an increase in cementitious material can be warranted. The increase in cementitious material content and its percentage may be based on experience and trial (This example is with an increase of 10% cementitious material content).

Cementitious material content = 392+(10/100)*392

= 392*(1.10)

= 431.2 Approximately= 431 kg/m^3.

Water content = 157 kg/m^3.

So, water-cement ratio = 157/431=> 0.364

Fly ash @30% total cementitious material content = 431*30%=> 129.3 Approximately= 129kg/m^3.

Cement (OPC) = 431-129 = 302 kg/m^3.

Saving cement while using fly ash = 392-302 = 90 kg/m^3. and

Fly ash being utilized = 129 kg/m^3.

The proportion of Volume of Coarse aggregate and Fine aggregate content:

From table 3 of IS 10262:2009, the Volume of Coarse Aggregate corresponding to 20mm Size aggregate and Fine Aggregate (Zone 1) for the water-cement ratio of 0.5 is "0.6".

In the 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 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 water-cement ratio).

Therefore corrected Volume of Coarse aggregate for the water-cement ratio of 0.40 = 0.62.

(Note: If the 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*(100%-10%)

=> 0.62*0.9

=> 0.558

=> 0.56

Volume of Fine aggregate content => 1-0.56 =>0.44.

Mix Calculations:

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

1. Volume of Concrete = 1m^3.
2. Volume of cement= (mass of cement / specific gravity of cement)* (1/1000)

= (302/3.15)*(1/1000)

= 0.096 m^3.

c. Volume of Fly ash = (mass of Fly ash/ specific gravity of Fly ash)* (1/1000).

= (129/2.2)*(1/1000)

= 0.059 m^3.

d. Volume of water = (mass of water/ specific gravity of water) * (1/1000).

= (157/1)*(1/1000)

= 0.157 m^3.

e. Volume of Chemical admixture = (mass of chemical admixture/specific gravity of admixture)*(1/1000)

= (2% of cementitious material / 1.145)*(1/1000)

= (8.62/1.145)*(1/1000)

= 0.007 m^3

f. Volume of aggregate ( CA & FA) = [a-(b+c+d+e)]

= [1-(0.096+0.059+0.157+0.007)]

= 0.681 m^3

Mass of Coarse aggregate = f * Volume of Coarse aggregate * Specific gravity of Coarse aggregate * 1000

= 0.681 * 0.56 * 2.74 * 1000

= 1044 kg/m^3.

Mass of fine aggregate = f * Volume of Fine aggregate * Specific gravity of fine aggregate * 1000

= 0.681*0.44*2.74*1000

= 821 kg/m^3

Results :

Mix proportions for Trial Number 1 :

Cement (OPC) = 302 kg/m^3

Fly ash = 129 kg/m^3

Water = 157 kg/m^3

Fine aggregate = 821 kg/m^3

Coarse aggregate = 1044 kg/m^3

Chemical admixture = 8.62 kg/m^3

Water cement ratio = 0.364

Trial Mix ratio = (Cement + Flyash) : Fine aggregate : Coarse aggregate

= (302+129) : 821 : 1044

= 431: 821:1044

= 1 : 1.90 : 2.42 (C+Flyash : FA : CA)

The Slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on the trail. The mix proportion shall be reworked for the actual water content and checked for durability requirements.

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 strength shall be plotted to work out the mix proportion for the given target strength for fields trials. However, durability shall be met.

2. Aim: Concrete Mix design for the M50 grade concrete without fly ash

Introduction:

Stipulation for Proportioning.

1. Grade designation: M50
2. Type of cement: OPC 43 grade conforming to IS 8112
3. Maximum nominal size of aggregate: 20mm
4. Minimum cement content: 320 kg/m^3 ( From table 5 of IS 456:2000 - Exposure condition)
5. Maximum water-cement ratio: 0.45 ( From table 5 of IS 456:2000 - Exposure condition)
6. Workability: 100mm (Slump value for pumpable concrete)
7. Exposure condition: Severe (For reinforced Concrete)
8. Method of Concrete placing: Pumping.
9. Degree of Supervision: Good.
10. Aggregate: Crushed angular aggregate.
11. Maximum cement content: 450 kg/m^3.
12. Chemical admixture type: Superplasticizer.

