Project on Concrete Mix Design for various grades of Concrete
1. Concrete mix design for M50 grade concrete without Fly ash
Data assumed:
I. Stipulations of proportioning:
a) Grade designation : M50
b) Type of cement: OPC 43 grade conforming to IS 8112
c) Maximum nominal size of aggregate: 20mm
d) Minimum cement content: 360 kg/m^3 (From Table 5 of IS 456: 2000- Exposure condition)
e) Maximum water-cement ratio : 0.40 (From Table 5 of IS 456: 2000- Exposure condition)
f) Workability: 100 mm (slump value for pumpable concrete)
g) Exposure condition : Extreme (for reinforced concrete)
h) Method of concrete placing: Pumping
i) Degree of supervision: Good
j) Type of aggregate: Crushed angular aggregate
k) Maximum cement content: 450 kg/m^3
i) Chemical admixture type: Superplasticizer
II. Test data for materials:
a) Cement used: OPC 43 grade conforming to IS 8112
b) Specific gravity of cement: 3.15
c) Chemical admixture: Superplasticizer conforming to IS 9103
d) Specific gravity of:
- Coarse aggregate : 2.74
- Fine aggregate : 2.74
e) Water absorption:
- Coarse aggregate : 0.5%
- Fine aggregate : 1.0%
f) Free Surface moisture:
- Coarse aggregate : Nil
- Fine aggregate : Nil
g) Sieve Analysis:
- Coarse aggregate : Conforming Table 2 of IS 383
-
Fine aggregate : Conforming to grading Zone I of Table 4 of IS 383
III. Target Strength for Mix proportioning:
f'ck = fck+1.65 S
Where, f'ck = Target average compressive strength at 28 days
fck = Characteristic compressive strength at 28 days
S = Standard deviation
From Table 1 of IS 10262: 2009, standard deviation, S = 5 N/mm^2
Therefore, Target strength = 50 + 1.65 X 5 = 58.25 N/mm^2
IV. Selection of Water-cement ratio:
From Table 5 of IS 456: 2000 for extreme exposure, maximum water-cement ratio = 0.40
Based on experience, adopted water-cement ratio is 0.35
0.35<0.40, hence O.K
V. 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 100 mm slump = 186 + 6/100*186 = 197
As superplasticizer is used, the water content can be reduced upto 20% and above
Based on trials water content reduction of 29% is achieved with plasticizer.
Hence the arrived water content = 197*0.71 = 140 litre
VI. Calculation of Cement Content:
Water-cement ratio = 0.35
Cement content = 140/0.35 = 400 kg/m^3
From Table 5 of IS 456 : 2000 minimum cement content for 'extreme' exposure condition = 360 kg/m^3
400 kg/m^3 > 360 kg/m^3, Hence OK.
VII. 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 I) for water-cement ratio 0.5 = 0.6
In the present case the water cement ratio is 0.35
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 0.35 = 0.63
(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 = 0.63 X 0.9 = 0.567
Volume of fine aggregate content = 1-0.567 = 0.433
VIII. Mix Calculations:
The mix calculation per unit volume of concrete shall be as follows:
a) Volume of Concrete = 1 m^3
b) volume of cement = (Mass of cement/Specific gravity of cement) x(1/1000) = 400/3.15 x 1/1000 = 0.126 m^3
c) volume of water = (Mass of water/Specific gravity of water) x (1/1000) = 140/1 x 1/1000 = 0.140 m^3
d) Volume of chemical admixture = (Mass of chemical admixture/Specific gravity of admixture) x (1/1000)
= 7/1.145 x 1/1000 = 0.006 m^3
e) Volume of aggregate (FA & CA) = (a-(b +c +d)) = (1-(0.126 + 0.140 + 0.006)) = 0.728 m^3
f) Mass of Coarse aggregate = ex Volume of coarse aggregate x Specific gravity of coarse aggregate X1000
= 0.728*0.567*2.74*1000 = 1019 Kg/m^3
g) Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000
= 0.728 x 0.433 x 2.74 x 1000 = 778 Kg/m^3
IX. Mix proportions :
Cement = 400 Kg/m^3
Water = 140 Kg/m^3
Fine aggregate = 778 Kg/m^3
Coarse aggregate = 1019 Kg/m^3
Chemical admixture = 7 Kg/m^3
Water-cement ratio = 0.35
Mix Ratio = 1 : 1.95 : 2.55
X. 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
XI. 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 out the mix proportions for the given target strength for field trials. However, durability shall be met.
