Project on Concrete Mix Design for various grades of Concrete

• Calculate the Concrete Mix Design for M35 grade concrete with fly ash.

Sol:

1. Stipulation for proportion:
   1. Grade designation: M35
   2. Type of cement: OPC 43 grade confirming to IS8112.
   3. Type of mineral admixture: Fly ash confirming to IS 3812
   4. Maximum nominal size of aggregate: 20mm.
   5. Minimum cement content: 320Kg/m^3 (From table 5 of IS456:2000 – Exposure Condition)
   6. Maximum water-cement ratio: 0.45(From table 5 of IS456:2000 – Exposure Condition)
   7. Workability: 100mm (slump)
   8. Exposure Condition: Severe
   9. Method of concrete placing: Pumping
   10. Type of Aggregate: Crushed Angular Aggregate
   11. Maximum cement content: 450Kg/m^3
   12. Chemical Admixture type: Superplasticizer

II.Test data for materials:

1. Cement used: OPC 43 grade confirming to IS8112
2. Specific gravity of cement: 3.15
3. Fly Ash: Confirming to IS 3812
4. Specific gravity of fly ash :2.2
5. Chemical Admixture: Superplasticizer confirming to IS9103.
6. Specific gravity of fine aggregate: 2.74
7. Specific gravity of coarse aggregate: 2.74
8. Water Absorption:
   1. Coarse aggregate: 0.5%
   2. Fine aggregate: 1.0%
9. Free Surface moisture:
   1. Coarse aggregate: Nil
   2. Fine aggregate: Nil
10. Sieve Analysis:

Coarse aggregate: Confirming to table 2 of IS383.

Fine aggregate: Confirming to zone I of table 4 IS383

III. Target Strength of Mix proportioning

Fck = fck + 1.65 X S

Standard division = 5 N/mm^2 (as per table IS 10262:2008).

Target Strength (fck) = 35+1.65 X 5.0

Target mean strength = 43.25 N/mm^2

IV. Selection of water/cement ratio:

Maximum water cement ratio = 0.45

Based on experience adopted water cement ratio is 0.44

0.44 < 0.45, Hence OK

Water- cement ratio = 0.44

V .Section of water content:

Maximum water content for 20mm aggregate = 186kg (for 25 to 50 slump)

(Increase water content by 3% for every 25mm above 50mm i.e. increase 6% for 100mm slump)

Estimated water content for 100 sumps

= 186 + (6/100)*186 = 197 liters

Water content = 197 liters

Based on trial water content reduction of 20% is achieved with plasticizer. Hence the arrived water content = 197 – [197X0.2] = 158 liters

VI. Calculation of cement content

Water-cement ratio = 0.44

Water content = 197 liters

Cement content = 158/0.44 = 359 Kg/m^3

From table 5 of IS456, Minimum cement content for ‘Severe’ exposure condition = 320kg/m^3

359 Kg/m^3 > 320kg/m^3, hence, OK

(The cementitious content has to be increased in order to attain good workability and strength. The increment required is determined on the basis of experience and research. Here we are increasing cementitious content by 10%)

Final cementitious content = 359 x 1.10 = 395Kg

So, water cement ratio = 158/395 = 0.4

Fly ash @ 30% total cementitious material content = 395 x 0.3 = 118.5 Kg/m^3

Cement required = 395- 118.5 = 277 Kg/m^3

Cement quantity saved due to fly ash addition.= 350-277 = 73 Kg/m^3

Cementitious material = 395 Kg/m^3

Cement = 277 Kg/m^3

Fly ash = 118Kg/m^3

w/ c ratio = 0.4

VII. Proportion of Volume of coarse aggregate and Fine aggregate content. (From table 3 of IS 10262-2009)

Volume of coarse aggregate corresponding to 20mm size and fine aggregate for water-cement ratio of 0.5 = 0.62

In the present case water-cement ratio is 0.50

Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content. As water- cement ratio is less 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 of)

Therefore, corrected volume of coarse aggregate for water-cement ratio of 0.44 = 0.632.

For pumpable concrete, these values should be reduced by 10%.

Therefore, volume of coarse aggregate = 0.632 X 0.9

= 0.568

Volume of fine aggregate = 1-0.568

= 0.431

VII. Mix Calculation:

1. Volume of Concrete = 1m^3
2. Volume of cement = Mass of cement / Specific gravity of cement X 1/1000

= 377/3.15 X 1/1000

= 0.0.87m^3

3.Volume of Fly Ash = Mass of fly ash/ specific gravity of fly ash x 1/ 1000

= 118/2.2 x 1/ 1000

= 0.053 m^3

4. Volume of water = Mass of water/ Specific gravity of water X 1/1000

=158 X 1/1000

= 0.158m^3

5. Volume of admixture = Mass of chemical admixture/ Specific gravity of admixture X 1/1000

= 7.6/1.145 X 1/1000

= 0.006 m^3

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

= 1 – (0.087 + 0.053+0.158+ 0.006)

= 0.696m^3

7. Mass of coarse aggregate = e X volume of coarse aggregate X specific gravity of coarse aggregate X 1000

= 0.696 X 0.568 X 2.74 X 1000

= 1077 Kg/m^3

8.Mass of fine aggregate = e X volume of fine aggregate X specific gravity of fine aggregate X 1000

= 0.696 X 0.431 X 2.74 X 1000

= 822 Kg/m^3

VIII. Mix proportions for Trail number 1.

1. Cement = 277 kg/m^3
2. Fly ash = 118 Kg/ m^3
3. Water = 158 kg/m^3
4. Chemical admixture = 7.18kg/m^3
5. Fine aggregate = 822 Kg/m^3
6. Coarse aggregate = 1077Kg/m^3
7. Water cement ratio = 0.44

Trial mix ratio: 1: 2.9 :3.8

IX. The slump shall be measured and the water content 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.

X. Two more trials having variation of 10% of water cement ratio in clause X shall be plotted to work out the mix proportion for the given target strength for field trials. However, durability shall be met.

