Project on Concrete Mix Design for various grades of Concrete

PROJECT TOPIC: CALCULATION OF THE CONCRETE MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH & M50 GRADE CONCRETE WITHOUT FLY ASH

INTRODUCTION

Concrete is a complex material and has the right mix of constituents, which if not done properly will have adverse effects on the properties of the concrete. Concrete mix design is the systematic process of choosing an economical relative proportion of various ingredients from available materials that give the concrete the desired workability. This project outlines the procedure involved in mix designing based on Indian Standards.

AIM

This project aims to calculate the mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash as per the guidelines given in Indian standards IS 10262:2019 and IS 456:2000. Test data for this project are assumed values as given below.

1. CALCULATION OF THE CONCRETE MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH

1)Stipulations for proportioning

• Grade designation = M35
• Type of cement = OPC 43 Grade conforming to IS 8112
• Type of mineral admixture = Fly ash conforming to IS 3812(Part 1)
• Maximum nominal size o the aggregate = 20mm|
• Minimum cement content = 320kg/m3 (From Table 5 of IS 456:2000- exposure condition)
• Maximum water cement ratio= 0.45 (From Table 5 of IS 456:2000- exposure condition)
• Workability = 100mm (Slump value for pumpable concrete)
• Exposure condition = Severe (For reinforced concrete)
• Method of concrete placing = pumping
• Degree of supervision= Good
• Type of aggregate= crushed angular aggregate
• Chemical admixture= Superplasticizer

2)Test Data for materials

• Cement used = OPC 43 Grade conforming to IS 8112
• The specific gravity of cement = 3.15
• Fly ash = Fly ash conforming to IS 3812(Part1)
• The specific gravity of fly ash= 2.2
• Chemical admixture= Superplasticizer conforming to IS 9103 with specific gravity 1.145
• Specific gravity of
• Coarse aggregate = 2.74
• Fine aggregate = 2.74
• Water absorption of Coarse aggregate = 0.5% & Fine aggregate = 1.0%
• Free surface moisture of Coarse aggregate = Nil & Fine aggregate = Nil
• Sieve analysis : Coarse aggregate = Conforming to Table 2 of IS 383 & Fine aggregate= Conforming to grading zone 1 of table 4 of IS 383

3)Calculation of target mean strength

Target mean strength, f’ck = fck + 1.65 S = 35+1.65 x 5 = 43.25 N/mm2

Or f’ck =fck + 1.65 X= 35+1.65*6.5 = 45.725 N/mm2

whichever is higher, where

fck = characteristic compressive strength at 28 days, in N/mm2;

S = standard deviation, in N/mm2 from table 2 of IS 10262:2019

X = factor based on the grade of concrete, as per Table 1 of IS 10262:2019

Since 45.725 N/mm2 is higher it can be taken as the target mean strength

4)Selection of Water-Cement Ratio

Maximum water-cement ratio as per Table 5 of IS 456:2000- for severe exposure condition = 0.45

Water cement ratio from Fig 1 of IS 10262: 2019 for M35 grade and OPC 43 Grade = 0.45

Since 0.45 ≤ Maximum water-cement ratio, it can be used as the water-cement ratio for this mix-design

5)Selection of water content

From Table 4 of IS 10262:2019 maximum water content per cubic meter of concrete for 20mm aggregate = 186 litres (for 50mm slump)

For pumpable concrete of 100mm slump the water content to be increased 6% (3% for each 25mm increase)

Therefore, the adjusted water content = 186 + (6/100) x 186 = 197 Litres

As super plasticizing admixture is added usually water content can be reduced up to 20 to 30 per cent

Therefore adjusted water content after reducing water content by 20 % based on trials = 197 x 0.80 = 157.6 ~158 litres

6)Calculation of Cement content

Water cement ratio = 0.45

Cement contentious material (Cement + fly ash) = 158/0.45= 351 kg/m3 ≥ 320Kg/m3, hence it is ok

To proportion a mix containing fly ash the following steps are suggested

1. The percentage of fly ash is decided based on the project requirement and quality of the materials
2. In some cases, an increase in cementitious material can be warranted. In this case, we consider a 10% increase in the cementitious material content.

