Project on Concrete Mix Design for various grades of Concrete
AIM: Calculate the concrete mix design for M35 grade concrete with fly ash
Data is taken from the example
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: 20mm
e) Minimum cement content: 320kg/m3 (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: 100mm (slump value for pumpable concrete)
h) Exposure condition: severe (RCC)
i) Method of concrete placing: Pumping
j) Degree of supervision: Good
k) Type of aggregate: Crushed angular aggregate
l) Maximum cement content: 450kg/m3
m) Chemical admixture type: Superplasticizer
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:
* Coarse aggregate 2.74
* Fine aggregate 2.74
* Chemical admixture 1.145
g) Water absorption:
* Coarse aggregate 0.5%
* Fine aggregate 1.0%
h) Free surface moisture:
* Coarse aggregate: Nil
* Fine aggregate: Nil
i) Sieve analysis data: Taken from the example problem
Target strength for mix proportioning:
f'ck = fck+1.65S
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 = 5N/mm2
Therefore, target strength = 35+1.65x5 = 43.25N/mm2
Selection of water-cement ratio:
From the fig 1 of IS 10262:2019, the water cement ratio corresponding to the strength of 43.25N/mm2 is 0.39 i.e., 0.4.
From table 5 of IS 456:2000 for severe exposure, maximum water cement ratio = 0.45.
0.4<0.45, hence OK.
Selection of water content:
From table 2 of IS 10262:2009, maximum water content for 20mm aggregate = 186litre.
(For 25mm to 50mm slump range).
Estimated water content for 100mm slump = 186+6/100*186=197litre.
As superplasticizer is used, the water content can be reduced upto 30%.
Based on trials water content reduction of 29% is achieved with plasticizer.
Hence the arrived water content = 197*0.71 = 140litre.
Calculation of cement content:
Water cement ratio=0.4
Cementitious material (cement+fly ash) content=140/0.4=350kg/m3.
From table 5 of IS 456 minimum cement content for 'severe' exposure condition = 320kg/m3
350kg/m3>320kg/m3. Hence OK.
Now, to proportion a mix containing fly ash the following steps are suggested;
a) The pecentage of fly ash needs to be decided based on project requirement & quality of materials.
b) In some cases increase in cementitious material content & its percentage may be based on experience & trial (in this example it is increased to 10%).
Cementitious material content = 350*1.1=385kg/m3
Water content = 140kg/m3
Water-cement ratio = 140/385 = 0.363
Fly ash at 30% of total cementitious material content = 385*0.3=115.5kg/m3
Cement (OPC) = 385-115.5=269.5kg/m3
Saving of cement while using fly ash = 350-269.5=80.5kg/m3
Fly ash utilized = 115.5kg/m3
Proportion of the volume of coarse aggregate & fine aggregate content:
From table 3 of IS 10262:2009, volume of CA corresponding to 20mm size aggregate & FA (Zone l) for water-cement ratio = 0.6.
In the present case the water cement ratio is 0.4.
* Therefore, the volume of CA needs to be increased to decrease the FA content.
* As water-cement ratio is lower by 0.1, 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 CA for the water-cement ratio of 0.4 = 0.62.
For pumpable concrete these values are reduced by 10%.
Therefore, volume of CA = 0.62*0.9=0.56.