• Concrete mix design for M50 grade concrete without fly ash.

Sol:

1. Stipulation for proportion:
   1. Grade designation: M50
   2. Type of cement: OPC 53 grade confirming to IS8112.
   3. Maximum nominal size of aggregate: 20mm.
   4. Minimum cement content: 320Kg/m^3 (From table 5 of IS456:2000 – Exposure Condition)
   5. Maximum water-cement ratio: 0.45(From table 5 of IS456:2000 – Exposure Condition)
   6. Workability: 100mm (slump)
   7. Exposure Condition: Severe
   8. Method of concrete placing: Pumping
   9. Degree of Suppression: Good
   10. Type of Aggregate: Crushed Angular Aggregate
   11. Maximum cement content: 450Kg/m^3
   12. Chemical Admixture type: Superplasticizer
2. Test data for materials:
   1. Cement used: OPC 53 grade confirming to IS8112
   2. Specific gravity of cement: 3.15
   3. Chemical Admixture: Superplasticizer confirming to IS9103.
   4. Specific gravity of fine aggregate: 2.74
   5. Specific gravity of coarse aggregate: 2.64
   6. Water Absorption:
      1. Coarse aggregate: 0.5%
      2. Fine aggregate: 1.0%
   7. Free Surface moisture:
      1. Coarse aggregate: Nil
      2. Fine aggregate: Nil
   8. Sieve Analysis:

Coarse aggregate: Confirming to table 2 of IS383.

Fine aggregate: Confirming to zone I of table 4 IS383

III. Target Strength of Mix proportioning

Fck = fck + 1.65 X S

Standard division = 5 N/mm^2 (as per table IS 10262:2008).

Target Strength (fck) = 50+1.65 X 5.0

Target mean strength = 58.25 N/mm^2

IV. Selection of water/cement ratio:

Maximum water cement ratio = 0.45

Based on experience adopted water cement ratio is 0.44

0.44 < 0.45, Hence OK

Water cement ratio = 0.44

V. Section of water content:

Maximum water content for 20mm aggregate = 186kg (for 25 to 50 slump)

(Increase water content by 3% for every 25mm above 50mm i.e. increase 6% for 100mm slump)

Estimated water content for 100 sumps

= 186 + (6/100)*186 = 197 liters

Water content = 197 liters

Based on trial water content reduction of 20% is achieved with plasticizer. Hence the arrived water content = 197 – [197X0.2] = 158 liters

Water content = 158 litres

VII. Calculation of cement content

Water-cement ratio = 0.44

Water content = 197 liters

Cement content = 158/0.44 = 359 Kg/m^3

From table 5 of IS456, Minimum cement content for ‘Severe’ exposure condition = 20kg/m^3

359 Kg/m^3 > 320kg/m^3, hence, OK

VIII. Proportion of Volume of coarse aggregate and Fine aggregate content. (From table 3 of IS 10262-2009)

Volume of coarse aggregate corresponding to 20mm size and fine aggregate for water-cement ratio of 0.5 = 0.62

In the present case water-cement ratio is 0.50

Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content. As water- cement ratio is less 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 of)

Therefore, corrected volume of coarse aggregate for water-cement ratio of 0.45 = 0.632.

For pumpable concrete, these values should be reduced by 10%.

Therefore, volume of coarse aggregate = 0.632 X 0.9

= 0.568

Volume of fine aggregate = 1-0.567

= 0.433

XI. Mix Calculation:

Volume of Concrete = 1m^3

Volume of cement = Mass of cement / Specific gravity of cement X 1/1000

= 359/3.15 X 1/1000

= 0.114m^3

Volume of water = Mass of water/ Specific gravity of water X 1/1000

=158 X 1/1000

= 0.158m^3

Volume of admixture = Mass of chemical admixture/ Specific gravity of admixture X 1/1000

= 7.6/1.145 X 1/1000

= 0.006 m^3

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

= 1 – (0.114 + 0.158 + 0.006)

= 0.722m^3

Mass of coarse aggregate = e X volume of coarse aggregate X specific gravity of coarse aggregate X 1000

= 0.722 X 0.568 X 2.74 X 1000

= 1123 Kg/m^3

Mass of fine aggregate = e X volume of fine aggregate X specific gravity of fine aggregate X 1000

= 0.722 X 0.431 X 2.64X 1000

= 821 Kg/m^3

X. Mix proportions for Trail number 1.

1. Cement = 359 kg/m^3
2. Water = 158kg/m^3
3. Chemical admixture = 7.18kg/m^3
4. Fine aggregate = 821 Kg/m^3
5. Coarse aggregate = 1123Kg/m^3
6. Water cement ratio = 0.44

Trial mix ratio: 1:2.28:3.12

IX. The slump shall be measured and the water content 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.

X. Two more trials having variation of 10% of water cement ratio in clause X shall be plotted to work out the mix proportion for the given target strength for field trials. However, durability shall be met.