Project on Concrete Mix Design for various grades of Concrete

AIM: To calculate 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 concrete, which if not done properly and will have adverse effect on the properties of concrete.
• concrete mix design is a systematic process of choosing economical relative proportion of various ingredients from available material that gives the concrete of dsired workability
• The process of selecting suitabile ingridients for producing concrete of required strength, durability and workability as economical as possible is known as concrete mix design.

1. Calculation of the Concrete Mix Design for M35 grade concrete with fly ash

I. Stipulations for propotioning

1. Grade designation : M35
2. Type of cement : OPC 43 grade confirming to IS 8112
3. Type of mineral admixture : Fly ash confirming to IS 3812 (Part 1)
4. Maximum nominal size of aggregate : 20mm
5. Minimum cement content : 340 kg/m^3 (From Table 5 of IS 456: 2000- Exposure condition)
6. Maximum water-cement ratio : 0.45 (From Table 5 of IS 456: 2000- Exposure condition)
7. Workability : 100mm (Slump value for pumpable concrete)
8. Exposure condition : Severe (for reinforced concrete)
9. Method of concrete placing : Pumping
10. Degree of supervision : Good
11. Type of aggregate : Crushed angular aggregate
12. Maximum cement content : 450kg/m^3
13. Chemical admixture type : Superplasticizer

II. Test data materials:

1. Cement used : OPC 43 grade confirming to IS 8112
2. Specific gravity of cement : 3.15
3. Fly ash : Confirming to IS 3812 (Part 1)
4. Specific gravity of fly ash : 2.2
5. Chemical admixture : Superplasticizer confirming to IS 9103
6. Specific gravity of:
   • Coarse aggregate : 2.74
   • Fine aggregate : 2.74
7. Water absorption :
   
   • Coarse aggregate : 0.5%
   • Fine aggregate : 1.0%
8. Sieve Analysis:
   • Fine aggregates: Confirming to grading Zone I of Table 4 of IS 383

1. Target mean strength for Mix propotioning:

f'ck = fck + 1.65S

Where, f'ck = target avg compressive strength at 28days

fck = Charactesistic compressive strength at 28days

S = Standard deviation

From table 1 of IS 10262: 2009, standard deviation, S = 5 N/mm^2

Therefore, Target strength = 35+ 1.65*5 = 43.25 N/mm^2

2. Selection of Water-cement ratio:

From Table 5 of IS 456: 2000 for severe exposure, maximum water-cement ratio = 0.45

Based on experience, adopted water-cement ratio is 0.40

0.40<0.45, hence O.K

3. Selection of Water Content

From table 2 of IS 10262: 2009, maximum water content for 20mm aggregate = 186 litre (for 25mm to 50mm slump range)

Estimated water content for 100mm slump = 186+ 6/100*186

= 197 liter

As superplasticizer is used, the water content can be reduced upto 30%

Based on trials water content can be reduction of 29% is achieved with plasticizer.

Hence the arrived water content = 197*0.71 = 140 litre

4. Calculation of Cement content:

Water-cement ratio = 0.4

Cementitious material (Cement + fly ash) content = 140/0.4 = 350kg/m^3

From Table 5 of IS 456 minimum cement content for 'severe' exposure condition = 340kg/m^3

350kg/m^3 > 340kg/m^3, Hence OK

Now, to proportiona mix containing fly ash the following steps are suggested:

1. The percentage of fly ash needs to be decided based on project requirement and quality of materials
2. In some cases increase in cementitious material can be warranted. Increase in cementitious material content and its percentage may be based on experience and trial (This example is with increase of 10% cementitious material content)

Cementitious material content	350 x 1.10 = 385 Kg/m^3
water content	140Kg/m^3
So, water-cement ratio	140/385 = 0.364
Fly ash @ 30% total cementitious material content	385 x 30% = 115Kg/m^3
Cement (OPC)	385 - 115 = 270Kg/m^3
Saving of cement while using fly ash	350-270 = 80Kg/m^3
Fly ash being utilized	115 Kg/m^3

5. 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 aggregate and fine aggregate (Zone 1) for water-cement ratio = 0.6

In the present case the water cement ratio is 0.40

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

- As water-cement ratio is lower by 0.10, the proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every +/- 0.05 change in water-cement ratio).

Therefore, corrected volume of coarse aggregate for the water-cement ratio of 0.40=0.62

(Note: If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably, based on experience)

For pumpable concrete these values are reduced by 10%

Therefore, volume of coarse aggregate = 0.62*0.9 = 0.56

Volume of fine aggregate content = 1 - 0.56 = 0.44

6. Mix Calculation:

The mix calculation per unit volume of concrete shall be as follows:

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

= 270/3.15 * 1/1000

= 0.086m^3

c. Volume of Fly ash = Mass of fly ash/Specific gravity of fly ash * 1/1000

= 115/2.2 * 1/1000

= 0.052 m^3

d. Volume of water = (Mass of water / Specific gravity of water) * 1/1000

= 140/1*1/1000

= 0.140m^3

f. Volume of chemical admixture = (Mass of chemical admixture / Specific gravity of admixture) * 1/1000

= 7.6/1.145*1/1000

= 0.006m^3

e. Volume of aggregates (FA & CA) = (a-(b+c+d+e))

= (1-(0.086+0.052+0.140+0.006))

