Project on Concrete Mix Design for various grades of Concrete

Project on Concrete Mix Design for various grades of Concrete

Aim: To calculate the concrete Mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash.

Introduction:

Concrete is a mixture of Portland cement, water, coarse and fine aggregates and sometimes admixtures. Proportioning a concrete mix for a given purpose is the art of obtaining a suitable ratio of various ingredients of concrete with the required properties at the lower cost. The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength. The method of concrete mix design consists of selection of optimum proportions of ingredients, i.e., water, cement, fine aggregate, Coarse aggregate and admixture if needed to produce Concrete of specified properties such as strength, workability, and durability. This project is illustrating two parts of Mix design concrete M35 grade with fly ash and without fly ash of M50 grade of concrete.

Objective:

In this project I have used the concrete mix proportion guidelines from IS 10262:2009 and recommended guide lines from IS 10262:1982

Procedure and Calculation:

Mix design for M35 grade concrete with fly ash:

Step 1: Stipulations for Mix Design Concrete

Grade designation: M 35

Type of cement: OPC 43 grade confirming to IS 8112

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

Maximum nominal size of aggregate: 20 mm

Minimum cement content: 320 kg/m

Maximum water-cement ratio: 0.45

Workability: 100 mm (slump)

Exposure condition: Extreme weather conditions (for reinforced concrete)

Method of concrete placing: Pumping

Degree of supervision: Good

Type of aggregate: Crushed angular aggregate

Maximum cement content: 450 kg/m³

Chemical admixture type: Super Plasticizer

Step 2: Test Data for Materials

• Cement used: OPC 43 grade conforming (IS 12261)
• Chemical admixture: super plasticizer conforming to IS 9103
• Specific gravity of cement: 3.15
• 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: Nil
• Free surface moisture of fine aggregate: Nil
• Sieve analysis coarse aggregate: conforming to Table 2 of IS 383
• Sieve analysis fine aggregate: conforming to Table 2 of IS 383

Step 3: Target strength for Mix proportion

ftarget = fck + 1.65 x s

ftarget is the Target Average Compressive Strength at 28 days,

fck is the Characteristic Compressive Strength at 28 days, and

S is the Standard Deviation

as per the table I of IS: 10262-2009, the standard deviation, s is 5.0 N/mm2

Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm2

Step 4: Selection of Water/Cement Ratio

Maximum water-cement ratio = 0.44

Step 5: Selection of Water Content

From Table 2 of IS 456:2000, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 186 =197 litres.

(Note: If Super plasticizer is used, the water content can be reduced up to 20% and above.)

Based on trials with Super plasticizer, water content reduction of 20% has been achieved. Hence the arrived water content = 197- [197 x (20/100)] = 158 litres.

Calculation of cement content

w/c Ratio = 0.44

Cement Content = 158/0.44 = 359 kg/m3

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 = 395 kg

From Table 5 of IS 456, minimum cement content,

For extreme conditions (320 kg) (395 kg/m^3 > 320 kg/m^3) hence ok.

New water cement ratio = 158/395 = 0.4

Fly ash content is taken as 30% of the total cementitious content = 395X0.3

= 118.5 kg/m^3

Cement required = 395- 118 = 277 kg/m^3

Cement quantity saved due to fly ash addition = 350-277

= 73 kg/m^3

Step 6: Proportion of volume of coarse aggregate and fine aggregate

From table 3 of Is 10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (zone I) for water cement ratio 0.50 = 0.62.

In the present case the w/c ratio is =0.44

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

As W/c ratio is lower by 0.06 the proportion of volume of coarse aggregate increased by 0.02 (at the rate -/+ 0.01 for every change in W/c ratio)

Therefore, corrected volume of coarse aggregate for W/c ratio of 0.44 = 0.64

For pumpable concrete these values are reduced by 10%

Volume of coarse aggregate =0.632 x 0.9 = 0.568

Volume of fine aggregate content = 1-0.568= 0.431

W/c ratio = 0.44, Water content = 158 litres = 158/0.4 = 359 kg/m^3

Step 7: Mix calculations

• Volume of concrete= 1m^3
• Volume of fly ash = (Mass of fly ash/ specific gravity of cement) X (1/1000)

= 0.0053 m^3

• Volume of cement = (Mass of cement/ specific gravity of cement) X (1/1000)

= (277/3.15) x (1/1000) = 0.0087 m^3

• Volume of 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 chemical admixture/ specific gravity of admixture) X (1/1000)

= 0.006m^3

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

= (1-(0.0087+0.053+0.006+0.158))

= 0.696 m^3

• 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

• 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

Step 8: Mix proportion

• Cement = 277 kg/m^3
• Water = 158 kg/m^3
• Fine aggregate = 822 Kg/m^3
• Coarse aggregate = 1077 Kg/m^3
• Water cement ratio = 0.44
• Fly ash = 118 kg/m^3
• Chemical admixture = 7.18 kg/ m^3

Trial mix ratio = 1:2.08:2.72.