2. Concrete mix design for M35 grade concrete with Fly ash:
Data assumed:
I. Stipulations for proportioning
a) Grade designation : M35
b) Type of cement: OPC 43 grade conforming to IS 8112
c) Type of mineral admixture : Fly ash conforming to IS 3812 (Part 1)
d) Maximum nominal size of aggregate : 20 mm
e) Minimum cement content: 340 kg/m^3 (From Table 5 of IS 456: 2000- Exposure condition)
f) Maximum water-cement ratio : 0.45 (From Table 5 of IS 456: 2000- Exposure condition)
g) Workability: 100 mm (slump value for pumpable concrete)
h) Exposure condition : very Severe (for reinforced concrete)
h) Method of concrete placing: Pumping
i) Degree of supervision : Good
j) Type of aggregate: Crushed angular aggregate
k) Maximum cement content: 450 kg/m^3
i) Chemical admixture type: Superplasticizer
II. Test data for materials:
a) Cement used: OPC 43 grade conforming to IS 8112
b) Specific gravity of cement: 3.15
c) Fly ash : Conforming to IS 3812 (Part 1)
d) Specific gravity of fly ash : 2.2
e) Chemical admixture : Superplasticizer conforming to IS 9103
f) Specific gravity of:
- Coarse aggregate : 2.74
- Fine aggregate : 2.74
g) Water absorption:
- Coarse aggregate: 0.5%
- Fine aggregate : 1.0%
h) Free Surface moisture:
- Coarse aggregate : Nill
- Fine aggregate : Nill
i) Sieve Analysis:
- Coarse aggregate : Conforming to Table 2 of IS 383
-
Fine aggregate : Conforming to grading Zone I of Table 4 of IS 383
III. Target Strength for Mix proportioning:
f'ck = fck + 1.65 S
Where, f'ck = Target average compressive strength at 28 days
fck = Characteristic compressive strength at 28 days
S = Standard deviation
From Table 1 of IS 10262: 2009, standard deviation, S = 5 N/mm^2
Therefore, Target strength = 35+1.65 x 5 = 43.25 N/mm^2
IV. Selection of Water-cement ratio:
From Table 5 of IS 456: 2000 for severe exposure, maximum water-cement ratio = 0.45 water-cement part
Based on experience, adopt water-cement ratio as 0.40
0.40 < 0.45, Hence O.K
V. 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 litre
As superplasticizer is used, the water content can be reduced up to 30%
Based on trials water content reduction of 29% is achieved with plasticizer.
Hence the arrived water content = 197 x 0.71 = 140 litre
VI. Calculation of Cement Content:
Water-cement ratio = 0.4
Cementitious material (cement + fly ash) content = 140/0.4 = 350 kg/m^3
From Table 5 of IS 456 minimum cement content for 'severe' exposure condition = 340 kg/m^3
350 kg/m^3 > 340 kg/m^3, Hence OK
Now, to proportion a mix containing fly ash the following steps are suggested:
a) The percentage of fly ash needs to be decided based on project requirement and quality of materials
b) 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 = 140 Kg/m^3
So, Water-cement ratio = 140/385 = 0.364
Fly ash @ 30% total cementitious material content = 385 x 30% = 115 Kg/m^3
Cement (OPC) = 385-115 = 270 Kg/m^3
Saving of cement while using fly ash = 350-270 = 80 kg/m^3
Fly ash being utilized = 115 kg/m^3
VII. Proportion of Volume of coarse aggregate and Fine aggregate content:
From Table 3 of IS 10262: 2009, Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for water-cement ratio of 0.5 = 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
VIII. Mix Calculations:
The mix calculation per unit volume of concrete shall be as follows:
a) Volume of Concrete = 1 m^3
b) volume of cement = (Mass of cement/Specific gravity of cement) x(1/1000) = 270/3.15 x 1/1000 = 0.086 m^3
c) Volume of Fly ash = (Mass of fly ash/Specific gravity of fly ash) x(1/1000) = 115/2.2 x 1/1000 = 0.052
d) volume of water = (Mass of water/Specific gravity of water) x (1/1000) = 140/1 x 1/1000 = 0.140 m^3
e) Volume of chemical admixture = (Mass of chemical admixture/Specific gravity of admixture) x (1/1000)
= 7.6/1.145 x 1/1000 = 0.006 m^3
f) Volume of aggregate (FA & CA) = (a-(b +c +d + e)) = (1-(0.086 +0.052 + 0.140 + 0.006)) = 0.716 m^3
g) Mass of Coarse aggregate = ex Volume of coarse aggregate x Specific gravity of coarse aggregate X1000
= 0.716 x 0.56 x 2.74 x 1000 = 1098 Kg/m^3
h)Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000
= 0.716 x 0.44x 2.74 x 1000 = 863 Kg/m^3
IX. Mix proportions for M35:
Cement = 270 kg/m^3
Fly ash = 115 kg/m^3
Water = 140 Kg/m^3
Fine aggregate = 863 Kg/m^3
Course aggregate = 1098 Kg/m^3
Chemical admixture = 7 Kg/m^3
Water-cement ratio = 0.364
Mix Ratio 1:2.24: 2.85
X. 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
XI. 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 out the mix proportions for the given target strength for field trials. However, durability shall be met.