= 0.716m^3

f. Mass of Coarse aggregate = e * Volume of CA * Specific gravity of CA * 1000

= 0.716*0.56*2.74*1000

= 1098kg/m^3

g. Mass of fine aggregates = e * Volume of FA * Specific gravity of FA * 1000

= 0.716*0.44*2.74*1000

= 863kg/m^3

7. Mix proportions for trial:

Cement =270kg/m^3

Fly ash = 115 Kg/m^3

Water = 140kg/m^3

Fine aggregate = 863 kg/m^3

Coarse aggregate = 1098kg/m^3

Chemical admixture = 7kg/m^3

Water-cement ratio = 0.4

Trial Mix Ratio = 1:2.24:2.85

2. Calculation of Concrete Mix Design for M50 grade concrete without Fly ash

I. Stipulations for propotioning

1. Grade designation : M50
2. Type of cement : OPC 43 grade confirming to IS 8112
3. Maximum nominal size of aggregate : 20mm
4. Minimum cement content : 320 kg/m^3 (From Table 5 of IS 456: 2000- Exposure condition)
5. Maximum water-cement ratio : 0.45 (From Table 5 of IS 456: 2000- Exposure condition)
6. Workability : 100mm (Slump value for pumpable concrete)
7. Exposure condition : Severe (for reinforced concrete)
8. Method of concrete placing : Pumping
9. Degree of supervision : Good
10. Type of aggregate : Crushed angular aggregate
11. Maximum cement content : 450kg/m^3
12. Chemical admixture type : Superplasticizer

II. Test data materials:

1. Cement used : OPC 43 grade confirming to IS 8112
2. Specific gravity of cement : 3.15
3. Fly ash : Confirming to IS 3812 (Part 1)
4. Specific gravity of fly ash : 2.2
5. Chemical admixture : Superplasticizer confirming to IS 9103
6. Specific gravity of:
   • Coarse aggregate : 2.74
   • Fine aggregate : 2.74
7. Water absorption :
   
   • Coarse aggregate : 0.5%
   • Fine aggregate : 1.0%
8. Sieve Analysis:
   • Fine aggregates: Confirming to grading Zone I of Table 4 of IS 383

1. Target mean strength for Mix propotioning:

f'ck = fck + 1.65S

Where, f'ck = target avg compressive strength at 28days

fck = Charactesistic compressive strength at 28days

S = Standard deviation

From table 1 of IS 10262: 2009, standard deviation, S = 5 N/mm^2

Therefore, Target strength = 50+ 1.65*5 = 58.25 N/mm^2

2. Selection of Water-cement ratio:

From Table 5 of IS 456: 2000 for severe exposure, maximum water-cement ratio = 0.45

Based on experience, adopted water-cement ratio is 0.40

0.40<0.45, hence O.K

3. Selection of Water Content

From table 2 of IS 10262: 2009, maximum water content for 20mm aggregate = 186 litre (for 25mm to 50mm slump range)

Estimated water content for 100mm slump = 186+ 6/100*186

= 197 liter

As superplasticizer is used, the water content can be reduced upto 30%

Based on trials water content can be reduction of 29% is achieved with plasticizer.

Hence the arrived water content = 197*0.71 = 140 litre

4. Calculation of Cement content:

Water-cement ratio = 0.4

Cement content = 140/0.4 = 350kg/m^3

From Table 5 of IS 456 minimum cement content for 'severe' exposure condition = 320kg/m^3

350kg/m^3 > 320kg/m^3, Hence OK

5. 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 aggregate and fine aggregate (Zone 1) for water-cement ratio = 0.6

In the present case the water cement ratio is 0.40

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

- As water-cement ratio is lower by 0.10, the proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every +/- 0.05 change in water-cement ratio).

Therefore, corrected volume of coarse aggregate for the water-cement ratio of 0.40=0.62

(Note: If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably, based on experience)

For pumpable concrete these values are reduced by 10%

Therefore, volume of coarse aggregate = 0.62*0.9 = 0.56

Volume of fine aggregate content = 1 - 0.56 = 0.44

6. Mix Calculation:

The mix calculation per unit volume of concrete shall be as follows:

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

= 350/3.15 * 1/1000

= 0.111m^3

c. Volume of water = (Mass of water / Specific gravity of water) * 1/1000

= 140/1*1/1000

= 0.140m^3

d. Volume of chemical admixture = (Mass of chemical admixture / Specific gravity of admixture) * 1/1000

= 7.6/1.145*1/1000

= 0.006m^3

e. Volume of aggregates (FA & CA) = (a-(b+c+d))

= (1-(0.111+0.140+0.006))

= 0.743m^3

f. Mass of Coarse aggregate = e * Volume of CA * Specific gravity of CA * 1000

= 0.743*0.56*2.74*1000

= 1140kg/m^3

g. Mass of fine aggregates = e * Volume of FA * Specific gravity of FA * 1000

= 0.743*0.44*2.74*1000

= 896kg/m^3

7. Mix proportions for trial:

Cement =350kg/m^3

Water = 140kg/m^3

Fine aggregate = 896 kg/m^3

Coarse aggregate = 1140kg/m^3

Chemical admixture = 7kg/m^3

Water-cement ratio = 0.4

Trial Mix Ratio = 1:2.56:3.26

• 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 requirements
• Two more trials having variation of 10% of water-cement ratio in Clause X shall be carried out and a graph between three water-cement ratios and corresponding strengths shall be plotted to work the mix proportions for the given target strength for field trials. However, durability shall be met.

Discussion:

• The grade designation representing the compressive strength
• Type of cement influences the development of Compressive strength of concrete
• maximum nominal size of aggregate to be used as prescribed by IS456: 2000
• Cement content to be limited from shrinkage, cracking and creep
• Workability of concrete for satisfactory placing and compaction.