Step 9: The slump shall be measured the water content and dosage od 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 requirements.

Step 10: Two more trials having variation of 10% of water cement ratio shall be carried out and a graph between three water cement ratios and corresponding strength shall be plotted to work out the mix proportions for the given target for field trials.

Procedure and Calculation:

Mix design for M35 grade concrete without fly ash:

Step 1: Stipulations for Mix Design Concrete

Grade designation: M 50

Type of cement: OPC 53 grade confirming to IS 8112

Maximum nominal size of aggregate: 20 mm

Minimum cement content: 320 kg/m

Maximum water-cement ratio: 0.45

Workability: 100 mm (slump)

Exposure condition: Extreme weather conditions (for reinforced concrete)

Method of concrete placing: Pumping

Degree of supervision: Good

Type of aggregate: Crushed angular aggregate

Maximum cement content: 450 kg/m³

Chemical admixture type: Super Plasticizer

Step 2: Test Data for Materials

• Cement used: OPC 53 grade conforming (IS 12261)
• Chemical admixture: super plasticizer conforming to IS 9103
• Specific gravity of cement: 3.15
• Specific gravity of Coarse aggregate: 2.74
• Specific gravity of Fine aggregate: 2.64
• Water absorption of coarse aggregate: 0.5%
• Water absorption of fine aggregate: 1.0 %
• Free surface moisture of coarse aggregate: Nil
• Free surface moisture of fine aggregate: Nil
• Sieve analysis coarse aggregate: conforming to Table 2 of IS 383
• Sieve analysis fine aggregate: conforming to Table 2 of IS 383

Step 3: Target strength for Mix proportion

ftarget = fck + 1.65 x s

ftarget is the Target Average Compressive Strength at 28 days,

fck is the Characteristic Compressive Strength at 28 days, and

S is the Standard Deviation

as per the table I of IS: 10262-2009, the standard deviation, s is 5.0 N/mm2

Therefore, target strength = 50 + 1.65 x 5.0 = 53.25 N/mm2

Step 4: Selection of Water/Cement Ratio

Maximum water-cement ratio = 0.44

Step 5: Selection of Water Content

From Table 2 of IS 456:2000, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 186 =197 litres.

(Note: If Super plasticizer is used, the water content can be reduced up to 20% and above.)

Based on trials with Super plasticizer, water content reduction of 20% has been achieved. Hence the arrived water content = 197- [197 x (20/100)] = 158 litres.

Calculation of cement content

w/c Ratio = 0.44

Cement Content = 158/0.44 = 359 kg/m3

From Table 5 of IS 456, minimum cement content,

For extreme conditions (320 kg) (359 kg/m^3 > 320 kg/m^3) hence ok.

Cement required = 359 kg/m^3

Step 6: Proportion of volume of coarse aggregate and fine aggregate

From table 3 of Is 10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (zone I) for water cement ratio 0.50 = 0.62.

In the present case the w/c ratio is =0.44

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

As W/c ratio is lower by 0.06 the proportion of volume of coarse aggregate increased by 0.02 (at the rate -/+ 0.01 for every change in W/c ratio)

Therefore, corrected volume of coarse aggregate for W/c ratio of 0.44 = 0.64

For pumpable concrete these values are reduced by 10%

Volume of coarse aggregate =0.632 x 0.9 = 0.568

Volume of fine aggregate content = 1-0.568= 0.431

W/c ratio = 0.44, Water content = 158 litres = 158/0.4 = 359 kg/m^3

Step 7: Mix calculations

• Volume of concrete= 1m^3
• Volume of cement = (Mass of cement/ specific gravity of cement) X (1/1000)

= 0.114 m^3

• Volume of 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 chemical admixture/ specific gravity of admixture) X (1/1000)

= 0.006m^3

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

= (1-(0.114+0.006+0.158))

= 0.722 m^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

= 0.696 x 0.431 x 2.64 x 1000

= 821 Kg/m^3

Step 8: Mix proportion

• Cement = 359 kg/m^3
• Water = 158 kg/m^3
• Fine aggregate = 821 Kg/m^3
• Coarse aggregate = 1123 Kg/m^3
• Water cement ratio = 0.44
• Fly ash = 118 kg/m^3
• Chemical admixture = 7.18 kg/ m^3

Trial mix ratio = 1:2.28:3.12.

Step 9: The slump shall be measured the water content and dosage od 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 requirements.

Step 10: Two more trials having variation of 10% of water cement ratio shall be carried out and a graph between three water cement ratios and corresponding strength shall be plotted to work out the mix proportions for the given target for field trials.

Results:

Mix proportion by weight of M35 grade of concrete with fly ash is 1:2.08:2.72 and its water cement ratio was found to be 0.4.

Mix proportion by weight of M50 grade of concrete without fly ash 1:2.28:3.12 and its water cement ratio was found to be 0.44