Project on Concrete Mix Design for various grades of Concrete
Q) CALCULATE DESIGN MIX FOR M35 GRADE CONCRETE WITH FLY ASH & M50 GRADE CONCRETE WITH OUT FLY ASH.
ANSWER:-
DESIGN MIX FOR M35 GRADE CONCRETE WITH FLY ASH :
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 15 3812 (Part 1)
d) Maximum nominal size of aggregate: 20 mm
e) Minimum cement content: 320 kg/m^3 (From Table 5 of 15 456: 2000 - Exposure condition)
f) Maximum water-cement ratio 0.45 (From Table 5 of 15 456: 2000- Exposure condition)
g) Workability: 100 mm (slump value for pumpable concrete)
h) Exposure condition: 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
l) 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=Nil
Fine aggregate=Nil
i) Sieve Analysis:
Coarse aggregate= Conforming to Table 2 of IS 383
Fine aggregate=Conforming to grading Zone 2 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
Based on experience, adopt water-cement ratio as 0.44
0.44<0.45, satisfied
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 so add 6% to it.)
Estimated water content for 100mm slump = 186+ 6/100 *186
= 197 litre
As superplasticizer is used, the water content can be reduced up to 20%
Based on trials water content reduction of 20% is achieved with plasticizer.
Hence the arrived water content = 197*0.8 = 158 litre
VI. Calculation of Cement Content:
Water-cement ratio = 0.44
Cementitious material (cement + fly ash) content = 158/0.44 =359 kg/m^3
From Table 5 of IS 456
minimum cement content for 'severe' exposure condition = 320 kg/m^3
359 kg/m^3 > 320 kg/m^3, Hence OK
The percentage of fly ash needs to be decided based on project requirement and quality of materials, in some cases, increase in cementitious material can be warranted. Increase in cementitious material content and its percentage may be based on experience and research 10% cementitious content increase.
Final Cementitious content= 359 x 1.10 = 395 Kg/m^3
Water content =158 Kg/m^3
So, Water cement ratio = 158/395 = 0.4
Fly ash@ 30% total cementitious material content = 395 x 0.3 = 118.5 Kg/m^3
Cement (OPC) = 395-118 =277 Kg/m^3
Saving the cement while using the fly ash=350-277= 73 Kg/m^3
Fly ash being utilized = 118 Kg/m^3
VII. Proportion of Volume of coarse aggregate and Fine aggregate content:
From Table 3 of 15 10262: 2009, Volume of coarse aggregate corresponding to 20 mm size aggregate 0.62 and fine aggregate (Zone 2) for water-cement ratio of 0.50.
In the present case the water cement ratio is 0.44.
- Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
- As water-cement ratio is lower by 0.06, 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 0.632 for the water-cement ratio of 0.44 (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 = 0.632*0.9=0.568
Volume of fine aggregate content = 1-0.568=0.431
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)
= (277/3.15) x (1/1000)
=0.087 m^3
c) Volume of Fly ash = (Mass of fly ash/ Specific gravity of fly ash) x (1/1000)
= (118/2.2) x (1/1000)
=0.053 m^3
d) Volume of water = (Mass of water/ Specific gravity of water) x (1/1000)
= (158/1) x (1/1000)
=0.158 m^3
e) Volume of chemical admixture = (Mass of chemical admixture / Specific gravity of chemical 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-(0.087+0.053+0.158+0.006))
=0.696 m^3
g) Mass of Coarse aggregate = f x Volume of coarse aggregate x Specific gravity of coarse aggregate X 1000
= 0.696 x 0.568 x 2.74 x 1000
= 1077 Kg/m^3
h) Mass of fine aggregate = f x Volume of coarse aggregate x Specific gravity of coarse aggregate X 1000
= 0.696 x 0.431 x 2.74 x 1000
= 822 Kg/m^3
IX. Mix proportions for Trial Number 1:
Cement = 277 Kg/m^3
Fly ash = 118 Kg/m^3
Water = 158 Kg/m^3
Fine aggregate = 822 Kg/m^3
Coarse aggregate = 1077 Kg/m^3
Chemical admixture = 7.18 Kg/m^3
Water-cement ratio = 0.4
Trial Mix Ratio = 1: 2.08: 2.72
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.
