Project on Concrete Mix Design for various grades of Concrete

Project on Concrete Mix Design

For various grades of concrete

1. Calculate the concrete mix design for M35 grade concrete with Fly ash.

Ans:

Aim: To determine the mix proportions of concrete ingredients such as cement, fine & coarse aggregates, water content, w/c ratio, chemical admixture content & fly ash content for M35 grade of concrete with fly ash.

Introduction: To design the mix proportions of M35 grade of concrete with fly ash, we should follow various IS code books to confirm the clauses and use of materials to achieve desired compressive strength and to get durability. The mix trails should be performed at least 2 or 3 times to get more precise concrete mix design. Following are the code specifications that are used for the M35 grade concrete mix design using Fly ash.

• IS 12269-1987 – Specification for ordinary Portland cement of 53 Grade
• IS 383:2016 – Specification for coarse & fine aggregates for concrete (2^nd revision)
• IS 456:2000 – Code of practice for plain & reinforced concrete (4^th revision)
• IS 1489:2015 (part 1) – Specification for Portland pozzolana cement Fly ash based (3^rd revision)
• IS 3812 (part 1) – Fly ash
• IS 9103:1999 – Specification for admixtures for concrete (4^th revision)
• IS 10262-2019 – Concrete Mix proportioning Guidelines (2^nd revision)

Data required:

• Grade of concrete = M35 grade
• Grade of cement = 53 grade of OPC confirming to IS 12269-1987
• Maximum nominal size of aggregate = 20mm (used)
• Exposure condition = Very severe
• Minimum cement content = 340 kg/m³ (IS 456:2000, table 5)
• Maximum water cement ratio = 0.45 (IS 456:2000, table 5)
• Workability = 75mm slump
• Method of placing = pumping
• Degree of supervision = good
• Type of coarse aggregate = crushed angular aggregate confirming to IS 383-2016
• Type of fine aggregate = natural sand of zone 1, confirming to IS 383-2016
• Maximum cement content = 450 kg/m³
• Chemical admixture = superplasticizer as per IS 9103:1999
• Fly ash use of 25% confirming to IS 3812 (part 1)

Test data:

• Specific gravity of cement = 3.15
• Specific gravity of coarse aggregate = 2.84
• Specific gravity of fine aggregate = 2.74
• Specific gravity of chemical admixture = 1.45
• Specific gravity of Fly ash = 2.2
• Water absorption of coarse aggregate = 0.5%
• Water absorption of fine aggregate = 1%
• Free surface of both fine & coarse aggregate = Nil

Procedure:

Step 1: Calculation of Target strength

The concrete mix has to be proportioned for higher target mean compressive strength f’ck to avoid the specified proportion of test results to fall below the characteristic strength.

Target mean strength f’ck = fck + 1.65*S

Where,

fck = characteristic compressive strength of concrete at 28 days in N/mm² = 35 N/mm²

S = standard deviation (IS 456:2000, table 8) or (IS 10262:2019, table 2)

S = 5.0 N/mm²

Target mean compressive strength = 35 + 1.65*5.0 = 43.25 N/mm²

Step 2: Selection of water-cement ratio

1. As per IS 456:2000, table 5, the maximum free water cement ratio mainly based on exposure condition for M35 grade of concrete = 0.45.
2. As per IS 10262:2019, fig 1 graph between free water cement ratio & 28day compressive strength of concrete in N/mm² & cement grade curves (53 grade curve) = 0.46.
3. Since 0.45 < 0.46, considering 0.45 as W/c ratio for this mix design.

Step 3: Selection of water content

As per table 4 of IS 10262:2019, the maximum water content per cubic meter of concrete for nominal maximum size of aggregate & for 50mm slump = 186 kg. (Aggregate size = 20mm considered)

Here, slump required = 75mm and method of placing is by pumping.

As per IS 10262:2019, clause 5.3, the required water content can be increased or decreased by about 3% for each increase or decrease of 25mm slump.

Hence water content for 75mm slump = 186 + (3/100)*186 = 192kg.

As super plasticizer is used, water content can be decreased by about 20-30 percentage (IS 10262:2019, clause 5.3)

Considering 20% decrease of water content based on trails.

Therefore, water content = 192-(20/100)*192 = 154kgs.

Step 4: Calculation of Cement, Fly ash & chemical admixture content

We know that water-cement ration i.e., w/c = 0.45

Water content, w = 154kg

Cement content = w/0.45 = 154/0.45 = 342 kg/m³ > 340kg/m³. Hence ok.

Here cement content is a combination of cement and fly ash being used.

Therefore, cementitious material i.e., Cement + fly ash = 342 kg/m³

As fly ash is used about 25%, the increase in cementitious material may be increased by 10% for preliminary trail. (IS 10262:2019, clause 5.4)

Increased cementitious content = 342 + (10/100)*342 = 376 kg/m³

Corrected water-cement ratio = 154/376 = 0.4

Fly ash content = 376 * (25/100) = 94 kg/m³

Therefore, Cement content = 282 kg/m^3.

Cement saving = 342-282 = 60 kg/m³

Chemical admixture content = 2% of cementitious content = 376*(2/100) = 7.52 kg/m³.