Cementitoius material contet = 351 x 1.10 = 386Kg/m3

Water content= 158litres

Therefore water cement ratio = 158/386 = 0.41

Fly ash at 30% of the total cementitious material = 386 x 30% = 116kg/m3

Cement(OPC) = 386-116= 270kg/m3

Saving of cement while using fly ash= 351-270= 81kg/m3

Fly ash being utilized = 116 kg/m3

7)Proportion of volume of coarse aggregate and fine aggregate

From Table 5 of IS 10262: 2019 volume of coarse aggregate per unit volume of total aggregate corresponding to 20mm aggregate and fine aggregate conforming Zone 1 for water-cement ratio 0.5 = 0.6

In the present case, the water-cement ratio is 0.45 and therefore volume of coarse aggregate needs to be increased to decrease the volume of fine aggregate.

The proportion of the volume of coarse aggregates to that of total aggregates need to be increased at the rate of 0.01 for every decrease in water-cement/cementitious materials ratio by 0.05

Therefore adjusted volume of coarse aggregate per unit volume of total aggregate for water-cement ratio 0.45 = 0.6+0.1= 0.61

For pumpable concrete, the volume of coarse aggregate need to be reduced by 10%

Therefore adjusted volume of coarse aggregate per unit volume of total aggregate = 0.61 x 0.9 = 0.549 ~ 0.55

Volume of fine aggregate = 1-0.55 = 0.45

8. Mix Calculation

Mix calculation per unit volume of concrete shall be as follows

1. Volume of concrete = 1m3
2. Volume of cement = (Mass of cement /Specific gravity of cement ) x (1/1000)= (270/3.15) x (1/1000) = 0.086 m3
3. Volume of fly ash= (Mass of fly ash /Specific gravity of fly ash ) x (1/1000)= (116/2.2) x (1/1000) = 0.052 m3
4. Volume of water = (Mass of water /Specific gravity of wqater ) x (1/1000)= (158/1) x (1/1000) = 0.158 m3
5. Volume of admixture = (Mass of admixture /Specific gravity of admixtrure ) x (1/1000)= (7.6/1.145) x (1/1000) = 0.006m3
6. Volume of aggregate = a-(b+c+d=e) = 1-(0.086+0.052+0.158+0.006) = 0.698m3
7. Mass of coarse aggregate = e x volume of coarse aggregate x specific gravity of coarse aggregate x 1000= 0.698 x 0.55 x 2.74 x 1000= 1052 Kg / m3
8. Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000 = 0.698 x 0.45 x 2.74 x 1000 = 860 kg/m3

9)Mix proportion for the first trial

Cement= 270 kg/m3

Fly ash= 116 kg/m3

Water= 158 litres/m3

Coarse Aggregate= 1052 kg/m3

Fine aggregate= 860 kg/m3

Admixture = 7 kg/m3

Water cement ratio= 0.41

Therefore, mix ratio is 1:2.22:2.72 (cementitious material: FA:CA)

2. CALCULATION OF THE CONCRETE MIX DESIGN FOR M50 GRADE CONCRETE WITHOUT FLY ASH

1)Stipulations for proportioning

• Grade designation = M50
• Type of cement = OPC 43 Grade conforming to IS 8112
• Maximum nominal size o the aggregate = 20mm|
• Minimum cement content = 320kg/m3 (From Table 5 of IS 456:2000- exposure condition)
• Maximum water cement ratio= 0.45 (From Table 5 of IS 456:2000- exposure condition)
• Workability = 100mm (Slump value for pumpable concrete)
• Exposure condition = Severe (For reinforced concrete)
• Method of concrete placing = pumping
• Degree of supervision= Good
• Type of aggregate= crushed angular aggregate
• Chemical admixture= Superplasticizer

2)Test Data for materials

• Cement used = OPC 43 Grade conforming to IS 8112
• Specific gravity of cement = 3.15
• Chemical admixture= Superplasticizer conforming to IS 9103 with specific gravity 1.145
• Specific gravity of
• Coarse aggregate = 2.74
• Fine aggregate = 2.74
• Water absorption of Coarse aggregate = 0.5% & Fine aggregate = 1.0%
• Free surface moisture of Coarse aggregate = Nil & Fine aggregate = Nil
• Sieve analysis: Coarse aggregate = Conforming to Table 2 of IS 383 Fine aggregate: Conforming to grading zone 1 of table 4 of IS 383