DESIGN MIX FOR M50 GRADE CONCRETE WITH OUT FLY ASH :
I. Stipulations for proportioning:
a) Grade designation: M50
b) Type of cement: OPC 53 grade conforming to IS 12269-1987
c) Maximum nominal size of aggregate: 20 mm
d) Minimum cement content: 320 kg/m^3 (From Table 5 of 15 456: 2000 - Exposure condition)
e) Maximum water-cement ratio 0.45 (From Table 5 of 15 456: 2000- Exposure condition)
f)Workability: 100 mm (slump value for pumpable concrete)
g) Exposure condition: Severe (for reinforcedconcrete)
h) Method of concrete placing: Pumping
h) Degree of supervision: Good
i) Type of aggregate: Crushed angular aggregate
j) Maximum cement content: 450 kg/m^3
k) Chemical admixture type: Superplasticizer
II.Test data for materials:
a) Cement used: OPC 53 grade conforming to IS 12269-1987
b) Specific gravity of cement: 3.15
c) Chemical admixture: Super plasticizer conforming to IS 9103
d) Specific gravity of:
Coarse aggregate= 2.74
Fine aggregate= 2.64
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 to Table 2 of IS 383
Fine aggregate=Conforming to grading Zone 2 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
Characteristic compressive strength= 58.25 N/mm^2
IV. Selection of Water-cement ratio:
Maximum water-cement ratio to design M50 grade concrete can be = 0.45
Based on experience, adopt water-cement ratio as 0.44
0.44<0.45, satisfied
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 so add 6% to it.)
Estimated water content for 100mm slump = 186+ 6/100 *186
= 197 litre
As super plasticizer is used, the water content can be reduced up to 20%
Based on trials water content reduction of 20% is achieved with plasticizer.
Hence the arrived water content = 197*0.8 = 158 litre
VI. Calculation of Cement Content:
Water-cement ratio = 0.44
Cementitious material (cement + fly ash) content = 158/0.44 =359 kg/m^3
From Table 5 of IS 456
Minimum cement content for 'severe' exposure condition = 320 kg/m^3
359 kg/m^3 > 320 kg/m^3, Hence OK
VII. Volume of coarse aggregate and Fine aggregate content:
From Table 3 of 15 10262: 2009, Volume of coarse aggregate corresponding to 20 mm size aggregate 0.62 and fine aggregate (Zone 2) for water-cement ratio of 0.50.
In the present case the water cement ratio is 0.44.
- Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
- As water-cement ratio is lower by 0.06, 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 0.632 for the water-cement ratio of 0.44 (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 = 0.632*0.9=0.568
Volume of fine aggregate content = 1-0.568=0.431
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)
= (359/3.15) x (1/1000)
=0.114 m^3
c) Volume of water = (Mass of water/ Specific gravity of water) x (1/1000)
= (158/1) x (1/1000)
=0.158 m^3
d) Volume of chemical admixture = (Mass of chemical admixture / Specific gravity of chemical admixture) x (1/1000)
= (7.6/1.145) x (1/1000)
=0.006 m^3
e) Volume of aggregate (FA & CA) = (a - (b + c + d))
= (1-(0.114+0.158+0.006))
=0.722 m^3
g) Mass of Coarse aggregate = f x Volume of coarse aggregate x Specific gravity of coarse aggregate X 1000
= 0.722 x 0.568 x 2.74 x 1000
= 1123 Kg/m^3
h) Mass of fine aggregate = f x Volume of coarse aggregate x Specific gravity of coarse aggregate X 1000
= 0.722 x 0.431 x 2.64 x 1000
= 821 Kg/m^3
IX. Mix proportions for Trial Number 1:
Cement = 359 Kg/m^3
Water = 158 Kg/m^3
Fine aggregate = 821 Kg/m^3
Coarse aggregate = 1123 Kg/m^3
Chemical admixture = 7.18 Kg/m^3
Water-cement ratio = 0.44
Trial Mix Ratio = 1: 2.28: 3.12
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.