Project on Concrete Mix Design for various grades of Concrete

M35 Grade Design Mix for concrete with fly ash

Aim: To calculate desing mix ratio for M35 grade using fly ash as admixture.

Introduction: Fly ash or pulverished fuel ash (pfa) is a finely divided powder thrown out as a waste material at the thermal power plants using pulverized coal for raising steam in the boilers. In the building industry the use of fly ash a part replacement of cement in mortar and concrete.

STIPULATIONS FOR PROPORTIONING

• Grade : M35
• Type of cement : 53 (OPC) Grade conforming IS 12269
• Maximum nominal size of aggregate : 20mm
• Minimum cement content : 320kg/m3
• Maximum w/c ratio : 0.45
• Workability : 100mm slump
• Exposure condition: severe (For reinforced concrete)
• Method of concrete placing : pumping
• Degree of supervision : good
• Type of aggregate : Crushed angular aggregates
• Maximum cement content : 450kg/m3
• Partial replacement of cement by fly ash: 30% (as per requirements)
• Type of mineral admixture: Fly ash conforming to IS 3812 (Part 1)
• Chemical admixture typre : superplasticizer

TEST DATA FOR MATERIALS

• Specific gravity of cement : 3.12
• Specific gravity of coarse aggregate : 2.74
• Specific gravity of fine aggregate : 2.56
• Specific gravity of fly ash : 2.2
• Water absorption of coarse aggregate : 0.5%
• Water absorption of fine aggregate : 1.0%
• Free surface moisture coarse and fine aggregate : nil

TARGET STRENGTH OF MIX PROPORTIONING

f'ck = fck + 1.65s
where, f'ck = target average compressive strength at 28days
fck = compressive strength at 28days
s = standard deviation
From table 1 of IS 10262:2009,
Standard deviation s = 5 N/mm2
Therefore target mean strength f'ck=35 + (1.65 x 5) = 43.25 N/mm2

SELECTION OF W/C RATIO

From table 5 of IS 456-2000, Maximum w/c ratio = 0.45

SELECTION OF WATER CONTENT

From table 2, maximum water content for 20mm aggregate = 186 litres
Estimated water content for 100mm slump (for every 25mm slump 3% water content is added) = 186 + 6% of 186 = 197 litres
As superplasticizer is used, the water content can be reduced up to 20% and based on trials 25% water content reduction is achieved.
hence the water content = 197 - 25% of 197 = 147 litre

CALCULATION OF CEMENT CONTENT

adopted w/c ratio = 0.45
cement content = 147/0.45 = 327 kg/m3
from table 5 of IS 456, minimum cement content for "severe" exposure conditions 320 kg/m3
there fore 327 kg/m3 > 320kg/m3 hence ok.
Now the percentage of fly ash needs to be decided based on project requirements and quality of materials. In some cases increase in
cementitious material can be warranted/ The cmenetitious matrial content is increased by 10%

• Cementitious material content = 327 x 1.10 = 360 kg/m3
• Water content = 147 kg/m3
• w/c ratio = 147/360 = 0.40
• Fly ash @ 30% total cementitious material content = 360 x 30% = 108 kg/m3
• Cement OPC = 360 - 108 = 75 kg/m3
• Saving of cement while using fly ash = 327 - 252 = 75 kg/m3
• Fly ash being utilized = 108 kg/m3

PROPORTION OF VOLUME OF FINE AGGREGATE AND CAORSE AGGREGATE CONTENT

From table 3 of IS 10262:2009 volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone II) for w/c ratio of
0.50 = 0.62.
In this case, w/c ratio is 0.45. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content as the
w/c 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 changes
in w/c ratio.
Therefore, corrected proportion of volume of coarse aggregate for w/c ratio of 0.45 = 0.64
For pumpable concrete these values are reduced upto 10%.
Therefore, volume of coarse aggregate = 0.64 x 0.9 = 0.576
Volume of fine aggregate content = 1 - 0.576 = 0.424

MIX CALCULATION

The mix calculation for per unit volume is as follow

• Volume of concrete = 1 m3
• Volume of cement = Mass of cement/(Specific gravity of cement x 1000)
  = 252/3.15 x 1000
  = 0.08 m3
• Volume of Flyash = Mass of Flyash/(Specific gravity of Flyash x 1000)
  =108/2.2 x 1000
  = 0.049 m3
• Volume of water = Mass of water/(Specific gravity of water x 1000)
  = 147/1 x 1000
  = 0.147 m3
• Volume of chemical admixture = 1.75 ltr/m3 (by trial and error method used 0.4% by the weight cement)
• Volume of fine aggregate and coarse aggregate = {a-(b+c+d+e)}
  = {1-(0.08+0.04+0.147+0.004)}
  = 0.729 m3
• Mass of coarse aggregate = e x Volume of coarse aggregate x specific gravity of coarse aggregate x 1000
  = 0.729 x 0.576 x 2.74 x 1000
  = 1151 kg/m3
• Mass of fine aggregate = e x Volume of fine aggregate x specific gravity of fine aggregate x 1000
  = 0.729 x 0.424 x 2.56 x 1000
  = 791 kg/m3

RESULT AND CONCLUSION

Cement = 252 kg/m3
Water = 108 kg/m3
Coarse aggregate = 1151 kg/m3
Fine aggregate = 791 kg/m3
Chemical admixture = 7.6 kg/m3
water-cement ratio = 0.4
Mix ratio for grade M30 = 252:791:1151
= 1:3.13:4.56 (C:FA:CA)

This trial mix ratio should match workability, durability, minimum strength of M35 grade concrete and increase of 10% should be done if it does not satisfy the above criteria.