Test data for materials:

1. Cement used: OPC 3 grade Conforming to IS 8112.
2. The specific gravity of cement: 3.15
3. Chemical admixture: Superplasticizer conforming to IS 9103.
4. The specific gravity of Coarse aggregate=2.74 and Fine aggregate=2.74
5. Water absorption: Coarse aggregate = 0.5% and Fine aggregate = 1.0%
6. Free Surface moisture: Coarse aggregate = Nil and Fine aggregate = Nil.
7. Sieve Analysis: Coarse aggregate

Fine aggregate: Conforming to grading Zone 1 of Table 4 IS 383.

Target strength for Mix proportioning:

f'ck = fck + 1.65 * S.

where f'ck = Target average compressive strength at 28 days.

fck = Characteristics Compressive strength at 28 days.

S = Standard Deviation.

From table 1 of IS 10262: 2009,

Standard deviation, S=5 N/mm^2

Therefore Target strength = 50 + 1.65*5

= 58.25 N/mm^2.

Selection of water-cement ratio:

From table 5 of IS 456:2000 for Severe exposure, maximum water-cement ratio = 0.45.

Based on experience, the adopted water-cement ratio is 0.40.

0.40<0.45, Hence OK.

Selection of water content:

From table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 liters ( For 25mm to 50mm Slump range).

Therefore estimated water content for 100mm Slump = 186+(6/100)*186

= 186+11.16

= 197.16 Approximately = 197 liters.

As Superplasticizer is used the water content can be reduced up to 20% and above based on trials water content reduction of 29% is achieved with a plasticizer.

Hence the arrived water content => 197*(100%-29%)

=> 197*(71%)

=> 197*(0.71)

=> 139.87 Approximately= 140 liters.

Calculation of Cement content:

Water-cement ratio=0.4

Cement Content = 140/0.4

= 350 kg/m^3.

From table 5 of IS 456 minimum cement content for Severe exposure conditions = 320 kg/m^3.

350kg/m^3 > 320kg/m^3. Hence ok.

The proportion of Volume of Coarse aggregate and Fine aggregate content:

From table 3 of IS 10262:2009, the Volume of Coarse Aggregate corresponding to 20mm Size aggregate and Fine Aggregate (Zone 1) for the water-cement ratio of 0.5 is "0.6".

In the 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 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 water-cement ratio).

Therefore corrected Volume of Coarse aggregate for the water-cement ratio of 0.40 = 0.62.

(Note: If the 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*(100%-10%)

=> 0.62*0.9

=> 0.558

=> 0.56

Volume of Fine aggregate content => 1-0.56 =>0.44.

Mix Calculations:

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

1. Volume of Concrete = 1m^3.
2. Volume of cement= (mass of cement / specific gravity of cement)* (1/1000)

= (350/3.15)*(1/1000)

= 0.111m^3.

c.Volume of water = (mass of water/ specific gravity of water) * (1/1000).

= (140/1)*(1/1000)

= 0.140 m^3.

d.Volume of Chemical admixture = (mass of chemical admixture/specific gravity of admixture)*(1/1000)

= (2% of cementitious material / 1.145)*(1/1000)

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

= 0.006 m^3

e.Volume of aggregate ( CA & FA) = [a-(b+c+d)]

= [1-(0.011+0.140+0.006)]

= 0.743 m^3

Mass of Coarse aggregate = e* Volume of Coarse aggregate * Specific gravity of Coarse aggregate * 1000

= 0.743 * 0.56 * 2.74 * 1000

= 1140kg/m^3.

Mass of fine aggregate = e * Volume of Fine aggregate * Specific gravity of fine aggregate * 1000

= 0.743*0.44*2.74*1000

= 896 kg/m^3

Results :

Mix proportions for Trial Number 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 = Cement : Fine aggregate : Coarse aggregate

= 350 : 896 : 1140

= 1:2.56:3.26 ( C : FA : CA )

The Slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on the trail. The mix proportion shall be reworked for the actual water content and checked for durability requirements.

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 strength shall be plotted to work out the mix proportion for the given target strength for fields trials. However, durability shall be met.