Project on Concrete Mix Design for various grades of Concrete

AIM: To determine the mix design for M35 concrete with fly ash and for M50 without fly ash

Part 1- Calculation of proportions of mix design for M35 with fly ash

• Grade designation: M35
• Type of cement: OPC 53 grade conforming IS 12269
• Type of mineral admixture: Fly ash conforming to IS 3812 (Part-1)
• Maximum nominal size of aggregate : 20mm
• Minimum water-cement ratio: 0.45 (Table 5 IS 456:2000)
• Workability: 100mm
• Exposure condition: Severe
• Minimum cement content: 340kg/m³
• Method of concrete placing: Pumping
• Degree of supervision: Good
• Type of aggregate: Angular
• Chemical admixture type: Super plasticizer

Test Data:

• Cement used: OPC 53 grade.
• Specific gravity of cement: 3.15
• Specific gravity of fly ash: 2.2
• Chemical admixture- specific gravity: 1.145
• Coarse aggregate- specific gravity: 2.74
• Fine aggregate- Specific gravity: 2.74
• Water Absorption:

1. Coarse aggregate-0.5%
2. Fine aggregate-1.0%

PROCEDURE:

• Target strength for mix proportion:-

F’ck= fck+ 1.65s (Table 1: IS 10262:2009)

F’ck=35+1.65x5

        =43.25 N/mm²

• Water cement ratio:-

Max. Water content for 20mm aggregate =186 liters. (Table-2: IS 10262:2009)

Water content for 100mm slump:-

From table 2 of IS 10262:2009 the water content is for 25mm to 50mm slump range. For every additional 25mm slump after the range, extra 3% of water should be added.

Hence;

Water content for 100mm slump= 186+ (6/100) x186=197liters.

However, super plasticizers is used, the water content can be reduced up to 20% to 30%.

Thus, the final water content= 197-(197x20%) =157.6 liters.≈160 Liters

• Cement Content:

Adopted w/c ratio=0.45

Cement content =160/0.45= 355.55kg/cum

From table 5 of IS 456:2000 min cement content for severe exposure condition is 340kg/m³

355kg/m³>340kg/m³

Hence, Ok.

• Fly ash content:

1. The fly ash content is selected as per the requirement of the project and the quality of the materials.
2. In some cases the increase in the cementitious material % can be warranted. Increase in cementitious material & its percentage may be based on trial and experience.

For this project we will take 15% of increase in cementitious content.

Cementitious material content=355+ (355x15%) = 408.25 ≈408 kg/m³

Water content= 160 liters

So, W/C ratio= 160/405=0.395

Fly ash @ 35% total cementitious content=408X35%= 142.8kg/m³

Cement (opc) =408-142.8=265.2 ≈ 265kg/m³

Saving of cement while using fly ash= 408-265= 143kg/m³

Fly ash used= 143kg/m³

• Proportion of volume of coarse aggregate and fine aggregate for w/c ratio:

From table 3 of IS 10262:2009 volume of coarse aggregate corresponding to 20mm size of aggregate and fine aggregate zone 1=0.6.

 Now, the water-cement ratio is 0.45. The volume of coarse aggregates is required to be increased to decrease the content of fine aggregate.

AS the water content is lower by 0.05, the proportion of volume of coarse aggregate is increased by 0.01.(at the rate of -/+ 0.01 for every 0.05 change in w/c ratio)

Hence, corrected volume of coarse aggregate for the w/c ratio of 0.45 is 0.61.

For pumpable concrete these values are decreased by 10%.

Therefore, volume of coarse aggregate= 0.61x0.9=0.55

Volume of fine aggregate=1-0.55=0.45

MIX CALCULATIONS:

1. Volume of concrete=1 m³
2. Volume of cement=(355/3.15x1000)= 0.112m³
3. Volume of fly ash=(143/2.2x1000)= 0.065m³
4. Volume of water=(160/1x1000)=0.16m³
5. Volume of chemical admixture super plasticizer (@2% by mass of cementitious material)= 8.16/1.145x1000=0.007m³
6. Volume of total aggregates= (a-(b+c+d+e)=(1-(0.112+0.065+0.16+0.007))=0.656m³
7. Mass of coarse aggregate= volume of aggregate x volume of coarse aggregate specific gravity of coarse aggregate x 1000= 0.656x0.55x2.74x1000=989kg/m³
8. Mass of fine aggregate= volume of aggregate x volume of fine aggregate x specific gravity of fine aggregate= 0.656x0.45x2.74x1000=809kg/m³

