Project on Concrete Mix Design for various grades of Concrete
AIM:
- To calculate the mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash
INDRODUCTION:
- Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure. Because every ingredient in the mix consists of different properties, it’s not an easy task to create a great concrete mix. It is imperative that all ingredients be tested to determine their physical properties and the bearing capacity of the project location.
- It is based on the relationships between the concrete properties, on one hand, and the composition of the mixture, on the other, when the concrete properties are the 28-day characteristic strength in the hardened state, and the workability in the fresh state
- This will ensure the structure will be sound and prevent failure of the mix
- is important to note that the ingredients for the mix might vary from one project location to another, so the physical properties must be tested for the requirements specified for each location.
Part 1 - Concrete mix design for M35 grade concrete with fly ash
Step 1: STIPULATIONS FOR PROPORTIONING
a) Grade designation : M35
b) Type of cement : OPC 53 Grade conforming IS 12269
c) Maximum nominal size of aggregate : 20mm
d) Minimum cement content : 340 kg/m3 (IS 456:2000)
e) Maximum water-cement ratio : 0.45 (Table 5 of IS 456:2000)
f) Workability : 100-120mm slump
g) Exposure condition : severe (For Reinforced Concrete)
h) Method of concrete placing : Pumping
i) Type of aggregate : Crushed Angular Aggregates
j) Chemical admixture type : Super Plasticizer ECMAS HP 890
Step 2: TEST DATA FOR MATERIALS
a) Cement used : OPC 53 Grade conforming IS 12269
b) Specific gravity of cement : 3.15
c) fly ash : confirming to IS 3812
d) Specific gravity of fly ash : 2.2
e) Chemical admixture : Super Plasticizer conforming to IS 9103
f) Specific gravity of
1) Coarse aggregate 20mm : 2.67
2) Fine aggregate : 2.65
g) Water absorption:
1) Coarse aggregate : 0.5 %
2) Fine aggregate (M.sand) : 2.5 %
h) Free (surface) moisture:
1) Coarse aggregate : Nil (Absorbed Moisture also Nil)
2) Fine aggregate : Nil
i) Sieve analysis:
1) Coarse aggregate: Conforming to all in aggregates of Table 2 of IS 383
2) Fine aggregate : Conforming to Grading Zone I of Table 4 of IS 383
Step 3: TARGET STRENGTH FOR MIX PROPORTIONING
f’ck =fck + 1.65 s
where
f’ck = target average compressive strength at 28 days,
fck = characteristics compressive strength at 28 days, and
s = standard deviation.
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2. Therefore, target strength = 35 + 1.65 x 5 = 43.25 N/mm2.
Step 4: SELECTION OF WATER/CEMENT RATIO
maximum water content ratio = 0.45 ( table 5 IS 456:2000)
Adopted maximum water-cement ratio = 0.41.
From the Table 5 of IS 456 for Very severe Exposure maximum Water Cement Ratio is 0.45
0.41 < 0.45 Hence ok.
Step 5: SELECTION OF WATER CONTENT
From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range) Estimated water content for 100 mm slump = 186+ (6/186) = 197 litre.
(Note: If Super plasticizer is used, the water content can be reduced upto 20% and above.)
Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content = 197-[197 x (20/100)] = 158 litre.
Step 6: CALCULATION OF CEMENT AND FLY ASH CONTENT
Adopted w/c Ratio = 0.41
Cement Content = 158/0.41 = 385 kg/m3
From Table 5 of IS 456, Minimum cement content for ‘ severe’ exposure conditions 340kg/m3
= 385 kg/m3 > 340 kg/m3 hence ok.
final cementious material content = 385 x 1.1 = 423 kg/m^3
water cement ratio = 158/423 = 0.373
fly ash is taken as 30% of total cementious content = 423 x 0.3 = 127 kg/m^3
cement required = 423 -127 = 296 kg/m^3
cement quantity saved due to fly ash = 385-296 =89 kg
Step 7: 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 0.50 =0.6 .
In the present case water-cement ratio is 0.41. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the 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 proportion of volume of coarse aggregate for the water-cement ratio of 0.41 = 0.62
NOTE – In case the coarse aggregate is not angular one, then also volume of coarse aggregate may be required to be increased suitably based on experience & Site conditions.
For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate =0.62 x 0.9 =0.558.
Volume of fine aggregate content = 1 – 0.558= 0.442.
Step 8: MIX CALCULATIONS
The mix calculations per unit volume of concrete shall be as follows:
a) Volume of concrete = 1 m3
b) Volume of cement = (Mass of cement)/ {(Specific Gravity of Cement) x 1000}
= 296/{3.15 x 1000}
= 0.009 m3
c) volume of fly ash = (mass of fly ash)/{(specific gravity of fly ash)x 1000}
= 127/{2.2 x 1000}
= 0.057 m^3
d) Volume of water = (Mass of water) / {(Specific Gravity of water)x 1000}
= 158/{1 x 1000}
= 0.158m3
e) Volume of chemical admixture = 1.54 litres/ m3 (By Trial and Error Method used 0.4% by the weight cement)
f) Volume of all in aggregate = [a-(b+c+d+e)]
= [1-(0.009+0.057+0.158+0.004)]
= 0.772 m3
g) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of course Aggregate x 1000
= 0.772 x 0.558 x 2.67 x 1000
= 1150 kg/m3
g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.772 x 0.442 x 2.60 x 1000
= 887 kg/m3
Step 9: MIX PROPORTIONS
Cement = 296 kg/m3
Fly ash = 127 kg/m^3
Water = 158 l/m3
Water/cement ratio = 0.373
Fine aggregate = 887 kg/m3
Coarse aggregate 20mm = 1150 kg/m3
Mix proportion - 1 : 2.09 : 2.71
Step 10: the slump shall be measured,the water content and dosage of admixture shall be adjusted for achieving required slump on trail.the mix proportion shall be reworked for actuall water content and checked for durability reqirements
Step 11: if it does not satisfy the above criteria,then 2 or more trails should be done.