M50 Grade Design Mix for concrete

Aim: To calculate desing mix ratio for M50 grade

STIPULATIONS FOR PROPORTIONING

• Grade : M50
• Type of cement : 53 (OPC) Grade conforming IS 12269
• Maximum nominal size of aggregate : 20mm
• Minimum cement content : 360kg/m3
• Maximum w/c ratio : 0.35
• Workability : 50-75mm slump
• Exposure condition: Extreme (for reinforced concrete)
• Method of concrete placing : pumping
• Degree of supervision : good
• Type of aggregate : Crushed angular aggregates
• Maximum cement content : 450kg/m3
• Chemical admixture typre : superplasticizer

TEST DATA FOR MATERIALS

• Specific gravity of cement : 3.12
• Specific gravity of coarse aggregate : 2.74
• Specific gravity of fine aggregate : 2.56
• Water absorption of coarse aggregate : 0.5%
• Water absorption of fine aggregate : 1.0%
• Free surface moisture coarse and fine aggregate : nil

TARGET STRENGTH OF MIX PROPORTIONING

f'ck = fck + 1.65s
where, f'ck = target average compressive strength at 28days
fck = compressive strength at 28days
s = standar deviation
From table 1 of IS 10262:2009,
Standard deviation s = 5 N/mm2
Therefore target mean strength f'ck=50+(1.65 x 5) = 58.25 N/mm2

SELECTION OF W/C RATIO

From table 5 of IS 456-2000, Maximum w/c ratio = 0.35

SELECTION OF WATER CONTENT

From table 2, maximum water content for 20mm aggregate = 186 litres
Estimated water content for 100mm slump (for every 25mm slump 3% water content is added) = 186 + 6% of 186 = 197 litre
As superplasticizer is used, the water content can be reduced up to 20% and based on trials 27% water content reduction is achieved.
hence the water content = 197 - 27% of 197 = 143 litre

CALCULATION OF CEMENT CONTENT

adopted w/c ratio = 0.35
cement content = 143/0.35 = 410 kg/m3
from table 5 of IS 456, minimum cement content for "extreme" exposure conditions 360 kg/m3
there fore 410 kg/m3 > 360kg/m3 hence ok.

PROPORTION OF VOLUME OF FINE AGGREGATE AND CAORSE AGGREGATE CONTENT

From table 3 of IS 10262:2009 volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone II) for w/c ratio of
0.50 = 0.62.
In this case, w/c ratio is 0.35. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content as the
w/c 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 changes
in w/c ratio.
Therefore, corrected proportion of volume of coarse aggregate for w/c ratio of 0.35 = 0.65
For pumpable concrete these values are reduced upto 10%.
Therefore, volume of coarse aggregate = 0.65 x 0.9 = 0.585
Volume of fine aggregate content = 1 - 0.585 = 0.415

MIX CALCULATION

The mix calculation for per unit volume is as follow

• Volume of concrete = 1 m3
• Volume of cement = Mass of cement/(Specific gravity of cement x 1000)
  = 410/3.12 x 1000
  = 0.131 m3
• Volume of water = Mass of water/(Specific gravity of water x 1000)
  = 143/1 x 1000
  = 0.143 m3
• Volume of Superplasticizer = Mass of superplasticizer/(Specific gravity of superplasticizer x 1000)
  = 8.2/1.145 x 1000
  = 0.007 m3
• Volume of fine aggregate and coarse aggregate = {a-(b+c+d)}
  = {1-(0.131+0.143+0.007)}
  = 0.719 m3
• Mass of coarse aggregate = e x Volume of coarse aggregate x specific gravity of coarse aggregate x 1000
  = 0.719 x 0.585 x 2.74 x 1000
  = 1152.5 kg/m3
• Mass of fine aggregate = e x Volume of fine aggregate x specific gravity of fine aggregate x 1000
  = 0.719 x 0.415 x 2.56 x 1000
  = 764 kg/m3

RESULT AND CONCLUSION

Cement = 410 kg/m3
Water = 143 kg/m3
Superplasticizer = 7 kg/m3
Coarse aggregate = 1152.5 kg/m3
Fine aggregate = 764 kg/m3
water-cement ratio = 0.35
Mix ratio for grade M30 = 410:764:1153
= 1:1.86:2.80 (C:FA:CA)