3)Calculation of target mean strength

Target mean strength, f’ck = fck + 1.65 S = 50+1.65 x 5 = 58.25 N/mm2

Or f’ck =fck + 1.65 X= 50+1.65*6.5 = 60.725 N/mm2

whichever is higher, where

fck = characteristic compressive strength at 28 days, in N/mm2;

S = standard deviation, in N/mm2 from table 2 of IS 10262:2019

X = factor based on the grade of concrete, as per Table 1 of IS 10262:2019

Since 60.725 N/mm2 is higher it can be taken as the target mean strength

4)Selection of Water-Cement Ratio

Maximum water-cement ratio as per Table 5 of IS 456:2000- for severe exposure condition = 0.45

Water cement ratio from Fig 1 of IS 10262: 2019 for M50 grade and OPC 43 Grade = 0.34

Since 0.34 ≤ Maximum water-cement ratio, it can be used as the water-cement ratio for this mix design

5)Selection of water content

From Table 4 of IS 10262:2019 maximum water content per cubic meter of concrete for 20mm aggregate = 186 litres (for 50mm slump)

For pumpable concrete of 100mm slump the water content to be increased 6% (3% for each 25mm increase)

Therefore, the adjusted water content = 186 + (6/100) x 186 = 197 Litres

As super plasticizing admixture is added usually water content can be reduced up to 20 to 30 per cent

Therefore adjusted water content after reducing water content by 20 % based on trials = 197 x 0.80 = 157.6 ~158 litres

6)Calculation of Cement content

Water cement ratio = 0.34

Cement content = 158/0.34= 465 kg/m3 ≥ 320Kg/m3, hence it is ok

7)The proportion of the volume of coarse aggregate and fine aggregate

From Table 5 of IS 10262: 2019 volume of coarse aggregate per unit volume of total aggregate corresponding to 20mm aggregate and fine aggregate conforming Zone 1 for water-cement ratio 0.5 = 0.6

In the present case, the water-cement ratio is 0.34 and therefore volume of coarse aggregate needs to be increased to decrease the volume of fine aggregate.

The proportion of the volume of coarse aggregates to that of total aggregates need to be increased at the rate of 0.01 for every decrease in water-cement/cementitious materials ratio by 0.05

Therefore adjusted volume of coarse aggregate per unit volume of total aggregate for water-cement ratio 0.34 = 0.6+0.032= 0.632

For pumpable concrete, the volume of coarse aggregate need to be reduced by 10%

Therefore adjusted volume of coarse aggregate per unit volume of total aggregate = 0.632 x 0.9 = 0.568 ~ 0.57

Volume of fine aggregate = 1-0.57 = 0.43

8)Mix Calculation

Mix calculation per unit volume of concrete shall be as follows

1. Volume of concrete = 1m3
2. Volume of cement = (Mass of cement /Specific gravity of cement ) x (1/1000)= (465/3.15) x (1/1000) = 0.147 m3
3. Volume of water = (Mass of water /Specific gravity of wqater ) x (1/1000)= (158/1) x (1/1000) = 0.158 m3
4. Volume of admixture = (Mass of admixture /Specific gravity of admixtrure ) x (1/1000)= (7.6/1.145) x (1/1000) = 0.006m3
5. Volume of aggregate = a-(b+c+d) = 1-(0.147+0.158+0.006) = 0.689m3
6. Mass of coarse aggregate = e x volume of coarse aggregate x specific gravity of coarse aggregate x 1000= 0.689 x 0.57 x 2.74 x 1000= 1076 Kg / m3
7. Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000 = 0.689 x 0.43 x 2.74 x 1000 = 811 kg/m3

9)Mix proportion for the first trial

Cement= 465 kg/m3

Water= 158 litres/m3

Coarse Aggregate= 1076 kg/m3

Fine aggregate= 811 kg/m3

Admixture = 7 kg/m3

Water cement ratio= 0.34

Therefore, mix ratio is 1:1.74:2.31 (cement: FA:CA)