Step 5: Proportion of volume of Coarse aggregate & fine aggregate content

Form table 5 or IS 10262:2019, the volume of coarse aggregate per unit volume of total aggregate for fine aggregate of zone 1 for w/c ratio 0.5 is & for 20mm coarse aggregate.

Volume of coarse aggregate = 0.6 m³

Since, w/c ratio is lower by 0.1 (0.5-0.4 = 0.1), proportion of volume of coarse aggregate is increased by 0.02 at the rate of +/- 0.01 for every +/- 0.05 change in w/c ratio.

Therefore, corrected volume of coarse aggregate = 0.6+0.02 = 0.62m³.

Since, mode of placing of concrete is by pumping, the estimated coarse aggregate content can be reduced up to 10%. (IS 10262:2019, clause 5.5.2)

Hence volume of coarse aggregate = 0.62 – (10/100)*0.62 = 0.558 m³

Volume of fine aggregate = 1 – 0.558 = 0.442 m³

Step 6: Mix calculations

1. Volume of concrete = 1 m³
2. Volume of cement = [(mass of cement/sp.gr of cement)*(1/1000)]

= [(282/3.15)*(1/1000)] = 0.089 m³

• Volume of fly ash = [(94/2.2)*(1/1000)] = 0.04 m³

1. Volume of water = [(154/1)*(1/1000)] = 0.154 m³
2. Volume of chemical admixture = [(7.52/1.45)*(1/1000)] = 0.005 m³
3. Volume of Coarse & fine aggregate = [1-(vol.of cement + vol.of flyash + vol.of water + vol.of chemical admixture)] = [1-(0.089+0.04+0.154+0.005)] = 0.712 m³

• Mass of coarse aggregate = 0.712*vol. of coarse aggregate*sp.gr pf CA*1000

= 0.712*0.558*2.84*1000 = 1128 kg/m³

• Mass of fine aggregate = 0.712*0.442*2.74*1000 = 862 kg/m³

Step 7: Mix proportion

Cement = 282 kg/m³

Water = 154 kg/m³

Fine aggregate = 862 kg/m³

Coarse aggregate = 1128 kg/m³

Chemical admixture = 7.52 kg/m³

Fly ash = 94 kg/m³

Water-cement ratio = 0.4

Final Mix proportion = 1 : 2.29 : 3

Result:

The obtained mix design proportion for M35 grade of concrete using Fly ash considering all the IS codes clause required is 1:2.29:3

The above mix design is calculated based on trial values i.e., percentage reduction of water content by 20%, considering fly ash percentage of 25%, slump value of 75mm and method of transportation and placing of concrete by pumping method. The mix proportion may vary by changing the above values as per IS 456:2000 & IS 10262:2019.

Conclusion:

• The slump shall be measured and water content, 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.
• Two more trails having variation of 10% water cement ratio in clause x shall be carried out and graph between water cement ratios & corresponding strengths shall be plotted to workout the mix proportions for the given target strength for field trails. However, durability shall be met.

2. Calculate the Concrete mix design for M50 grade concrete without Fly ash.

Ans:

Aim: To determine the mix proportions of concrete ingredients such as cement, fine & coarse aggregates, water content, w/c ratio & chemical admixture content for M50 grade of concrete without fly ash.

Introduction: To design the mix proportions of M50 grade of concrete without fly ash, we should follow various IS code books to confirm the clauses and use of materials to achieve desired compressive strength and to get durability. The mix trails should be performed at least 2 or 3 times to get more precise concrete mix design. Following are the code specifications that are used for the M50 grade concrete mix design.

• IS 12269-1987 – Specification for ordinary Portland cement of 53 Grade
• IS 383:2016 – Specification for coarse & fine aggregates for concrete (2^nd revision)
• IS 456:2000 – Code of practice for plain & reinforced concrete (4^th revision)
• IS 9103:1999 – Specification for admixtures for concrete (4^th revision)
• IS 10262-2019 – Concrete Mix proportioning Guidelines (2^nd revision)

Data required:

• Grade of concrete = M50 grade
• Grade of cement = 53 grade of OPC confirming to IS 12269:1987
• Maximum nominal size of aggregate = 20mm (used)
• Exposure condition = Extreme
• Minimum cement content = 360 kg/m³ (IS 456:2000, table 5)
• Maximum water cement ratio = 0.4 (IS 456:2000, table 5)
• Workability = 80mm slump (considered)
• Method of placing = pumping
• Degree of supervision = good
• Type of coarse aggregate = crushed angular aggregate confirming to IS 383-2016
• Type of fine aggregate = natural sand of zone 1, confirming to IS 383-2016
• Maximum cement content = 450 kg/m³
• Chemical admixture = superplasticizer as per IS 9103:1999

Test data:

• Specific gravity of cement = 3.15
• Specific gravity of coarse aggregate = 2.84
• Specific gravity of fine aggregate = 2.68
• Specific gravity of chemical admixture = 1.08
• Water absorption of coarse aggregate = 0.5%
• Water absorption of fine aggregate = 1%
• Free surface of both fine & coarse aggregate = Nil

Procedure:

Step 1: Calculation of Target strength

The concrete mix has to be proportioned for higher target mean compressive strength f’ck to avoid the specified proportion of test results to fall below the characteristic strength.