Volume of FA content = 1-0.56=0.44
Mix calculations:
a) Volume of concrete = 1m3
b) Volume of cement = (Mass of cement/Specific gravity of cement) x (1/1000)
= (269.5/3.15) x (1/1000)
= 0.085m3
c) Volume of fly ash = (Mass of fly ash/Specific gravity of fly ash) x (1/1000)
= (115.5/2.2) x (1/1000)
= 0.0525m3
d) Volume of water = (Mass of water/Specific gravity of water) x (1/1000)
= (140/1) x (1/1000)
= 0.140m3
e) Volume of chemical admixture superplasticizer (@ 1% by mass of cemetitious material)
= (Mass of chemical admixture/Specific gravity of chemical admixture) x (1/1000)
= (2.76/1.145) x (1/1000)
= 0.0024m3
f) Volume of aggregate (FA & CA) = [a-(b+c+d+e)]
= [1-(0.085+0.0525+0.140+0.0024)]
= 0.720m3
g) Mass of coarse aggregate = f x volume of CA x specific gravity of CA x 1000
= 0.720 x 0.56 x 2.74 x 1000
= 1104.76kg/m3
h) Mass of fine aggregate = f x volume of FA x specific gravity of FA x 1000
= 0.720 x 0.44 x 2.74 x 1000
= 868.032kg/m3
Mix proportions:
Cement = 269.5kg/m3
Fly ash = 115.5kg/m3
Water = 140kg/m3
Fine aggregate = 868.032kg/m3
Coarse aggregate = 1104.76kg/m3
Chemical admixture = 2.76kg/m3
Free water-cementitious materials ratio = 0.354
Trial mix ratio : 1: 3.22: 4.09
AIM: Calculate the concrete mix design for M50 grade concrete without fly ash
Data is taken from the example
a) Grade designation: M35
b) Type of cement: OPC 43 grade conforming to IS 8112
c) Maximum nominal size of aggregate: 20mm
d) Minimum cement content: 320kg/m3 (from table 5 of IS 456:2000-Exposure condition)
e) Maximum water cement ratio: 0.45 (from table 5 of IS 456:2000-Exposure condition)
f) Workability: 100mm (slump value for pumpable concrete)
g) Exposure condition: severe (RCC)
h) Method of concrete placing: Pumping
i) Degree of supervision: Good
j) Type of aggregate: Crushed angular aggregate
k) Maximum cement content: 450kg/m3
l) Chemical admixture type: Superplasticizer
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:
* 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 data: Taken from the example problem
Target strength for mix proportioning:
f'ck = fck+1.65S
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 = 5N/mm2
Therefore, target strength = 50+1.65x5 = 58.25N/mm2
Selection of water-cement ratio:
From the fig 1 of IS 10262:2019, the water cement ratio corresponding to the strength of 58.25N/mm2 is 0.34.
From table 5 of IS 456:2000 for severe exposure, maximum water cement ratio = 0.45.
0.34<0.45, hence OK.
Selection of water content:
From table 2 of IS 10262:2009, maximum water content for 20mm aggregate = 186litre.
(For 25mm to 50mm slump range).
Estimated water content for 100mm slump = 186+6/100*186=197litre.
As superplasticizer is used, the water content can be reduced upto 30%.
Based on trials water content reduction of 29% is achieved with plasticizer.
Hence the arrived water content = 197*0.71 = 140litre.
Calculation of cement content:
Water cement ratio=0.34
Cementitious material (cement+fly ash) content=140/0.34=412kg/m3.
From table 5 of IS 456 minimum cement content for 'severe' exposure condition = 320kg/m3
412kg/m3>320kg/m3. Hence OK.
Proportion of the volume of coarse aggregate & fine aggregate content:
From table 3 of IS 10262:2009, volume of CA corresponding to 20mm size aggregate & FA (Zone l) for water-cement ratio = 0.6.
In the present case the water cement ratio is 0.34.
* Therefore, the volume of CA needs to be increased to decrease the FA content.
* As water-cement ratio is lower by 0.1, 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 CA for the water-cement ratio of 0.34 = 0.632.
For pumpable concrete these values are reduced by 10%.
Therefore, volume of CA = 0.632*0.9=0.568=0.57.
Volume of FA content = 1-0.57=0.43
Mix calculations:
a) Volume of concrete = 1m3
b) Volume of cement = (Mass of cement/Specific gravity of cement) x (1/1000)
= (412/3.15) x (1/1000)
= 0.130m3
c) Volume of water = (Mass of water/Specific gravity of water) x (1/1000)
= (140/1) x (1/1000)
= 0.140m3
d) Volume of chemical admixture superplasticizer (@ 1% by mass of cemetitious material)
= (Mass of chemical admixture/Specific gravity of chemical admixture) x (1/1000)
= (4.12/1.145) x (1/1000)
= 0.0036m3
e) Volume of aggregate (FA & CA) = [a-(b+c+d)]
= [1-(0.130+0.140+0.0036)]
= 0.7264m3
f) Mass of coarse aggregate = e x volume of CA x specific gravity of CA x 1000
= 0.7264 x 0.57 x 2.74 x 1000
= 1135kg/m3
g) Mass of fine aggregate = f x volume of FA x specific gravity of FA x 1000
= 0.7264 x 0.43 x 2.74 x 1000
= 856kg/m3
Mix proportions:
Cement = 412kg/m3
Water = 140kg/m3
Fine aggregate = 856kg/m3
Coarse aggregate = 1135kg/m3
Chemical admixture = 4.12kg/m3
Water-cement ratio = 0.34
Trial mix ratio : 1: 2.07: 2.75