RESULT:

Mix proportion obtained:

Cement=355 kg/m³

Fly ash=143kg/m³

Water=160 Liters

Fine aggregates= 809kg/m³

Coarse aggregate=989kg/m³

Chemical admixture= 7.1kg/m³

W/C ratio= 0.45

Mix proportion by weight= 1:2.279:2.786

Conclusion:

The slump should be measured and the water content and admixture can be adjusted  to obtain the required slump. The mix proportion can be adjusted and reworked as per requirement.

Part 2- To calculate the design mix proportions for M50 grade concrete.

• Grade designation : M50
• Type of cement: OPC 43 grade conforming IS 8112
• Maximum nominal size of aggregate: 20mm
• Minimum water-cement ratio: 0.a5 (Table 5 IS 456:2000)
• Workability: 100mm
• Exposure condition: severe
• Minimum cement content: 300kg/m³
• Method of concrete placing: Pumping
• Degree of supervision: Good
• Type of aggregate: Angular
• Chemical admixture type: Super plasticizer

TEST DATA:

• OPC 43 grade conforming IS 8112
• Specific gravity of cement: 3.15
• Chemical admixture: Super plasticizer
• Specific gravity of:

Fine aggregate=2.74

Coarse aggregate=2.74

• Water absorption:

Fine aggregate=0.5%

Coarse aggregate=1.0%

1. Target strength (f’ck)=fck+1.65s (s from table-1 from IS 10262)

                                     =50 + (1.65 X 5) =58.25 N/mm²

2. Selection of water cement ratio:

From table 5 of IS 564:2000 depending on the moderate exposure the maximum w/c ratio should be 0.45

3. Calculating the water content:

From table 2 of IS 10262:2009, the maximum water content for a slump range of 25mm to 50mm for a nominal maximum aggregate size of 20 mm should be 186 liters.

As the slump here is 100mm so an additional 3% of water will be added for every extra 25mm.

i.e., Water content= 186 + (6\100 x 186) = 197 liters

As we are using superplasticizers in the mix, the water content can be reduced by 20% and above based on trials.

Here we are reducing the water content by 20%.

Hence, the final water content= 197 x 0.8 = 158 liters.

4. Calculation of cement content:

The adopted w/c ratio is 0.45. And the water content is 158 liters.

Hence the cement content= 158/0.45= 351 Kg/m³

From table 5 of IS 456:2000 minimum cement content for severe exposure is 300kg/m³

351kg/m³>300kg/m³.

5. Proportion of volume of Coarse aggregate & Fine aggregate content:

The volume of coarse aggregate corresponding to the nominal maximum size of aggregate of 20 mm & fine aggregate (zone 1) from table 3 of IS 10262:2009  is 0.6.

As the w/c ratio adopted is 0.45 ANF THERE IS NO CHANGE IN THE MAXIMUM W/C ratio and the adopted one, the volume of coarse aggregate will also remain same i.e., 0.6.

For pumpable concrete the value of the volumes are reduced by 10%.

Hence, Volume of coarse aggregate= 0.6 x 0.9 = 0.54

              Volume of fine aggregate= 1-0.54 = 0.46

6. Mix Calculations:
7. Volume of cement = 1m³
8. Volume of cement = 351/3.15x1000= 0.111m³
9. Volume of water= 158/1x100= 0.158 m³
10. Volume of chemical admixture= 7.02/1.145X1000= 0.006m³
11. Volume of aggregate= (1-(0.111+0.158+0.006) = 0.725m³
12. Mass of coarse aggregate= 0.725 x 0.54 x 2.74 x 1000 = 1072Kg/m³
13. Mass of fine aggregate= 0.725 x 0.46 x 2.74 x 1000 = 913 Kg/m³

7. Result:

Mix proportion obtained:

Cement= 351Kg/m³

Water= 158 Liters

Fine aggregate= 913 Kg/m³

Coarse aggregate= 1072 Kg/m³

Chemical admixture= 7.02 Kg/m³

W/C ratio= 0.45

Mix proportion by weight= 1:2.601:3.054

Conclusion:

The mix proportion calculated should be tested for slump and if the required slump is not obtained then the water content and admixture can be adjusted as per requirement.