Target mean strength f’ck = fck + 1.65*S

Where,

fck = characteristic compressive strength of concrete at 28 days in N/mm² = 50 N/mm²

S = standard deviation (IS 456:2000, table 8) or (IS 10262:2019, table 2)

S = 5.0 N/mm²

Target mean compressive strength = 50 + 1.65*5.0 = 58.25 N/mm²

Step 2: Selection of water-cement ratio

1. As per IS 456:2000, table 5, the maximum free water cement ratio mainly based on exposure condition for M35 grade of concrete = 0.4.
2. As per IS 10262:2019, fig 1 graph between free water cement ratio & 28day compressive strength of concrete in N/mm² & cement grade curves (53 grade curve) = 0.34.
3. Since 0.34 < 0.4, considering 0.34 as W/c ratio for this mix design.

Step 3: Selection of water content

As per table 4 of IS 10262:2019, the maximum water content per cubic meter of concrete for nominal maximum size of aggregate & for 50mm slump = 186 kg. (Aggregate size = 20mm considered)

Here, slump required = 80mm and method of placing is by pumping.

As per IS 10262:2019, clause 5.3, the required water content can be increased or decreased by about 3% for each increase or decrease of 25mm slump.

Here for getting the water content for 80mm slump, we’ve to interpolate the values of 50mm & 100mm slump.

Water content for 100mm slump = 186 + (6/100)*186 = 197kg.

Slump value (mm)	Water content (kg)
50	186
80	X
100	197

y = y₁ + (x-x₁) * [(y₂-y₁) / (x₂-x₁)]

y = 193

Therefore, water content required for 80mm slump is 193kg.

As super plasticizer is used, water content can be decreased by about 20-30 percentage (IS 10262:2019, clause 5.3)

Considering 30% decrease of water content based on trails.

Therefore, water content = 193-(30/100)*193 = 135kgs.

Step 4: Calculation of Cement content & Chemical admixture content

We know that, w/c ratio = 0.34

Water content = 135kg

Therefore, cement content = w/0.34 = 135/0.34 = 397 kg/m³ (>360 kg/m³ & <450 kg/m³) Hence ok.

Chemical admixture content is taken as 2% of the cement content = 397* (2/100) = 7.94 kg/m³.

Step 5: Proportion of volume of Coarse aggregate & fine aggregate content

Form table 5 or IS 10262:2019, the volume of coarse aggregate per unit volume of total aggregate for fine aggregate of zone 1 for w/c ratio 0.5 is & for 20mm coarse aggregate.

Volume of coarse aggregate = 0.6 m³

Since, w/c ratio is lower by 0.26 (0.6-0.34 = 0.26), proportion of volume of coarse aggregate is increased by 0.05 at the rate of +/- 0.01 for every +/- 0.05 change in w/c ratio.

Therefore, corrected volume of coarse aggregate = 0.6+0.05 = 0.65m³.

Since, mode of placing of concrete is by pumping, the estimated coarse aggregate content can be reduced up to 10%. (IS 10262:2019, clause 5.5.2)

Hence volume of coarse aggregate = 0.65 – (10/100)*0.65 = 0.585 m³

Volume of fine aggregate = 1 – 0.585 = 0.415 m³

Step 6: Mix calculations

1. Volume of concrete = 1 m³
2. Volume of cement = [(mass of cement/sp.gr of cement)*(1/1000)]

= [(397/3.15)*(1/1000)] = 0.126 m³

• Volume of water = [(135/1)*(1/1000)] = 0.135 m³

7. Volume of chemical admixture = [(7.94/1.08)*(1/1000)] = 0.007 m³
8. Volume of Coarse & fine aggregate = [1-(vol.of cement + vol.of water + vol.of chemical admixture)] = [1-(0.126+0.135+0.007)] = 0.732 m³
9. Mass of coarse aggregate = 0.732*vol. of coarse aggregate*sp.gr pf CA*1000

= 0.732*0.585*2.84*1000 = 1216 kg/m³

• Mass of fine aggregate = 0.732*0.415*2.68*1000 = 814 kg/m³

Step 7: Mix proportion

Cement = 397 kg/m³

Water = 135 kg/m³

Fine aggregate = 814 kg/m³

Coarse aggregate = 1216 kg/m³

Chemical admixture = 7.94 kg/m³

Water-cement ratio = 0.34

Final Mix proportion = 1 : 2.05 : 3.06

Result:

The obtained mix design proportion for M50 grade of concrete considering all the IS codes clause required is 1:2.05:3.06

The above mix design is calculated based on trial values i.e., percentage reduction of water content by 30%, slump value of 80mm and method of transportation and placing of concrete by pumping method. The mix proportion may vary by changing the above values as per IS 456:2000 & IS 10262:2019.

Conclusion:

• The slump shall be measured and water content, 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.
• Two more trails having variation of 10% water cement ratio in clause x shall be carried out and graph between water cement ratios & corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trails. However, durability shall be met.