Part 2 - Mix design for M50 grade concrete without fly ash
Step 1: STIPULATIONS FOR PROPORTIONING
a) Grade designation : M50
b) Type of cement : OPC 53 Grade conforming IS 12269
c) Maximum nominal size of aggregate : 20mm
d) Minimum cement content : 340 kg/m3 (IS 456:2000)
e) Maximum water-cement ratio : 0.45 (Table 5 of IS 456:2000)
f) Workability : 100-120mm slump
g) Exposure condition : severe (For Reinforced Concrete)
h) Method of concrete placing : Pumping
i) Type of aggregate : Crushed Angular Aggregates
j) Chemical admixture type : Super Plasticizer
k)Maximum cement content : 450 kg/m^3
Step 2: TEST DATA FOR MATERIALS
a) Cement used : OPC 53 Grade conforming IS 12269
b) Specific gravity of cement : 3.15
c) Chemical admixture : Super Plasticizer conforming to IS 9103
d) Specific gravity of
1) Coarse aggregate 20mm : 2.67
2) Fine aggregate : 2.65
e) Water absorption:
1) Coarse aggregate : 0.5 %
2) Fine aggregate (M.sand) : 2.5 %
f) Free (surface) moisture:
1) Coarse aggregate : Nil (Absorbed Moisture also Nil)
2) Fine aggregate : Nil
g) Sieve analysis:
1) Coarse aggregate: Conforming to all in aggregates of Table 2 of IS 383
2) Fine aggregate : Conforming to Grading Zone I of Table 4 of IS 383
Step 3: TARGET STRENGTH FOR MIX PROPORTIONING
f’ck =fck + 1.65 s
where
f’ck = target average compressive strength at 28 days,
fck = characteristics compressive strength at 28 days, and
s = standard deviation.
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2. Therefore, target strength = 50 + 1.65 x 5 = 58.25 N/mm2.
Step 4: SELECTION OF WATER/CEMENT RATIO
maximum water content ratio = 0.45 ( table 5 IS 456:2000)
Adopted maximum water-cement ratio = 0.4.
From the Table 5 of IS 456 for Very severe Exposure maximum Water Cement Ratio is 0.45
0.41 < 0.45 Hence ok.
Step 5: SELECTION OF WATER CONTENT
From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range) Estimated water content for 100 mm slump = 186+ (6/186) = 197 litre.
(Note: If Super plasticizer is used, the water content can be reduced upto 20% and above.)
Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content = 197-[197 x (20/100)] = 158 litre.
Step 6: CALCULATION OF CEMENT CONTENT
Adopted w/c Ratio = 0.4
Cement Content = 158/0.4 = 395 kg/m3
From Table 5 of IS 456, Minimum cement content for ‘ severe’ exposure conditions 340kg/m3
= 395 kg/m3 > 340 kg/m3 hence ok.
Step 7: 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 0.50 =0.6 .
In the present case water-cement ratio is 0.41. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the 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 proportion of volume of coarse aggregate for the water-cement ratio of 0.41 = 0.62
NOTE – In case the coarse aggregate is not angular one, then also volume of coarse aggregate may be required to be increased suitably based on experience & Site conditions.
For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate =0.62 x 0.9 =0.558.
Volume of fine aggregate content = 1 – 0.558= 0.442.
Step 8: MIX CALCULATIONS
The mix calculations per unit volume of concrete shall be as follows:
a) Volume of concrete = 1 m3
b) Volume of cement = (Mass of cement)/ {(Specific Gravity of Cement) x 1000}
= 395/{3.15 x 1000}
= 0.125 m3
c) Volume of water = (Mass of water) / {(Specific Gravity of water)x 1000}
= 158/{1 x 1000}
= 0.158m3
d) Volume of chemical admixture = 1.54 litres/ m3 (By Trial and Error Method used 0.4% by the weight cement)
e) Volume of all in aggregate = [a-(b+c+d)]
= [1-(0.125+0.158+0.004)]
= 0.713 m3
f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of course Aggregate x 1000
= 0.713 x 0.558 x 2.67 x 1000
= 1062 kg/m3
g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.713 x 0.442 x 2.60 x 1000
= 819 kg/m3
Step 9: MIX PROPORTIONS
Cement = 395 kg/m3
Water = 158 l/m3
Water/cement ratio = 0.4
Fine aggregate = 819 kg/m3
Coarse aggregate 20mm = 1062 kg/m3
Mix proportion - 1 : 2.07 : 2.68
Step 10: the slump shall be measured,the water content and dosage of admixture shall be adjusted for achieving required slump on trail.the mix proportion shall be reworked for actuall water content and checked for durability reqirements
Step 11: if it does not satisfy the above criteria,then 2 or more trails should be done.
Results:
| Grade | Mix proportion | water/cement ratio |
| M35 (with fly ash) | 1 : 2.09 : 2.71 | 0.373 |
| M50 (without fly ash) | 1 : 2.07 : 2.68 | 0.4 |
- M35 grade concrete (with fly ash),design mix proportion is 1 : 2.09 : 2.71 and has a w/c ratio of 0.373
- M50 grade concrete (without fly ash),design mix proportion is 1 : 2.07 : 2.68 and has a w/c ratio of 0.4