Project on Concrete Mix Design for various grades of Concrete

M35 Grade Design mix for concrete with Fly ash

Aim : To calculate the design 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

^{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 : 320 kg/m3 (IS 456:2000)
e) Maximum water-cement ratio : 0.45 (Table 5 of IS 456:2000)
f) Workability : 100mm slump
g) Exposure condition : severe (For Reinforced Concrete)
h) Method of concrete placing : Pumping
i) Degree of supervision : Good
j) Type of aggregate : Crushed Angular Aggregates
k) Maximum cement content : 450 kg/m3}

^{l) Partial replacement of cement by Fly ash : 30% ( as per requirement)}

m) Type of mineral admixture : Fly ash conforming to IS 38I2 (Part I)

^{n) Chemical Admixture : Superplasticizer (conforming to IS 9103)}

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 of coarse and fine aggregate : Nil

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

SELECTION OF WATER CEMENT RATIO

rom Table 5 of IS 456-2000

Maximum water-cement ratio = 0.45

SELECTION OF WATER CONTENT

From Table 2 of IS 456, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 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 25% has been achieved, Hence the arrived water content = 197-[197 x (25/100)] = 147 litres.

CALCULATION OF CEMENT AND FLY ASH CONTENT

Adopted w/c Ratio = 0.45
Cement Content = 147/0.45 = 326.6 kg/m³
From Table 5 of IS 456, Minimum cement content for ‘severe’ exposure conditions 320kg/m³
= 326.6 kg/m³ > 320 kg/m³ hence ok.

Now the percentage of fly ash needs to be decided based on project requirements and quality of materials.ln some cases increase in cementitious material can be warranted. The cementitious material content is increased by 10%.

• Cementitious material content = 327 x 1.10 = 360 kg/m3.

• Water content = 147 kg/m3.

• water cement ratio = 147/360 = 0.40

• Fly ash @ 30% total cementitious material content = 360 x 30% = 108 kg/m3.

• Cement(OPC) = 360-108 = 252 kg/m3.

• Saving of cement while using fly ash = 327-252 = 75kg/m3.

• Fly ash being utilized = 108 kg/m3.

PROPORTIO0N 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 II) for water-cement ratio of 0.50 =0.62 .

In the present case water-cement ratio is 0.45. 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 0.45 = 0.64

For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate =0.64 x 0.9 =0.576.

Volume of fine aggregate content = 1 – 0.576= 0.424.

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}
= 252/{3.15 x 1000}
= 0.08m³

c)Volume if flyash = (Mass of flyash/specific gravity of fly ash)X(1/1000)

= 108/{2.2 x 1000}
= 0.049m³

d) Volume of water = [Mass of water] / {[Specific Gravity of water] x 1000}
= 147/{1 x 1000}
= 0.147 m³

e) Volume of chemical admixture = 1.75 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-(0.08+0.04+0.147+0.004)]
= 0.729m³

g) Mass of coarse aggregate= f x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.729x 0.576 x 2.74 x 1000
= 1151 kg/m³

h) Mass of fine aggregate= f 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

Results and Conclusion

Cement = 252 kg/m³

Fly ash =108 kg/m³

Water = 147 kg

Coarse aggregate =1151 kg/m³

Fine aggregate = 791 kg/m³

Chemical admixture = 7.6 kg/m³

Water cement ratio = 0.4

Trial mix ratio : 252 :791 :1151 = 1: 3.13: 4.56 ( C: FA: CA)

• This trial mix ratio should match the workability ,durability, minimum strength of M35 grade concrete .

• If it does not satisfy the above criteria two or more trials for increase of 10 % should be done .

M50 Grade Design mix for concrete

Aim : To calculate the design mix ratio for M50 grade.

M35 Grade Design mix for concrete with Fly ash

Stipulations for Concrete Mix Design

• Grade designation : M 50
• Type of cement : OPC 53 grade confirming to IS 8112
• Maximum nominal size of aggregate : 20 mm
• Minimum cement content : 360 kg/m³
• Maximum water-cement ratio : 0.35
• Workability : 50-75 mm (slump)
• Exposure condition : Extreme (for reinforced concrete)
• Method of concrete placing : Pumping
• Degree of supervision : Good
• Type of aggregate : Crushed angular aggregate
• Maximum cement content : 450 kg/m³
• Chemical admixture type : Super Plasticizer

Test Data for Materials

The following data are collected by performing standard tests in a laboratory.

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 %

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

SELECTION OF WATER CEMENT RATIO

from Table 5 of IS 456-2000

Maximum water-cement ratio = 0.35

SELECTION OF WATER CONTENT

From Table 2 of IS 456, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 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 27% has been achieved, Hence the arrived water content = 197-[197 x (27/100)] = 143 litres.

CALCULATION OF CEMENT

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’ condition = 360 kg/m³
= 410 kg/m³ > 360 kg/m³ hence ok.

PROPORTIO0N OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT

From Table 3 of IS 10262 volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 =0.62.

In the present case, the water-cement ratio is 0.35. Therefore. the volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio).

Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.35 = 0.65.

For pumpable concrete, these values should be reduced by 10 percent.

Therefore, volume of coarse aggregate = 0.65 x 0.9 = 0.585.

Volume of fine aggregate content =1 – 0.585 =0.415

MIX CALCULATIONS

a) Volume of concrete = 1m³

b) Volume of cement = (Mass of Cement/ Its Specific Gravity ) X (1/1000)

= (410/3.12) X (1/1000)

= 0.131 m³

c) Volume of Water = (Mass of water/specific gravity of water) X (1/1000)

= (143/1) X (1/1000)

= 0.143 m³

d) Volume of Superplasticizer = (Mass of Superplasticizer / Specific gravity of admixture) X (1/1000)

= (8.2/1.145) X (1/1000)

= 0.007 m³

e) Volume of all aggregate = (a – (b + c + d))

= 1 – (0.131 + 0.143+0.007)

= 0.719 m³

e) Mass of coarse aggregate = Volume of All Aggregate X Volume of Coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000

= 0.719 x 0.585 x 2.74 x 1000

= 1152.48 kg

f) Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000

= 0.719 x 0.415 x 2.56 x 1000

= 763.86 kg

Results and Conclusion

Cement = 410 kg/m³

Water = 143 kg/m³

Super plasticizer = 7 kg/m³

Coarse aggregate =1152.48 kg/m³

Fine aggregate = 763.86 kg/m³

Water cement ratio = 0.35

Trial mix ratio : 410 :764 :1153 = 1: 1.86:2.80 ( C: FA: CA)